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Old 02-23-2021, 01:44 AM
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Jay S Jay S is offline
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Join Date: May 2018
Location: Nebraska City, Nebraska
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Quote:
Originally Posted by PontiacJim1959 View Post
Here is a photo from the magazine article on the RA IV. Maybe Tom can ID the piston tops. I know magazines will toss in "parts" just to make the article up, but you can see the piston on the right has different valve reliefs. The article sounds like the piston on the left is the cast RA II piston, and the one on the right is the forged RA IV piston.

The article also states the RA IV forged pistons are 50 grams lighter than the old cast RA II pistons.
Piston on the right in post 40 appears to be a 428 piston

Interesting stuff. Tom was the RA 4 SD engine an over the counter deal in just 1970?

So it likely would have been balanced totally differently than a regular RA 4 with that Kellogg crank if it had 421 SD rods and RA 4 pistons? It would be fun to see one of those. The regular 70 RA 4 crank appeared to be a Arma crank like a 389 with the part # ground off and restamped for the ra4 part #. Not sure how the factory balancing compared to the older arma cranks. I know a friend has one out of his RA4 that he stroked.

Back when the 48 head thread was going on I had several heads out and was looking at chamber, I remember the 62 had a squarer looking chamber versus the 48 and 16. I have been curious if the 13 looked like the 62 or had a different shape?

If someone has a 13 laying around I would like to see the combustion chamber shape.


Last edited by Jay S; 02-23-2021 at 01:54 AM. Reason: Edit