Defeated at GoodGuys
 

Short version: We got our a$$ kicked by 4 corvettes and a Camaro

Long version complete with excuses:
We took 3170 to Goodguys SouthWest Nationals last weekend with high hopes for winning. We arrived on Thursday morning about 6:00 am after driving all night and found that the course had some extremely slow, and tight areas compared to last year which are not good for our set up.
We have been developing the car all year on 315x18 Falkens as many of you know from following my ramblings. Some very talented and winning autox drivers convinced us that Falkens were not the way to go and that we should retry Rivals and the new RS3 Hankooks which are killer on newer Corvettes.
All these tires are 200 TW and are legal for use at GoodGuys.
We have been testing all three tires both together and/or in combination for the last 4 weeks. What we found was the Rival 335x18 rears had so much rear traction that the car pushed like a dump truck with all other front tires including Rivals. This despite a spring change front and rear and a huge rake angle change. We have pictures of the car exiting a corner with both front wheels almost off the ground at 40 mph! Now a smart person would probably go back and just run a known set up with new Falkens but as you have probably guessed I am not the sharpest knife in the drawer so we arrived with Rivals on all around.
Friday Testing: We were 2.3 seconds slower than the fast people all morning.
The tight area I spoke of earlier had the engine in the 1900 -2000 rpm area
which isn't very good with a 297 degree duration cam @ .050. We had a really bad stumble there because of no port velocity and the car was pushing like a dump truck (what a surprise). We cranked up the rake even more in the pits and picked up about .3 seconds. A great guy who is with JRI shocks
suggested we needed to throw some rear spring at it. We drove it back to our trailer at noon and put 800 lb/" rears in and came back to find we missed two practice runs and that we were only going to get one more run before they shut down for the day. This time the car was marginally better but not what we were looking for. We picked up another .3 or so and were roughly
1.7 seconds slow. We decided at that point to really get after the pig and change some stuff. The only smart move I made prior to coming was to buy another set of Jongbloed wheels and mount last summers well used Falkens to bring as a back up. When we got back to the trailer I spent about 30 minutes with the computer tuning on the EFI to try and make it respond at idle rpm (it actually got better in that tight area). Scott Fraser my excellent driver and friend and I then changed every shock setting, all four springs, ride heights and all for wheels and tires. We had to do a lot of the work in the parking lot in the headlights of my truck but we got it done.
Saturday was limited practice , then qualifying for a spot on the ladder and then the big shootout. We took the car up Saturday morning and it was much better out of the box, after adjusting brake bias we got it to within
.6 of the fast people on a 70 second course still not great but better.
We ended up qualifying 5th out of 32 cars to start the ladder. At noon they started the shoot out and Scott won round one with ease and also won round two with not much effort still being careful because if you hit a pylon
you would be out unless you were over a second faster. Now although the crowd loved our engine sounds and acceleration they really don't know how little throttle is being used. Both Scott and I like to brag about that so at the finish he gave it about 3/4 throttle to show them how much was really there and promptly sheared off a half shaft yoke. Lots of people including the winning driver pushed the car back into the pits and then helped work on the car. We have a picture of Robby Unser under the car helping us change to a
spare half shaft that I carry. There were four guys under the car at one time. They got the car done but missed the call to grid by two minutes so they would not let us make the next round of eliminations. I don't know if we could have won but Scott is best when there is pressure and it would not have surprised me to see him pull it off. The man who won overall Brian Hobaugh is a good friend and we have run with him all year in California.
The Cobra was significantly faster (1-2 seconds) on those meetings but not at GoodGuys . What I have learned: don't change from a well developed proven set up at the last minute! Plans for next year: make the car more drivable in super slow conditions and change our spring, shock and differential package to eliminate low speed push on super tight and slow courses.

Bringing a shotgun to a knife fight sounds like a good idea, until you learn the fight is inside a phone booth.

Knife fight
 

Well said, just about what happened. Pretty funny too!

I watched one of your autox videos and afterward considered that driving your incredible car on a course like that must be like riding the race horse Secretariat and holding back on the reins the entire race. :eek:

I bet you'll go to the next event ready to hunt bear!

David

Bear Hunting
 

Thanks David,

I am working on some ideas now to help with low speed handling, I'll share here and let everybody know what worked and what didn't. Looking at everything from front geometry to more tunable shocks to changing clutch pack pre-load in the diff. Scott has some in car video's that I'll post a link to when he gets them up. One thing that really helped was having cockpit adjustable brake bias. The Rivals took three complete turns more to the rear than Falkens, normally a 1/4 turn is all that we move bias. Falkens also need a lot more negative camber to work properly.

Is bringing a different diff with a deeper gear ratio an option so you could swap it out on a really tight course so you can keep the RPM's up higher at lower speed? Or would you end up spinning the tires more and breaking more stuff?

Diff
 

Yes, the reason I went with the 3.31 was to control wheels spin but I think you are on to something when the course is so tight that we are running at or below idle speed a 3.70 would really help. Just need the discipline on the throttle to keep from lighting the tires at higher speeds. These cars are so light and the tires do not grip like drag radials so breakage is not usually a problem. I need to find some forged yokes and sliders that are like the original Hardy Spicer parts
but made of better material (modern). I use drag race zerkless U-joints,they have been very good although hard to load during assembly because of the thickness. Driving technique is kind of like a sprint car floor it with little or low velocity in the manifold and start getting out of it before it comes to life.
When the rpm is too low it stumbles a couple of times then explodes and blows the tires off so a 3.70 would give us more control.

I always enjoyed the chase, the hunt for the right combo is never ending. We no longer compete but reading this thread sure lights the fire.

Thanks for taking the time to regale us with the auto-crossing saga. I really enjoy hearing how you're going.

Good luck for future rounds

guess this is the site (?) https://www.good-guys.com/events/goodguys-autocross

LoBelly

Video of breakage
 

Thanks LoBelly,
Here is an in car Video that shows how far off the Cam the car was and what happens when you give too much throttle to an overstressed part

[ame]https://www.youtube.com/watch?v=UgqcHLt81jo[/ame]

Great story!! Good luck sorting out your suspension options (and getting some bullet proof parts for behind that crazy motor!). Higher rear end gear sounds like a great option as well.

What are you running for anti-roll bars, are they tuneable?

Do you have the ability to change rear toe-in or out settings?

Keep us posted on your progress, always highly interesting and entertaining.

Tuning
 

Yes, everything is adjustable including front and rear anti roll bars. We were running only .070 rear toe and although we thought about going to 0 or toe out the car was already not very stable on the fast turn so we just went after rear spring rate. The gear and new tires would have put us in a good position to win but I wasn't smart enough to do that.

Have you looked at the custom half shafts that the later Kirkham cars have? I remember reading about them during the Billlet car build and they were custom made out of titanium and looked pretty impressive.

Half Shafts
 

Do you mean the ones running Porsche CV joints or something else?
I have heard that U joints are actually able to take more punishment than CV
but don't have any knowledge in that area. The joint failed in the yoke area and looked like it had been cracked for some time. I was thinking that getting new parts and deburring them along with a cryogenic treatment might be enough since I haven't broken one in years. Titanium would be nice for rotating inertia but might have some durability issues with welding or heat treatment.

The Half Shafts Chapter from the Kirkham Billet Car Design Book: http://www.kirkhammotorsports.com/book_aoe/aoe_11.pdf

It does not say that the half shafts are made out of titanium though. There is a comparison of the Kirkhams use of 17-4 PH steel heat treated to H900 to the titanium alloy used in F-22s on page 110 though.

Aw hell Bruce...what fun would it be if you won every time?

Changing rears to 3.7 may not be enough. Maybe 4.11's-4.30's to get the rpm's up 25%. Also, smaller diameter tire?

what about a truck 2 speed rear? :JEKYLHYDE

Maybe sprint car style quick change? :D

Somebody was making a ford 9" center section interchangeable with the dana. I think he had a machine shop in CA, made remote oil filter brackets for cobra's, and owned csx3020 at one time. If you switch to a 9", swapping out the rear gears I think would be a lot easier.

Fun
 

You are right Jamo, it gives me a reason to keep going. Working on new front geometry, different locker, new rear ratio and new shocks with more droop travel
already. Car should have all the improvements installed by March. If we had won I would not have anything to do.

Rear ratio
 

Thanks for the comments Anthony but putting a higher numerical ratio like a 4.11 is like poking a hornets nest with a stick. That car will bow the tires off
if you give it any kind of advantage. I run a 3.31 to try and control the high wheel torque. I am thinking a 3.54 might be just enough. The package of the rear end is so tight I don't think you could change gears let alone package a quick change without surgery which is a no no on this car.

This is Scotts first run where he used a little too much throttle on the straits and you can hear it getting really loose. The car would be much faster with a 300 HP small block but what fun is that?

[ame]https://www.youtube.com/watch?v=QdAzFgheJBw&index=3&list=UU0CJQuj-tI4J89NccUhpJ1Q[/ame]

The car would be much faster with a 300 HP small block but what fun is that?

Yep! :D Nasty is better. :3DSMILE:

David