[Diy_efi] boosted compression ratio

[Bernd Felsche]

On Mon, Dec 23, 2002 at 12:39:13PM +0000, Mike wrote:
> At 07:09 AM 23/12/2002 +0800, you wrote:
> >Mine's not a turbo engine.

> mmm Well OK, then I interpret you are after max ignition advance
> as a fuel economy measure and havent modded the chamber or
> built an engine from parts so arent facing a high/unclear CR
> issue which necessitates highest octane... ?

I'm not looking for maximum economy - I'm pretty much getting that
anyway. The aim is to reduce pinging and possibly knock that causes
the ECU to retard timing from it's target, resulting in a drop in
output torque. An improvement in economy is expected as a
side-effect.

No modifications inside the head. The engine was stock-finnicky.
ECU is stock - very difficult to get any modifications done for
ADR-spec'ed Digifant. The only changes on the car are a modified
filter box, K&N filter element, a slightly warmer camshaft and a
tweak on the spring pressure of the air flow meter.

Engine management is mostly closed-loop so even changing the fuel
pressure regulator didn't increase fuelling.

> If that were the case, then I'm not sure max economy would be
> consistent with max ignition advance *just prior to detonation*,
> there may well be a shifting 'window of opportunity' etc.

> And it depends a lot on the ECU and its mapping, changing the
> base timing may do very little to overal economy, remapping
> the ECU will likely give you more economy gains at the expense
> of driveability.

Changing the base timing by up to 10 degrees changes nothing as far
as detonation is concerned; it'll still advance timing until the
onset of knock.

> There seems to be some anecdotal evidence and I seem to recall
> observations from others on this list that max power wont
> necessarily happen where ignition is advanced to just before
> the point of detonation.

Depends on *many* factors. 

> How about extractors, using that with ULP might well be (in the
> long run) cheaper than BP 98 and high ignition advance ?

I've spent the last 5 years of my spare time looking and waiting for
extractors for my car... no luck. Looks like I'll have to go
overseas, buy them, put them on a pallet and ship them back home.

If I use normal ULP, the 7c/litre saving is offset by a 10 to 15%
increase in fuel consumption. And then there's the crap in the fuel
that gums up injectors to they need a "dose" every 15,000km as
well... not been required since 99% of the fuel used has been 98.

> You also mentioned you want the engine to last another 250,000K
> or so - well your aim of max ignition advance before detonation
> may be inconsistent with that due to the 'silent detonation'
> issue which robs power just prior to readily noticable detonation
> and may stress the rod bearings etc !

Well, the car's been "pinging for 267,000km" and so far there's no
problem to be seen. When the head was removed after I blew a gasket
(selected 2nd instead of 4th gear approaching Shell) at around
160,000km, the tops of the pistons and the head showed no evidence
of damage.

> I'm curious what your engine configuration is and what your
> objective re ignition advance is ?

To stop the knock/ping and let the ECU reach it's nominal target for
advance. It seems to do that at certain times anyway; depending on
conditions.

-- 
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