exhaust size
#1
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Car: 1984 chevy camaro
Engine: 355
Transmission: turbo 350 2800 stall
Axle/Gears: 3:73 detroit locker posi
exhaust size
i currently have hooker shorty headers to 2 1/4 inch pipe to dynomax bullet mufflers dumped under rear seats. is this sufficent enough for a 400hp small block street strip motor? or should i go bigger?
#2
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Car: 87 IROC
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Re: exhaust size
Engine size (cubic inches) is less important than the horsepower in determining the appropriate exhaust size. Depending on which chart you believe, the dual 2 1/4" is good for 200-300 HP. Stepping up to dual 2.5" will be good for 350-400hp. So, no. You're dual 2.25" is likely not enough for 400hp and is limiting flow above 300hp.
This thread includes a chart and discussion.
HP Single Dual
200-300 3" 2.25"
300-400 3.5" 2.5"
375-450 4" 3"
450-550 4.5" 3.5"
Here is a similar chart from Magnaflow.
HP Single Dual
100-150 2-1/4" 2"
100-200 2-1/2" 2-1/4"
150-350 3" 2-1/2"
250-550 4" 3"
This thread includes a chart and discussion.
HP Single Dual
200-300 3" 2.25"
300-400 3.5" 2.5"
375-450 4" 3"
450-550 4.5" 3.5"
Here is a similar chart from Magnaflow.
HP Single Dual
100-150 2-1/4" 2"
100-200 2-1/2" 2-1/4"
150-350 3" 2-1/2"
250-550 4" 3"
Last edited by MoJoe; 02-17-2014 at 11:11 AM. Reason: ETA: you said 400hp, not 400ci. Doh!
#3
Supreme Member
Re: exhaust size
Just as important as the exhaust pipe size is the flow rating of your muffler(s). Just like the carb.
It's been tested that 2.2 cfm of muffler flow per HP is needed or the mufflers will start to limit power output.
Don't get flow confused with inlet and outlet sizes. Many muffler manufactures simply increase these dimensions while leaving the muffler case and it's flow capabilites the same. CFM data is what's needed and it's not as readily availble as it should be.
It's been tested that 2.2 cfm of muffler flow per HP is needed or the mufflers will start to limit power output.
Don't get flow confused with inlet and outlet sizes. Many muffler manufactures simply increase these dimensions while leaving the muffler case and it's flow capabilites the same. CFM data is what's needed and it's not as readily availble as it should be.
Last edited by skinny z; 02-17-2014 at 11:22 AM.
#4
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Re: exhaust size
If you go by the 2.2 cfm per hp and David Vizards 115 cfm per sq inch of pipe area,
2" single supports 164 hp
2.25" is 208 hp
2.5" is 257 hp
3" is 369 hp
3.5" is 503 hp
4" is 657 hp
5" is 1026 hp
These are numbers for a zero pressure system, more hp can be made but the pipe size starts to become a restriction. Dual 3" is supposively rated to 739 hp but i make ~1200 hp thru dual 3" and 4 mufflers total. Yes its restrictive but kinda limited in what you can do
So dual 2.25" in your case should support 416 hp.
2" single supports 164 hp
2.25" is 208 hp
2.5" is 257 hp
3" is 369 hp
3.5" is 503 hp
4" is 657 hp
5" is 1026 hp
These are numbers for a zero pressure system, more hp can be made but the pipe size starts to become a restriction. Dual 3" is supposively rated to 739 hp but i make ~1200 hp thru dual 3" and 4 mufflers total. Yes its restrictive but kinda limited in what you can do
So dual 2.25" in your case should support 416 hp.
#5
Supreme Member
Re: exhaust size
I've wondered about that spec before. I'm assuming it's for a given length of straight pipe. Obviously the flow is reduced in the bends in the pipe but by how much I haven't been able to find other than these charts and lists.
http://www.exhaustvideos.com/faq/how...pipe-diameter/
http://www.titantalk.com/forums/tita...o-numbers.html
There are many more. You have to be careful comparing values as the test parameters change.
http://www.exhaustvideos.com/faq/how...pipe-diameter/
http://www.titantalk.com/forums/tita...o-numbers.html
There are many more. You have to be careful comparing values as the test parameters change.
#7
Supreme Member
Re: exhaust size
Just reinforces my resolve to improve the exhaust flow in my Coupe.
With a single Flowmaster (possibly a 10 series muffler with less than 300 cfm of flow) in the system, I have a serious restriction. Un-capping the cutout just before the muffler netted 2 mph in the 1/8th.
With a single Flowmaster (possibly a 10 series muffler with less than 300 cfm of flow) in the system, I have a serious restriction. Un-capping the cutout just before the muffler netted 2 mph in the 1/8th.
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Car: '85 camaro z/28
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#12
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Car: 1984 chevy camaro
Engine: 355
Transmission: turbo 350 2800 stall
Axle/Gears: 3:73 detroit locker posi
Re: exhaust size
ya putting anything bigger then 2.5 inch would be a pain unless run a single to the rear. im going ti look into the 2.5 inch setup
#14
Supreme Member
Re: exhaust size
dual 2.5" will go over the rear axle pretty easy.
the style mufflers your running should flow good.
the style mufflers your running should flow good.
#15
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Re: exhaust size
If you have shorties you can run dual 3" down stock location and over axle fairly easily. 2.5" is much easier to work with and you can go under axle to really make it easy and have tons of clearance. I just finished up a dual 2.5" on my 4th gen which basically is same as thirdgen from driveshaft tunnel back. Tons of room with 2.5". Even tho my future build could use 3", there are more choices in 2.5" mufflers and the extra clearance is nice. Also less weight
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