Hemi Closed Loop Tuning, MDS and Gas Prices

[magnuman]

Now that gas prices are over $4.00 in most places, can you please (no, pretty please with sugar on it) add features to the Predator that will allow us to manipulate the timing during closed loop operation? Also, many of us with the Hemi MDS would like to be able to make slight adjustements to the MDS to make it come on earlier and stay on longer. I understand this can be done relatively easily. I have a Dashhawk on my 05 MagRT and never see KR in closed loop operation, leading me to believe that timing could be added. I know these items can be done with CMR tunes, but the cost would be prohibitative because it would take numerous trips to the tuner to get it zeroed in. I would also be interested in using my Mag as a test mule for this, if you decide to do it. Thanks!!

[Quick]

Timing in closed loop is not going to make a difference. You can put the timing anywhere you want and it's still going to spray basically the same amount of fuel. It's the fuel you want to change and then change the timing to match. Right now the car is programmed to hunt for 14.7:1 a/f (google gas engine stoichiometric) in closed loop (at least in the "cruising" mode). It's also programmed to run most efficiently within emission constraints. You could run leaner but then your cats don't work right. I'm not sure that running lean will hurt your cats like running rich will but you might end up costing yourself a whole lot more than the little bit you save on gas. I don't think you're going to improve on that.

Now MDS on/off might be a different thing. Not sure how the car is going to know when you want power NOW or when you want to strain the engine to save gas. Again you may end up costing yourself a lot more in the long run.

I think it's safe to say that gas is not going to come down significantly in the forseeable future. You might want to bite the bullet and get something more fuel efficient.

[Mike_Levy]

I don't understand the bitching about gas. Damn, you drive a V8, deal with it or buy a Honda. I've dropped $120 on gas this week and am getting 8.4mpg, but I'm not bitching. Which do you want, performance or economy? You can't have both. More power and performance requires more gas.

[Quick]

Well... he may have decided to give up on the performance for economy at the moment. Problem is I don't think that's possible with our engines, cars, and drive train. I don't think you can turn a 340 hp engine into a 150 hp gas miser just by turning the tuning dial. I suppose it's possible you could change the MDS parameters but probably not a lot. Move the switch over line and you're putting more load on a 4 cylinder. Probably can't go too far before it costs you a whole lot more than you saved. I'm guessing you might get 3 to 5 mpg? Not worth it.

Haha, 8.4 mpg! You don't need a gas pedal, all you need is an on/off switch

[mnunes]

I think magnuman's original thought was that if you add timing you make a little more power with the same amount of gas. If that's true, you can use slightly less gas and still get enough power to get where you're going. That said, I doubt that the amount of power you'll gain from adding a little timing is going to be measurable at the gas pump.

[Quick]

Yea. I think a little more timing would give you knock under any kind of load. To use less fuel you'd have to cut back the fuel (lean it out) and then pull timing to match. That would work but you'd have to get around a LOT of PCM programming and address all the closed loop modes. For example in the "cruising" closed loop mode the PCM programming is constantly hunting for 14.7:1, the narrowband sensors are centered (0.5v) at 14.7:1, etc. Basically you'd have to reprogram (a lot) for a fixed a/f without adaptives. Not feasible. For open loop (WOT) adjustments it's simply (haha, relatively speaking) a matter of tweaking constants. I don't believe the Predator changes ANY executable code or algorithms in the PCM.

[mikel]

Which do you want, performance or economy? You can't have both. More power and performance requires more gas.

While I agree 100% with your ideas here Mike, I always feel a need (in my GM biased mind) to point out that we should all be driving Corvettes....lol.
Stock C6 (436 hp) gets like 28+ MPG, plenty of people see over 30 on the highway, and the Z06 (505 hp) is rated at 27 MPG but in reality can get better than that as well....food for thought....

[Mike_Levy]

Yeah, but thats because of the weight and gearing. Throw out the 0.50 6th gear and tack on another 1000lbs, and then see what its mileage looks like.

[mikel]

Lol...yeah?
Thats kinda my point.....lighter cars with better gearing=better mileage and big power!

[SRT8Tech]

Im starting to miss my 95 Firehawk. Damn thing got right at 30mpg on the highway. Wasnt as fast as my SRT8 though.

[Quick]

Lol...yeah?
Thats kinda my point.....lighter cars with better gearing=better mileage and big power!

But then all the savings go for the butler to follow you in the Bentley with the luggage... (who said that? Ferrari or Lamborghini)