Engine and Transmission Tech

Question is what area of unit body car, to pick up majority of engine torque ? Some say over front suspension is best. I suspect at the firewall, used in shear,to back of block/bell housing bolt pattern should work. Work even better if firewall is well triangulated to forward unit body structure(front stringers). I suppose this is similar to "elephant ear" plate off of bell housing bolts. Anyone ? Cheers, roverman.

Art, I agree. Somewhere near where the firewall intersects with the front main chassis members would be ideal. Any farther forward and you start stressing the inner fender panels which you may need to trim out a bit for header clearance.
If you are planning on a roll cage structure then depending on the design your options increase quite a bit, but I still like the idea of an anchor for the torque around the firewall area and let the front of the chassis carry the suspension loads by itself.

Bill and clan, as we consider this, the unit body is a "type" of torsion bar. This receives torque from engine and transmits through body/rear suspension, to rear wheels. The "longer" we make this crude torsion bar, the easier to twist. By this logic, if we can shorten distance by using bell housing for torque pickup, = less twisting. The extreme might be using tailhousing mount, rigid mount cross member to trans and rubber isolate at ends ? roverman.



Edited 1 time(s). Last edit at 10/26/2011 03:04PM by roverman.

Not really extreme Art.
Think Camaro or Miata etc. Long torque arm connnecting trans to diffy.
Not actually meant to transmit torque from engine to rear end, but it could be made to do so easily.
Porsche and a few others did the real thing and Alfa came close with the rear clutch/transaxle cars.
Cheers
Fred

Pontiac had a torque tube on the Tempest back in the early '60s when they were using the 215 with a rear mounted transaxle and flexible driveshaft. Pretty high tech stuff for those days. Anyway if you think of the torque tube's requirements the strongest, stiffest and lightest one would be very large in diameter, very short, and very thin. The body tub satisfies those requirements pretty well, leaving only the details of attachment which is more of a practical concern, and details of transfer to the suspension. Basically you can either couple the torque through the rear suspension on a live axle and deal with the suspension being unevenly loaded side to side, or you can go to IRS and transfer all the torque loading to the long axis.

JB

Clan, I'll be using RX7 irs, so no torque tube. Turbo Supra trans appears quite sturdy, so I'm considering that rigid beam on mount and tunable hardness urethane bushing on ends, to work in concert with similar bushings at BH. Thanks, roverman.

With a unibody a big part of the challenge is finding a suitable location and means for distributing the load. Plus, unless you do something different than the standard rear mount attachment to the tailhousing you run the risk of pulling the bolts out. So there are two issues to resolve with your plan. A plate that bolts on using all of the tailhousing attachment bolts to the main case should be a viable solution for one issue, and the rails that the stock crossmember bolts to should be sturdy enough for the other but run some numbers first, max torque multiplied by 1st gear and then divided by the distance between the rails should give you the loading in pounds. Then it's a judgement call as to whether the rails are rigid enough. Or you could do a static load test to see what deflection you get.

JB

Jim, Points are valid, but I suspect major torque to be controlled by BH mounts with trans mount to reduce deflection in the door ways. Engine block/trans "might" be strong enough for rigid mount. That would be my last resort.For dedicated race cars running the sbb/rover engine AND a sturdy girdle on the mains, I suspect rigid mounting the girdle to the chassis, to be beneficial. I think I can improve unit body beam/torsional strength with improved latching mechanisms on doors. Car wants a cage. We shall see. Thanks, Art.



Edited 2 time(s). Last edit at 10/27/2011 04:57PM by roverman.