First track day w/ 3.6 conversion!!
 

Today I took my '76 S with 993 '97 Vario Euro engine to the track for the first time.

Overall I am extremelly happy. I do have some issues to solve...but that's what all of this is about, isn't it?

I had two main issues:

1) Extremelly spongy brake pedal..once hot

I put new Motul racing brake fluid and power bleed the system, before going to the track, and I also had almost new Brake Pads.
What can be the problem? My only guess would be that my rubber brake lines are too old. Any other suggestions??

2) Too much understeering.

I have stock suspension, except for 21mm torsion bars front and rear. I have 245/35 18 in the front and 295/30 18 on the rear.

What should I do to generate more oversteering?

Some pics of today

For some reason pics didn't upload the first time. Let's try again

http://forums.pelicanparts.com/uploa...1148416933.jpg

http://forums.pelicanparts.com/uploa...1148416961.jpg

Wow, your '76 doesn't look anything like mine. It seems you have done a few modifications.
Did you upgrade your brakes to handle the extra power?

As far as the suspension is concerned, I think you need to go heavier on the torsion bars in the rear. You might try 30's or even 31's.

Or with that 3.6 you could try some more right foot to cure that oversteer.

Rich

Are you running the stock 76 brakes? If so, you might want to consider at leas upgrading to a Carrera setup, if you're tracking the car.

Understeer could be caused by a long list of things. I assume by 21mm bars front and rear, you mean antisway bars. Are they adjustible? If they're not, things like alignment settings and even tire pressures can be adjusted to tune the car's handling. Is it low speed understeer, high-speed understeer, understeer on entry to corners, or on exit, or in mid-corner?

21mm torsion bars or sway bars??

Your pedal goes soft when the brakes are hot because they are too hot! The fluid in the caliper is boiling and introducing air into the system, making the pedal spongy feeling. Investigate some brake cooling ideas as seen on this forum.

Cheers

To echo what the others have said, the reason your brakes are setting fire is because your current brakes are designed to reign in 150 or so horses, and you now have around twice that. Look into some cooling, maybe coupled with slightly larger brakes like the aforementioned Carrera set up.

Thanks for all your comments.

Yeah, I meant 21mm antisway bars...sorry

Regarding the boiling of the brake fluid. I assumed that the fact of having small brakes would imply less stopping power but not necessary a spongy pedal. Am I wrong?

Yes - you are boiling the fluid. Small brake calipers (and more importantly, rotors) will just transfer the heat more quickly. Having a bigger tire patch will quicken the process.

I'm suprised you even had brakes after 10 minutes into a session.

Easiest way to introduce more oversteer is with tire pressures. Go down on the front and up on the rear.

So.... Where are you getting the Understeer???

It's just the opposite. Any Porsche brake will give you all the stopping power you need. Stock brakes will allow you to lock up the wheels just as well as any upgrade. But the chief virtue of larger components is that they dissipate heat better.

Thanks again for all your help.

With the brakes it seems clear..go bigger!!

Regarding the understerring. this is what I am experiencing: When I go into the turn, the car seem to respond well. i assume the weight transfer to the front helps to reduce the understeering and the car enters the turn nicely. Now, when I start giving some gas, I experience a strong understeering. Again, i assume this is caused by the weight now being shifted to the back.

Doing some research on the forum I found the following chart:
http://forums.pelicanparts.com/uploa...1148484893.jpg

Jeremy, according to this chart in order to increase oversteering I should increase tire pressure on the front and reduce on the rear, which is opposite to what you suggested. Which one is correct?

Any other advice would be greatly appreciated.

Thanks again

Mario

Question: Will a strut bar increase, reduce or do nothing to understeering?

Thanks

A strut bar will have no effect on understeer.

What are your suspension settings currently? Camber and toe settings are probably the most effective way to dial out your corner-exit push.

Hello there,
Having a 1975 911S that has a 3.6 varioram in it I understand your debacle. The beauty of Porsches is the unique balance of power, braking and handling-as a package. Though I tried to tell myself that the engine conversion did not really upset this blalnce, after trying different tricks like cooling ducts for brakes, wider rubber, corner balancing tweaks, I realized the power overwhelmed/stressed the other elements. (A photo of the car at speed on the track really woke me up). Suspension was first, and I was fortunate to have the help and expertise of someone who has done these conversions and built many a fine 911 race cars. He explained to me the way suspensions work as an integral unit, torsional rigidity, compression and rebound of dampers, and tying the corners together through anti-sway bars. (Read Fred Puhne's book "How to Make A Car Handle") I did it once the right way and hit bullseye. Later, came the realization of a brake upgrade-I went with Brembo rotors and 930 calipers specially machined for this car's application. If you are not saavy in engineering your car, it is well worth the time and $$$ to talk to someone who is-in my case Steve Weiner at Rennsport Systems. He designed and spec'd the car from a long way away, and I put it together. It's stunning and visceral.
Good luck, you've opened Pandora's Box!

Nick

Also: does the car have a limited slip differential?

Jack, no, i have not LSD.

My alignment parameters are as follow:

Front:
Camber = L: -0.18 deg; R: -0.51 deg
Caster = L: 5.32 deg; R: 5.72 deg
Toe = L: 0.09 in; R: 0.10 in

Cross Camber: 0.33 deg
Cross Caster: 0.40 deg

Rear
Camber = L: -0.94 deg; R: -1.11 deg
Toe = L: .19 in; R: .33 in

Are this acceptable? If not, what should i aim for.

Thanks again

I am pretty sure it is reversed.

Oversteer in Porsche 911 is more pressure in front, less in rear.

This makes the rear break free sooner.

Ditto re the last comments on brakes. Your brakes were NOT "designed to stop 150 HP"; they were designed to stop a 2900 lb car. It does not matter how much HP the car has now; it is still 2900 lb. They are getting hot because you are using them harder (on the track, for one, and at slightly higher speeds for another). Vent them and they will work fine.

You might do a search on this forum. Bill Verburg has forgotten more than most of us will ever know about brakes and he is the resident expert.

He has a SC with a 3.6. Will send him a note and get him in on the thread.

JoeA

Thanks Joeaksa. I have already done a lot of research on brakes and started a separate post in which Bill already contributed with his great expertise.

Thanks again.

Mario,

Stick with what Bill says and you will do fine.

What part of Guatamala are you in? I lived in Guatamala City for a while way back in the '80's. Enjoyed the area and people. Was not able to explore as much as I wanted to as it was a bit "rough" at that time in the areas but would love to return someday.

If you are tracking a 3.6 Varioram car with stock 1976 brakes and are running at any sort of pace above beginner......you are quite frankly insane. ;)

I mean this constructively - get better brakes. I'd recommend a C2 setup; Bill Verburg is a brake pad customer of mine and knows exactly how this is done.

Thanks Craig. I am beginner, but not insane. Got to the track ones with these brakes but not twice. I am already looking for alternatives to upgrade.

I will probably go with 964/944t brake for now. I am trying to find a set of 993 calipers, but they are TOO expensive. Still not sure!!

Joeaksa, I live in Guatemala City also. I arrived only 4 months ago and I am really enjoying it.

Thanks

C2 is too vague a referrence, 964 C2 will be marginal.

993C2 will be fine, as will 930, better is often bigger here.

1990-1994 C2 brakes - this range is commonly called "C2". Takes a 930 sized pad. Pretty decent. Readily available.

993 is......993. Takes quite a bit bigger pad and is much hard to find these calipers used.

At any rate, what you have is flat out dangerous as-is.

Bill, here is where I get confused. Fromyou site, I understood that 964 can used the same pads and rotors as the 930. Then why is that you are suggesting that 930 brakes would be fine, but 964s only marginal improvement?

Thanks for the clarification.

Yes, but the pad is NOT the problem, the rotors are.


The 993 calipers do not require the major machine operations that the 964 do.

The issue w/ your car is the rotors and their ability to process heat.


Stock 283x20 & 290x20 are way too small for the weight and performanvce potential of your car

as are 298x28 & 290x24 964 rotors

930 are 304x32 & 309x28 and are going to be the minimum to reliable work on track

better would be 322x32 & 322x28 993RS rotors

PS the 993 calipers would go on 930 rotors

Would $800 be a decent price for a set (frt & rear) of 993 calipers??

I am assuming another $600 for the rotors, is that ok?

Thanks again

That's what I am asking for my powder coated and rebuilt set.

here's 1 front and 1 rear
http://forums.pelicanparts.com/uploa...1148675768.jpg

the rear rotors are Pelican part # 911-352-041-08-M259 @ $90.50 ea.

the best front rotors are Pelican part #930-351-048-00-M136 for a right front @ $399.75 and $407.75 for a left front.

You would also need rotor hats and caliper adaptors in the front

Steve W/ @ Rennsport can supply somewhat cheaper(I think) rotors and the other parts as well,