Re: Why : No vacuume advance on inboard boats?
What vacuum do you see under the conditions you are describing? Boats are literally going uphill both ways. Check it under the towing at 2100rpm 27mph condition if you have not already.
I have no idea what distributor you are playing around with, but if you think your engine can stand it, and it appears you do since you have tried something already, you could try some kind of solenoid controlled Y valving between the ported vacuum source and the distributor can. You would want the distributor can to "see" only atmospheric pressure in one position yet have the carb port be closed. The other position would connect the ported vacuum to the can. I think you would need the venting on the distributor side to make sure there is no residual vacuum keeping the advance working when you have it "off". Close the valve when you need hammer time to turn off the vac advance. Turn it back on when you are in the safer vacuum usage conditions. You would still need to limit the mechanical advance some, it seems that auto engine distributors have quite a bit of mechanical advance built in, hard to keep the total under 34 with the initial up to 8 or so. Sometimes the cans have too much as well, all told it can hit 50 degrees or more advance.
Or you could run a really long vacuum hose up to the helm and just suck on it then pinch it off when you are cruising
kidding of course.
Modern EFI rigs use knock sensors to be sure the timing does not stay near the detonation point for any length of time. Without some kind of pre-detonation sensor in play then playing with more timing advance can be a dangerous game for your engine.
More timing advance burns the richer mixture better and essentially acts the same as leaning out the mixture so you have to watch the EGT (exhaust gas temp) as well, don't want to melt all the rubber exhaust components just trying to save a little gas.
Sorry for the delay on my part,, My comp. surver has been down for almost a week. I'm sorry . I'm looking forward to this information. I see more has come back... Glad to be among the living. H.S.
To answer your first statment,,, I checked it, the vacuum is near 15. My condition is 2100 rpm @ 20 mph. Engine 350 chevy. I was surprised at that vacuum, I was thinking more at 12.... for that rpm.. at that speed, the timing is near stock, is 18-20*. When I go to the dist. at that speed, I can advance it to about 30, no ping, plenty of safety room, and the motor speeds up, and vacuum gets better, 17-18. But I don't dare keep it there, cause it still will advance more when I speed up and then I am in the area of early spark for a dense charge of mixture.
I have recurved it to stop it's advance earlier and us lightr springs, but then I better not hammer it all out with the throttle or it could ping.
My idea was to use the manifold vacuum at the dash pod of the secondary lever to open the top butter fly. I checked it and it acts like maniford vacuum.
Vacuum advance will stop when it's hammer time. (slolom 4 skiiers)
Good points Cheif.... I checked the total range of mechanical.. I was surprized too. on the dist. I'm testing. If I start my timing at 10*, then when it is all in, it only goes to 24* ( no vacume advance of course.).So I take it that the mech. advance is a tot of 14*. That is good with me . My boat at WOT loves 25* total. Sounds beautiful. no strain. and no more extra power.
As for running that long vacuum line to the helm,,,,, I've sucked on worse things.......
You are correct on the danger of pinging. I do all my test with the engine cover off. I'm right there with it.
Actully, Rich or lean, thin mixture takes longer to burn than thick. Like high compresion or full throttle. My exhaust gas temp. does come down when I advance with the thin mixture. This is common science with internal combution eng. I use less gas, get more energy out of less fuel. easier on everything.
Later on this thread I will write what has now happened since this last week. Good news.
thanks cheif
