Boost levels

[Phil Wall]

I know this has been covered on the BBS many times and I have spent time searching through previous posts relating to the subject.

 

I have a Hiper and HKS cat removal pipe with number one cat still in place. I have fitted a TRL FVCC. shortly after the exhaust and cat removal.  I recently fitted a Greddy peek hold and warning boost gauge.

 

I have found my maximum boost level to be 1.12Kg/cm - 1.1 Bar - 15.93psi.  

 

1. Does anyone else have this set-up if so what boost levels are you getting?

 

2. I have a SS Chris Wilson down pipe ready to fit, given the above what psi might I expect?

 

3. If putting in the down pipe gives OTT boost, what psi can I expect if I put the second cat back in?

 

4. As boost controllers only allow boost to be raised, (I am aware that Leon has kept 4 cars to 1 bar with a DSBC) and as I don’t want to have to drive with my eye on the boost gauge( pillar mount) what should I do to regain some control of boost via a DSBC,?

 

5. What sort of BHP do J- specs run on 15,16,17,and 18 psi?

 

[Alex]

1. Not Me

2. If you pull out the other cat you'll see 1.4bar easily. This is because you will have 1x 2.5" and 1x 3" decat pipes - boost only seems to be limited if you have the 2x 2.5" pipes - I'm now hitting 1.25bar with 2x 2.5" CW pipes with the SBC-iD turned off...

1.4 bar is too high for the fueling and infact I think you're at the best boost level right now. I would get some extra fueling then add your decat pipe. Or put it in and add a restrictive gasket into the mix.

3. Probably similar to what you've already got maybe an extra psi.

4. Pass though my SBC-iD seems to control it a bit and I didn't exactly do anything special to it....sorry.

5. 14 psi is ~1 bar - that's the ECU's preferred setting.

16-18psi is what I run with a Mines ECU and stock fueling - the mines ecu has a map for upto 1.1bar (15-17psi) so it starts to run lean after that point so I am taking a risk.

My higest ever was 1.46bar about 21 psi but that was on a cold night for about 6 seconds with some Toluene in the fuel mix....i think/hope!

18psi seems to be the favourite but its your engine...your choice

[Phil Wall]

Thanks Alex, I guess I will have to try it and see what happens.  Looks like I may as well stuff the second cat back in, at last it will make it easy at MOT time.

[matt]

Hey Phil

 

I have a similar set up to yours and am too considering losing the front cat and replacing with a CW pipe. Mainly 'cos I hear it is the most restrictive ..........

I would be interested to hear how you get on.

 

I'm not 100% certain ...... but if you do find you're overboosting with the front cat replaced with CW's downpipe it might be possible to bring it down with a restrictor plate. Supplied by that man SeeDubya ....

 

I am running a similar set up to your present one (DualDrager and Blitz 3'' pipe) and max boost is only 0.9 bar ........

Now whether or not this is because the Hiper is more efficient than the DD , I'm not sure.

I've also read that different j'specs respond differently to decats ........... but never established why.

[Phil Wall]

I'll keep you posted Matt.  

 

There really is nothing in the way in the Hiper, I remember stuffing my arm to my sholder into the pipe from the rear before I fitted it. From my reading of many previous posts, it is pot luck as to what boost level you get when you decat.

[Phil Wall]

My1.12 Kg/cm level was achieved with an ambient air temperature of about 3 degrees. Today at around 15 degrees, boost just failed to reach 1.0 Kg/cm no matter how hard I tried. Most WOT runs were closer to Matt's 0.9. This lower figure is much closer the 14-psi limit that I used to reach in early autumn before I fitted a TRL FCVV.

 

This makes more sense, as I would have been hitting fuel cut all the time with 16 psi, but I was only hitting it occasionally, a couple of times a day.  I am making a temporary 2.5in restricting ring just in case I see unacceptable levels.