I finally received my Aldon-rebuilt and recurved distributor from Seven
Enterprises on Thursday afternoon (back-ordered since September! Build
date 2/96).
My problem, especially after adding the Janspeed headers, was a loss of
power between 2000 and 2500 RPM. Not so good for autocross!!
After dropping in the Aldon (it comes with points, cap, and its own
pinch-clamp, checking the dwell (49.5 degrees, not bad) and setting the
timing to about 13.5 degrees BTDC at 1100 RPM, I was off!
The dip is totally gone. Now there is smooth power all the way from
where it should be on a stock engine. The surge starting at 2500 and
rising past 3500 is still there, but does not stand out as much because
the dip is filled in.
Over the weeks I was driving the car (in town) with this dip in the power
curve, I developed a throttle feathering technique which reduced it. I
believe I was basically preserving manifold vacuum with this technique.
On the old distributor (stock), the most I could get without pinking was
about 10 degrees advance at this RPM. The vacuum advance added its own
(about 5-7 degrees, I think). With the headers, manifold vacuum falls
off faster than with the stock manifold, due to lower extraction velocity
at lower RPMs, due to the larger cross-section. Anyway, it seems to me
the vacuum advance was pooping out early, the centrifugal advance had not
come up to speed yet, and so I was some few degrees short on advance, in
that 2000-2500 RPM range. Comments?
The Aldon distributor is a late-model distributor, the one right before
the Luminition. It seems to fit right into the place of the earlier one,
though. I recommend it highly, but you better have money ($220 from
Seven Enterprises) and plenty of patience!
The other option is to re-curve your own distributor, of course. The
main trick seems to be to limit the total advance to prevent pinking with
a higher initial advance. There may very well be a spring change as well.
John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock
"1st Law of OleoHydroDynamics - Little British Cars Leak. - JMT"
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