[Healeys] Healey 100-4 timing

[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>
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> 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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