[Healeys] Healey 100-4 timing

[Kees Oudesluijs]

The maximum advantage should be limited to prevent damage to the big end 
bearings. In general, depending on the engine, this is around 32° to 35° 
/*total*/ advance. The distributor advance system with the weights and 
springs is limited to about 17°, the vacuüm advance or retard (depending 
on engine) may produce another 5° or so advance or retardation. This 
means that when the ignition of an engine with a vacuum advance system 
is set at say 10° static, the maximum advance is a safe 32° at anything 
over about 2500rpm.

Kees Oudesluijs



Op 3-11-2018 om 03:05 schreef Michael Salter:
> Thanks for your input on ignition timing Michael.
> I have always found the factory specs to be a little confusing.
> They state 6 degrees BTDC as the timing (which I presume to be 
> "static") and then state that the distributor produces 16 - 18 degrees 
> at 2000 RPM (distributor speed) which I figure to be 32 -36 degrees at 
> 4000 engine RPM.
> I interpret that to produce 6 + 34 (2 x 17) degrees BTDC at 4000 
> engine RPM for a total of 40 degrees which sounds like an awful lot.
> My engine does not sound at all happy with 40 degrees even with 110 
> octane!!
> I'm wondering if I have been over thinking this process and the stated 
> advance is meant to be "at idle" with the vacuum connected (not normal 
> practice as far as I was taught) which would add 6 degrees of vacuum 
> advance which would vanish at full throttle producing a net of 34 
> degrees over 4000 at full throttle.
> I have been setting the timing to 32 degrees BTDC with the vacuum 
> disconnected at 4000 RPM and the engine runs fey well and very cool, 
> in fact too cool without a 180 degree thermostat.
> I am running 8.3:1 compressions with an M cam.
>
> M
>
>
> On Fri, Nov 2, 2018 at 9:16 PM Michael Oritt <michael.oritt at gmail.com 
> <mailto:michael.oritt at gmail.com>> wrote:
>
>     Wayne--
>
>     Exactly right--it is total advance that matters and I arrived at
>     that number by gradually increasing advance and seeing the effect
>     upon water temperature at speed and under full load.  Anything
>     more and the car would begin to overheat. A bit too much less
>     advance and performance fell off.
>
>     BTW I am running a DW "fast street" cam and tubular header and a
>     Mallory non-vacuum advance distributor fired with their Unilite
>     module.  I too have a Smitty's five-speed and the Toyota box, 180
>     XAS's and 3.54 diff set give me about 72-73 mph at 3K rpm's indicated
>
>     Best--Michael Oritt
>
>     On Fri, Nov 2, 2018 at 6:03 PM Wayne Schultz <waschu2 at gmail.com
>     <mailto:waschu2 at gmail.com>> wrote:
>
>         Thanks to Michael and others I am going to stick with 34 - 35
>         degrees total advance for now. What, I think this means, is
>         that the advance at idle is secondary and not as important as
>         total advance. Cruising with the the Toyota five speed or the
>         original overdrive on the highway is right in the 3K RPM range
>         so I think this the perfect RPM to limit total advance. I
>         might make a run to my local airport and buy some 100LL fuel.
>         I have worked in aviation since 1967 so I have a few friends😃
>
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