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Discussion Starter · #1 ·
Good Afternoon,

Is there anyone out there who has tuned MegaSquirt?

I currently have it on a 99 5.2L magnum and am having some trouble figuring out where I should be looking.
The truck is supercharged, running, and driving on megasquirt, but making very little power. My AFRs look fine so my only guess would be it has something to do with my timing. I have no idea what a timing curve should look like for these trucks.

Anything helps!
 

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I use Megasquirt but on a 68 Triumph inline 6 cyl. I have not done any tuning with supercharged (or turbocharged) engines.
That said I can give suggestions about how to set timing for the non-supercharged ranges. I would also suggest going to the Megasquirt pages and look for information.
Years ago Direct Connection, which was later Mopar Performance, published racing manuals with timing max advance guidelines. Big block V8s were recommended to use a max of 38 deg BTDC; I think small blocks were 34-36 deg. Max advance (not including vacuum advance) should come in by 3000RPM. This is termed mechanical advance since it has nothing to do with the manifold vacuum.
What's critical is timing under load, accelerating with low vacuum.

Be sure to check that it's been system is setup correctly first. Under "ignition settings" then "ignition options" there is a setting for "fixed advance" This is normally set to "use table'. Set it to "fixed timing" and then under "timing for fixed advance" set the timing to say 10 deg. This only needs to be done once and at idle is fine. Check using a timing light that your timing really is at 10 deg BTDC. Then you can go back to the "use table" setting.

Keep in mind that too much advance can destroy the engine, particularly at high RPM and high load. (WOT at 4000+RPM). If the engine knocks the advance is too high.

The ignition table in Megasquirt has the Y axis as load (vacuum) and the X axis as RPM. When decelerating the load gets low - close to 20 or less - indicating vacuum. When accelerating at wide open throttle on at normally aspirated engine the load goes to 100 - no vacuum. For a supercharged engine it will go higher - 150,200,300? - depending on how much pressure the supercharger is putting out. My table is set with a max load of 100, yours should have a max load higher.
For a non-supercharged engine the row at 100 load would start out at say 10 for idle 1000RPM, increase in steps to 34 at 3000RPM then stay at 34 all the way to the max RPM. You then add in vacuum advance slowly for load values less than 100 to give it vacuum advance. Max vacuum advance can be about 15 deg. For a more stable idle don't use any vacuum advance below say 1100RPM.

Vacuum advance is not important for acceleration - there is little to no vacuum. It tends to make the engine run better when cruising/decelerating.

I don't know what max advance should be for a manifold under pressure (boosted) but on your table in the load ranges above 100 I expect it would be no more than what it is at 100 load (34 deg) and very possibly less. I suggest doing some research on the Megasquirt site.

I've posted the table I use as an example but it does not include boosted ranges. Note that I'm using pretty conservative values and this is for an older 6 cyl engine.

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Discussion Starter · #3 ·
I use Megasquirt but on a 68 Triumph inline 6 cyl. I have not done any tuning with supercharged (or turbocharged) engines.
That said I can give suggestions about how to set timing for the non-supercharged ranges. I would also suggest going to the Megasquirt pages and look for information.
Years ago Direct Connection, which was later Mopar Performance, published racing manuals with timing max advance guidelines. Big block V8s were recommended to use a max of 38 deg BTDC; I think small blocks were 34-36 deg. Max advance (not including vacuum advance) should come in by 3000RPM. This is termed mechanical advance since it has nothing to do with the manifold vacuum.
What's critical is timing under load, accelerating with low vacuum.

Be sure to check that it's been system is setup correctly first. Under "ignition settings" then "ignition options" there is a setting for "fixed advance" This is normally set to "use table'. Set it to "fixed timing" and then under "timing for fixed advance" set the timing to say 10 deg. This only needs to be done once and at idle is fine. Check using a timing light that your timing really is at 10 deg BTDC. Then you can go back to the "use table" setting.

Keep in mind that too much advance can destroy the engine, particularly at high RPM and high load. (WOT at 4000+RPM). If the engine knocks the advance is too high.

The ignition table in Megasquirt has the Y axis as load (vacuum) and the X axis as RPM. When decelerating the load gets low - close to 20 or less - indicating vacuum. When accelerating at wide open throttle on at normally aspirated engine the load goes to 100 - no vacuum. For a supercharged engine it will go higher - 150,200,300? - depending on how much pressure the supercharger is putting out. My table is set with a max load of 100, yours should have a max load higher.
For a non-supercharged engine the row at 100 load would start out at say 10 for idle 1000RPM, increase in steps to 34 at 3000RPM then stay at 34 all the way to the max RPM. You then add in vacuum advance slowly for load values less than 100 to give it vacuum advance. Max vacuum advance can be about 15 deg. For a more stable idle don't use any vacuum advance below say 1100RPM.

Vacuum advance is not important for acceleration - there is little to no vacuum. It tends to make the engine run better when cruising/decelerating.

I don't know what max advance should be for a manifold under pressure (boosted) but on your table in the load ranges above 100 I expect it would be no more than what it is at 100 load (34 deg) and very possibly less. I suggest doing some research on the Megasquirt site.

I've posted the table I use as an example but it does not include boosted ranges. Note that I'm using pretty conservative values and this is for an older 6 cyl engine.

View attachment 111596
Thank you so much!! I plan on hetting some dyno time here soon to tune for boost, but this is unbelivably helpful. I had no idea what right would even begin to look like.
 

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I took a quick look on the megasquirt forums located at:
Searching for timing and supercharged I did find and example of timing for a boosted engine, although not a Mopar 5.2L:
The critical item I see about this timing table is that under boost the timing is significantly retarded.
I would do some research on this site - there is a lot of information and probably someone who has already done this work.
I really like Megasquirt and the ability to tune the engine from a laptop, even when running & driving.
 

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Also, if you don't already have it get the tuning program for a laptop - Tuner Studio MS is what I use. Then you can use the customizable dashboard while driving the car to monitor what it is doing. There is also an Android app for the phone that is similar - I use Shadow Dash MS.
I would (at least eventually) make sure the firmware on the Megasquirt controller is up to date.
Note that I'm running the Megasquirt hardware (MS3X) which includes sequential port fuel injection. I'm also using a wideband O2 sensor.
Megasquirt is to a large extent open source software. If you plan on doing much tuning yourself it does take quite a bit of research to understand everything including acceleration enhancement.
I ran Accell DFI on a 68 Charger which also worked well. I've worked with electronics for years and I switched to Megasquirt for my next install since it provides the schematics for the controller board including all the component part numbers. I bought the kit you assemble yourself. With the schematics and part numbers if something fails I can fix it myself at a component level; much cheaper than having to send in the ECU to have it fixed.
 

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I have MS3X on my twin turbo 93 Dakota. I've been running and using megasquirt since around 2011. I can send you my tune or whatever tables you need. I run traction control, boost control, flex fuel, launch control, etc with my setup. Email me at [email protected] with what you need.
 
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