Specs on subframes?

[David Pozzi]

For starters it would be nice to see more of what Pozzi has done, publish your numbers and tell everyone how you got there.

Sorry I haven't contributed before now, I've been buisy.

I'm a ways from getting my Camaro running but let me offer a fiew observations on suspension.

THE WHOLE PACKAGE:
The whole driver/car combination is critical to accomplishing a performance goal or benchmark, if any one thing is deficent, the goal won't be met. You can have a killer car but if the driver can't handle it, nothing is accomplished, likewise a poor tire or spring choice will shoot down an otherwise good car from setting a good time, etc.

SUBFRAME
It must have good torsional rigidity, - at least as good as the factory sub. Some of the aftermarket subs look rather flexable in this respect. At least GM put some thought and engineering into trying to make the sub rigid. The geometry sucks but can be fixed, how good is perfect geometry if the subframe is wanking around?

SUBFRAME WEIGHT SAVINGS
I hear different claims of saving weight from the factory sub.
Here's what a GM sub weighs:
SUBFRAME WEIGHT additon list
Bare sub 110
knuckle assys 92
springs 22
A arms - upper 20
A arms - lower 22
Shocks 6
Ctr link and tie rods 17
Trans Crossmember 10
Sub total 299

PS box, hoses, pump 44
TOTAL 343
================================================== ======
SUBFRAME WEIGHT additon list
Bare sub 110
knuckle assys 92
springs 22
A arms - upper 20
A arms - lower 22
Shocks 6
Ctr link and tie rods 17
Trans Crossmember 10
Sub total 299

man steering box 16.5
TOTAL 315.5
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A fiew lbs can be saved over stock, but not hundreds of pounds in my opinion.

I like Rack and Pinion steering, if I got a sub as light and stiff (or stiffer) as stock and it had a front steer power rack, low scrub radius, good neg camber gain, lots of pos caster, zero bumpsteer, good brakes, I'd be pretty happy with it. But it seems there can be lots of little things that can creep in to cause extra or unexpected problems. Most aftermarket subs don't have as much neg camber gain as a stock Camaro with Guldstrand mod. My experience has shown you need -2 to -2.5 deg neg camber static setting even with the Guldstrand mod on an open track Camaro. One thing that helps the late vettes get by with less neg camber gain is very very low chassis roll and high amounts of positive caster.

REAR SUSPENSION
I've been told by Herb Adams personally and read in several books that the multi-leaf spring layout as used in a Camaro is pretty darn good, (not the springs themselves but the overall design). Is there better? Sure, but how much better, and did you do the "better" system properly or is the better suspension have some geometry errors hurting it's performance?

There are most likely certain conditions where one suspension might do better than another, I think on a pretty smooth surface like Laguna Seca, there would be little to gain from a three lnk rear, but on a rougher surface it might do better.

I'ts important when comparing to compare best to best, and the best leaf setup I suspect is the Global West Cat 5 leafs. It is the most free from bind and I'm guessing the rate and design are good for handling and pretty much eliminate wheel hop. I haven't tried these leaf's but the design looks good to me. I don't know the best three link design geometry but some of the books have starting suggestions.

There was mention of Corvette composite leaf designs. The major benefit of this design was isolating the wheel vibrations from the chassis and convienient packaging, - coil springs take up room, require extra chassis bracing, and make the CGH slightly higher, but the leaf springs can be slung underneath where there is more strength in the chassis down low. The chassis is probably easier to make or assemble too. I've had a couple of C3's with rising rate multi-leaf rear cross springs, and they rode terrible in the rear, and they had lots of drivetrain and wheel noise. GM put composite rear springs on them in 80 or 81, and it was an improvement in ride quality. From a handling perspective, the chassis really doesn't know if the spring is a coil or leaf the way the C4 or C5 vette suspension has them connected. Race Corvettes are converted to coils because they are easer to change to different rates.

I have read several posts of the Vette Brakes fiberglass Camaro springs breaking, also of wheel hop problems. If the horsepower is low, they seem to work OK but when you get close to 400hp, they don't work.

TESTING/COMPARING
I guess I'm a bit too skeptical to believe it can be done well enough to be of use to "us". As Salt Racer more-or-less said, it only takes one thing amiss and the car won't do well. The car or cars would have to be well developed, not just a subframe thrown on and timed in a slalom, etc. Most guys who have bought aftermarket subs say they are great but say they are not experienced in suspension tuning or mods.



I would like to see comparisons of chassis stiffness in ftlbs per degree for each subframe system. Comparison of neg camber gain, roll center height and movement, SVSA, FVSA, bumpsteer weight added or saved, F/R weight changes, rear RCH, and movement, rear anti-squat/anti-dive.

Things that stick out in my memory:
I attended a road race at Laguna Seca in the early 90's, I saw a worn out looking 69 Camaro in vintage TA configuration running in second place with a bunch of tube-framed plastic bodies GT1 Corvettes and Camaros! The leader Corvette fell out with mech problems and the 69 was LEADING THE RACE!

After a fiew laps, he got in a little over his head at turn 9, and spun off while leading all the other guys. This car had LEAF SPRINGS but it must have had a pretty good overall package! ;)
The guy found the car parked by a garage, bought it, and threw an engine in it, hopped in and just flew! The car was previously owned by a very successful local racer who parked it long ago.

My point here is, sometimes a simple plain combo that is well sorted will win over another car that is much more exotic. I stress the "sometimes" part!

A plain "stick" rear axle has lots of benefits when putting the power down when exiting a corner, leaf or coil/three leaf, it compares very well to an independent rear axle if the pavement is smooth.

I'm going with rear leaf on mine so I can get my car going in my lifetime... I have lots of other projects. I'm going to count on driver talent and a superoir driver/car package to get me by others on the track. If the talent thing doesn't work out well, I'll try other rear setups if I can find the time to do so.

For those who want to try a three link, I think there is a little to be gained, maybe a little better feel powering out of a turn, - stability kinds of things. More traction? - maybe, faster track time? could be a tenth or two but if comparing to a dynamite leaf combo maybe not much. This is just my speculation, not based on solid on-track comparisons, so I may be wrong on the gains possible for rear suspensions.