930 correct boost gauge source point

[MDPorsche]

What is the best place to tap for source boost for my boost pressure gauge?

I have an 86 930 running a 3.4L EFI with Garrett G35 & Tial waste gauge. I have a Andial tattle-tale 2 bar boost gauge in lieu of the clock and am running a 0.8bar Tial wastegate spring.

When I tap the boost source at the Tial the gauge works & tracks boost well BUT bounces the tattle-tale to 1.8bar on shifts. I then moved the tap point to the throttle body and solved the bounce problem but the gauge only shows boost under a hard pull and then only momentarily BUT does stop at the correct 0.8 bar.

Recommendations?

[Alan L]

Up front - off your brake boost line.
Alan

[Mike80911]

As stated above get an adapter to tap off the vacuum line for the brake booster

[MDPorsche]

Manual non-boosted breaks on this one.

[Alan L]

You are kidding, right? No vacuum assist brakes?
Alan

[smurfbus]

Where can one find a wonky adapter for that booster line? I havent seen one in regular autostores.

[RarlyL8]

You've already got a line to the engine - where the boost line belongs. Pipe it below the throttle plate so the gage only sees the boost that the engine sees. Above the throttle plate you will see chop throttle spikes. Cutting into brake vac lines is nuts, those are your BRAKES.

[boosted79]

Tapping into the brake booster line for a boost gauge has no effect on brake booster action, it's still a closed system. For my AEM boost gauge and data logger I tee'd into the rubber booster line on the inside right behind the go pedal. It connects to the steel line in the tunnel that runs back to the engine bay and then goes to the manifold with a rubber line.

[Alan L]

Brian - makes no difference to the brakes. At all. Think about all the manifold leaks and hose leaks in the engine when you have tuning issues. They also feed into the brake vacuum system. No effect. Your engine is a 3.3 l vacuum pump. It overwhelms any leaks - even assuming you have a leak at the boost gauge line. Think about all the cracked and missing hoses - makes no difference to the brakes.
Regards
Alan

[VZ935]

I didn't have a booster on my 930 either

[MDPorsche]

Thanks Guys... I'm tapped into the intake below the throttle plate. Works without spike but is not very sensitive to partial boost. And yes, no power brakes or steering on this one... pure.

[Alan L]

Originally Posted by VZ935

I didn't have a booster on my 930 either

So, forgive me, but why wouldn't you run a brake booster on that beast? Was it the physical limitation of fitting it in? You must have developed some strong thigh muscles. Maybe that was the reason :-)
Alan

[Rawknees'Turbo]

Originally Posted by Alan L

You must have developed some strong thigh muscles. Maybe that was the reason :-)
Alan

Based on all his awesome cars, past and present, I'm pretty sure that Big V used (uses) his d**k to actuate the brake pedal!!!

[VZ935]

Nice even peddle. Easy to modulate and no real strength needed. Won every Frozen Rotor "Best Braking" award in every race I ran that included cup cars with ABS. Stacked up those free Cryogenic treatments.
I swear if I dialed all the brake to the front I could stand that car on its nose if I wanted to.

Originally Posted by Alan L

So, forgive me, but why wouldn't you run a brake booster on that beast? Was it the physical limitation of fitting it in? You must have developed some strong thigh muscles. Maybe that was the reason :-)
Alan

[VZ935]

Originally Posted by Rawknees'Turbo

Based on all his awesome cars, past and present, I'm pretty sure that Big V used (uses) his d**k to actuate the brake pedal!!!

Glad its not that long and strong or my only option would be to mate with animals on the Serengeti

[Rawknees'Turbo]

Originally Posted by VZ935

Glad its not that long and strong or my only option would be to mate with animals on the Serengeti

Hmmmm, some of those are pretty hot!!!

[bpu699]

Originally Posted by VZ935

Nice even peddle. Easy to modulate and no real strength needed. Won every Frozen Rotor "Best Braking" award in every race I ran that included cup cars with ABS. Stacked up those free Cryogenic treatments.
I swear if I dialed all the brake to the front I could stand that car on its nose if I wanted to.

How?

My 930 got towed at the track, motor off. I didn't have enough power to slow down and not hit the tow truck if it stopped suddenly. It required a 500% increase in force...

With the motor running, can stop from 120 pushing down with my pinkie toe...