Compression ratio of hybrid JZ engines.

[2JZR31]

More

http://www.supraforums.com/forum/sho...chamber+volume

http://www.motorolacup.com/img/tif/ToyotaSupraTurbo.pdf

I'm not stating the claimed CC's as there are so many slight variations in my findings.

[2JZR31]

More

http://www.clublexus.com/forums/show...light=GTE+Head

[1jzracing]

cheers is some interesting stuff there, they like to calc things the hard way

its all verry well but those guys on that forum are all using the factory CR to work backwards and estimate things like heads and pistons volumes etc or the CR change with different thickness gaskets

i saw claims of everything from 40cc to 44.5cc for 2jz- gte and ge heads

one claim was that they were near identical, my bet is all 3 are near identical!!!

i have some slight updates to my calcs, the HG hole diameter is in fact 87mm, 1mm larger than the bore and is more like 1.3mm compressed not the 1.2mm i was using so the gasked vol may be 7.8cc

plus if you want to get REALLY pedantic about it, there is also 0.47cc between the piston and bore above the top ring ..... but thats at room temp

this still gives the 1j CR of more like 8.7:1 ..... its getting closer if i kjeep it up ill get it down it to 8.5:1 yet

still no one with actual measured 2j head vol's ??

[2JZR31]

There were a few claims based on supposed "common knowledge" etc. But yeah, I would put money on it being 2cc either side of 42cc, same as the 1JZ head. The highest of 44.4cc and lowest claimed figure or 40cc would seem to support this. Either way a 2JZ headed 1JZ is not going to cause any stupid CR probs.

[mic*]

Total of above measurements for 1J head & 2j piston;

=63.37cc

63.37cc X 6 (cylinders) = 380.22cc

380.22cc X 8.5 (C/R i beleive?) = 3231.87cc

Maybe the 2J head is a touch smaller. Considering you (1Jracing) have got closer and closer to the Toyota engineers claims, if you just take their word for it, you have all the other variables to work it out...

EDIT: Sorry i jumped the gun a bit there? The 13.whatever cc for the piston is is a 1J block and im sure its not in a 2J.

[jzk25]

The engine is still in the car and it's resting in the other shed while I work on a Subaru. I will have a go at it when I get it back in the big shed.

[chris davey]

5 rep for you when you get some data mate!

[1jzracing]

i dont know what you calculated there!! but its not a valid calculation for anything

CR = (Vswept/Vcombustion)+1

where Vswept = displacement of 1 cylinder
and Vcombustion = volume above the piston at TDC

that 13.8cc piston volume is identical on BOTH blocks as the 1j and 2j pistons have exactly the same crown height

ie. both pistons come exactly flush with the top of the block when fitted to a 1j and im sure you would find the same would apply fitted to a 2j block

we still have no idea what comp a 2j turbo head on a 1j will be

or even MORE interesting is the CR of a 2j-GE head with its biger ports and valves on a 1j bottom end!!

[mic*]

Well what i calculated was this;

The combustion volume (of a 1J head & effective 2J bottom end), by adding up your measurements = 63.37cc

I think its the same thing, but i would write; CR = Vswept : Vcombustion,

The CR (I think) is 8.5:1

Therefore 8.5 / 1 = (disp of 1 cylinder of a 1J head on a 2J)cc / 63.37cc

... 8.5 / 1 = (disp of whole motor)cc / 380.22cc

...(disp of motor - 1J head on 2J) = 8.5 X 380.22cc = 3232cc

...disp of 2J = 2997cc

Thats why i said maybe the 2J head is a bit smaller???

Im sure there is probly something wrong there. Was just bored and started playin around with your numbers...

[1jzracing]

CR = vol above the piston at BDC divided by the vol above the piston at TDC

which is the swept vol PLUS chamber vol divided by the chamber vol

the displacement cant change!

[Enchanter]

Bringing this thread back from the dead.

Im researching the data I need for custom pistons to raise my CR, so I measured the volume of my 2jzge combustion chamber today. It came out at 43cc.

How does everybody else do this, it was a PITA !!

Oh and does anyone know of a thinner HG that may be suitable for raising the CR a touch.

[EldarO]

thinner HG/machining a bit of meat off the head will raise the CR, just be careful how much is done, as it causes drastic differences.

Eldar.O.

[Enchanter]

I would be willing to bet the only volume difference in all of the engines are the pistons, (and the stroke 1j vs 2j). The 2jzge pistons are also flush with the top of the block. ---> http://i21.photobucket.com/albums/b2...07oct06011.jpg
I did have some trouble measuring the volume of the combustion chamber due to the kero leaking past the valves even after I had tried to seal them with bearing grease so the 43cc could be very slightly over but definately not under.

So how much do I need to shave off the head to acheive 11:1 CR using the standard HG (same part no as turbo) knowing the factory CR is 10:1 ?

I will need to be sure Im not going to bananna the valves but custom high comp pistons are looking too scary to my wallet this year.

Another alternative may be using different stock pistons such as 1jzge or a VVTi 2jzge and possibly use an off the shelf thicker HG to adjust the CR if needed.

Anyone see any flaws in this ?

Edit: the HG cant be the same part number ge vs gte (REPCO computers told me it was). My ge one measures only 0.3mm thickness so its volume is only about 1.8cc

[gianttomato]

Can confirm the 2JZGE combustion chamber volume in the head is approximately 41-42mL, as measured with a 20mL syringe, turpentine and a sealed perspex top face. I also saw a pdf file for the American Production Car series IS300 2JZGE VVTi - its comprehensive spec sheet also made mention of the 42cc in head combustion chamber volume. Unfortunately, I lost said file in a hard drive crash.

Shaving approx 0.8mm off the 2JZGE head brings CR up to 10.7:1.

Here is a comparison between the 2JZGE non VVTi (left) and VVTi (right) pistons.



The VVTi piston has shorter skirts and is considerably lighter (384 vs 356g). Compression height is identical. As you can clearly see, the flycuts are much smaller, and the noise is that lift is much less than the non VVTi motor. I will eventually check and confirm.

[Enchanter]

The VVTi looks at a glance like it would be a lower compression even though Im pretty sure it higher

Do we know if the VVTi head combustion chamber is the same size as the non VVTi ?