I've got 2 exhaust questions...

[Ron Sutton]

Hey Todd,

Hang tight until I get Tony's exhaust worked out & I'll have some answers for you.

[Todd in Vancouver]

Hey Todd,

Hang tight until I get Tony's exhaust worked out & I'll have some answers for you.

My car is hanging on a rotisserie so I will need an answer by the summer of 2015, or so.

I would think that mine is typical of what the majority of guys build at home.

[Ron Sutton]

My car is hanging on a rotisserie so I will need an answer by the summer of 2015, or so.

I would think that mine is typical of what the majority of guys build at home.

Whew! I better hurry then !


Just as a precursory primer ...
Of course the exhaust size matters ... so we'll work that out for your application. But it is pretty simple, based on horsepower level & rpm. For an engine to make Xxx HP ... it has to flow Zzz cfm of air into the engine & Yyy cfm of air (exhaust) out of the engine.

Muffler placement matters ... and affects power ... but not to the point of killing the power if they're not in the "happy spot."

H-pipes and/or X-overs ... can really help a high power performance or race engine to achieve optimum performance ... if they are placed correctly. On the other hand, they can hurt the engine's power output significantly is placed wrong. Adding H-pipes and/or X-overs to an exhaust system is a potential power gain ... with a potential risk of power loss.

It's all about the exhaust pulses. If the H-pipes and/or X-overs are placed correctly for your engine's unique pulse pattern ... the exhaust pulses on one side are "relieved" at the point of the H or X ... and that pressure slips into a "traffic opening" on the other side. On the other hand, If the H-pipes and/or X-overs are placed incorrectly for your engine's unique pulse pattern ... the exhaust pulses on one side "start to be relieved" at the point of the H or X ... and that pressure runs into "exhaust pulse traffic" on the other side ... causing both sides stall up. Just like on the freeway. This reduces exhaust flow ... sometimes drastically ... and hurts engine power output on a level equal to the flow problem.

Muffler placement does become more important when H-pipes and/or X-overs are utilized, because the muffler acts as a "Yield" sign ... slowing up exhaust flow traffic to a degree. Tubing size becomes more important too ... as size of the exhaust tubing plays a role in the velocity of the exhaust gas pulses.

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I am a big fan of H-pipes and/or X-overs ... as long as they are placed correctly for the specific engine.

The formula I utilize to calculate this requires:
Peak HP
RPM at peak HP
Bore
Stroke
Rod length
# of cylinders
If odd fire, specific firing degrees of the cylinders
Compression ratio
# of intake valves
Intake valve diameter
Intake valve stem diameter
Max intake valve lift
Intake cam lobe duration @ .050"
# of exhaust valves
Exhaust valve diameter
Exhaust valve stem diameter
Max exhaust valve lift
Exhaust cam lobe duration @ .050"
Actual degreed cam centerline
Lobe center angle
Exhaust Port centerline length

Then, I need decisions on plans for ...
Header primary tube: standard, 2-step or 3-step
Header design: standard or tri-y
Collector: Standard or merged (reduced)
If for racing, ran as "open headers" with no mufflers or anything past the collectors
If for racing, ran with mufflers right out of collectors
If Vortex cones are used for sound suppression or not
If an H-pipe is to be utilized
If an X-over is to be utilized

With this info, we can spec every detail of the headers & exhaust system for optimum performance. To me, this is just as critical as all the time & detail that went into he engine build. Building a killer engine, then just throwing on an exhaust "that fits" would be like throwing on any old carb that's laying around.

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This is too involved for most PT builds.
I think it only makes sense when we're talking extreme PT machines, Track Cars & Race Cars. I provide this service for race teams I consult to.

Here is an example of optimum & worst placement for the PT/track car I'm building for myself. All dimensions are from the end of the header primary tubes to the center of the H or X.
H-Pipe: Best power = 15.7" / Worst power = 23.5" **
X-Over: Best power = 62.7" / Worst power = 47.0" or 94.0" **

** This "worst" dimension creates the worst exhaust pulse traffic jam, therefore kills power the most. You'll notice the H-pipe dimensions aren't that far apart, because the closer to the primaries you work, the more sensitive the exhaust pulses are. I've seen shops place the H-pipe where "it fit well" ... and reduce the engine power output ... a lot.

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I hope you found this interesting, but again, I think it is too involved for most PT builds.

[Todd in Vancouver]

That's amazing Ron and I agree its way past what the majority of guys would do. I do find it amazing to try and understand though and do you have any recommendations on where a garage hack like myself can do a bit of reading and research to try and understand this a little better?

Also, here is the website for our local supplier and they have a pretty good section on calculators.

http://www.mopacautosupply.com/calculators.html

[Ron Sutton]

That's amazing Ron and I agree its way past what the majority of guys would do. I do find it amazing to try and understand though and do you have any recommendations on where a garage hack like myself can do a bit of reading and research to try and understand this a little better?

Also, here is the website for our local supplier and they have a pretty good section on calculators.

http://www.mopacautosupply.com/calculators.html

Unfortunately, I do not know of any books on the subject.

[IMPALA MAN]

In most cases (not always) you can typically pick up some high end HP by going larger on the tube size. This of course is at the expense of giving up some low end TQ in the lower rpm ranges. It's (almost) always a trade off. The opposite is usually true for the opposite...smaller tube, more low end TQ, at the expense of less high end HP. So why do so many people go too big on the tube?
I will share two scenarios and let you answer.
Scenario 1: A guy walks into his engine builder's shop after he is told he can pick up the engine because it is complete. What is the first question EVERY customer asks as soon as the builder tells him the dyno process is complete? HOW MUCH HP DID IT MAKE. Does anyone ever ask how much TQ did it make? Seldom, but at best it's the second question. So back to the scenario. So the engine builder knew he would be asked this question. So he spits out a true number of 515 HP. He then tells you some additional specs like header tube size (which seems a little large to you). You go away happy.

Scenario 2: Same scenario except this time the engine builder put a header on it that would best fit the applications demands. Some low end for stoplight to stoplight driving and not so focused on the high end, high rpm number that you may use at say 7000 rpm. So when you ask the HP number he spits out and accurate 505 HP. Now you are disappointed because your buddy had he same engine built down the road and it got 515 HP!!! The next engine build you take to the guy down the road.
Now who's fault is it that everyone goes too big on the tube size?

Engine builders get put in a tough spot by customer demands of HP. If they design the engine to give you the best OVERALL PERFORMANCE, you go down the road. My best advice, listen to your engine builder, tell him what you are going to do with the car and give him some freedom to build you the best engine for the given demands. AND DON'T get so wrapped up in the HP number.

[Ron Sutton]

Too true. That's why I often use the term "power" ... instead of horsepower ... because in our racing engines we're looking for the most torque under the curve of usable rpm. Who cares what one peak number is.

On the street ... I feel more emphasis needs to be on power in what I call the "most likely rpm curve" ... which for most is somewhere around 1800rpm to 3500 rpm. They young guy I was helping work out engine combinations on here recently made a smart choice. I showed him two engine combinations ... with two different powerbands ... & a predicted dyno curves. (I attached it).

It's hard to see an engine with 30 more horsepower & 10# of extra torque & say "no." But he wisely chose to go with the package that made more power below 4500 rpm ... where he will enjoy the power more. Unless you're seriously tracking your car often, that is where most PT & Muscle cars spend their daily lives.

[SSLance]

It's always fun to listen in when Ron's talking...

I ran what I always supposed was an ill-advised H-pipe position on my exhaust for a lot of years...because that's what was on my car when I bought it. Ran 1.5" long tube headers for the same reason, always wondering in the back of my mind how much power this was robbing.

Had to change headers after my T56 install, ended up with a set of 1 5/8s" Hooker shortys and changed to an X-pipe after my cross member at the same time, mainly due to fit reasons. Wasn't sure how that was all going to affect my power range but didn't have much choice at the time. Thankfully it added power in the right places (according to my butt dyno) and sounded better as well. The car picked up about 50 hp at the rear tires the next time I had it on the chassis dyno, but I'm certain the T56 addition plus some tuning changes helped in that regard along with the exhaust changes.

Had I known Ron at the time I would have spent the time to get him the info he needs like noted above and found out for sure what was the best exhaust scenario for my set up.

And BTW, coming from someone that has a 340 hp "truck engine" that puts 400 ft lbs of torque to the rear tires at 2000 RPM, I can vouch for "power" over horsepower in the fun factor.

[77tony]

Thanks for getting back to me Ron. Dyno chart for the LS376/525 injected motor. The plan is to lay out the exhaust configuration tomorrow similar to the bottom pic but without headers. Running with the stock manifolds to a 'Y' pipe and onto a 3.5" ? single PIPE back to a magnaflow muffler where the "Y" pipe is now located, or all the way back as in the pic below. Would like for the system to sound very much like the video link below (scroll to .25 seconds-on) TIA. 77tony

http://www.youtube.com/watch?v=PVtXzsCBMH8

[Kennymax]

I bought my 67 camaro with a 327 that has a very large cam. My "very young" cousin put a 3" pipe with racing flowmaster mufflers cut at the muffler down ward under the seats. My result was a very loud drone in the car obnoxious to myself and others. I know that loud is the way to go but this was annoying. So went to the muffler shop where the guy is a master at classic cars he went down to a 2.5 inch pipe and some mufflers." Forgot the kind" now it sounds like a POS. I can't stand it. So my question is? Do I keep the 2.5 inch and change my mufflers? If so what's the best to be heard before your seen in a cool classic sound "cam American muscle popping crisp and deep"? Or should I have just kept the 3" and changed the mufflers and ran them out the back? Thanks I'm new to all this

[pro68chevelle]

Hi Ron,

This is Scott from the aero tread, I had a question about the size exhaust I should use 2.5 or 3.0. I am using a GM LS376/480, it makes 480HP @ 5,750 RPM and 475 LB. @ 4,500 RPM, max recommended RPM is 6,600 with stock GM exhaust manifolds. I will be using a set of Kooks LS swap long tube headers with 1 7/8 primaries and 3" collectors and a Magna flow exhaust system with an x pipe. I may add power at some point in the future but should never be over 600HP.

Thanks Scott

[MonzaRacer]

Here are some tip I learned over many years, 6k or lower rpms, street driving, limited track time, keep primaries on smaller side like 1 1/2-1 5/8, run 4 into 2 into one (Flowmaster has great set of collectors) take them, extend them ,if needed.
Upon final tuning of the engine paint cheap, flat white paint stripe down side. then make hard full throttle pass and where paint quits burning cut there and install reducer to exhaust pipe size.
Most mid level and lower performance cars, etc 2 1/2 in pipe is fine, duals should use x pipe or h pipe. Larger mufflers usually deeper and quieter.
If engine is gonna go over 6k add 1/8in for every 1k rpm over in general. Same collector tuning as before.
3 in exhaust flows more free, but you will get more resonance at idle also.

Up to around 350-375 cid 2 1/2 is fine UNLESS you exceed the rpm rule, rpm needs free breathing. lower rpm needs more exhaust velocity, hence smaller pipes.
Only reason for smaller tail pipes after mufflers on stockers is noise reduction.
These are just some of the observations of a mechanic/hot rodder/drag race engine builder for budget minded folks.
Kind of develop and perfect theories over period of time building a guys car up a little more every year from stock to totally off the chain full blown race engine. Took a guy from stock rehoned mild cam 350 all the way to a full on 350 billet crank, h beam,forged piston,aluminum head roller engine. He went from high 9s in 8th on mild cam to high 6s all in same car over 7 yr period of time, then sold that engine for much more than he had in it, and built a full on race engine. THEN car was not up to it so he get s race chassis and retires car,,now son has soon to be cool car for school!
He still has old 2 1/2 duals and flow *******s in attic, the next incarnation with 3 in pipe, dynomax race mufflers, and full on $1000 set of stainless headers from full blown engine.
Lucky kid, dads car, and all left over parts.

[socoken]

I have a question about exhaust cutouts. I realize that open headers on a street car is likely to cost power, but I like the cool factor. My question is, does having that split just after the header affect flow when they are closed? It just seems like a split with a dead end would act like a resonance chamber and interrupt flow as it passes.

[Ron Sutton]

Hey Scott,

Hi Ron,

This is Scott from the aero tread, I had a question about the size exhaust I should use 2.5 or 3.0. I am using a GM LS376/480, it makes 480HP @ 5,750 RPM and 475 LB. @ 4,500 RPM, max recommended RPM is 6,600 with stock GM exhaust manifolds. I will be using a set of Kooks LS swap long tube headers with 1 7/8 primaries and 3" collectors and a Magna flow exhaust system with an x pipe. I may add power at some point in the future but should never be over 600HP.

Thanks Scott

You are on the right track, but your two situations ... 480 hp now & 600 hp later ... will have different optimum set-ups. For what you're doing now, 2.5" would be the optimum exhaust size. This size would help build a good torque curve with no sacrifice in power in the upper rpm range.

But the headers with 1 7/8 primaries and 3" collectors are larger than optimum for the 480hp. That size of header ... although you didn't state the primary tube length other than "long" ... is more in line with your future 600 hp needs & will provide a less than optimum torque curve with your current engine combo.

When & if you build up this engine to make 600 hp, the headers will be spot on & the 2.5" exhaust would still work well, providing a great low-to-mid-range torque curve ... but giving up some power above 5500 rpm. If that upper rpm matters to you, you would want to increase the exhaust size to 3".

[Ron Sutton]

I have a question about exhaust cutouts. I realize that open headers on a street car is likely to cost power, but I like the cool factor. My question is, does having that split just after the header affect flow when they are closed? It just seems like a split with a dead end would act like a resonance chamber and interrupt flow as it passes.

First, open headers will produce more power, if designed correctly.

Second, your question of "will the turn out act like a resonance chamber and interrupt exhaust flow pulses as they pass?"
I "think so" ... but I do not know "for sure" ... as I have never done this. Most of my advice is hands-on, been there-done that and know the results kind of advice. I've never done what you're asking, so I don't really know.

Maybe someone else on here has tried this & will share their experience. Otherwise, if you try it, you can let us all know.