Car won't hold boost at launch!

[Nick Micale]

Why is it that owners complain about a vacuum system will not allow enough boost when launching?

It is the same pads and brake shoes as the PM or other assist since you apply the brakes BEFORE you get into boost.

The most common issue like you have is the torque converter is not matched to the turbo.

Just this year so far I have already changed one converter for a 60mm turbo, one on the lift now getting a new 3600 stall converter, and one waiting for a new converter.

This is the most common performance issue the turbo cars I deal with that have been built elsewhere, and with the proper converter, the car then performs like it should.

Most of the converters I replace are non-lock up as it will spool much better.

I have been doing these cars for years and hear lots of comments about top end slippage with a loose converter, but street or strip, the car that leaves the best is usually the winner as MPH does not win a race, getting there first does!

In your case with a 60mm turbo, I just installed a 3300-3400 converter in a GN last week, and it is awesome.

 

[dank GN]

Okay try this do your burnout then pull to line . Put it in neutral with your foot on the brake and rev it acouple times . You will notice the brake pedal goes down further . Then without releasing what you just had to rev to get your pedal to proceed to brake boost . U should be able to hold Alil more boost . And to adjust the brakes spin the adjuster screw till you can just feel it make contact with the drum .

 

[Fitman]

I definitely don't have this valve.
Special order or any auto parts store will have?

 

[Chuck Leeper]

Sorry for dumb question but measure diameter at widest point of drum?

There should "no widest point". They should be round. They should also be the same diameter at the outside of the contact face, as the inside. [IE: No taper.]

As for the HB...I had the metric rotors/calipers on the ft of the 55, 8" dbl diaphragm booster, Wilwood adj prop valve, 9" FORD brakes. 2.125x11. REALLY poor performance.
MAYBE, 850psi at the calipers. HB on, could make 2100 w/ serious pedal pressure.
I had my blood hound riding w/ me. I was setting the prop valve. The car stopped so fast, I had to pull Rosco's asshole back to his tail.!! True story!

Also.. a 2400 stall isn't helping things.

 

[Fitman]

I checked and yes my system already has a brake booster check valve.
My convertor is a 3400 PTC, not a 2400

Thanks again for everyone's help.

 

[Fitman]

i guess i need to focus on adjusting my rear drum better...

 

[haywire4130]

And power bleed the brakes, i would bet you have air in the system. If they were that far out of adjustment you would have a lot of pedal travel.
Stupid question: your wheel cylinders/axle seals are sound and not leaking fluid inside your drums?

 

[Fitman]

Not leaking any fluid at all.

 

[Fitman]

Thinking maybe when I installed my line lock I didn't get all the air out, but my car really wouldn't hold boost before then anyways.

 

[No disintegrations]

Adjusting the rear shoes doesn't really give more braking. It gives a higher pedal so it feels like there is.

You may have glazed drums. How do the brakes work while driving?

 

[Fitman]

That actually work very well.
In non-drag racing applications.

 

[No disintegrations]

How about if you also use the e brake and snap it loose to launch?

 

[Fitman]

Haven't tried that yet

 

[dank GN]

Not leaking any fluid at all.

Is it running that would be one of the first Buick's in history that didn't leak and ran lol jk