Exhaust size for HP

[Fisher]

Tried the search but it isnt working? Any way, i am building a 400 hp 340 with 1-5/8 headers. Will a 2-1/2" X pipe system be sufficient for this application? Going to dump it at the rear axle, no tailpipes.

 

[1970Duster]

Yes that's fine.

 

[mopardude318]

yep. 2.5" will be juuuuussst fine.

 

[1Fast340]

yep that will work well.
only reason to go bigger is if you plan to make more power in the future or want a bigger/Deeper sound

with bigger sound i dont say louder, bigger pipes just tend to have a bigger sound somehow of course depending on choice of mufflers aswell.

 

[Fisher]

Ok thanks guys. I didnt want to give up any bottom end, or choke it off up top, i plan to spin this motor to 7000 rpm

 

[340 8BBL]

i recently went from a 2.5 x to a 3" x pipe with ultraflows.currently its dumped and feels like someone is under the car tapping the floor with a rubber mallet.i did expect to lose some low end and gain a little up top ,but the results were not what i expected.it seemed to pick up power(not a huge amount mind you) everywhere in the rpm range.it also seems to rev faster and have sharper response.the down side is its loud.with a chambered muffler like brand F it would be down right painful lol.i have plans on running tail pipes with custom resonators im fabricating similar to the 273 hi-po design.it should make it more pleasant on longer drives.

 

[Fisher]

Thanks for the reply Guys.

 

[pettybludart]

Go stainless steel if you can afford it.Mines been on my car going on 15 yrs.

 

[273]

Why 7000rpm a 340 should make 400hp around 5800rpms?

 

[rumblefish360]

Why 7000rpm a 340 should make 400hp around 5800rpms?

Dang! You took the words right out of my mouth.

What cam are you running?!?!

Exhaust companies like Flowmaster etc… have on there sites, charts for pipe side vs. HP. IIRC, they will recommend a 3 inch pipe at your level, but more so for a drag car, not street car, which would be 2-1/2 inch.

 

[crackedback]

Please tell me your not going to put an XE268H in that engine...

400hp on a 340, 2.5" pipes will work fine. If you wanted to go 3" that would work too. No tailpipes makes fitting it up much easier.

 

[Fisher]

Going with a Lunati Solid lifter cam.

 

[Fisher]

7000 rpm was just a number. The dyno will tell me where its done etc

 

[Dusterguy]

"As far as ability of an exhaust system to flow enough air for a given amount of horsepower without causing significant back pressure, this is from one of David Vizard's books:

1. For avoiding significant restriction from back pressure, the pipe should flow at least 2.2CFM per horsepower produced.

2. A straight pipe will flow ~115CFM per square inch of area (using inside diameter of the pipe)


Mufflers usually won't flow as much as a straight pipe of the same inlet/outlet diameter, so you have to factor that in, also."

http://www.hotrodders.com/forum/exhaust-diameter-formula-49188.html

 

[Revhendo]

I have a 3" system for my Valiant that I have yet to install. I also picked up a set of resonators off of a new 392 Chally that I may use if it's too loud.

You can tune an exhaust, too. Right?