Where to find exhaust tech info?

[SRD art]

Anybody know where I can find fact based (not opinions, or vendor supportive magazine articles sponsored by a specific company) tech info about exhaust? I'm going to put a new motor in the Pumkinator with roughly 550 hp/ 500+ft lbs and have a bunch of questions about design such as...

• effects of different size tubing (2.5", 3"...)
• 2 into single vs duals
• X vs H pipe
• muffler flow considering muffler design and placement
• how critical is back pressure and how does it affect power numbers
• power reduction/ increase, if any, with tail pipes
• effect of different size tail pipes than head pipes, i.e. 3" into 2.5" for clearance over the axle
• hp advantage/ disadvantage for using side pipes like old Vettes and Cobras
• Choosing the best header tube size based on the engine

etc...

Currently I have abbout 325 hp and 400 ft lbs. through 1 5/8 cheapo headers, 2.5" head pipes into a Flowmaster Y pipe, then 3" through a Dynomax race bullet, 3" over the axle, then into a 3"x 18" Dynomax round Stainless muffler exiting through dual 4" tips under the center of the rear bumper. I love the way it sounds and I'd like to keep the rear center exit, but there's only room for one muffler out back. I've been thinking about some stealthy flat black side pipes too. Just need some decent solid good info.

Thanks!!

[jlcustomz]

Ben, most info out there to some degree is always opinionated & has variables due to application.
The right size for your particular application is definitely important. Modern engines with better flowing heads such as LS & cobra engines seem to like larger exhaust than older engines such as gen1 sbc. This applies to header size also. Burns Stainless is one of the top places for supplying the best header parts & figuring the optimum custom sizes for your application. Their tri-y designs can make more all around & top end power than others. Pricy though.
X-pipe can be marginally better than h pipe most of the time, but this subject gets opinionated fast. Different sound between the 2 , which best choice can vary per application.
Most really good mufflers can all give very similar performance when done correctly .
A large single setup can come close to dual performance with less weight, but won't draw out as much heat.
Tailpipes can become smaller than rest of system, which increases velocity. Having a few nice mandrel bends shouldn't matter much, but just one single crush bend will effectively restrict the entire diameter.Tailpipes likely would never increase power, but shouldn't hurt it on your intended power level.
Sidepipes would be as much for coolness as anything else these days. Building a system with cutouts running to a set of loud sidepipes would be a cool option. Check out the cherry bomb Camaro done a few years back. Could run quieter mufflers outback, then open up, allowing exhaust to be able to flow through all 4 exits.
That's some of the best thoughts I can hand you based on years of trying to pay attention.

One last thing everyone may not think to tell you here:::: have fun with your personalized choice of tailpipes if you run em. Something for yourself at the end of the day.


https://www.google.com/?gws_rd=ssl#q=cherry+bomb+camaro

[SRD art]

Here's my current system 2.5" into single 3". Only difference is I have a Dynomax round muffler just upstream of the dual tips because the race bullet was just too loud.

G body engineers seem to have not been concerned with modifying the cars, one of the many issues is it seems it's near impossible to install a symmetrical exhaust system. I'm wondering if having different bends and tube lengths between bends would cause differences in flow from side to side too?





This is the rear muffler- http://www.dynomax.com/media/catalog.../1/7/17263.jpg

[jlcustomz]

Different lengths & bends on each side shouldn't really matter, But that existing y-pipe has some pretty sharp crush bends in it. Lots of room for improvement there.

[SRD art]

Different lengths & bends on each side shouldn't really matter, But that existing y-pipe has some pretty sharp crush bends in it. Lots of room for improvement there.

Nobody local has a mandrel bender. :(

[jlcustomz]

No local shops do, got crush bend stuff myself to get rid of. For my upcoming exhaust project, I picked up a Pypes 3" x-pipe kit unused for cheaper than direct new. Got 3 used factory truck aluminumized 3" tailpipes, which have mandrel bends & a few parts from a muffler shop , & an 8' new length of pipe for about $100. Gonna cut up & make my own, since local shops can't do what I want. Not that I want to do this at home with no lift, but sometimes to get what you want, got to take control yourself.



Not sure if you saw it before, started making my own tri-y headers from old race headers. Just waiting for time to take vehicle apart to test fit & finish up with some proper tig welding.
https://www.pro-touring.com/threads/...ers-for-g-body

[jif]

Here is some great stuff I found over the last few days while looking into exhaust design.

X-Pipe's Design
http://www.surefloexhaust.com.au/exh...pipe/xpipe.htm

X-Pipe vs Y-Pipe
http://my350z.com/forum/intake-exhau...roduction.html

Motordyne has some interesting threads/articles around flow
http://www.motordyneengineering.com/index.php?cPath=2_9

Discussion's on back pressure
http://my350z.com/forum/intake-exhau...k-for-n-a.html

[SRD art]

Thanks for the great links Jif. I read through some of the info from Motordyne. I will read more of this after work today. When I first started this thread I talked on the phone with very nice and helpful Greg at Dynatech Headers, and what he was suggesting was right in line with what the Motordyne guys are saying. In a Pro Touring car we will not very often be close to hp peak, but rather the key is highest possible torque to pull out of corners. Typically Smaller tube creates velocity over big tube which is what you want ahead of the merge, so Both Greg and the Motordyne guys seem to agree there is a definite place for a Y into single exhaust for pulling max torque AND decent HP figures. Choosing the right tube size and keeping the y close to the motor seems to be a key factor. On the other hand LS engines seem to like larger tubes so a dual 3" with an X pipe seems to work well for them. Still some more reading and research to do, but I think I'm going to try my exhaust as is with the new motor and go from there.

[jlcustomz]

As I hinted on in my first comment, definitely is a difference between what higher flowing late model engines & gen 1 engines seem to like. VERY conflicting lines of thought.

I do think it is more important to gear towards your particular use than listen to all the drag race related ls talk you may hear on ls1tech.

For your application, nothing wrong with a good y-pipe setup, Just need sufficient size out back for your power level.

With all the bla bla about exhaust sizes on ls engines, won't be much difference in mid to upper mid power between lets say a true 2.5 or 3" system with only a small difference up top. Same for between 1 3/4" or 1 7/8" headers.

As far as headers, ever see my tri-y thread here I started on a few months ago? The old thinking in tri-y's was they were mostly for mid range. The new thinking, as with burns stainless, is they can be superior in all rpm ranges & even see use on pro stock dragsters when properly designed. Still lots of conflicting info out there on them, But if nascar & other race classes returned to them AND pro stock dragsters also run them, something to be said for proper header design.

[SRD art]

Good thoughts JLC.

Just sharing some thoughts after doing some reading...

I did some more surfing on the subject last night. Most of the info I found was outdated, 8-10 years old. Motordyne speaks of needing backpressure as a myth, and as expected I read people saying in these older threads you need more backpressure to make torque. That sounds backwards to me, why would you need to slow the exhaust down and create resistance to make power? Scavenging comes up in the more intelligent forum conversations, and it seems that single exhaust is a fantastic way to scavenge.

Then there's tube size. Back in the 90's I remember reading an article that said a single 3" has similar flow capability to a 2.5" dual system. Last night I read people (and exhaust companies) saying that a dual 3" system is good for up to 600 or so hp, and a single 3" is only good for about 330 hp, while dual 2.5s are good for 450 hp. What??

Most (but not all) of the newer info I saw on single exhaust was related to turbo cars. There were many examples of folks claiming high dyno hp figures, in the 600+ RWHP range, some over 700 hp, running through single 3" exhaust. Those that actually tried both 3" duals and 3" single said they gave up anywhere between 20-40 max rpm hp on the dyno going to single but felt that was reasonable considering the weight reduction and ease of packaging. I saw several times people saying the power reduction is less with lesser hp engines. But there were still several naysayers (without any dyno figures to back their naysaying I might add) that said single exhaust is too restrictive and a traditional small block over 500 hp needs 3" duals. I would lean more towards believing the turbo car guys, firstly there were several examples of different cars building these power levels and they claimed to have actual dyno figures, not seat of the pants "yeah that old Corvette 327 in my car makes 4,000 hp at idle" opinions. Logic says to me it would seem that getting the exhaust to flow through the turbo as fast as possible would equate to more boost/ power, while restriction in exhaust would reduce boost and power capability. So it would make NO sense for A LOT of them to be running a single exhaust if duals were significantly better. I have zero experience with turbos and don't know if my logic is correct, but those guys stand behind it so it's got to have some validity.

[jlcustomz]

Reading can be dangerous sometimes. I'd steer clear of any turbo related info, as boost changes things.

Just remembered , I do have the SA277 book on performance exhaust. Like any book , It doesn't say everything I need to know, & the info isn't written by god if ya know what I mean. Anyways, the general pipe size chart says you should have 4 to 4.5" for a single pipe in your power range or 3" for duals.

Any general info by David Vizard, though may be a little old now, may be as good as any.
Another interesting study on exhaust is street bikes. My knowledge is all old on them , but many of the top exhaust systems on the big inline 4 engines of the late 80's or so were 4 into 1 , rather than 4 into 2. Weight was also a factor, but even these older modified superbikes pumped out some serious airflow through 1 outlet, rather than 2. Hmmmmm????

[jif]

A few more links which explain back pressure and flow velocity much better than I can.
http://www.gomog.com/allmorgan/exhaustbackpressure.html

http://www.mikekemper.com/elantra/diyexhaust/

We found similar results when modifying the exhaust on turbo subaru's and actually tapering the exhaust from 3" down to 2.5" from the rear diff to the rear muffler, gave better results than 3" all the way back.

I just have to find the right balance in size between gas volume and velocity for my 4.8L. Dual 2.5" vs 3". Interesting that mercedes benz use 2.75" on their AMG v8's.

Might have to try 3" from the cat thru to mid-pipe (where the hotter gases take up more volume) and taper back to 2.5" for the rear muffler (as the gases cool down and the smaller pipe will help keep the velocity flow up)

At the end of the day, the tuning and intended use can't be ignored as the rpm band for a track car vs street car are quite different and a car being used in both will have to comprise somewhere.