Higher compression on stock ecu

[T-man]

Just after some help from someone more knowledgable.

Just wondering how this will effect things. If all else was equal are fuel requirements similar?

My case:
I will have a 16V 4age
Stock JDM ae86 ecu (so early, 9.4:1)
82mm bore, ~10.5:1 compression, maybe a tad more (10.7), have to CC to confirm
Stock Bigport cams
Stock bigport injectors (i have later slightly higher rated later 4age ones available too)
No O2 sensor (will make it run richer?)
Stock timing

I know people have run small ports on bigport management..

any thoughts on how will timing and fuel be? also suggestions on sparkplugs?

cheers

[CrUZida]

Its not ideal to run higher compression on a stock ecu, as the timing in the top end isn't set up right.
I'd want to get the thing on a dyno before you start thrashing it, have someone listening for knock.

98 octane fuel is a MUST
A cold air intake is a MUST
Maybe a S-ITC would be the go to pull some timing in the top end (if you can find one)

[oldeskewltoy]

dynamic compression ratio will be high with 10.7 static CR and stock cams.... recommend a small cam bump, to a 256, or a 264 type

[Shifty]

I don't know why you would go to the trouble of building a motor combo and then running the stock ECU.

You have three scenarios:

BEST: It runs, but not optimally
MODERATE: It won't run at all
WORST: It runs and goes bang before long

Save yourself the hassle and put a proper ECU on it, or at the VERY LEAST get it run up on a dyno.

As for spark plugs I'd be running two steps from the stock plug.

[YGT04A]

I have a couple of questions along the same lines
I have just had my 3SGTE re-built with 1mm os pistons and the head/block will have been shaved/machined to make shore they are square and flat
Questions
1. Will this increase the compression ratio by much?
And
2. Will it be enough to cause problems with running the stock ECU?

Motor will be run up/in on the dyno to check everything anyway
Cheers
Jono

[wilbo666]

I have a couple of questions along the same lines
I have just had my 3SGTE re-built with 1mm os pistons and the head/block will have been shaved/machined to make shore they are square and flat
Questions
1. Will this increase the compression ratio by much?
And
2. Will it be enough to cause problems with running the stock ECU?

Motor will be run up/in on the dyno to check everything anyway
Cheers
Jono

A lot depends on the CR of the new pistons.

Cheers
Wilbo

[YGT04A]

true true
according to there website the cr of the pistons is 8.5 but it that for the standard or the o/s?

all the info is here
http://www.aclperformance.com.au/Toy...gedPistons.htm

[RONA]

Personal experience from Ed's old 7mge with 10.7:1 Comp is not well. But it had a bigger throttle body and ported head as well.

Had a massive flat spot between 3000 to about 4000rpm where the ecu had NFI what was going on. Was pulled of the dyno because it was detonating.

Aftermarket ECU & a tune and the power band was smooth all the way through. That being said the engine lasted like 3 years and 50,000kms running on the standard ECU with the same issue and is still going strong.

[abently]

The only thing a compression increase with stock cams will achieve is more knock triggering auto timing retard. It really depnds how much the increase is and if the ECU/vehicle was manufactured for 92 Unleaded. This gives you a reasonable amount of leeway when bumping the CR to allow you to change to 98Ron fuel and then if still necessary drop static timing 2 or so degrees.

A 1 point increase in CR is possible to get away (assuming oem ECU was tuned for 92ron) with but anything more and it really is a guessing game unless you are following a proven setup.

[YGT04A]

Cheers
I am not following a proven setup I got the motor rebuilt and it needed 1mm os pistons and when I spoke to the guy I am running it in with he mentioned the cr might have changed so it is something I am starting to look at

I have always run the car on 98 but I think it only needs 95 possibly 92 I can’t remember the car is a 91 GT4 GroupA

[T-man]

I don't know why you would go to the trouble of building a motor combo and then running the stock ECU.

I have my reasons. Biggest one being budget constraints, though with the Oz dollar going up again, megasquirt looks good again.
Couldn't really justify a standalone ecu seeming the engine rebuild is sub $500 (inc machining , bearings, gaskets etc) & i'm not after huge power.
Like the sound of how the 7mge worked out.
Thanks for all the input.

[cambelt]

I think RONA maybe the bigger throttle body may have been the problem as ive built many a M series engines with high comp and all have run fine on stock managment .
The only problem ive found the mixture needs a little leaning and the cold start injector needs to unplugged as its far to rich for starting.
Dave

[Shifty]

I have my reasons. Biggest one being budget constraints, though with the Oz dollar going up again, megasquirt looks good again.
Couldn't really justify a standalone ecu seeming the engine rebuild is sub $500 (inc machining , bearings, gaskets etc) & i'm not after huge power.
Like the sound of how the 7mge worked out.
Thanks for all the input.

I am all for budget setups & running stock ECUs when the process is thought out.

When something is thrown together and the ECU is an afterthought, then I reckon you're crazy.