[flash]

since i had to remove the transaxle, so as to beef up the torque tube to handle some extra power i plan to add to my car, it seemed the perfect time to take advantage of the new torque and change the gearing in the transaxle.



the stock 5th gear ratio is .912 and 6th is .778. stock 5th and 6th are very close together, but this is as far as they could go, given the torque available from the engine.



i am changing to .857 and .684. i will have the torque to spin taller gears, so i'm going to take advantage of it



this will drop the rpms in 5th about 200 rpm in 5th at the same speed, and about 400 in 6th. it will also even out the gear spacing a bit.



that should give me about 10% better fuel economy



it should also give me a top end of about 180, assuming i can keep the car on the ground.

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[Scott Collins]

Bob,



That sounds great, and something I have thought about every time I take a road trip.



The fuel economy should be excellent, not to mention a quieter ride at highway speed.



Where are you getting the gears? Could this be another Design 1 product?



-Scott

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[flash]

lol - nope - bought them from the dealer



yes, the noise reduction is going to be a big plus too

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[tamathumper]

Will we all have to upgrade the torque tube to use the sc upgrade?

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[flash]

no reason to think so, assuming it's in tip top shape - that was something that had to be considered before installing the kit anyway



that work on my car is due to something else entirely. i can't go into it yet though.

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[tamathumper]

Finally dropping in that v8 you've been champing at the bit about, eh?

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[flash]

lol - you have no idea just how close to that i got a couple of weeks ago

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[Cloud9...68]

As long as you have the torque tube out, why not use is as a mold/template to make one out of carbon fiber? I'm kidding...... I think....

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[flash]

lol - don't think i didn't look at that. i also looked at aluminum.



the problem is that the size the tube would have to be in order to handle the torque would not fit in the tunnel. bonding to the transaxle also presents a problem.



even aluminum is problematic.



remember that you still have to retain the shaft, the couplers, the tail piece and the bearings. the steel tube just isn't that heavy. it's only about 40lbs

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[MB968]

I haven't done any calcs to verify this, but to me, the torque tube looks big enough to handle a 1000 ft-lb. Won't deflections/windup of the driveshaft be a bigger issue?

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[Cloud9...68]

Are you going with the "super bearings"?

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[flash]

deflection is a problem, which is why there are 4 bearings in there. this problem would get worse with any material that flexed, which is why you would need to have a very large carbon tube, or a very thick aluminum one. there is somebody right now screwing around with this, but they aren't very good at math, and when they build it and it tweaks, they are going to feel pretty foolish. i already spent quite a bit of time with people who make nothing but driveshafts, and we all came to the same conclusion.



this just isn't the place to worry about weight.



yes, among other things being done, i am having super bearings installed.

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[Cloud9...68]

[quote name='flash' timestamp='1334188501' post='124997']

yes, among other things being done, i am having super bearings installed.

[/quote]

Cool. Those things look like they could hold up to swapping in a ZR1 motor and then driving it on the track for 500K miles.

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[flash]

yeah - they are pretty tough. the real problem is the design of the tube itself. in reducing the vibrations, they introduced more deflection, which results in bearing failure when you either run the car hard, or add a bunch of power. the failures are at the end bearings, particularly the front one.



stock it's fine for street duty even up to a bit over 300hp, but go much past that, or plan on abusing the car (though i have to argue that driving it hard is abuse, and in my mind nursing it is more like abuse) then you should plan to upgrade the bearings.



a new problem is that the plastic collar that goes between the bearing and the shaft is no longer made, and hasn't been for quite some time. even the shops that rebuild them have to install used collars. that just plain sucks.

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[MB968]

What's the possibility of beefing up the area around the front bearing on the outside of the tube?



And, how much of the issue of the front bearing might be the sliding coupling. Could it be causing the bearing to be taking a lot more radial load. Maybe improving the way that coupling is clamped onto the internal spine would help.

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[flash]

you're on the right track



the problem is that the slit porsche put in the front 1/3 of the tube on the 968, in order to reduce vibrations, also allows the bearing to "walk" as it flexes under load and the slit expands. as soon as it is cocked a few thousandths of an inch off of perpendicular, the collar essentially threads its way out, leaving it spinning loose on the shaft, and a large gap between the shaft and the bearing. the bearing itself is subjected to side loading while this is happening, thereby wearing it out. the narrow nature of the bearing does not help this problem. even the super bearings can walk.



the rear bearing is another known problem area. lots of torque, especially like in a turbo where it comes on abruptly, causes a similar problem there. hard shifting will as well.



it's not a simple problem to fix. i'll let everyone know how it turns out.

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[robadams56]

I interested to hear of what you are using to make even more ponies. Saw a show last night that had a Hennessy Ford GT, which if I heard correctly, had twin turbos installed on top of the factory supercharger for a total of 1,000 hp.

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[flash]

well, that's off topic, but i'll release all of the details on that as soon as the design registration is complete, and of course the testing is done. this design is something a bit "out of the box", and i don't want anybody knocking it off and calling it their own. i've been watching enough of my design ideas get swiped already.



back on topic, i am really looking forward to seeing how the new gearing works out. i think i've chosen right, but it makes me nervous. i'd hate to have to drop the transaxle and change them out for different rations again. i know what the turbo had, and i'm going just a tad taller. i might run out of poop in 6th a bit earlier, but i don't think that sacrifice will be worrisome, as i am really looking for more highway drivability and fuel economy than i am ultimate top end.



it is also my hope that between the new torque tube, and a couple of other new changes, that i might reduce or perhaps even eliminate the transaxle rattle that came in when i went to the solid mass flywheel. i have already been able to significantly reduce it. it will be interesting to see how it changes with this round of mods.



by the way, when this installation of engine, tube and trans is done, i will have crossed over the $125k mark that i have spent on this car

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[tamathumper]

Holy, um, FLARK!

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[MB968]

Does anyone have a crossection (could just be a sketch) of how the TT bearings are mounted. I'd like to see the design in case I could see an improved way mount them.

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