exhaust velocity question for turbo guys....

[H2Ogbodies]

I've just been thinking about this and was wondering what experience anybody here has with respect to the best place to mount the exhaust housing.

Now, I know you want to place the turbo on a V8 for example where the exhaust gas velocity is the highest which on a header would be at the collector closest to the four runners as possible (assuming TT here.) I wonder why kind of lag issues anybody may be having when mountign the turbos further down the exhaust route? For example I've seen some setups where the runners are pretty long and either a goofy pipe is plumbed inline with an exhaust housing pad welded on or worse-on a single turbo, I've seen a long crossover exhaust pipe connect to two headers facing towards the front of the car.
What I want to know is, wouldn't that contribute to a significant amount of lag and even worse once an intercooler is plumbed in? I'm working on my own turbo system now fo rmy Cutlass and am working out details between a single and TT setup. Nothing is available in a kit form that looks reliable imo so I am making my own but a lot of what's out there I am not sure about. I am building for maximum exhaust velocity (and heat retention) and zero turbo lag (or as absolute as little as possible). It doesn't matter that this is all in an 80 Cutlass...moreover this is just a question of exhaust velocity relating to turbo lag. Thoughts?

[WS6]

Heat flow not air velocity causes a turbo to spool.

[exwestracer]

I can tell you that on the "no-buck" setup, we tried to balance the exhaust flow between banks. Admittedly this would be tougher to do if the turbo were mounted off to one side. A general rule is the closer the turbo is to the head, the quicker it spools.

BTW, we had ZERO turbo lag. It crossed into boost at 2000rom, and was at 15lb by 2800

[shmoov69]

Three letters......STS!!! They are hanging below the back bumper and work just fine! I always thought the same thing, but after seeing some of theirs work, I must say it isn't that relevant!! Or at least not for a street car.
BUT that is MY opinion!

[overZealous1]

heat flow causes the turbo to spool? so you're saying if you sat there with cold compressed air it would not spin or create boost? turbos do not work because of heated air.

op has a valid question, but you are talking very minute moments of time. the compressor wheel will see force obviously to make boost. in turn, the turbine will see equal amounts of resistance, with the outcome being it will slow the exhaust flow. this will create back pressure in the exhaust. more boost, more force to create it, more back pressure on turbine/exhaust side. in the simplest terms, think of it as the old air pump/compressor theory. your engine is the air pump, your exhaust would act as the tank trying to be filled with pressure. how fast do you think backpressure will be built up knowing the size of the pump in relation to the tank? now think of it at 2500rpm. pretty effing fast!
in other words, there is some validity to the question, and yes, there would be minute measureable difference. it more so would be lag on the compressed side though. unless you plan on putting them in a trailer behind you, i would not worry about it. your focus is better spent on getting the correct SIZE turbo for your power goals.

[WS6]

Heat is energy and it flows like a fluid. Yes, it is heat(energy) that causes a turbo to spool. Contain the heat and you'll spool faster and better. Moving air contains very little energy as compared to heated air. Can you move the impeller with cool air? Yes, but not as effectively. This is simple thermodynamics and is why steam turbines use steam to turn the turbines and not regular air. This is also the reason you must monitor EGT's on a turbo system.

http://www.turboclub.com/turbotech/
http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html

[overZealous1]

•The high temperature gas then continues on to the turbine (6). The turbine creates backpressure on the engine which means engine exhaust pressure is higher than atmospheric pressure
•A pressure and temperature drop occurs (expansion) across the turbine (7), which harnesses the exhaust gas’ energy to provide the power necessary to drive the compressor

kind of hilarious you post up turbo 101 links to a guy who used to manufacture turbo parts and exhaust for turbo cars and building turbo engines, lol.

now if you look closely at the wording in the above qoutes from your link (the other one was to weak to even prove a point with). in a way, you proved my point, was just trying to make the wording simpler. where he mentions a "temperature and pressure drop occurs across the turbine" he is simply explaining the release of the backpressure, which makes the turbine spin. the first one where he states "high temperature gas" is simply referring to your exhaust, which better be hot or not alot of stuff is happening if it isn't! hahaha
now i will give you one thing, heated air does have energy in it. the type of energy that can be converted to work, as in your steam example. but your steam idea is completely wrong. they don't use regular air, because it is the expansion of the water vapors creating the energy!! hahhaa. ofcourse they use steam and the relation between the 2 of a turbo and steam engine/pump is TOTALLY separate. but, they can be compared to an extend. boiler=your engine, steam=your exhaust, pressurized system=back pressure in your exhaust, harnessing the pressure to drive a pump or piston.
yes, both create heat, but the common denominator is creating PRESSURE to drive something. heat is a byproduct of this process.

a little test for ya. hit the dyno. then wrap all your exhaust and turbo's so they are easily touchable by your hands. redyno. in your theory, there would be lots of power there to be had right? keeping all the heat in that is. see that on alot of race cars, other than to protect bodywork or other pieces close to the exhaust?

ok, no, any of these reasons are not why you monitor egts!!! egt's is basically a tuning tool to keep you from detonation. n/a tuning or forced induction. older light aircraft have them so they can adjust fuel mixture in flight depending on air density. this is just a tool to keep an eye on exhaust temps. to hot and you are running lean. to cold you are running rich.1600 is about the limit you want to see. again, this goes for n/a tuning also.

not trying to get into an arguement here, but just wanting to keep the info correct being posted.

[exwestracer]

I'm NOT a turbo expert, but if I were trying to "optimize" the hot side of a turbo system, I'd look at simple thermodynamics. Exhaust is a gas, right? As you heat a gas it expands. Expand it in a confined space (like a header with a turbine wheel at the outlet) and you are going to build pressure. The more pressure you have, the harder the gas is going to press against the turbine blades on it's way out. The same is true with cold air...60 psi out of a blow gun is going to spin the wheel faster than 10 psi, no? The more chance you give heat to escape through conduction with the wall of the header, the lower the gas temp inside, and the less pressure is available to spin the turbine. Think about how loud an open header or manifold is, versus a pipe (with no muffler) that runs all the way back. That is expansion making that noise, the same expansion that provides energy to the turbine. Obviously there is a limit to how much pressure we want to see in the exhaust, due to reversion and other factors; but to say that heat energy isn't important to spool time may be an oversimplification...

[overZealous1]

not implying that heat has zero effect on it, but in this example, it is the pistons creating the force/pressure generated, not simply heated air.
so to answer the op's post, don't worry about it. now using a 2 step launch control on your turboed car DOES help spool the turbo based on a type of thermodynamics. not burning the fuel in some cylinders to shove raw fuel into exhaust manifolds to explode to help spool the turbo. that is closer to how a turbine engine works to create output off the drive turbine. in a normal running car, your expansion already happened in the cylinder with the work being used to spin the crankshaft thus making another piston expel the spent gases (this is pretty much my point, the piston expelling the spent gases is the the force driving the turbines, not simply heat). only reason for gases to exploded in the exhaust is cam overlap, a non-firing cylinder, or using a 2 step to spool the turbo's from a stop.

the example on the exhaust sound though, is sound waves. basically you are allowing more waves to cancel (due to exhaust bends) before exiting the pipe (yet some octaves may get amplified) and allowing more area for sound waves to bleed off from the pipe resonation itself. also, reflective surfaces under the car (bottom of car, and road surface) contribute to higher pitched sounds and the sound waves traveling through the floor boards.
excellent example. i used to have glass packs right off my headers many years ago. they exited right under the drivers seat. car was very low so sound waves just bounced between ground and floor pan. i was crossing a bridge once. it had a large section of expanded metal grating. the second i hit it, i thought my engine shut off. i mean, i could not hear it when right before you needed ear plugs!! the sound waves were no longer getting trapped between the car and ground.
sound waves are not the same energy to spin the turbine. sound waves are created in this type of rapid expansion. example- grab a loudspeaker, seal it to your turbo inlet, crank it to 10hz. will the turbine move? yup, it will spin forward and BACKWARD at 10hz. ;)

[ace_xp2]

Actually losing heat reduces the enthalpy of the system, any time you can keep heat in the bounds in an open system, you can increase the available work.
This doesn't mean that Rear mounts can't work, but it does explain why those who wrap the exhaust all the way back find boost sooner. And also why rear mount guys usually lose boost when they switch from manifolds to long tubes.
Most relevant post in a great thread about rear mount systems:
http://www.ls1tech.com/forums/5064162-post48.html

[19,69camaro]

Ohh boy this is getting pretty heated.....sorry I had to

[overZealous1]

i didn't say there was ZERO effect from the heat, just not nearly as much work is being done by the heated spent gases as the engine itself is creating in pressure. put a convection heater in front of a turbine (seal it if you like) or a cold air supply under pressure. i will bet which one spins the turbine. thats about as simple as it gets.
heat is described as energy basically because it can convert to energy. yes, thermodynamics, where heat boils water to expand it (thats the converted energy) and can be used as a force.
yes, heated molecules are moving at a faster rate, but for this example, heat is not the prodominant force by itself.

btw- in my turbo system, i am mounting the turbo's off of cast manifolds, ceramic coated inside and out, then wrapping them. hahhahaha. point is i think we lost the main point awhile ago and each is right in most of the points.

[RSX302]

i didn't say there was ZERO effect from the heat, just not nearly as much work is being done by the heated spent gases as the engine itself is creating in pressure. put a convection heater in front of a turbine (seal it if you like) or a cold air supply under pressure. i will bet which one spins the turbine. thats about as simple as it gets.
heat is described as energy basically because it can convert to energy. yes, thermodynamics, where heat boils water to expand it (thats the converted energy) and can be used as a force.
yes, heated molecules are moving at a faster rate, but for this example, heat is not the prodominant force by itself.

btw- in my turbo system, i am mounting the turbo's off of cast manifolds, ceramic coated inside and out, then wrapping them. hahhahaha. point is i think we lost the main point awhile ago and each is right in most of the points.

Years ago when I purchased my twin turbo Incon system, I asked about wrapping the manifolds with the ceramic coating. Incon told me not to do it as it will crack the manifolds. I didn't do it to prove if he was right or wrong..just what I was told..

Yes I agree..from what I know about turbos..exhaust flow will spin the blade..heat energy along with exhaust flow will increase velocity giving you quicker spool-up. Also I hear that a siphon effect can occur thru the turbine since it's spinning so damn fast.

[WS6]

here's the entire thread for anyone wanting to read it instead of just one post. It's a good read

http://www.ls1tech.com/forums/forced-induction/529173-switched-headers-manifolds-rear-mount-turbo-results-inside.html

[exwestracer]

here's the entire thread for anyone wanting to read it instead of just one post. It's a good read

http://www.ls1tech.com/forums/forced-induction/529173-switched-headers-manifolds-rear-mount-turbo-results-inside.html

WARNING! Serious egghead alert! But yes, good stuff, and an example of a lot of the various misinformed opinions out there.

[RSX302]

here's the entire thread for anyone wanting to read it instead of just one post. It's a good read

http://www.ls1tech.com/forums/forced-induction/529173-switched-headers-manifolds-rear-mount-turbo-results-inside.html


That was a good read..Just need to get my head around increasing temp reduces backpressure?

I wonder if that is what the "siphon" effect I mentioned would be? Increased temp across the turbine spins faster pulling exhaust from the manifold?

[WS6]

Does the fact that the engine does not create pressure but works against pressure make sense to you? Keep in mind pressure is an indication of a restriction.

[Nothingface5384]

so would electric cutouts at the X-pipe make a turbo spool a tad bit quicker?

same question to if you have 3.5 downpipes and 3in for the rest of the echaust instead of 3in all the way back? or will these actually work against turbo spool?

[RSX302]

Does the fact that the engine does not create pressure but works against pressure make sense to you? Keep in mind pressure is an indication of a restriction.

Yea...the restrictions create backpressure on the piston. This backpressure on the piston hurts horsepower because it takes energy to push spent exhaust gases out.

This is what's routing around in my brain: The engine is a pump, as the exhaust flow exits the cylinder (being pushed out by way of piston like a reciprocating compressor), the first restriction this flow encounters is in the head (valve and exhaust port). So I figure anything smaller than this area on the primary exhaust tube will be considered added restriction. (Typical right?) If we have an appropriate free flowing manifold then this flow will be backed up at the next restriction. In this case, the turbine. This is ultimately the bottleneck. As this back up occurs, it will start building pressure in the exhaust manifold to a point that it will equate its flow rate thru the turbine that is being pushed out by the engine. At idle this pressure will/should be low. At peak rpm, this pressure I'd suspect will be much/much higher.

Now we add heat energy to the equation.. When you go from a high pressure, high heat area (before turbine) to a lower pressure area, (after turbine) you cool the exhaust gases rapidly. This heat change across the turbine is what I'm thinking spins the turbine faster than just the exhaust flow by itself, hence creating a pulling affect reducing backpressure.

Reading previous posts about wrapping to keep heat in or he only had 2 psi boost—if you have no heat energy at all in the manifold (just flow) , this kills that extra turbine spin to a point that it’s like perpetual motion on both blades.

or at least this is how I'm interrupting it..

[overZealous1]

can't forget about the forces generated by the compressor. that is the main reason for the back pressure. if the turbine was not connected to anything, it would simply catch up to the speed of the exhaust and cause very little resistance or bottleneck. more boost, needs more exhaust pressure to create it. the compressor wheel takes more power to make more boost. it is trying to slow down the turbine. powering the compressor is the work being done by the turbine.
this is the reason for blow of valves or recirculating vents in a turbo system. lift to shift, and you cut out your exhaust flow/power. pressure in the intake would try to stop the compressor from spinning, hence, the turbine also. no bov and you will have to wait for the turbo to spool up again. it can make a car fall flat on it's face with every shift. vent the compressor side for that instant and it allows the turbo to free spool, so once you get into it again, the bov shuts and you have a turbo that lost hardly any rpm and will be making boost.

on the 3.5" to 3" down pipe thing. it has been explained to me that the purpose is to allow the circular exhaust flow into linear again. in my opinion, i think it would need to be like 10" back to 3" to make a real difference.
one thing to note- i was the first person to actually test putting an x pipe (not the cheap ones either, handmade like burns stainless) behind a twin turboed vq35 (350z) and test its effectiveness on that engine (has a perfect bank to bank firing order) with turbos. i argued with every ****ing shop in country about the idea and argued it for months. finally came dyno day with my first prototype, and the testing which was done by a 3rd party (jim wolf, he had his prototype twin turbo set up on it) and low and behold the car picked up 70lb ft and 45rwhp at the same boost setting, no changes and no retune even. the down pipes were 3" and stayed 3" all the way out the back of the car. point i am making here, is that adding or keeping your x-pipe can make a difference in turbo spool up. i never tested the exhaust without the xpipe in it to make a solid comparison, but the numbers surely speak for themselves of the effectiveness.
btw- my n/a and turbo versions of that exhaust still holds the highest bolt on power rating out of even all the dam copy cats trying to recreate it even 6 years later.

[WS6]

This is what's routing around in my brain: The engine is a pump, as the exhaust flow exits the cylinder (being pushed out by way of piston like a reciprocating compressor), the first restriction this flow encounters is in the head (valve and exhaust port). So I figure anything smaller than this area on the primary exhaust tube will be considered added restriction. (Typical right?) If we have an appropriate free flowing manifold then this flow will be backed up at the next restriction. In this case, the turbine. This is ultimately the bottleneck. As this back up occurs, it will start building pressure in the exhaust manifold to a point that it will equate its flow rate thru the turbine that is being pushed out by the engine. At idle this pressure will/should be low. At peak rpm, this pressure I'd suspect will be much/much higher.

Now we add heat energy to the equation.. When you go from a low volume, high heat area (before turbine) to a larger volumearea, (after turbine) you cool the exhaust gases rapidly because of the rapid expansion of the gas (this is how an AC system works to remove heat from the air). This heat change across the turbine is what I'm thinking spins the turbine faster than just the exhaust flow by itself, hence creating a pulling affect reducing backpressure. Not sure about the pulling affect. I have never heard that and would have to read up on it. However, that aside you're correct. Turbos spin at extremely high RPMs and you need a lot of heat to do that. The example by Engr Mike about a diesel under load or not is a great example.

Reading previous posts about wrapping to keep heat in or he only had 2 psi boost—if you have no heat energy at all in the manifold (just flow) , this kills that extra turbine spin to a point that it’s like perpetual motion on both blades.

or at least this is how I'm interrupting it..

Ok back from training. Really the only thing else I wanted to add was that the restrictions add up in the system. It's not a matter of the worst one dictating the pressure build up. It's all the restrictions that are causing pressure to build. Restrictions can include bends, merges, forks, cross sectional area, and even material surface properties. The reason higher temps lower back pressure is the energy needed to spin the turbine is present there by removing a restriction in the exhaust path ie the turbine that's not spinning fast enough to be less of a restriction.

Using too small of a down pipe could cause the volume of the gases to remain unnecessarily low there by keeping temperatures on the backside of the turbine high. This would lower the temp differential across the blades and there by restrict the amount of energy available to spin the turbine as quickly as it could. This is why race cars use large down pipes or use open down pipes. The exhaust temps are lowered on the outlet side of the turbo by increasing the volume into which the exhaust gases dump. The result is a quicker spool time which equates to more power available sooner. The same as if you wrapped or did whatever necessary to retain the heat in the system. Only you're increasing the heat going to the turbine while leaving the down side the same. The temperature differential is still increased which is what's needed.

[Nothingface5384]

good to know, i'll be using a 3in pypes exchange setup ..electric cutouts are at the end of the x. maybe i wont waste my time with 3.5 dp off the manifolds to the pypes system..
everyone I talked to said the X is a waste on a turbo cause the turbo takes away the scavenging pulses ..but apparently you proved them wrong lol

[overZealous1]

thats exactly the arguement i was battling with everyone. it just so happened they were shops also making exhausts for the turbo vq35 crowd though.
the pulses will get muddled a little bit, but you are not talking extreme psi of backpressure. you have to look at it like an air compressor tank. you can create pressure in the tank (exhaust manifolds in this situation) but at every push in of more volume, will create a spike. that spike will still travel through the turbine. the vq35 engine though had a perfect firing order of bank 1 then bank 2 through the sequence. the ls1 or older small blocks are not as effecient for the use of an x-pipe. i also used aeroturbine mufflers. if you don't know about them, look them up.

[RSX302]

see bold

At least I’m in the ball park..not too many bold corrections. lol

When you say Low Volume, I assume you are referring to the area in the exhaust manifold?
You say like an A/C system…now you’re talking my language as that’s my background… You removed Pressure? Pressure must be there to overcome the resistance of the turbine as previously stated. Example: as the wastegate opens, it releases “pressure/flow” around the turbine to slow it down—path of least resistance.

Here's a hypothetical:
Let's say both turbine and compressor impellers are the same flow (1:1) and just flow was present at the exhaust turbine (no heat), the flow on the compressor side will be the same—right. So if we do nothing but add high heat to the exhaust turbine flow, this would spin the shaft faster due to the heat energy. By spinning faster, this will create increased flow on the compressor side? So theoretically if the exhaust turbine flow remains the same and the turbine impeller is spinning faster, it will take less input pressure to turn...That’s kinda where I came up with the pulling/sucking theory to lower backpressure...

[WS6]

Ron I was editing my post while you replied. You'll want to read what I wrote again as I added more info.

[WS6]

At least I’m in the ball park..not too many bold corrections. lol

When you say Low Volume, I assume you are referring to the area in the exhaust manifold? Yes or even the area inside the turbine housing since it's tight and the tolerance with the turbine blades in minimal
You say like an A/C system…now you’re talking my language as that’s my background… You removed Pressure? Pressure must be there to overcome the resistance of the turbine as previously stated. Example: as the wastegate opens, it releases “pressure/flow” around the turbine to slow it down—path of least resistance. The waste gate doesn't release pressure. It increases available volume for the gases to flow through which results in a pressure decrease as well as a temperature decrease. It's a very important distinction even if it sounds like I am splitting hairs.

Here's a hypothetical:
Let's say both turbine and compressor impellers are the same flow (1:1) and just flow was present at the exhaust turbine (no heat), the flow on the compressor side will be the same—right. So if we do nothing but add high heat to the exhaust turbine flow, this would spin the shaft faster due to the heat energy. By spinning faster, this will create increased flow on the compressor side? So theoretically if the exhaust turbine flow remains the same and the turbine impeller is spinning faster, it will take less input pressure to turn...That’s kinda where I came up with the pulling/sucking theory to lower backpressure... That sounds like it could be correct. I say could be because I question if the design on the impeller blades could create a low pressure are in front of the blades. This low pressure area would be needed to suck the air forward into the blade. I actually posed a similar question to my fluid dynamics teacher in reference to wind turbines and oscillating fans. Does a lower pressure or vacuum area exist in front of a fan at a certain point or does it only push what it comes into contact with? He couldn't tell me but believed that it could only push what it comes into contact with.

Now I realize a fan or wind turbine blade and a turbo's impeller blades are different. To further question the possibility of your thoughts, it is possible for a submerged water pump to move water with such speed and volume that it does create pockets of air in front of the impeller because there is not enough water volume and there by weight above the pump to keep the water forced against the blades. This is an example of how cavitation can occur. Cavitation is very bad. When this occurs, is a vacuum area created right in front of the blades? If so, is it just not strong enough to pull the water down into the blades fast enough? I honestly don't know.

[WS6]

can't forget about the forces generated by the compressor. that is the main reason for the back pressure. if the turbine was not connected to anything, it would simply catch up to the speed of the exhaust and cause very little resistance or bottleneck. more boost, needs more exhaust pressure to create it. the compressor wheel takes more power to make more boost. it is trying to slow down the turbine. powering the compressor is the work being done by the turbine.
this is the reason for blow of valves or recirculating vents in a turbo system. lift to shift, and you cut out your exhaust flow/power. pressure in the intake would try to stop the compressor from spinning, hence, the turbine also. no bov and you will have to wait for the turbo to spool up again. it can make a car fall flat on it's face with every shift. vent the compressor side for that instant and it allows the turbo to free spool, so once you get into it again, the bov shuts and you have a turbo that lost hardly any rpm and will be making boost. To further explain since this does get a little complicated for anyone new that maybe trying to learn. A gas motor has a throttle plate either in the throttle body or the carb. The pressure present in the intake pipe would slam and hold the throttle plate shut if you removed your foot from the pedal which is what was keeping it open in the first place. Because of inertia and the exhaust flowing through the turbine on the other side of the shaft from the compressor impeller, the impeller doesn't just stop instantly. You can do serious damage to a turbo if this pressure is trapped inside the intake pipe hence the need to relieve the pressure by increasing the volume available to the charged/compressed air.

on the 3.5" to 3" down pipe thing. it has been explained to me that the purpose is to allow the circular exhaust flow into linear again. in my opinion, i think it would need to be like 10" back to 3" to make a real difference.
one thing to note- i was the first person to actually test putting an x pipe (not the cheap ones either, handmade like burns stainless) behind a twin turboed vq35 (350z) and test its effectiveness on that engine (has a perfect bank to bank firing order) with turbos. i argued with every ****ing shop in country about the idea and argued it for months. finally came dyno day with my first prototype, and the testing which was done by a 3rd party (jim wolf, he had his prototype twin turbo set up on it) and low and behold the car picked up 70lb ft and 45rwhp at the same boost setting, no changes and no retune even. the down pipes were 3" and stayed 3" all the way out the back of the car. point i am making here, is that adding or keeping your x-pipe can make a difference in turbo spool up. i never tested the exhaust without the xpipe in it to make a solid comparison, but the numbers surely speak for themselves of the effectiveness.
btw- my n/a and turbo versions of that exhaust still holds the highest bolt on power rating out of even all the dam copy cats trying to recreate it even 6 years later.

To help someone that may still question if the pulses are still there which would be the only reason an xpipe could scavenge, simply ask them if they have ever been to a place with turnstiles. If a whole mass of people are slowly going through a turn style, you obviously see the pulses. Each person is one pulse. Now say Godzilla is attacking and that same mass of people is now forcing its way through those turnstiles. Even if they are getting two people through it at one time and everyone is moving fast enough to make it look like it's one continuous line, is the turnstile not still spinning?(obviously assuming no one is jumping over the turnstile) The air's still pulsing and with the firing order of that engine, it's pulsing in step with respect to each bank. You proved that. I honestly don't see why you caught such resistance with the idea

[WS6]

Nothingface

In general you should be fine with the cutouts after the x-pipe or right off the down pipes. The problem is the question is too vague to be able to fully answer. It's like asking do I need a 2.5" dual exhaust or 3" dual exhaust for my NA motor without listing specs.

You could experiment with the location of the cutouts though and see which works best. I think that would be interesting to see.

[overZealous1]

To help someone that may still question if the pulses are still there which would be the only reason an xpipe could scavenge, simply ask them if they have ever been to a place with turnstiles. If a whole mass of people are slowly going through a turn style, you obviously see the pulses. Each person is one pulse. Now say Godzilla is attacking and that same mass of people is now forcing its way through those turnstiles. Even if they are getting two people through it at one time and everyone is moving fast enough to make it look like it's one continuous line, is the turnstile not still spinning?(obviously assuming no one is jumping over the turnstile) The air's still pulsing and with the firing order of that engine, it's pulsing in step with respect to each bank. You proved that. I honestly don't see why you caught such resistance with the idea



i like the fact you got a godzilla reference into a turbo conversation, hahha.
i caught resistance because nobody had tried it. i do stuff in both import and domestic worlds and have for years. i don't consider myself an import guy or a domestic guy, just a car guy. so i feel it gives me a slight advantage to be able to combine the knowledge from both worlds that don't necessarily communicate that well together.

the propeller cavitation thing is basiclly a relationship between pitch, rpm, efficiency. look at the pitch on a frieghters prop, then a hydroplane. pockets of air takes away area you are pushing against.

to figure out the pushing/pulling thing, i like to think of it this way. a fan, where the fan itself is stationary, and you are moving something through it, you are creating a low pressure that is needing to get filled in. now, think of a boat prop, where the water is stationary (lets say no current for the sake of the example) and you are moving the boat. then you are pushing against it. ideas the same, but depends on which one is so called stationary.
plane=pushing against
pump=drawing in

[RSX302]

That sounds like it could be correct. I say could be because I question if the design on the impeller blades could create a low pressure are in front of the blades. This low pressure area would be needed to suck the air forward into the blade. I actually posed a similar question to my fluid dynamics teacher in reference to wind turbines and oscillating fans. Does a lower pressure or vacuum area exist in front of a fan at a certain point or does it only push what it comes into contact with? He couldn't tell me but believed that it could only push what it comes into contact with.

Now I realize a fan or wind turbine blade and a turbo's impeller blades are different. To further question the possibility of your thoughts, it is possible for a submerged water pump to move water with such speed and volume that it does create pockets of air in front of the impeller because there is not enough water volume and there by weight above the pump to keep the water forced against the blades. This is an example of how cavitation can occur. Cavitation is very bad. When this occurs, is a vacuum area created right in front of the blades? If so, is it just not strong enough to pull the water down into the blades fast enough? I honestly don't know.
I don't know what the pressure is in a turbo manifold or what the ideal target should be, but I'd imagine that there needs to be a target when sized properly. That would be like putting a 115mm turbo on a stock little 4 banger. It would blow right through the blade without spinning it—or you would need to be revving 8000rpm. Talk about turbo lag..lol

I wouldn't say low pressure in terms of vacuum. If you had the capability of spinning the turbine at a given point a little faster with no change in exhaust flow, then you will drop the overall pressure in the manifold.

I've dealt with cavitation on water pumps for cooling towers. This was a classic engineering failure by someone sizing the pump inlet distribution line too small (14" vs 16") and not having the appropriate NPSH. In this case it was reading 0 psig on the 14" line. Inlet to the pumps reduce to the impeller about a foot out. If the proper NPSH isn’t present at that point, you will go into a negative pressure situation entering the pump impeller. Aka; gas bubbles, big marble sounds, etc….as you said..not good.

[Nothingface5384]

Nothingface

In general you should be fine with the cutouts after the x-pipe or right off the down pipes. The problem is the question is too vague to be able to fully answer. It's like asking do I need a 2.5" dual exhaust or 3" dual exhaust for my NA motor without listing specs.

You could experiment with the location of the cutouts though and see which works best. I think that would be interesting to see.

yea i Understand
truthfully it'll just be a stock 73 buick 350...so a measily 180-90 hp or so and around 245 ft lbs and 8 lbs of boost on top of tthat with a sheetmetal s/p intake
once it blows up goes the built 355 or perhaps 370(6.4" honda rods) with lots of head porting, chevy 1.7 roller rockers and maybe a roller cam with 4-7 swap(ta212 cam profile)
aiming for 750 hp and simlar torque..but atleast 650 min

[alfatwin]

seems to me that the size of the restriction (turbine tunnel) in relation with the amount of exhaust flow has more effect on the speed of the turbo shaft than simply heat. The surface area of the turbine vanes and the size of the inside of the turbine vs the amount of exhaust gas trying to get by them has a direct effect on how fast said turbine accelerates to an effective speed to pressurize the intake or, as we say, spools up (the smaller the hole the faster the velocity of the air going through it). I can't say the hot gas doesn't effect the spool up time as Ive never tried to power a turbo with cold air, but as the exhaust gas is the remains of fuel/air mixture that has ALREADY EXPANDED TO MOVE THE PISTONS, unless there is still burning fuel in your exhaust under throttle (check your timing) this "expansion" would be minimal.. can we get Mr. Garrett to solve this?

[RSX302]

Found this read to help explain..

http://www.thedodgegarage.com/turbo_fun.html

[overZealous1]

So, in real world terms, what does this tell us? All else being equal, The amount of work that can be done across an exhaust turbine is determined by the pressure differential at the inlet and outlet_ (in english, raise the turbo inlet pressure, lower the outlet pressure, or both, and you make more power) Pressure is heat, heat is pressure.

^^ most relevent sentence quoted from your link. if you check back to my post back on #7, it pretty much sums up his paragraph, in different words. common denominator is pressure. heat does make a difference, but to quote him "a measureable difference". heated gases is kind of the icing on the pressure cake, lol.

[RSX302]

This was a great thread...I learned a bunch about turbo operation...Thx everyone..

[supernatural]

I have been worked with turbo systems for years, and I have to say that this tread http://www.ls1tech.com/forums/forced-induction/529173-switched-headers-manifolds-rear-mount-turbo-results-inside-3.html has a lot of misinformation.

overZealous1 put some quality info.


Alex

[RSX302]

Found this in garretts site..good read

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech102.html#b

"Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing, as it is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel. This provides increased turbine power at lower engine speeds, resulting in a quicker boost rise. However, a small A/R also causes the flow to enter the wheel more tangentially, which reduces the ultimate flow capacity of the turbine wheel. This will tend to increase exhaust backpressure and hence reduce the engine's ability to "breathe" effectively at high RPM, adversely affecting peak engine power.

Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds."
_________________
Also, I got to tune (FAST EFI) the STS system..Worked well, and yes there is a little more lag than if it were at the engine. Thing still moved out nicely..just keep the rpm up.

[alfatwin]

It looks like I may have a lot to learn about temperature effects on gasses with expansion, where could I go to get info? I mean besides "back to school!" can I find a text relating to this? my knowledge is based on average temp gas with restrictions and pressures/ volume etc. how much do the thermodynamics effect them?

[MonzaRacer]

I've just been thinking about this and was wondering what experience anybody here has with respect to the best place to mount the exhaust housing.

Now, I know you want to place the turbo on a V8 for example where the exhaust gas velocity is the highest which on a header would be at the collector closest to the four runners as possible (assuming TT here.) I wonder why kind of lag issues anybody may be having when mountign the turbos further down the exhaust route? For example I've seen some setups where the runners are pretty long and either a goofy pipe is plumbed inline with an exhaust housing pad welded on or worse-on a single turbo, I've seen a long crossover exhaust pipe connect to two headers facing towards the front of the car.
What I want to know is, wouldn't that contribute to a significant amount of lag and even worse once an intercooler is plumbed in? I'm working on my own turbo system now fo rmy Cutlass and am working out details between a single and TT setup. Nothing is available in a kit form that looks reliable imo so I am making my own but a lot of what's out there I am not sure about. I am building for maximum exhaust velocity (and heat retention) and zero turbo lag (or as absolute as little as possible). It doesn't matter that this is all in an 80 Cutlass...moreover this is just a question of exhaust velocity relating to turbo lag. Thoughts?


OK as for the info I learned from some discussion with Gale Banks a long time ago, is that in turbo systems, turbo placement is not as critical as proper selection AND keeping the heat and velocity UP. After reading what the guy on l1tech did, basically his switch from long tube headers to cast manifolds had a two fold effect, one was it upped his exhaust velocity enough to help his spool issue, same as having three sets of turbo headers with different tubing sizes will change the lag effect, and cast iron would allow the heat to stay in the exhaust a little more where as his long tube headers would radiate more heat out effectively losing the thermal dynamic and slowing the exhaust gas velocity.
I designed a 3 in exhaust for a guy many moons ago when working for a Meineke shop while in school. He had a stroked 305 (400 crank)
and his car would only run hard if he let it sit and get good and hot in the exhaust, then it would pull hard till he drove a bit then get little doggy. The car would hammer most guys if he ran short runs and had let car sit. So I pulled him back in and we wrapped it when turbo wrap was like uber expensive Indy car stuff(lucky this was in Indy where the 500 is ran and I had a friend at Patrick Racing, we double wrapped his complete exhaust to the mufflers and tada he could run that little 305 soooo hard. All from the exhaust being large enough to let it breath for the stroke, but if it wasnt hot , it was laggy , like a turbo.
He built the car back up after a minor wreck that ripped exhaust off and we went back with an odd 2 3/4 pipe we had in shop,,,,and dies to bend at the time,,,,never seen any since. The car NEVER ran as hard since going to the 2 3/4 pipes, even wrapped or with out mufflers, I cant remember the muffler brand but the came with cool paint job on them, said sonic turbos.
After telling Gale about this as he was telling me to think turbos back when I was thinking about blowers and NOS was becoming in vogue. Guess I should have listened more huh?
Everything I have been told in turbos is to not restrict the engine enough to hurt power but to not make turbo headers too large so to as effect exhaust pulse velocity,,, oh and this was many moons ago I talk to Gale and he was saying that even if you pulled a muffler and put a turbo on the car back there it would still work and even have some benefits as the piping going up front would allow the air charge to cool down. But you would have to keep proper size on the exhaust pipe to turbo and keep it warm enough, but then the STS setup has one benefit as to packaging but it also has limitations on how quick it will spool up. But its not set up as a hammer you back from a dead stop type system.
I always thought of proper turbo setups for driving should run like a properly set up Qjet, you should just feel it start pulling like gangbusters NOT bog (lag) then slam you into the seat.
Some means of design might be done on paper but a lot will need to be done on car ,in person.