Downdraft

I recently replaced the MSD cap and rotor and asked my engine builder (United Racing Engines built my 487HP 383 c.i.) the correct timing. The instructions are:

set initial timing at idle between 26° & 29° degrees then set overall timing at 38° at 3,800 RPM and no vacuum advance.

Well. if I set at 26° then my overall timing goes to 45°.

If I set my overall timing at 38° at 3,800 RPM then my initial timing goes to 22°.

The car runs well with the 22°-38° set up.

I just changed the cap and rotor - the springs and weights remained the same. Am I missing something?

Alex

DansYellow66

I can't tell from the pictures - do you have vacuum advance? If so, it needs to be disconnected and the vacuum line to the engine plugged when setting timing. A total of initial and centrifugal timing 0f 38 deg (probably somewhere above 3000 rpm) is a bit high but probably OK. Initial timing (vacuum advance disconnected) can seldom be more than 16 to 18 degrees without having problems with the motor turning over. Sounds to me like you are setting inital timing with the vacuum advance connected which is incorrect. If I'm wrong (or you don't have vacuum advance on the distributor) then set max timing (initial + centrifugal all in) at about 36 degrees (requires a dial-back timing light) and let the inital timing fall wherever it falls. Connect the vacuum advance up again and your done.

kellsdad

That's a lot of debris. Did you solve the problem that caused the rotor damage? Did you get all the debris out of the springs and mechanical advance assembly?

Downdraft

United writes " Make sure the vacuum advance is not hooked up. The engine is designed for mechanical advance only.

Downdraft

Kellsdad, The problem was that the screws that was holding on the rotor came off
(both) one stuck on the rotor, you can see at at about 11 o'clock. The other screw was sticking out of the cap (the threading). Maybe the screws were not tightened? The have the cup shaped washers that should never come off. I did drive the car about 5,000 miles in 2 years - and no issues. This was a cheap fix. I first vacuumed and then blew out any remaining debris - it is nice and clean now. The car is blindingly fast – I set the MSD box at a max rev of 6,000 (it redlines at 6,200) - my issue was that I cannot follow the builder’s instructions and have 26°-29° initial AND 38° overall.

JohnZ

Typical "race motor" setup - they've obviously never read "Timing 101", and remain among the great unwashed who don't know how vacuum advance works. They need to read this:

http://www.camaros.org/pdf/timing101.pdf

Does the distributor have a vacuum advance canister, or is it just not connected, or ?? Can't tell from the photos.

DansYellow66

I would like to know how you can even turn the motor over with 26 - 29 degrees initial advance - it would have to have almost no cranking pressure? If it will start and run OK at 22 degrees (amazed it would start hot at that also) then I guess you are where you want to be.

Downdraft

Now it's set at initial Bouncing due to choppy idle from 19.5 to 20.6° and at 3,800 rpm exactly at 38°.. Runs like a champ

DansYellow66

OK - how are you measuring timing down to a tenth of a degree?