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What size exhaust pipes for 525hp?

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4.8K views 28 replies 12 participants last post by  67RS502  
#1 ·
My 468ci is making about 525hp on engine dyno, I would guess. I've got 10.5:1 compression, full Crane roller cam setup (peaks at 5,500rpm on chassis dyno), Edelbrock Performer RPM alum heads, 2" Hooker Super Comps, Accel DFI. Also using Muncie 4-spd and 3.73 rear gears. Street car only, no drag racing.........

Right now I'm running 3.5" collectors, reduced to 3" x-pipe, then reduced again to 2.5" 50-series Flowmasters and full tailpipes that exit out back.

My question is: are the 2.5" mufflers and tailpipes holding back some power at upper rpm's??????????????

thanks for any opinions

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#2 ·
I would first reduce the primary tube size to 1-3/4", run a 3" collector with a 3" x-pipe then reduce to 2-1/2" after that.
 
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#3 ·
I think youre loosing some power from the 2 1/2" tailpipes.
But I can give you an example:
70 chevelle, mild 454, car ran 12.0s @ 110 with 2 1/2" exhaust.
Switched to 3" exhaust it went 11.50s @ 115, since it picked up 5mph, it cost us about 50hp.
This was 3700+lbs car, so the 454 was makin around 500+hp.
I say get 3" tailpipes, and a set of Dynomax turbos - it will make more power, and be quieter.
 
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#4 ·
67RS, thanks for the info, that's exactly the feedback I was hoping to see, from someone who had done the switch with no other mods. I have a chassis dyno just down the street from me, so it's real easy to test the results.

RE: your Dynomax Turbo's, do those have much interior resonance? My Flowmasters are a tad loud outside, but it's the interior resonance I hate......................

thanks man
 
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#5 ·
I have 3.5" Magnaflows on my 502, but have Dynomax turbos on my Luv, it is 2.5" with a 20" case - very quiet. The 3" version my friend has on his chevelle is still quiet for a 11sec. car. - typical muscle car sound.
No interior resonance.
 
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#6 ·
I had Magnaflows on this car for a short time, but they had HORRIBLE interior resonance. How are Magnaflows on your 502?

I don't have room for a 20" case, that's another issue with the Dynomax..........

I'm gonna dyno the car with open headers and see what kind of difference there is. If I pick up say.......... 40hp, just by uncorking the headers, would that indicate a too-small exhaust?

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#7 ·
Magnaflows are ok, at 3.5" and 500cubes - it aint gonna be quiet.
As for fitting a 20" case, I do it all the time, the muffs dont have to sit in the stock location (under the back seat). Position the rear of the muffs where you need them for your tail pipes, then run pipes from the headers to the inlets on the muffs, while keeping the muffs tucked up (1/4" from the floors will do.)
If you un-cap a the exhaust, you really need to have (18") header extensions bolted on for it to get a lagit TQ reading.
 
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#8 ·
67RS502 said:
As for fitting a 20" case, I do it all the time, the muffs dont have to sit in the stock location (under the back seat). Position the rear of the muffs where you need them for your tail pipes, then run pipes from the headers to the inlets on the muffs, while keeping the muffs tucked up (1/4" from the floors will do.)
How does it look from the side ??? I tried using a longer muffler once,and it was an ugly affair.

3" tailpipes on my 500 hp BB were worth a .10 and 1 mph at the track. Probably good for 20-30hp on the chassis dyno.


bob
Click to expand...
Click to expand...
 
#9 ·
You guys got me convinced. 3" mufflers and tails coming soon........

67RS, there's only so much room for the muffler case, as the floorpan has a recessed area formed into it for the mufflers to sit up into. A 20" muffler case with tailpipes going up over axle just won't fit right.

thanks for feedback gents

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#12 ·
Borla Sportsman, that's a thought. A 16" case would be perfect. I typically weld ball/socket joints onto muffler/tail, to make for easy dis-assembly, but that make a 18" case real tight. 16" would be perfect..............

thanks

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#13 ·
502prostreet if you are running the Spintech Sportsman XL what size pipes and how is the interior resonance? I'm seriously considering a set of Sportsman XL or even the RV which is the quietest. Either of these outflows every other muffler out there, nothing comes even close. My 3 inch system is just too loud for me right now, but before scrapping it I'd like to try the Spintech, at least the quieter versions like you're speaking of.
 
#14 ·
SY1, please keep me posted if you find something. Like you, I'm concerned about interior resonance and I'd like a powerful, but somewhat subdued sound.


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#15 ·
Are you guys claiming a increse in performance from 3" TAILPIPES or a 3" SYSTEM?

I was under the impression that tailpipe size was not really important as the gases cool down by the time they hit the muffler. So, you could run a 3" system, and 2.5 tails w/no lose of performance.
 
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#16 ·
I will bet a dollar to a donut hole that a W/D/T smooth perforated inner pipe TYPE glasspack will flow about as much as the best going And even a bit more IF they were made in 3" jobbers!!

Probably cackle too much for most guy's so just mount them one right behind the other to tone her down!

Isn't that what the Borla's are after it is all said and done, just FANCY high dollar glasspacks??????

pdq67
 
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#17 ·
pdq67, there are basically two styles of mufflers, either chambered or packed with some sort of media (glass, steel wool, stainless steel wool). Within those basics design has a lot to do with flow and sound. The "old school" glass pack you mention are not great for performance and are loud as all get out. They are also not made in performance sizes (as far as I know). They have their place, lowriders, bombs, some Impalas, etc.. (IMO).

Borlas XR1 Sportmans which is what I have, are stainless steel and have a million mile warranty, the design is great, they flow well, and do a great job with sound. Yes, they are expensive at ~$125 each. It's money well spent if you have a loud car that you need to tame a bit. They are in no way the same as a $20 Cherry Bomb.
 
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#19 ·
I can't speak for just the tail pipes, but on my 427 small block I picked up switching from my 2.5" system with Hooker Super Comps to a friend 3" system and Flowmasters. Now I just need to bite the bullet and build a new exhaust.:(
 
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#20 ·
SY1,

I have 3'' pipes all the way through with a Dr.Gas X-pipe and Torque Tech tail pipes.. They are not AS loud as the Flowmasters I had. With the X-pipe the car has a different pitch at WOT, they sort of sound like a nascar. At idle they let the my big block sound like a big block. The resonance is nothing like Flowmaster IMO. I just went through inspection in Delaware and the decibal level was 99.5. I guess it all depends what you like. I went with Spintechs because nobody around was running them and I liked the sound of them.:thumbsup: Now, everyone wants to know what exhaust system I have. Also,without touching a thing the car idle about 300 rpm's higher when we fired it up.
 
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#22 ·
Thanks 502 that's good info. I'll try a set of Spin techs over the Winter. I've got 3 inch stainless and it all welded with an H pipe. I wish it were an X pipe. And it's heavy .090". Whoever built it was certainly proud of their work. They "signed" one of the exhaust pipes by welding their name down the side.

I think the Sportsman XL or maybe the RV but I don't think the RV will fit, it's a few inches longer.
 
#23 · (Edited)
Spin Tech looks like a good choice. The 3443XL would be my choice for a 3" system:
http://www.spintechmufflers.com/spintech/spintechindex.asp

Here's a sound clip (short movie file) with a couple of Camaros using Spin Tech mufflers. Nice sound.
http://www.spintechmufflers.com/spintech/sounds/2spintech.wmv

I love the fact that the 3443XL has a 16" case, as length is a vital consideration when trying to make mufflers tuck up in the floorpan. This means it will be easy to fit, using large 3" tailpipes that exit all the way out back. I called Flowmaster and the part number they gave me for those 3" tailpipes is 15822.............

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#24 ·
I'm gonna dyno the car with open headers and see what kind of difference there is. If I pick up say.......... 40hp, just by uncorking the headers, would that indicate a too-small exhaust

Did you try this yet? I am curious, as my 427 made better HP and TQ with a 2 1/2" mandrel bent system than open headers.
 
#25 ·
Have not tried this yet. I realize there are plenty of harmonics and pressure waves bouncing back and forth, so least resistance is not always best for power.

My first test will be fuel injection in open loop (disables self-correction), then run baseline pull. Then take off tailpipes and run another pull. The finally, open headers and run a third pull.

I'll be sure and post results when completed..............

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#27 ·
SS
If you run open headers, I guarantee you will loose a ton of mid-range.
Without header extensions you will loose primary tube scavenging, which will
cost you power everywhere except the very top end rpm. If you uncap a car,
you need to stick some 18" header extensions on it to make it a fair comparison.
 
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