2 1/2" exhaust versus a 3" system. 30 HP? REALLY ???

Kern Dog · Jun 17, 2013

The recent Mopar Muscle has an article where they do an install of a 3" TTI exhaust on a Sport Fury. The change from 2 1/2" to 3" bumped the HP by 30.
Really?
I've had the same 2 1/2" system on the car since I installed the first 440 in 2002. It was done at a local muffler shop. Now articles like this come out to say any engine making 450 HP or more is choking itself with a 2 1/2" system.
Who here has experience with this sort of upgrade?

benno440 · Jun 17, 2013

I know this isn't correct, but I like the idea of bigger is always better with muscle cars. im disappointed now because I have been told my 1 7/8" headers are too small and should be 2", ahh well

BeastlyBirdie · Jun 17, 2013

You did notice the TTI advertising really close to the article, right? Mopar Muscle seems IMHO to find amazing amounts of HP, but only from vendors in their magazine. In exhaust, bigger is not always better. Too large of pipes, be it exhaust or the actual head pipes will slow down the flow. Add to that the bends and mufflers, and there is a lot more than just 'go bigger.'
I'm sure someone on here can post up the gas flow calculations through pipes.

HEMI-ITIS · Jun 17, 2013

Have a 4 inch collector going into 4 inch stainless pipe with an "X" ending at the rear bumper.I don't bother dropping the exhaust at the track.too much of a pain in the azz!

lewtot184 · Jun 17, 2013

a 30hp gain would probably depend on how radical the engine is. on the average sensible street engine i doubt there's that much real gain. if that's 30hp (40-45hp at the crank) at the rear wheels then the 2 1/2" system must've been very crummy.

terzmo · Jun 17, 2013

I read the articles and don't put alot of faith in any of them as there are many things that can be changed as far as tuning a car for one dyno run vs another. Stock hemis and 6 pak cars had factory exhausts smaller than 2.5 stock. If you are a serious racer, you won't run an exhaust...if a street "casual" racer, the HP difference isn't worth the investment as far as I'm concerned. I ran a 3 inch to the rear axels and it was nasty loud through 40 series flowmasters...I then used 2.5 to run it the rest of the way.....quieted it some...no noticeable difference with a 498 stroker.

kiwigtx · Jun 17, 2013

In my experience with a stock 440, the use of 2-1/2" or larger headers, or open headers, actually reduces HP when racing. Bigger is not better, unless you have a serious engine and appropriately setup for huge exhausts. More noise does not mean more power.

I currently run the TTI 1-7/8" headers, X-pipe, Flowmaster 2-chamber mufflers and 15" resonators, and they run great with an honest 312 RWHP as checked on a Dyno.

Hemirunner · Jun 17, 2013

I have 2-1/4 tube 3-1/2" collector TTI headers feeding a full 3" exhaust. We dropped the exhaust and went a half second quicker, back to back passes. The 1-7/8 would be fine on a stock stroke unit but I won't put anything less than a 2" tube on a stroker BBM.

Kern Dog · Jun 18, 2013

As stated elsewhere, I am still sorting out the problems with detonation and excessive cylinder pressure. Many have told me that with the right combination of parts and tuning, I should be able to generate over 500 HP to the tires. The small cam , unported heads and small exhaust system are standing in the way. It is very tempting to open the wallet and see what this engine can really do.

Stumper · Jun 18, 2013

I read it too and I think the power gain was more from the muffler change. He went from baffled to straight through Ultraflos I believe. Still it seemed high for what appeared to be a relatively mild 440.

Meep-Meep · Jun 18, 2013

BeastlyBirdie said:
You did notice the TTI advertising really close to the article, right? Mopar Muscle seems IMHO to find amazing amounts of HP, but only from vendors in their magazine. In exhaust, bigger is not always better. Too large of pipes, be it exhaust or the actual head pipes will slow down the flow. Add to that the bends and mufflers, and there is a lot more than just 'go bigger.'
I'm sure someone on here can post up the gas flow calculations through pipes.

It's much more complex than just flowing gas because of the interrupted flow, but the thing about flowing gas or anything through a pipe is the inner diameter is effectively smaller because of the boundary layer. I have read you loose about 1/8" on the diameter, so with a 1.74" exhaust valve a 1-7/8" header pipe will do well. 1.81" valves then go 2".

BeastlyBirdie · Jun 19, 2013

Meep-Meep said:
It's much more complex than just flowing gas because of the interrupted flow, but the thing about flowing gas or anything through a pipe is the inner diameter is effectively smaller because of the boundary layer. I have read you loose about 1/8" on the diameter, so with a 1.74" exhaust valve a 1-7/8" header pipe will do well. 1.81" valves then go 2".

That's the calc I meant, thanks Meep.

HEMI-ITIS · Jun 20, 2013

Hemirunner said:
I have 2-1/4 tube 3-1/2" collector TTI headers feeding a full 3" exhaust. We dropped the exhaust and went a half second quicker, back to back passes. The 1-7/8 would be fine on a stock stroke unit but I won't put anything less than a 2" tube on a stroker BBM.

Did just slide the collectors to the side holding with one bolt or remove the system??Sometimes just the weight of the system is the pick up in E/T:blob1:

Hemirunner · Jun 20, 2013

HEMI-ITIS said:
Did just slide the collectors to the side holding with one bolt or remove the system??Sometimes just the weight of the system is the pick up in E/T:blob1:

We disconnected it at the collectors, moved the H pipe over so only 1 bolt was holding it on each side and ran it. I have the 3" super turbo muffles on it and it's just too big of a restriction for a 572ci engine, especially on the spray. I have since put in cut outs and we just uncap them and run. It really needs a 4" collector, but TTI only offered 3-1/2" at the time.

2 1/2" exhaust versus a 3" system. 30 HP? REALLY ???

Kern Dog

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benno440

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BeastlyBirdie

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HEMI-ITIS

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lewtot184

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terzmo

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kiwigtx

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Hemirunner

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Kern Dog

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