On a stock 951, if you were to remove the vacuum line going to the wastegate, would it make you run high boost or no boost?
Thanks.

 

I asked this question recently and was told that the wastegates (without vaccum) revert to the fully closed (no bypass) position - in other words all the exhaust flow goes through the turbo. I'm a bit suprised that Porsche set it up this way, since the resulting situation is very bad and typically means a blown engine. Most turbos that I'm familiar with (on aircraft) very deliberately default to the full-bypass (open) postion. This way if a turbo wastegate fails, you still get normally-aspirated performance out of the engine, rather than having it grenade itself.

If you pull the vaccum line to test (so I'm told) on this engine, be VERY careful when revving it up - monitor your boost levels carefully and don't take longer than you need to. Also keep in mind that this is putting a lot of thermal stress on the "hot" side of the turbo - let it warm up for at least a couple of minutes before you rev it up.

 

It would run higher boost, dependant on how strong the wastegate spring was. But it should trigger the overboost protection, so might run rough if this can cut fuel retard / ignition as well as attempting to open the wastegate which it wont be able to do.
Tony

 

The wastegate will still open due to the exhaust pressure on the valve ut with a good spring maybe not early enough.
Tony

 

thanks

 

That is also a way of testing for WG failure, by clamping that vacuum line and watching out for really high boost.

 

Lol quite a car collection there. Whats your favorite? Hows the 951 keep up with that viper?

 

True, although I know better than to implicitly trust the overboost protection. . . I know of a couple of cases where it has failed and unfortunately there's no way to know it has until the damage is done. Easy to test, but just keep an eye on the boost level and you'll be fine.

 

I have removed the vacuum line to the wastegate and on my car, it will spike to about 19-20 psi and then settle to about 16-17psi. I decided this was a bad idea and put it back on.

Ian

 

Yes without that line the overboost protection loses its control over the wastegate
Tony

 

"The wastegate will still open due to the exhaust pressure on the valve ut with a good spring maybe not early enough."

Exhaust pressure varies with RPM. Only in the higher-RPms, like 5500rpm+ does exhaust-pressure get above 50psi (minimum required to force wastegate valve open). This means at the turbo's most efficient range, around 3500-4500rpm, you're gonna see a tonne of boost, like 25psi+.

 

even with a very weak spring?