posted 05-23-2002 11:55 PM               

With 230 pistons on a 250 crank, the pistons will hit the head (0.140 above the height of the 250 piston).

Of course, all said and done, you've just built a 250 (since this was the only difference anyway).

If you really want to go nuts, try the 292 crank in your 230 block. This, however, takes special (non-stock) pistons, plus the rod journal size is 0.100 larger than the 230/250 crank.

Greg

posted 05-24-2002 02:39 AM               

5.700 for 194,230,250 rods &6.760 +/-.003
storke 194,230 3.250 250 block 3.530 difference Being 0.28 piston compression height 194,230 is 1.795 250 is 1.655 difference being 0.140 Hope this helps
}[oooooo]

posted 05-24-2002 10:28 AM               

As for the original question, have you tried the block casting number against the list on this site? Failing that, how about actually measuring the stroke on the engine you have.

posted 05-24-2002 02:26 PM               

If you have the crank out.... well, I can't think of any "good" way to do it. Anybody else have some good ideas? For this exercise, you only need to be accurate to 1/8" since the 250 is 3.53" stroke and the 230 is 3.25" stroke. Maybe lay the crank in the block and use a large outside caliper to measure the difference in stroke to a fixed point on the block oil pan rail.

Alternatively, you could measure the compression height of the pistons you have and infer the stroke from that.

230 - 1 51/64 (1.797")
250 - 1 21/32 (1.656")

posted 05-24-2002 03:24 PM               

Twisted L6s beaten V8s Ya gota luv it

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NovaMan/Twisted6/Larry

posted 05-24-2002 06:50 PM               

Do you know why the 230 pistons didn't have the dish? I'm thinking the engine and combustion chamber size is the same, so by just changing the compression height of the pistons (to correct for the stroke), the non-dished piston should have a higher CR.

What gives?

Thx,
Greg

Oh, by the way, glad to hear bbf557ci figured out that he really had a 250.

posted 05-25-2002 12:29 AM               

First is that the '67 engine could have more tired rings or valves which do not seal perfectly. I would guess this is probably not the cause of the difference in this case.

The more likely answer is camshaft timing (overlap). The one lower PSI engine may have a cam that has just enough more overlap to allow a little of the pressure to leak out at low (cranking) rpm. I would expect to make that back up at higher rpm if all your other components work together to allow an increase (intake and headers are appropriate for the rpm ranges in which you wish to operate).

That is the primary reason "they" say that pressure differences between engines is less relevant than pressures between cylinders in the same engine. You want all cylinders in a given engine to be within 10% of each other, and ideally there would be 5% or less difference between any two cylinders.

Hope that helps,
Steve

posted 05-25-2002 01:21 AM               

My 1975 250 reads 160 PSI cranking compression, but I suspect that has to do with a wimpy cam with no overlap. It kind of figures that the 67 would have a better cam then the 79.

In any event, I'd scrap the integral head. Not much potential (except to crack )

posted 05-25-2002 05:08 PM               

Ps Sorry I didn't have a better answer for you on that.

posted 05-25-2002 08:35 PM               

It must be related to the relative drop in CR due to lower displacement, but with the same combustion chamber size. I suppose it's possible that the dish on a 292 piston is even more pronounced than a 250 for the same reason (since, as you said, the CRs are about the same across the line).

Well, I just had to check, so here's the approximate deal. A 250 with an 8:1 CR would become a 7.4:1 CR with 230cid if the head and pistons stayed the same. A 292 with the 250 pistons and head would have a 9.3:1 CR.

I guess that explains why GM did what they did.

Have a good Sunday,
Greg