Ignition timing curves per gear

banjo · Post by **banjo** » Sun Oct 02, 2022 1:58 pm

I want to experiment with a different timing curve in each gear and I am looking for some "rules of thumb" for things to try or point me to some reading material.

Car is a 74 nova, 3350 pounds,sbc 406 on methanol. Has a glide and 5.13 gears.

Car has always run hard down low and has picked up when I went to a deeper gear, but would lose mph. This to suggest something isn't optimal in high gear.

Engine accelerates very different in 1st vs high. 1st, it's nearly 900 rpms/per second and in high its around 200 rpms/per second. Can help but think there would be different timing requirements.

BOOT · Post by **BOOT** » Sun Oct 02, 2022 3:48 pm

Try less total as heat builds

Alaskaracer · Post by **Alaskaracer** » Sun Oct 02, 2022 3:59 pm

Carb or injection? If it's injection, you might need a high speed lean out to pull a bit of fuel away up top. If you're running a belt drive and a Ron's setup, that's something that's normal. Pump output is usually set up to deliver about twice what engine will ever need, and as rpm increase, output does too. If you want to try a high gear retard, pull 1 degree after the shift and see what happens....

banjo · Post by **banjo** » Sun Oct 02, 2022 4:35 pm

This is carburated.

PackardV8 · Post by **PackardV8** » Sun Oct 02, 2022 5:07 pm

Your theory is correct. Low gearing hides a lot of less-than-optimum tune.

I don't have a lot of experience with this application, but don't most run a locked distributor (i.e., no curve in the distributor) and pull timing with a box?

banjo · Post by **banjo** » Sun Oct 02, 2022 5:35 pm

I plan on pulling timing with my 7530t, just playing with timing in high gear at first. I am hoping to be able to correlate an improvement with my datalogger by comparing the time it takes the engine to accelerate though a set rpm range in high gear. I plan to take 2 degrees out and add two degrees in and compare those to the base run.

Post by **In-Tech** » Sun Oct 02, 2022 6:02 pm

It's definitely worthwhile, in our Hyabusa testing we did boost and timing per gear including neutral and 2 step control. Once dialed we went from a 7.70ish to a 7teenish in the 1/4

As you would think, more timing in the lower gears. It's a time thing, think about the flame kernel.

steve cowan · Post by **steve cowan** » Sun Oct 02, 2022 6:05 pm

Some thing to consider in my opinion -
In a drag racing application where you are turning rpm past peak (500 - 1500) before the finish line,TQ /HP/ VE going down,do we need to adv or retard ignition timing to try to help carry??

rebelrouser · Post by **rebelrouser** » Sun Oct 02, 2022 6:13 pm

Back when my drag car was running 10.50's in the 1/4 mile I played with the timing, at the time it had 4.56 gears. What I did was I used an MSD box and it retards the timing 4 degrees after 5,000 rpm. I have left it hooked up for a lot of years and assume it still works, car is running 9.60's now. But on a 440 Mopar stroked to 500 cid it liked 38 to 40 degrees at the launch, and 36 at the finish line. I looked and I don't think they even make the box I am using now. But I believe this one will do the same thing.

https://www.jegs.com/p/MSD-Ignition/MSD ... 2/10002/-1

Don Terrill’s Speed-Talk

Ignition timing curves per gear

Ignition timing curves per gear

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