Why do I here about racers locking the advance on their distributors, what is the purpose and doesn't it make it hard to start.

 

[X(] ive never heard of that. it may refer to taking a vacuum advance type dist and making it mechanical only(any thoughts anyone) and yes it would be difficult to start especially with higher compression numbers kurt

 

I just researched my question. The distributor is locked completely at full advance so that timing does not jump around. Two methods are used to start the car, crank the engine before you power up the distributor (very tricky).
Use a electronic delay box to retard the timing while cranking. The advantage is rock solid timing without timing jump at warm up and low idle speeds that can cause stall when the advance jumps around, my problem. I guess I'm off to the mail order performance store.

 

[X(] sounds like a high dollar full on race application kind of trick. you shouldnt see more than a couple degrees of variation in a newer or tight engine and should be less variation when loaded. as for steady timing you wont see it move much when setting it at 3500 rpm. also im not sure how streetable this set up is going to be i think youll be inviting more drivability problems than you have now. while i dont race with the big boys and cant afford the $25,000 motors, i have been playing with the generals powerplants for a couple decades now and i have never run across anyone using this locking method(might be a circle track trick or other niche use) are sure you dont have slop in the engine elsewhere? are these all new parts were working with? there are millions of people who are running around without locking thier dist and the engines are working great. is your idle set too low? anything with a cam will want to idle closer to 1000 rpm than 500-750 rpm kurt

 

Thanks, I appreciate your input. I am a high school vo tech teacher, this is our Auto shop car, we only take it to the track for bracket racing. There is no control box other than a rev limiter. Were running a Ford 9 inch with 4.30 gears and a turbo 350. Our results with this combo have been somewhat disappointing. 12.72 at 107.4 is our best. So we called Lunatic for a cam recommendation and this is what we got. The car hasn't been to the track yet as we are trying to get it sorted out now, just finished the cam install 5 days ago. It now runs so rough is stalls under 1400 rpms thats our issue. Our jets are 76 prim and 80 secondary, could also we need to fatten up. Any ideas, thanks Dave by the way it does feel strong above 3,000

 

Hopefully your car will be able to light op the tires off the line, or have a pretty loose converter, otherwise you will get some serious pinging if the engine should bog. As t90jetpilot mentioned, the distributor will be fully advanced at 3500 RPM and is going to stay there. Fluctuating spark advance at low RPM is normal if your engine has a lopey idle, andvaries in sync with the RPMas it is supposed to do. The proper way to set the advance on a wild engine (no computer control)is to determine the RPM when max advance occurs, raise the RPM another 500, just to be sure,and set the maximum timing with a light, and lock the distributor there. Also, very important is to taylor the advance curve to the needs of the engine. This is best done on a dyno whee the spark advance manually adjusted for max output at 500 RPM increments, and logging the results.This is done through the entire RPM range, and then the spark advance curve on the distributor is tailored to those specs.

 

I thought about this alot and think I will try to tailor the spark curve. Right now with the weakest advance springs in, full advance is all in about 2,000 rpms and according to one advance kit chart starts in at about 800rpms. I think the problem is with the cam needing to idle at about 1200 that the advance is too jumpy. If I can bring in full advance by 3000 rpms while keeping the weights from jumping around at 1200 I'll be happier with it, what do you think? This may require a little more initial advance. The converter I,m using is a 3600 stall

 

[X(] i looked at some of your specs for this motor (87 camaro 383) and parts seem to be pretty well matched including the stall. the one thing that may be a bit wild is the cam and i wouldnt suspect your gonna get it to idle anything less than 1200-1400. this combo of parts probably wont come to life until the 3000 rpm mark you mention and will be rather lopey and vary rpm's below that. id try bringing in the timing a little later(stiffer springs) the light springs and lope of the cam may be causing the erratic idle timing. initial timing will probably be in the 2-6 range. remember this combo of parts is designed to make power in the 2500-3000 rpm+ range and so bringing in all the timing before that is not real beneficial. bringing it in in the 800-2000rpm range is good for fuel mileage but not for the race motor youve got. let me guess your not concerned with fuel mileage? you may find that after you switch springs it may idle a little lower kurt

 

Pete and Kurt thanks for your input. I'll be in school next week, but the week after I'm going to play with this combo and your ideas and see what kind of performance it has. I'll definitely get back to you with the results. I'm trying to get it sorted out before school in the fall so we can have the kids work on losing some weight and see just how quick this car can be. Dave

 

gto64dr,

A few questions and all will be O.K.

What is the .050 duration of your cam? Man if I didn't get a dollar for every time someone posts the lift and not the duration. Duration is FAR more valuable in the performance/characteristics of an engine than the lift.

Are the timing chain and gears new?

Are you only using the Pertronix distributor for your ignition? Was it "curved" for you when you bought it? (It should have been according to the co.)

Is this car strictly for the local dragstrip (and the kids of course)?

If it is for the local dragstrip only, why do you care where it idles?

If you are using a 3600RPM stall convertor,why do you care what the timing curve is below that? (Hint: Unless you are a regular bracket racer and know what to ask for when getting your convertor built,it willNEVER stall at the advertised spec. AND if you bought that convertor before the cam swap it WILL stall higher than before).

It's funny how most of the posts here have been talking about locking a distributor like it's some sort of voodoo. It's one of the simplest tricks out there and it does serve a purpose.

After your answers, you'll get more grasshopper.

Sorry Pete but you know I'll write a novel again.

RM