What are ideal intake and exhaust tube sizes?

[afroman006]

I am fixing to make a snorkel and a set of stacks for my trail truck and am wondering what size intake tubing and exhaust tubing to use. It is a bone stock 6.2. Right now I have 2" dual turndowns on it and it runs well enough but what is the best size dual exhaust to use? As far as the air intake, what size tube should I use? 3 or 4"? I am planning on using a generic K&N cone air filter so I need to know what size to get. Thanks

 

[tRustyK5]

Factory duals were 2.25" as far as I know, and it's not like diesels need backpressure...so I'd run 2.5" or 3" duals. If I can physically fit them I'll run 3" duals someday.

Intake tube I'd guess 4 or 5"...

Rene

 

[colbystephens]

maybe a lame question, but what is it about gas engines which makes them need backpressure and why do diesels not need it?

 

[6.2Blazer]

No engine needs "backpressure"..........too big of exhaust pipes can hurt, but it's not because of any "backpressure" issues........

Anyway, the stock dual exhaust on most 6.2's was 2.25". I currently have stock size 2.25" pipes that then use an adaptor up to a pair of 2.5" mufflers and tailpipes. When I redo the rest of the exhaust the pipes coming coming off the manifolds will replaced with 2.5" pieces.

 

[colbystephens]

No engine needs "backpressure"..........too big of exhaust pipes can hurt, but it's not because of any "backpressure" issues........

can you explain that a little more? i've always heard that gas engines need a little back pressure.

 

[imiceman44]

can you explain that a little more? i've always heard that gas engines need a little back pressure.

Actually too big of pipe on a gas engine is bad.
There has been sooo many people, and I am one of them who tried different size exhaust pipe and there was a sweet spot, the right size for the right amount of backpressure for a gas engine, not for diesels though.
A gas engine a burning explosion and it will not be complete by the time the valve opens so a little backpressure will keep the explosion kind of in the cylinder to help push the piston down, too much backpressure and the gases can not go out fast enough after the combustion so not enough mixture can go in for the next round.
In a nut shell you need the right amount of back pressure.
With diesel it's a compression explosion and when it's done it's done you want to get out as fast as possible so more air can get in and the faster it will get out the more vacuum it will create to suck in more air from the intake.

 

[6.2Blazer]

A gas engine a burning explosion and it will not be complete by the time the valve opens so a little backpressure will keep the explosion kind of in the cylinder to help push the piston down, too much backpressure and the gases can not go out fast enough after the combustion so not enough mixture can go in for the next round.
In a nut shell you need the right amount of back pressure.
With diesel it's a compression explosion and when it's done it's done you want to get out as fast as possible so more air can get in and the faster it will get out the more vacuum it will create to suck in more air from the intake.

What are you talking about????? That really makes no sense at all.

Anyway, the correct size (or actually size range) exhaust pipe is somewhat important. You need something that is big enough to let the volume of exhaust gases out of the engine while also maintaining a decent flow velocity which leads to the scavenging effect. Once the pipe gets to be a lot larger than needed to handle the volume, then the velocity really starts to drop and you start having turbulence issues (gases tumbling around inside the pipe instead of exiting it) and little to no scavenging effect.

 

[imiceman44]

What are you talking about????? That really makes no sense at all.

Anyway, the correct size (or actually size range) exhaust pipe is somewhat important. You need something that is big enough to let the volume of exhaust gases out of the engine while also maintaining a decent flow velocity which leads to the scavenging effect. Once the pipe gets to be a lot larger than needed to handle the volume, then the velocity really starts to drop and you start having turbulence issues (gases tumbling around inside the pipe instead of exiting it) and little to no scavenging effect.

So you put it in better description but yeah size does matter

 

[rjfguitar]

I've got a turbo to tail pipe 5" exhaust system coming in the mail of my Cummins....would 5" work on a 6.2?

I'd think all you'd need is 3" single for a 6.2.

 

[afroman006]

I dont have room for a crossover pipe so I'm sticking with duals.

 

[rjfguitar]

Go dual 2.25" or 3". I don't really think it's all that critical.

 

[afroman006]

Go dual 2.25" or 3". I don't really think it's all that critical.

Specially not with a piece of **** motor like mine.