Quote:
Originally Posted by PontiacJim1959
Keep in mind that the RA IV used aftermarket forged pistons. Have you ever compared any Pontiac cast pistons to the RA IV forged piston. Could easily be differences in pin height or even deck height. From what I have seen, if the magazines are showing an actual RA IV piston, the tops do have a different valve relief configuration. Maybe a true side by side, measured, comparison between the cast and forged piston would settle it. Maybe you could find an NOS RA IV piston and provide the comparative specs, and then we would have some facts to fall back on for the sake of argument.
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How many have actually worked on original RAM AIR IV engines.
I have only worked on two of them as mentioned in previous posts.
All of the Pistons were supplied by TRW. Both of the RA-IV Engines had Forged Pistons vs stock Pontiac Cast Pistons. The RA-IV pistons also used the 200 gram Piston Pins vs the aftermarket TRW Forged 2262 Pistons which used a 250 gram Pston Pin. Normal Pontiac Pistons were delivered with Cast Aluminum pistons. Put a 200 Gram Piston Pin in a TRW Forged 2262 Forged Piston and you had a RA-IV Piston.
Very likely that the Valve Reliefs on the RA-IV Forged TRW Pistons had a deeper 4 Valve Relief Pocket as the engines were designed for a higher lift .470" valve lift and 1.65 ratio rocker arms. Deeper and Larger Valve Pockets
= a lower measured compression ratio.
So I think that it is possible that Kenth's numbers are close to reality.
I owned a full set of new Forged RA-V Pistons (given to me by the Chief Engineer at TRW Pistons). I later swapped them to Tom Jeffers in Ohio for some Sheet Metal body pieces for my 64 GTO. (Floorboard and Trunk Pans).
Never owned a RA-IV vehicle. Have driven several of them. Have worked on two of them, I have owned all of the unique parts for the engines Valvetrain and Heads/ intakes, Camshafts, Forged Steel RA-IV SD crankshafts.
But I am not a expert on the engines like some here.
Tom V.