When do you need 5" exhaust.

G

GLHS

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Looks like I will need to change my exhaust to race at the track this year. New rules at Bandimere state Diesel exhaust must be directed up and away from the lights if you are a registered racer; suggested if your not registered.

Keeping future mods in mind, at what hp level should 5" be mandatory?
Any dyno comparisons; 4" vs 5"?
 
Normally anything past 550HP is when I start putting 5 " on. Or when a set of twins are installed,
 
You want the exhaust to exit as fast as possible. So less restriction is better. I don't think there is much of a difference from 4-5 inch as far as power. Mostly just a difference in sound. What will make more of a difference is the size of your down-pipe. If your using a 3" down-pipe it wont really matter what size the exhaust is because its still restricted up front. Someone correct me if I am wrong but thats always how I understood it.
 
i would think you would want it to exit as fast as possible like stated above to keep the egt down but if you go too big i would think you would not be able to build enough pressure to push the exhaust out and if you go to small then it would not allow the exhaust to exit fast enough. just my opinion.
 
You need to keep the velocity up. The first 24" is the most crucial part of the system.
 
Bponci said:
You need to keep the velocity up.

The first 24" is the most crucial part of the system.
Click to expand...

i agree brad

dont really understand why they choose the hx-40 flange when they started machining the s300 housings?

a step pipe works better than just throwing the ex gases into a 4" dp

don
 
I've been debating this too!! I've got the 5" down pipe from my MPI twins into a 4" back with straight through muffler. At almost 800 hp I'm wondering if I need 5" all the back..... Jeff says Yes....
 
Big Swole said:
I've been debating this too!! I've got the 5" down pipe from my MPI twins into a 4" back with straight through muffler. At almost 800 hp I'm wondering if I need 5" all the back..... Jeff says Yes....
Click to expand...

If you decide to go to 5 inch I will buy that 5-4 inch reducer...
 
Big Swole said:
I've been debating this too!! I've got the 5" down pipe from my MPI twins into a 4" back with straight through muffler. At almost 800 hp I'm wondering if I need 5" all the back..... Jeff says Yes....
Click to expand...

If I were at 650+ hp, I would not be asking this question. I think it's safe to say you need 5 inch!
Five inch pipe has 56% more area than four inch.

Where do you get a 4"-5" adapter?
 
GLHS said:
If I were at 650+ hp, I would not be asking this question. I think it's safe to say you need 5 inch!
Five inch pipe has 56% more area than four inch.

Where do you get a 4"-5" adapter?
Click to expand...

If you mean 5" into 4", Nathan at MPI supplied it with my whole kit I purchased. Im sure he'll sell it separate.
 
A few years back I was talking to Rip Rook @ Source Automotive about exhaust and sizing...5" straight pipe gave him 615hp, 4" with a Muffler was 605hp if I remember the numbers correctly.

Basically, 550-600hp and up, 5" is OK, but still not a huge necessity...below that, I'd think it could hurt power, and I know it hurts spoolup. I've seen that on my trucks.

Chris
 
GLHS said:
If I were at 650+ hp, I would not be asking this question. I think it's safe to say you need 5 inch!
Five inch pipe has 56% more area than four inch.

Where do you get a 4"-5" adapter?
Click to expand...

Airflow or any big rig place will have the adapter, about 15 bucks.


Would 6" be overkill on twined 650+ trucks?
 
what's the record on 4"? 800? more?

most people will benefit from 4" before they'll benefit from 5"

with overly large pipe, the gas stalls and eddies around bends more than with a smaller diameter pipe, so it's actually a RESTRICTION having too large of a pipe.

with that said, just pick whatever size you like... I like the sound of the larger dia pipe... I usually run 4" for a few feet and then go to 5" or 6"
 
Big Swole said:
I've been debating this too!! I've got the 5" down pipe from my MPI twins into a 4" back with straight through muffler. At almost 800 hp I'm wondering if I need 5" all the back..... Jeff says Yes....
Click to expand...
One ride in my truck you'll stack it:charger:
Billy
 
wpeschel said:
If you decide to go to 5 inch I will buy that 5-4 inch reducer...
Click to expand...

Sorry, i missed this post earlier..

Sure man....I won't have a need for it....

PM me your number and I'll call ya when I do the swap...


BTW...Anybody close want a great deal on a VOLANT Polished T-304 4" with a straight through muffler....
 
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