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BN1/2 Maximum disty advance

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healeynut

healeynut

Jedi Knight
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Hi -

I posted this question elsewhere for my A90 Atlantic and no one knows... so I'll ask for the 100 which has the same motor.

What is the maximum distributor mechanical advance for the standard BN1/BN2 motor?

I bought the 123Ignition disty for the Atlantic and I need to know what max setting I should program the 123 disty with. I know the Atlantic is slightly detuned even from the stock 100...
 
Hi Alan,
The BN1/BN2 distributor is Lucas number 40495. It is a model DM2P4. These distributors had a very odd "toggle" mechanism on the centrifugal advance which was NOT very accurate or reliable.

FWIW, these specs were published for the centrifugal advance. Engine rpm & engine degrees.
@ 1200 rpm - 2 degrees
@ 2500 rpm 18 degrees
@ 5000 rpm 34 degrees

As you can see, to avoid detonation at high rpm, the safe initial advance would only be about 2 degrees.

For the 123 distributor I would probably try the "9" curve ie.
500-1000 rpm = 10 degrees
2000 rpm = 19 degrees
4500 rpm = 33 degrees
Maybe increase the distributors initial advance by about 3 degrees to 13 or so.

This sounds like an interesting project. There are many setting possibilities. Let us know how it works out.
D
 
Dave -

Thank you so much for the recommendation, it is much appreciated.

The Atlantic's horsepower is commonly quoted at 88 bhp, which compared to the BN1's 90, means they were quite close.

The compression ratio is, if you can believe it, around 7:1 so that's probably the bulk of the difference between the A90 and the stock BN1 hp spec.

Static advance on the car is spec'd at 6.5 deg BTDC so I think the advance curve you suggest should be just about right.

The A90 is about to have the pan dropped (I think a bearing spun /bcforum/images/%%GRAEMLIN_URL%%/wall.gif ) hopefully I can get by with just changing the bearings.... I won't know for a month or so what the result is with the 123, but I'll let you know. It sure is a pretty looking unit.
 
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