GT2 porsche beats cobra

[coyled]

I ran at PIR in Phoenix on Friday with NASA in group 4. I ran 2 sessions and then lost an oil line and was done for the day. In both sesions, I passed the zo6's, 911's and bmw's. In the second session, a gt2 porsche passed me. I stayed with him for most of the infield but he ran and hid from me in nascar turn 3 and 4. He had more balls or more aero, or both. Anyway, I ran a 1:10 and the porsche was at 1:07, both of us had transponders. I am still sorting out the adjustable shocks, suspension set up and a brake issue. I think I will be a little faster next time out after a few adjustments. There are lots of walls at PIR, but it sure was fun. No cobra's on the track other than mine. Scott

[newBDR]

I'd say more balls to put a $180k car on a racetrack.

[marcocsx3121]

Porsche GT3s (more civilized versions of the GT2) driven by experienced Porsche-pushers can run low 1:40s at Road Atlanta, as can well set up Z06s. I've never seen a Cobra break 1:50 here, but a big piece of the difference may be tire tech.

[SCOBRAC]

Hmmm... More aero at Phoenix? You've got a 700 pound advantage over the GT2 which weighs 3150. The GT2 goes almost 7 lbs per hp.

Even if you are "only" making 400 hp you should be close to 6 lbs per hp. The Porsche runs 12 and change in the 1/4.

Certainly the GT2 has more in the brakes but with a 700 lb disadvantage it needs it.

Better luck next time.

[SCOBRAC]

http://www.bondurant.com/courses/courses.html

[Gordon Levy]

Scott, It sounds like you had fun. We were out on Sat with 4 Cobra's. 1 was run in the 2 hr enduro, Phil's 427 SO ran HPDE4, and 2 spec racers.
I have seen the Cobra's run as quick as a 1:04 but with the new walls on the infield and the big wall in NASCAR 3-4, being conservitive is not a bad thing.

[Morris]

Scott

That's the part of Racing we all love.....chasing the clock..... and it sounds like you were doing a great job..... considering the technology....

What kind of shocks did you finally put on...??

Morris

[moneymanager]

HI gang, it's "Doc" in Mesa. I had paid to be at PIR on Sunday but wasn't able to make it due to breaking my Cobra on the Friday races at Firebird. Sorry I had to iss the fun. Maybe next time.

My car ran well at Firebird but midway into the third run it felt like I broke something and I had to pull in the pits. We couldn't figure out what it was at the time so we ended up on the trailer and headed home early.

Today I discovered the problem. My power brake booster was leaking bigtime and was causing my brakes to activate on their onw every time the engine decelerated. Kinda like a poor man's anti lock brakes. Ha Oh well, at least it's an inexpensive fix as compared to some things it could have been.

See ya next time.

Doc

[coyled]

Michael, you obviously have not spent much time on a road course or ever driven PIR. Thanks for the Bonderant idea. Maybe the instructor driving his zo6 that I walked away from can be my instructor? Gordon, who runs 1:04's in a cobra at PIR? Other than Bob Bacon's can am cobra? Boris qualify's at 1:04 and is running 1:05 to 1:06 race times in a full tilt M3. The ASC stock car guys qualify at 1:06. Next time your at PIR with a cobra, lets all have transponders and see what the real times turn out to be. A 1:04 seems pretty optimistic to me, at least in a cobra. Scott

[coyled]

Morris, I went with the ohlin's. On full throttle corner entry it was pushing. On corner exit, a slight push. I was going to go down in bump in front and up in bump in back, but the oil leak ended my day. The cobra is much stiffer in wheel rate now so I am relearning how to drive it. Turn in is much better. I also had a low brake pedal after back to back corners. I am thinking of using a residual pressure valve to reduce piston knock back? Ever used them? Scott

[Gordon Levy]

Scott, Other than Bob. Jim Click has turned 1:04's in his FIA car. I have turned 1:06's in a car familiar to you a few years ago.
Have you tried Castrol GT racing brake fluid in your car? It might help the pedal.

[coyled]

Gordon, Don Roberts has raced Jim Clicks cobra for years and has run 1:06's to 1:08's consistently. Maybe he pulled off a 1:04 somewhere. Don is in my opinion, the best cobra driver at PIR out there. He has been racing cobra's for 30 years and Click's well sorted cobra for many years. I have the video of you driving my cobra a few years ago and the time is a 1:13 if thats what you are refering to. I am running the castol. After a few corners the pedal is lower. After only one corner, the pedal is fine. I think its piston knock back caused by spindle flex in back with the 4 piston wilwoods. The old pbrs calipers floated, the willwoods don't float. We will see. Scott

[Gordon Levy]

Scott, I think is was a different time. Don Roberts came up to me afterwards and said he had me at a 1:06. It is possible that you de have some knock back. I would be a little surprised for the spindles to flex if they are the ones I think they are. Another possibility would be rotor warp. Running the tires you do, they can mask some warpage in the rotors. Just a thought.
As for the 1:04 in Clicks car. I had him at that time pretty consistant as a VARA event several years ago.

[Mike Simard]

Scott, sounds like you did very well indeed with the aero of a Cobra. I would love to hear about your car and it's supension setup, stuff like swaybars, suspension mounts and springs. I've been tuning my own car and doing stuff like putting spherical bearings in all suspension points and making different size swaybars. So what do you drive?

[coyled]

Mike, the front sway bar is a 1 1/4 speedway bar, no rear bar. The cobra has coleman stock car spindles. 600 pound front springs and 800 pound rear springs, no rear bar. Wheel rate in bump is 385 in front and 335 in the rear. It is pretty stiff. The nut behind the wheel needs the most work as usual. Scott

[Morris]

Scott

Put some Temp paint on the rotor's....start at 900*degrees and do 1000*, 1100*, 1200*degrees.....(paint a H on the vent exit holes of the rotor) that will tell you if it is a fluid issue or some sort of piston movement .... I've never used a residual valve.... and you shouldn't have to.....

If the pedal went down.... there's only 2 reasons ....Temp of fluid....or air in lines.... other than piston movement from a rotor or caliper movement..... many times the Heat will cause them to go down but stay hard as a rock.... is so it may be M/C size....It takes heat to make the brakes work like they should.

I wouldn't think that you are using the rear brakes that much.... when we balanced the brakes we would shoot for 1100*-1000* in the front and about 900*degrees in the rear....

Also bring your rear rebound up a couple of more notches.... this will help rotate the car on entry and maintain it in the middle and exit of the corner....... maybe soften bump on front one notch to get it to stick just a bit better...

Hope some of this makes sense and helps

Morris

[ItBites]

Scott,
Having run PIR with ASRA not too long ago in the drivers-ed group, I understand your comment that the GT2 guy may have had more balls (or less brains) in going around NASCAR 3/4. That wall is pretty ominous.

My instructor (Bill) kept telling me I could go 110 around there... I told him "not with me in the car". He said not to worry, that his seat was going 10 mph faster than mine and he wasn't worried. - I finally managed a little over 85 in NASCAR 3/4

It was my first time driving in about 9 years and I putted around at 1:21. Man, I don't know where I'd get 11 or more seconds? 1:10? - Wow - nice times Scott!!!

[coyled]

Morris, your comments make sense, thanks. The lower pedal only occurs through a right left transition with no braking, then the next corner, lower pedal. Around one corner and the pedal is pretty good. I am pretty sure it is spindle flex. I have spoken to some of the shelby spec racer guys which have similar setup's and they have had the same issue. The solution is bigger bearings which is tough to do with pin drives and or float the rotors. I don't know that the residual pressure valve will fix a mechanical problem. The fix is either left foot brake and pump them once. Or, AP racing has some knock back springs that go behind the pistons in the calipers. Any experience with knock back springs? I might go up in rear rebound but I do not want to potentialy keep the inside rear lifted at mid corner and exit. Thanks again, Scott.

[Morris]

Scott

float the rotors..... easy to do...and not that expensive.....

One of the things I like about the Kirkhams cars is they use the Porsche 935 rear bearings on all 4 corners with the Pin drive hubs.... should stop the flexing....

No we haven't use any Knock back springs....don't like the idea....seems like a band aid for another real issue...

Do you know what temp your brakes are running....??

Morris

[coyled]

I don't know the brake temps. I was busy driving and trying to figure out what shock adjustments to make. I run the same hub as the Kirkhams. Its a band aid but hey, the whole cobra is really a band aid on the track. What I really need is the stock car hubs with the big bearings and floated rotors. I will check brake temps next time out. I went to the performance friction 01 pad in front. They actually worked really well in a hard brake zone of which there is only one at PIR. I am still running the R4's in the rear. Scott