F40/F41 Springs and Judging

[Alan D.]

Re: F40/F41 Springs and Judging

YUP ! There's some items one can get from GM called ??? so I will just list all the lines on cover (word separated by a "," is on a line) : Chevrolet, 1964, Corvette, specifications, Genuine Chevrolet (sorry for not knowing title)

Sheet labeled "Section II - Page 32, dated Dec 2, 1963" has a note which states J56 & F40 require use of option G81,L84, & M20.

Later a sheet labeled "1964 Corvette General - 5", dated Jan 1964, shows F40 for all models.

And Noland lists that same restriction for the J56 option alone.
So I think when one ordered the old Z06 package, J56 & F40, then the L84 was only available and this wording is missing from Nolands note.

It does appear that the F40 was available for all cars.

[Jack H.]

Re: F40/F41 Springs and Judging

There's a SUPER SECRET book called the NCRS Judging Reference Manual. In it you'll find that for a part to qualify for condition point scoring, it must have scored AT LEAST 10% when it was judged for originality. So, no originalty points = no condition points either...

[Gary B.]

F40/F41 Springs and Judging

Jack,

Maybe I'm being dense here, but assuming an incorrect spring has the correct finish and is installed correctly, couldn't one argue that it still should get 1/2 of the originality points based on the 4 (5 minus date) factor matrix system? After all, it looks like a GM spring, acts like a GM spring ...

Gary

[Darwin O.]

Re: F40/F41 Springs and Judging

Hey Gang!

Well, now I'm confused...

I'm reading from this thread that there is a document that supercedes the info in Noland's book that says the F40 suspension could have been ordered without the L84 if you also didn't order J56.

And, if so, that it could get full points. Or, that if you couldn't order the F40 without the L84 that the springs might get a 50% deduction, or no points at all.

I feel like I opened a can o' worms...

Cheers,
Darwin.

[Duke W.]

Re: F40/F41 Springs and Judging

The F40/41 suspension was tuned for high speed road racing, so the ride rate and understeer is greater than what is probably best for low speed autocross.

As with any other competition, the first place to start is installing the stickiest legal tire you can find. Then it's just a matter of tuning the suspension to get the desired dynamic response.

The base suspension with more negative camber than you would run for road use is probably not a bad place to start.

Duke

[Darwin O.]

Re: F40/F41 Springs and Judging

The F40/41 suspension was tuned for high speed road racing, so the ride rate and understeer is greater than what is probably best for low speed autocross.

As with any other competition, the first place to start is installing the stickiest legal tire you can find. Then it's just a matter of tuning the suspension to get the desired dynamic response.

The base suspension with more negative camber than you would run for road use is probably not a bad place to start.

Duke

Agreed, however as the original springs are somewhat saggy after 45 years, they should be replaced if I'm going to auto-x the car. So, I need to establish the height of the car as part of the wheel/tire selection. I'm looking at 225/45-17's or bigger if I can get them in there (I've heard that the drum brake cars can accommodate a wider rim than the disk cars, but I'll need to measure it up before-hand).

And so the arms race begins.

I've heard from some other guys who auto-x their C2's, and they run either F40/41 springs, or fiberglass equivalents. If I'm going to replace the springs, and if I'm going to take a full hit by using the F40 springs, then I will likely go with a modern package. I think they would suit the kind of driving I do with the car (I have a Z51 6-speed 99 FRC as a daily city driver).

The car missed 2nd flight by a 1/2 percent before I started doing any work to it, and I'd be more than happy with a solid 2nd flight with some tastefull, intentional deviations. But, I'd like to minimize the hits if possible - thus all the questions on F40 springs and judging. Or, I might just get some (much smaller) sticky tires for the steel 15x6's, new shocks and be content with slower times...

Thanks again for all the comments, Gentlemen!

Here's a couple of shots from the first event of the year:






Cheers,
Darwin.

[Dick W.]

Re: F40/F41 Springs and Judging

Just remember the better the traction you get, the more parts break.

[Duke W.]

Re: F40/F41 Springs and Judging

Unless the springs are seriously corroded, they are not "saggy". Do some archive searching on this subject.

The C2 has high roll centers, which results in lots of camber and toe change with suspension travel (which actually helps offset roll to keep the tires more vertical with the pavement). Modern cars with low roll centers have little camber/toe change, and camber relative to the road is controlled with high roll stiffness.

The bottom line is than modern low profile tires are not well suited to the C2 suspension architecture.

I don't see how you could run 17" tires in a "stock" class, but local club rules vary widely.

Avon makes a V-rated 215/70R-15 DOT legal racing tire. IIRC the model is CR6ZZ. (Google Avon to find it.) This tire on a 6-7" wide wheel with the base suspension, some adjustable shocks like Spax or QA-1, and some rigorous shock/alignment tuning will likely outperform a C2 with some "suspension kit" and typical "ultra high performance" large diameter short profile tires with typical 200-300 DOT wear ratings.

Ultimate grip is purely a function of tire adhesion. Suspension geometry, ride and damping rates, and roll stiffness are just tuning parameters to exploit the tire's adhesion characteristics for the type of service. To build a competive competition car, you start with the tires and then work the ride, damping, and roll stiffness rates to maximize grip.

Duke

[Darwin O.]

Re: F40/F41 Springs and Judging

Unless the springs are seriously corroded, they are not "saggy". Do some archive searching on this subject.

The C2 has high roll centers, which results in lots of camber and toe change with suspension travel (which actually helps offset roll to keep the tires more vertical with the pavement). Modern cars with low roll centers have little camber/toe change, and camber relative to the road is controlled with high roll stiffness.

The bottom line is than modern low profile tires are not well suited to the C2 suspension architecture.

I don't see how you could run 17" tires in a "stock" class, but local club rules vary widely.

Avon makes a V-rated 215/70R-15 DOT legal racing tire. IIRC the model is CR6ZZ. (Google Avon to find it.) This tire on a 6-7" wide wheel with the base suspension, some adjustable shocks like Spax or QA-1, and some rigorous shock/alignment tuning will likely outperform a C2 with some "suspension kit" and typical "ultra high performance" large diameter short profile tires with typical 200-300 DOT wear ratings.

Ultimate grip is purely a function of tire adhesion. Suspension geometry, ride and damping rates, and roll stiffness are just tuning parameters to exploit the tire's adhesion characteristics for the type of service. To build a competive competition car, you start with the tires and then work the ride, damping, and roll stiffness rates to maximize grip.

Duke

Thanks for the info, Duke!

I understand that C2 springs can still be good, but in my case it looks like I've got a crack in one of my leafs, and my front springs are being bolstered by a couple of screw-in coil separators on each side. This was how it was when I got it a couple of years ago.

You are correct, if I go with the 17" wheels I move into Street Prepared (no Touring class for 2-seaters...), and face some pretty serious cars. I am looking for a modification/repair strategy that, ideally, minimizes the hits on the Judging Field, but maximizes the gain on the auto-x. If I can stay in the Stock class while doing so, then even better. I'll look into the Avon tires, but I drive the car on the street more than the track, and whatever tires I get will have to do double duty, as I can't bring a second set out on race day.

I've been a mechanic for 20 years, but have not done any racing before - so I'm on a learning curve again. Thanks for your help.

Cheers,
Darwin.

[Duke W.]

Re: F40/F41 Springs and Judging

As "DOT legal racing tires" the Avons are street legal, though they may not be the best in rain due to minimum grooving and less than normal new tread depth. Their wear rating is 100 or less, so they might provide 5000-10000 miles of gentle street driving, which will obviously be reduced by racing.

In any event, they are perfectly okay for normal road driving especially if it is limited - not a daily driver, go to work car.

I run DOT legal racing tires on all my cars where there are suitable sizes that fit the OE wheels, but each also has a set of OE wheels with normal road high performance tires, so I can choose whichever set meets my immediate driving requirement from long road trips on freeways to race track hot lapping.

You might be able to replace the broken leaf and restore the OE rear spring. You should pull the front springs and measure the dimensions listed in the AMA specs. If they conform, they are probably okay, and I believe the same variable rate front spring was used on most SB Corvettes from '64 to '67. They are out there.

Spring spacers effectively stiffen the spring, and NASCAR teams add and subract "spring rubbers" to alter wedge during races. Even if the car ends up a little low, that is usually an advantage due to lower CG, as long as you don't run out of jounce travel.

I suggest you buy Fred Puhn's "How to Make Your Car Handle". It's old, but the basics haven't changed, and it's a good primer on vehicle dynamics and suspension tuning.

Duke

[Jack H.]

Re: F40/F41 Springs and Judging

Yep, you can argue that point, but I don't think your argument will fly with a knowledgable judge. Here's why...

The Finish, Date, Installation, Configuration and Completeness point allocation system is a POLICY of NCRS. Perhaps, it'll finally be officially recognized as a RULE in the next release of the NCRS Judging Reference Manual...

That book does have a HARD RULE requiring dealer/owner inspired vehicle option configuration changes shall be dealt with by judges taking FULL DEDUCTIONS on all of the aspects of the car that were affected by the change.

So, go argue away...maybe you'll be sucessful in pursuading this/that judge.

Hey, that's what good lawyers are all about. Their job is convince a judge/jury that this/that set of facts in the case which invoke this body of law actually outweigh these other set of facts in the case which invoke this other body of law. Sometimes if you can't convince with fact you can bamboozle them with BS!

[Darwin O.]

Re: F40/F41 Springs and Judging

Yep, you can argue that point, but I don't think your argument will fly with a knowledgable judge. Here's why...

The Finish, Date, Installation, Configuration and Completeness point allocation system is a POLICY of NCRS. Perhaps, it'll finally be officially recognized as a RULE in the next release of the NCRS Judging Reference Manual...

That book does have a HARD RULE requiring dealer/owner inspired vehicle option configuration changes shall be dealt with by judges taking FULL DEDUCTIONS on all of the aspects of the car that were affected by the change.

So, go argue away...maybe you'll be sucessful in pursuading this/that judge.

Hey, that's what good lawyers are all about. Their job is convince a judge/jury that this/that set of facts in the case which invoke this body of law actually outweigh these other set of facts in the case which invoke this other body of law. Sometimes if you can't convince with fact you can bamboozle them with BS!

Thanks for the insight on Judging interpretations. If I did swap springs (and bars, etc.) I would not be trying to convince Judges to award me points, I just wanted to know what the hit was going to be should I do so. If the hit is 100% for the F40 setup, I may as well go with somthing modern, if I go that route.

As "DOT legal racing tires" the Avons are street legal, though they may not be the best in rain due to minimum grooving and less than normal new tread depth. Their wear rating is 100 or less, so they might provide 5000-10000 miles of gentle street driving, which will obviously be reduced by racing.

In any event, they are perfectly okay for normal road driving especially if it is limited - not a daily driver, go to work car.

I run DOT legal racing tires on all my cars where there are suitable sizes that fit the OE wheels, but each also has a set of OE wheels with normal road high performance tires, so I can choose whichever set meets my immediate driving requirement from long road trips on freeways to race track hot lapping.

You might be able to replace the broken leaf and restore the OE rear spring. You should pull the front springs and measure the dimensions listed in the AMA specs. If they conform, they are probably okay, and I believe the same variable rate front spring was used on most SB Corvettes from '64 to '67. They are out there.

Spring spacers effectively stiffen the spring, and NASCAR teams add and subract "spring rubbers" to alter wedge during races. Even if the car ends up a little low, that is usually an advantage due to lower CG, as long as you don't run out of jounce travel.

I suggest you buy Fred Puhn's "How to Make Your Car Handle". It's old, but the basics haven't changed, and it's a good primer on vehicle dynamics and suspension tuning.

Duke

Thanks for the info, Duke. I've dug a bit into the Avon tires - Tire Rack carrys them, but not the model you reference. Where do you get them from? If I could get 10,000 miles out of them they would last me 3-4 years on the '64. I do drive it fairly spiritedly on the twisty highways, so maybe I'd need something with a little higher wear rating.

When it's time to take the suspension apart, I will do a thorough investigation of the springs - if they can be repaired/salvaged I will certainly consider keeping them and tuning with shocks and allignment. I'm going to buy that book.

Cheers,
Darwin.

[Duke W.]

Re: F40/F41 Springs and Judging

http://www.avonracing.com/road_legal_page.aspx