EA82T compression ratio options?

[All_talk]

According to the ’89 FSM all Subaru engine are designed to use 87-octane fuel… which got me thinking, if I commit to running better fuel and/or an intercooler I bet I could run higher compression and maybe a bit more boost. The trouble is there isn’t a good mid compression option using stock EA82 parts (around 8.5), 9 and 9.5 are the other options. I know someone is running 9.5 but it requires race gas to run normal timing, my car will be a long mileage daily driver so 100+ octane is not an option.

 

 

I noticed the carbureted EA81 has an 8.7:1 CR, which would be perfect but will the EA81 pistons fit in an EA82? I think I read somewhere that they will. And, do all Subaru heads have the same chamber volume?

 

 

In the end what I’m hoping for is:

 

 

8.7 CR, 7-8lb boost (stock), intercooler on 87-octane for commuting

 

and

 

8.7 CR, 10-12lb boost, intercooler on 92-octane for weekend fun

 

 

Any thoughts?

 

Gary

[calebz]

Why not use the 8.5:1 Carb stuff?.. Jst looked again at your post.. you have an 89 FSM.. that wouldn't have carb stuff in it

 

BTW.. even in stock form.. no turbo car I have ever owned runs worth a damn on 87.

[simpreza2]

IM still a n00b but I thought that the ea82t needs 91 octane:confused:

[calebz]

The owners manual says "87 octane or greater".. but I wouldn't run 87 in mine.. it only get 93

[All_talk]

Well I don’t doubt it runs better on 92 , I’ve only had my RX for a couple of weeks and am still running on the tank of 92 the previous owner left me (thanks rxpilot ). But for my 170 mile commute 87 sure would fix the budget better (paid $2.00/gal this morning filling the wagon) and I’m not going to be doing a lot of performance driving on the way to work, just lots of 5 gear cruising. If I see enough of a mileage increase with the better fuel I might just run it all the time.

 

BTW I got the 8.7 CR Carb info from my Chilton’s (hope its right).

 

Will the EA81 pistons fit? Anybody measure the head volume?

[oddcomp]

i run cheap gas all the time with no problems

still more or less stock boost right now

if your worried about detonation under boost

you could look into what ia m going to try

get a saab apc unit

it uses a knock sensor to bring boost down below knock level and when there is no knock i raises it back up

so supposedly you make the most power for whatever conditions are on hand

 

http://www.geocities.com/MotorCity/Garage/6776/apc.html

basically what i am talking about

[NoahDL88]

The 87 FSM recommends 90 or higher on all models.

 

I'd also go with the thought that anything with a turbo shouldn't have 87, it should have midgrade or higher, thats just me though.

[subiemech85]

can someone tell me why the 85 4 door sedan dl with 4 spd trans has a 9.5 cr, 6* timing at 650 rpm and an the same hp as the other carb engines?

[All_talk]

Shadow, great info, I read through a lot of info on that site and they seem to be coming from a very intelligent and informed point of view. The consensus, apparently backed up with dyno results, is that for low octane fuels (below 100 or so), you can make more power with low compression and high boost than the other way around. So the 7.7 will stay, I was hoping to use the higher compression to increase the low RPM pre-boost power but free flowing intake and exhaust will help with that and also bring the boost in sooner.

Gary

[WJM]

You can run 93 octane on the 9.5:1 setup. You just have to play with the timing a bit to get the optimum setting for power/no detonation.

 

If you run race fuel, and run the timing up....thats when you get some serious power.

 

The reasons I am going back to 7.7:1 are....ive got lots of turbo shortblocks laying around, im toying with the idea of lots o boost and IC....and the next time I do 9.5:1, it will be more porper, and not a last minute thing. Proper will: Cams, IC, and some other things....