CSX3170 2019 updates

[Cobra #3170]

We will be racing CSX3170 for the first time this Saturday at the Pleasanton Goodguys event. The car has a major upgrade to the front suspension.engineered and manufactured by David Kirkham and his Son.
They produced all new front uprights and lower arms along with stainless hubs that duplicated my fabricated steel parts and geometry. The new system uses cartridge bearings to eliminate caliper knock back and suspension flex. The new design allows the use of less camber and therefore will improve braking with a larger tire patch. I already have David's rear differential, drive flanges and stub shafts in the rear and now the front suspension is just as well done. These pieces are as nice as anything you would see on any race car in the world. The drive pins are machined from a solid billet of stainless that makes up the entire hub instead of being bolted in like originals. We ran a quick test and Scott says the suspension resulted in a sharpness in response that he has never seen before. I also upgraded the data acquisition system to include throttle, steering angle, brake pressure and yaw angle to reduce our set up time. We are going to start looking at total steering degrees used per lap in an effort to reduce that through set up which should improve lap times. Scott has never had full confidence in the brakes because my old design used a stock original spindle that flexed enough to cause caliper knock back. The new Kirkham design is rock solid with perfect pedal on all stops no matter what the steering input is. I also reduced the rev limiter to 9100 rpm because I found two valve springs with broken tips during winter maintenance. I installed all new valve springs this winter with the engine in the car, not a fun task but I have it down pretty well now. I had to modify a tool that works with T&D rockers but did not work with Blue Thunder high rise heads. Hopefully all the new stuff is ready and works well.
Scott has not driven it in competition since November of 2018. I really think that the front suspension was the last weak link in this car, we will know soon
I tried to inbed pictures not sure if I did it correctly though

[https://photos.app.goo.gl/dwiQHrrxtWNF7oYH6

https://photos.app.goo.gl/wZViKNH1mg1dwcPv7

https://photos.app.goo.gl/JHdBmdRpghYiNG5v9

[1795]

Pretty impressive looking. Looking forward cohering about the results.

[twobjshelbys]

Wow, is there anything left of the original?

Good luck this season!

[Morris]

Bruce

Have you considered adding 1” length to both UCA & LCA & increase the back spacing on the wheels.....

Also when you say stand up the tire .....do you mean reduce the castor.....on my Nat Champ Corvette we ran 0 castor with the motor as a integral part of the chassis.....but we still used a lot of camber.....

Just some thoughts....

[Cobra #3170]

Originally Posted by Morris

Bruce

Have you considered adding 1” length to both UCA & LCA & increase the back spacing on the wheels.....

Also when you say stand up the tire .....do you mean reduce the castor.....on my Nat Champ Corvette we ran 0 castor with the motor as a integral part of the chassis.....but we still used a lot of camber.....

Just some thoughts....

Morris,
I extended lower arm length about 4" 18 years ago when I first did this design. I also shortened the upper arm to get proper camber gain and re-positioned it to reduce anti dive, and get the front roll center where I wanted it. My outer rim is 1.5 " with a 9" inner so big back space to achieve a zero scrub radius. I run 5 D. of caster and camber is 2.8 negative instead of 3.2. This geometry has worked well for me since 2001 but it did not exhibit the stiffness that the new Kirkham parts do. I have run as low as 3 degrees of caster but found the car was happiest at 4.5 to 5.5. Camber is tire construction dependent, we have run as high as -5 on Falken's to get best results.

Tony, the frame and Body are original with the exception of frame upgrades, all the other stuff is bolt on so going back would be easy. I would never want to but the buyer from my widow will have that option.

[Jdata]

Awesome update! I didn't know Kirkham was providing those those types of service.

[Sawdust]

Very impressive, good luck! I look forward to hearing about your results.

[6TNCRZY]

I am interested in the details of what you did to install the quick ratio power steering.

[Cobra #3170]

Originally Posted by 6TNCRZY

I am interested in the details of what you did to install the quick ratio power steering.

It is fairly complicated: I bought an Appleton rack (very narrow design for oval track cars) with quick steering and positioned it in the car so it would allow the steering shaft to clear the headers and other parts. I made an adapter that connected the AC Cobra steering shaft to the Appleton rack that used clamps on the splines. I then made extenders for the rack ends so that both sides were the same distance from the steering turning axis. These adapters gave me the right length tie rods for my particular suspension design for minimal bump steer. I worked that out a Solidworks, I also shortened the steering arms on the uprights to about half the length of stock arms and moved the rack as far rearward as I could for Akermann. I had a new steering rack mount fabricated to fit in the original bolt holes on the car but that positioned it correctly in all planes. the right hand side of the rack is much longer than the LH side because the steering is offset to the left. I used a GM power steering pump with remote reservoir. The pump is mounted on the LH cylinder head with an adapter I fabricated that uses the existing taped holes in the cylinder head. I have a ribbed belt driving the pump off the very front of the crank it barely clears the stock front cross member. Bump steer is very important to handling so the design must be correct if you go into it. This set up took me about a month to get right I mocked everything up first before making hard parts.

[Jdata]

What's the ratio of the rack or turns?

[hinoonaz]

Does this mean a return to Scottsdale Good Guys?

[Cobra #3170]

Originally Posted by Jdata

What's the ratio of the rack or turns?

400 degrees lock to lock

[Cobra #3170]

We had some relatively good results from Pleasanton but also more car issues.
Saturday the car was fastest but not by as much as I thought it should be because we had understeer on turn in, mid corner and even exit. We made a change or two and it improved but not as much as I thought it should. Sunday morning we raised the rear by 1/2" (big change) and picked up a second on the field. We have a friend who brought his Optima winning Z06 complete with Katech engine and aero package. He had Kuhmo Viper tires mounted that are illegal everywhere now but he was just doing fun runs. This is a very serious car as an example he beat Scott in my GT3 at the Fontana Optima autox a couple of years ago with those Kuhmo's when they were legal. Scott was national champion in 2016 and 2017 in that Porsche and defeated a whole bunch of Corvettes and Porsche's. Sorry this is so long but I wanted to establish Corvette credentials. He beat Scott by .4 seconds at Pleasanton so not too bad considering we gained 2 seconds over Bridgestone's last year with Kuhmo's when they were legal. The transmission started making really nasty noises on decel so Scott wanted to withdraw from competition immediately. The crowd saw us get beat by a Chevy so I could not stand that and convinced Scott to take one more run. We raised the rear another 1/4" and added two sweeps of rebound to the front shocks. Scott then beat the Corvette's time by 1 full second and I am sure that we could find 1 more second if necessary. Lynn Park stopped by and got to see the Cobra make a pass so that was great too because he has only seen it on video.
We won ProX but did not run in the shootout. To put it into perspective the winning time for Prox in the shootout was 78.4 Scott ran a 74.6 in the Cobra.
The new suspension really helped braking, we are picking up time on every stop. Once we figure out tuning I am sure it will be even faster, all in all I am very glad we made this change.

[twobjshelbys]

Actually sounds like a pretty good run for the first time on all the new gear.

Are you now satisfied with the engine and all tuned up with the fuel injection controller? As I recall you spent quite a bit of time getting that whipped into submission last year.

[Cobra #3170]

Originally Posted by twobjshelbys

Actually sounds like a pretty good run for the first time on all the new gear.

Are you now satisfied with the engine and all tuned up with the fuel injection controller? As I recall you spent quite a bit of time getting that whipped into submission last year.

Tony,
The EFI system has been perfect for the past year or so, pipe color looks good, air fuel ratios are always good in the data and the traction control works well too. Yesterday it had Scott down to 19 degrees of advance exiting corners.
We need to see how much slip we can tolerate before losing acceleration.
Scott feels it is actually accelerating harder with fairly high slip %. Everything is adjustable, we just need to take the time to look at the data and change the curves in the computer. I need to get it back in the garage, up in the air and start pulling the seats so we can pull the transmission and find out what is wrong now.

[Jdata]

Great upgrade evolution! So you're finding that you need to raise the rear and play with rebound. Is their a rear ARB?

Sounds for that course, you have some in time on the table

[Cobra #3170]

[quote=Jdata;1462684]Great upgrade evolution! So you're finding that you need to raise the rear and play with rebound. Is their a rear ARB?

Sounds for that course, you have some in time on the table[/QUOT

I am sure everyone is sick of this thread by now but I will give you a short explanation on our tuning logic.
First of all, of course it has a rear anti roll bar and it is adjustable as is the front bar. We use a very small rear bar because too much rear bar will lift the inside tire and hurt corner exit. The rear bar on this car is a very small % of roll stiffness so it has a small effect on balance. We use it for fine tuning only. The desirable thing to do is increase grip on the end of the car that is not working, In this case our front bar was full soft already and changing springs between rounds is not something we do (although we have in the past). The fastest way to change static balance is to change the roll axis which is what we did. Dynamic balance is done through shock adjustments. To illustrate what we achieved through those two changes we were getting a peak of 1.17 lateral G, after balancing the car our peak was 1.34 which resulted in a big time gain.
The car has less Ackermann now so we had to compensate with the other changes to get it re-balanced. We could have changed toe but took the easy route and raised the rear for mid corner and increased front rebound to improve exit front grip. If we had more time Scott wanted to try a combination of rear and front rebound changes but the transmission noise ended our day. On the subject of rear bar, you would need a Detroit locker or spool to use a large rear bar and the negatives of those approaches out weigh any advantage in my opinion.

[Morris]

Bruce

You are doing a great job.....keep up the good work.....

I enjoy the updates as you provide them....

Morris

[Cobra #3170]

Thanks Morris, that means a lot coming from you!

[Jdata]

Thank you for the explanation! And please this thread isn't an annoyance. I love threads like these.