Megasquirt questions

[Jaxx_]

While I would still recommend disabling EGO control while tuning, it is my understanding that auto-tune accounts for ALL corrections already, so it wouldn't necessarily be detrimental to leave it on. Same with MAT correction, etc. etc.

OP why leave the AFM in there if you have a MAP sensor? Add in a variable TPS, it's cheap and easy and much more suited for Megasquirt.

You're probably right. In either case it's one less thing to account for. An O2 sensor is already a tool that inherently has delay, it seems foolish to tune on top of an unknown you can remove.

He needs the AFM for the IAT, removing that I'm sure he would pick up a few ponies

[citizen_insane]

You're probably right. In either case it's one less thing to account for. An O2 sensor is already a tool that inherently has delay, it seems foolish to tune on top of an unknown you can remove.

He needs the AFM for the IAT, removing that I'm sure he would pick up a few ponies

Yeah, but you can wire the GM style IAT directly into the AFM plug and then remove the AFM and run MAP. I highly suggest doing that.

[Digitalwave]

Yes, I would do that asap as the VE tables are going to change when you remove the AFM from the intake tract.

[Jaxx_]

Yeah, but you can wire the GM style IAT directly into the AFM plug and then remove the AFM and run MAP. I highly suggest doing that.

I agree, if he doesn't mind spending more money on a iat sensor.

Yes, I would do that asap as the VE tables are going to change when you remove the AFM from the intake tract.

I am curious why VE would change, and how significantly. What's been your experience? Is it only the top end or the entire table? I would be surprised if it was the entire table

[Digitalwave]

Have you seen how tiny the opening is on the vane AFM? :p Put a 2.75" straight tube in there and it should make a noticeable difference. My M20 made 10-20 hp & tq more throughout the entire powerband when I switched from Motronic to Megasquirt, mainly from deleting the AFM (nothing else on the setup changed).

[Jaxx_]

Have you seen how tiny the opening is on the vane AFM? :p Put a 2.75" straight tube in there and it should make a noticeable difference. My M20 made 10-20 hp & tq more throughout the entire powerband when I switched from Motronic to Megasquirt, mainly from deleting the AFM (nothing else on the setup changed).

I believe the torque increase, but did you really retune the VE table? I just don't see removing a restriction changing VE of the engine besides at resonate rpms

[Fraser]

While I would still recommend disabling EGO control while tuning, it is my understanding that auto-tune accounts for ALL corrections already, so it wouldn't necessarily be detrimental to leave it on. Same with MAT correction, etc. etc.

OP why leave the AFM in there if you have a MAP sensor? Add in a variable TPS, it's cheap and easy and much more suited for Megasquirt.

Definitely. I have a spare M50 tps adaptor plate laying around you can have if you want, then all you need is the ~$30 tps and you're off and running.

[e30davie]

I believe the torque increase, but did you really retune the VE table? I just don't see removing a restriction changing VE of the engine besides at resonate rpms

On my M20B23 I am seeing approximately 4kpa pressure drop at WOT ~6500rpm with the AFM . This is with the mega squirt measuring at the intake manifold and seeing a maximum of 96kpa (close to 101kpa atmospheric pending weather).

I just swapped out the AFM for a bit of 2.75" pipe the other day (which fit perfect), i havent got a chance to check the logs again but if i have gained 4kpa of pressure (which wouldn't surprise me) it will change the VE of the engine and ill need to re-tune (As there is more pressure forcing air in). That additional VE would account for the ~10-20hp i guess.

(note: i was quite surprised how small the opening was on the AFM, reduces down to like ~40mm^2 or something)

[digger]

4% is 4% so a 100hp engine will gain 4hp a 200hp engine 8hp etc approx

I gained heaps getting rid of the larger m30 AFM going standalone.

[Jaxx_]

I believe it. My point was that re-tuning the VE of the engine would surprise me. The AFM is a restriction, but it shouldn't change the volumetric efficiency of the engine—at the same time, I don't know enough about tuning to say this with confidence

[e30davie]

I....but it shouldn't change the volumetric efficiency of the engine—at the same time.....

why not?

definition of VE is percentage of air in the cylinder compared to what it would be at static atmospheric conditions. if the pressure in the inlet manifold goes up a few kPa, then more air will go in when the valve opens. and more volumetric efficiency will be evident. more VE = more air = needs more fuel to achieve same AFR = moar power. Thats how i understand it anyway.

[Jaxx_]

Perhaps my thesis wasn't clear after a few posts: fuel load(kpa) will change. VE should not until—maybe—when you get into a point where the AFM is actually a restriction for resonate areas. My point is that it doesn't make sense that you would have to retune the VE table for what is effectively the equivalent of a throttle body not opening as far as it could.

If VE changes when removing the AFM, you are also saying that by removing the AFM, you will run lean everywhere.

[e30davie]

Perhaps my thesis wasn't clear after a few posts: fuel load(kpa) will change. VE should not until—maybe—when you get into a point where the AFM is actually a restriction for resonate areas. My point is that it doesn't make sense that you would have to retune the VE table for what is effectively the equivalent of a throttle body not opening as far as it could.

If VE changes when removing the AFM, you are also saying that by removing the AFM, you will run lean everywhere.

hmm you might be onto something. Cause all that will happen with my additional 4kpa (or percentage of pending rpm) is that in the VE vs RPM table for the same RPM i will be in a different load cell,which should already be tuned....2000rpm 70kpa becomes 68kpa or whatever.

I will have to do some more testing, i still haven't really driven it though i did notice that at idle and light throttle when i moved it around the garage last night it did seem a bit leaner than i expected, but i put that down to the weather being a bit cooler now than it has been and my intake temp correction not quite dialed in.

[citizen_insane]

Jaxx is correct that changing the intake conditions shouldn't require retuning VE. Like you said yourself, it will just cause the engine to operate at a different load setting in the VE table since the Y-axis of the table is already MAP. You will gain some power though since your charge density will increase.