Thoughts on a 3"/2.5" exhaust system?

CMCE , that is exactly what I am running on my stage-2. A 3'' pipe with 3" muffler to 2.5 tail pipes mandrel custom made for my application. My theory was the same as yours, the smaller pipe would help increase velocity. Due to my custom trunk aluminum pan, ladder bar suspension and the straight up & down coil over shocks I was limited on tail pipes. Not sure if it helps performance or not, I have no reference data to compare but it is very quiet. I love how quiet it is, especially idling. Have a friend I've helped a lot with a 70 Challenger Maxi-wedge cross ram that we did the same thing many years ago and that car never slowed down. So far I have to say that that set up works until proven not.
Fernando

 

Standard fluid mechanics. You can take a class at any school that teaches mechanical engineering.

In a nutshell:
Total pressure drop through a system is the sum of the pressure gradients.
Pressure gradient is determined by a combination of viscosity (which in this case is controlled by temperature), volume of fluid, velocity, cross-sectional area, and turbulent vs. laminar flow.

The actual math would make your head spin, but the point is that the pressure drop through the whole system is the sum of the pressure drop through each point in the system. Not just any single restriction point.

-Bob C.

 

So by this theory the smaller the tailpipe the faster the car?
If you were talking about a fixed RPM, hence steady flow rate, you could tune for that. Cars don't operate at a fixed RPM so the math is out the window. There is only one point that matters if you run a full exhaust. That is the end of the pipe that is open to atmosphere.

 

No, the smaller the tailpipe the higher the pressure gradient. And the higher the pressure gradients, the higher the total pressure required at one end to force a volume through the pipes to atmosphere. And since one end of the pipe is open to atmosphere, the other end (engine) needs to create more pressure (work harder) to evacuate the same amount of exhaust. And the harder the engine needs to push on the exhaust gasses, the less power remains to push to the transmission and accelerate the car. Math isn't out the window at all, but the numbers and formulas are more than can be discussed in a forum post.

-Bob

 

Best sound of any car I own is the 3" on the stage 1 with the MT headers with that huge collector. The exhaust scavenging sounds when shifting was just the best.

On the Mustang I run long tube headers into a 3" exhaust with a crossover tube after the transmission to full 3" in/out mufflers then reduce to 2-1/2" over the axle to the rear of the car. I love the Summit 2 chamber racing mufflers quiet deep rumble at idle absolutely no drone and sound great (loud but no rap, rap, rap) at WOT, 508 hp/511 tq.






Mikey

 

My point to this thread was (and is) to see if the A-Body community out there thinks that a 3"/2.5" system is something that would be worth marketing by Pypes. Not sure how many 600-750hp street driven A-Bodies there are out there, but I'm guessing there's a bunch. There's been some disagreement here on whether or not 2.5" tailpipes are a detriment to HP at the 600-750hp level, and that's fair, but the purpose of these systems are to provide higher HP street driven cars the added clearance and sound reducing qualities of 2.5' tailpipes without sacrificing much, or any, power. So my question to the owners of those cars that fall into that hp range is - does this seem marketable to you?

 

and you can have the following Gary Paine 462 in.³, @600hp, TA aluminum stage one SE, Scotty Brown camshaft, full 3 inch system with delta 40 flowmasters and not lose any power. I’m sure any competent exhaust shop could rig up the tail pipes to accommodate your N25 bumper.

 

I did a lot of homework on 2-1/2 vs 3 inch exhaust. There are guys who hit the 650-675 crank horsepower level on shorty headers and 2-1/2" full exhaust on a well built combo. Of course the correct long tube headers and 3" exhaust added 6%-8% more power. We have guys in the 11's with full bodied cars on stock exhaust manifolds. So what are they running for exhaust?

Mikey

 

There are F.A.S.T class cars running low 10's/high 9's through manifolds (extrude honed) and a full 2.5" X-Pipe system, usually with Dynomax UltraFlo mufflers. Those engines are in the 850hp range.

 

CMCE to answer your question whether or not to offer the system in that configuration would be a yes. You (Pypes) already make both sizes correct? So it won't be a big deal to offer the tail pipes in a different size. Kind of a mix and match the system. I say go for it.

 

To be clear, I am not Pypes. I'm the owner of Classic Muscle Car Exhaust. I'm a dealer for Pypes, MagnaFlow, and Flowmaster, and I sell exhaust systems for '60's-'70's muscle cars. I do however, have a fairly close relationship with Pypes, as I have known the owner for 20+ years and I live close to their facility. Of those 3 manufactures, it's my opinion that Pypes has put the most thought and effort into a like-for-like exhaust upgrade for muscle cars. They offer some kits for cars that the others don't (Cougar, G-body), offer specific kits for 442 and GTO thru the bumper/valance tailpipes, and offer OEM style tips to complete a 2.5" or 3" system. They also offer nearly all of the kits w/o mufflers- no one else does that except for the Flowmaster A-Body kits. Their current 3"/2.5" 'Hybrid' kits as they're called does not include the GM A-Body, and I'm trying to convince them to do so. They use specific mufflers for this application too- a 3" muffler with a 2.5" outlet. I spoke to them about also offering kits w/o mufflers, just put 2.5" tailpipes with reducers into the box along with the 3" X-Pipe. This way you can use any 3" muffler you want. They think it's a good idea, but they would like a little feedback first. That's why I'm asking all of you- you're part of their marketing research!

https://classicmusclecarexhaust.com/

 

I'm running a full 3" mandrel bent system on my '67 Skylark with a 464cu in Buick. After a couple friends did the same, and lost no E.T. or MPH at the track, I went with it. Much quieter in the car. I'd stay 3" all the way back. I bought 3" mandrel pipes through Bobb & Geoff at Finishline. They are not cheap! You can buy mandrel pre-bent sections, to weld together, which is what I should have done. Can't recall the manufacturer. We did 'modify' them a bit to mate them to existing pipes.

 

I cannot tell you how it will fit through the bumper yet because I have not reinstalled the body. It is supposed to be correct for the N25. It is the pypes stainless system with the original N25 tips.




.

 

I question the validity of mandrel bends verses regular.
In testing on the dyno, smashing the header tubes did nothing to affect output, how would mandrel bends down the line where the exhaust gas is colder and slower effect anything?

 

I am also currently contemplating 3 inch / 2.5

I currently have hooker headers that go into a full length 2.5 system. It is a 455 with ported 430 heads and a crower 4 cam.When I open up the cutouts, it seems to breath easier and feels a bit lighter. Might be the butt dyno.

I ended up buying a 3 Inch Xpipe with built in cutouts which I have yet to install. I was thinking of dumping the exhaust out in front of the rear tires since I will be installing coilovers and most likely 3 inch tailpipes might not fit too well. Then again, the car is lowered so I doubt 3 inch side exit exhaust would leave any clearance for speed bumps.

Maybe I should keep the 2.5 mandrel tailpipe and add the x-pipe out front. Just not sure if it will quiet the car too much

overthinking it maybe, but I want a nice growl

 

Here is what I did a long time ago. TA headers with 3.5 inch collector. Went to Pypes 3 inch to 3 inch x pipe. 3 inch pipe to 3 inch cheap can muffler (Flowmaster clone.) Then went to custom mandrel bent 2.5 inch mandrel bent over axle pipes to N25 exit. Basically the muffler flows the same as a 2.5 inch pipe. The system works great and sets behind a 700 HP Procharged 462.

A buddy of Mike Garrison did the 2.5 inch pipes. I do not know if he still does them but the fit is really great.

 

Also my N-25 exhaust tip broke. Replace with Pypes GTO tips. I like them better. Gives it a Ferrari look. All of $55

 

Thanks for the input,

My set up would be:

Hooker Super Comp headers with a 3in collector
to 3 inch reducer
to 3 inch Xpipe
to 3 inch Flowmaster Flow FX straight case/ straight through mufflers
Then dump before the axle.

I was thinking of leaving the 2.5 Flowmaster mandrel bent talpipes I have instead of dumps but I was afraid it might quiet it down too much from what iv'e been reading.

Here's the current 2.5 flowmaster tailpipes