Megasquirt VE map
Turbo Mini Forums

I am setting up Megasquirt soon with throttle-body injection using a GM TBI 700 body on a downdraft Weber manifold.

Does anyone have a volumetric efficiency map to share? Would give a nice starting point. Whatever you have from a turbo A-series, even if from another ECU, would be helpful.

I've found lots of Megajolt maps, but nothing for the fueling table.

1275 with Back Door Turbo

VE maps are specific to your engine and the injectors you use, unless ssome one has the same injectors as you, you will unfortunately have to start from scratch.

Doesnt Megatune have a table generator built in? This will at least give you a starting point

The injector characteristics are actually captured in a calculated injector pulse width. The VE table truly is entered in terms of % volumetric efficiency.
Certainly it will depend on the engine spec.
Yep, Megatune has something built in. I'll probably use autotune as well, since I have a wideband. Just hoping to see some results others arrived at.

1275 with Back Door Turbo

The standard Megasquirt map that came loaded on my ECU was actually from a small block chevy and seems very close to what needed for the A-series. When you consider the general design of the two engines, it's not hard to see why.

I can send you a .vex file of mine, but it is NA only at the moment.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Thanks, Paul. E-mail is wkever@comcast.net

Also, do you have it set up for 1 squirt per cycle or 2? I was thinking I needed two squirts per cycle (two rotations), but with that my pulse widths get too small on the single injector that is sized large enough to meet the power delivery goal.

1275 with Back Door Turbo

Paul is using port injection which is the equivalent of 2 squirts per cycle.

Since you want to use throttle body injection you should use 4 squirts per cycle to have the best possible fuel distribution. With 1 of 2 squirts per cycle, you risk having very uneven AFR between cylinders.

When you say the pulse width becomes too small, how small is that? The best would be to use 2 injectors in alternating mode which would allow running smaller injectors for better control.

Jean

http://www.jbperf.com/

With the throttle body that will fit the manifold, there is only one injector. To get the fuel flow needed under boost, said injector is a big boy, 85lb/hour.

With the Megasquirt req_fuel calculation, it gives me a 4.8msec pulse at 2 squirts per 720 degrees of crank rotation. Recommended minimum is 6msec. But I'll probably just do it that way anyhow. The idle pulse is estimated at just under 1.5msec, but with MS-II you get 1-microsecond pulse width adjustment so it should be OK.
Given that the pulse width is already pretty small, I'm not keen on trying four squirts.
Gotta get the thing set up first to try anything, of course. It's probably going to be around the end of June, if things go reasonably well. :cool:

1275 with Back Door Turbo

Thanks for the VE map, Paul.

Sprocket: You and I have different readings of the Megasquirt documents. The req_fuel calculation is the pulse width required at 100% volumetric efficiency and stoichiometric fueling, and MAP=1bar pressure.
I sized the injector from the power goals as follows:
lb/hr of fuel required is what we're calculating.
130HP * 0.55lb/hr/hp => 71.5lb/hr
The injector is rated at 100% duty cycle. Recommended use is about 80% duty cycle.
71.5/0.80 = 89.4lb/hr.
With an 85lb/hr injector, I'm at 84% duty cycle which should be OK.

I'll learn a lot along the way I'm sure. My reading of the documentation right now says the VE map is the VE of the engine - but I haven't gone through the build project yet.

1275 with Back Door Turbo

Fortfun,

I believe that you are correct. The Megasquirt documents appear to confirm this.

The VE table is the VE of the engine, but factored at higher MAP to give a 12.5:1 AFR.

I also agree with what Sprocket is saying except that if you change the injector size, it should only be necessary to adjust the REQ_FUEL value. You do not need to change the VE table.

Edited by Paul S on 26th May, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Im sure the VE is a % of the required fuel for the size injector used. By adjusting the required fuel your basically altering the increments of the numbers. The smaller the required fuel number the smaller each inrcrement is between numbers (finer tuning). If you have a req. fuel of say 4 but set it to 2 you will need double the value in each box in the table to give the same amount of fuel.

Best to work out the req. fuel, put that value in first then adjust the table to suit. If you decided to change the injector at some point only the req. fuel value should need changing.

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1/4mile in 13.2sec @ 111 terminal on 15psi