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gvy

ignition timing topic

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Hi everyone,

 

I started this topic , not because there is a problem, but I would like to share some thoughts about ignition timing.

 

I always used to set my timing static at 7°BTDC . When I measure with the strobolight, this gives me a 7° advance at idle and about 25° max advance around 3500rpm .

These values are as in the technical data , workshop manual for S1. (907 engine european spec)

 

Now my car is an S2.2 (912 european spec with dellortos).

The distributor is a Lucas 43D4 (no vacuum)

But I have a pertronix module build in

Coil is a flamethrower epoxy 3 ohm 40611

 

changes to the engine:

better flowing K&N airfilter in original housing

original cast Exhaust manifold is changed by SJ sportscars SS tubular manifold , no resonator, free flowing muffler.

engine intake and exhaust ports are portmatched to intake and exhaust manifoldports. They are considerably widened.

 

As a test today I played with the ignition timing and set it at 12°advance at idle and this gives a max total advance of around 32° above 3000rpm.

I did one short testdrive ( engine was warm because I reset the timing while idling in my garage) and it seems to react OK. Very subjective of course. No signs of knocking. The idle is around 100rpm higher. I did not yet recalibrate the carbs. (I syncronised them 1 week ago)

 

Now the reason I started this topic , is to hear what others are setting their ignition timing at.

Also because I find it strange, that most people I talk to with classic cars ( with sport engines) find that the Lotus numbers 7°/max25° advance seems really low and retarded.

Also on the internet I see that it is common to have around 12°static and go as far as 36° max advance on many engines.

 

 

Greets

 

Geert

Edited by gvy

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There will also be a school of thought that suggests the engine has more efficient combustion if it needs less advance to achieve the optimal setting.   However, as you have an NA, I would run it with the most advance it will accept without knocking under load conditions - e.g. accelerating up a moderate incline in top gear   

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Hello Geert,

   My S1s all have Dellortos tuned to UK/European spec with either 50s or 55s as idle jets, and Lumenition Optronic ignition. One has original federal cams in Federal timing, another is federal cams with UK/European cam timing, a third has the E-cams with European timing, and the fourth I don't know.  They all have factory stock Lotus exhaust systems and U.S. spec pistons.  All are otherwise stock.

   They all seem happiest at 10-12 BTDC at idle.  I try to keep the maximum advance between 30-33 degrees BTDC (on the distributors in the U.S. cars (25D?), this can require putting sleeves on the posts so the weighted arms don't swing out so far).  In the limited amount of experimenting I've done, I've found my cars to be happiest that way, have gotten as much as 30-31 miles per gallon on the expressway (but usually 28-30), and the engine just seems "happiest", both off idle and from 3000-6000RPM.

   With more advance (I've gone up to 36 degrees), I have never heard pinging/knocking, but the car feels like it is losing something in the higher rpms.  With less advance, it can be a little hesitant off of idle.   I set my idle speed at 1000 RPM, following an old practice in the U.S. where some believe that the marginally faster circulation of the coolant (actually recommended 1100 RPM) helps the car run cooler in hot climates.

   I am quite happy at 10-12 BTDC at idle, but I would like to try limiting the advance to maybe 27 or 28 degrees, to see if the car runs better and smoother in higher RPMs.  But as that involves work to fix something that isn't really broken, I keep putting it off!   :)

Long story short:   I'm happy with 10-12 idle, 30-33 max, but am open to others' input.

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Side note:   My observations of idle jets

50 -- car runs "light" -- runs clean, but lacks power. 
55 -- ideal balance of power vs. rich exhaust

57 -- noticeably more power from approx 2000-2500 rpm, but very rich at idle, and exhaust goes "blub blub blub"

 

This is for my climate/elevation.

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Hi Geert,
 
Probable the modest 7° BTDC was special for the S1 with his heat problems (original distri: you can manipulated by hand the timing, I had it always on 10°, nice but need better cooling in the enginebay what I did, you know)
 
The later versions with better cooling are 10° not an issue.
With mine HC engine I use 10° and have also experimented with the springs of the distributor for faster reaction.
Result: max 32° at 2500 rpm; difficulty: the moving parts have to follow: extreme balanced. And a lot of try and error to get it right.
Tri-jet carb’s settings: idle jet: 58
I must mention that I use higher lift cams and adjustable camsprockets; other main jets and main air correctors.

 

I find out that the spark plugs from the turbo (7) gives a better ignition.
All together a better cold start and drives comfortable, only the consumption is higher. (a little, sometimes more)
 
I use this setting on mine Excel (except the distri springs) & Esprit.
That’s all in memory now because the latest years I did use mine Lotuses not much. (lack of time)
 
The next thing would be a double ignition system than you could return to the standard setting.
 
Cheers,
 
Jean
 

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Hi Tony,

 

I went from 55 to 58   1,5year ago when I performed a revision of the carbs.

My engine is the 2.2. You are right, the exhaust is burbling , but The low rpm torque seems better.

 

Anyway, ignition,

 

I also got an answer of Tim Engel in another forum and he seems to agree with 12-14 static and 32-34 BTDC as a reasonable limit for a street car.

 

Now my own experience setting it to 12 static 32 total advance and that of others  makes me wonder why it is so far away from the lotus manual at 7°BTDC static and 25°BTDC total advance?

edit : Jean you probably explained it in your post although I find similar settings in the S3 manual???, but not for all specs

 

 

 

Let the comments and experiences of other people coming please.

 

Geert

 

edit

Jean, thanks for the input.

Edited by gvy

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Geert, I found some info on the tech docu from Lotus:

 

2,0 engine: 7° BTDC, max 25°; (for USA: 10 - 12°, max 30 - 33°?)

2,2 engine: 9° BTDC, max 25°

Turbo engine: 12° BTDC, max 28°

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A very late reply as I only just found this thread. I believe that ignition timing is slightly retarded from the optimum as standard in order to meet emissions regs. Slightly retarded ignition will tend to reduce HC and NO emissions. This would explain why some people have experienced better performance and higher idle speed by advancing the ignition. All this is imho as I have no documentary evidence from lotus sources.

Edited by rjwooll

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Hi Richard,

Not only the ignition timing, but also this post is slightly ""late timed" :P

On the other hand : If I read JeanVM post good , I understand that USA spec cars had a more advanced timing spec  I thought that in those times USA emission were more stringent, 

Still, interesting input. I kept mine at 12 static - max 32

Edited by gvy

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Hi there yes my timing isn't great! It's difficult to directly compare US and European spec cars as the cams and carbs are also different (and there may be air injection on some cars - Californian spec?)

The timing on spec 6 engines (early esprit, US spec) can be compared with spec 5 (European spec.) The mechanical advance characteristics are very different - spec 6 advances all the way up to 6000rpm while the spec 5 tops out at 3000 rpm. At idle and typical steady speed rpm (say 2000-3000 which would have been used for emissions testing) the mechanical advance is less on spec 6 than spec 5. Add to this the fact that spec 6 uses the 8 degree retard vacuum canister and you get significantly more retarded timing at idle and steady speed. At higher rpm the spec 6 engine does have more mechanical advance but this would probably not have affected emissions testing much.

e&oe as usual!

Richard

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From what I have read, the confusion on ignition timing specs for the Lotus 9xx series engines hinges upon semantics, the limitations of clarity when English is used in more than one way to describe a fact. The consensus seems to be that Lotus intended the printed specs to be understood as follows:

1) - Idle timing when checked with light on running engine to be as described; i.e. 10 degrees as printed means 10 degrees read with the light;

2) - Mechanical advance specs, i.e. 25 degrees all in by 2500 rpm, means what would be seen with the distributor on a machine built for the testing and adjustment of a distributor, figured in crankshaft degrees;

3) - Total timing, not ever helpfully spec'd in the manuals, to be the sum of the idle setting plus the advance added via distributor mechanism(s). So 32 - 36 degrees total for the N/A engines. This concurs with abundant comparable examples found in engine modeling software widely in use today.

4 - One noteworthy real-world case to demonstrate how troublesome has been the Lotus protocol for these specs was when the owner of a G-body Turbo participated in a Road & Track magazine top speed comparison test with other fast exotics, back in the '80's. Owner was vexed by his Esprit's inability to get near to its maximum speed, as declared by Lotus. He thought total timing was to be as what seemed to be spec'd in the manual at 28 degrees. Later was given a non-qualifying run with timing set to the sum of distributor plus idle figures and - voila(!) - the car lit right up, accelerating with gusto to higher than its claimed top speed. The official test outcome would have put the Lotus at the top of the list, if not for the confusion which arose via the peculiar way Lotus chose to describe these timing specs.

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I am not sure where the confusion lies because the Lotus service notes are very clear. For examples of confusion caused by poor English check out Ferrari manuals! 

The table in the service notes has a column "Ignition timing to be set at" which has the figures for exactly that. Such that for a standard n/a spec its 25 deg at 3500-4000 RPM. Thats the setting which should be set with a timing light. Its different for USA spec engines.

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Yes, they're clear to me as well but if you don't read them carefully you can come unstuck (as the esprit owner above amusingly did!)

The thing that initially puzzled me about the timing on some engines was the vacuum retard function. I hadn't come across that elsewhere but I can understand the reason it's used.

Richard

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