Thread: dome volumes and comp ratios

dont know if this will help some people with comp ratio calculations, but i have been majorly confused last couple of days with different threads quoting different dome volumes for the standard pistons made by nissan

need to know for clarification the dome volumes (from anyone who has measured these):
*16ve pistons
*16ve N1 pistons
*20de pistons (UK)
*20de pistons (US)
*20det pistons (gtir)
*any type of off the shelf custom piston

by using the quoted comp ratio from nissan for each engine, i have got some ballpark figures:
US 20DE (9.5:1) = 2.9cc dish
UK 20DE (10:1) = 0cc flat
JDM 16VE (11.1) = -11.5cc dome
JDM 20VE (10.4:1) = -3.2cc dome
JE custom 87mm pistons (8.5:1) = 14.3cc dish

using following calcs:
Bore = 86mm[3.39in]
Stroke = 68.7mm[2.7in](VE), 86mm[3.39in](DE)
head volume = 41.8cc(VE), 46.5cc(DE)
gasket bore = 87mm[3.43in]
gasket thickness(compressed) = 1.09mm[0.04in]
deck clearance = 0.5mm[0.02in]

anyone want to put these values in to their own calculators and clarify them? or correct me on some figures?

Steve

I just tried to find out the CR of a standard USDM SR20DE using your numbers and I got a compression ratio of about 37.2:1

CR = Volume with piston at BDC ÷ Volume with piston at TDC

CR = (piston dish + cylinder swept area + headgasket area + head volume) ÷ (piston dish + headgasket area + head volume)

CR = (2.9 + 1998 + 5.8 + 46.5) ÷ (2.9 + 5.8 + 46.5)

CR = 2053.2 ÷ 55.2

CR = 37.2

I haven't had the best reputation for doing math recently though, so I'm sure I'm missing something.

Lol, I know what I did wrong. I used engine displacement instead of one single cylinder displacement for swept area. Let me do it again.

CR = (2.9 + 499.5 + 5.8 + 46.5) ÷ (2.9 + 5.8 + 46.5)

CR = 554.7 ÷ 55.2

CR = 10.0

Quite close, but not dead on. Maybe I'm not taking the deck clearance into account when I should?

Not quite, Nissan advertised compression ratios are not exactly what they say.

16VE pistons come to about -6.8cc
20VE and DE pistons are not that different, if anything VE have more dish because of valve notches
Deck clearance to be about 0.05mm, not 0.5mm

hmm, using -6.8cc as the dome volume brings 10.6:1 thats quite a bit off the advertised

anyone else with any evidence? ie. measured volumes

Steve

I have a 9.5:1 DE piston right here on my desk. Just eyeballing it and doing a little math it looks like a dish of about 66mm (6.6cm) in diameter and 1mm (0.1cm) deep which gives a volume of about 3.42cc for the dish instead of 2.9cc like you have.

Use that and you get 9.96:1 compression ratio. =(

I'm not helping am I? =/

thanks for checking Ben, anyone else?

realised a few errors in my sheet, probably still more
but came up with the following list


20DE US 5.50cc
20DE UK 2.24cc
16VE -8.66cc
20VE 4.58cc
16VE N1 -6.52cc
20DET 15.16cc
20VET 13.88cc

Steve

any updates? final numbers?

Sweet. 12 lbs of boost and your set!