3" cold pipe for 12psi?

[neilsan]

ive got a generally stock s13 sr and want to get out of my SMIC.

I can pick up the Hybrid piping kit for a reasonable price and ive got my eye on a used 31x6x3 intercooler 3" in/out to go with it. My current goal is to run around 12psi till the t25 bites it and then upgrade accordingly later for more boost, with an eventual 250-280whp final goal. The cold pipe in the kit is 3" though, and I know most setups for 400whp dont even run that large.

Would 12psi at the throttle body be overworking the turbo since its a larger volume to fill? Also where's the best place to run a boost line for a controller solenoid with a front mount? currently my profecII is getting its PSI reading t'd off under the dash from my mechanical boost gauge, which is run off the throttle body. The control solenoid is interrupting the stock actuator hose off of the smic cold pipe (obviously), but I dont see any fittings on the Hybrid for it. am i missing it or do you run the actuator solenoid off the throttle body with a fmic?

cost effective-wise is this a good option, or for $250 more should i just get a greddy v-spec kit and forget about it. i already have a greddy hotpipe anyway for the smic and id need to do a little fabbing to it to meet the lower hot side of the hybrid.

[NemeGuero]

It doesn't over-work the turbo, you just have more lag due to increased spool time.

[neilsan]

ah. So it kind of just catch 22's? i.e. the exhaust is what spins the turbo but you wont have the volume until there is enough intake to produce it. hard to believe there isnt a pressure drop though.

[NemeGuero]

Well there is.. the larger diameter piping creates a pressure drop. This is what creates the added lag time.

And yes, since the compressor and turbine spin on the same shaft, they will only work together.

[neilsan]

I know the turbo shaft is solid.

To better detail my concern:

These numbers will be inaccurate, but say if the turbo has to spin at 150,000rpm to generate 12psi with my sidemount, It's not going to hurt it if it has to spin 225,000rpm due to the extra volume of filling a 3" core and 3" cold piping to get the same psi?

Is compressor efficiency only based upon how much pressure the compressor can work against, as opposed to actual shaft RPM? Is there not a point in rpm's where the compressor just can't 'process' the amount of air that the turbine is making it spin to do?

Or more simply i think... is the lag is because the turbo has to spin faster, and is this extra turbine speed that harmful to a T-25.

by how much do you guess lag would increase by? currently with my 2.25" hotpipe, oem smic, tubular manifold and greddy dump boost comes on generously at about 2500rpm.

[Max_PSi]

Simply, a 3" pipe will require more air to fill it then a smaller pipe for the same application. The RPM's should be the same for the turbo, it will simply take that little bit longer for the intake system to be pressurized, hence turbo lag.

[neilsan]

well that makes sense. i tend to overcomplicate.

[NemeGuero]

Yah, what he said.