exhaust size ?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

idaho66stepside · 04-08-2010, 04:58 PM

Hey gang I have a 66 C10 lwb stepside my Dad and I are doing an engine swap and new exhaust in about a week. I just don't know what size of exhaust I should run. The engine is a 350 with 600 cfm carb I can't think of all the head info other than 64cc chambers, 185 intake, a cam that isn't quite 0.5 lift(?) and 1.5 inch primaries on the headers. Is 3" pipes too big?? Thanks guys!

63 & 64 Bowties · 04-08-2010, 05:14 PM

Girls too pretty, too much money, a car too fast, and exhaust pipes too big.... there's no such thing.

TheDark1 · 04-08-2010, 05:59 PM

I have 3" running thru Borla XR-1 race mufflers on a 300HP 350, with no problems at all. They're a little loud with exits in front of the rear wheels, but as far as horsepower losses from them being too big are zero. I had 2.5" before thru some cheap-o turbo mufflers and I couldn't squeak 3rd gear, now I can. I have the back pressure in the headers though. My header primary is only 1.5" compared to some that are 1.75". Hope this helps. Jeff.

markeb01 · 04-08-2010, 06:04 PM

If you do a Google search for "optimal exhaust size", you can lose your marbles trying to consider all the variables associated with the answer. For a shorter opinion, my perception is a 2" exhaust is probably adequate for a stock 350 system. If the engine has a cam and headers and is mostly used on the street a 2 1/2" system is probably ideal. 3" is more likely needed if you have a tunnel ram, spray, blower, or a big block. The trade off is loss of low end torque, which might be substantial on a stock engine.

But if the cool factor is more important than practicality, exhaust systems fall into the same category as jugs and motor mounts, too big is just right!

astrochimp · 04-08-2010, 07:33 PM

http://www.pontiacstreetperformance....p/exhaust.html

I would run a 2.5 because of cost and routing.

idaho66stepside · 04-08-2010, 11:44 PM

Thanks for the info. I wasn't sure if I'd lose too much backpressure with bigger pipes but that is probably only a concern at the cylinder heads. I'm new to wrenchin' so sure do appreciate the help from this forum!

63sbssbbw · 04-09-2010, 05:38 AM

Well put Mark LOL
T

*lakeroadster* · 04-09-2010, 07:59 AM

Bigger is not always better.

Here is what Magnaflow states: http://www.magnaflow.com/wideopen/performdata.asp

Engine Size Horsepower Muffler Inlet / Outlet Size (assumes dual exhaust )

150-200 CID - 100 to 150 - 2"
200-250 CID - 100 to 200 - 2" to 2-1/4"
250-300 CID - 150 to 250 - 2" to 2-1/2"
300-350 CID - 200 to 350 - 2-1/4" to 2-1/2"
350-400 CID - 250 to 550 - 2-1/2" to 3"

And here are some out takes from a truly "mind-numbing" Super Chevy article on exhaust systems.

"so many racers worry about having a large-diameter pipe in and out of the muffler. This concern is totally misplaced, as in almost all but a few cases, the muffler is the point of restriction, not the pipe".

"Don't be fooled into thinking that big tailpipes contribute to power. In all my years of dyno testing, I never have seen that work.... I have seen mistakes in this area cost 85 horsepower."

http://www.superchevy.com/technical/...exh/index.html

padresag · 04-09-2010, 09:33 AM

[QUOTE=lakeroadster;3909831]

Bigger is not always better.

but can grab your attention and imagination faster at times, but may not make it any better. perception
ron

vin63 · 04-09-2010, 10:10 AM

Quote:

Originally Posted by idaho66stepside

Hey gang I have a 66 C10 lwb stepside my Dad and I are doing an engine swap and new exhaust in about a week. I just don't know what size of exhaust I should run. The engine is a 350 with 600 cfm carb I can't think of all the head info other than 64cc chambers, 185 intake, a cam that isn't quite 0.5 lift(?) and 1.5 inch primaries on the headers. Is 3" pipes too big?? Thanks guys!

I would go with the largest diameter you can comfortably fit and afford. For your engine and application, the diameter of the exhaust tubing you use will not make a significant difference above 2 inches, other than sound volume.

idaho66stepside · 04-10-2010, 01:11 PM

Holy crap Lake that article did fry my brain would have rather read a nudey mag!

JRBECK64 · 04-10-2010, 03:32 PM

A friend of mine built a 327 that was pumping out about 360HP and he was running a 2 1/4 exhaust with a crossover. He was running a 3.08/1 gear in the back with a saginaw 3 speed originally that he changed to a Muncie Four Speed and he was getting about 21 miles to the gallon on the freeway at about 65 MPH and that thing was a screemer. It was extremely fast at least for me it was. One thing to remember about exhaust is the bigger diameter the slower the velocity and the louder it will be. It will also slow down your low end. Good luck with your exhaust system.
JRBECK64

04-08-2010, 04:58 PM	#1
idaho66stepside Registered User Join Date: Feb 2010 Location: Twin Falls, ID Posts: 119	exhaust size ?? Hey gang I have a 66 C10 lwb stepside my Dad and I are doing an engine swap and new exhaust in about a week. I just don't know what size of exhaust I should run. The engine is a 350 with 600 cfm carb I can't think of all the head info other than 64cc chambers, 185 intake, a cam that isn't quite 0.5 lift(?) and 1.5 inch primaries on the headers. Is 3" pipes too big?? Thanks guys!

04-08-2010, 05:14 PM	#2
63 & 64 Bowties and a few others Join Date: Jun 2007 Location: Blue Ridge Mountains of VA Posts: 5,638	Re: exhaust size ?? Girls too pretty, too much money, a car too fast, and exhaust pipes too big.... there's no such thing. __________________ Bill US Army Vet -193rd Infantry BlueRidgeMuscleCars.com “The greatness of a nation and its moral progress can be judged by the way its animals are treated” Gandhi

04-08-2010, 05:59 PM	#3
TheDark1 Intentionally Left Blank Join Date: Dec 2008 Location: Broussard, LA Posts: 355	Re: exhaust size ?? I have 3" running thru Borla XR-1 race mufflers on a 300HP 350, with no problems at all. They're a little loud with exits in front of the rear wheels, but as far as horsepower losses from them being too big are zero. I had 2.5" before thru some cheap-o turbo mufflers and I couldn't squeak 3rd gear, now I can. I have the back pressure in the headers though. My header primary is only 1.5" compared to some that are 1.75". Hope this helps. Jeff. __________________ 1965 C-10 Short Fleet 468/TKO 5-Speed 2004 2500HD Crew 496/Ally Blacked Out (SOLD!!) 1997 Formula WS6 2004 Jeep Wrangler (Sold) 2013 Jeep Wrangler (Sold) 2017 Jeep Wrangler (Blacked Out on 35's) 2011 GMC D-Max Dually Denali 3500HD (Sold) 2015 GMC D-Max Dually Denali 3500HD (Sold) 2018 GMC D-Max Dually Denali 3500HD (Sold) 2020 D-Max Dually Denali on 33x12.50's 1979 GMC Short Bed Step-Side 4x4 350/350 Low Miles

04-08-2010, 06:04 PM	#4
markeb01 Senior Enthusiast Join Date: Feb 2007 Location: Spokane Valley, WA Posts: 8,356	Re: exhaust size ?? If you do a Google search for "optimal exhaust size", you can lose your marbles trying to consider all the variables associated with the answer. For a shorter opinion, my perception is a 2" exhaust is probably adequate for a stock 350 system. If the engine has a cam and headers and is mostly used on the street a 2 1/2" system is probably ideal. 3" is more likely needed if you have a tunnel ram, spray, blower, or a big block. The trade off is loss of low end torque, which might be substantial on a stock engine. But if the cool factor is more important than practicality, exhaust systems fall into the same category as jugs and motor mounts, too big is just right! __________________ My Build Thread: http://67-72chevytrucks.com/vboard/s...d.php?t=444502

04-08-2010, 07:33 PM	#5
astrochimp Registered User Join Date: Aug 2009 Location: Unionville Mo. Posts: 217	Re: exhaust size ?? http://www.pontiacstreetperformance....p/exhaust.html I would run a 2.5 because of cost and routing.

04-08-2010, 11:44 PM	#6
idaho66stepside Registered User Join Date: Feb 2010 Location: Twin Falls, ID Posts: 119	Re: exhaust size ?? Thanks for the info. I wasn't sure if I'd lose too much backpressure with bigger pipes but that is probably only a concern at the cylinder heads. I'm new to wrenchin' so sure do appreciate the help from this forum!

04-09-2010, 05:38 AM	#7
63sbssbbw UCA63 Join Date: Aug 2005 Location: Lloydminster AB Can. Posts: 1,637	Re: exhaust size ?? Well put Mark LOL T __________________ member#7816 "63 sb ss bbw 350\350 12 bolt rear Pwr Fr Disc PS tilt '61 GMC in progress '63 GMC to use for parts '90 Chevy Ext cab sbfs 5.7l (current d d)

04-09-2010, 07:59 AM	#8
lakeroadster Account Suspended Join Date: Sep 2009 Location: High Plains of Colorado Posts: 2,485	Re: exhaust size ?? Bigger is not always better. Here is what Magnaflow states: http://www.magnaflow.com/wideopen/performdata.asp Engine Size Horsepower Muffler Inlet / Outlet Size (assumes dual exhaust ) 150-200 CID - 100 to 150 - 2" 200-250 CID - 100 to 200 - 2" to 2-1/4" 250-300 CID - 150 to 250 - 2" to 2-1/2" 300-350 CID - 200 to 350 - 2-1/4" to 2-1/2" 350-400 CID - 250 to 550 - 2-1/2" to 3" And here are some out takes from a truly "mind-numbing" Super Chevy article on exhaust systems. "so many racers worry about having a large-diameter pipe in and out of the muffler. This concern is totally misplaced, as in almost all but a few cases, the muffler is the point of restriction, not the pipe". "Don't be fooled into thinking that big tailpipes contribute to power. In all my years of dyno testing, I never have seen that work.... I have seen mistakes in this area cost 85 horsepower." http://www.superchevy.com/technical/...exh/index.html Last edited by lakeroadster; 04-09-2010 at 08:20 AM.

04-09-2010, 09:33 AM	#9
padresag Registered User Join Date: Feb 2008 Location: Sidney,b.c. Posts: 4,425	Re: exhaust size ?? [QUOTE=lakeroadster;3909831] Bigger is not always better. but can grab your attention and imagination faster at times, but may not make it any better. perception ron

04-10-2010, 01:11 PM	#11
idaho66stepside Registered User Join Date: Feb 2010 Location: Twin Falls, ID Posts: 119	Re: exhaust size ?? Holy crap Lake that article did fry my brain would have rather read a nudey mag!

04-10-2010, 03:32 PM	#12
JRBECK64 Registered User Join Date: Sep 2008 Location: Cornelius Oregon Posts: 1,073	Re: exhaust size ?? A friend of mine built a 327 that was pumping out about 360HP and he was running a 2 1/4 exhaust with a crossover. He was running a 3.08/1 gear in the back with a saginaw 3 speed originally that he changed to a Muncie Four Speed and he was getting about 21 miles to the gallon on the freeway at about 65 MPH and that thing was a screemer. It was extremely fast at least for me it was. One thing to remember about exhaust is the bigger diameter the slower the velocity and the louder it will be. It will also slow down your low end. Good luck with your exhaust system. JRBECK64



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