[Healeys] Healey 100-4 timing

Kees Oudesluijs coudesluijs at chello.nl
Sat Nov 3 04:07:19 MDT 2018


Sorry should read max advance with a/vacuum retard system/

Kees Oudesluijs

Op 3-11-2018 om 09:48 schreef 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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