Mike, So now you have some track time with your car. I know you spent a lot of time on frame stiffening schemes. I gotta know, do you think they were a (big, medium, small) improvement?
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'69 suspension upgrade
- Thread starter 69427
- Start date
69427
The Artist formerly known as Turbo84
Well Larry, to be honest, in the times when I've been out on the courses driving the car, I'm so damn busy trying to not hit anything that I haven't really been able to discern any torsional differences with the car. LOL And, given that I made changes to both the frame AND suspension, it might have been hard to tell which change produced the difference in feel behind the wheel, anyway.
When driving slow, I have noticed a couple things. There's less squeaks and rattles going on. I do enjoy that improvement! And, I do notice that when I pull into my driveway, I have to come at it straighter, as it's easy to lift a rear tire when going up the initial ramp in a diagonal fashion (trying to not tear up the spoiler). The (relatively) stiff rear spring limits the rear wheel vertical travel, but thank goodness the frame doesn't just bend in torsion and drop that wheel back down on the ground.
So far I've had to leave off one stiffening contributor. The torsion tube between the trans crossmember and the pinion crossmember interferes with the present exhaust system. This tube contributed a couple hundred foot pounds of torsion at not much weight, so I'm looking forward to being able to put it back on the frame. (I'm welding up a new exhaust over the winter.)
I don't have a quantifiable answer to how much the frame improved. I had already done several of the modifications (cutting out some pieces, and welding in other pieces) before I decided to do the torsion measurements. I guess I would have to rate it as medium improvement. Given how absolutely weak (in torsion) these frame are, I'm pretty happy with the changes I was able to work in. As we had discussed before, I would have liked to have built a torsion box in the trans tunnel, but the 5 spd just eats up all the available volume in there.
When driving slow, I have noticed a couple things. There's less squeaks and rattles going on. I do enjoy that improvement! And, I do notice that when I pull into my driveway, I have to come at it straighter, as it's easy to lift a rear tire when going up the initial ramp in a diagonal fashion (trying to not tear up the spoiler). The (relatively) stiff rear spring limits the rear wheel vertical travel, but thank goodness the frame doesn't just bend in torsion and drop that wheel back down on the ground.
So far I've had to leave off one stiffening contributor. The torsion tube between the trans crossmember and the pinion crossmember interferes with the present exhaust system. This tube contributed a couple hundred foot pounds of torsion at not much weight, so I'm looking forward to being able to put it back on the frame. (I'm welding up a new exhaust over the winter.)
I don't have a quantifiable answer to how much the frame improved. I had already done several of the modifications (cutting out some pieces, and welding in other pieces) before I decided to do the torsion measurements. I guess I would have to rate it as medium improvement. Given how absolutely weak (in torsion) these frame are, I'm pretty happy with the changes I was able to work in. As we had discussed before, I would have liked to have built a torsion box in the trans tunnel, but the 5 spd just eats up all the available volume in there.
SCCA VETTE
Well-known member
I am not sure what the difference is from inside the car but you can see a big difference between this car and other C3's on the track (stock and modified). When we were working the corners at Grissom it looked pretty level going through the turns, even when it was going through them sideways. I also noticed it seemed there was very little travel in the rear when hitting bumps, you can actually see this in the videos I took. From where we were sitting it looked like it was hitting the bump stops there was so little travel.
Just an observation from watching it go around the track all day for what it is worth!
Just an observation from watching it go around the track all day for what it is worth!
69427
The Artist formerly known as Turbo84
I am not sure what the difference is from inside the car but you can see a big difference between this car and other C3's on the track (stock and modified). When we were working the corners at Grissom it looked pretty level going through the turns, even when it was going through them sideways. I also noticed it seemed there was very little travel in the rear when hitting bumps, you can actually see this in the videos I took. From where we were sitting it looked like it was hitting the bump stops there was so little travel.
Just an observation from watching it go around the track all day for what it is worth!
I did hit the bumpstops quite often on the rough portion of the course (the crossover X just before your corner) but I don't recall sensing any bottoming out for most of the rest of the course. I looked at the stops and knuckle area while I've been fabricating a rear bar mounting setup, but I don't see any wear or polish marks indicating a lot of contact. I'm running the '84 411 lbs/in rear spring (BMF code), which is also shortened, so I'm guessing the actual rate is perhaps 420-430 lbs/inch. The antisquat geometry in the rear seems to help keep the car level while I was in the throttle. I never liked the way the stock C3 suspension sat down on its ass whenever you nailed the throttle. The car finally feels a lot more level and steady than it used to.
Now, if this rear bar restores the neutral handling I had before I bumped up the front roll stiffness, I'll be a happy guy, and I can take a break and start working on the new engine.
69427
The Artist formerly known as Turbo84
Jeesus what a nice chassie!!
Have you been on the track any more?
Sotened it out?
//Ricky.
Thanks for the kind remarks.
I've been out a couple times since these pictures. I did change the front sway bar to reduce the understeer. I got a tubular sway bar off a '93 Firebird and modified the ends to fit the suspension width I'm running. The handling is pretty neutral right now, and the bar is 4 pounds lighter than the 1.125" bar that was on the car previously.
The next project is to get the corner weights measured and adjusted. I've taken some weight off the car recently and need to see what sort of balance issues I might still have.
Jeesus what a nice chassie!!
Have you been on the track any more?
Sotened it out?
//Ricky.
I agree
69427
The Artist formerly known as Turbo84
Damn, they fit!
I was getting the car ready for an upcoming track day (test and tune), and thought instead of starting out on Hoosiers (given that it's not a competition event) I'd just run street tires. I decided to run some semi-decent tires, so I took the tires off the '84 (while it's not running at the moment). The wheels are 16 x 9 with the usual 255 size tires (and using VB&P adapters). After swapping the front tires from the '84 to the '69 I started on the rears. In the process I remembered I have an extra set of wheels and tires for the '84 in the basement. The fronts are 255 again, but the rears are Michelin 315/40-16 (out of production now, unfortunately). They look great on the '84, and have done several track days with them. Just for kicks I tried one on the rear of the '69.
Hey, it fits, with no interference. The adapters are 2.25" width, but I've got enough inside tire clearance to put a 1.75" adapter (same as on the front) on instead to tuck the tire in a bit more. I might just get another couple 1.75" adapters and run these tires on the street for a change of pace look on occasion. The tires have a few years on them, but are in great shape and only have about a thousand miles on them.
I was getting the car ready for an upcoming track day (test and tune), and thought instead of starting out on Hoosiers (given that it's not a competition event) I'd just run street tires. I decided to run some semi-decent tires, so I took the tires off the '84 (while it's not running at the moment). The wheels are 16 x 9 with the usual 255 size tires (and using VB&P adapters). After swapping the front tires from the '84 to the '69 I started on the rears. In the process I remembered I have an extra set of wheels and tires for the '84 in the basement. The fronts are 255 again, but the rears are Michelin 315/40-16 (out of production now, unfortunately). They look great on the '84, and have done several track days with them. Just for kicks I tried one on the rear of the '69.
Hey, it fits, with no interference. The adapters are 2.25" width, but I've got enough inside tire clearance to put a 1.75" adapter (same as on the front) on instead to tuck the tire in a bit more. I might just get another couple 1.75" adapters and run these tires on the street for a change of pace look on occasion. The tires have a few years on them, but are in great shape and only have about a thousand miles on them.
69427
The Artist formerly known as Turbo84
Doing some tweaks on the front suspension and geometry. I'm not happy with the lack of grip I'm experiencing in the slow corners. I'm going to try to get a little more camber gain by dropping the UCA pivots back to where I had them originally, and play around with some more anti-dive to help increase the camber in mid turns. Also I'm moving the coilover upper mounting point outward to get the spring more upright. I initially had the coilover leaned in to clear the A-arm in case I had to make some significant camber adjustments. Experience with the car has shown me I don't need that much extra clearance, and for the past year I've run the upper coilover mount shimmed outward. The new UCA mount will just reposition the coilover mount so I won't need the shims. Also, the new UCA mount will let me experiment with more caster range if it looks productive.
Here's what the UCA mounts look like in this ancient picture (bolted to the top of the frame).
You can see how angled the coilovers were originally.
Here's a shot today taking the A-arm off the left front. You can kind of make out the A-arm bracket on the frame.
This picture shows the bracket unbolted and removed. I made most of the suspension attachment points as bolt-in brackets so that I could modify the geometry, or just fix a geometry mistake. In the lower part of the picture you can see a couple of the bolts holding in the lower crossmember (somewhat similar to a C4 design).
I'll weld up a couple of replacement brackets and install them in the near future. If the geometry changes improve things, great! If it's a flop I'll just pull out the new brackets and put the old ones back in until I figure out the correct design.
Here's what the UCA mounts look like in this ancient picture (bolted to the top of the frame).
.................
You can see how angled the coilovers were originally.
Here's a shot today taking the A-arm off the left front. You can kind of make out the A-arm bracket on the frame.
This picture shows the bracket unbolted and removed. I made most of the suspension attachment points as bolt-in brackets so that I could modify the geometry, or just fix a geometry mistake. In the lower part of the picture you can see a couple of the bolts holding in the lower crossmember (somewhat similar to a C4 design).
I'll weld up a couple of replacement brackets and install them in the near future. If the geometry changes improve things, great! If it's a flop I'll just pull out the new brackets and put the old ones back in until I figure out the correct design.
phantomjock
Well-known member
There are some great software aids to help identify where you "might" want those chassis mounting points to be.
Some software is free, and some have 30 day free trials. Might save you a bit of re-welding! :idea: There is a long list over at the IRS forum - FRS is the same - just at the other end - and hopefully with a lower roll center!
Cheers Jim
bobs77vet
Well-known member
looks good, i like the attitude of try and see....As i say to my kids its just metal we will win!
