09-27-2010, 10:30 AM #1
Ignition Timing - The holy grail to 4Tec performance
Since the Motec ECU is fully programable I started increasing ignition timing at higher RPM this past summer and noticed big gains in performance. Not knowing where the limit was ( i.e. deto ) Nils loaned me an SKM and Motec Pete guided me through how to set it up which allowed me to picked-up over 500 RPM and a significant amount of accelleration so you may want to give this a read.
As it turns out these 4Tec's like lots of advance at high RPM and very little advance at idle. So first was to characterize the knock signature so we could get a clear distinction between normal combustion and a knock event. This proved to be very elusive with a 4Tec motor as normal combustion is very noisy in the frequency range where you look for knock. I could bore you with the details and there are more than one way to skin the cat but I found that using a high center frwequency and a late window gave excellent distinction and balance between cylinders in fact after laboring through this for a few weeks I now question anyone ( Riva, Les Cook and even Seadoo ) who does knock sencing as its very easy to get a false read which will hurt your performance by decreasing ignition advance. Below is a comparison of the sound captures ( full spectrum ) for normal combustion vs deto. The knock window depicted was an interim solution and I eventually moved the knock window much later. So if you have an SKM I recommend these settings for a 4Tec:
SKM / ECU Manager Settings:
Center Frequency - 16 KHz
Start Angle - 90 deg ATDC
Window Width( fast ) - 90 deg
Window Width(slow ) - 90 deg
Gain Cyl #1 - 1.0
Gain Cyl #2 - 1.0
Gain Cyl #3 - 1.0
Knock thershold 75% with 0.5 deg retard for each 1% above thershold
There is alot more to this but the good news is that you can now just focus on the results. I could attach my map but I have moved around a lot of I/O so the sensor inputs and auxiliary outputs are not compatible with a stock ski. I think the best summary is:
Idle ( 1600 - 1700 RPM ) 0 deg BTDC. If you use more advance you will need to increase your idle speed to get a consistent RPM but it will also give you a little more lively responce from idle.
Midrange ( 3500 - 7000 RPM ) 47 deg BTDC. You can put in more advance with 93 octance but the midrange will get softer not stronger.
WOT ( 7800 - 8800 RPM ) 41 deg BTDC with 93 OCTANCE ONLY. This was peak power for me running 16 - 17 psig boost. Most pump gas engines would meltdown with this much advance but the 4 tec motor has a unique combustion chamber design. Any more timing resulted in deto and less peak RPM's. If you are not using an SKM ( which most of us aren't ) then I would use a safer 39 deg BTDC with 93 octance. If you do not have 93 ocance available then I would recomend 2 deg less per 1 octane point. I also did some testing with 87 octance and the difference in deto was significant a higher boost levels. With 87 octance I was getting hard deto with only 31 deg BTDC
Make your table with smooth transitions and you will have some new found power from your engine. It was amazing to me how different the 4tec motor responded to "A"-typical ignition timing and this is truely the holy grail to making these motors perform.
09-27-2010, 11:05 AM #2
- Join Date
- Aug 2009
- Discovery Bay, CA
wow good work i know very little of skm or motec for that matter but for you to post all that info (which most people keep for themselves after all that hard work) is very generous of you and i'm sure there are people out there that will absolutely love that info.
i hope your in the HIGH 80's with the motec and 3rude!..... cant give all your secrets away though
09-27-2010, 11:07 AM #3
- Join Date
- Feb 2008
Very interesting !
conclusion that 4tec seadoos, need advanced ignitions close 0 at IDLE / 47 degrees at mid / 7000 -8800 41 degrees.... very hard numbers i think
09-27-2010, 11:14 AM #4
- Join Date
- Aug 2010
- Slidell, LA
Thanks for posting, this is excellent info!
09-27-2010, 12:08 PM #5
I'm glad I had something to share ! This was a real education for me but I loved every minute I spent as it paid off in performance. Every piece to the puzzle was not what you would expect based on other engine expeience.
09-27-2010, 12:25 PM #6
09-27-2010, 12:31 PM #7
- Join Date
- Apr 2005
41 degree on boost at high RPM is not save . I work with mappings for the 4-Tec engine every day and have access to a dyno ad well. You can go as high ad 31 -33 degree at high RPM and 93 pump gas. All rotax racing ECUs and also the Les Cooke mapping have aggressive timming setup, and work very well
09-27-2010, 12:49 PM #8
- Join Date
- Feb 2008
09-27-2010, 02:47 PM #9
Well I'd like to see the data which supports your claim of "not safe". I have a lot of files, sound captures, log files etc ... which show normal combustion and no deto. Even better yet I have done long WOT runs and no signs of deto, hung valves etc.... However there are alot of things in play here so lets qualify. First I'm talking about standard compression pistons and 93 octane from a good source ( Mobil, Sunoco, etc.... ). If you have bad gas then even 31 deg BTDC is "not safe". Second you need to make sure your A/F ratios are in check which mine are. At WTO I'm running lambda at 0.82. For those intrested log file attached. Also need to make sure you Crank Reference Position in the ECU is set properly. Lastly, your cam timing needs to be in the ball park of correct. If it is pushed too advanced then you could get deto but that would be pretty far off and the motor would be missing hundreds of RPM's in that case.
Now all of that said there are very few ECU's out there that you can adjust the ignition timing and for the ECU's that are not adjustable ( Riva, Les Cook, Rotax Racing, etc ) it is nearly impossible to find out what the timing is at high boost and RPM ... belive me I've tried measuring with a timing light, water flying around etc...
So please let us know what test data you have and how it was measured to make the statement 31 - 33 deg BTDC is the limit for 93 octane ? There is very little public data out there on ignition timing curves for 4tec motors ... I've looked.
09-27-2010, 03:41 PM #10
Thanks for writing that all up
I have to say that I would be nervous about running that much ignition timing with out a knock control system on board
It certainly appeared that your engine was fine with that amount of ign and I just came off the dyno last night with similar results.
I have also seen other 4tecs giving det spikes at 36 and left unchecked that would certainly have destroyed the engine.
The amount of ignition you can get into an engine is dependant on many parameters, combustion chamber shape and compression ratio are big factors along with air and engine temp, AFR effects it and oil temp and and and on it goes.
One thing is for sure, they make power all the way to 40 degrees, if you put in race fuel you can run there, anything less of a fuel and I would make sure you had knock detection happening.
Again thanks for your time in letting the guys know and giving us your feedback
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