Hey guys, why do some racers lockout the centrifugal advance in their distributors? And apparently run with full spark advance all the time?

Is the car more consistent, or maybe has a quicker vehicle reaction time? Is it only for very high-stall torque converters?
Thx!
Troy

Steadier ignition timing, easier setting idle rpms as timing doesn’t back off at lower rpm and the fact the motor operates above full advance on a non locked distributor while going down the tract are few reason I do it.

One less thing to go wrong

All the above true. But I have been running a standard mechanical advance distributor for 20 years, no problem with anything. It goes full advance at 3500 RPM. Car is consistent as anybody's.

Either way is good.

quote:

Either way is good

32* of timing @ 1000 rpm just seems crazy to me. But a lot of people do, and have, done it w/out incident. Old weighted mechanical advance was simple enough to comprehend. A gradual upward slope as rpm progressed. With todays ability to monitor spark advance on street cars, it doesn't come close to that scenario. I can't decipher any kind of a pattern. I guess there is so many inputs it's forever changing.

consider two situations;

*The first is a dedicated drag race engine with a big cam and high stall converter and stiff rear gear. In this situation, the engine only operates at wide-open throttle in a narrow RPM range. Plus, with a big cam, full-timing idles better. And also, because of the big cam, cylinder pressure is bled off at cranking speed so kicking the starter is not a problem. Think about the number of drag race engine you see with a crank trigger pickup. [fixed timing] And MSD sells a distributor with locked timing so it is a popular option.

*The second situation, is a stock or mild engine that is daily street driven. In this situation an advance curve tailored to the engine need is desirable. Modern, EFI, computer equipped engines vary the ignition widely to suit the need at the moment.

I’ve seen written, that some of those with high compression using a start retard, have experienced kick back when cranking, the same as the lower timing you’d experience from a mechanical advance.

I agree 100% with markemark. Been there, done that.

I have experimented with both electronic timing retard and mechanical advance. In both cases, with a fully modified drag race engine, fixed timing is best for the engines I build. Fixed timing in a full race engine has enough benefits to overcome any shortcomings.

most of the time the kick-back is due to a lean condition.we have had high compression motors that needed no retard(11 deg),and actually would crank better on full timing.most all of mine i pull 10.my experience is the further i got from a lower hp motor the more it liked fixed timing,as mentioned above

I was running a 500 cu in former pro stock motor, 15 to 1 1030hp, 38 degress timing. I used a MSD start retard with 10 degrees retard. I would regularly break flex plates and starters. Took the start retard off and no more problems.

quote:

Originally posted by Joe C:
I agree 100% with markemark. Been there, done that.

Programmable ignition can allow one to control the locked advance for reduced timing when starting (and running) if desired. This method can quickly give the operator the ability to modify for best results.

I too use start retard, does what I want it to, and looks like this in programming. The faster the engine turns the less start retard it allows.

I spin my motor over and hit the ignition switch. Starts so quick it almost scares you...on gas that is. I had one of those msd start retard boxes in one of my cars. Nothing but trouble to start it and i swear it never sounded right to me. Ripped that thing out and never looked back.

Had issues with start retard as well. Even with 16v. Removed it, put really light springs in the distributor. All in by 800 RPM (32). Bearings show nothing abnormal, and I am embarassed to say that it's been 12 years since any major overhaul has been needed-inspections only. ~700hp SBF. Real simple old school setup that works as well as I could ask it to.

I had issues with kickback until I started cranking and then flipped the ignition switch. fired right up no strain no kickback ever.

I had kickback issues for years that progressively got worse, turned out to be 7AL2 going bad. I tried everything to counter it. Got it fixed two years ago and no kickbacks since and running a lot faster too since box was fixed and only thing changed.

Starting kick back issues are caused by mainly timing issues, voltage/current issues or lean staring conditions (mostly with alky vs gas).

Timing Issues
For crank trigger setups, I have seen issues develop from distributor moving causing spark to jump to the wrong cylinder. Those using slip collar distributors are really prone to this issue. For those using start retard in the 10 degree range or more, need to make sure your rotor is phased correctly. Even more important to do this with small diameter caps such as the small crab caps.

Voltage/Current Problems
When cranking your motor, the system needs to maintain at least 9 volts when measured at the starter! If it won't then the starter can be over powered by spark and ignition in a firing cylinder before TDC and push the crank backwards. Other than battery issues, most of this is usually caused by bad grounds or wire that's too small for the job causing too much voltage drop at the starter.

Lean Start Condition
I really haven't seen this with a gas deal but have many times with alky, especially on the first startup of the day.

Start Timing Retard
I wish I could say if you have this then do that but in all the motors I have had, each one wanted something different (I use a crank trigger) so don't be afraid to try different retard values. Same for your startup procedures with carbs, one pump, two pumps etc, crack the throttle blades, leave then closed, etc. If you are having starting issues with no other issues as noted above, try different start procedures to see what works. Probably need one for cold and warm starts.

Thank you for all the great responses, guys!
T.

One less thing to move around and cause problems.

On most drag cars we have plenty of stall so we are not really loading motor down at low RPM so mechanical advance is not needed IMHO.