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

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.

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?

**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.

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, 03:16 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

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

gcburdic · 03-26-2009, 09:33 AM

Here's mine....350, full length headers, H-Pipe, 40 series Flowmasters, dumps out under truck right after the cab....love it, but will probably extend to dump out back at some point!

**kwmech** · 03-26-2009, 10:41 AM

I vote for a 3'' single pipe, won't be obnoxious loud and flow just as good if not better

**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

spinning wheels · 03-26-2009, 12:56 PM

Quote:

Originally Posted by gcburdic

Here's mine....350, full length headers, H-Pipe, 40 series Flowmasters, dumps out under truck right after the cab....love it, but will probably extend to dump out back at some point!

If your truck is anything like mine. A stereo is a waste of money, or only good while your parked

In case you have a hard time hearing.........NICE TRUCK. I SAID, NICE TRUCK

gcburdic · 03-26-2009, 02:56 PM

Quote:

Originally Posted by spinning wheels

If your truck is anything like mine. A stereo is a waste of money, or only good while your parked

In case you have a hard time hearing.........NICE TRUCK. I SAID, NICE TRUCK

What did you say?!?!?

....Thanks man!!!...Yeah a stereo isn't good during cruisin, just the purr of the tree-fity!!!

MrC1 · 03-26-2009, 03:02 PM

There is no truth to backpressure being a good thing or part of any design for a reason. The only thing you have to worry about if you go too big is loss of velocity, which could actually hurt power. This has nothing to do with backpressure, but rather comes on after you pass the point of zero back pressure and get into overkill pipe volume. (this is referring to scavenging....again, nothing to do with backpressure)

The exhaust recommendation chart does not take mandrel bends into consideration. If you go with mandrel bends, your pipes will flow equivilent to larger crimp-bent ones....to a point.

2.5" crimp bent would be great on your setup. If you're worried about noise, go with a high flowing, multi chamber muffler to better control the sound.

spinning wheels · 03-26-2009, 06:56 PM

Quote:

Originally Posted by MrC1

There is no truth to backpressure being a good thing or part of any design for a reason. The only thing you have to worry about if you go too big is loss of velocity, which could actually hurt power. This has nothing to do with backpressure, but rather comes on after you pass the point of zero back pressure and get into overkill pipe volume. (this is referring to scavenging....again, nothing to do with backpressure)

The exhaust recommendation chart does not take mandrel bends into consideration. If you go with mandrel bends, your pipes will flow equivilent to larger crimp-bent ones....to a point.

2.5" crimp bent would be great on your setup. If you're worried about noise, go with a high flowing, multi chamber muffler to better control the sound.

In engineering terms, backpressure means one thing. In street hot rod lingo, it means another

Not being an engineer, but working at an engineering firm. I prefer the hot rod street lingo, those engineers have no sense of humor

03-25-2009, 09:45 PM	#3
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, 09:46 PM	#4
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	#5
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	#6
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, 11:47 PM	#7
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	#8
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	#9
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	#10
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

03-26-2009, 09:33 AM	#13
gcburdic Restoration Virgin! Join Date: Jan 2008 Location: Huntersville, NC Posts: 8,298	Re: 2 1/4" or 2 1/2" Dual Exhaust? Here's mine....350, full length headers, H-Pipe, 40 series Flowmasters, dumps out under truck right after the cab....love it, but will probably extend to dump out back at some point! Attached Images __________________ Geoff with a G 1968 Chevy C10 SWB The Mistress 1972 Custom Deluxe C20 Suburban A Suburban Named Isabella 1966 Ford Mustang Mama's High School Graduation Present

03-26-2009, 10:41 AM	#14
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,499	Re: 2 1/4" or 2 1/2" Dual Exhaust? I vote for a 3'' single pipe, won't be obnoxious loud and flow just as good if not better

03-26-2009, 03:02 PM	#18
MrC1 Dork For Days Join Date: Aug 2005 Location: Dallas Posts: 407	Re: 2 1/4" or 2 1/2" Dual Exhaust? There is no truth to backpressure being a good thing or part of any design for a reason. The only thing you have to worry about if you go too big is loss of velocity, which could actually hurt power. This has nothing to do with backpressure, but rather comes on after you pass the point of zero back pressure and get into overkill pipe volume. (this is referring to scavenging....again, nothing to do with backpressure) The exhaust recommendation chart does not take mandrel bends into consideration. If you go with mandrel bends, your pipes will flow equivilent to larger crimp-bent ones....to a point. 2.5" crimp bent would be great on your setup. If you're worried about noise, go with a high flowing, multi chamber muffler to better control the sound. __________________ 1972 C20, 402/700R4 - My first classic truck, bought in September 2005. 85% transformed from "Farm" to "Cool" status! 1970 Dodge Challenger 440, 4sp (my other toy) 12.67 @ 117 MPH, with a pathetic 2.022 60' 2007 Dodge Charger SRT-8 2008 Cadillac CTS All-American garage, baby! Last edited by MrC1; 03-26-2009 at 03:03 PM.

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