Wham Bam….Trans Am!!!

 One of the great knowledge gaps in Mopar history surrounds the 303 cui Trans Am/ SCCA (Sports Car Club of America) cars. 
All too often, we hear deluded owners or those who don’t know any better claim that the Factory produced 340 cui Challenger T/A and AAR Cuda 6 pack were “like they raced in Trans Am”…when the truth is very very different!

Posey’s Race motor – notice the anti-slosh oil fillers, dry sump pump, LD340 dual plane intake and remote oil system

6 pack

Factory 6 pack motor – featured almost none of the real “go-fast” goodies the race cars used….

Below is a list of specs supplied by Keith Black to Hot Rod magazine in 1971, detailing exactly how he built the Posey motors for the bright green 303 cui Challenger – and more importantly, showing the significant differences in the motors specifications to the factory 340 motor.


Block – These were a special order 4 bolt casting designed to take the extra large 4 bolt main caps.

 Crank – These were a special order forging from Chrysler – 4340 steel,  continual cross drilled, special fillets.

 Rods – Special order from Fred Carillo, utilising NASCR hemi rod bolts – much stronger than the factory 340 rods.

Bearings – Clevite 77 set at .003 to .0035″ clearances

 Slugs Special order from Forged-True.  These had:

  • A higher dome yielding around 12:1 compression and had many hours of dyno time perfecting the optimum flame front. 
  • Wrist pin retainer was completely re-designed using a “locking spring” style rather than a lock ring.

 Oil – Dry sump oiling using an Aviaid three section pump – frst two sections are used for scavenging and the third provides pressure.

Timing Chain Reynolds roller style timing chain in the SCCA/TA and in the Indy cars a gear drive was used.

 Cam – Special Engle grind flat tappet solid. Red line of 8500.  Black stated that as peak power was at 7800 he saw no need for a roller cam shaft.

 Heads – For the SCCA/TA cars, these were the off set rocker large port iron 340 heads. Fir the Indy cars, these were the Weslake heads.

Valve gear – The SCCA/TA cars had raised rocker shafts almost ½ inch higher than factory. This was to accommodate a higher lift camshaft, improve pushrod geometry  and allow for the use of heavy duty HEMI valve springs. 

  • Rocker shafts were chrome hardened and drilled for extra oiling holes.
  • Springs are seated in specially machined valve spring cups.
  • Valve seats are machined using a radiused stone
  • Valves were 2.02 hollow long stem intake and the exhaust were sodium filled to resist heat effects

Intake – For the SCCA/TA cars it was the venerable LD340 dual plane , port matched with plenum modifications

 Induction – Carb was a Holley 800 cfm, 1&11/16 bores, the Indy cars ran fuel injection.

Cooling – A re-worked water pump with a smaller impeller.

 Other interesting points

 – Cheating the rules was almost expected…and tech inspection was “relaxed” to say the least…..

 – 20 ft/lb variation in torque from 4500 to 8000 rpm

 – Posey’s Challenger used a modified Watts linkage type suspension which was an abject failure and caused significant axle tramp under brakes going into corners.

 – Black’s engines allegedly made more HP than any other teams.

To quote Posey “Keith Black was a genius. He was a drag racing specialist who turned to road racing to produce our engine. He never missed a beat, he made reliable engines, he made extremely powerful engines. It was the strongest part of our car by far”.
Certainly more than his stable mates Gurney’s AAR Cudas, which regular blew up!
Blown up Cuda

A Gurney/Savage Cuda in its death throws…. Oiling failures were common – although its not known if they persisted with a wet sump or not.

 – Reports vary on HP – but somewhere between 480 and 515 FWHP is a safe bet.  Fuel injected variants not used in Trans Am showed an additional 20 HP

 – The T/A cars had an acid dipped body shell – on one occasion Posey’s roof was so thin it buckled, so it was covered by a vinyl top!

 – The transmissions and rear ends had housings that were made out of magnesium with a little metal glued on them so when the tech inspector tried with his magnet, the magnet would stick to it!


Posey spins

Posey spins


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