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Post by noddy on Aug 20, 2017 18:24:21 GMT
Hi all,
Bit of a techy question - but does anyone know the advance curve for the Lucas distributors fitted to our cars?
I'm having a few ignition issues (pinking at medium/heavy load + difficulty starting) and havent got a clue on the advance curve the dizzy should have. Reset the timing yesterday -using the workshop manual 6deg BTDC static - to find car pinking at very low revs and undriveable! I wonder if my lightly modified engine would make that much difference to set up? (standard cam and compression - just a big valve gas flowed head!)
Any thoughts welcome and/or info on the dizzy advance curves.
Roger
Research has shown that the Riley 1.5 was fitted with either of the following:-
Lucas DM2 40510 - adv.curve 546 - also fitted to MGA, MGA 1600 & Magnette.
Lucas DM2 40587 - adv.curve 665 - also fitted to the Mganette.
(Mine is the 40587!)
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Post by canuck on Aug 22, 2017 13:05:37 GMT
Hello Roger This is a subject worthy of discussion. FWIW I have played about with my distributors and will admit I have failed.  caution, one can spend quite a bit of £ on springs & weights. What I do know is that whatever was thought 'way back when' does no longer apply. We have modified our engines, compression ratios, camshaft timing and the fuel we use. All this has bearing on the placing of the power band through the RPM range. I have a rebuilt/re curved contact breaker distributor built by 'your side of the pond' equivalent Martin/Distributor Doctor. Standard Lucas coil and no problems.  actually in all my cars.
Have a read of the following, this may put this in context?
www.teglerizer.com/mgstuff/lucastuning.pdf
Let me have a think and I will get back to this thread.
B |
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Post by 2robert4 on Aug 22, 2017 18:57:07 GMT
I have a copy of the curve given to me by the Distributor Doctor from when he overhauled my Distributor in Jan 2017, I am not sure how to attach pictures so have not been able add them to this post.However since fitting the Distributor I have had no further problems with pinking or loss of power when climbing hills. Although I have always used Shell 99 Octane fuel at all times for some years now.
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Post by canuck on Aug 27, 2017 16:59:08 GMT
Roger If you choose top play about with your distributor, particularly the vacuum advance unit, pay attention that there is ported units, (vacuum at carburetors) as our Riley, or manifold units, think modern MG B etc.
B |
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Post by noddy on Aug 27, 2017 18:41:37 GMT
Hi Bruce, Thanks for the vacuum warning - however I am now running without any vacuum advance! I was finding that with the lightest of throttle (at any revs) I was getting pinking - once the vacuum was removed it was much better. Have now re-set the timing with max mechanical advance at 25deg. I know that most experts (John Twist & MGA Guru etc) say 32deg is best - but my car seems much happier at 25 - any more than that and it starts to pink. I am still wondering if this difference in timing is down to the fact that my engine breathes much better than standard - but still runs the standard cam  . Unfortunately I am now getting out of my depth a bit - ie relationship between timing, cam, engine breathing, gas flow, compression ratio etc and how they effect the engine! Anyway car seems to be running much better now - pulls well and I am getting 29mpg - even though I am not hanging around  Regards, Roger |
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Post by canuck on Aug 27, 2017 21:33:01 GMT
Roger This is interesting. Am I to understand that you are now blocking the vacuum port from the carburetor and not having any influence to the vacuum advance can on the distributor? Ummm?
This would now give a situation of only centrifugal advance, purely Mechanical (the distributor cam weights and springs) and is now is purely RPM-responsive, nothing changes your advance curve except changes in RPM. This is usually desirable at WOT driving only, think your racer car. Is this a good thing for the lanes/roads?
With the vacuum advance working correctly, now the ignition timing will respond to engine load and cold/hot engine operating conditions, giving you the correct degree of spark advance at any point in time based on engine load, fuel charge regardless of RPM. This will/should accommodate both lean and rich mixture conditions, at idle or at speed on road.
So as far as I am concerned, vacuum advance is a good thing. George right now sports the OE camshaft, but does have a ported & flowed bigger valve cylinder head with slightly higher than OE compression ratio. I have had his distributor re curved to match and quite frankly cannot ask for more. FWIW I have a distributor on the shelf waiting for my 1800 engine. This has been built (curved) to match the 1800 engine build.
What happens when you suck on your vacuum advance unit? Are you able to see/feel/hear the breaker plate move? If you suck on the vacuum advance and block the end does the breaker plate stay put? If not the diaphragm in the vacuum can is punctured. Martin @ Distributor Doctor can rebuild the vacuum unit or sell you a new one. If the vacuum can is working then you have other issues.
B
PS: you can map your advance curve with a strobe if you want to know what you have.
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Post by noddy on Aug 29, 2017 18:33:02 GMT
Hi Bruce,
I thought that might raise a few eyebrows - esp with you! ... and yes I am running without any vacuum advance.
My rational behind it, is that when an engine has been modified you have to treat it differently and find out what suits that engine the best.
From what I have read, vac advance is beneficial in two areas, engine pick-up at low revs and fuel economy when cruising.
I have found that with my engine (light flywheel and better breathing) engine pick-up is really good without vac adv. - so no need for it. Fuel econ is not really a big factor for me - and as I am getting around 27-30mpg anyway on richer needles - then there is no real point in fitting vac adv..
Almost every race engine doesnt run vacuum advance and I have just read that Brown and Gammons now supply a non vac dizzy for our application ...
"From our experience in restoring and driving MGAs we have developed a modern Lucas type distributor to suit the MGA engine running on modern fuel. This is supplied in non-vacuum advance form as the vacuum advance tends to cause “pinking” in the 2500 to 3500 rpm range on modern fuel."
Its interesting to note that the 'pinking' at 2500-3500rpm is exactly what I have experienced in my car!
Anyway - after a lot of experimenting I have now got to a dizzy setting where the car is running well, picking up beautifully and not pinking at all. 2robert4 has kindly sent my a copy of his dizzy curve as supplied by the Distributor Doctor - which makes very interesting and useful reading. It shows that he gets full mechanical advance at 2000 rpm and that is a full 25deg ! (equating to a 12.5deg advance at the distributor). As noted in my previous post I am running at about 25deg max advance - so I am reassured and happy.
Unless anything untoward happens, I am now going to leave it well alone and just enjoy!
All the best,
Roger
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Post by canuck on Sept 1, 2017 20:07:38 GMT
Roger Curious results for sure. I am almost certain you are leaving something, (acceleration, MPG, easier starts or whatever) on the garage floor. Interesting how our results vary.
Since the beginning of time, with the internal combustion engine installed in automobiles, think Ford Model A that had a lever on the steering wheel to adjust timing advance. Think modern cars have a ECU to play with timing advance, fuel charge etc.. This all makes sense to me.
My Riley is engine more modified than yours reads, (compression ratio, cylinder head mods, lightened stuff etc..) as well I have a highly modified MGB (long story but dynamite results) and both have a vacuum driven timing advance installed. I will mention however that both these distributors have been worked on to optimize the curve so all is well. My 1800 engine I am building for George is mildly modified, and will sport a re curved distributor with a vacuum advance.
All I know is there is not a 'one size fits all' advance curve so as much as I respect B&G that quote sounds like marketing to me.
Speak it Martin to ask his opinions on vacuum advance, very interesting subject indeed. You can map your advance curve with a strobe to find out what it is, with and without the vacuum timing advance.
You are happy, and I agree with you, if what you have works, leave it where it is and enjoy.
salut
B
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caution, one can spend quite a bit of £ on springs & weights. 
actually in all my cars.
. Unfortunately I am now getting out of my depth a bit - ie relationship between timing, cam, engine breathing, gas flow, compression ratio etc and how they effect the engine!