i know that this has been discussed over and over, but this is something that i was wondering

about what is the average for the Deck Height in a 390?

and about what is the average Piston top volume cc's for stock pistons and .030 over pistons? (i called summit for my cc's for the pistons that i got from them i was told that they do not show it listed. so i am trying to do some around about guessing. or how can i check for myself?)

I guess 7cc that seems what i have heard before but i can not remember. the kit i got from summit is part number FEM-MKP601N-311

how could i check my Combustion chamber volume? I figured both the low and the high cc specs that i have.

for my C8AE-H heads i am showing 67-70cc

what would be to much compression. I have a set of felpro head gaskets .041 thickness, and i was thinking about going with the shim .018

I do not have my pistons and rods in my block yet so i am not sure of an exact deck hieght

i have been using this sight that Tracy had listed but i am still kind in the blue

 

I'd like to know too, maybe one of the compression wizzards can help me too. I'm doing a 390 std bore but using C8OE-N heads

 

Deck height is the measurement from the bottom of the rod to the top of the deck -- average for a 390 is 10.17 inches for all years. That's standard -- assumes no deck-work.

You might be talking about deck clearance, which is the distance from the top of the piston at the top of travel to the deck, which varies widely depending on year. Give me the year of the block and I'll let you know what was standard for that year (assuming all parts (rods, pistons, etc.) remain standard for that year).

mojo

 

i have a 63 block a 2U crank and the rods are 67 428 rods i do not know the rest of the number. (i do know that when i check them they were HP 428 rods)

 

WRONG!!!

Deck Height is measured from the center line of the crankshaft main bearings (not from the bottom of the rod?)

And the clearance your talking about is known as Piston to deck height...

The Easiest way to measure your Deck height is take the measurement of the block from the deck to the main cap saddle and add the thickness of your bearing and 1/2 the O.D. of your crankshaft main= Block Deck height!!

PS. But it real hard to do, If you dont have a Height gage and a granite table at home...

Russ

 

Taken straight from the diagram on page 39 (and the numbers from page 38) of Christ's book. And, by the diag, when the piston is at tdc, the bottom of the rod is in the middle of the crank. Additionally, d = 'deck clearance' by Christ's definition, and I did say "might".

I'm not just making this up as I go. Argue with Christ, I guess; I think we're arguing semantics.

mojo

 

Note how that drawing is layed out. What they really do, is go from the midpoint of the stroke, to the cylinder block deck. This is your deck height. The fact that the bottom of the rod happens to be at the midpoint of the stroke in that particular drawing has nothing to do with it. With a shorter stroke, the bottom of the rod would be farther down, and with a longer stroke it would be above. Also, the center of the stroke circle is always equal to the crank centerline. So, the distance from the crank centerline to the deck, is your deck height.

Trust me, the bottom of the rod has ABSOLUTELY NOTHING to do with it. I think they could have layed out that drawing in Steve Christ's book a little better so as to be not as confusing. It just so happens that in that particular drawing the bottom of the rod is at the centerline.

Oh, on the original compression question:

Assuming 70cc combustion chambers:
.018" shim head gasket = 10.68:1
.041" Fel-Pro = 10.03:1

I highly doubt your C8AE heads will be in the 67-70cc range. I have a set of D2TE-AA's, that are supposed to be 68.1 - 71.1cc. The machine shop said they came out to 73cc. Your best bet for CC-ing heads to go to a machine shop and have them do it. They can CC heads in their sleep. Besides, the calibrated buret and stand costs about $100 if I remember correctly.

Take 'em a piston too and have 'em see how many CC's the valve reliefs take up too. After you get the head and piston numbers, then we can nail down a fairly close number. Then, put a piston and rod in and measure deck clearance. Then, we can give you an absolutely correct number for compression, no more of this guesswork.

 

Brandon,

I agree that the best thing is to get the measurements done at a machine shop. The pistons are probably around 10 cc valve reliefs. If your block deck hasn't been surfaced I think your pistons will end up around .012 below. You will be able to get a good measurement on this when you assemble. You do need to get a measurement on the heads...if they were to measure less than 70 cc then the .018 gaskets will probably put your compression too high. I'm no expert...I think anywhere from 9.5 - 10 is optimum....you might push it to 10.5 but I think anything beyond that just isn't good for a street machine with today's octane gas. Again, that's just my opinion.

Good Luck!

Tracy

 

MoJo, I wasnt picking on you, or didnt want it to sound like I was.. I dont own a Steve's Book even tho I know there's some good info in there... But my Dad taught me how to check deck height back 35 years ago...And since we were both Machinist..His shop was well equipt with a couple of Granite Tables and plenty of Measuring Tools.. Including a Valadex Cordination Table..and air probes for mearsuring Hole Diameter's down to the Million's...

Anyway just wanted to say, I wasnt picking on you..and I think Kurt put it in a way most people could understand...

Russ

 

i had to have the head shaved 10 so that would more then likely boost the comp up even more.