Engine high compression 7A-FE

high compression 7A-FE

I know im still really new here but i got a good one for everybody.... basically like the title says i have an idea for a High-compression 7AFE.

4afe pistons are the same as 7afe except for one thing... they have a 8cc dish instead of 12cc if you do the math putting 4afe pistons in an otherwise stock 7afe it will give you about 10.5 : 1 compression!

my question is will 91 octane be ok doing this? its hard to get 94 as only sunocco sells 94 so it really really needs to run on 91?

There are plenty of motors that run 11:1 & 11.5:1 just fine using 91 octane. 10.5:1 I think you are fine with 89 but always better safe than sorry. BTW Where are you getting the info about engine internal specifications?

PS I dislike your altezzas

im getting my info from head volume, bore, stroke, piston dish, deck height i got some measurements from my service manual some from the web (verified) and some measured and others needed but not listed were back calculated i donno if its gonna be exactly 10.5 but 10.4 - 10.6 for my poor accuracy.

I have had a few people say no workie but most have said it should work so im probably gonna dive into it over the winter

The only potential problem i have noticed is that the wrist pins are a fair bit tighter on the 4A-FE pistons


BTW i seriously need to update the sig its ancient and practically another car

but the 4afe is a 1.6 liter and the 7afe is a 1.8 liter, meaning the 4afe has smaller pistons that the 7afe

Even with the higher compression, how much hp do you expect that to produce?

I'm not sure, but you get better results if you pair the bottom end work with a custom cam or other head work.

The site below I found to have a good roadmap of what work is needed to get to what power levels.

http://www.billzilla.org/4agmods.htm

I remember something like this being done before; 4A pistons with 7A con rods.. it was a while back so I dont remember the specifics but I remember the person doing it said he had to machine the hole for the wristpin on the 4A pistons a bit larger.. If only I can remember where I read that at.

But I agree with NinetyFour, a "G" head swap would be more advantageous and a bit easier to do.. but having 4A pistons might not hurt either.

the g head has larger chamber aswell so its a compression killer as for the pistons being different sizes

the only difference between the two is stroke

7afe
bore: 81mm
stroke is 85.5mm

4afe
bore: 81mm
stroke: 77mm

what someone saying about the pins being tighter (4A) seems to be true they may need to be honed smaller

Oh and i figure 10% more compression so maybe around 10% power increase 125-130 hp

the big reason behind this is because i have a set of .030 over pistons that i got a killer deal on.