How about a nice simple question about Spark Tables??

Most anything I've read on automotive tuning and the couple of spark table calculators I've found seem to suggest a Spark timing table should look something like...


Most advance bottom left, least advanced top right.

Indeed an awful lot of the Harley maps I look at are the same generic shape. So here's the question...

Why do older Dyna/Softail 358 map spark timing tables look like this...



Looking at the current Harley maps for 358 configuration files, they have both types, even at stage 3 or 4. The current Dyna/Softail have switched to 617 maps with the top "more typical" (if that is the right way to look at it) strategy.

So, Pro tuners, do you have your own spark tables or which is the right? best? whatever? style to use and why?

Now I know the trick about making flames come out of the exhaust that the ricers/showmen use, but from a tuning perspective, what do you think Harley is doing here? Is one strategy better than the other?

cheers

 

My guess would be that the spark tables that is calculated is based on trapped air/fuel and compression ratio. The actual maps is based on empirical measurements for performance with one slight twist. Once the useable part of the timing table was mapped the guy tuning stopped. The High RPM/Low MAP pressure section is not really seen that much. It's typically on deceleration. it possible that some other function shuts off fuel during this time so the spark advance is not needed.

Bet Cole knows..

 

No fuel, who cares when the spark happens ...that makes sense

I've also heard about changing the amount of engine braking effect, and if you look at F1 (maybe not quite as popular over there, sorry) they keep putting fuel in and use part throttle during deceleration so as not to hammer the crank ...or something like that anyway ...although Harley EFI was maybe not designed with quite that level of techie input?

 

I believe f1 uses this strategy to avoid turbo lag. The idea is to keep the turbo spinning so when the driver gets on the throttle there is instant boost awaiting...so no lag.
Bob

 

One thing to note is that other than idle and starting, you run in the region outlined.. The areas where with higher map have more critical timing for performance and lower map for cruising.. Cruise timing is not as sensitive but of value for achieving better gas mileage.

 

So in terms of the parts of the table that actually matter, the two are effectively pretty much the same, give or take a bit around cruise?

 

FWIW, the far right (100kpa/1000-2000rpm) needs to be addressed, both fueling and timing, because when aggressively taking off from a stop, the engine will go to 100kpa especially below 2000 rpms.
Bob

 

Good point, possibly the trickiest part of the whole tune to get right, all the tables seem to be crucial around that area

 

Its the high revs low kpa deceleration area I suppose I'm left wondering about making any real difference or not.

From the newer maps, I'm guessing the 358 is something of an older strategy ...whatever it was

 

Yeah.. If you like to lug it..