how bad would this be

[dannyho]

I'm not sure this belongs here, but seeing as it's the torsional stiffness i'm concerned about from a safety standpoint, maybe it belongs...

On my roadrunner, i had planned on using a supra transmission, and using a dodge dakota bellhousing it all works fine, however the transmission is basically a close ratio truck transmission, so it's pretty huge. This means that i'd have to significantly modify the tunnel. Furthermore I'd have to cut out and replace a section of the front crossmember.

In the picture its the cross beam on the right, towards the front of the floorpan. the torsion bars insert into the tube sections of it. The goal was to use the toyota transmission cuz its bulletproof, good ratios and moreover a very low budget 5 speed, but it's getting out of hand. I'm not afraid of doign some welding, I'm confident enough in it that I think It will be strong enough. But what would you guys say? is the loading from the torsion bars going to kill that idea?

[David Pozzi]

You need to maintain the strength where the crossmember runs around the tunnel somehow. Hopefully there is room for you to intrude inside with it.

[MrQuick]

I agree, before you do any cutting make sure you weld in support bars and reinforcements. Be cognizant on placement as not to get in the way during fabrication.

I would brace then try to cut a shape in the floor that would mirror the trans, this means a lot of mocking up. Do a full cut from bellhousing to tail shaft with the engine sitting where you want it.

I would also be looking in to modifying the lower control arm, making coil over mounts and losing the torsion bars.

[aggressive male]

Just curious, why would you use a toyota transmission in a roadrunner? Sounds like something a desperate man in china would do. Are you going to be able to get this tranny hooked to your driveshaft, clutch, motor and shifter alright? Whats wrong with the transmissions roadrunners come with?

[High Plains Mopars]

I agree. With Tremac and Gear vendors available almost anywhere, there are decent OD transmissions that don't require any cutting and have tremendous strength capability and a choice of ratios. I don't know what type of power Supras are producing, but I couldn't imagine that the ones available stateside are strong enough to stand up to V8 torque.

If you do go this route, I'd say torque boxes and subframe connectors are a must. I'd go beyond stock style torque boxes and fab up your own that will tie in a greater portion of the sills into the structure. This would create more a of a perimeter frame arrangment. I'd also go beyond simply frame connectors and make an X in the square created by the torque boxes. You might also consider a boxed, diagonal brace from the cross member to the front frame rails just in front of the torsion bar. Since you'll have to fab the trans mount, box it up real good too.

[spooledx2]

Newbie chimming in. I do have quite a bit of expierience with real imports such as the Supra and Skyline. Depending on the year.... 93-98 Twinturbo tranny from behind a 2JZ will handle over 1000 HP unmodified. Earlier trans like the one behind the 7M-GTE will take about 650 before destruction(trust me I have destroyed a few units). This is actually a great idea and they are very cost effective units, and if they will hook up I say great idea.

Late

[wendell]

I like the sound of your contraption. I'm backing it! It's awesome to see some one hot rodding instead of screwing things together that they bought on the internet.
Brace everything before you cut to keep the car square. No matter how much crossmember you have to cut out, replace with a similar structure e.g. a member that spans from one frame rail to the other and is tied to the floor completely. Look at a modern SCCA A-Sedan or NASA CMC car for inspiration. They're limited by the number of attachment points so the designes are elegant. Use their designs but sink them into the pan.
I've never seen the bottom of a roadrunner. Looks decent. Tie the rear rails into the rockers with some thin wall box tubing where the stamped sheet stuff is. Maybe cut a set of frame connectors in from the end of the rear rails to the front rails (CarlC style, completely tied to the pan.) You'll be rocking. Keep us up to date.

[EFI69Cam]

Sounds like something a desperate man in china would do.

[wendell]

Sounds like hot rodding to me.

[gt1guy]

I would also be looking in to modifying the lower control arm, making coil over mounts and losing the torsion bars.

Great advice here. Doing this would make one less job the crossmember has to perform. You would, however, have to address the load paths of the coil-overs up front.

And yes, this is true hotrodding.

Good luck,

Kevin

[dannyho]

well the supra trans (2nd gen) has been known to hold 600ft lb motors at the dragstrip. It has an issue with a thrust bearing that is stupidly weak, and it's a shame because in order to replace it you have to completely disassemble the transmission, unpress all of the gears and hten press them back on.

I've found some pictures of a guy who did this. I personally would rather drop the driveline 3 inches than go this route, probably would be easier. But given the work involved here, I might try something else.Keisler is hugely expensive, and the budget issue is because i'm in school. I'll have a real ME job this coming summer and money shouldn't be soo tight then. So perhaps I'll wait. And I'd like to keep the torsion bars. I find nothing wrong with them at all. They make exhaust management a little harder but I'll manage.

anyways here's the pics of one guy who hacked up his valiant fitting one of these.



yeah, it's a job and a half
But it looks to me like his driveline angle is off compared to what I had seen when i was underneath the RR. The output shaft should be lower than it is, unless toyota did something crazy and the output shaft isnt concentric with the input shaft, which can't be right.

[wendell]

Looks like that guy had the right idea. He's exicution leaves a little to be desired and I would have invested in some new box tubing but that's just me. Start cutting!

[High Plains Mopars]

That does look like a lot of work, and for the effort, motor plates could lower the engien the needed amount much easier.

So how cheap are these Supra transmissions? If money is an issue, you could always contact Passon Performance about their A833 overdrive conversion. It duplicates the aluminum 4 spd overdrive of the early 80s to the iron case 833, so you end up with an OD that will stand up to becoup torque, unlike the aluminum case versions. No, it isn't as glamorous as a 5 or 6 speed, but it is effective and fits with no mods to the chassis.

[dannyho]

i got my trans for 300 and the bellhousing needed for 60, but i might want to rebuild the tranny before i do it and replace the weak thrust washer with a stronger one. however i think for now i'm going to back-burner it til a. i have more free time and motivation to cut the thing up and start soem welding, or b. i have enough money to do one of the 5 speed kits. i really dont need a 6th gear

[High Plains Mopars]

That's not bad, but factor in a rebuild and you going to be in it for a fair amount. To have an 833 four speed rebuilt and add the overdrive conversion would run you around $300-400.

[wendell]

Not for nothing but it's really not a lot of work. About the same effort and detail as cutting in some thru-floor subframe conectors. Measure twice, cut once. All you need is a wizzer wheel, a chop saw and a MIG. Get to it!