im just wondering. i have my custom made turbo kit i did and im using a TDO5h eclipse turbo. i am using all 2.5" piping and a Greddy SMIC . but i was just wondering if this piping is too big for the turbo i have . im only running 8 psi and i see the stock piping for the 4g63 is only like 2" or something. im just wondering if i could squeeze a lil more out of it but downsizing a bit or would this be not worth it.

91 civic hatch, homemade turbo+ LS motor = 12 sec street car.

you wont gain horsepower, but i would think you would gain back some lag and spool time.

ok . should i go with 2" instead

91 civic hatch, homemade turbo+ LS motor = 12 sec street car.

sure

No, no, no... don't listen to him. 2.5" isn't too big. It's bigger than what most of the guys here run with HRC kits, but there's no good reason to redo all of your intercooler piping to be like everyone else. I ran 2.5" piping with a .48/.42 T3 turbocharger and Starion intercooler and the performance was very good. When I went down to 2" pipe, the car was noticably slower. I ended up putting the 2.5" piping back on. I think it maybe had to do with the turbocharger spinning faster and operating within a higher efficiency range. That's just a guess though, as I did nothing to verify that guess.

The point is that 2.5" piping isn't overkill and will work great with your turbo. There's nothing significant to gain by decreasing the diameter of the piping. It'll also leave you some room for growth and save time and money.

Also, don't listen to siueclipse... he's not very technical and sometimes gives advise on topics that he's unfamiliar with.

I agree. I don't know about when it gets down to specifics but that .5" is not worth the time or money. And I'm sure one day you will want to up the boost... boost brings out the greed in all of us.

ok ill just leave it alone i guess. i do wanna up boost but $ i dont have for now..

91 civic hatch, homemade turbo+ LS motor = 12 sec street car.

I think the larger piping will increase the transient response anyway, which is what you want on a hard driven road car.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

Yea your 2.5 should be alright. You are running 8 PSI now anyway so that's a plus.

Im curious,

Why do most turbo kits come with only 2" piping for normal size turbos, but when you run larger turbo's.. like the 25g you bump up to 2.5".

There must be a reason for it. Im going to call HRC and ask them why they have setup their kits that way.

But, even the 20g uses the 2" piping.

So... what's your point? Are you trying to say that because HRC supplies 2" and 2.25" with their kits, that there's nothing better? I know from experience what works.

they offer the 2.5" stuff with the 25g. that comes in that kit

Think about this: What's the outlet size on a 25G? What's the outlet size on a 20G, 16G?

If you have a 2" outlet, use 2" piping. if you have a 2.5" outlet, it makes sense to use 2.5" piping.

If you have a 2" outlet but eventually might upgrade to something larger, its not going to hurt anything to use 2.5" piping.

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It's not as simple as that, Dino. Piping diameters are dependent mainly on engine airflow which is a function of HP. You also have to take into consideration the length of the piping, the size/volume of your intercooler end tanks, the volume of the intercooler core, the pressure differential between the inlet and outlet of the intercooler, and the size/volume of the manifold and throttle body. You can't just use piping that's the same diameter of the turbocharger compressor outlet because "it makes sense"... it really doesn't make sense.

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'99 Eclipse RS-T (daily beater)
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I would think that having larger pipe than your turbo and IC would cause the turbo to fill up the larger space before it could flow through the system. Granted im sure its pretty instant, but in my mind it would cause laggg

I used to run 2" on the S16g to a stock 1st gen SMIC, then 2" out from the IC, then bumped up to 2.5" at the HRC stage1 piping about 18" before the TB. Worked fine. I then got the HRC universal FMIC, redid all my piping in the process. I used 2.25" from the turbo outlet to the IC inlet, 2.25" from the IC outlet to the same 2.5" HRC piping as before. I noticed a BIG gain in spoolup rpm(about 200 or so rpm sooner), and a gain in top end rpm power. Granted, this was only a butt dyno, but there was a definate noticable difference. Too large of piping before the IC, will *usually* hurt velocity up to the IC, and hurt your spoolup time. Too small diameter, and it hurts top end flow. If anything, keep the piping from the compressor outlet, to the IC inlet, smaller(turbine outlet size or .25" larger), and then up the piping size maybe .25" from the IC outlet to the TB inlet. It's best IMO, to up the size a little bit out of the IC, as the air is being cooled, it expands, much like exhaust gases in an exhaust system(granted they are much cooler temps). With the expanding air from the IC, and slightly larger piping size, velocity *should* remain constant in a perfect world. This is how i've seen many, many turbo setups run, ones that are not stock, and make good power anyway(all other things being equal). The best way to figure the best size to use for a particular setup, is to use a dyno.

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(post edited; useless)

Any turbocharged car will have really good top-end power, but being a 4 cylinder, I think that smaller piping will help to maintain velocity.

That being said, there are bigger fish to fry in the intake path than IC piping; manifold, intake ports, shrouded intake valves, exhaust ports, casting shifts in the head, poor exhaust manifold, horrible WG placement, etc...

Well...

I wish Brad from HAHN would post, but to sum what he said.. Its pointless to run larger IC piping compared to your turbo and IC. Not only is it pointless but it will actually hurt you because of resistance.

Well that doesnt explain why James. More resistance? where in the piping to IC transitions?

Dougie if you can post the calculations you speak of i would appreciate it.


Terry

So if Im understanding correctly, if I run 2" or 2.25" from the compressor to the IC, then run 2.5" from the IC to the TB, I would prolly get less lag, better response, as upposed to me running all 2.5"?

Damn that was long, lol

No way.....

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If you change from a 2.0 outlet to a 2.5 pipe, you're going to get abrupt changes in air flow and create a vortex and dead air spots. Most companies use 2.0 and transition up to the size of the TB... like HRC. It from 2.0, to 2 1/8, to a final 2.25 to the TB. Small changes create a cleaner flow path and less wasted energy. Most times it isn't enough to even care about, so going from a 2.0 to 2.25 or 2.5 transition on the compressor outlet is nothing uncommon. The V6 kit we produce uses a kick from 2 to 2.250, no problems thus far and It generally acts like a reversion hump when the throttle closes at low boost when compressor surge is most likely to happen. Works out pretty well.

I'd leave it. It's not going to change much like if you were to swap the manifold piping diameter or downpipe sizing.

Exile Racing Technologies, Inc.

im just gonna leave it 2.5" . its running great so why mess with it now..

91 civic hatch, homemade turbo+ LS motor = 12 sec street car.

Well this thread made me decide to try it. So yesterday I made a 2" piece from the compressor to the IC, then from the IC to the TB I left it at 2.5". All I have to say is WOW!! There was a very noticeable difference. It feels alot smoother during the vac to boost transition and I also lost some of me lag. It also hits full boost quicker aswell.

Next Im gonna try what ^^^^^ said about stepping the sizes. SO Im gonna have 2" from the compressor to the IC, 2.25" from the IC to the beginning of the BOV pipe, then 2.5" the rest of the way.

I run 2.5" all the way from the compressor to the IC (which has a 2.5" inlet/2.5" outlet) and have to lag problems at all. The outlet on my t4 compressor is 2". I have a 2-2.5" reducer on there attached to the IC pipe going to the intercooler. The way I see it is that the less resistance getting the air to the IC is the less the IC has to work to cool it down. I.e., compressed air raises inlet temps. Now I am not talking about massive piping because you want to keep the velocity up as well. 2.5" piping is a good size for our cars making the power that they do. IMO I would just leave the piping the way you have it.

Dude, Your fucking engine bay is clean as hell! Makes me want to pick up a can of engine bright and some armor all and start detailing my engine bay.. To bad I dont have a nice fat turbo under my hood though.

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To really get a better feeling of how your intercooling piping were setup I would suggest buying Maximum Boost by Corky Bell. Some of the information in there is a little bit dated, but the fundamentals are quite nice and it does give lots of physics equations in calculating the different efficiencies and why you should go one way over another. If I wasn't at work at this point in time I would look up some of the different equations and throw it out there for you. I may do that later on tonight if I have time.

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