[mrsuds]

I've been doing some research on a street 454 buildup. My problem is that the math regarding compression ratios does not add up. Here is what I'm thinking about so far.

454 4 bolt main bored .60 over
Eagle cast crank and "I" beam rods upgraded with ARP bolts standard length.
Speed Pro H581CP60 pistons (summit has the dome at +33.00 cc or .340 dome)
Edelbrock aluminum RPM Rect port heads 118cc chamber
Edelbrock RPM airgap intake
Thinking about a Lunati 60212 cam but will pass it by UDHarold before I order anything.
I'd like to keep the compression ratio between 10:1 and 10.5:1

The rest of the parts are still up for discussion.

I ran the numbers thru Ray Kelly's DCR Calculator and am coming with a compression of 10.8:1. I researched the piston on this site and on the Net and everything I'm reading states that the piston with that combustion chamber should give me a compression ratio of closer to 10:1.

Can somebody please check that I'm not doing something wrong? I think the overbore has something to do with it.

Mark

 

[77 cruiser]

I come up with 11.07 with zero deck & .04 gasket.

 

[GoatDr]

I get 11.1:1. That won't be any good on pump gas with iron heads. You probably need about a max of 10 cc dome to get to get to 9:1.

 

[blue66]

For not much more you can get a probe forged....9.5:1 piston. /118cc
Similar to the old TRW but with better valve reliefs and lighter.
The piston you have has too much dome for your application.
http://www.probeindustries.com/Pistons/Pistons_FPS/fps_chev_454.htm

 

[mrsuds]

I can get a whole balanced Eagle rotating assembly from a buddy for a good price but that is the piston that comes with the kit. I could buy the kit and a new set of pistons but that would defeat the whole balanced thing.

Anybody else have any input. I'm all ears..

 

[blue66]

I get 11.1:1. That won't be any good on pump gas with iron heads. You probably need about a max of 10 cc dome to get to get to 9:1.

He doesn't have iron heads.

If you pay particular attenetion to quench, and cam design you could probably get away with 11:1. If this is gonna be a driver with a real mild cam, you may not. Also depends on vehicle weight, gearing etc. You could polish your chambers. That will help. Thermal coat the chambers and tops of the pistons, etc.etc. What is your deck height?? What thickness head gasket? And have the heads been cc'd, because published numbers don't always mean much. If your gonna run that close to the edge it will take some planning. And a good cooling system. Can it be done...yes, I am assuming your looking for the 10-10.5 for pump gas. Also what is the highest octane available to you at the pumps?

 

[Harold Sutton]

There are a couple of things missing here. What is the real, measured, deck height and what is the compressed thickness of the head gasket? Those two things will affect the compression quite a bit too. You also need the "exact bore" of the cylinder. If it's 4.315" or 4.3125", you need that correct to the thousandths also. The head gasket volume figure in those books may be a little off as the gaskets are usually a little bigger than the bore diameter of the cylinder. Lots of little things that add up. I would think that a (11.2-1) figure would be nearly right on if the block is zero decked. Normal deck heights would be lower than this though by probably .020".

 

[mrsuds]

I don't know the deck height. I don't have any of the parts yet. The only things that I can get quickly is the block and rotating assembly. The block will have to be bored as it is currently 30 over but needs to have the cylinder bore cleaned up. Plus the block has to be decked. I can probably get away with a .039 Felpro head gasket. I looking for a large motor with good street manners. Based on what I'm reading the pistons are getting close to pump gas limits. I spoke with a machine shop and they might have the pistons I would need. I think he said H693cp60, I might be wrong on the number. I will run the numbers to see what I get.

I also ran the numbers based on everything else I would need to buy to build the block and I'm getting real close to a GMPP crate motor or I have seen some good deals on ebay. I won't get the Aluminum heads but it would put me ahead of the curve.

This urge to have a big motor could get expensive.

 

[RB69SS396Conv]

I come up with 10.1:1 at the most likely un-machined deck height (.045"), 10.5:1 at stock deck height (.025"), and 11:1 at zero deck.

Looks like if you don't know the deck height, you're pretty much .... in the dark. You gotta establish that before you know where you're going to end up.

Personally, if it was mine, I'd shoot for just under 10.5:1 with zero deck height, if at all possible. To do that, you'd need to lop probably .100" off of the domes.

If you want to run it as it comes out of the box, looks like you need some different heads; or to do some chamber unshrouding or something. If you could lose 8cc of metal you'd be back down in the range you need to be.

 

[Augustboy2009]

Here are 2 engine compression ratio CALCULATORS. This may help you out.

This one...
http://www.csgnetwork.com/compcalc.html

or....
http://cochise.uia.net/pkelley2/crc.htm

 

[onabudget]

Need your deck height. It can make or break the combo. I believe they also have gaskets up to .075 to lessen CR if needed.

 

[mrsuds]

Okay, I found the calculations to determine deck height.

If I leave the block alone, assuming the deck is square and based on a 9.800" block height, I get a deck to piston clearance of .025".

If I deck the block, which I think it would need, to 9.780", I get a clearance of .005". I am fully aware that the dimensions can vary by several thousandths across the block.

Based on the above numbers, I just ran the DCR calculator and I'm 10.9:1 with a head gasket bore of 4.370 and a thickness of .039, quench is .044.

If I use a 4.540 head gasket bore and a thickness of .051 I'm down to 10.5:1 but my quench is .056 which I have read is not ideal.

Looks like all signs point to a smaller dome piston.

 

[mrsuds]

He doesn't have iron heads.

If you pay particular attenetion to quench, and cam design you could probably get away with 11:1. If this is gonna be a driver with a real mild cam, you may not. Also depends on vehicle weight, gearing etc. You could polish your chambers. That will help. Thermal coat the chambers and tops of the pistons, etc.etc. What is your deck height?? What thickness head gasket? And have the heads been cc'd, because published numbers don't always mean much. If your gonna run that close to the edge it will take some planning. And a good cooling system. Can it be done...yes, I am assuming your looking for the 10-10.5 for pump gas. Also what is the highest octane available to you at the pumps?

It would be going into a 70 Chevelle, 3900ish lbs, 4 speed w/ 3.73 gears. The best gas I can get around me is 93 octane. 10-10.5:1 would be the range.

 

[RB69SS396Conv]

Those pistons are almost certainly .020" extra down in the hole.

Don't assume ANYTHING. Don't believe the "specs" you read in the catalog for that, because often as not, they'll give the stock compression height instead of the actual compression height for the product. Assume nothing, measure everything, BEFORE it's too late to go back and change. You don't want to discover that you have to deck .045" off your block to get it to where you want it, which then requires customizing your intake as well.