turbo, built engine..blah, blah...anyways i want to retard the ignition to be on the safe side of detonation...oh yeah, im at custom je 9.6 pistons.... anyways, i have a msd dis2...whats a good value to start with... any help..thanks
doug

Originally posted by lickscissors
turbo, built engine..blah, blah...anyways i want to retard the ignition to be on the safe side of detonation...oh yeah, im at custom je 9.6 pistons.... anyways, i have a msd dis2...whats a good value to start with... any help..thanks doug

Well, exactly how much ignition timing you will have to pull out is kind of a guess and check.

Are you going to try to see how much power you can make on 93 octane?
Are you going to be doing it Home Depot style by mixing in xylene to see how much you can stretch it without leaded gas?
Or do you want to just run C16?

For a xylene mix (like dumping in 1 gallon when you have about 1/2 of a tank, seems to work the best for me, lets me run about 1.3-1.4 bar on stock timing, if I don't add any xylene I can get 1.1 bar on a good day) or pump gas, you will have to figure out how much retard you need on your own, you will probably need a MSD knock alert (XtremeRS has one, saw it at the Shootout, it's pretty cool) in order to figure out exactly when you start to detonate and how effective pulling out X degrees per Y PSI of boost is. I've found that the upper limit for my setup (8.8:1 pistons, 93 octane, 11.5-12.0:1 AFR, ~20 degrees of advance) seems to be about 1.0-1.1 bar of boost. I haven't really played with my MSD unit much at all, I'd rather run a little less boost on a more advanced timing curve, but these days I've though about retarding the timing a little so I can get closer to the peak efficiency of the 16G in order to supply enough airflow for these cams... But anyways...

If you're going to run C16 at all, you probably will want to leave the timing alone.

If you just HAVE to get a number so you can go out an try it, start off with 3 degrees of timing pulled back for every 15 PSI of boost. I just pulled that number out of my ass, give it a try, see what happens. If you think that you're loosing a bit more power than you'd like and your EGT's are higher than they should be, try to lower the number a little until you start to hear detonation, then raise it a little to give yourself a little saftey margin.

see, right now im running 9.6 compression with a 14b, 30# injectors, sfmu, and about 9#'s...now i havent had any detonation (that i know of), but i have this msd and im not doing a damn thing with it....im pretty sure that i should pull timing a bit, but wasnt sure on how much or when i need to.... im not going crazy with the home depot stuff...just wanted to be safe than sorry.... i do have plans on 450 injectors, water injection, bigger turbo, and more..mmm...boost..... so just wanted to get it running as good as i could before throwing her back in the garage for the winter....thanks for the reply and let me know some more if you can
doug

You don't need to retart the timing unless you're getting detonation, which you shouldn't be. I'd leave it alone, you'll only lose power.

i understand that...but im not sure how i know if im getting detonation...id rather lose a little power than lose all my time and money put into the engine....i just wanted a rough estimate on how to adjust it, when and why...i see you can have it start to pull timing at certain rpm's, i was just going to try maybe 1-3 degrees at like 5650rpm's????? anyone?
thanks
doug