Ulimate 98 in a n/a ecotec V6 ?

[Holden202T]

I know when towing my race car with my Alloytec V6 Ute, I used to always use 98 when towing, and one time there was nothing other than 91 or 95 at this servo, and dead set I couldn't believe the difference, the economy not so sure about but certainly I noticed a marked dropped in power, it was dropping back on hills more than it did before hand and generally just didn't love it as much, and that was 98 -> 95!

I also notice with my holden cruze (1.6ltr turbo petrol) I get considerably better power and economy with 98 over 95 doing the same work trip!

[immortality]

That's the thing though, the ecotec engine (or rather the PCM) was never set up for high/low octane fuel. It uses only one ignition map and has the ability to retard timing to prevent knock and that's about it.

It comes back to the fact that running 98 in a engine tuned for 91 won't show any gains other than your wallet been lighter than it should be. The other issue I see here is that for most of us, we are talking about tuning and modifying engines that aren't exactly spring chickens any more and probably not running 100% ideal. IF you do see gains running 98 instead of 91 it would suggest that something is off, either it's running a bit lean or things are getting a bit hot and the PCM is pulling a little timing which won't happen with the better fuel.

Newer modern engines like the alloytec are a different story and can adjust depending on the fuel used.

[OZ38]

IF you do see gains running 98 instead of 91 it would suggest that something is off, either it's running a bit lean or things are getting a bit hot and the PCM is pulling a little timing which won't happen with the better fuel.

A little confused with this ^^
Why would using 98 premium prevent the engine running a bit lean or getting a bit hot & the PCM pulling a little timing ?

[immortality]

What I mean is that it may not run ideal on 91 due to any number of reasons (Dodgy O2 sensors, mechanical wear and tear with age can cause many issues that mean engines no longer operate at peak efficiency, carbon build up in the combustion chamber creating hot spots etc). Running 98 in such an engine may mask some of these issues because the fuels ability to resist knock.

98 won't prevent it running lean but where it might knock with 91 it may well not knock on 98 if it's a marginal issue as can happen when O2 sensors get dodgy.

[Charlescrown]

Love threads like this. Sorry I haven't contributed for some time but stuck in hospital after getting a new ball joint. Getting back to what jayme said the leverage angle ends up almost identical for all engines. Think if the ignition has max cyl pressure @tdc the piston would push directly in a straight line against the crank (no leverage, no power) and like wise if it was at 180 deg after tdc the same would occur so some where in between is the magic point. Its not so easy to say that 90 degrees atdc should be the correct point because of the fuel burn rate and trying to convert as much of the fuel energy to power. Comparing alcohol fuel to petrol might not be a good thing. Some tuners have made the mistake of tuning up to detonation and with alcohol you will hammer the guts out of the bearings due to the rod/crank angle obtained without detonation.

[Gareth]

So then is tuning to a certain cylinder pressure the better way to do this?

If so whats ideal?

[vlad01]

So then is tuning to a certain cylinder pressure the better way to do this?

If so whats ideal?

thats what we do when we use a dyno, we are tuning for peak pressure at idea crank leverage angle

[Gareth]

Yes I understand that, but we don't actually know that as a number on the dyno, it seems that there is a trend towards tuning using an in cylinder pressure sensor (as they have become somewhat affordable).

As stated above, the ignition timing that can be achieved with alcohol can over load the engine without any sight of knock, surely this could be accounted for using cylinder pressure as a reference.

[vlad01]

there is advantages and disadvantages of using cylinder pressure monitoring.

The advantages is ability to see knock as its happening. See misfiring on individual cylinders. Individual cylinder tuning. Get very close results without a dyno.

Disadvantages is no actual engine output readings and peak pressure vs ideal crank angle is not 100% bang on as it varies depending on engine design by some number of degrees. You rely on the logged pressure graph to estimate MBT.


Dyno has the ability to dial it timing based on actual torque output which IS the idea timing (peak pressure at correct idea crank angle) but lacks ability to probe whats happening in the cylinder itself which allows refinment of the engine, eg. ignition, plugs, manifold, chamber, ports etc etc. More of an R & D tool than strictly tuning tool.

Both these tools together would be the best thing. So big G, when are you getting the in cylinder pressure monitoring gear? lol

[OZ38]

Comparing alcohol fuel to petrol might not be a good thing. Some tuners have made the mistake of tuning up to detonation and with alcohol you will hammer the guts out of the bearings due to the rod/crank angle obtained without detonation.

I think you have high lighted to me a fault I was seeing when helping a friend out pit crewing his Methanol Mechanical fuel injected Camaro drag car.
I noticed the way they would set their spark timing was lock in at something like 34-38 degrees BTDC on the crank trigger device. Then they would set the fuel injection pill (return line jet) based on the EGT they got at the end of a run, fatter (rich) or thinner (lean) they would refer to it as. After seeing the engine fail one time with a ARP big end bolt letting go shortly after a rebuild by recognised race engine builder. I started to wonder if the point of peak pressure was happening a little to close to TDC. Tuning of these engines didn't seem to have the benefits of engine management that could control knock. Or so it seemed by the way these guys were playing with them & winding then locking spark advance so far forward at the high idle.