Derf,
According to the APT web site:
For maximum performance from your British Sports car engine the timing of
the spark must be accurate, and when compression ratio and camshaft in
particular are changed, a re-curved distributor is essential.
Maximum compression ratio for any road car running today's pump gas should
be at the most 9.6:1 (unless the car is always at above 3000 feet
elevation).
For road cars with less than 10.0:1 compression ratio you should use a
vacuum type distributor, to make sure there is enough advance at idle and
cruise.
Use manifold vacuum if possible, only switch (in most cases) to "ported"
vacuum if the engine rattles for a couple of seconds when you go quickly
from cruise to full throttle.
If your compression ratio is above 9.6:1 you may be best to go with the
non-vacuum road performance type distributor. Aldons refer to these as
"yellow" and race as "red".
I'm not sure I should have copied the above excerpt from the APT web
site, but the new HIF44 that I bought from APT has a port nipple for
vacuum, but the web site recommends manifold vacuum for road cars
under 10.0-1 CR. My car is exactly 9.0-1 CR. I know this because
the block was decked to within .005 of TDC Per David Anton's
instructions and the head was CC'd to produce 9.0-1 CR by David along
with some aggressive porting. I'm using a 266 cam profile and 1.5
ratio rockers. So, an advance curve should be fairly easy to plot
out. I am going to have Advanced Distributors restore and re-curve a
Lucas distributor Frank gave me. There is a rolling road dyno that
comes to APT when David gets enough requests and I will take both
distributors with me so I can tell you which one is better for
performance.
Mike MacLean
60 Sprite
56 BN2
derf
>> So, I've got a single HIF44 on my 1275 with a 266 cam and ported head.
>> I
>> am using a Mallory dual point distributor. If what you are saying is
>> true, I am wasting gas except at WOT. The brand new S.U. HIF44 I bought
>> from APT has a nipple for port vacuum for timing. I have a Lucas
>> distributor 41400A that Frank gave me. I have been told it is for
>> manifold vacuum, not port vacuum. What are my options for distributors?
>> Mike MacLean
>> 60 Sprite
>>
>>
> Your options are whatever distributor you want. Lucas, Mallory,
> Nippon(Isuzu), Hitachi(Nissan), 123, FlameThrower, or whatever you desire
> can be made to work. I've had Lucas, Hitachi, and Nippon on my 1275.
> Hitachi works fine but there is very little clearance between the body and
> the dizzy cap. I am currently running the Nippon.
>
> I am running a single HIF6 on my 1275. I use a spacer (phenolic? maybe)
> and
> have it tapped for vacuum for the dizzy and/or PCV. I think APT sells the
> spacers. Something like this with the proper vacuum advance dizzy would
> probably be best for you, too. But, I don't think it would be much better
> than the Mallory. You might gain a little in economy but why sacrifice
> the
> reliability of the Mallory for the Lucas?
>
> If you do switch please let us know what difference it really makes.
> Cheers,
> Derf
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