4age to 7age Questions

[Libbor]

Hello all

This is my first of many posts and I guess my question has been asked a thousand times before.

I am doing the 4age to 7age.

I dont really want to leave the standard 7a pistons in the conversion as I have heard that the compresion ratio will be low.

I have measured the gudgeon pins on the 7afe and they are 20mm press fit. I have had a look for pistons to suit the 4age and it appears that 18mm pins are press fit but 20mm pins are circlip. Is this correct or is my listing incorrect.

Ive read some of the posts on this subject on this forum and I know that standard 7afe bottom end with 16valve small port head will give me low 8 CR.

Can someone let me know what a standard 100kw engine 's compression ratio is and what the 7age engine will be with 4age pistons installed.

Also, will the factory ecu still run this mod or do I need to go down the aftermarket ecu route

Cheers all and congrats on this fantastic forum

Darren

[Nomuken]

Standard 100kw (smallport AE92 engine?!) has a CR of 10.3 to 1. If you now put these pistons in the 7AFE block you will get ~11.0 to 1 with the 4AGE head.
4AGE pistons are circlip 20mm, but a good engine builder will be able to hone the 7AFE conrods to match the circlip pins from the 4AGE pistons.

Standars ECU might be possible to run that setup, but you'll have to use the smallport injectors and raise your fuel pressure until you get good AFR readings.

[Libbor]

Thanks for the reply mate. Is there pistons i can use which will keep the compression at about 10-1. I just didnt really want to go to 11.

Also is it true that if I get the rods honed out for circlip pin, I will also have to get a bush fitted in the rod too?

Cheers


Darren

[Nomuken]

There should be some rare GZE pistons that will put you toward 10-1.
Its a pretty simple calc:
If you mate a 4AGE head to a 7AFE Block with adding the pistons to the 7AFE Block, you will raise the compression ratio by 0.7 from the values you got in the 4AGE

Check Sam's calcs, they are pretty useful!!!
http://s-86.com/s-cr-chart.html

[corolla4agze]

http://www.romut-radalle.com/viewbig.php?img=14290

4age na power... =)
4ag "inside 7a block" etc big stuff

[oldeskewltoy]

not sure what CR you want to run... but a 10.3 4A piston in a 7A(stroke is 85 vs 77) the CR is well above 11 to 1, maybe close to 12 to 1.

Quote:Check Sam's calcs, they are pretty useful!!!
http://s-86.com/s-cr-chart.html

without the math.... I don't trust the calculations... IE, my example above... with the chamber volume inaccuracies




I'd look into using either a TVIS piston(9.4 to 1), OR a later 4AGZE piston(8.9 to 1) might just be perfect when fitted to a 7A with 8mm more stroke.

I'd check a CR calculator and try to calculate which 4AG piston(77mm stroke) will work best in a 7A with 85mm stroke

[Nomuken]

So, I did some math and 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.