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ST185 ECU & Hi-Compression Pistons

PostPosted: Fri Feb 06, 2015 6:07 pm
by masco
Hypothetical Question:

Stock Gen 2 3S-GTE (CR 8.8:1) with Gen 2 3S-GE (CR 10:1) pistons.

How would the stock ST185 ECU react to that?

Re: ST185 ECU & Hi-Compression Pistons

PostPosted: Fri Feb 06, 2015 11:45 pm
by sleeper
With stock timing, it would knock really bad... you could adjust timing some degrees back, but then you would prob loose what you gain..

Re: ST185 ECU & Hi-Compression Pistons

PostPosted: Sat Feb 07, 2015 1:22 am
by alltracman78
On stock boost? The ECU is able to adjust timing [at least to some extent].
I'm not saying it won't knock; I have no experience with this.
But it might be an interesting experiment.

Re: ST185 ECU & Hi-Compression Pistons

PostPosted: Sat Feb 07, 2015 9:29 pm
by masco
I know hi-comp pistons will change the engines VE. At WOT I know the stock tune runs quite rich, hopefully that will be fine. In closed loop the motor should run decent.

We know that higher compression pistons need less spark advance to reach optimal combustion as the process happens quicker. Hopefully the knock control system doesn't have to intervene and reduce the fun.

So preliminary thoughts point towards helping to prevent knock.

1) Reduce temperature of intake charge
- Install Front mount intercooler
- Run ct26 at its most efficient pressure ratio
2) Reduce temperature of coolant in the jackets
- 170 Degree (cooler) thermostat
3) Remove heat from combustion chamber
- colder spark plugs
4) Maximize Quench effectiveness
- thinner headgasket to minimize air present in the quench area

The last thing might be to reduce the gap in the spark plugs to ensure a strong spark at the increase cylinder pressures.

Re: ST185 ECU & Hi-Compression Pistons

PostPosted: Sat Feb 07, 2015 10:20 pm
by sleeper
masco wrote:I know hi-comp pistons will change the engines VE. At WOT I know the stock tune runs quite rich, hopefully that will be fine. In closed loop the motor should run decent.

We know that higher compression pistons need less spark advance to reach optimal combustion as the process happens quicker. Hopefully the knock control system doesn't have to intervene and reduce the fun.

So preliminary thoughts point towards helping to prevent knock.

1) Reduce temperature of intake charge
- Install Front mount intercooler
- Run ct26 at its most efficient pressure ratio
2) Reduce temperature of coolant in the jackets
- 170 Degree (cooler) thermostat
3) Remove heat from combustion chamber
- colder spark plugs
4) Maximize Quench effectiveness
- thinner headgasket to minimize air present in the quench area

The last thing might be to reduce the gap in the spark plugs to ensure a strong spark at the increase cylinder pressures.



It`s not really the fuel that`S the problem with the stock ecu.
Problem is that the stock ecu have a really aggressive ign timing as stock, and there is no "adaptiv" ign timing in it. just a knock sensor that pulls timing if knock is present ( short therm adjustment)
You might get away with it if you run a higher octane fuel ( more than 93 MON), but in my head, it`s not worth it..

A comp rise of 1.2 will just give you a few % more power, but the loss you will have to take to be able to run it without knock ( less timing/boost) will make you lose more than what you gain if not running a better fuel.

Re: ST185 ECU & Hi-Compression Pistons

PostPosted: Sun Feb 08, 2015 1:24 am
by masco
I'm not looking for a power increase, just looking for more power out of boost.

I know that getting it tuned is going to be a critical piece of the puzzle, but until then I'm just hoping I can drive it around conservatively on the stock tune.