Hope i have the right forum here. Need some info on a recently purchased motor. Block #14093638 (5.7) dated E263 (93?). Bored .010 over with Sealed Power H859CP10 pistons (2 valve relief with a dish, 12cc), the block has been decked to .000 piston height, .040 fel-pro gasket and the heads are 624's that have had extensive work done (2.02/1.60, screw in studs, comp springs 110lbs seat pressure with rotators removed, gasket matched porting and they have been magnafluxed and no cracks) It has a Comp XR258HR-10 cam no induction system basically a long block. My problem is the static compression ratio comes out at the 8.5 range and I was wondering if I had that right. I pulled the pan and heads and the motor is in excellent condition, the PO said there was less than 30 hours on the build and it looks that way he also stated the motor ran strong. Should I switch to vortec heads and if so would I need to change my push rods etc. The vortecs that are avalable to me have the Crane spring/retainer kit #10309-1 already so I am not worried about lift issues. I am wondering about compression with the decking to zero. Did i figure it wrong? I will be putting an RPM Performer and an Edelbrock 625 AVS on it.

 

I think 8.5 is about right for a 350 with dish pistons and the 76 cc chamber heads.

 

Thanks. That is what i keep on getting. Didn't the L98 vettes with the 624's have 9.0 to 1 compression?? With the zero piston height I would it would have at least that. I might spend the money on the vortecs but the previous owner said this motor made LOTS of power/torque with a carb setup the way it is.

 

8.5 is about what I come up with too, given what you are telling us. That's making the almost unmakeable assumption that the block is REALLY zero-decked to those pistons. AFAIK all of those in that series have the extra .020" of "rebuilder" clearance; which means, they would have had to take .045" off of it, more or less (mostly more) to get to zero.

I can't imagine how it would be possible to have 9:1 compression with those heads, unless "pop up" pistons were used. AFAIK the factory never did that to any motors that had those particular heads. In any case, that was the classic recipe every lop-eared kid built back in the 80s; yerbasic stock short block except with TRW "pop ups", 624/882/993 heads, usually too much cam, then wondered why it was slower than stock and spark-knocked like all hell.

If it WASN'T zero-decked, i.e. stock decks maybe "cleaned up" a bit, the CR might be as low as 7.8 - 7.9. Worst case, which would be the 80cc version of those heads (note also that putting in larger valves increase chamber volume anyway) with the full .045" deck clearance, you're down into the mid 7s. You won't ACTUALLY know the truth until you take it apart and measure.

That said, paired with a tiny cam like that, and however low compression, will give you a high-torque, low-RPM setup. BIG rush of butt dyno from a stop, NOTHING past 4500 RPM or so.

I can't think of very many worse head castings to spend machine work money on, than 624. Especially not with just jamming larger valves in them and then doing no REAL port work. ("gasket matching" is NOT port work, it is only eye candy to impress the uneducated, like chrome timing cover and valve covers, UNLESS all of the REAL port work was done FIRST). They were pretty much the worst of the worst in their day.

I can't find anything about Crane 10309-1. What springs does it include? What retainers?

The Vortec heads will outperform 624s, NO MATTER WHAT has been spent on them. By SO MUCH, you won't even think it's the same motor. I'm gonna guess, 50 HP AT LEAST. And more torque besides, due to the higher compression. Which, even assuming TRUE zero deck, will be in the low-mid 9s; 9.2 - 9.5. Entirely manageable.

Obviously you're new to all this. Let me let you in on a little secret: EVERY motor's seller will tell you "it ran strong". EVERY ONE. Do you honestly think they're going to tell you "this thing was a slug, that's why I'm asking so much for it"? REALLY?? What they won't tell you, is why they're selling it, i.e. why they're dissatisfied with it and why they're moving on from it. They ALSO won't tell you how much stronger it WOULD HAVE run with better decision-making, not least because they don't know; but also, because to admit they put together some piece of crap that they made some poor parts decisions on, wouldn't help their sales effort. Which is not to say that it DIDN'T "run strong", subject of course to that individual's idea of what "strong" is; only, that however "strong" it might run as it is, it might run AHELLUVALOT STRONGER with some changes.

Buy the short block. Let him keep the heads. Measure the ACTUAL deck clearance. Get the Vortecs. Make sure the spring/retainer combo supports the lift, which is MORE THAN a matter of the part #s. Try to get more seat pressure if you can: that series of cams needs 120 - 125 lbs on the seat to work their best, and more is better, up to the point that the valves and seats can stand it. Which if they're stock valves, best to keep it right around that 125ish range. If they're better valves then you can go for more seat pressure. But 110 really isn't "enough".

I'd STRONGLY recommend some other carb. The Holley 6210 would probably be the best choice.

What is this going in? Weight? Converter? Gears? Purpose?

 

Am I missing something as these pistons come up as a 1.425 in. compression height?
What's the engine stroke and rod length? I'm getting 3.75" with a 5.7" rod for that piston.

https://www.summitracing.com/parts/slp-h859cp30

 

I didn't look em up; but that would mean this engine is a 383. They're for a .030" over 350 block. Not .010".

Sounds like more and more of what the PO told you, doesn't add up. Although in this one respect it's in the positive direction. Still in all, inaccurate is inaccurate. If it really matters to you what you bought, do your due diligence. Tear it down far enough to see what you've REALLY got before making any decisions; since what you've been "told" is so clearly wrong.

What car is this going in? Weight? Converter? Gears? Purpose?

 

I couldn't find a 10 over piston with that part number. I went with whatever Summit threw out in a search. Everything from 20 to 60 over but no 10.
But the piston height carries over between all sizes.
And yes, it would be a 383 (give or take).

The Sealed Power catalog doesn't list a 10 over either.

https://www.drivparts.com/brands/sealed-power.html