4.5" stroke on 1970 SCJ block?

1460 Views 4 Replies 5 Participants Last post by rmcomprandy, Aug 10, 2010

walt6076

Discussion Starter · Aug 9, 2010

I've got a 1970 production SCJ 4-bolt block engine that is all finished, in the car, and read to start in a couple of months when the rest of the car is complete. Target is street / strip. Aluminum SCJ heads, mechanical roller... nasty but not insane. Turbos may come later. I just saw the article in Car Craft about their Boss build up and now I'm worried about piston rock. Their early block and 4.5" stroke is exactly what I've just built and they unequivocally said this combo pulls the piston too far out of the cylinder on the down stroke. Do I need a late model or motorsport block to be safe with a 4.5 stroke?

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Mark Laczo

· #2 · Aug 9, 2010

Piston Rock

Do you have 6.7" or 6.8" rods. I think the issue is with the 6.7" rod. Randy @ R&M has mentioned this before and has some info on this. I think it is a bit harder on rings but will still work as that has been ran before in the 70' block. I am doing this but using a 6.8" rod to keep the pin up a little higher(+.100). I guess you are wanting to keep the engine in as long as possible between freshing or ? Some of the experts will chime in and add some more info.

FWIW Mark

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Lem Evans

· #3 · Aug 9, 2010

I just did a SCJ block/FRPP SCJ headed deal with 4.5" stroke.....track only engine. It's not as of a big deal as the Camaro Craft says but, a 4.3" thing would be some better, long term, for a street engine.
I would not trade the SCJ 4 bolt caps for the longer cylinders of a D9 block. A D9 block with aftermarket caps would be a different matter.

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Paul Kane

· #4 · Aug 10, 2010

walt6076 said:
I've got a 1970 production SCJ 4-bolt block engine that is all finished,.... I just saw the article in Car Craft about their Boss build up and now I'm worried about piston rock. Their early block and 4.5" stroke is exactly what I've just built and they unequivocally said this combo pulls the piston too far out of the cylinder on the down stroke. Do I need a late model or motorsport block to be safe with a 4.5 stroke?

For years and years, the 545/557 4.5 stroke stroker kits were available with the 6.7 rod only, and initially the D9TE block was mistakenly presumed to be the block to avoid. And so today there are tens of thousands of these 4.5/6.7 rodded stroker kits out there running in D1VE blocks. How many have you heard of failing based on the 4.5/6.7 combination? Yes, the 6.8 rod is the better choice technically speaking, it does not mean that the 6.7 rod combo is necessarily as disastrous as you fear.

Paul

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rmcomprandy

· #5 · Aug 10, 2010

Technically, how much that piston rocks has a lot to do with where on the skirt, the fat part of the piston is located and the piston to wall clearance at the bottom...

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