I think in the ideal world, you would need to fire at TDC to create the biggest pressure rise to move the piston when the moment on the crank is at its highest; however, this is done with the assumption that at TDC you will burn all the fuel resulting in the highest “push/pressure”….. Unfortunate this is not the case since flame propagation depends on a number of variables, fuel energy content, geometry of the combustion chamber, compression…etc hence why we need to fire pre-TDC inorder to achieve the best trq or results.

With gasoline and since it has a higher content of energy vs ethanol, many are able to predict where that sweet spot occurs not by measuring pressure but with observing a study idle that can overcome the pumping loses and external loads (electrical & mechanical).

According to wiki Gas is at ~44 Mj/kg and Ethanol is ~ 26.
Maybe some of the guru's can pitch in and explain as well.
Hope this helps!

ps. Under 500 rpm, the ecu is in cranking or start-up mode and I don't think it runs off the spark surface, if you log a start-up, then you will note a max of 5* if I am not mistaken!...someone may confirm?

 

2.3, HX35, S2 cams, 93oct, 27 psi tapering

not fully tuned yet, will take suggestions

 

Yes you are correct. The ECU locks the timing at 5* when cranking. There was a definition out there some time ago which allowed to manipulate the table; not sure if it ever worked though.

 

Do you have a log?

How does the knock look at 330 load and 5250rpm?

 

timing seems abit high for 93 octane at peak TQ, just my opinion, got a data log?

 

my tuning laptop got knackered, so don't have access for all my files in it..

but there is no knock at peak torque area and at higher rpms as well
I mainly suffer from spool-up knock, somewhere in 180-300 load area

is spool-up timing high ? afrs in that area are 12.6 tapering to 11.6

 

Maybe drop the spool up timing by a degree to see if it helps. You also have a section from 250 load to 280 that goes 7-6-7-6 during spool.

 

well that maybe true however you normally dont want to be on the edge of a motor knocking. You never want to tune a car by upping the timing and then as soon as it knocks lowering it by a degree, you tune for power. If a car makes 455hp at 9 degrees and knocks and then makes 454hp at 8 degrees and doesnt knock but makes 450hp at 7 degrees, you put that car at 7 degrees. This is why if you have access its ALWAYS better to tune on a load based dyno so you can go cell to cell and tune based off power and tq not just when the car stops knocking. Your AFRS are fine for spool up in my opinion. I cant see your timing map right now though.

 

I wish I could "like" this post.

Well said.

 

What do u guys think about mine?
Idle 14.6-15.2 Crusing is the same.
Mods Stock injectors, Kelford 272, Tomei turbo, TBE, 10.5;1 pistons.
It was tuned at 22.5psi and since I have turned down the boost bout little over a full knob.
Im getting it retune in 2-3 weeks.
I'll do some logging tmrw.

 

Pump gas? looks like too much timing, and the map doesn't look particularly good to me.

 

Yes, its on pump. What would be good timing map at my power level? Im gonna be running bout 19-20psi max on pump.

 

Start looking through this thread for examples. The biggest things that are issues with your map are:

-Too much timing from 100 load through the rest of the load range
-At peak load you should be between 0* and 4* timing and end around 10* to 13* at 7k with your boost level and mods
- Timing should vary from cell to cell no more that 5* with a 20 load difference and 3* on a 10 load difference

Hope this helps you.

 

Being a 10.5cr engine I probably wouldn't push it even that far. Something closer to 0-2 peak and 8-10 at 7k, IMO.

 

Overlooked that portion thanks for the correction