How do i get brakes to hold boost???

[KEVINS]

15psi launch with a stock conv is a bunch of $%$^% Maybe with slicks and a baby turbo. My 2cents worth.

FWIW, Stock turbo and MT slicks.
After knowing what some of my friends boost pressures are during launch I feel that it is in the braking system. Maybe our rear brakes are adjusted a bit tighter.. My buddy Blair launches with MUCH more than I do using a foot brake.

He holds the brake and watches the boost gage go up rather quickly and when it gets to what he wants he lets go of the brake. So the boost gage doesn't actually hold steady at the boost, it's "on the rise". He runs MT 10x26's and 3 1/2" wheels up front and he launches at 18-20psi with only the foot brake. His car only has 34k miles so maybe this has something to do with it to..

I can hold a steady 17psi with the slicks on but I have never tried more.

Regards
KS

 

[c&cgn]

Originally posted by Turbonut


You must be using the factory tach! Whatever floats your boat.

uhhh okay Guess you didn't look at my sig? Turbolink with boost sensing, so I know exactly what is happening. I can foot stall my D5 to 2500 rpms all day long with no changes to the prop valve. I flash it to 2800-300rpm and have consistent 1.72 60' on Nitto's all day long. Slicks is good for 1.6's.

It's not anywhere near as cut and dried as you make it out to be. It takes knowledge, skill, the ability to adapt to the conditions and partially just dumb luck as to what the car is capable of and how you are able to work with what you have.

 

[Turbonut]

I don't get it? If the stock D5 is so good and holds so much boost then WHY is there aftermarket 2800 to 4000+ stall converters??? They would be out of business! I guess i'm dumber than I thought and I own a piece of ****!

 

[KEVINS]

Steve Yaklin was concerned a bit about which converter I had so I tested it in the driveway to verify that it was a D5. I used Chad S's results for comparison and mine match his. I had the ol' street tires on and I power braked it, and held it at 5psi and it was stalling to 2800+ according to the scanmaster.

Hope this helps..
Regards
KS

 

[Turbonut]

Thats about what I get, 8psi@2800rpm on my stock D5 w slicks and NO tire spin. Any higher and I shoot accross the lights!

 

[TurboBuickSix]

Me and a freind have identical cars except for the torque convertor.Somehow mine ended up with a non stock (D6)convertor in it and I could'nt get any boost holding so I tightened my brake adj until it was resistant on the drum a little put it back together and I can get a pound or two before it breaks loose and I have a good posi and decent tires.My buddies car holds 10 #'s of boost effortlessly with his 2800 stall all else the same.I have to subscribe to the convertor theory.It seems to be tight and if I just dump the throttle from a start it is dead for about 30 ft then all hell breaks loose,it sucks.

 

[KEVINS]

I have an idea:
When I press on the brake pedal to build boost, the brake pedal will hit the stop. I can keep pushing beyond that point though. I always figured this "stop" was part of the rear brakes in the master cylinder or something. If so, maybe that's why some can hold more boost???

My question is:
For those that can hold over 10psi on the line, are you feeling this stop and pushing harder past it? My answer is yes.


KS

 

[Eric Stage I]

Could it be the difference between the older cast iron combination/proportioning valve and the newer brass ones? I have 2 GN's and neither one will hold more than 2 psi on the foot brake. If I use the e-brake, they'll hold at least 10 psi. Both of them have the older cast iron valve.

For the people with adjustable proportioning valves, I assume you have the factory valve removed?

Eric

 

[Phatman]

I sprang for the new brass valve when I converted over to vacuum...did a through brake job...replaced all the lines...fresh cut on all surfaces...yadi,yadi,yadi.

On the foot brake with street tires...2800 stall...te44...Wendy's value meal in my lap and the Cherry Popping Daddy's on the radio, 2 to 3 psi with converter flashing around 2650.

I'm thinking of installing a vacuum canister...I do have a Wilwood adjustable on the shelf along with larger wheel cylinders, at the time I opted not to install it. I just consider the money spent as an investment in our future.

 

[UNGN]

Originally posted by Turbonut
I don't get it? If the stock D5 is so good and holds so much boost then WHY is there aftermarket 2800 to 4000+ stall converters??? They would be out of business! I guess i'm dumber than I thought and I own a piece of ****!

A stock D5 will flash stall higher than 2600 rpm but the turbo has to be spooling (or atleast starting to spool) in order to do it. A larger turbo that won't spool below 2500, won't be able to pull a D5 higher. A torque converters stall speed depends on the torque being input to it. The higher the torque, the higher the stall speed. When the turbo spools, torque more than doubles in the span of only a few hundred RPM's.

With enough brake or with a transbrake, I can see where flash stalling a D5 to 4000 RPM is possible (using a stock turbo or a TA49 or some other turbo that is set up to spool quickly), but it has to be very hard on the equipment.

 

[Ron]

Have a tranny brake Installed, works great.