Stock ST/GT fuel pump limit, FYI - dont go beyond 12 psi on a stock pump Options

[scothaniel]

The stock fuel pump in my 96 ST finally reached it limits last week and chocked at around 16 / 17 PSI of boost. I thought I hit fuel cut at first, but I didn't get the usual warning light and was able to boost again without restarting the car. I'm using the stock ST205 fuel pressure regulator with a set of RC 550 injectors. Looking at the BGB's, the base fuel pressure for the ST205 appears to be 36 psi (or between 33-39), so it chocked around 52 psi (only estimating, I don't have a fuel pressure gauge in the cars cabin). Both the GT and ST use the same pump.

So for a year I was boosting around 12 -14 PSI without issues, even running rich due to the 10cc larger injectors (and the fact that the stock ECU runs rich) . I was probably pushing the limits at 14psi, so I wouldn't recommend anyone going over 10 or 12 psi on the stock pump.

This post has been edited by scothaniel: Jul 31, 2007 - 11:34 AM

[lagos]

what car/motor was this on?

trying to save 90bucks by not upgrading the pump is a very foolish idea.

[scothaniel]

It was on my 3rd gen 3S (basically a 3SGTE but using a 3SGE motor to start with).

I didn't upgrade the pump because I was curious what it could do. I still believe the pump is suitable for the stock st185 motor running at 8 psi.

[lagos]

sure, but 8psi is safe mode boost... not stock boost.

[scothaniel]

Thats for the ST205, right? 12psi stock boost (limited to 10 in first gear) and 8psi under failsafe mode.

For the 165/185, the stock boost level is spec'd as 7-11psi in the BGB, but thats taken at the turbo, not the head. The turbo vsv limits boost in 1st and 2nd gear to 7 psi, and 3rd-5th gear get 9 psi normally. IIRC, safe mode on the st185 was no boost - but its been a long time since I ran the stock ECU in my st185.

[lagos]

The turbo vsv limits boost in 1st and 2nd gear to 7 psi, and 3rd-5th gear get 9 psi normally. IIRC, safe mode on the st185 was no boost - but its been a long time since I ran the stock ECU in my st185.

no thats not correct at all. the only time the tvsv limits boost, is to put you into safe mode. when in safe mode, youll be limited to 7psi. the reason why you see less boost in 1st, 2nd gear is because those gears cant create enough load on the motor to fully spool the turbo. there are no gear specific limitations inside of the ecu.

This post has been edited by lagos: Aug 1, 2007 - 1:24 PM

[scothaniel]

You know, I never thought about that before. The only connections on the trans are the speedometer and neutral switch, no way for the ECU to know gearing. I read about the vsv limiting boost by gears a long time ago and never looked back. It just goes to show how much mis-information is on the net:

http://www.gtfours.co.uk/what/abbrev/abbrev.htm
http://k1ano.co.uk/boostcontrol/rvgt4specifics.htm
http://www.celicatech.com/forums/showthread.php?t=1161

I was confusing 'safe mode' with 'limp mode' - code 34 on the st185, where the ecu pulls timing after over boosting so you cant get any boost.