Is it possible to enforce a MAP limit via DBW throttle on a G4+?

[Pete_89t2]

Subject is the gist of my question. I know and use the MAP limit engine protection features that are built into my G4+, which cuts spark & fuel when you hit your MAP limit. But since my car is equipped with a DBW throttle controlled by my G4+, I was thinking that having the protection feature pulling the DBW throttle in lieu of a spark/fuel cut when the MAP limit is breached would be a bit easier on the engine, as it would avoid possible backfires and going too lean.

Is what I'm suggesting even possible with the G4+ (Fury to be specific), and if so, how would it be setup?

I'm thinking if I could program the DBW throttle to be pulled back say 50% of wherever the throttle was at when the MAP limit was breached would effectively do the job. So let's say I hit my MAP limit at 75% throttle, the protection feature would override the accelerator pedal and reduce the throttle to 25%, and then go back to tracking the accelerator pedal position vs throttle position map after the MAP limit breach is cleared.

Cheers,

Pete

[Adamw]

You could achieve that by putting MAP on one axis of the throttle target table, or switch to a 2nd target table with smaller max opening when a certain MAP is exceeded. 

But be aware throttle is way too slow to act as engine protection.  An ignition cut stops combustion instantly, closing the throttle you've still got full combustion pressure for probably 200ms or so - at 6000RPM that is 10 full engine cycles with excessive cylinder pressure.    

MAP limit should only be used to prevent damage if something goes wrong, it should not be hit during normal operation - if you are then you have a boost control issue.  

[Pete_89t2]

39 minutes ago, Adamw said:

You could achieve that by putting MAP on one axis of the throttle target table, or switch to a 2nd target table with smaller max opening when a certain MAP is exceeded. 

But be aware throttle is way too slow to act as engine protection.  An ignition cut stops combustion instantly, closing the throttle you've still got full combustion pressure for probably 200ms or so - at 6000RPM that is 10 full engine cycles with excessive cylinder pressure.    

MAP limit should only be used to prevent damage if something goes wrong, it should not be hit during normal operation - if you are then you have a boost control issue.  

Thanks Adam. My DBW table is currently RPM vs Accel. Pedal position, and I'm using it to enforce a soft RPM limit; basically the last column is 250RPMs higher than my adjacent "redline" column, and that's where I pull back throttle 50% less than the target in the adjacent "redline" cell. Works really nice as an RPM limiter. I think I understand the idea of switching to a 2nd target table when a MAP threshold is exceeded, but I'm not following how to program that? I'm guessing there's a way to use MAP data to drive a virtual switch/digital input, which would toggle the 2nd DBW target table?

Didn't consider the response time of the throttle for engine protection, but perhaps it won't matter for the application I have in mind. Car in question is single turbo FD RX7; but since the 13B-REW engine's internals are unmodified OEM, in the interest of reliability the plan is to keep the engine's max power output to no more than 370~400RWHP at max boost, which should be somewhere in the neighborhood of 14~15psi MGP. My problem is the turbo I have and the supporting hardware can easily boost way beyond that level in a hurry if boost control were to fail. So assuming my final max boost number is 15psi MGP, the thought is to use a DBW enforced "soft" MAP limit at say 16psi MGP, and then a hard MAP limit of perhaps 17~18psi using the rotary mode spark/fuel cut based engine protection. That way if I hit the limit on the road, I'll instantly feel it and let off the gas, so it most likely won't reach the hard MAP limit.

[Adamw]

[Pete_89t2]

Thanks Adam! Got it now, I'll give that a try.