deck height 3.4L

[StudlyCamaro]

anyone have a clue as to what the deck height is ... im wanting to play with some CR #'s and i dont have a clue as to what the deck height is

[phantom505]

That's a quetion we all would probably like to know.

I would do this... use a CR of 9.6, .060 gasket, and 28cc combustion chamber, and back calculate it.

[StudlyCamaro]

is that for a flat top piston?

[geoffinbc]

That wont work. Too inaccurate.

[RacerX11]

224mm is the blueprint deck height spec for all of the 660's.

Marty

[StudlyCamaro]

thank you

[GordSipko]

The 224mm number provided by RacerX11 is the distance from the crank centerline to the deck surface and I don't think this value will help in determining CR numbers.

Deck Height is normally considered to be the distance the piston sits above or below the deck surface of the block at TDC . Having this measurement and knowing the volume(s) due to configuration of the piston top (ie, dome, valve pockets, chamfer, etc) allows you to calculate a correction value for the clearance volume used in the CR calculation.

[StudlyCamaro]

yeah i realized that after i posted... i know that the piston wasnt 224MM from the top of the block on my spare motor.. anyone else know what it might be?

[RacerX11]

The deck height measurement I provided is very crucial to calculating compression ratio. This, along with crankshaft stroke, rod length, and piston compression distance determines the position of the top of the piston in relation to the top of the block. There is a spreadsheet archived somewhere on the main site that I put together that has all the specs and calculations for calculating CR on the various engines. You can vary all of the critical measurements and find out how they affect CR. This allows you to see what things like different rod lengths and head gasket thickness can do. I will look and see if I can find it.

Marty

[StudlyCamaro]

please do, im looking to see how thick of a head gasket i would need in order to use the stock pistons on my camaro and have the 3400 heads on the car, and not have an insanely high CR

[camaro_dakota]

yeah id like to know as well! I have a huge cam tho and i think i have no choice but to go to the dish pistons (because of possible piston to valve issues not sure tho)... if there is any way to use the stock camaro pistons with the flat top that would be awesome tho

[GordSipko]

The deck height measurement I provided is very crucial to calculating compression ratio.

Marty,

I don't disagree about it's usefulness for doing theoretical CR calculations, but you need to know crank stroke, rod length and piston dome height to be able to use it and the end result is still suspect. The 224mm number is a factory spec with a tolerance and if you're using spec stroke, rod length and dome ht, tolerances apply there as well and tolerances can stack up in very unexpected ways... Plus you still have to account for volume in the piston top. Domes reduce clearance volume. Valve notches and dish both increase clearance volume. Any amount of chamfer around the piston dome increases clearance volume.

The end objective is to determine the Clearance Volume used in the CR calculation. Clearance Volume = chamber volume + gasket volume + net block volume. The gasket volume can be calculated (because it's pita to cc), but both chamber and net block volume should be measured directly by cc'ing.

If the piston sits below the deck at TDC, cc'ing is very straight forward and net block volume will be a positive number. If the piston is sitting above the deck, then the piston must be positioned a known distance below the deck, cc'd and a calculated (bore area * known distance) gets subtracted from the cc volume to get the net block volume (and yes it will be negative).

This method accounts for piston configuration and the tolerances that exist in all components without having to know any component dimension or tolerance.


StudlyCamaro,

Deck height numbers aren't normally published and for what you are doing is only matters if the piston sits above the deck.

You can back calculate the total clearance volume as phantom505 suggested. Start with the specs for the lower end you are using. Iron head chamber volume is 53cc and the production gasket thickness is 0.035". This will let you get an estimate of the net block volume (which you were trying to derive from the deck ht). Once you have this, you can do the what if's with the small chamber head and get an estimate of the CR.

[Corpse]

The Block deck height is the earlier mentioned number of 224MM. Which is 8.736". Although, the GM info I have list 224MM, the IN values are not accurate, strange. I would not exactly go by the 224 number for anything. My GM manuals list 224 but, 3 of them have different IN values that do not equal 224MM.

Realistically, it is more accurate usually to Add stroke, rod length, piston compression height then find the deck clearance and work it into CC or CUI, then work in the dish/dome, head gasket and head numbers.

You are not going to get the real world number by calculating the mechanical compression ratio anyway. (Your cam among other things all have an effect) Realistically, to get the most accurate mechanical compression numbers, you would need to compensate for some more things.

Blowby, piston side clearance, valve losses, sparkplug air space, cam valve timing and duration, etc.. weird stuff.

The minimum specified Block Deck Clearance on a Gen II is .006 above. I dunno as for Gen III but it would be a little higher.

"if there is any way to use the stock camaro pistons with the flat top that would be awesome" - You could get them cut for valve reliefs but, that only goes so far and may weaken the piston as it is stock. How big of a cam are you talking? You can only go so large before you have interference with connecting rods.

Also, you may just have to go with a little less lift and a different duration (ie: more) and you may get almost as good results. or better, depends what you want in the end.

Here's a tip though: Always measure your own motor, do not go by what people post or what you see on the web. In the real world, unfortunately, things can be a bit off, always measure your own CC Volumes and such and make sure you are working with the right numbers first, before making a serious mistake. Scientific calculations are only as good as the numbers that are used.

-Dave

[StudlyCamaro]

im just trying to get a rough estimate.. and its pretty hard to take measurements when your motor is still assembled in your engine bay