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Old 05-07-2019, 10:04 PM   #1
Yuri
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base ignition map m20b25 turbo

I have been searching around for a halfway decent base ignition map for my build.

After a year of collecting parts, I just got the old girl purring again and the last thing I need is a safe ignition map for boost. I found this, where a guy outlined the basics of building a base ignition map and I wanted to get your opinion on it.

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Do you guys have any basic rules that you follow to start a base map? my plan is to get the thing running and driving so I can enjoy the weather and slowly adjust the base map. This car is a hobby vehicle and I am not relying on it to daily drive so I want to get as much hands-on tuning experience without obviously sending metal through the hood.


I've found a lot of super eta maps or heavily modded ignition maps, but I haven't been able to find anything that's a safe m20b25 map. So if you have one laying around id much appreciate it if you posted it up; otherwise, general rules and calculations would also be very helpful!
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Old 05-08-2019, 12:37 AM   #2
Jaxx_
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This is a good primer for tuning, albeit dated:
http://www.megamanual.com/begintuning.htm
http://www.megamanual.com/ms2/tune.htm

I'll go ahead and say that the easiest and best way to figure out the best timing for the motor is on a dyno.

93 pump gas, I assume? Yes, 2 degrees per psi is a very safe bet. You probably want to limit your timing pull to no more than 50% of your max advance at 100kpa--for example, if you run 30 deg at 100kpa, you probably won't want run to run less than 15 degrees, even at fairly high boost. In most cases you are OK to leave a little timing in until you really start transitioning out of atmospheric, but this well depend on the setup and environment. I don't usually take timing out until 2-3psi over atmospheric, simply to help the turbo spool. Generally, after a certain RPM you won't gain much from more advance as the combustion chamber turbulence helps ignite the mix. This is why you'll often hear people talking about having timing "all in" at 3k. However, the beauty of modern ECUs is that your ignition map is no longer 2D along the WOT curve.

Just a vague comment to make you lose sleep: I recently read that M20s had a little bit of a 'hole' in the factory ignition map at peak torque and peak HP to prevent pinging. I think the RPMs mentioned were 4200 and 5200rpm.



Helpful things for me (personally) to remember for a safe base tune:
There is very little power (percentage wise) to be gained or lost from 11:1 to 13:1 AFR.
Your AFR reading is an average of all the cylinders.
Your fuel mix will also relate to your ideal ignition values(flame speed).
You will have been detonating long before you began to hear it in the cabin.
There are diminishing returns as you reach best timing, and the harder it will be on your bearings.
You can always trim to be more aggressive, you can't go the other way once you've scattered your internals and driven over oil.


Forgive the brain dump as I'm headed to bed. I also suggest that you pick up an extra set or two of spark plugs (maybe 1 heat range colder) and have them ready to throw in after a bit of running. I find NGK/Denso/Bosch copper to be best for boosted applications if you don't mind the easier fouling and shorter life. Even if you're buying 6, they're usually pretty cheap at $2-3 a plug.
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