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Old 05-03-2011, 12:12 PM
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Chevy 350 rebuild questions

I am in the process of rebuilding a 350 for my 1980 chevy K10 4X4 truck. I currently have the block and crank in the machine shop. The motor was tore down due to low oil pressure. The bearings were pretty chewed up, but there were no major failures in the engine. The engine had 150K-180K miles on it. I am trying to make sure that I have a good parts match for the engine.

The block is a 4-bolt main 350 crate from the early 90's. Apparently the previous owner blew the factory engine up in it. I threw the heads that came with it into the scrap iron pile. I bought a set of 4416 305 HO heads that have been pocket ported, have 1.94 intake valves and z28 springs installed in it for cheap. I am also going to buy my rebuild kit from Northern Auto parts. Here is the optional parts list I am thinking of getting in the rebuild kit:

Brass Freeze Plugs
Sealed Power H423ACP coated dished pistons
Speed Pro 1500-4000 RPM 204/214 .50 duration .420/.443 lift
or
Speed Pro 2000-4500 RPM # CS1013R 214/224 .50 duration .443/.465 lift

With the 305 heads having a 58-60cc chambers, I calculated the dish pistons would have a 9.5:1 compression with A ,040 gasket, and the piston .020 down the hole. I calculated the compression would be way too high with flat tops.

With the two cams listed, what do you think would work for my application? I'm looking for a little more snort than it had, but not hot rod by any means. The truck has stock 3.08 gears and 31X10.5 tires.

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Old 05-03-2011, 12:20 PM
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The pistons will be around .045 to .050 in the hole. Why is because the pistons have a compression height of 1.540. The correct compression height is 1.560. These are called "rebuilder" pistons because shops that do countless rebuilds and sell them. I`ve delt with Northern many times and they offer good parts. The pistons in the kit you want will hurt power due to lower compression and somewhat of a sluggish burn from lack of quench.
As for getting a piston that would have the correct dish with the right compression height isn`t cheap, and the cheapest ones you`ll find are from KB pistons and not only do these cost more, but the ring gaps must be set.
I would think for your combo you would need a piston with around a 22cc D shaped dish to keep compression in check. These pistons with a head gasket thickness of around .018 you`d have decent compression and good quench.
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Old 05-03-2011, 01:41 PM
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Quote:
Originally Posted by DoubleVision
The pistons will be around .045 to .050 in the hole. Why is because the pistons have a compression height of 1.540. The correct compression height is 1.560. These are called "rebuilder" pistons because shops that do countless rebuilds and sell them. I`ve delt with Northern many times and they offer good parts. The pistons in the kit you want will hurt power due to lower compression and somewhat of a sluggish burn from lack of quench.
As for getting a piston that would have the correct dish with the right compression height isn`t cheap, and the cheapest ones you`ll find are from KB pistons and not only do these cost more, but the ring gaps must be set.
I would think for your combo you would need a piston with around a 22cc D shaped dish to keep compression in check. These pistons with a head gasket thickness of around .018 you`d have decent compression and good quench.



X2 i was just about to go there

a major question i would ask is why on earth would you use a .040 head gasket if your pistons would be .020 down in the whole which actually if you calculate it 3.48/2 = 1.74" + 5.7" + 1.560 = 9.00 (normall compression height of 350 piston), standard block height from the center of the crank is 9.025 which would put the 1.560 piston down in the whole .025", with these "rebuilder" pistons being 1.540, now it is 1.74 + 5.7+ 1.540 = 8.98, now with the standard deck height being 9.025 you are now down in the whole .045". Optimal quench (area between the piston @ TDC and the head surface) is .039-.046". so say your pistons was down in the whole .025 then you would need to find a head gasket in the range of .015-.020 (which are normally shims) and with the "rebuilder" pistons that you plan to use you will already have .045 in the cylinder without a gasket, putting a .040 or .041 gasket on it will give you a quench of .085" this is absolutley horrible, not mention as DV said that those pistons don't have a good quench pad for good burn charictaristics, so that will make your burn even worse. spend the extra bucks and get the KB pistons with the D-cups as they have a flat area on the backside of the dish for a better burn. make sure they are 1.560, then have you will be able to use a gasket in the .025" range and still get a quench around .050 (this isn't bad), you may even want to have the block decked .010" to get you right at .040". and DV is right about the 22cc dish these with the 58cc heads and decent quench will put you right about 9.0-9.1:1, and 18cc dish will put you at about 9.4-9.5:1

the 201/214 cam sounds like a good choice, it wont be too much for the heads, it would acutally be about perfect. but i would seriously advise going with a set of 4.10 gears, that is the worst thing about all the late 70's and 80's vehicles, they had really high gears which gave them no low end. you would be amazed what the difference a better set of gears will do for these vehicles.
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Old 02-12-2013, 07:44 PM
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piston selection

I am going to rebuild a 350 and am trying to decide what pistons to pick. If I have heads with 64cc's and pistons with 1.562" Compression Height and am aiming for 9.5 to 10:1 ratio, should I go with D-dish pistons? Thanks for the help.
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Old 02-12-2013, 09:36 PM
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You should really post this in a new thread. But the answer to your question is: if you are looking for 9.5:1 then go with a 12cc dished piston (with a quench of .040-.046") but if you want to use flat tops with around 6-7 cc valve reliefs then you could get 10:1 with a quench of around .044-.048 which is still a very acceptable range.
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Old 02-13-2013, 12:07 AM
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Sorry for not starting a new thread, just one more question if that's ok. With that information you told me what thickness gasket should I use? Thanks again.
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Old 02-13-2013, 09:53 AM
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Quote:
Originally Posted by Swarley View Post
Sorry for not starting a new thread, just one more question if that's ok. With that information you told me what thickness gasket should I use? Thanks again.
You said that the compression height on the piston is 1.562 (1.560" is facotry), then since said that you rebuilding a 350 (and the compression height matches a 350) the crank you are using is a 3.48" stroke. Then again based on the compression height of the pistons I would assume that you are using standard sized 5.7" rods.

here is how you do the math: stroke 3.48/2 = 1.74" + rod lenght 5.7" = 7.44" + piston compression height 1.562" = 9.002"

since standard small block chevys have a crank to deck height of 9.025" (un-plained or milled) then your piston should be .023" down in the cylinder at TDC.

Quench/squish is the area between the piston head/crown at TDC and the actual cylinder head its self. This area you want to be around .038-.048". Since your pistons are down in the whole at TDC .023" then you would be looking for a head gasket with a compressed thickness of .015-.025".

I would strongly recomend having the block properly decked/bored/align honed. In doing this it will give you a proper mating surface, and a true geometry for the deck and rotating assy. But this can also cause one bank of the block to be taller than the other (within a small range this is fine). Your best bet is to hold off on buying the head gasket until you have all the machine work done, and the short block assembled so that either you or the machinest can measure each piston/deck clearences and then from there decide which gasket you will need to go with in order to make all the cylinders within the targeted quench range.
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