Thought I'd throw this out there to others for opinion please...
So, it's well known that a "solex" U20 has no vac advance and that you change the initial timing from 17 to 20 degrees. I've heard that is done because "big carbs like or need lots of initial advance." With the Megajolt and now the Microsquirt I can do any timing map I want. With the Megajolt I continued to set initial at 20 degrees and worked from there (it automatically retarded timing while cranking to be nice to the starter). However, as I switch to EFI (40mm from 45mm carbs with 37mm chokes) I'm wondering if it makes any sense to continue the 20 degree initial timing, or go to a more common 17 or so.
Are you close to getting your efi up and running yet? I would say stay at 20 initial and try it. I thought Datsun engines love a lot of advance anyway. We are all waiting with much anticipation on these Jenvey's.
70MTRoadster wrote: Sat Dec 19, 2020 5:07 pm
Are you close to getting your efi up and running yet? I would say stay at 20 initial and try it. I thought Datsun engines love a lot of advance anyway. We are all waiting with much anticipation on these Jenvey's.
Thanks man, I'm excited too!
Everything is ready... no leaks, initial fuel and timing maps uploaded, parameters set... just waiting for my wife to be available as she wants of be there for the first attempt, and she's put up with my constant talking about it so it's the least I can do... she loves the Datsun almost as much as I, just doesn't understand it. Monday?
I think the U20 SOLEX was set at 20* initial due to the fact that they couldn't get significant vacuum due to the 4 throttle configuration and relied only on mechanical advance?
I'm not sure about starting with 20* initial advance.
1) you have a significantly higher compression ratio than stock.
2) you have a much higher power ignition than stock.
These suggest to me a faster ignition of the mixture, and a slight retard of initial timing. (any info contrary to this I would like to read, please.)
The faster the burn, the less ignition advance needed.
An engine which 'requires' less ignition advance will be more efficient and make more power.
I know you've complained of the BPR (projected nose) plugs causing detonation/pinging in your engine before, but, this might be a good time to experiment with them and see how they work when you can program the timing at any rpm and possibly reduce the timing a bit also.
*Projected nose plugs (NGK BPR type) move the spark into the combustion chamber a bit. This is supposed to help the burn 'speed' by getting the spark kernel closer to the centre of the combustion chamber.
I don't have any idea how much vacuum will be present at idle, or how quickly it dissipates. It is something you may want to investigate further as you go along. Considering both your VE table and ignition advance table are vacuum and rpm based I'm not sure how these tables will be different than what I'm used to with the plenum manifold I was using....
Do you know how much vacuum is present at idle? (kpa for your map)
Wait....What is wrong with the ignition map you were using with the Megajolt? I thought you had that tuned on the dyno - just the WOT?
I would hunt down some Megasquirt ignition maps for an older 2 valve/cyl engine with similar combustion chamber (wedge) and ITB's and see what they have done.....
I had the 'cranking' ignition advance set at 10*BTDC and it always cranked and started easily, settling into about 14* advance at idle (1800cc R stroker).
Again, just my (occasionally incoherent) $0.02
Thanks for posting, following this with great interest as I'm on a similar path with my stroker.
Thanks for all the thoughts Daryl, you always add good info. I did pretty much transfer my other timing map to the new system, but we were always mainly focused on timing at WOT and max torque when on the dyno. I've also decided to start using Boostane to bump up octane levels... if this stuff works it will become a regular additive as it is so much more economical and effective than anything else I've seen/read about (I have not added it yet). Once I get the EFI working well, I'll be back to the dyno with decent octane to set safe max torque timing.
I've decided that things should be safe at 17, so I adjusted the map accordingly (so easy in Tuner Studio). Firing soon!
There is a wide range of ignition advance that the engine will idle at. How to get to the sweet spot, I don't know.
I tried one time adjusting the timing to find where I thought the engine idled best, just by ear. I went as low as 10* and up into the 20's, other than the extremes, there was very little noticeable difference, although I wasn't watching the A/F ratio while doing it. I do remember the engine temperature coming up at the lower ignition advance.
Good question for Google....How to find best idle ignition advance setting?
Greg
Since I will be doing this myself soon, you got me looking into it....
Seems with higher octane fuel and longer duration cams you need to increase the timing... http://www.megamanual.com/begintuning.htm#spark
