Overboost

[Timb2117]

Hi please advise (as I am trying to not become Ron.R's nemesis)

'92 Turbo, ROW spec, with larger exhaust. Popped on Everest chip, shocking overboost, ported turbo out to 20mm (just - trying to not be the typical boy that "more is better") and overboost better but not cured, full throttle she cuts, engine light and fault code 31.

Checked wastegate actuation all good pipes all new, can avoid it by using 3/4 throttle, but that's not a cure.

Q? go back in and port out to the full 21mm? & double check internal gas flow way is smoothed out? Any other ideas? Does the extra mil really tip the balance?

Many thanks in advance for both your patience and advice. Timb2117

[Tuga2112]

check if yout trhotle position sensor is setup correctly

[Timb2117]

Thanks Tuga I think that would have come up on elanscan as a fault though?

[Timb2117]

Just checked the readout and TPS is within range (thankyou to the gods of creation for making elanscan)

[Steve A]

You'll find a great deal of discussion on here about over boost, it's worth searching it out. I like you initially went for a conservative 20mm, but found that it wasn't quite enough, which is quite annoying given the work it took. My advice would be to go as big as you can, as long as your turbo is in good order. I had mine overhauled recently, and they not only re-ported it, but made sure the waste gate linkage had no play.

[steve matthews]

Round off any interior corners in the exhaust manifold.
This will give you cleaner flow and a couple HP.

[Timb2117]

thanks Steve x 2 I appreciate your experience I will do exactly as you say......Bracing for starting removal of turbo process all over again (Nah actually its easier x2)

[Timb2117]

okay update, so porting out to 21mm helped a bit but not much, so without having elanscan perfect yet I tried new fuel pump, walbro 255 and bingo fixed, so the old one struggled to keep mixture rich enough and ECU was just doing its job. Nice to get to bottom of that one, I am trying to do only one thing at time but will pop on new injectors soon.

[RonR]

Great to see you're sorted Tim

[Rocklobster]

Just in case you're still checking this thread. Have you checked your actuator arm length adjustment? If it's set too short (I think it's that way round), it won't fully open the wastegate and you'll be more likely to encounter overboost. I've got an everest chip and bigger exhaust and it's ported to 19mm, runs fine since I adjusted the actuator arm correctly. There are instructions in the service manual.

Before porting, my wastegate was 16mm dia which = 201sqmm. 19mm dia = 283sqmm. That's a 40% increase in CSA and a lot of exhaust gas.

21mm dia = 346sqmm which is a 72% increase in CSA. You're not flowing 72% more gas.

Just a thought.