Weird MegaSquirt + boost question

I'm not sure this would be useful/necessary or anything, but started thinking about it, knowing that MS is capable of map switching.

What about an "analog" style boost knob. In other words, all the way left is 6psi and and all the way right is 20psi. Obviously the halfway point would be a 13psi map and adjustable in-between.

Just curious.

So you want... an EBC with built in map switching for certain boost levels?

Why not just scale your fuel and spark maps for 20 psi? That way you can always run lower boost if you want to.

PseudoSport wrote: Why not just scale your fuel and spark maps for 20 psi? That way you can always run lower boost if you want to.

I like this. Simple is good.

PsuedoSport, I'm still learning MS, but is that something you could "scale" using an outside input on the fly?

92CelicaHalfTrac wrote: So you want... an EBC with built in map switching for certain boost levels?

Essentially.

And not even sure I "want" it, was just curious if it was possible. I'll likely just use the map switching capability and make a hi boost tune and a low boost tune.

I think the map switch might be over complicating things. On my old Miata I had my maps tuned for 18 psi but most of the time I only ran 10-15 when driving around. Also on our turbo Cherokee our maps are scaled for 12 psi of boost but we have been autocrossing it naturally aspirated.

The only benefit I see to map switching is having more resolution in low boost for drivability. It should be pretty easy to wire a button that allows the EBC to turn on and MS switched maps.

^Yeah, switched maps are no problem for MS, literally flick a switch.

That's why I was curious about a more "analog" solution where say you could dial up 6psi, 12psi, 17/9/11, etc "on the fly" so to speak.

Z31, i have an interesting boost controller that might suit your needs if you want to do this.

There's an analog knob on there that sets the boost, and a toggle switch that turns the unit on and off.

With the toggle switch OFF, you run wastegate pressure. With it ON, you run whatever you've got the knob set to.

I imagine it'd be pretty simple to wire the map switching on the toggle switch as well. Set your low boost map for whatever you'll run off the wastegate, toggle position OFF.

Set your high boost map for whatever you'll run with the EBC with toggle switch ON.

Interested? I got it off a built Probe about a year ago. I can get you pics.

It's the old EE-Enhanced EBC V1.0, apparently.

Just scale the map for the highest boost you will use and run the boost controller wherever you want it at the time. A 12X12 Table will still have plenty of resolution for excellent driveability. If you are worried go with a 16X16 table.

Map switching would be useful for E-85 but for this you are overthinking it.

Now the real question. Why in the world would you want to dial BACK the boost?

^On a car like mine... it's a good idea.

On something that should spool a bit better, and have at least a little power out of boost, meh. Overcomplicated.

Or if you want to autox on a lower boost setting so you get traction, then go really fast at the drag strip, maybe?

ditchdigger wrote: Just scale the map for the highest boost you will use and run the boost controller wherever you want it at the time. A 12X12 Table will still have plenty of resolution for excellent driveability. If you are worried go with a 16X16 table. Map switching would be useful for E-85 but for this you are overthinking it. Now the real question. Why in the world would you want to dial BACK the boost?

Because at 17-19psi the engine should be capable of much more power than any street tire you can fit on an E30 can handle.

With MS in essence your map will always be tuned to what ever boost/rpm/load the MS is "seeing". There for there is no need to swap maps just based on boost.

I guess you could set something up where if you limited the boost but wanted to run more timing you could set it up that way. It would be as simple as a duel pole switch one circuit would change the map and the other would change the wast gate settings.

I'm with the folks that don't understand the need. Just get a cockpit-adjustable boost controller and tune the MS for the highest boost level. Voila, done.

I've never felt the need to be able to turn down the boost on a car. If I don't want full boost, I don't use full throttle.

Keith wrote: I've never felt the need to be able to turn down the boost on a car.

When E85 is not available (!0psi), you can flip to the 93 octane fuel map (5 psi). I've got a switch on the dash for just that purpose.

Ah, if you're switching fuels, that's different. The fuel delivery and timing tables for E85 and 93 octane are totally different. And you'd have to turn down the boost then as well.

z31maniac wrote:

ditchdigger wrote: Just scale the map for the highest boost you will use and run the boost controller wherever you want it at the time. A 12X12 Table will still have plenty of resolution for excellent driveability. If you are worried go with a 16X16 table. Map switching would be useful for E-85 but for this you are overthinking it. Now the real question. Why in the world would you want to dial BACK the boost?

Because at 17-19psi the engine should be capable of much more power than any street tire you can fit on an E30 can handle.

There already is a progressive switch for that in the car. Look under your right foot

Realistically, if you're tuned properly for peak boost, you can simply use a boost controller to limit the boost while puttering around on street tires. MegaSquirt should be able to compensate.

My buddies and I do this on our 30psi capable Holset boosted XR4Ti. The map is tuned up as far as we can go, and we just dial our manual boost controller to where we want it. We're in the process of adding a 'go baby go' button on the steering wheel along with an electronic boost controller to switch from 15psi to 30psi on the fly

For reference we're MS-I and still have plenty of resolution over the whole RPM/duty cycle range, just takes time to dial in...

Ahhhh I did not get that there were different fuels involved here. IF that is teh case then you will need to swap maps. Again as simple as a duel pole switch as noted above.

I don't think z31maniac was talking about different fuels, he just wants dial-a-yield. Fifty was using the multiple fuels as an example.

^yeah, I was wanting to use the MS as the EBC, but just didn't know if there was anyway other than just "Xpsi" = max, and that's all I could do.

dean1484 wrote: Ahhhh I did not get that there were different fuels involved here. IF that is teh case then you will need to swap maps. Again as simple as a duel pole switch as noted above.

Actually, one thought was to install the GM flex fuel sensor, so MS could handle putting E85 in the tank when available.

The best way to deal with flex fuel is to have the ECU blend the maps depending on the gravity of what's going through the sensor. Not all E85 is 85% E, either.

^That's what it does, if I understand correctly.

For some reason, what you guys were suggesting wasn't clicking yesterday, but I think I get it now.

Tune the car with MS to it's max boost, then use a SEPARATE EBC to turn down the boost as desired? Or am I still missing it?

I don't know the MS EBC, but that's the easy way. Heck, you can use an MBC if you want.

EBC only if you want a single toggle switch to also swap maps. Otherwise ya, tune to max boost and a manual boost control gets the job done.