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post #1 of (permalink) Old 08-08-2001, 02:04 AM
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350 heads on 305

Hey all ,
I snagged a motor out of a mid - 80's caprice for " dirt cheap". It is a 305 and am aware of it. Was planning to freshen it up to put in my cj5 to at least get it on the road. As far as I know this engine is factory and has never been worked on or gone through. As I tore it down to start an over-haul I noticed that the head gasket bore is larger than the cylinder. So I measured -4 1/8 " on the gasket but only 3.75 on the cylinder. Then matched the gasket to the heads and it seats up to the egdes of the combustion chamber.

Is it possible that this engine came from the factory with 350 heads on a 305 block? The heads are the 882 series. My question is, does it give less compression to keep these 350 heads on 305 block than to go with matching heads?
Thanks all,, I've never seen this on a factory engine before.

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post #2 of (permalink) Old 08-08-2001, 07:21 AM
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Re: 350 heads on 305

882s were only used on 350s and 400s. Somebody swapped them on there.

'70 CST Blazer, 350, SM465, NP205.
'87 Suburban 4X4, 350, 700R4
'01 GMC 2500HD, Duramax/Allison
post #3 of (permalink) Old 08-08-2001, 11:38 AM
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Re: 350 heads on 305

As far as the head gaskets, they are all made to be used with the largest bore for a smallblock, which I beleive is 4.125. At that point, the cylinder walls are a little thin for my taste. They are made that way for ease, because rebuilds are always .030 over bore. Otherwise you would have about 20 part numbers for the same head gasket.

As far as the heads, putting 350 heads on a 305 will lower the compression, due to the larger chamber. This is the OPPOSITE with 305 heads on a 350, but 305 heads usually kill what little flow you had, due to the smaller valves. If you have 882's, I would have them checked for cracks, then put 202/160's in them, and go. Alot of guys are using the vortec heads now, and they are cheap, and give alot of go, but also requires a plumbed EGR, and a special intake for the new 8 bolt pattern. Edelbrock sells all the intakes, and you can get a set of heads for about $500 bucks.


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post #4 of (permalink) Old 08-08-2001, 12:25 PM
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Re: 350 heads on 305

I've got a set of 305 heads that have been rebuilt. If your interested in 305 heads, send me a private email. The intake valve size is 1.84", exhaust valve size is 1.50" and combustion chamber measures 60cc's. Usually the 305 piston has about 12cc of dish volume. Using 60cc heads with 12cc dish pistons should get the 305 compression ratio close to 8.8, which should run fine with 87 octane unleaded gas.

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