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!

[ChrisFoley]

Will a T fitting be OK with this setup? Thanks!

It might work, since you will have lots of weight over the rear wheels, larger front brakes, and larger rear tires.
I'd want to try some threshhold braking tests in a safe place before assuming its ok though.

[pcar916]

What are these v8 conversion weights and front-to-rear ratios?

I suppose it would be too much to ask about roll centers but if anyone has calculated it/them on their 914's it would be interesting to see.

[mittelmotor]

I'm thinking the finished car will weigh about 2300 lb., and the weight distribution shouldn't change all that dramatically, as there's 50-60 lb. of radiator and shrouding up front. Certainly, the V-8's weight is carried somewhat higher in the car, so I'll be curious to see how that affects handling. Going with Koni adjustables, 21-mm torsion bars, stock front anti-roll bar, and 200-lb. rear springs with adjustable perches (for starters!).

[yeahmag]

Depending on your driving style the 21mm front torsions may dictate a heavier rear spring. With 21mm torsions and Koni Yellow's all around I moved from 180 -> 225 -> and now will be trying 300's in the rear.

[Andyrew]

M calipers up front and stock rears with vented rotors on my car, braking is very neutral.

21mm tbars with 250lb springs rear, no sway bar up front. Handles very good with a lift throttle over steer and full throttle oversteer. I really like it.

[mittelmotor]

Thanks for the input, guys. I think softer rear springs to start will work well...it's nice that the rear springs are so easy to change. If it bottoms too easily, or pushes too much I'll definitely bump the rates.

Finally got a front corner back on the car, and mounted a wheel for the first time...15x7 ATS. I think this is a good ride height.

[stewteral]

 914_Project__Chassis_setting_worksheet.xls ( 22.5k ) Number of downloads: 284

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

[mittelmotor]

Thanks for your input, Terry, but I have to disagree with your assessment of Renegade. Steve and Scott have been extremely helpful, returning phone calls and emails quickly, and providing additional photos when asked.

The quality of the parts I've received is absolutely top-notch...flawless welds on the radiator, a wonderful billet-machined bracket for the alternator, etc., etc. They may not make their stuff in-house, but they apparently pick excellent suppliers. Their cooling system comes highly recommended by many, and seems to be well thought out.

I think with my brake/tire setup, I'll be fine without the valve. That said, I'm not throwing it away either. I plan on doing some heavy straight-line and trail-brake tests to see how the car behaves in a lock-up or near lock-up situation.

--Doug

[stewteral]

Thanks for your input, Terry, but I have to disagree with your assessment of Renegade. Steve and Scott have been extremely helpful, returning phone calls and emails quickly, and providing additional photos when asked.

The quality of the parts I've received is absolutely top-notch...flawless welds on the radiator, a wonderful billet-machined bracket for the alternator, etc., etc. They may not make their stuff in-house, but they apparently pick excellent suppliers. Their cooling system comes highly recommended by many, and seems to be well thought out.

I think with my brake/tire setup, I'll be fine without the valve. That said, I'm not throwing it away either. I plan on doing some heavy straight-line and trail-brake tests to see how the car behaves in a lock-up or near lock-up situation.

--Doug

OK Doug,

I can only try to share my experience with Renegade. I hope your engine mount crossbar doesn't still bow in the middle from being under-designed as they did in the past.

Renegade aside, my info on braking was real. So I invite you to try some SERIOUS late braking and trail-braking into a 2nd or 3rd gear corner on a REAL race track (where you are pushing to front-wheel lock-up) and see what happens. Of course, wimp-braking will get you by, but you will also be passed by a number of real drivers.

It's all you choice.

Best of luck,
Terry