2 1/4" or 2 1/2" Dual Exhaust? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cwilkie · 03-25-2009, 09:31 PM

I have a 396BB with oval closed chamber heads and stock exhaust manifolds. I am going to get new dual exhaust with glass packs on it in the next few weeks but I was wondering what size pipe to get. I can't decide between 2 1/4" or 2 1/2" pipe. What do you guys think is better? What are the benefits and drawbacks to each size? Thanks guys.

Sport/Truck · 03-25-2009, 09:39 PM

I'm running 2.5 on my 383 and its good to 400 hp on my sbc.
s/t

Here's where I got my bases for my size....

Quote:

Originally Posted by LUV2XCLR8

This is thread #1,000,000,000,000+ on Exhaust questions

and I'm not even
going to put my dog in this fight, however I always post this chart to helpout
others here, it is out of the Dealers Part book for Flowmaster products, cya

big_al_71 · 03-25-2009, 09:46 PM

I am also running 2 1/2 with a built "406"

cwilkie · 03-25-2009, 10:36 PM

My truck is actually a 396 bored .060 so I think that makes it a 408. So I think I am going to go with 2.5" dual exhaust with glass packs. What do you think?

jbristo67 · 03-26-2009, 03:16 AM

Quote:

Originally Posted by cwilkie

My truck is actually a 396 bored .060 so I think that makes it a 408. So I think I am going to go with 2.5" dual exhaust with glass packs. What do you think?

I think they are too loud. lol Does that make me old

**americanmusc1e** · 03-26-2009, 12:50 PM

Quote:

Originally Posted by cwilkie

My truck is actually a 396 bored .060 so I think that makes it a 408. So I think I am going to go with 2.5" dual exhaust with glass packs. What do you think?

if you have a modified engine that revves to a higher rpm than stock, use the 2.5 pipes
If you have a stock or near stock engine, use the 2.25 pipes

**Green Machine** · 03-25-2009, 10:36 PM

My vote is for 2.5 duals also. 2.25 might be a little quieter, all else being equal, but 2.25 dual are really for a smaller small block like 283-305. I don't think engines are designed to run with back pressure, they are tuned to run with the back pressure they have. Change the backpressure, change the tuning to run right.

Sammy · 03-25-2009, 09:45 PM

Personally I wouldn't run anything smaller than the 2 1/2. Engines were designed to have a certain amount of back pressure for proper operation. I think stock 396's had 2 1/2 diameter and some small blocks, and the 6's the 2 1/4. my 2 cents.

tim21391 · 03-25-2009, 11:47 PM

i got stock manifolds going into 2 1/4" pipes going into original 40 series flowmasters true dual and it sounds good and then my tips are 2 1/4" inlet into 3.5" outlet and they are 22" long

Nitroblood · 03-26-2009, 01:35 AM

Depends on what your tolerance to noise level is. The "packs" are going to be pretty obnoxious, I'd go with Turbo muffs on a 2.5 pipe.

I prefer rumble to blat. Just my 2 pennies.

spinning wheels · 03-26-2009, 01:44 AM

2 1/2" with a cross over / X pipe. With stock exhaust manifolds, I don't think you would notice much difference between the 2 1/4" and the 2 1/2". Glass packs, I guess that is a personal preference. As the glass packs get older, they will loose some of their glass packing and become louder and with less back pressure.

So.Cal.Super · 03-26-2009, 03:07 AM

Full length headers, 2.5" back into an X pipe and Flowmaster 40's. I love it. Can't say the same for the neighbors.

jbristo67 · 03-26-2009, 03:18 AM

Quote:

Originally Posted by So.Cal.Super

Full length headers, 2.5" back into an X pipe and Flowmaster 40's. I love it. Can't say the same for the neighbors.

Thats more my speed

03-25-2009, 09:46 PM	#3
big_al_71 Registered User Join Date: Jun 2008 Location: South Florida Posts: 11,375	Re: 2 1/4" or 2 1/2" Dual Exhaust? I am also running 2 1/2 with a built "406" __________________ Get your facts first, and then you can distort them as much as you please!!!!!. Sylvester's build thread >>>http://67-72chevytrucks.com/vboard/s...ht=big+rebuild

03-25-2009, 10:36 PM	#4
cwilkie Chance Join Date: Sep 2001 Location: Belcourt ,ND, USA Posts: 750	Re: 2 1/4" or 2 1/2" Dual Exhaust? My truck is actually a 396 bored .060 so I think that makes it a 408. So I think I am going to go with 2.5" dual exhaust with glass packs. What do you think? __________________ 1968 Chevrolet Stepside BB 396 w/TH400 1972 Chevrolet 3/4 Ton 4x4 BB 496 w/TH400

03-25-2009, 10:36 PM	#7
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: 2 1/4" or 2 1/2" Dual Exhaust? My vote is for 2.5 duals also. 2.25 might be a little quieter, all else being equal, but 2.25 dual are really for a smaller small block like 283-305. I don't think engines are designed to run with back pressure, they are tuned to run with the back pressure they have. Change the backpressure, change the tuning to run right. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

03-25-2009, 09:45 PM	#8
Sammy Registered User Join Date: Apr 2000 Location: Bonne Terre, Mo Posts: 3,005	Re: 2 1/4" or 2 1/2" Dual Exhaust? Personally I wouldn't run anything smaller than the 2 1/2. Engines were designed to have a certain amount of back pressure for proper operation. I think stock 396's had 2 1/2 diameter and some small blocks, and the 6's the 2 1/4. my 2 cents. __________________ '69 Chevy Long Fleet & '71 GMC Short Step & Project "ODD BALL" "You can wash a pig, soak it in most expensive perfume. In the end it is still just a pig." ODD BALL build thread http://67-72chevytrucks.com/vboard/s...d.php?t=478629"

03-25-2009, 11:47 PM	#9
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: 2 1/4" or 2 1/2" Dual Exhaust? i got stock manifolds going into 2 1/4" pipes going into original 40 series flowmasters true dual and it sounds good and then my tips are 2 1/4" inlet into 3.5" outlet and they are 22" long __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796

03-25-2009, 09:31 PM	#1
cwilkie Chance Join Date: Sep 2001 Location: Belcourt ,ND, USA Posts: 750	2 1/4" or 2 1/2" Dual Exhaust? I have a 396BB with oval closed chamber heads and stock exhaust manifolds. I am going to get new dual exhaust with glass packs on it in the next few weeks but I was wondering what size pipe to get. I can't decide between 2 1/4" or 2 1/2" pipe. What do you guys think is better? What are the benefits and drawbacks to each size? Thanks guys. __________________ 1968 Chevrolet Stepside BB 396 w/TH400 1972 Chevrolet 3/4 Ton 4x4 BB 496 w/TH400

03-26-2009, 01:35 AM	#10
Nitroblood Registered User Join Date: Sep 2005 Location: Montclair, California Posts: 163	Re: 2 1/4" or 2 1/2" Dual Exhaust? Depends on what your tolerance to noise level is. The "packs" are going to be pretty obnoxious, I'd go with Turbo muffs on a 2.5 pipe. I prefer rumble to blat. Just my 2 pennies. __________________ 1972 C / 20

03-26-2009, 01:44 AM	#11
spinning wheels Registered User Join Date: Sep 2001 Location: Hacienda Heights, California USA Posts: 474	Re: 2 1/4" or 2 1/2" Dual Exhaust? 2 1/2" with a cross over / X pipe. With stock exhaust manifolds, I don't think you would notice much difference between the 2 1/4" and the 2 1/2". Glass packs, I guess that is a personal preference. As the glass packs get older, they will loose some of their glass packing and become louder and with less back pressure. __________________ '72 GMC custom camper 350/350

03-26-2009, 03:07 AM	#12
So.Cal.Super It'll Buff Out! Join Date: Apr 2007 Location: San Diego Posts: 603	Re: 2 1/4" or 2 1/2" Dual Exhaust? Full length headers, 2.5" back into an X pipe and Flowmaster 40's. I love it. Can't say the same for the neighbors. __________________ "Instructions are just another mans opinion" Become a Supporting Member http://67-72chevytrucks.com/vboard/payments.php Man Card Rules http://67-72chevytrucks.com/vboard/s...d.php?t=634550 72 Chevy Cheyenne Super 400 LWB



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