Boosting Problems...

[mini-e]

Just had my j-spec TT6 BPU on the rolling road again and seem to have ran into some issues.

 

First a little history...

 

The car was first dyno'd nearly a year and a half ago, at this stage it just had exhaust/intake/1st cat out. I knew it was goin to hit fuel cut(as i had experienced this numerios times) but i decided to run it anyway. It made 300bhp (269whp) and 338 lb ft torque before hittin fuel cut at about 4700rpm/.9/1bar.

 

Soon after i fitted a thor TRL FCD which eliminated the fuel cut problem. Also fitted a boost gauge.

 

After some time i decided to go full BPU, taking out the second cat and fitting a 1.2bar restrictor ring. Also fitted a walbro fuel pump. This was no lenght ago.

 

Enter Dyno No.2 (today)!

 

The tuner ran the car but had difficulties. It was experiecing boost cut and not revving out fully. There was a spike around 4100rpm before power dropped off. The car made 290bhp and 367 lb ft torque.

 

He said that I should fit a proper boost controller which should hold the boost out fully. He didnt think the second decat/ restrictor ring combo was the best idea. Is this correct, as in will this allow me to run 1.2 fully out so i can get my true power figure? And how come im expeciencing these problems?

 

Also, he mentiond that i should definetly get a FMIC if im running that sort of boost. Again, is this correct? Is a FMIC needed for a BPU car? It being a 97 car, and having less than a 100k klms (bout 60k mls) the standard smic it in decent condition im led to believe.

 

So, any input on the above would be greatly apperciated.

[mini-e]

Sorry just another input. There was some mention about the FCD i fitted. The trl fcd raises the fuel cut from standard(correct?), what does it raise it to? Would this be the source of my problem?

[Chris and Alana]

the thor FCD raises the factory fuel cut from 1.0bar to 1.25 bar and from what iv read a stock SMI in good nik should be fine for BPU but I would have thought your BHP figures would be higher than that or is that rear wheel BHP figures youve posted. Anyway hope that helps

[mini-e]

No mate, he couldnt run the car fully, as it kept cuttin.

That was just the bhp at the time it cut in. ie.it was 290bhp when it cut at just over 4000rpm. The car should have rev'd out to about 7000rpm, probably making much more power. I was hoping for about 380ish, maybe more.

 

Thinking about it, I have the distinctive feeling that possibly theirs something up with the restrictor ring, and that the car may be boosting to 1.25bar, resulting in the boost cut. Im in no way technical at these sort of things, but do you think this could be the problem?

 

Note: I never noticed the boost goin over 1.2 bar, but its a possibility, il be goin for a blast tomorrow and keeping a close eye on the boost gauge....

[Bob]

The spike around 4100rpm would be the 2nd turbo coming on-line, the drop off in power could be due to the turbo not spooling properly, or having been spat out the back (worst case scenario, more liekly to be a split hose somewhere).

 

the standard SMIC should be mor than adequate for BPU, espeically as it's still relatively young.

 

The restrictor ring is there to prevent boost creep; the car if J-spec will generally boost to around 1.2bar on its own if de-catted. You shouldn't need a boost controller for that, but you should have a boost gauge to keep an eye on your boost.

 

If it's hitting boost cut (and I don't think it is if it's not boosting past 4100rpm) then you should be able to adjust the Thor doodah to compensate.