TII Shelby Z 16psi questions....

[mattquerio]

My buddy had a 87 Shelby Z with boost control issues. He would have to feather the throttle to keep it from "overboosting" (term he used) when trying to accelerate hard. If he didnt feather it the car would bury the boost guage past 16'bs and the whole car would jolt in shock, it was terrible, like the engine sputtered HARD from it.

What was going on in reality with this scenario? Any opinions?

I don't know what was wrong with the car to make it do that.

Im sure this sounds stupid but I've always wondered what the hell was wrong with that car, so please help put this thought in my head to rest. Thanks

[cordes]

Overboost cutout is at ~14.7 PSI. It cuts the fuel, and is what has been happening when the waste gate pegs.

The waste gate arm is either seized shut, or there is no boost signal getting to the waste gate can. You need to check the vac lines to it and also make sure that the waste gate arm will move freely. It will take some effort to open the gate by hand, but you can do it by grabbing the rod on a stock setup fairly easily. Just make sure the motor is cold when you do it.

[mattquerio]

Overboost cutout is at ~14.7 PSI. It cuts the fuel, and is what has been happening when the waste gate pegs.

The waste gate arm is either seized shut, or there is no boost signal getting to the waste gate can. You need to check the vac lines to it and also make sure that the waste gate arm will move freely. It will take some effort to open the gate by hand, but you can do it by grabbing the rod on a stock setup fairly easily. Just make sure the motor is cold when you do it.

He no longer has it, he didnt know how to fix it during the duration of his ownership. Its always been a mystery as to what it was to me, although I will say when he managed the throttle properly the car hauled serious butt.

[cordes]

Well, at least you know what to do if it happens again.

To an extent he is very lucky the thing lived like that. The part throttle tables have less fuel and more timing than the WOT tables which can make for a dangerous situation while manipulating the throttle to control boost in situations like that with a small turbo.