jimlab

First, you can't compare a 30-year old car with a solid rear axle and leaf springs (probably) to a modern unibody car with IRS. The IRS will soak up a LOT of the twist that might put the body at risk.

Second, the differential and suspension is more isolated from the body because of the separate subframe with bracing of its own. At most, it'll bottom out one of the rear shocks, probably.

Third, the 3rd gen. is far more rigid structurally than a 30-year old car, and my car only has 13,000 miles on it. It hasn't fatigued anything yet, or even worn out anything. If it had the original engine in it, it would only have had 3 or 4 oil changes by now.

Fourth, the 5-pt. bar ties the rear of the car together as does the rear strut brace. The Nova has no such bracing stock, and even with a roll bar, the rear of the car is still weak. Extra plate area was added to the shock towers and floor pan to strengthen the rear even further.

Fifth, the Nova has a big, flat floor pan. The RX-7 has a fairly small, convoluted floor pan with structural bracing, including the transmission tunnel braces.

Sixth, in order to twist the car, you need to have the front tires off the ground. I don't plan on running slicks ever, since slicks on an IRS car capable of these speeds isn't my idea of fun at the far end of the track. I'll stick to drag radials, keep the front of the car on the ground, and make the tire the limiting factor.

Seventh, there are Supras with far more torque than I'll be making, running slicks, without any cages at all, and they're not having any problems. The Supra is heavier and has bracing for the removal of the targa hatch, but if you've ever driven one with the hatch removed, you'll realize how sloppy the body feels compared to an RX-7.

In other words, I'm not too worried about it.

FastX7

Thanks for the explaination
They always said you won't learn anything unless you ask questions or question why things are done. I get alot from just reading your posts Jim

jimlab

One thing I forgot. IRS tends to launch straighter than a solid axle car with anything but a ladder bar or 4-link setup.

The car below doesn't have the benefit of an articulated rear suspension and it has slicks. Look at the twist between the rear of the body, which can't move because it's planted to the ground, and the front, which is free to twist because it's in the air.



I'll bet he has subframe connectors, though. First gen. Camaros tend to split the quarter panels at the rear edge of the side window if they don't. Ask me how I know.

My car will likely look a lot more like this...

http://www.z06vette.com/media/mtiz06.mpeg

FastX7

How do you know?

jimlab

I ended up replacing both quarter panels on my '67 Camaro after cracking open someone else's repair job on previous cracks shortly after the new engine went in the car.

j9fd3s

iTrader: (3)

the early mustangs do that too, except they do it just driving around.
my vote is to use the best of both. i wonder if a porsche has a hub that will take the power? they had some badass racing cars back in the day. jim you know you are going to do the custom stuff anyways, we just have to help you find the right path.

mike

jimlab

Yeah, the decision is pretty much made to go with a 9" IRS. I'm just trying to find some suspension parts (still need upper control arms and lower I-beam for both sides of the rear, as well as a differential mount) to use for mocking up the rear suspension out of the car for measurements for fabrication.

I'd use mine, but I'd rather sell my polished suspension pieces with Unobtainium bushings and M2 toe links and trailing arms without having bolted them to anything prior.

jimlab

More pictures to consider...





This setup was developed for Cobra kit cars but bolts in place of the live axle on a Mustang. Something similar would work very well for a bolt-in solution for the FD. The Ford hubs (5 x 4.5") are the same bolt pattern as the FD.

The ride height can be adjusted via the coilover shocks, and there are no forward links required to prevent fore and aft wheel deflection under acceleration or braking because of the wide lower control arm. Camber and toe are easily adjusted, and there is no bump steer.

The optional brakes are either 12" or 13" rotors, both use Wilwood Billet Dynalite II 4-piston calipers and have provisions for parking brake. 2 different sway bar setups are also available.

This IRS also uses the Ford 8.8, and they claim increased torque handling because of the stability of the mount, but I'm going to contact them about doing one with a Ford 9", and spacing the control arms wider with a "cage" meant to bolt into place on the FD using the stock mounting points.

Thoughts?

dclin

iTrader: (4)

You're a basket case.

jimlab

True, but a well-equipped basket case, you have to admit.

yzf-r1

iTrader: (1)

love the video Jim

what E.T.s are you planning to hit with and without the nitrous?

jimlab

Shooting for low 13s with nitrous, mid 13s without...

Import Convert

Dana 60. All that needs to be said!

jimlab

Yeah, but what will I use for a transfer case?

Dr Wankel

The suspension set-up looks very sweet. I think that would be the best/easiest solution to the problem. That is if they are able to make one for you with the correct pick-ups to bolt right up. That unit looks like it should give a nice tight feel to the rear end with the sherical bearings in place of bushings. And I wouldn't think that you will have any problems with that big old rear end in there. And with the narrow arms that it has you shouldn't have to worry about clearance issues if you try to get a big wide tire under there.

LT1-7

yeah, probably with drag radials

nrolfes1

For the amount of money and free time Jimlab must spend on this "hobby" project that has been sitting in his garage for the last few years, my theory is that Jimlab = Bill Gates.
They both live in Redmond Washington.
They both like to take a good thing and make it "blasphemous".
They both have the amount of free time equivalent to software-giant-owning multi-millionaire
I can't believe Jim can fund this hobby selling unobtainium bushings, although they were rather expensive last time I checked.
Just what exactly do you do for a living, Jimbo?

jimlab

They state on their web page that the rod ends are Teflon coated and that they use urethane bushings for the lower control arms and Delrin for the top, neither of which is ideal. I'd probably just make replacements from Nylon anyway.

The only thing I'll have to worry about is the inner wheel well, probably. Still, a P315 drag radial (on a properly sized rim) is a lot better than a P275 or P285 under the back of the car. Maybe this thing will stand a chance of hooking up yet.

jimlab

In reverse.

maxpesce

Jim:
You are Crazy BUT in a GOOD way.

When you are ready to sell your polished suspension w/unobtaiums let me know.

LUV94RX7

iTrader: (3)

Jim, I think you should tell all your vendors that you should get a good deal and they should deliver ASAP as your car will probably be in car magazines and it would be to their best interests to get you the stuff soon. They will benefit in the long run.

Ken

jimlab

OK, the project was crazy before, but I think I've officially lost it now.

Not only have I tracked down someone to whom I'm going to hand over a completely functional rear suspension on the rear subframe for the development of an IRS Ford 9" replacement with Denny's HD aluminum axles, but now this...

I'm probably going to go with the Jerico clutchless 5-speed road race transmission. And if that weren't enough, I think I'm going to duplicate or at least approximate the gearing (including differential) of the F40.

The Borg Warner (now Tremec) T56 6-speed has an almost worthless 6th gear (0.50:1) which is good only for fuel economy, really. Why would I care about fuel economy? A 0.77:1 5th gear (F40) is far more usable, and would still be loafing at around 2,000 rpm @ 70 mph, and 2,600 rpm @ 90 mph and get very good fuel economy. So much for needing a 6th gear.

Switching to a 2.91:1 differential (F40 gearing) isn't going to pull the front wheels off the ground, but that wasn't my goal anyway, and it may keep 1st and 2nd gear usable. In other words, keep from turning the tires into greasy lines on the pavement. This would eliminate the need for the RaceLogic traction control device I've been looking into, which is another plus.

I've been playing with gear ratios and using the McLaren F1 and Ferrari F40 for comparison. Both have very similar redlines, and both have very similar peak power (but not powerbands) and weights. The F40 is actually a little heavier than I expect my car will be.

Both cars turn exceptional quarter mile times on stock tires for cars that are geared for the top end; 11.6 and 11.8 respectively. However, neither has the low end torque that I will have. I suspect that it might be quite easy to build a very low 11-second or high 10-second car (on street tires, no less) that pulls like the supercars (and not a glorified Camaro) on the high end as well. Mind you, this is only theory so far.

For comparison purposes, I've used a P275/45-17 in all calculations. The F40 and F1 would have slightly higher gear limited top speeds with their respective stock tires.

McLaren F1 - 2,840 lbs.
Redline - 7,500 rpm
Differential - 2.37:1
1st gear - 3.23:1 - 74.8 mph max
2nd gear - 2.19:1 - 110.3 mph
3rd gear - 1.71:1 - 141.3 mph
4th gear - 1.39:1 - 173.8 mph
5th gear - 1.16:1 - 208.3 mph
6th gear - 0.93:1 - 259.8 mph

Ferrari F40 - 2,980 lbs.
Redline - 7,750 rpm
Differential - 2.90:1
1st gear - 2.77:1 - 73.7 mph max
2nd gear - 1.71:1 - 119.3 mph
3rd gear - 1.23:1 - 165.9 mph
4th gear - 0.96:1 - 212.5 mph
5th gear - 0.77:1 - 265.0 mph

Now compare my car with a "stock" geared 4.10:1 differential and T56...

My car - ~2,850 lbs.
Redline - 7,500 rpm (arbitrary)
Differential - 4.10:1
1st gear - 2.66:1 - 52.5 mph max
2nd gear - 1.78:1 - 78.5 mph
3rd gear - 1.30:1 - 107.4 mph
4th gear - 1.00:1 - 139.7 mph
5th gear - 0.74:1 - 188.7 mph
6th gear - 0.50:1 - 279.3 mph

It should be pretty obvious that 6th gear is not as strong as the F1's 6th or the F40's 5th gear because of the poor ratio. It certainly has an impressive gear limited top speed, but in your average V8 Corvette or Camaro, 6th gear is worthless because the car falls out of its powerband with the deep overdrive and cannot gain rpm against the wind resistance at those speeds. I won't have that problem to such a large degree, but I do intend to join the 200+ mph club with this car eventually. I don't want to have to fight to do it, if I don't have to.

The 4.10:1 differential means that if I go with my current setup that it's going to go through the first couple gears like crazy, and probably blaze the tires uncontrollably without heavy throttle modulation. I've seen the Darius videos. Final drive in first (2.66 * 4.10) is 10.91:1, compared to the Ferrari's 8.03:1 and the F1's 7.66:1. That means that torque multiplication is going to be much higher, and I already have much higher low end torque than either of the other two cars as it is. Not good. If you can't get your power to the ground, it's worthless.

Since running 9s is not my goal (in this car, at any rate), and since I doubt I'll put a full cage in the car which means that I'd get booted from the track immediately on breaking out of the 10s, such a "short" differential gear is not advantageous. However, dropping the rear gear ratio for a taller gear means that the 0.50:1 6th gear is even more worthless, although with a 3.42:1 differential I could probably push the car to about 220 in 5th. Still not ideal, and I've got a wasted gear.

To sum it up, gearing the car like the F40 (Jerico isn't available with 6 gears, unfortunately) means the following benefits:

1. With my powerband, possibly a 10-second car on street tires, NA.
2. Pulls far better on the top end, giving the car VERY long legs.
3. Makes first and second gear really usable at WOT again.
4. Clutchless trans, gearing and redline mean I cover more ground in each gear and take almost no time during shifts... nice.
5. Jerico trans is stronger and weighs about 40 lbs. less than T56. (80 lb. magnesium case vs. 122 lb. aluminum case)
6. 0-60 using only 1st gear.

Personally, I just want to ensure that what I've built not only can hold its own in a stoplight match-up, but can also hold its own very, very well against big single turbo cars on the top end. I don't want any excuses or weaknesses. It'd make a hell of a road race, One Lap, or Silver State Classic car.

Any thoughts?

Crashunit

Your , but like he said, in a "good way."

LT1-7

I'm glad you looked into it Jim. I will probably get one on the next GB from www.twinturbo.net.

jimlab

I've already got enough electronics as it is, I'd rather keep the "system" as simple as possible.