Issues getting boost built on footbrake? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 15 Old 04-20-2011, 08:49 PM Thread Starter
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Issues getting boost built on footbrake?

Recently got my c4 swap done in my car.
Motor is currently running 5-6 psi.

Im new to the whole auto thing but the auto swap is definatly the way to go with the turbo, the turbo and auto were made for each other LOL.

Anyways im having issues building boost on the motor with just footbraking. If i use the transbrake, the motor alone with no boost stalls 2500 rpm, then as the turbo comes in it will stall higher, at 5 psi it stalls 3800-3900 on the transbrake. no 2-step. I planning on turning to boost up to 10-12 psi. I am guessing the stall will go up even slightly more with a little more boost pushing on the converter?

Thing is on the foot brake, i can get to around 2400-2500, but it doesnt take much throttle, if i try to give it more gas to spool the turbo, the car just starts doing a burnout. I dont know how in the world i could even dream of footbraking boost. My street tires are 255/60, not too wide. I am guessing drag tires at the track heated up will hold traction better but i dont know how much.

Reason im asking is ive never messed with the auto so i dont know if this is common to have issues not being able to footbrake boost. of if a have a brake adjustment issue. I can yank the e-brake hard and it helps a bit but the drums are adjusted out to where the drums barely slide on, so i dont think there is an adjustment issue.


Brett
91 GT 302 CID c4 w/brake
TFS TW heads, f-cam, typhoon
70mm masterpower single turbo setup.

Last edited by foxfan88; 04-20-2011 at 10:14 PM.
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post #2 of 15 Old 04-21-2011, 02:09 AM
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well you answered your own question. the rear breaks arnt up to the task of holding all that power. if you wanted to footbreak and get more boost you will have to ditch thoes drums and get a set of disks from a new model GT or cobra. then you might be abel to get a few more LBs of boost out of it on the line. if you wanted to get a little more without upgrading i would try a 2 step and let it build that way should keep it from overpowering the breaks and still get the boost up cause you getting the boost from the2 step wich is just burning the gas outside the motor wich spining the turbine faster rather then footbreaking wich just uses engine load alone.


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post #3 of 15 Old 04-21-2011, 06:27 PM Thread Starter
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Yeah i think i will get the two step anyways to be able to control the launch RPM alot better.

Brett
91 GT 302 CID c4 w/brake
TFS TW heads, f-cam, typhoon
70mm masterpower single turbo setup.
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post #4 of 15 Old 04-21-2011, 06:48 PM
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I could only build a couple psi before I would spin the rears on my car. I could build about 5 with the e-brake cable and the full 9 with the 2 step. Make sure you back brakes are set up right and then try using the e-brake. I have my 2 step hooked up to the e-brake.
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post #5 of 15 Old 04-22-2011, 08:46 AM
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i can build 5 LBS with my car on a two step and bone stock brakes, Make sure your rears are adjusted correctly and get a two step.
Ty
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post #6 of 15 Old 04-22-2011, 09:25 AM
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IMHO the only reason you should use the footbrake is if you have a timing issue of building boost as you approach the line, otherwise, use the transbrake for what it is intended for.

If you plan on going the footbrake on the first beam route you may want to invest in a 3-step as boost builds faster under load if you have a stage associated with the foot brake via the brake light switch.

My car will hold with properly adjusted sn95 rear disks. What I "try" to do is foot brake it until i see the boost gauge move, then bump into the second beam and stage on the transbrake. That seems to make the car spool faster.

Also worth noting, none of this nonsense was necessary with my smaller turbo, that thing spooled right up, it is the 88 that is a bit slower.

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post #7 of 15 Old 04-22-2011, 10:47 AM
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My car never built boost on the footbrake either, your not flooring it/not getting a load. On the transbrake you matt the throttle getting load so theirs your boost.

I always footbraked in the past to where the car was about to break loose, when I launched the car would still pull a baby wheel and the boost would build almost instantly (1.45 60'). I re-did my converter recently and will be using the transbrake from now on because I'm ready to go fast.

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post #8 of 15 Old 04-29-2011, 07:36 PM
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Quote:
Originally Posted by 4Jenna View Post
My car never built boost on the footbrake either, your not flooring it/not getting a load. On the transbrake you matt the throttle getting load so theirs your boost.

I always footbraked in the past to where the car was about to break loose, when I launched the car would still pull a baby wheel and the boost would build almost instantly (1.45 60'). I re-did my converter recently and will be using the transbrake from now on because I'm ready to go fast.
With an 88 mm turbo it just doesn't work like that any more....

When I had the 78 my car was like yours. It is easier to drive now but you have to be organized to get it to build boost. My 60's are normally in the 1.4-1.45 range which is kinda weak for the power I'm making. I had one freak 1.388 only. I got a number of pieces of advice on things that may not be "right" that I'm going to have ready for Atco.

Turbo cars are a chore to stage....

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post #9 of 15 Old 04-29-2011, 09:13 PM
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why worry about the footbrake when you have a TB???

89 Hatch 6.65 @ 106...
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post #10 of 15 Old 04-30-2011, 12:46 AM
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Quote:
Originally Posted by 4Jenna View Post
I re-did my converter recently and will be using the transbrake from now on because I'm ready to go fast.
9.90s not fast??
lol


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post #11 of 15 Old 04-30-2011, 10:08 AM
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For cars that are footbraking with a 2-step are you wiring the 2 step to the brake light switch or what ?

1990 Notchback stock bottom end , TW's , F cam , Systemax and 66mm in the works.
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post #12 of 15 Old 05-01-2011, 10:59 PM
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My 2-step is wired to the brake light. I have a seperate switch, when on, makes the brake light be the signal. As soon as I let off the brake pedal, it defaults back the original rev limit. I recently adjusted my back brakes a little better and am now seeing about 6 #'s at 2600 on the footbrake. That's on my street tires! I can probably get a couple more hundred RPM's on drag radials at the track. (and hopefully another pound or two!)

'91LX Vert- Stock Shortblock, Stock Cam, Cobra Intake, Edelbrock Performer 1.9's, 42#er's, PMAS 3", AOD, 3.27 gears, B&G 70mm Single, 3500lbs w/ me
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post #13 of 15 Old 05-01-2011, 11:50 PM
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Quote:
Originally Posted by sweat90lx View Post
9.90s not fast??
lol
LOL

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post #14 of 15 Old 05-02-2011, 08:34 PM
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My 2-step is wired to a button, just as if it had a transbrake. Best 60ft to date is a 1.39

Here's my best pass in the 1/8. 1.44 60ft leaving on 3psi @ 2000rpm


88' Coupe
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post #15 of 15 Old 05-02-2011, 10:25 PM
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Quote:
Originally Posted by rdub79 View Post
My 2-step is wired to a button, just as if it had a transbrake. Best 60ft to date is a 1.39

Here's my best pass in the 1/8. 1.44 60ft leaving on 3psi @ 2000rpm

YouTube - 5.0 Mustang 70mmturbo coupe Stock bottom end, camshaft, intake, and AOD trans


thats nice.

1993 GT 357W T76
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