[Diy_efi] boosted compression ratio

[Bernd Felsche]

On Mon, Dec 23, 2002 at 02:47:55PM +0000, Mike wrote:
> At 01:35 PM 23/12/2002 +0800, you wrote:
> >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.

> mmmm OK, I take it you mean the ECU reaches its own max advance
> by virtue of a knock sensor - which we assume is operating correctly
> (I say that as these are high impedance devices and dont need much
> in way of connector contamination to go a little haywire), though
> its weird an ECU would be arranged to keep advancing until knock
> on a production car ! <phew>

Well, advance at least until as far as the desired set-point.
VW made a big thing about Digifant being able to adapt to a wide
range of fuels. So it _might_ be that they do advance to the onset
of knock and then back off for steady-state.

> >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.

> Eeeek - You get much better performance going for a hot wire type
> AFM than the vane types ! If I recall the factory AFM on my VL

It's not a standard Bosch AFM but a special version for VW's
Digifant. Linearised output IIRC.

> turbo is a pretty much generic Bosch type in that it was intended
> to replace many vane types - I have a spare which you are welcome
> to try (you are in PErth?)  - the pin configuration may well
> be similar, you only need to put in a burn cycle ?

One of the "projects" that I've had to shelve because of dire lack
of free time and money, was to "map" the output of the present AFM
against the now-cheap MAF by putting it in series (!!) with the aim
of eventually replacing the AFM with the MAF and a small processor
to handle the translation for what the ECU expects, provide an air
temperature "reading"; and to do the special handling of the MAF of
which the ECU is blissfully ignorant.

> >Engine management is mostly closed-loop so even changing the fuel
> >pressure regulator didn't increase fuelling.
> 
> So why did you tweak the spring on the AFM, you did make the
> spring a little weaker - right ?

Backed off 3 teeth on the pre-tension cog. The tip-in "response" lag
disappeared after that so I glued the cap back on... It's only for
dealing with transient enrichment anyway.

> Bear in mind most ECU's are designed to have only minimal shift
> from initial settings so as to avoid wild fluctuations affecting
> overall stability. So if you start out quite lean then the ECU

I don't know about the "minimal" fluctuations. I was able to drive
the car when the camshaft was installed retarded by 30 degrees...
no mean feat for any engine management system. For some reason, the
sub-contractor who pulled the head down to replace valve guides (the
head was off the block anyway), took the cam sprocket off the
camshaft. And then assembled it backwards... of course there were
"timing" marks on the wrong side of the sprocket. But not in the
right place.

> may not have enough opportuntiy to make it richer, hence you
> are hearing ping ! I've messed with mine to some degree and found
> that it won't change fueling by more than about 8% from the
> base settings - ie. It will try then hits an aysmptote. So
> as long as I set it up to a median then it can go a little
> lean or rich as needed but wont go far from the base settings.

Well, it's operating closed loop and the control algorithm on my car
tends to favour the lean side of stoich. That's steady-state
operations; which is not where the (audible) ping occurs anyway.

> There is an adjustment pot on my AFM (which goes only to the
> ECU) which is a rich/lean trim and this has about a 15% affect
> (or maybe a little mroe) on ECU injection DC - its a 22 turn pot.

That'd be the base CO adjustment.

> >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.
> 
> Thats a little strange, you are saying the ECU is designed/programmed
> to keep advancing timing until it detects knock - how long does it
> keep it there, or does it 'try again' a bit more etc etc ?

3 seconds or thereabouts when advancing in small steps and
"immediately" in large steps upon detecting knock - cylinder
selective.

> >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.

> hrrrmmm, they are not difficult to make, I had a 3" full exhaust
> system made just a few months ago for my car by 'Exhausts r us' in
> Osborne Park - ended up with full stainless steel and new cat
> along with dump pipe etc etc. The main guy there is Dale who often
> makes custom extractors for several non Australian cars. In about
> 6 - 8 months I'll be looking seriously at a twin turbo setup and
> he'll likely be doing the manfiold. They are a bit idiosyncratic
> but the best people seem to share that trait but, he wont 'jerk
> you around' and I had maintenance done on it (free) after damage
> from a 1800km drive when going to/from Monkey Mia with a full load
> of gear and 4 passengers!

Space behing the engine of a Golf is very tight and the steering
rack is quite close. All the LHD ones interfere with the steering
rack. What's more, the engine moves around a lot so there has to be
some flexible coupling; and it has to connect to the cat. converter
because I'm not too chuffed at the prospect of a $20,000 fine.

> >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.

> Did you do a double blind trial ;-)

Ermm no... but I checked my fuel bills and consumption over 3 months
on different fuels - PULP was a big improvement; 98 made a small
difference again - as well as reducing audible ping to days when it
is too dry. Even with PULP, it'd ping most of the time.

> Its amazing how much of the economy gain is defined by rate of
> change of foot pressure, know anyone with a dyno and fuel

The foot pressure is probably as much, but for shorter periods
because I'm at a higher speed sooner when accelerating. This I've
tested from a standing start on a hill. Now hitting the sign at the
top at almost 100kmh, used to be just over 85kmh with ULP and over
90kmh with PULP.

> consumption test setup ?

They'd be inconclusive anyway; pretty much a waste because of day to
day variations. The only proper way to do it would be to put the car
in a controlled environment and run it in there.

> I 'seem' to get about a 5 - 10% improvement in economy when
> going from ULP to Premium but havent noticed much at all when
> going from Premium to BP 98 - havent tried optimax yet - partly
> because here in Perth there arent many outlets.

Not many? Are there _any_??

Price difference between 98 and PULP is usually only one or two
cents and the car seems happier (less audible ping and better
throttle response) so it's worth it to me.

> >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.
> 
> Nice bit of irony there, no problems after 267,000K. But blew
> a head gasket - huh ?

Happens if you change into 2nd after redlining in 3rd! Rev counter
needle spun way past 7000 rpm before I pushed in the clutch again.
Big mistake on my part! Not the engine's fault by any means. It was
the nut behind the steering wheel.

It went more than 1000 rpm past the rev limiter.

And the synchros went in so easily too! :-(

> The head gasket is the weakest - did you retorque it after it
> was first put in - I did mine after 1000K of a new head some
> 2 years ago and yes all the head bolts were showing different
> settings - trick was to release by 1/2 turn before retorquing.

Not on a Golf. They're stretch bolts. If you loosen them, you have
to put in new ones. Well, you could upgrade to Raceware stuff and I
probably will next time the head needs to be done - I just didn't
want the car off the road for 2 weeks while the snazzy stuff makes
its way across the Pacific and through Customs.

> CLearly you are not getting major ping thats enough to damage
> pistons (or rings perhaps), but enough to weaken the gasket
> seal - so I 'feel' its something else thats happening here !

YOU try redlining in one gear and with the car doing about 120kmh,
start to ease out the clutch when in the next-lower gear.

That's massive abuse! And I was indeed fortunate to have still been
able to drive the car after the exercise; albeit with some
coolant-injection!

> I wonder if there isnt something else thats occuring here,
> 
> i mean you've 'tweaked' the spring in your vane AFM and assume
> the ECU has wide range over which to control fueling.

On transients. It's been fooled into thinking that there's a greater
inrush of air so it provides additional enrichment.

Steady-state and it reverts to (the lean side of) stoich.

> What you may have here is a combination that results in the
> ECU not being able to fuel because its base is out of its
> median control range ?

Only if it was made that way at the factory.

> Do you have a TPS - with functioning acceleration sense,
> ie Rate of change.

No TPS. Only idle and WOT switches.

> Have you looked at the injector duty cycle change when
> in stead state cruise and how this changes between fuels
> for the same cruise conditions ?

No... I don't have the diagnostic gear. Digifant is deaf and dumb,
so it doesn't provide any cap[ability to read that information.

> What sort of plugs are you using ?

Bosch Super 4. Brought in a set from the UK in 1997 to try and
haven't had a reason to use anything else.

> Just occured to me, have you changed/upgraded the capacitor
> which is near the ignition coil, ie The one which goes from
> coil +ve to ground. I had an odd problem for a few months

There's no capacitor there on my car; nor on the factory
current-flow diagrams for the car. Ignition is controlled by
Digifant using standard Bosch ignition amplifier.

-- 
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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