autox_vette

Has anyone heard of or seen a torque tube shortened? I know it sounds like a strange question.

A friend and I are discussing the future direction of his autox car (DP miata). We trying to decide where to build a new DP legal motor (4 cyl. buzz bomb, no torque), or since he has gotten a taste of the glorious torque of a LS6 driving my C5Z this year, we are discussing transplanting a LS* drive train into his Miata and doing a full assault of EM. Only question right now is what to do with the rear suspension. Either live axle with 3 link and watts link, or something independent.

Since I've not been into the bowels of a C5 drivetrain, I'm not sure if shortening a C5 torque tube would be a possibility so we could run a C5 transaxle or if we would have to run a Camaro trans and some kind of live axle.... Either way, it should be fun to drive

Thanks,
Kenton

C6Roadracer

Yes it can be shortened very easily. It will require a good welder though.

LG Motorsports

Been there, done that.

Let us know if you want to go that way.

I don't know if I would say "easily" but to do it right you have to do the drive shaft also, and you have to keep the bellhousing and rear mating surface at the diff totally square in every direction. If you don't, you will "whip" the drive shaft into pieces. And shorten and move the shifter and mounts.

LG

drivinhard

Just did a '99 miata LS6 conversion. Used an F-body T56, custom length driveshaft, and a Ford iron cased IRS 8.8" and 8.8" inner/outer CV's, custom axles, and custom hubs for the 8.8" CV sized spline. Some bracing for the diff mount, rest is miata rear pieces.

Like LG said, you'd need to keep both ends of it dead square if you did it.

LS V8 miata is like driving a beer can with a jet engine on the back

Solofast

For an Emod Miata you want as much weight in the back as possible. If you don't you aren't going to have sufficient traction to put down the power that you will have.

The Corvette torque tube system puts the tranny ahead of the rear axle. Better than an F body trans mounted to the engine, but not really what you need to make this work. What you really want is a tranny that is mounted behind the rear axle, like on an Audi front drive setup, or something from a mid engine car. The torque tube idea is fine, but if you can get the transmission behind the rear axle you will be able to put down a lot more power...

If you don't get the weight moved aft, you are just spinning your wheels (both literally and figuratively)....

drivinhard

For sure having in back would help, trying to achieve what the C5 did. However, space is at a premium in the rear. We couldn't even fit an alum case 8.8 IRS back there (it's larger than the iron case, has more ribbing, etc). You will be doing some serious fab work to get the C5 tranny/diff to the rear. At that point, (IMHO) you're into some pretty serious turd polishing. (you could argue we've already polished it pretty good putting an LS6 in there, but 1 coat ain't as bad as 5 coats

At the end of the day, it's a pretty flexy chassis. On my 2 post lift, the door gaps open significant, and the passenger door has a hard time closing correctly. So how crazy do you want to get, when at the end of the day, it's a miata? It's torsional stiffness numbers are pretty low.

The one we I just did (friend's car) hooks up in a straight line better than I thought it would. Gearing (speed in each gear) is the same as the C5Z06, it will hang on through 1st gear WOT, as long as you don't dump it at high rpm. And the C5Z will roast the rears just as easy if you do that.

It's a fun car, nothing I'd probably do myself, but it's fun. 2 door, short wheelbase, open top, big V8. Cruising around town, what's not to like. The amount of fab work we did was enough for me. Anything more, and I'd want to have something more than a miata when I was done

AlwaysInBoost

^ I'd like to see pics of that if you have them, sounds like an interesting project.

drivinhard

The guy I bought my land from when I built my house always wanted to do a V8 miata. We have become good friends and started in this around March. It's mostly done, still have some small stuff to do (air inlet piping will change location, heater hoses will once the AC lines go in, real brakes, etc) But we got it running and just kinda shaking it down. The exhaust is pretty sweet, it's bent up and over the axles like the C5, only in about half the space. Probably less restriction going straight under, but he wanted it so you couldn't see stuff hanging below the car. Don't have any pics handy of the exhaust.

AlwaysInBoost

very cool!

Solofast

Agree with all of the above. The shorter wheelbase gives you more aft weight transfer under acceleration than a Vette, so you have more bite than one would expect.

BUT, the stated purpose was to build an all out E mod autocross car. If you look at what is already in that class, cars like Steve Tamandli's Fireo (Basically an old Brabham formula car with a plastic Fiero body and a V8 put longitudinally in the back) and some of the other cars like the Strelniks (sp) three rotor RX-7, you are looking a some very serious purpose built autocross cars.

IF you want to play in that game it's gonna take a serious car, and I agree that there probably isn't room for the vette rear mouted gearbox in the back of the tunnel as it sits, you are looking at an engine mounted tranny as compared to one mounted in the trunk. In that case, the amount of power you could put down in first and second, coming off of corners is going to be key to success, and a front mounted tranny just isn't going to do it.

As to chassis stiffness, since you are starting with a D prepared car it is gutted anyway, and if it doesn’t have some stiffness already added, a cage is probably a good idea so you can address that when you rip out the old stuff.

Face it, you are doing a lot of work to transplant the V8, if you don't do a rear mounted tranny you won't have a prayer in Emod, so it's simply not worth the work if you don't do it right.

Just get your sawzall out and make it all fit in the trunk.

BrianCunningham

Sweet!

0Randy@DRM

I had a 91 in my garage for about 3 weeks. Then I bought my vette and sold the miata. Way easier to go fast in a vette then redesign a miata into a speeding missle. Plus the vette shows off some of our products better

Good luck it sounds like a fun time. Get the torch out if you are looking at putting a rear mounted transmission.

Randy

drivinhard

I'm an auto-x class ignoramus, so I didn't know how much you'd be hacking up the car (cage, sawing out rear sections). So more powa to ya

autoxer6

Hi Kenton,
Just curious, who is looking to build this? Sounds like a great project!

Chris Shay

autox_vette

Greg.
He's trying to decide if he wants to continue down the DP path or something a little more "exotic". After all, it's only time and $$$, and we all have lots of both.