Mike, this won't give you a definitive answer as to what advance at what
RPM, but it will give you a little insight as to what mods affect what
direction you should be looking at in setting your curve. Specifically,
this is about MGB "B" series engines, but the theory should be the same.
http://www.mgparts.co.nz/Setting_up_Ignition_timing.html
Larry D
----- Original Message -----
From: <rrengineer@dslextreme.com>
To: <spridgets@autox.team.net>
Sent: Thursday, September 14, 2006 5:20 PM
Subject: What Curve?
Besides the question about manifold vacuum as opposed to throttle plate
port vacuum, how do you figure what curve you need for the cam (266
profile), compression, etc for my engine? I have a 25D dizzy (Lucas 41400
from a 73 Midget that Frank sent me, thanks Frank)) that Jeff at Advanced
Distributors says that manifold vacuum is specified. I guess the question
boils down to: what dizzy (vacuum or non-vacuum) and what curve and where
vacuum is taken would be the best for a 1275 street motor with a 266 cam?
Do I have other varaibles to consider? The 25D from Frank is a total
advance of 18 degrees at 2600 rpm. I don't think this is enough for my
motor. Phil at APT says a total advance of 26 degrees in a vacuum dizzy
would be a great starting point until a dyno test could be done.
Mike MacLean
60 Sprite
56 BN2
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