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#11
Re: Calculating compression ratio
ddgonzal
Posted on: 2016/1/11 23:37
Quote:
if I use a centered dish piston will my compression go up?  
#10
Re: Calculating compression ratio
TexasMidget
Posted on: 2016/1/11 15:29
DD...I have the offset dish and the engine came with the H95 head which I will replace with the GX head. So if I use a centered dish piston will my compression go up?
#9
Re: Calculating compression ratio
ddgonzal
Posted on: 2016/1/11 6:33
There are at least 5 different factory A15 pistons, all with different dishes. Because A-series heads are all around 30cc, the dish is used to vary compression from USA 8:1 and 8.5:1 to JDM 9:1
* Centered dish shallow * Centered dish deep * Offset dish Also the shape varies to correspond the chamber design. The Offset pistons enable some quench without flattops. The H95 head is the only one with a larger chamber CC, so uses the smallest piston dish.
#8
Re: Calculating compression ratio
TexasMidget
Posted on: 2016/1/11 5:56
Ok thanks everyone. I will get a more precise syringe tomorrow and check the cc's again. Will report back later.
#7
Re: Calculating compression ratio
thaifrog
Posted on: 2016/1/11 5:38
I just plugged the figures into this calculator:
http://www.csgnetwork.com/compcalc.html and got 8.44 CR using the above figures. This is why i used the mazda flat top pistons when i did my rebuild, though it seems i ended up with too much CR.... Use the mazda pistons but machine off 1.5mm rather than 1mm and it should be about 10.5:1 CR
#6
Re: Calculating compression ratio
dvr1000
Posted on: 2016/1/11 1:46
By your calcs
Swept volume plus c/c volume (head only) plus gasket divided by chamber volume (piston and head) plus gasket A15 = 371.75cc per cylinder Chamber 29.57 + 14.79 = 44.36 Assume 1mm gasket = 4.5cc So 371.75+4.5+29.57 = 405.82 divided by 44.36+4.5 = 8.3 cr
#5
Re: Calculating compression ratio
TexasMidget
Posted on: 2016/1/10 15:57
Might need more help with this. Do I need flattop pistons? I will remeasure today.
#4
Re: Calculating compression ratio
ddgonzal
Posted on: 2016/1/10 9:10
am I doing it wrong? Says 8:1. That'll run like a dog ...
Piston dish may be too much
#3
Re: Calculating compression ratio
lamb_daiquiri
Posted on: 2016/1/10 8:21
CR=Vc/(Vc+Vs)
Vc = clearance volume 1.5oz in your case Vs = swept volume = stroke x cylinder area Just be consistent with units and you can use what ever units you want.
#2
Re: Calculating compression ratio
ddgonzal
Posted on: 2016/1/10 6:54
I like to google for a compression ratio calculator
Figure your head gasket thickness * 1.2 mm standard gasket * 0.6 mm high perf Nissan gasket * 0.8 mm Tomei gasket Your parts sound fairly typical, I'm gonna guess 9:1, good for regular fuel
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