[chrispicide35]

i just used a comp. ratio calculator and i want to make sure it is right.

454 .060 over
standard stroke
These pistons:http://www.summitracing.com/parts/SLP-L2349F60/
781 heads. 118 cc i think.. does that sound right?
.039 Fel Pro head gasket.

below is a screenshot of the results, i think it's right.. let me know if it is.

 

[70-SS454]

If you do the math 2 & 3 times, and have all of the variables correct....it should be correct... Why not create a spreadsheet...???

 

[Tom Mobley]

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

that compression is way too high for a pump gas engine. At least a full point. think in terms of 9.5:1 with a typical street cam. 9.0 is better. Look for a piston with about half that much dome.

I used 4.31, 4.00, 4.4, .038, 118, 18cc dome, .020 deck., get 9.3, perfect.

 

[Tom Mobley]

that calculator you used is ignoring deck clearance or using some undisclosed assumed number. same with the head gasket.

 

[chrispicide35]

that calculator you used is ignoring deck clearance or using some undisclosed assumed number. same with the head gasket.

Deck clearance means what?? how far the piston is in the hole? because that wasnt available in that calculator so it wasn't taken into consideration. i will have to find out how far in the hole they are because that should bring it down some. head gasket figure is right, they have a .039 compressed thickness. they are these: http://www.summitracing.com/parts/FEL-1037/

that compression is way too high for a pump gas engine.Look for a piston with about half that much dome.

The short block is already together. the guy i bought it from said i was 10.5-1. the motor got taken apart and cleaned from a cam failure a few years ago. the last time it was in the car it ran fine on 93 octane, Sunoco ultra.

I used your calculator tom, just guessing deck clearance and playing around with a reasonable number it brought it down one whole point, see below. I will have to find out how far in the hole the slugs are.

 

[Tom Mobley]

where did you get that .045 deck? it'll be between .010 and .020 unless somebody has milled the block to get zero deck, in which case the CR will be higher.

the head gasket has two dimensions that matter, diameter and thickness. I'd guess their calc is using the bore diameter. Not likely they're ignoring it or they wouldn't ask the thickness. they probably are ignoring the deck clearance. Use the one I posted for better results.

assuming some number like .045 isn't realistic.

 

[Busted Knuckles]

I used Ross pistons' calculator, come up with 10.7:1 assuming .005 in the hole and .035 compressed gasket. Summit's listing shows -30cc dome, which would be a big dish, so I assume they're wrong, it's a +30cc's dome.

 

[GOSFAST]

Hi Chris, with unmilled decks and the numbers you have listed you will be at 10.1:1 nominally!

This would be with a .020" (nominal) deck clearance!

We do have this C.R. running satisfactorily here on 93 octane. The added "Ethanol" (10%) in our pump-fuel helps control the detonation level!

Slight variations in the numbers will change the C.R. minimally!

(Add) You will most likely have inteference with those pistons (domes) and the chambers in the oval-port heads? Some "massaging" will be required!

Thanks, Gary in N.Y.

P.S. Back in the later '70's and early '80's, G.M. was using the original LS-6 short blocks with the C.I. "open-chamber" heads (118 cc) installed and selling them as "Pump-gas Specials" over the counter at the dealers! These were rated at a 10.25:1 C.R. Very similar to all your dimension. The head gasket thickness was slightly less at .022" (nominal) using a "steel-shim" piece.

 

[Tom Mobley]

I get it 10.4 with numbers given. 4.31, 4, gasket 4.4, gasket thickness .039, deck .015, chamber 118, dome 30. Heads have likely been milled in the past considering their age. 10.4 engine will ping itself to death in short order, that would be a premium gas engine when premium was 100 octane, not 91-93. If those are solid dome pistons I'd recommend cutting off half the dome by volume, end up with a dome CC around 15cc.

 

[chrispicide35]

where did you get that .045 deck? assuming some number like .045 isn't realistic.

Your right.. i just threw that deck number in as an experiment. i wanted to see what the .045 would bring the CR down to compared to the calc in my first post. it dropped from 10.88 to 9.87 just an experiment is all.

knowing all the numbers i have are correct, (except my actual deck which i don't have ATM) using a conservative .015-.020 deck, every CR Calc i have used says it will be right around 10.5:1 which is what the guy i bought the motor from said it was.

I will get the actual deck the first chance i get, maybe tomorrow after work. i cant just walk out the door and check it as the car/motor is across town in a garage i rent.

As said earlier this motor ran before and ran fine on Sunoco 93, we also have 100 available at the pump at some locations. there are some variables and some leeway i could always use a thicker head gasket.



P.S. this whole thread started because i wasn't sure i was doing the Comp ratio calculator right ( not weather the motor will run or not or how well)
At first using the calculator i didn't even know what to put in for the numbers, i had to look all those up.. bore, stroke, gasket, dome etc.

P.S.#2 Thanks guys for all the help... i will post back tomorrow or Saturday i should have the actual deck number by then. supposed to be in the fifty degree temps this weekend. :hurray:

 

[chrispicide35]

Summit's listing shows -30cc dome, which would be a big dish, so I assume they're wrong, it's a +30cc's dome.

They are definitely dome not dish, so summits site has a type-o it should be a + not a -. you are right sir

 

[Bill70]

I would think your cam selection would influence whether your CR is too high or not. I calculated mine at 9.9:1 but becuase of my cam I only get 170 psi cranking compression. Car runs fine with 36 degrees of timing and 91 octane. Have even run 87 on occassion. Can you run a compression check?

 

[chrispicide35]

Can you run a compression check?

Not At the moment..the motor is in short block form. I did not get a chance to get the deck number today i will be going over there tomorrow and will update in the evening.

 

[chrispicide35]

UPDATE:

Well i got the deck number today and it is .020 so it looks like my comp ratio will be 10.4:1