What size exhaust?

MN71W30 · April 6th, 2009, 07:40 PM

I am getting exhaust put on my Olds and the Mechanic is trying to sell me 2.25 head pipes and 2" tail pipes. The engine is a mild 71 455 with a cam. I went from 2" to 2.5" tail pipes on a 454 LS5 Chevelle and picked up at least .3 tenths at the track and a couple miles per hour. I'm thinking 2.25 the whole way, but why not 2.5?

Thanks for any advice.
Dave

citcapp · April 7th, 2009, 08:50 AM

I would go 2.5 all of the way with mandral bends. Sure helped wake up my 455

Eric Anderson · April 7th, 2009, 09:08 AM

Quote:

Originally Posted by citcapp

I would go 2.5 all of the way with mandral bends. Sure helped wake up my 455

x2

MN71W30 · April 7th, 2009, 01:24 PM

I kinda thought 2.5 was the way to go. I think the shops like installing smaller pipe to make things easier.
Thanks guys,
Dave

68Tom · April 7th, 2009, 02:23 PM

Hey Dave, just curious what kind of prices you're being quoted to purchase and install your system.

MN71W30 · April 7th, 2009, 02:33 PM

I had a local guy that does a nice job quote me $300 for aluminized 2.25 headpipes, 2" tailpipes and mufflers. The price is right. He will allow me $50 because I have my own mufflers.
Dave

68Tom · April 7th, 2009, 02:35 PM

That's pretty cheap. I have a guy in Phoenix quoting me $590. That's with 2.5" pipe and Flowmaster 40s. Guess it's decent.

Cameo White · April 7th, 2009, 08:24 PM

Anyone on here tried the larger diameter repro cast exhaust manifolds that mimic the originals? How about the ovalized 3 inch pipe I see advertised in this area?

wmachine · April 8th, 2009, 06:49 AM

Quote:

Originally Posted by MN71W30

I kinda thought 2.5 was the way to go. I think the shops like installing smaller pipe to make things easier.
Thanks guys,
Dave

Actually that is the stock size, at least in the mid-60s. But 2-1/2s are definitively better from the performance standpoint.

mugzilla · April 9th, 2009, 09:17 PM

I put a crossover back of the trans and 2 1/2 pipes with stock bends ...

mugzilla · April 9th, 2009, 09:21 PM

Quote:

Originally Posted by Cameo White

Anyone on here tried the larger diameter repro cast exhaust manifolds that mimic the originals? How about the ovalized 3 inch pipe I see advertised in this area?

Link ...

plz ...

RAMBOW · April 10th, 2009, 05:58 PM

Whatever the outlet of your manifolds/headers are is as big as your headpipes should be.

If you have manifolds and the exit is 2.25, it does you no good- (actually probably hurts you) to run bigger headpipes.

If you have headers with a 3" collector or 2.5" collector, then run that size pipe. A lot of racers will cut off a 3" collector and weld on a 12" gradual reducer to go from 3" down to 2.5". (or from 3.5" to 3")

The idea with exhaust is it needs to gradually, and smoothly get smaller- so as to keep exhaust velocity up as it cools down. By the time the exhaust gets to the mufflers its cooled down enough that the size of the tailpipes really doesn't matter. Stock they stepped down one more size in tailpipes, but for performance, you could run the same size as the headpipes, or no tails at all- most performance tests show them to be roughly equal.

Cameo White · April 10th, 2009, 07:33 PM

Here is the local company I see all the time at the swaps swelling oversize repro exhaust manifolds and oval pipes:

http://www.ramairrestoration.com

mugzilla · April 13th, 2009, 11:06 AM

Quote:

Originally Posted by Cameo White

Here is the local company I see all the time at the swaps swelling oversize repro exhaust manifolds and oval pipes:

http://www.ramairrestoration.com

Thanks ...

I'll check out my car for which manifold I have ...

I have a stock set up so velocity may be more important than capacity ...

April 6th, 2009, 07:40 PM	#1 (permalink)
MN71W30 Registered User Join Date: Dec 2008 Location: oakdale, Minnesota Posts: 530	What size exhaust? I am getting exhaust put on my Olds and the Mechanic is trying to sell me 2.25 head pipes and 2" tail pipes. The engine is a mild 71 455 with a cam. I went from 2" to 2.5" tail pipes on a 454 LS5 Chevelle and picked up at least .3 tenths at the track and a couple miles per hour. I'm thinking 2.25 the whole way, but why not 2.5? Thanks for any advice. Dave

April 7th, 2009, 08:50 AM	#2 (permalink)
citcapp Super Moderator Join Date: Nov 2007 Location: Bothell, WA Posts: 3,445	I would go 2.5 all of the way with mandral bends. Sure helped wake up my 455 __________________ Pat 1957 Super 88 with a 455 1948 2dr series 76 with a 455

April 7th, 2009, 02:23 PM	#5 (permalink)
68Tom Registered User Join Date: Apr 2008 Location: New York, NY Posts: 835	Hey Dave, just curious what kind of prices you're being quoted to purchase and install your system. __________________ 1968 Olds 442 Sports Coupe 4-speed/bench seat

April 7th, 2009, 02:35 PM	#7 (permalink)
68Tom Registered User Join Date: Apr 2008 Location: New York, NY Posts: 835	That's pretty cheap. I have a guy in Phoenix quoting me $590. That's with 2.5" pipe and Flowmaster 40s. Guess it's decent. __________________ 1968 Olds 442 Sports Coupe 4-speed/bench seat

April 10th, 2009, 05:58 PM	#12 (permalink)
RAMBOW Registered User Join Date: Mar 2009 Location: Bothell, WA Posts: 111	Whatever the outlet of your manifolds/headers are is as big as your headpipes should be. If you have manifolds and the exit is 2.25, it does you no good- (actually probably hurts you) to run bigger headpipes. If you have headers with a 3" collector or 2.5" collector, then run that size pipe. A lot of racers will cut off a 3" collector and weld on a 12" gradual reducer to go from 3" down to 2.5". (or from 3.5" to 3") The idea with exhaust is it needs to gradually, and smoothly get smaller- so as to keep exhaust velocity up as it cools down. By the time the exhaust gets to the mufflers its cooled down enough that the size of the tailpipes really doesn't matter. Stock they stepped down one more size in tailpipes, but for performance, you could run the same size as the headpipes, or no tails at all- most performance tests show them to be roughly equal. __________________ Ben R. 1966 Cutlass 330/320hp, HD 3spd Vid: My old elcamino gets owned by a Soccer mom in a volvo!

April 7th, 2009, 01:24 PM	#4 (permalink)
MN71W30 Registered User Join Date: Dec 2008 Location: oakdale, Minnesota Posts: 530	I kinda thought 2.5 was the way to go. I think the shops like installing smaller pipe to make things easier. Thanks guys, Dave

April 7th, 2009, 02:33 PM	#6 (permalink)
MN71W30 Registered User Join Date: Dec 2008 Location: oakdale, Minnesota Posts: 530	I had a local guy that does a nice job quote me $300 for aluminized 2.25 headpipes, 2" tailpipes and mufflers. The price is right. He will allow me $50 because I have my own mufflers. Dave

April 7th, 2009, 08:24 PM	#8 (permalink)
Cameo White Registered User Join Date: Oct 2008 Location: Chicago, IL Posts: 330	Anyone on here tried the larger diameter repro cast exhaust manifolds that mimic the originals? How about the ovalized 3 inch pipe I see advertised in this area?

April 9th, 2009, 09:17 PM	#10 (permalink)
mugzilla is Fast Enough ... Join Date: Jul 2008 Location: dogtown Posts: 848	I put a crossover back of the trans and 2 1/2 pipes with stock bends ...

April 10th, 2009, 07:33 PM	#13 (permalink)
Cameo White Registered User Join Date: Oct 2008 Location: Chicago, IL Posts: 330	Link, as requested Here is the local company I see all the time at the swaps swelling oversize repro exhaust manifolds and oval pipes: http://www.ramairrestoration.com

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