timing settings

[71VERT]

Does anyone know the timing setiings for a 1969 427/435 hp with transistorized ignition. I found some int he chiltons manual but I do not know if they are correct for a TI distributor.

Thanks
Jerry

 

[JohnZ]

The original production timing map for your car with the 1111928 T.I. distributor called for 4* BTDC initial timing (vacuum advance disconnected), and the centrifugal advance system provides an additional 30* @ 3800 rpm, for 34* total. This is a "smog" curve, along with the "ported" connection for the vacuum advance so it doesn't provide ANY advance at idle.

The centrifugal system starts with 2* @ 1100 and ends with 30* @ 3800; if you set the initial advance any higher than 6*, you'll have to take some off the top of the centrifugal curve or you risk detonation. Ideally, you want 20*-24* in the distributor and 10*-14* initial to keep the total at 34*-36*, with the centrifugal "all in" by 2800 or so.

It will also run MUCH better and run cooler at idle and in traffic (verified on many other L-71's and L-72's) with the vacuum advance connected to full manifold vacuum (tee it into the choke pull-off diaphragm hose), and a vacuum advance can that is fully deployed at idle (the one you have now isn't) - get an Echlin #VC-1810, about $9.00 at NAPA.

Suggest you take the distributor to a shop with a distributor machine to set up (and limit) the centrifugal advance curve as outlined above - you won't believe the difference.

 

[71VERT]

John,
Thanks for the reply I am still a little niave when it comes to timing, I have a digital timing gun with advance and a I bought a spring set and weight. If you have time could you explain exactly how I go about doing what you explained. Or is it easier to pull the distributor and take it in. I am very handy so I do not mind trying either suggestion however I would like to learn how to properly set it up myself.

Regards,
Jerry

 

[JohnZ]

Jerry - It's a bit lengthy to explain here, but you have the right tool already (the dial-back timing light); if it was just a matter of swapping different tensions of weight springs until you get the curve you want, it's pretty basic. However, in your case, the centrifugal advance curve needs to be limited (reduced), which involves using different sizes of limit bushings on the autocam pin (or shortening the slot the pin moves in if the larger bushing doesn't limit it enough). Here's a photo of the pin and its slot, just above the end of the condenser, in the autocam plate (click on the link). This needs to be done by a distributor specialist, with the distributor out of the car.

My article "Timing And Vacuum Advance 101" in the current (October/November) issue of "Corvette Enthusiast" magazine will give you a thorough understanding of ignition timing and both centrifugal and vacuum advance, and the follow-on article in the December issue (out in about two weeks) explains how to "map" your advance curve and optimize it at home without special tools.

Check out www.corvetteenthusiast.com for info.

 

[71VERT]

Thanks John,
I will probably try to take it out and take it in to be recurved but I appreciate the advice. I dont have a problem taking the distributor out but is there any tricks to putting it back in myself thats the only part that makes me a bit nervous, making sure everything is lined up correctly.

Regards,
Jerry

 

[JohnZ]

Update - the follow-on article I mentioned above in the December issue of "Corvette Enthusiast" magazine is out today - just got mine in the mail - it will answer most of your questions. I highly recommend reading my ignition articles in the October/November and December issues - they take all the "smoke and mirrors" out of distributors and advance systems and de-mystify them in terms anyone can understand so you can be confident in doing your own work at home.

Re-installing the distributor is no big deal - just mark the position of the distributor base collar to the intake, and the position of the rotor tip to the distributor housing (a Sharpie and/or tape works fine) before you remove it, don't disturb the engine while it's out, and it'll drop right back in - then re-set dwell and timing.

 

[Gunther]

Hi

Chilton says 4 degrees. That's not enough.
I followed Lars's instructions ( from corvetteforum.com , sorry ) and my big block became a different engine.
No bogging anymore when hitting the gas pedal hard ( double pumper carb ) and above 3000 RPM, you need to hold yourself tight on the steering wheel.
I have 37 total mechanical advance now, total including vacuum goes up to 52 degrees at mid RPM range.
Initial timing , if I remember is at 12 or slightly higher.
The engine is a solid lifter 11.5 to 1 compression and I did not get any detonation yet.
CHILTON's setting seems to be a average for all possible climates, but surely not set to top power.

Gunther