formula271

Has anybody tried advancing the timing on a 502 MPI ? If so what did you see for gains in rpm? I have done this in the past on small block carb motors and gained rpm. What is the best way to advance the initial timing? Will the ECM take over higher up in rpm? Thanks for any input.

hotbeek

I'm interested in this idea too.

Some people who dyno'd their motors. How many/much HP/TQ did you gain per degrees.(28-30;30-32;32-34 etc.) I realize there's a point where you'll be losing HP. Any real life stats ?

mcollinstn

The MPI has a knock sensor and will pull out timing if it senses knock. Bottom line is you will only be able to advance a few degrees before the sensor starts reacting and going beyond that will only make the motor hard to crank when warm.

WETTE VETTE

I do not have any experience with these motors, but I did read on some other posts that these motors will run better on 87 octane than on 93 which tells me the speed of the burn on 93 octane is to slow. Perhaps if the timing is advanced to 36 or 37 and 93 octane fuel is used there will be a gain. Maybe even try some 100 octane unleaded racing fuel from Union 76. The better fuel will possibly keep the pinging down as the timing is advanced and some power gains could be realized. Just a thought. Most BBC like 36 or so degrees of timing in naturally aspirated form. Merc has a warranty to satisfy therfore they set the knock detector a little on the sensitive side. Try it and let us know.

Vinny P

Wette Vette;

That is an interesting possiblity. I am sure that you could get away with running a motor like that. But, I don't understand the need or desire to advance timing past 36 maybe 38 in a marine motor. Adding timing takes away top end power, and isn't that what we all want. I understand that too little timing is no good either but there really isn't a big window to play with here. This is why in my old drag racing (cars) days, I spent alot of time and money getting a triple step timing retard system to work right. 40 degrees initial, then 2 degrees retard in 3, 4 , 5 gear leaving 34 degrees through the lights.

WETTE VETTE

My motor picks up RPM on top going from 36 to 38 degrees timing. Going to 40 doesn't show a gain so I set it at 38 degrees. My motor is 13:1 compression so the flame needs time to get over the piston dome and more timing gives it just that. I also have very efficient combustion chambers so that actually helps the flame travel a little better. Reducing the timing at say 6500 or 7000 rpm will net some HP gains, but from what I have seen on naturally aspirated, unported motors up to about 540" 34 degrees is a good safe place to run and 36 to 38 will be where the most speed will be obtained in the 5000 to 6000 rpm range. The only way to find out is to give it a try. Hell you never know some motors like 32 degrees.

HPJunkie

ttt