Anyone ever run a 2.5" uppipe?

[cool 84]

I have the KB 2.25" right now and while it's much better than stock, I think I need more. I'm having one made regardless, just wondering if anyone has tried it. I'm just a little concerned that it might affect spoolup. I know my intercooler plumbing didn't affect spoolup one bit and I'm wrapping the pipe with header wrap to keep as much heat in as possible.

My old KB downpipe (the part I didn't run over lol) is bent almost perfect. All I really need to do is a little cutting and have flanges welded to the ends.

 

[fullahotair]

My only two cents would be that as you increase the diameter of the up-pipe, volume in the pipe obviously increases, but with the increased volume the velocity of the gas decreases which would effect spooling.... which is what you were getting at. You also don't want the pipe too small, because then it would be a restriction for the exhaust gases......

As far as what diameter pipe is optimum, i am sure it if a fine line and would require a few iterations/trials.... I would guess that you wouldn't want to go much larger the opening in the exhaust housing or header.

I would wonder what benefits would be had if you were to coat the inside of the uppipe with a "slippery" coating like they put in the NASCAR air cleaners, which would reduce the friction on the walls of the pipe and thereby increase the velocity even more?!


Nathyn

 

[FJM568]

I would think that with the TE64 and the 4.1L motor, you might be able to get away with running a 2.5" up-pipe...You've got the extra volume because the motor is bigger...PITA to build, but it can't hurt to try it...Good luck and let us know how it works if you do it...

 

[cool 84]

Hopefully it won't be that bad. My old KB downpipe is within half an inch of fitting so there should be a minimum amount of cutting and welding. All of the complex bends are there already. I just can't see pushing all that exhaust through a single 2.25" pipe.

I have to get the car running first with the 2.25" pipe so I'll have some back to back experiences to share hopefully.

 

[buick83-T]

Has anyone compared stock vs bigger up-pipes to see how much of a gain they are getting? (not adding any other upgrades at same time)

 

[FJM568]

There is a big difference between the stock and the bigger aftermarket up-pipes...But if you go to big woth the aftermarket pipe, then you lose velocity and it hurts the spoolup...In cool 84's case, I don't think it will hurt him much(if at all, might actually help) because he is running the 4.1L motor, which is about 10% bigger motor...

But going to a 2.25" mandrel bent up-pipe from the stock 2" bellowed crimped right angle bent tubing that is used on the stock up-pipe on a stock 3.8L motor, you WILL see a big difference...

 

[84turbogn]

What does it cost for the up pipe? I'd like to notice a big difference!

 

[buickpower]

do any vendors sell a 2.25" mandrel bent up pipe? Is the one atr makes 2.5 or 2.25"? would it be worth upgrading from stock? it seems i may have overlooked this, i assumed the atr was 2.5, which i thought was too large for my setup

 

[turbogimp]

i have the ATR inlet pipe and do belive it is 2.25 inch. i will check it out tomorrow and post for sure.