Boost Control

[KiwiRS4T]

I have an RB30 with a GT3540, Synapse 50mm W/G, G4 Link, Mac Valve and Greddy copy FF plenum.Gradually building up boost currently at 20psi will settle on 25 - 28 finally. My tuner claims to have trouble getting the boost above 20 although i can't see why. I have bought a stronger W/G spring but figured that it should have been possible to acheive the target just on the Mac/Link alone. I will probably go to another tuner who should be able to sort it out but meanwhile there are a couple of questions to which i have been unable to find the answer.

There is a manifold coming off the FF plenum with hoses going to the Map sensor and boost gauge, W/G, Mac Valve, Bov, FPR I think that's about it.

But everything I read on connecting the W/G and ebc say to take the feed from a non vacuum source before the T/B ideally a nipple off the compressor housing. Why is that?

1. I can see that coming off the compressor housing would give the actual boost the turbo is making but isn't the pressure in the plenum of more interest?

2. And why a non vacuum source? Will the vacuum in the plenum under off boost conditions cause harm to the W/G or Mac valve?

(and don't ask why I need so much boost - that's a whole other story that we are working on!)

[gotRICE?]

Personally i think off the compressor housing, or a nipple post intercooler is the most ideal place to take your wastegate source from.

I think if 28 or so psi is your target, then getting a combination of springs to get you as close as possible, then use the boost control to get you the extra few psi would be the best way to go.

I dont know 100% if its true, but a friend of mine that tunes cars and does lots of Link installs etc mentioned that the mac valves dont like vac too much. This isnt my opinion, as i dont know so corrections welcome!

Another thing, are you 100% sure your boost control is turned on/ working/ on the correct output?

If you turn your ignition on (without starting) go into your Auxiliary outputs, click the output you have boost control set to, (Aux8 for me) and change the "Function" to "TEST PWM". If its all good, the solenoid will buzz like crazy.

Edited July 29, 2012 by gotRICE?

[KiwiRS4T]

Yes I will probably fit a nipple to the outlet pipe of the turbo - I guess maybe its so that you get a quicker reaction to rising boost and are less likely to get overboosting even temporarily. Also that way there will be no vacuum to the Mac Valve - didn't know they didn't like vacuum but all the instructions do say to use a non vacuum source although they never say why.

I agree that getting close to target boost with W/G springs is the way to go but thought that it should at least have been possible to increase boost to any figure just with ebc. I have got a new spring anyway so will fit that with the Mac valve by-passed and see what it makes on the spring alone.

[gotRICE?]

Yeah i read that too.

You dont need to bypass the valve, just turn the output off and it will be open Saves alot of hassle changing lines around lol.

What spring do you have in the wastegate now? If its a light one, maybe the mac valve cant keep up as it has to work too hard to bring the boost up? Running out of duty cycle or something?

[KiwiRS4T]

I can't control my Link - don't have a laptop ATM.

I have the stock spring in the Synapse Wastegate - will do about 18psi max. I have just bought a 90lb spring which should get it into the mid 20's. If it stops raining tomorrow (no garage) I 'll stick it in and see what it does.