7AGE

[mooreofit]

dont let that discourage you, theres a lot of good info in there.

[dr.occa]

+1 with alan.

just checked out your formulas page. much more to the point than my Porsche reference pages; 3 pages of explanatory calculations and then the formula examples...

[nomuken]

So, I did some math
Was quite stoked about the results. Probably I should re-think some things before starting an 7AGE engine!

So we all know that static compression is

[(Pi/4) x Bore^2 x Stroke]+ Vc
--------------------------------------
Vc


With VC being the clearance volume. So Vc stands for the combustion chamber volume + volume of the headgasket + (or - if domed) the volume of the piston dish + the piston to deck clearance volume. So let's find a few values. Correct me if I get a value wrong!
Combustion chamber: 37cc => 37000 mm3
Headgasket: [(Pi/4)x82^2x1mm) => 5281 mm3
Piston dish: 9.4piston source:club4ag => 900 mm3
Piston to deck: [(Pi/4)x81^2x0.3mm) => 1546 mm3

So VC for a standard 4AGE headgasket with 1.0mm compressed height, 9.4:1 dished largeport pistons and a pretty standard largeport head results in VC = 44727 mm3

So CR is:

[(Pi/4) x 81^2 x 85.5] + 44727
-------------------------------------
44727

CR = 10.85 : 1



With 10.3:1 hi comp pistons, you'll have a dome volume of -3650mm3. This will result in:

CR = 11.96:1 (still with a 1.0mm 4AGE compressed headgasket and the largeport head)

Please correct me if I got a value wrong or missed something.

[Sam-Q]

thats pretty neat however a compressed head gasket is around 1.2mm and also the answer relies upon measurments from club4ag, which is a great source of completely wrong info at many times. Also the 9.4:1 pistons have a 18mm press fit gudgen pin which you can't use as the 7afe engine has a 20mm press fit pin.

For your 10.3:1 pistons I get 11.3:1, hey change your calculations to suit the 1.2mm head gasket and see how your figure compares to mine, I think it might be really close.

[nomuken]

HI Sam,
but your calculations rely on the CR that was advertised by Toyota. I don't trust that info's either
The only data I took from club4AG is the piston dish/dome. HG values, combustian chamber and deck clearance was all calculated or measured.
With a 1.2mm compressed HG thickness my calcs result in 11.68:1 for the 10.3:1 pistons. The reason why I chose to take 1.0mm HG thickness in my previous calcs was that Felpro states in their info's that their HG is 0.04" thick

I wouldn't run 11.68:1 on stock ECU. But I can always trim the ignition advance under low rpm and partial/full load with my Haltech to avoid detonation.

[Sam-Q]

yeah neither do I, hehehe

It would suggest that the Felpro is thinner then by 0.2mm.The compression is getting pretty high so I suggest the OEM gasket.

[mooreofit]

puting a g head on an fe motor will drop the compression ratio to around 8.5-1 unless the g pistons are reused. the fe cylinder head has a smaller combustion chamber.


all those numbers are making me dizzy.

[nomuken]

puting a g head on an fe motor will drop the compression ratio to around 8.5-1 unless the g pistons are reused. the fe cylinder head has a smaller combustion chamber.

Slapping a G head to an FE block without changing pistons,... will result in an 8.9:1 so perfect for FI

Edit, just to be complete, redid the calcs.
7AFE Block complete as is + 4AGE head complete as is + 4AGE headgasket => 8.8:1
7AFE Block complete as is + 4AGE head complete as is + 7AFE headgasket => 9.1:1


My goal is to have an 150rwhp NA 8k-8.5k rpm everyday driveable 7AGE. This will require some work better rods, pistons, balanced crank, ported and polished head, cams, ...

[mooreofit]

i would say 10.5-1 is a better ratio for boosted application.basically all a turbo is doing is raising the dynamic compression ratio anyways.so starting off with a higher static ratio has more benifits than negatives.

i did the math when i put my first turbo on my 4afe and at around 8psi i had a dynamic comp ratio of around 15.0-1

basically it all comes down to how much timing you can run at wot. you may gain 2-6* of timing droping from 9.5 to 8.5 but is it worth the compression loss its up to you. also if you plan on running certain cams this may change the dynamic ratio due to lsa and i like to have a little to keep things cool and help with lag so starting of with a higher comp ratio has a little effect here also.

also vw's 1.8t has a static comp ratio of 10.5-1 ish from the factory.

[CBR_TOY]

this last bit of info is pretty interesting. i plan to go boosted and was curious about my TRD .5mm hg on my motor

sounds like it should decent

[Sam-Q]

you have to be very carefull using the 7afe gasket with 4age pistons as the gasket is made for pistons with a lower compression height.

10:1 is a good compromise between power and response. Compared to an engine with 8.5:1 it will be much more responsive.

moorofit: while your right about raising the dynamic compression ratio at higher compression ratios there is less of a volume to fill with the more compressed gas. However this can be offset by using a larger turbo as having a higher compression engine automaticly brings boost on earlier.

[mooreofit]

[McKenney]

I'm debating on doing a 7AGZE setup now. I have all the stock 1989 ZE SC12 and intake parts. ZE ecu and harness and all sensors. Could I use the stock 7A bottom end? and what would the compression come out to with a bigport head? Thnks and sorry for the thread jack...

[Sam-Q]

I forgot to mention that using 7A pistons might make the engine an inteference design, also they wouldn't be very strong compared to ZE pistons

[McKenney]

FE head has a different combustion chamber than a GE but I don't think it would be interference. Obviously the ZE ones are stronger but I'm looking at funds and I can get a 7AFE shortblock fresh rebuild for $150. Thought I might see how long it lasts! You never know...