3 inch intercooler pipeing? or 2.5?

[bigcarl]

is there any gain to be made upgrading from 2.5 to 3 inch intercooler pipeing, when running a gt30 on an rb25 equipped with 650mmx300mmx80mm intercooler with 3 inch inlet and outlet running 20psi and 260 plus rwkws? will it cause more lag ? is it overkill for a mid to high 200 rwkw combination? any info would be much appreciated thanx. i will be running standard plenum.

[jazza08]

2.5' will give less lag and is good for around 450hp at the wheels.

If your going higher than this than 3' piping will help breathing at hp levels this high!

Anyone can correct me if im wrong

[R31Nismoid]

SK posted heaps of info on this, search for it in the depths...

this was asked last week and he wasnt gonna post it all again i think

[Sydneykid]

Here is one I prepared earlier;

Hi guys, here is an example of 4 intercooler setups and pipework we have actually used;

1. R33 GTST Standard Intercooler and standard R32 GTST pipework

150 rwkw = 27 lbs of air per min @ 13 litres of i/c & pipework

2. Supra Intercooler and matching 63mm pipework

180 rwkw = 30 lbs of air per min @ 15 litres of i/c & pipework

3. Standard GTR GTR and 63/75mm pipework

250 rwkw = 40 lbs of air per min @ 21 litres of i/c & pipework

4. Greddy 600 X 300 X 115 and 80 mm pipework

400 rwkw = 60 lbs of air per min @ 28 litres of i/c & pipework

If you look at the numbers you can see that the rate of air flow and the volume of I/C and pipework have a fixed relationship (27 = 13 , 30 = 15 , 40 = 21 , 60 = 28). This is not an accident, I designed it that way. The reason is I wanted to keep the throttle response as close what it was when the car had 150 rwkw, because I though that was very nice response.

The theory I followed was, the more power the engine produces the more air it needs. Thus if I keep the increase in the volume of air inside the inlet system in the same proportion as the power increase, then the throttle response should stay the same. This is based on the engine using the air in the same time frame.

So when people say they fitted a FMIC and have not noticed any less throttle response, my response would be, that is what I would expect. As long as they went from 150 rwkw to 180 rwkw. On the other hand, if there was no power increase then it would be simply physically impossible for there to be no decrease in throttle response.

The problem of poor throttle response arrises when you have a 220 rwkw engine with a 28 litre inlet system. This is something I see way to often.

Hope it helps:cheers:

[bigcarl]

thankyou very much for this , you have answered my question. think i will stick with 2.5 inch.