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AK427
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Discussion Starter · #1 · (Edited)
SBC block casting 3932388 - pistons (pic)?

I've got my eye on an SBC engine that's for sale. Being sold as a 3932388 block casting with 4-bolt mains and 3927186 heads with 2.02"/1.60" valves. Apparently, a 350hp motor.

Here's a pic of the pistons...





Can anyone tell me what pistons they are (spec, forged or not, etc)? Wondering what the static CR would be on this motor assuming stock deck height, etc.

Thanks,
Ian.
 

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AK427
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Discussion Starter · #3 ·
Look like GM pistons. Originally made by TRW. These were the high compression forged factory 350 pistons. Compression around 11 1/4- 1. With 64 cc head.
Thanks. Can you tell that these are the forged high-comp pistons just by looking at the pic? I'm aware that this block casting was also made to a 300hp spec with non-forged pistons, I believe.

By the way, are the pistons in the pic considered flat-top with valve reliefs? Oh, and are the stock rods in this block cast or forged?

Thanks!
 

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More for Less Racer
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Bob's got it right on what they are, the 11-1 compression LT-1 piston from 1970, they are not a flat top piston. They have about an 1/8" raised flattened dome with a trough type(single cut) valve relief. They look forged in the picture, and should be forged unless they have been replaced with cast copies. Doesn't look like it though.

The 300 hp-spec engine would have a true flat top piston with no raised dome, just valve reliefs.

All SBC rods are forged until you get to the powdered metal rods of the 1990's
 

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AK427
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Discussion Starter · #5 ·
ericnova72 said:
Bob's got it right on what they are, the 11-1 compression LT-1 piston from 1970, they are not a flat top piston. They have about an 1/8" raised flattened dome with a trough type(single cut) valve relief. They look forged in the picture, and should be forged unless they have been replaced with cast copies. Doesn't look like it though.

The 300 hp-spec engine would have a true flat top piston with no raised dome, just valve reliefs.

All SBC rods are forged until you get to the powdered metal rods of the 1990's

Thanks a lot for the info. Given the CR, do you think this engine would run OK on 93 octane? I'm thinking of using my existing Holley SysteMAX alloy heads (20* valve angle, 68cc chambers), but I'm not sure if they'll clear the piston domes. Being alloy and having slightly larger chambers, they should help with the octane issue though. If they don't fit, I'd be stuck with those stock iron heads which I'd probably also need to have hardened exhaust seats installed on. Guess I could use a bigger cam to bleed-off some CR though. Comp XE274 or Magnum 280, perhaps.

Any estimates on power with the stock 3927186 iron heads and an XE274 or Magnum 280 cam? I'd hope IRO 400hp-450hp?
 

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I'd use the Holley heads and just clearance the chamber by hand to clear the dome if needed. It will be a very small amount somewhere around the edge of the dome and edge of the chamber if it hits or comes too close(less than .040" clearance). The Aluminum and the slightly larger chamber(68cc) will put you at a perfect spot for 93 octane.

I wouldn't bother with the 186 heads, compression will be too high for an all-iron combo on pump gas, sell them off to someone else. Your Holley's are perfect for this engine even if you do have to clearance things a little.

Your power estimates are fair for the iron combo, 450 or more with the Aluminum head.
 
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