4 replies to this topic

[mariner]

Not F1 but I know that some of the regulars here seem to have close knowledge of what went on at GM USA a while back so maybe this thread will ring a bell.

I was looking at a book recently on GM experimental Corvettes which had the CERV II in it. This was a 1960's test vehicle designed loosely to compete with Ford's GT 40. I am not sure if it could do that too well but it had a four wheel drive system I have never seen since. The car was mid engined with a 7 litre "big block" i.e 600 bhp++. ) - 60 was claimed in 2.8 seconds.

Basically GM fitted a 3 speed and torque converter rear transmission ( reputedly as on the Chaparral) but also a torque converter at the front connected directly to the front of the crankshaft. This converter was scaled for the lower power to be sent to the front wheels.

On the surface this is a rather attractive scheme as the rear transmission can be scaled to 65% or so of the full 600bhp and no complex centre diff is needed as the two torque converters "solve" the wheel speed diferential. Also you save part of the prop shaft length. Also by part draining the converters you can control the power split dynamically.

Having built a car with a big block engine I can say that finding a strong enough trans. is hard. However there are many auto transaxles now that can probably take 65% of 600bhp in a light car so the idea of replicating the CERV II layout seems appealing. You could also minimize the front transmission weight by only using, say , two speeds if the rear had 3 or 4 and just fully drain the front converter fluid above 100 mph or so as then 4 wheel drive is less essential.

So it all sounds plausible but it never re-appeared after CERV II so does any know of the drawbacks of this idea of power from both ends of the crank to two auto transmissions for 4WD?

I would worry about the front crank fixing off a Woodruff key, getting all the front auxilaries also powered and any complex crank vibrations as potential risks.

Any thoughts?

[cheapracer]

Maybe oil supply problems for the converter, you need ample oil and cooling - how to do for a sole converter? Mazda's 13B rotary engined TQ over manual 5 speed gearbox fed the (engine) oil thru the crank (by the way it had a manual clutch too).

[McGuire]

The CERV II used a pair of conventional three-element torque converters, one on each end of the engine: a small-diameter (Corvair) torque converter at the front (hung off the front off the front transaxle) and a large-diameter (V8 Powerglide) torque converter at the rear for front/rear torque bias, with a two-speed manual crash box at each end. No clutches. The rear half of this setup is essentially what was in the Chapparal IIc, the car that popularized left-foot braking. I don't know how the drive at the front of the engine was taken -- I presume some kind of splined coupler pressed onto the crank snout. For me, the first disadvantage that comes to mind is too many torque converters.

CERV II was of course a Zora Arkus-Duntov production. There were supposedly plans for at least six of these cars, three for FIA prototype racing against the Ford GT (ha) and three for testing -- CERV stood for Chevrolet Engineering Research Vehicle. Thin sheet-steel .025 monocoque with stressed engine... which did not work for the chassis or the engine; a tubular rear subframe more than doubled the torsional rigidity. The car's body and aerodynamics were designed by Larry Shinoda (who later went to Ford with Bunky Knudsen) and Tony Lapine (who went on to Opel and then Porsche). However, as a racing program it was essentially deadheaded by GM Chairman Fred Donner's total ban on all racing activities in January 1963. CERV II was eventually fitted with a ZL1 all-aluminum big-block Chevy V8 and used as a tire-testing mule.

At some point CERV II (and CERV I also if I recall) was donated to the Briggs Cunningham Museum, a noble gesture I suppose, but since then the car was sold into the hands of private collectors and GM will probably never have it back. It so happens that while I was reading this thread yesterday afternoon, I was talking to a GM Performance Division powertrain engineer on the phone. He had never heard of it. I am glad they are looking forward over there and not back, but still...

http://www.google.co...59-1#PPA1967,M1

[mariner]

Thank you, Mcguire. I knew there would be a Guru on this subject on the forum but I did not expect a patent listing too!

Two things, one a puzzle, one an idea.

I can see that the engine needed extra help with torsional rigidity on this car but the BB chevy was used as a structural member on many Canam cars with wing induced chassis loads and they seemed to survive. Maybe GM's durabilty standards were different.

I take the point on two converters but there is still the possibilty of using converter empyting or clutch pack release ( probably quicker) to control the front/rear torque split dynamically in a way that mechanical front/rear drives can't do so easily. They can but all the locking/unlocking means extra centre diff complexity versus this approach. Maybe modern electronics would have helped this concept.

[McGuire]

I am no guru on the CERV II. I have never actually seen it in the flesh. All I know is what I have read or heard over the years. Semi-legendary stuff.

Far as I know, the Can-Am cars typically used the BBC as a semi-stressed member... there was a tubular subframe or tubular elements between the engine and bell housing and the trailing arms fed into the rear bulkhead. You wouldn't try that today knowing what we know now... that the BBC has trouble keeping its main webs in alignment on a good day, and that is before you twist chassis loads into it.

FWIK, CERV II was originally built with an aluminum SBC using the first run of Reynolds blocks, not a happy part. It was just an aluminum recasting on the iron patterns and not very robust at all. I have seen these and they are pretty nasty. Reports I have read/heard say that on CERV II the front cylinder bores pulled way out of round, hence the addition of the subframe...which increased the torsional rigidity from 2k to 5k. Later on the aluminum BBC was installed.

The SBC has had a spotty record as a stressed member as well. Only Gurney got away with it I believe, using the Donovan aluminum sprint car block and a massive main cap girdle/sump casting arrangement. Stock- blocks used as stressed members scare me under the bed.