GT2 porsche beats cobra

[a427sc]

Hey Scott. Your really getting serious with that FIA. I had a similar knock back problem with my ERA with the outboard brakes. I went with 4 piston AP's in the rear, and would get a low pedal after a long corner or a series of switchbacks when I went back to the brakes. My problem was the Jag taper bearings ERA uses. Can't get them too tight or they seize, and that leaves room to wobble. Joe Rodimista's FIA has the same rear, but uses the Vette floating calipers ERA uses. No problem there. I called Essex Racing, the AP dealer, and spoke to their lead engineer about the problem. I wanted to try floating rotors. He said the pressure required to move the rotor on the pins was enough to also move the pads on the outboard side of the calipers when the bearings wobbled. Then the rotor would runout inconsistantly. The bearing runout was the problem and was not fixable, at least with what I could do. He suggested a 2psi residual valve in the line. This would seal the caliper, making the inner pads move in conjunction with the outers, maintaining their position to the rotor. Not the ideal, but inexpensive and easily doable. I never ran the car after that (sold it last November) so I'm not positive how well it works. Good luck

Don

[RACER X #99]

Good post Don,

As a track record holder at WGI in a Cobra, Don knows what he is talking about.

He has done more experimenting with chassis and brake setup on a Cobra than most anybody in the Northeast.
I am now FINALLY heeding his advise and in the process of setting up my own car similar to his former car.
Getting faster too.

Scott, give that residual valve a try, its a cheap experiment and it just might work.

RD

[sirelesar]

Don,
Just getting into tuning my car. I have a lot to learn, but am enjoying the ride. What master cylinder (s) would you recommend?
Darren

[coyled]

Don, thanks for the advise. Wilwood was not very helpful. Wilwood thinks that the g forces are causing the calipers to drain back to the master which is lower than the calipers. The reservoir is much higher on the firewall. The g force issue and the master location is why they think I need a residual pressure valve. Spidle flex because of small bearings was unheard of to wilwood. The csx spec racers have had the same issue with the exact same set up that I run. They have not seen a difference with the residual pressure valve. We did talk to AP racing and they think the knock back springs will solve the problem. I think I will try that first. Maybe I will try the pressure valve next. One thing I have learned is to do one thing at a time. That PBR single piston floating caliper I had in back does not look so bad now. Too bad is was about on fire at road america. Scott

[Big-Foot]

Thought you might be interested in a little video from my camera on the fastest road race track in the USA. BIR is a 3 mile track with the front straight being 4700' long. It is flat out through T1 and a slight lift in T2. You are in the throttle all the way for well over 1 mile. We enter the straight at roughly 80mph.
You will experience Terminal Velocity on this track.

http://joe.phatzo.com/BIR.wmv

This was the first of two races my Cobra teammate Ken Olson and I were in this last August at Brainerd International Raceway.

The first lap we enter Turn 1 at roughly 140mph. It was very windy and the tires were cold on the first lap. Turn 2 is about 10mph or so slower. Turn 3 is roughly 50 mph. I will admit that I was too busy to look at the speedo.

The second lap the tires are feeling much better and we enter T1 at 150mph and T2 at roughly 10mph slower. With the wind we had that day, 150 was about all the little 302 could pull. I have had it up to 155 but it was getting so light and twitchy at that speed, I had to let off to enter the first turn.

Having just had eye surgery for a detached retina, my eyes (both for some reason) are very sensitive to light and fumes. By the second lap my left eye was buring quite badly and the pain was distracting. The right eye was watering so bad I could barely see. Ken, who is still faster than I - but not for long - gets under me behind an E-Production Miata going into T3. I didn't figure out until a couple of laps later that if I opened my visor that I could actually start to see again. I was just about ready to pull off the track when I had made this discovery. I ended up finishing about 12 seconds behind Ken, but our fastest lap times were .2 seconds apart.

What this video shows is that Spec Racer Cobras (with stock 302) can go fast, but Turbo Porsches with much slicker aerodynamics and huge brakes can go even faster!

My car was a handful. I don't blame the 2 year old tires as Ken was experiencing the same "skating" that my car was when we were at speed.

Results - one of the two Porshes had dropped out with a flat tire, the other went on to take 1st place in SPO with Ken and I coming in 2nd and 3rd respectively.

My vision is now 20-15 with my new glasses so I was not a hazard on the track. I was, however, driving for almost a full lap (about lap 4) where I could not concentrate very well or see well enough to manage traffic so I pulled over with the visor open until my vision cleared.

[RACER X #99]

Randy,
Great video of a very fast track. Do you know the course record for Brainard? Watkins Glen 2.5 mile short course has alway been known as the fastest road course in the USA with an avg. 1 lap speed of 159MPH by a GTP car a few years ago. Perhaps that record has been broken.

RD

[coyled]

Randy, very cool video. I have been told that brainard is very fast. I am a little suprised that a stock 302 can push a cobra with bad aero and all, to 155 mph. I would think it would run into a wall of wind at a lower speed but maybe not. Great results. Scott

[ItBites]

My car has been 165 at Brainerd with my dad driving a few years back. The 427 BBC shifts at 7500 rpm and the rear gears are 3.08. It pulled to 7100 RPM on the straight.

At 165, the windshield began to buffet/shake very badly and dad prudently lifted. There is a good reason for those little racing deflectors. Also, the car is super-low and has a spoiler under the nose to keep air out from under the car.

Brainerd may not be the official fastest lap track (I don't know), but the straight is long enough and the entry speed is high enough that peak mph may be higher there than any other track. It is in my long-legged car.

[Anthony]

Scott, I'm no expert, but it does seem as if you are getting some flexion in the rotor, like you said during hard transition before braking, pushing the caliper pistons back into the caliper, leaving you with a low pedal due to increased clearence. Sounds like it would be either due to wheel bearing play or spindle deflection.

This is very simplistic, and I'm sure you do this, but you must set the wheel bearing preload without any brake pads installed. I was used to setting preload as I did on my other 60's cars with drum brakes, where I always set the preload with the wheel and brakes installed on the car. Last summer, while trying to align my cobra, I could never get consistant settings when I would recheck my toe/camber after setting them. I'd check the wheel stability and it always seemed as if the wheel bearings were a little loose, but when I'd spin the wheel and set the bearings, they seemed just right, not to over tighten them. After 2 or three times of this, I'd thought I'd take the pads out and check them. The wheel nut turned about an extra 1/2 turn, and this solved the problem. The brake pads, as installed, must have been applying some pressure to the rotor, giving me a false sense of proper wheel bearing clearence/preload.

Good luck.

[a427sc]

Scott Just because the reservoir is higher than the caliper doesn't mean the pads can't push the pistons back. The mass of the pad plus the mass of the two pistons under side g's is a lot more than gravitational pressure of the reservoir fluid (unless you have a 2 gallon container up there ) . I think the fixed caliper design in conjunction with the "wobble" from the hub flex/bearing play is the culprit, and any of the suggested fixes are bandaids. But then, bandaids often do work. And it's all about having a consistant pedal at 150+ at the #2 marker, isn't it.

Don

Thanks for the extra hat size Cranky!

[Big-Foot]

Racer-X; Brainerd's track record - Good question. Records are typically kept not by the track but by the sanctioning bodies that race there.
Since Brainerd has lost their SCCA certification due to safety concerns, the information is no longer available (that I can find). I do recall that Jerry Hansen ran roughly a 1.12 lap there with his 5 liter ASR car back in the late 70's. That is roughly 150mph average. When I call it the "fastest" track, I meant to say that the track has the longest straight-away with the fastest final and first turns leading up to it. Competitive Trans-Am (GT1) cars will hit 200mph on the straight. I am sure that if CART ever ran a race there that they would top that by 20mph easily.
While BIR is my home race track, my all time favorite is Road America.

Scott - The 302's we run are essentially full stock 5.0 long blocks but instead of EFI we are running 600 Holley double-pumpers (4776) on an Edelbrock Performer RPM intake. We also run MSD ignition systems and Factory Five's headers. With the wind conditions we had on the day of that race, we indeed did run into the wall of wind at 150. While there was still room-to-rev, the engines were just out of power and pulling as hard as they could. Another thing to remember is that these cars accelerate hard to 110-120, they take a long while to get to their absolute peak velocity with these little engines.

ItBites - The Windshield (full) on your Cobra was one of the things that was holding it down on the track. We run the low-profile single spec racer lexan windshield that is maybe 8" tall at the tallest point.

Brake pad knock-back: One of the ways we have been successful at combating this and a number of other little niggling problems is by incorporating a 2# residual valve in both the front and rear brake lines. This also helps maintain a taller pedal under all conditions. Given that most Cobra replicas are manual brakes, we have a tendancy to size the master cylinder smaller to increase the leverage of the pedal. When we do this, we increase the required stroke to fully engage the brakes. The 2# residual valve helps this by keeping the pad continuously engaged with the rotor, thereby lessening the amount of fluid movement required to brake the car.

[coyled]

I did recheck the bearing clearance front and rear and they are fine. I am running a 3/4 front master and a 13/16 rear. Bigger would help but would require a stronger leg. Scott

[a427sc]

Scott, run 7/8 and 1" masters, add 4# of lead to your right shoe at least two weeks before any event, and extend the brake pedal 1-1.5". Or pick any 2 of the above.

D

[coyled]

Gordon, who ran in the enduro in the cobra and who was driving the spec racers? Just curious? Thanks, Scott

[Gordon Levy]

Scott, The car that ran the enduro was brought out to prepare drivers for the 25hr at Thunder Hill. The drivers were, James Bondurant, Rob Drew, and Jeff Ceck.
The spec racers that ran the sprint race was Bob Woods. I was going to run Tim Sharps spec racer in the sprint race but decided against it. I found that the nerve damage in my left arms hasn't healed enough for me to feel confortable running the race.

[coyled]

Gordon, I checked the times at mylaps.com. James Bonderant is listed with a best time at 1:10 and change. Bob Woods is listed at 1:14.50. I am assuming these guys are competent drivers being in a race with a cobra and one of the last names in particular. No 1:06's as for lap times. Gordon, if you set these cars up, I know they are well set up. I only ran 2 sessions with my new set up so the cobra is not dialed in yet. A sinking brake pedal and then an oil leak ended my day. But, my time of 1:10 is looking pretty good. Scott

[Gordon Levy]

Scott, Bob is still getting used to the car. I think he will be in the 11"s or 12"s before to long. James is a very quick driver and this was his first time in the FFR spec racer. 1:10's are a very good time for a 230hp spec racer, no matter who is driving.
You should feel good about your 1:10's. I know you will get quicker and I know your car is very capable. The object is to have fun and keep it off the wall.

[coyled]

Gordon, power is not a big advantage at PIR. I agree that 1:10's are quick in any cobra, regardless of power or driver. My point was, the 1:06's are a long way away for a cobra regardless of power or driver. And those walls tend to get closer the faster you go. Scott

[Gordon Levy]

Actually power is a great advantage if you are willing to drive it through the oval. That #11 car that I took to RA that year with you and mike turned consistant 1:08's at PIR on a transponder. 1:06's or better are very possible if the driver has a well set up car and is willing to drive it through the oval.
The proper set up for PIR it to make a car that turns left. There are only 2 right hand turns and they are both slow. If you set the car up for the oval you will turn some excellent times.
I have seen a T/A car turn 58's set up like this.

[coyled]

If power matters, I must be really slow at PIR. The #11 cobra ran a 2:48 with you driving at Road america while I ran a 2:30 last year. Plenty of walls at both places but Phoenix is a much more technical track. My bigger point is that I always read about how fast somebody is or there car is at a track but yet when I see the lap times via a transponder, the times are not quite as fast as they claim. This is not directed at you Gordon, just in general. Scott