Thread: 20V + 16VE pistons CR

Hi,

just measured my 20V head and 16VE pistons, results below:

chamber volume: 43,5cc
gasket volume: 7,05cc (assuming it is 1,2mm compressed, 86,5mm bore)

(volume of piston 2 wall clearance to the first ring) MINUS piston dome: -6,1cc

swept volume, as always, 499,6cc

So, (499,6+43,5+7,05-6,1)/(43,5+7,05-6,1) = 12,24 CR

All data except swept volume and gasket volume is measured with water by myself. Measured many times to be sure. Gasket thickness 1,4mm uncompressed. Thinking it is 1,2mm compressed.

Anyone stated 13,6 CR VE with 16VE pistons???

BTW, I think chamber volume is the same for old-school SR20VE.

would be nice to see if someone can dismiss this? as it goes against everything i have heard about the 16VE pistons i always get it will be close to 13:1 in a 2.0 :S
thy werent N1 pistons were they just regular 16VE pistons?

All CR calculations I saw, based on 11:1 CR in 16VE engine.
But who really measured 16ve CR? Who really measured 20ve CR?
I really want a discussion here...

After some chamber job, chamber volume will rise, so I think CR will come to desired 12:1.

BTW, SR16VE piston laying in chamber gives 4,5mm piston2valve clearance. Add another 1,2mm gasket height, and we are getting 5,7mm valve clearance at TDC!

i agree with you would really like to see some discussion about where the figuers used for 13:! compression ect come from.. i have a set of 16VE pistons waiting to go for work i want 12.5:1 or around that.. so at the moment i either need no work, or 1mm taking of the top and the notches working 1mm deeper i would really like to know before i spend cash on the pistons only to end up with them being usless..

Exactly, the figures were taken from published factory spec and not measured. The factory specs are probably rough estimate. People then take those numbers and do a simple reasoning like if A=B and B=C then A=C. It's probably wrong but I guess it's close enough.

I doubt anybody will come up with the same compression ratio for the SR16 piston as you. Most don't take into consideration the piston clearance volume. I commend you for doing so. I have also seen figures for the combustion chamber as 41cc to 42.5cc. The head gasket volume might be different depending on the type. For the regular graphite VE head gasket, I got .9 to 1.02mm compressed gasket thickness around the fire ring.

so sr16ve pistons in a sr20ve will give you 12:1? im confused im hearing so many different numbers

I measured combustion chamber many times before to post this information. The combustion chamber including SPARK PLUG volume (~0,5cc between electrodes). Remember it is 20V engine, not usual 20VE. But I think combustion chambers are the same. Maybe I'll have an opportunity to measure standard VE combustion chamber of another engine I'm help to tune, but I don't know when I can do it.

Guys here have measured standard 20VE CR and they came to 10,3:1, but I don't know the actual numbers. I will ask them if they have that numbers.

Which piston clearance you mean? Piston to deck clearance? It is 0mm in my engine.

Anyone takes in account piston-to-bore-to first ring-clearance ???

And the headgasket is 20V metal-type.

Yes, I meant the piston to deck and ring land clearance(1st compression ring to piston crown). I believe you are the only one taking them in to account.

I heard a very accurate way to measure compression ratio ,but time consuming, is to assemble the engine with the head on the block. With the piston placed at tdc and sparkplug removed, cc the combustion chamber through the sparkplug hole. Fill the chamber up to the first sparkplug thread. By then everything is taking into account.