4AGE bigport, best way to get more compresion on a budget?

[StuC]

Sorry, let me rephrase that- get the rotating assembly balanced with a lightweight fly. Balancing should only cost you 100 bucks thereabouts. Lightening the crank will cost some serious dollars. The ae86 boys have light flys for sale quite often so have a look on rollaclub, twincam etc and see whats around.

[lowau]

When I rebuilt my 3 rib bigport 4age my machinist had to deck the block as it had pitting on it around the water galleries, I don't know how much it was decked but the pistons were sticking out of the block a little when assembled, felt by running my hand along the block.
I also had my head decked and am running a .8mm TRD head gasket.

I had no problem with valves hitting the head as one cam was 180 out when I first started the engine. It now runs fine(cams aligned) on 98 and the std JDM ECU.

I don't know how much compression it works out to be but it will be a fair bit from std.

If you want to raise compression don't used the cardboard head gasket that you get in the rebuild kits, a TRD metal one is ~$80

[ae86trueno]

I cant comment on running with a standard ECU,
But I had no problems running a TRD 0.5mm gasket with standard smallport pistons on 98octane fuel on the last 4AG that i built.(both the head and block were decked a little as well)
You should have no problems running the 0.8mm, but you really are not going to get 100%out of it until you run an aftermarket ECU.

Ben.

[wiso]

stock bigport CR = 9.4:1

stock smallport CR = 10.3:1

the car won't run well on the stock ECU if you bump up the compression too high. you say you only have 1k to rebuild the engine? rebuild it to oem spec and stick in a thin headgasket and leave it be.

What would you think this number would be? Looks like I am going with standard smallport pistons 10.3:1 stock 1.2mm headgasket but they have had to shave minimal on the block and head to make flat, could be losing up to another 0.3-0.4mm hence this may raise compression to about 10.6 or 10.7:1 I was thinking now maybe I should take out the sharp corners in the combustion chamber this may lower it back a little.

Does anyone believe I may have issues with this on a standard ECU?

[Dangerous Beans]

What would you think this number would be? Looks like I am going with standard smallport pistons 10.3:1 stock 1.2mm headgasket but they have had to shave minimal on the block and head to make flat, could be losing up to another 0.3-0.4mm hence this may raise compression to about 10.6 or 10.7:1 I was thinking now maybe I should take out the sharp corners in the combustion chamber this may lower it back a little.

Does anyone believe I may have issues with this on a standard ECU?

The issues that the ECU has with too much comp would be due to too much advance right? If so, you may be able to get around it by retarding the engine at the dizzy.
Or I might be talking out my arse

[oldeskewltoy]

The issues that the ECU has with too much comp would be due to too much advance right? If so, you may be able to get around it by retarding the engine at the dizzy.
Or I might be talking out my arse

no... not talking out your ase... you can fudge the ignition timing to get 11 to 1 to run on an AFM(USA) AE86.

IF you get camshaft timing gears you can adjust dynamic compression ratio by advancing the cams a bit to get it to run better as well

[mattysshop]

i had a 20 thou cut off the head (smallport), with stock smallport pistons (10.3)... 0.8mm TRD head gasket.. Bigport cams, mildly cleaned up ports

ran the whole thing on an ADM AE82 bigport (map sensored) ECU with a billet TechnoToyTuning quad throttle adaptor, with S/T 20v quads... ran about 20 deg advanced timing (base)

made 118rwhp (AE86)... no pinging, very strong, and torquey.. (compared to stock) used 98RON

then fitten an adaptronic, didn't make any 'more' power... but used ALOT less fuel (due to the almost lack of vacuum to the map sensor).. and was a bit more stronger midrange... so it probly made more average power..