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Old 02-27-2008, 04:03   #1 (permalink)
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Calling all engine builders!

I am having an OEM rebuild done on the original 429 scj motor from my 1970 Cobra. It is a street motor that, will see a couple hundred miles a year cruising duty. Everyone including the enigne builder said it would be a good idea to lower the compressions a bit so I don't need to run race gas in the car. That would involve having a set of dished pistons made for the motor.

At the same time, a new set of .30 over OEM replacements as well as pushrods fell in my lap. I showed them to the engine builder and he said I could use them, of course, but they were OEM replacements and purely "old school". They have the original style skirt, which he says are "hard on the bore" and would not lower compression. He also prefers a one piece chrome moly pushrod over the OEM pushrods which have the balls welded on the ends.

He spoke to his piston guy and in order to lower the compression he would have a set made with dished tops and modern skirts and the price is like $700...that sounded like an awful lot of money to that what custom order pistons go for? He also recomends if I can get away with a .20 over he would do that and save some of the bore and claims the difference in price between the .20 (custom) and .30 piston (norm) was negligible.
Am I being silly worrying about the skirts and compression? For the limited intended use of the vehicle on the street the skirt wear will be minimal and I could use race gas. It would save $700+ on pistons and pushrods...what about using the OEM push rods?

What would you motor heads do?

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Old 02-28-2008, 12:04   #2 (permalink)
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cool Re: Calling all engine builders!

Originally Posted by GregM View Post

What would

$700 is the basement starting price for custom pistons. Unfortunately, the 429 has almost zero piston options for lowering compression. The 460, on the other hand, has endless pistons options and this includes dished pistons.

My advice is simple, and I strongly recommend that you take it: Rebuild the engine with a 460 crankshaft. This way, you'll get a free 37 cubes (.030" over is a 466) and plenty of dished pistons from which to choose (for much less than $700). I strongy recommend a "D"-shaped piston dish. Also, the CJ heads are way, WAY too big for the little 429, so you will also have much better throttle response with those heads atop a 460. The 429 would be a complete dog of a motor with low compresison.


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