This is my first build i wanna know what would be a good exhaust diameter for my setupnote this motor is in process has not even been installed or started im jus wondering what would be a good exhaust size)

Block JDM B18C GSR
Bore 81.50mm
Stock p72 rods w/ arp bolts
Oem crank, bearings, WaterP, OilP
Pr3 pistons
11.5:1 Compression Ratio

Head USDM B16A2
Full supertech valvetrain minus keepers nd seals
Pro1 cams w/ GE camgears
Performer X manifold
RDX 410cc injectors
Aem FPR
Pro Products 68mm TB
This is all i can think of the top my head.. Any help much appreciated

 

I would like everyone reading this thread in the past, present, and future to know that the answer to this question, REGARDLESS OF YOUR SETUP, will be 3". Period. Always.



























Yes, even then.

 

Ok thank you

 

Theres been gains when using 3", but alot has to do with header used and if a proper collector is used.

It will be louder then 2.5, so figuring out which parts will kill the rasp/drone is all on you. (ask me how I know)

 

For something this clean and easy, 2.5" will do anything those injectors can throw at it. 3" helps with a bit more peak power, but doesn't seem to help the important areas of the midrange.. Yeah, I've seen dynos. Its a little different with a good final drive.

 

How do you know?

 

Thats called a rhetorical question.

 

Depends on your application. If its a daily drive then 2.5" is just perfect. 3" will make more power but you will have to sacrifice the bottom end a bit.

If its not a race or drag car stick with 2.5"

Jignesh

 

Thanks

 

I'd love someone to show me a dyno where someone ran a bigger exhaust and lost power ANYWHERE. That's a myth.

It will be louder, but it will make power everywhere. Anything past your last merge collector is just a restriction.

If you're concerned with noise run a resonator.

 

^^
Agreed.

Since torque is acceleration, if that myth was true, you would see dragsters and modified track cars with piping out the back.

 

3" with at least a 12" long resonator to stop the rasp and droning. Matted to a good muffler and it should be nice.

 

I'd love some to show us a dyno where someone ran a larger exhaust and gained power with exhaust diameter being the ONLY variable. The myth that 3" exhaust will conclusively gain power EVERY time is hard to believe when EVERY dyno so far has resonators and muffler type and catalytics changed/removed.

 

I have a 20" resonator (not the best) and mine is loud and raspy.

I am replacing it in 2 days with 2 vibrant 18" resonators with a magnaflow muffler

 

There is PLENTY of information out there, this is 2013, none of this is new.

https://honda-tech.com/forums/all-motor-naturally-aspirated-44/who-says-3%22-too-big-k20-dyno-2341715/
https://honda-tech.com/forums/showth...%27%27+exhaust
https://honda-tech.com/forums/showth...%27%27+exhaust
https://honda-tech.com/forums/showth...%27%27+exhaust
https://honda-tech.com/forums/showth...%27%27+exhaust
https://honda-tech.com/forums/showth...%27%27+exhaust

 

Thanks, you reinforced my point for me. Not ONE dyno shows the diameter being the only variable. Models of mufflers were changed, resonators removed, cats removed, etc. Pipe diameter is not the ONLY variable.


Show me a dyno where the resonators, catalytics OR test pipes, and mufflers are the EXACT same with the exception of diameter. I.E. 2.5" Vibrant cat, resonator, and muffler and pipe versus same model Vibrant but in 3.0".


You can't.

 

Exactly.... I love it.

 

With a 3" diameter, no matter what resonator or muffler removed or added, theres still not enough to cause a restriction. This brand vs that brand doesnt matter.

So your attempt to criticize this 3" or that 3" is really a mute point. 3" flows better then 2.5" regardless.

 

Hmmmm.....let's see if this makes sense. All of the comparsions seem to to go from a 2.5" or smaller diameter, usually have a cat, at least one resonator, a chambered muffler or something more restrictive to a 3.0" with no cat, no resonator to a straight through, better flowing muffler. And the 3.0" exhaust hands down makes more power in every case. How was because of the cat delete, resonator removal and muffler change? "None, 3.0" rules the MTFW!!!!"


I am not criticizing anything about a 3.0" exhaust. I am saying show us the scientific proof, not some bullshit random experiment which these all basically are.

Do a dyno with the ONLY variable being the pipe diameter. That is the only scientific way to conclude if the diameter increase is 100% responsible for the power increases everyone "claims".

 

^^Good discussion re isolating a single variable.

 

Who says all 2.5's have a cat, chambered muffler, etc,etc?

Some people could have a cat delete with a free flowing exhaust. Not all people are running stock or restrictive exhausts before swapping to 3"

So if thats your argument that 2.35 or 2.5 has restrictions vs 3" free flow, then sure, I could see that..

Theres no way to tell either way.


then again, theres also other engine parts that might also hinder the exhaust outcome..

larger TBs
different manifolds
intake size

all would play a factor in how the engine performs on the dyno..

I mean, since we want to get all technical

 

Thanks for volunteering! Let us know what the results are.

 

If I had the money, I would have done it already.

 

One would have to take a honda in stock trim and do a run..

then swap to a 2.35/2.5 then do a run with cat and resonator/muffler

then w/ cat removed

then swap in the 3" and run again to get a true reading.

 

LOL is OP the guy that has CJ's muffler shop bitching on facebook about a customer who canceled their 3" exhaust order because they had to "go check the forums"