20 replies to this topic

[KernowCooper]

They may well run with a 1275 distributor in a 998 but it wont run at it optimum the 998 and the 1275s have different advance curves

 

Quote by Calver

Any dizzy can be set to get maximum power. No problem. Unfortunately that's only one spot on the whole power curve/rpm range. If the curve isn't right elsewhere, the engine will be either loosing power - in some instances by substantial amounts - or detonating its self into oblivion and a costly re-build.

 

Large-bore engines are less fussy about exacting ignition requirements than small-bores. The 1100-type being the most difficult to get right, with very particular requirements mid-range when tuned and worlds apart from large-bore curves. This should be remembered when swapping distributors from one engine to another. An 1100 dizzy in a 1275 will at run OK, but a 1275 in an 1100 can be courting disaster.

 

Full article here http://www.calverst....eries_needs.htm

 

I would question anyone selling one distributor thats fits every A series Engine, ask Aldon or H H Ignitions

Edited by KernowCooper, 07 July 2013 - 09:49 PM.

[Earwax]

If you want to look at the differences in curves go to CSI, or 123, or any other programmable curve.  The differences in the speed of uptake of the curve and the max timing are slight but obviously do make a difference. 

[KernowCooper]

And those difference even slight could be costing you 5bhp+ at a given point in the curve, Its easy to get a engine to produce its max power with any distributor its what its producing between 2000rpm and max power that could make the world of diference.

[Captain Mainwaring]

An advance curve is not tailored to a CC of engine unless were talking factory stock, once you have modded your engine it may need a different advance curve to stock to perform best, so for example a modded 850 might like a stock 1275 advance curve.

 

you need an adjustable distributor and rolling road time to dial it in perfectly.

 

With a more powerful spark you may not need as much advance as it lights the fuel charge easier 

 

what ever curve a distributor has you should be able to set it about 8/12 (base timing) at idle and get it to run though.

 

 

Not necessarily so - what matters is the spark duration. CDi and some electronic ignition sparks can be too short a duration for high revs and lean mix. Even in conventional kettering type type systems, it is the closing of the points for the next cycle that quenches the spark.

 

I think a lot of guys into home tuning are very optimistic regarding the accuracy and repeatability of spring controlled advance systems. 

[Captain Mainwaring]

And those difference even slight could be costing you 5bhp+ at a given point in the curve, Its easy to get a engine to produce its max power with any distributor its what its producing between 2000rpm and max power that could make the world of diference.

 

More and more difficult now with emissions being top priority for most applications. 

When people weren't so concerned about what came out of the back, there was a lot more flexibility to get close to maximum available power with a little compromise. 

 

I remember years back taking my Cooper S to Mann Egerton for a "tune up" - they set everything by the book - it was undriveable. 

Ended up with everything back to just the way it was. All in the days when rolling roads weren't available to the great unwashed.

Edited by Captain Mainwaring, 08 July 2013 - 03:20 AM.

[Captain Mainwaring]

 

 

An advance curve is not tailored to a CC of engine unless were talking factory stock, once you have modded your engine it may need a different advance curve to stock to perform best, so for example a modded 850 might like a stock 1275 advance curve.
 
you need an adjustable distributor and rolling road time to dial it in perfectly.
 
With a more powerful spark you may not need as much advance as it lights the fuel charge easier

That seems logical and is what I thought would be the case, so the question is how far out are these aftermarket distributors? Even looking at a complete stock engine, I can't see one dizzy being perfect for an 850, 998, 1098 and 1275. So what ARE they set up for I wonder?

 

I come from a VW background and know vw on the aircooleds used over 50 different distributors all with different curves/limits and vac ranges, every change of engine spec go a new factory best curve.

 

I would think they will have picked a generic sport/road curve.

 

If there anything like the same Chinese crap distributors you can get for the vw's they wont even have the same curves from one to the next.

 

If you have a good timing light with rpm dial etc you can plot you own (centrifugal advance plug vac off) with it.

 

I hope mini people arent going to have the same bunch of nightmares vw people are having, I have seen some of these aftermarket distributors have 10 degrees advance so have 20, some 30 some non!!! Bunch of *******!!

 

 

 

I'll be honest and say that I don't think the Lucas distributors are hugely accurate, just look at the technology that's inside them. Yes, you can just about create a curve using centrifugal weights, you'll have to balance up the pivot position versus the spring rate versus rpm...oh, and versus temperature too, 'because the spring rate will change slightly hot to cold. The tiniest variation in spring rate and pivot position will cause things to end up not as intended, even more so as our distributors are running half engine rpm.

 

Do I think you stand half a chance with a chinese aftermarket distributor? Absolutely not - better keep you old Lucas unit and stick the electronic on it (and no, £15 for electronic ignition is not going to be any good).

 

I think if you really care what happens between no advance and maximum, then you'd better spend proper money on a programmable system with a trigger wheel that doesn't rely on one chain transfer and one gear transfer to time the spark to piston position.

 

Personally I want something that produces power somewhere close to spec without requiring unnecessary complications and resetting every five minutes - ideally without CB's.