Overboosting

[jure]

Who could ever say that too much boost isn't good

Situation is following:...
T25, K-tec (Collins) T3 actuator, cup mode (of course), in-car boost (completely closed) and car is overboosting. No matter how much I make actuator arm longer it just prevents spooling in first and second gear but in other gears maximum boost is around 1.5 bar and than ignition cuts off. Is spring in actuator to hard or there is some trick? The situation is same as one when you run normal boost/vacuum circuit and remove one way valve...

[Brigsy]

Is the diaphragm ok in the actuator? check to see if it holds a vacuum.

Make sure the wastegate arm/button on the turbo isn't sticking & moves ok.

Spring could possibly be too strong, use a footpump with a gauge to see what pressure it opens the wastegate at.

[Philclubman]

New poster! (less than 10 posts)

Try using a foot pump and a boost gauge connected upto the actuator and see what pressure is needed to open it, if it does opens at low boost, check for any leaks or splits in the hoses to the actuator and associated pipework.

Otherwise the problem could possibly be the size of the hole in the wastegate, I had this problem when I fitted free flowing exhuaust to my old Toyota Supra I had. Even with the actuator removed and the wastgate wide open it would eventually overboost. I had to take the turbo off and enlarge the diameter of the hole which cured the problem.

[jure]

Actuator is brand new. Less than 1000km. All pipes/hoses also brand new silicon ones. Actuator arm working fine.

2Phil: I have tubular manifold, BMS downpipe and 2.5 inch all the way exhaust but still it is .49 rear which lot of peeps use here and do not have problems.

Just to add... It doesn't cut off ignition if I slowly increase pressure on the accelerator pedal but if I press it to the ground than problem appears.

[Philclubman]

New poster! (less than 10 posts)

If you slowly increase the throttle pedal, can you achieve full throttle and full boost? If you can and it only triggers the overboost when you sudenly floor it, maybe your getting abit of a boost spike which causes the overboost ignition cut to trigger. Have you tried disconnecting the overboost sensor wires and watching what the boost does on your gauge?

[jure]

That is the problem and reason why I'm confused. Overboost wires are not connected at all. If I slowly increase throttle I achieve 1.6 bar on carb top and cca 6500 rpm without cutting off.

[Philclubman]

New poster! (less than 10 posts)

Sounds like your igintion should be fine then, could is possibly be a fuelling problem, Mine used to hessitate or sometimes violently shudder when you stamped on the throttle, watching my wideband you could see it went very lean to the point where it wouldn't run. This occured as the boost came on from maybe 2 or 3psi as it shoots round to say 15psi.

I wounder what other people think?

[jure]

Could be fueling problem since i'm running 130 main and 90 ac at the moment, which is way to low for 1.5-1.6 bars, but I cannot hear car pinking just ignition cutting off

[Philclubman]

New poster! (less than 10 posts)

Could be fuelling, I had to modify the needle valve that opens for the first and second stage boost enrichment. I had to file it so as the second stage would come on sooner. You can also drill out the end of the housing, there is a screw underneath which you can loosen to bring in the second stage earlier. There was some good threads on the old site .

Mine never pinked or knocked as it did it, just stopped sudenly if you floored it. But like you say you could feed the throotle in fine.

Hope its of some help

[jure]

It is. Thanks Phil. Will play with enrichers when I get my hands on wideband these days. Still I need to see why maximum boost is always around 1.5 bars no matter how much wastegate "button" is open

[Philclubman]

New poster! (less than 10 posts)

Try totally disconnecting the wastegate arm, so the flap is loose and fully open, if it still overboosts then it is the diameter of the hole that needs enlarging. It can't flow enough air. It'll be down to that loverly freeflowing exhaust you've got. Thats the problem I had with my supra.

[jantheeven]

Could be fueling problem since i'm running 130 main and 90 ac at the moment, which is way to low for 1.5-1.6 bars, but I cannot hear car pinking just ignition cutting off

That's not true mate... I'm also running 1.6 bars and I have a standard main jet and had to INcrease my a/c jet from 0.9 to 1.0mm because it was still running too rich @ WOT & full boost! (I have a wideband kit installed)
But this is a bit of topic...

[jure]

Good to hear that but what about 2nd enricher? I know that there is difference from car to car... Some guideline for 130/90 is 1.1 bars (without messing with enrichers). I played a bit with actuator and I managed to limit maximum boost to 1.2 bars but I can reach only 0.5 in first and 0.7 in second. Is that OK since I'm running 5000ccm FMIC? It feels little too laggy

[jantheeven]

Good to hear that but what about 2nd enricher? I know that there is difference from car to car... Some guideline for 130/90 is 1.1 bars (without messing with enrichers). I played a bit with actuator and I managed to limit maximum boost to 1.2 bars but I can reach only 0.5 in first and 0.7 in second. Is that OK since I'm running 5000ccm FMIC? It feels little too laggy

I drilled the 2nd stage to 1.2mm. Do you have a bleed valve?

[jure]

No. I have in car boost which is basically the same. What are you aiming at?

[jantheeven]

Well... I couldn't make 1.5 bar with just my T3 actuator... I shortened the rod to the point where it wouldn't get any shorter and I only made 1 bar. So I added a bleed valve for the extra 0.5 bar
I don't believe in in-car boost controllers by the way
They feck up the AFR, as it's impossible to fuel correctly for e.g. 0.7 bar and 1.5 bar and everything in between...
Pick one boost setting and modify the carb jets to suit that... that's what I did and what many others did as well...
But again, that's off topic

[jure]

I am aiming to use in-car boost for 1.5 bars while running everyday on 1.2 bars, so I think it wont be pain in the ass to set nice AFR. With my actuator I can reach too much boost

I encourage OTs if they are usefull

[Philclubman]

New poster! (less than 10 posts)

If it was me i would shorten the actuator arm so the wastegate is just held shut, then Id connect the actuator pipe to a boost source as near to the turbo as possible without the incar bleed valve just to see what the minimum boost the actuator will give.