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Old 09-07-2005, 12:05 AM
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350 SBC: '70 top end on '90 block?

I have a 1990 (or 91, I forget) 350 block that I bought from a junkyard a few years ago. I ended up stroking it into a 383 originally meant for a 1990-91 3/4 ton tow rig. Well, I ended up moving away for college and never finished the engine. It's sitting in a machine shop at the moment, consisting only of the block, crank, rods and pistons. We had purchased a cam and heads for it, but ended up returning them and never finishing the motor.

I currently have a '70 Nova with it's original 350 in it (some minor mods) that could use a rebuild. I was wondering if the 20 years difference between the engines makes the parts non-interchangable?

Best case scenario is I use the '90 block (383) and bottom end, and swap the '70 heads, Streetmaster intake, and Holley 4160 750 onto it, with a new cam to match. I end up with a decent 383 for free, if it's possible. New heads are a possibility if I can scrape up the cash, but for now lets just assume I use the heads off the 1970 engine.

Can I swap the parts? How much, if any, machining is needed (besides the clean-up and reconditioning of the parts)?

One more thing: The '90 383 has flat-top pistons; with the 1970 stock heads, what compression ratio am I looking at?

Thanks.

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Old 09-07-2005, 07:38 AM
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Without the heads casting number there`s no way to guess what the CR will be since we don`t know the chamber size. But the parts will interchange without a problem.
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Old 09-07-2005, 11:39 PM
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Which is the later engines had the revserse cooling passages? I cant remember when. But if the block was designed for reverse flow cooling passages then the heads wont work but I dont believe a 1990 was (was it just the LT1s and LT4s?). The heads should work. You can pick up some Vortec heads for a very reasonable price and they would be far better than the 1970 heads.
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Old 09-08-2005, 02:23 AM
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Head casting number is 3832441.
Date code: A 8 0

I haven't been able to find this casting number on MorTec or any other site to get the specifics.

Anybody with a book?
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Old 09-08-2005, 05:08 AM
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Reverse flow cooling didn`t come along until the LT1 engine in 1993. Standard small blocks still used standard flow. The 441 casting is a common early smog casting, the casting number is on Mortec, I don`t see how you could miss it, just look at the last 3 digits or 441. A 8 0 is the date code, January 8th 1970, they had 74cc chambers, 160cc runners, 1.94 1.50 valves, they were heavy casted heads, and they respond well to basic porting.
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Old 09-08-2005, 07:11 AM
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Ah, thanks DoubleVision. I was looking for the entire number, not just the last three digits.

So 74cc chambers and flat top pistons... Any thoughts on compression ratio in a 383?
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Old 09-08-2005, 10:55 PM
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This is from an old KB catalog for a 383 with flat-tops (7cc valve reliefs)

Head vol.-
Comp.ratio
58cc -11.7
62cc - 11.1
64cc - 10.9
76cc - 9.6
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Old 09-09-2005, 01:49 AM
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Thank you Jim!

I was hoping for a slightly lower CR since this will be a daily driver (though I don't drive far or often) and would like to keep the octane down. But I think I can deal with that.

Thanks again to everybody who contributed.
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