Intercooler piping size
 

So I see setups with all different sizes. It’s been said (I read anyways) that 2.5” charge pipe is adequate for decent power levels (at least 700hp) but I can’t help but wonder. I really ever see anyone with that small of a pipe. I see usually at least 3”. Went to a car meet last night and I mainly saw 3”. I’m the only one with 2.5”. I can’t help but wonder if there’s any benefit to using 3” or 3.5”?

Heres my conventional wisdom thinking:

2.5” pipe would fill up with air quicker, possibly causing quicker boost.
But, 2.5” might be a overall restriction causing extra heat in the air?
The motor might be able to “breathe” better under normal driving? It would be nice to up my gas mileage a little
I’m sure over all the 3” would have more power potential but would it pick up anyways? I can’t help but think it will because why else would we put a cam in and freer flowing heads.

Thoughts? I’ve searched. And the info I’ve found had left much to be desired. Any new info. Anyone tried it and found power. Lost power. Lost spool?

in for the info

So the funny thing is, I read that 2.5 will be fine with my power goals (700ish) but I’ve yet to see anyone except me and 4cyl cars with 2.5” pipe. Wonder why that is?

Because 3" looks cooler

The larger throttle bodies on big motors adapt more easily to 3" piping from the IC. You could probably hit your power goals with 2" pipe, but where would you get an adapter to fit it to a 90mm TB? Plus, of course, it would look silly.

3" would be more common as most decent size blowers or turbos and intercoolers will already be 3" for a single application.

Unless it is for a smaller car or engine, where 2.5" is more common.


On boost....2.5 will be fine, although I'd still prefer 3".

Off boost and lower loads....3" may help there as the engine still has to suck through all that pipework.

3.5" if you can fit it...no harm either, but often with all other accessories still in place, that's a big pipe to route everywhere.

4"...good luck fitting that in ! lol

I’m running 2.5” intercooler piping too. Cars gone 9.8 at 136 with a gt45.

I just sent viren at vs racing an email this morning asking about having to bump up the size to 3” if I decide to go with his billet wheel s480 billet wheel. No money for fuel upgrades on top of the turbo so I’m looking to go as far as sd80’s
on 110 race gas will take me.

robert have you looked into SEP injectors>?

Yeah eventually I’ll sell these sd80s, add another aem 400 pump and grab some snake eaters

im running dual 450s and 142lbs and e85 >:) the funs

See off boost is what I was more interested in. Although my car drives fine, has plenty of response but the fuel mileage around town and at idle is not good at all. Highway is 20ish. But around town I average 12-13 keeping my foot out of it. I think that because the exhaust is always spinning the turbo it’s more or less blowing air at the motor but who knows if it’s enough. I’m considering trying 3” just to see.

air cant get into the motor if the throttle is closed...and there will be no energy to drive the turbo with any significance at low loads.

So the turbo is a restriction in terms of both turbine and compressor at low loads, although probably not a significant one in terms of fuel economy which will be largely driving style and tuning.

Im a dummy. Good point, I wasn’t thinking that way. I’m gonna put the 3” pipe on my list of things to do. Right now I’m just enjoying driving it. Since I fixed the trans I’ve been driving it as much or more than my truck. It’s raining today and I still drove it.

I would defo say go for the 3". Would be hard to justify 3.5 though although if there was room and it was easy...why not.

Again, it would be another good one for the likes of Engine masters, to dyno a few with varying pipe sizes, lengths, and for a laugh a bunch of 90deg silicone couplers all stuck together.

This is why a lot of applications used to run Bypass valves ,, to allow the engine to suck air till the turbo
spun up enough to start building pressure, with the better tech in the turbos than in the "olden days"
you don't see it as much now..

Just for complete info,, the bypass valve was a valve that allowed air from in front of the turbo to go directly to
the throttle body and was actuated like a backwards blow off valve.. Closed under any positive intake
manifold pressure and opened under vacuum. It meant another pair of "T"s and a pipe and a second blow
off valve that flowed in to the intake pipe just ahead of the throttle body so on a small import it was fine on
the big twin setups plumbing was painful.

Why mess with it when its back on the road and running? Unless you're seeing too much boost or high IAT's I wouldn't screw with it. Your idle/part throttle fuel mileage has nothing to do with your cold side diameter. Tune needs work, but it's also cammed/stalled/turbo motor so it's only going to get so good.

Yea you are right. I am enjoying driving it. But I can’t keep my hands out of it lol. I’m currently working on my tune some more and I enabled lean cruise this morning. I’ll see how it does on the way home

Good luck with the lean cruise. I experimented some with it, and never got results that seemed useful. Hopefully you get better results. I never really delved into it far enough to say anything definitive one way or another.

yea, I tried it again the other day. I now remember my problem with it. It'll go into lean cruise just fine, actually shows another mpg or two......Then when i let off, it goes rich and stays there until i put it in neutral and rev it up. So now I'm gonna have to find another way

I have a friend in Dallas with a rear mount turbo ls1 vette with a n/a cam very wrong choice but it was in the car. He used 2" cold/charge piping from back to front with a decent pinch in the pipe by the starter. On3 78/75 turbo. With 12# it made 629rw and 615rw on two diff dunes.
That's on par with a a&a or ecs blower kit with 12# for vettes with ls1s or 241 heads
these fbodys dyno diff for diff variables.
But your 2.5 charge is fine.:drive: