Ignition timeing, very low compression(8:1) engines...
Turbo Mini Forums

Got the engine in and runningn before i went into work . took it for a wee spin round the block.

anyways had to set the ignition timing at around 8-12 degrees advance(vac disconected@1kRPM) before it would even run half decent, and it is stil worryingly sluggish., like slower than a standard 998 with a blocked air filter sluggish.

It is my understanding that if the volumetric efficiency of the engine is lowered(i.e. lower the CR) then more advance is needed as the fuel burns slower.. so how much advance can i safely use?! lust advance it til it pings and wind it back a few degrees?? If no one knows il experiment anyway, but be nice to have a rough guestimation to start from :)

Another anoying side effect of this is regardless of how much i lean off the mixture my colortune is always yellow right until the mixture is so lean the engine stalls! Im asumeing this is a side-effect of the slow combustion at the wrong time... wel i hope it is

NB it aint runnign forced induction yet..

Cheers,
Denis.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Just looked at my ignition map for you
@ 1000rpm I run 22degress this goes up to 56 degrees @ 7500 and at full boost, I'm retarding 8 degrees of that.

Hope this helps a little

Team Racing

Jimster,

you?re kidding right ???????

56 degrees at 7500 rpm ???? Retarded at 48 degrees at full boost ?????? What the hell are you talking about ?????

I would expect total advance around 25-28 degrees at 1 bar boost for any A-series engine size.

Jukka

Cheers, What CR you running out of curiosity? and 56degrees beter start looking into mapable ignition myself then! as il no doubt have to run more.:(

Guna have a fiddle b4 i go to uni, but cant right now as the single box is a tad anti-social for this hour of the morning :cool:

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

good news mate!

sorry, thats my only contribution

I have reading of around 40 degrees on mine Jukka - I suspect that the software was not properly Zero'ed to TDC, and that Jims is the same!(yes Jim, i know i was there!)...
You should ideally be retarding more than 8psi at full chat Jim... But of course, it does depend on how the map is configured... On a low inertia/lag turbo like the T2, where it is only around 1000 RPM between no boost and full boost, you may well end up with a map that simply has a 'step in it, rather than relying on the full use of the ignition retard.
Both work just as well, as realistically, you don't give a monkeys what your advance figure is at 6500rpm with full throttle when at 1psi boost, as you're never going to be in that area of a map!

D

just thought about this more Jim...

That figure you quoted, which throttle site was it at??? I'm going to take a guess and say the 0-3% load colum/row- ie the point that you would only ever be on the overrun???

Dave Walker set my mini up with shed loads of retard at high rpm, with zero throttle - ie so that when driving, and you take your foot off the gas when changing gear, the revs drop like a bomb, so your RPM is about right for the next shift.
Great for drag racing, a real arse when pootling around, as the revs drop too far, and it spits flames from the back, because there is so much retard!

Hmm, But just read this again, and realised i'm going off at a tangent, so ignore my drivel please!!!

Edited by turbodave16v on 18th Nov, 2003.

AlexF

U sure!? I was under the impression VE was a function of the amount of power obtained from a given volume of fuel/air.(now you can see why i failed thermodynamics and fluid mechanics....)

Wel iv bin messing around and the colortune has been a great help, mixture appears to go white hot if i advance to much, so can set the advance jstu before this point, pulls better but stil very lacking at the top end(can only asume that the dizzy has not got enough mechanical advance) but on boost that wont matter so im not to fussed. Stil got a few more things to try.

Engines comeign back out so i can re check the cam timeing(jsut incase i didnt get it absolutely spot on) and im putting in a 3.44FD, because with the current 3.11FD and 0.9333:1Drops !st gear is waaay to tall. so this should also help. Also changeing the head as it appears the valve guides are worn on the current one. May get the head skimmed while its off getting reconditioned! depends how the car feels with the 3.44.

p.s. that post toppic button is annoying

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

lol u keep posting new topics instead of repling too!!

yeah I am pretty sure... Compression Ratio is just the amount the chage is compressed, Volumetric Efficiency is how well an engine "breaths"...

or in someone else's words....

Volumetric efficiency is a measurement of how well the gas is passed through the engine. It requires large and unobstructed ports offering the minimum obstruction to the flow of gases ? both air and exhaust. This is why engines are gas flowed for additional power; fettling the cylinder heads to match the shape of the manifolds, and radiusing unnecessary metal inside the ports

CR does effect timeing massivly... you can run more advance as the charge burns more slowly... you should be able to get all the advance you need on a std unit... just the curve and idle advance will be out...

I'd skim a std head right down... if your def going to run the engine in NA... I wouldn't bother!!! Engines really don't need masses of running in and A-series are particularly sensitive to ring seal... old bores and turbos will smoke and be down on power!

alex

AlexF

the engiens getting turboed, just not yet.. cant afford the ??? for insurance+parts. should be ok ?-wise in a month though. just wana get the engine so its driveable off-boost. as this car is a daily driver too.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Yeah,

I can understand that there are big advance numbers at low revs/load, that?s what the vacuum advance canisters are for in the distributors.

If the basic setting for maps is off (the trigger setting relative to TDC) then the values in the whole map are basically worthless to anyone else. Well, engines differ anyway...

I am surprised that such a basic setting is not done correctly. E.g. Haltech has a feature that allows one to lock the ignition at 10 deg BTDC. It is then simple to check with a stroboscope if the trigger is correctly set. If not, the trigger position is adjusted to get that 10 deg setting in reality.

Same for the retarded setting, there is no such feature in a mechanical dizzy and usually they have no problem dropping the revs. Too much retard will only cause abnormal thermal loads which is not good in the long run.

Jukka

vacuum advance canisters are more used for light throttle opperation to improve economy and emissions... at idle their effect is much less.

alex

AlexF

Evo, i was in the same boat as you, but i had 7.5:! !!
I ran about 30' total advance at 5500 Rpm, but it was all in by 3500....
Yea it was a bit flat, but it was a very low compression 998 !
I still have the flatness off boost, but it comes onto boost so fast and smooth it doesnt matter ! - 3rd gear @ 2000, nail it and you are at 6000 before you know it ! very scary for a 1 litre !

Cheers
J

were you the guy i e-mailed a while back!?

As you can see i got hooked on big bore power when the insurance co only wanted a few extra notes for a 1275... keeping my old 998 short block though, may resurect it!!!

Wel engines runnign better, was suffering a few gasket problems. But still very sluggish off the line! Sure it wil be fine on boost, but that doesnt help me jsut now

What initial advance were you running at 1kRPM?! jsut out of curiosity! jsut going out to experiment myself. Did you run the vac advance unit?! as this seems to be giveing me waaaaay to much advance on part throttle if i set the dissy to work its best on full throttle :S

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

sounds like you need a dizzy curved for your engnie!!


alex

AlexF

The latest Metro turbo dizzy gives roughly 20 degrees advance at idle. Mate?s engine refused to pull past 4000 rpm (tuned by ear in winter conditions, slippery and no grip). The operator did not first understand that it was timing related issue but thought that it did not get enough fuel. Finally he checked the timing at it was about 50 deg at 1000 rpm. Without the vacuum it dropped to 30 degrees. The timing was retarded to 10 degrees @1000 rpm without vacuum, vacuum reconnected and we were rewarded with some 60 extra hp. Note that it did not even pink, it simply would not pull past 4000 rpm ! The turbo was an ancient Holset that hardly gave any boost below 3500 rpm...

I don?t know which dizzy you run but Metro turbo dizzy could be a good starting point. Mine is mix of various parts, (like Aldon yellow body and weights, Metro turbo vacuum canister, suitable choice of unknown springs etc, plus points !). Static setting is 8-10 deg BTDC, total advance around 28-30 deg.

Jukka

running the electric dizzy of a last-of-the-line carbed minis. Iv got it running as best as i can, pulls consistantly and i guess kinda well. but im fed up with the low end power. Really fed up, actually makes me hate driving the car. So heads off to get 1mm taken off it

less boost, but more driveable.

Cheers for th input though! :)

Edited by evolotion on 21st Nov, 2003.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

or get another head!!!

AlexF

but then id need to get that skimmed.... Im actualy guna get a recent, std unleaded 12g940 skimmed as opposed to the MG head as it was giveing me al sorts of gasket grief, and on closer inspection it doesnt have unleaded insers. may use it as the basis for my next head, if i take this project that far.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.