Proportioning valve needed for LS1 conversion? Options

[mittelmotor]

Renegade Hybrids suggests doing away with the rear proportioning valve for their LS1 V-8 conversion, and replacing it with a T fitting. I know in stock configuration this could increase the likelihood of rear lockup. My car has the stock MC, stock 914-4 rear brakes and 911 "M" calipers & vented rotors up front. It'll also have a bit of tire stagger, 205s in front and 225s in rear. Will a T fitting be OK with this setup? Thanks!

[stewteral]

 914_Project__Chassis_setting_worksheet.xls ( 22.5k ) Number of downloads: 288

Renegade Hybrids suggests doing away with the rear proportioning valve for their LS1 V-8 conversion, and replacing it with a T fitting. I know in stock configuration this could increase the likelihood of rear lockup. My car has the stock MC, stock 914-4 rear brakes and 911 "M" calipers & vented rotors up front. It'll also have a bit of tire stagger, 205s in front and 225s in rear. Will a T fitting be OK with this setup? Thanks!

Hey Mittlemotor,

I guess I'm the contrarian here, but please consider my argument:

-Braking comes down to some fairly simple physics: In braking, weight transfer forward. Because of this, street cars do 70% of the braking with the front brakes and race cars do 80% or more. The weight transfer plants the front end while making the rear of the car light and unstable. To counter the instability, Porsche installed the brake pressure proportioning valve that comes into play under hard braking.

-With the V8 conversion, you are not only adding more weight but a mass with a higher CG. Thus, to my mind,
making the rear of the car more unstable under braking. While you might get away with eliminating the proportioning valve for a long time, just one unusual emergency braking situation or slippery surface and your car will SNAP SPIN. I would not take that risk, especially on the street.

-My V8 car is a track car and I installed the Wilwood dual master cylinder with balance bar between them. (Summit Racing has great prices for the pedal & master assembly: Balance bar pedal assy = $113; each Mstr Cyl w/ remote reservoir = $67) This allows front/rear bias adjustment, is the BEST way to balance the brakes (other than ABS) and gives a rock hard brake pedal. It was not a hard job to do: bolt the assembly on a plate and weld or bolt it to the floor.

-As an example: Just a couple months ago, I ran my car at the high speed Willow springs track with the brake bias set for the tight Streets of Willow Springs track. On my first lap, I braked for T-3, the rears locked and I spun of the track like a top. After turning the bias adjustment knob, the proper rear adjustment was set and braking was great for the rest of the day.

-Lastly, I’ve learned that very little from Renegade can be trusted: They have no one with any engineering education, they make none of the parts they sell, their shop (as of a few years ago) had NO equipment other than hand tools. Their workmanship has been so bad that they were sued by a car dealing in Los Angeles some years ago. I met and know the owner, who was the one to inspire me to start my conversion. I did mine with none of their parts. Buyer beware.

-While my car is heavier with the iron block SBC + 70 lbs of rollcage, I’m attaching my chassis data sheet to show corner weights and front/rear weight distribution.

Offered only to help,
Terry