wicks

Amazing how often this happens. There should be a sticky topic maybe - always check the throttle body o-ring and the silicon hose clamps and everything else connected to the intercooler first when a 964T isn't idling or running right or failing to boost normally, especially if it's a sudden change from how it was just running.

Scott Dunavant

SO... I still had crappy boost pressure and a bit of bucking. The waste gate would have been loud. We talked about the recirculation valve.
I upgraded to the Turbosmart valve. Bit of a hybrid with a blow off feature. What an upgrade! Considerable more boost pressure and perfect flow when quickly letting off the throttle.
I'm running 1 bar and short gears. Short gears figure with this test because the boost pressure comes on faster and you shift faster. I went with N/A gears.
It's adjustable to let more boost into the atmosphere. For now, there's a small amount of boost going into the atmosphere. I can hear it. But I don't think the passenger would hear it.
Easy and affordable upgrade.

spartansix

@Scott Dunavant That's very interesting. What's the advantage to venting some of the boost to atmosphere rather than recirculating it?

fritz k.

The differences between open and closed blow-off valves are not dramatic. Control with closed systems is more harmonious overall and places less strain on the engine management system, idling should be more stable. In addition, the noise emission is lower, which is why the open blow-off valves are illegal over here.

None of this plays a role in motorsport, which is why open systems are used almost exclusively there. In addition, the response behavior is said to be better with open BOVs.

There are also BOVs that can be switched between open and closed if you want to try out different systems.

Here is example of an open BOV sound in its most beautiful shape:

Scott Dunavant

I'll mount my Insta 360 camera back there. When increasing your boost pressure along with headers, cams etc. There's more pressure. When shifting gears your vacuum still pulls the fuel head. The increased boost for that short time throws the fuel meter off. Causes bucking on modified cars. Much smoother with the Turbosmart hybrid. I noticed a massive difference because my original valve was bad allowing air to recirculate between .7 and 1 bar. Very messy feeling.
This valve going bad has probably caused most garage visits with the ownership of these cars. Owners would believe that there's serious Problems and it felt like it. BUT I replaced 100% of my car except this valve. The last item to be replaced.

urquattro20Vt

I'm pretty sure the loud "screeching" noise is actually compressor stall - that said - yes hard to beat the sound of a fire breathing 5 cylinder turbo.

Brandon
'91 Turbo

wicks

That Pikes Peak footage reminds me of the award winning film Peugeot/Vatenen. Watch full screen.

spartansix

The Turbosmart part looks very trick, but I don't love the "service every six months" design when the original part is essentially service-free.
APR makes a diverter valve that says it doesn't require extra servicing, but it doesn't vent anything to atmosphere.

heliolps2

Hi Scott,
Please share more about the gears. I installed a G50-01 in my 911 with a 930 engine with a 8;32 ring and pinion, What a rocket ship. 0-100 was crazy. I though of putting NA gears in my 965, G50-52 Changing 2nd, 3rd, and 4th gears, I was told first gear can't be done, I would keep the stock 5th for HWY cruising

Scott Dunavant

GBox in Colorado add N/A 2,3,4, and a shorter 5th. I don't need an over drive gear.
He knows the need combination as I'm not the expert.
I always have healthy boost.