Chrysler Crossfire SRT-6 Throttle Response Needs Help

Let me see if I understand you. You have taken a collection of unspecified aftermarket modification kits and bolted them onto your Chrysler Crossfire. You've tested the horsepower on a dynamometer and found that the horsepower has been boosted by 20 HP from the supercharged 3.2 liter V6 but when you actually try to use this new configuration on the street you believe that the throttle is sluggish to the point of being virtually unusable. So instead of investigating any of the myriad of feedback systems and automatic controls that the engine computer is trying to deal with, you added another aftermarket gizmo. Do I have this right?

Well now, I think you've found the fundamental problem of making too many changes at once. I suspect that you've also not made enough testing at each intermediate stage of upgrading to know where you've lost the throttle control response you once had or that your expectations of what the throttle control should be are unrealistic.

A good engineer knows that no engineering change to any machine doesn't come without some drawbacks for each reward earned. One of my own personal mantra's in making a change to anything is that I have to find a drawback before I proceed. If I cannot find a drawback, then I probably don't understand the machine well enough to proceed with the change. I naturally prefer to only find a trivial drawback, but I have to be already very familiar with the engineering to accept a trivial drawback as a qualifying drawback.

Oh one last comment for you to consider, did you compare the change in the engine rpm vs. torque curve when you did the dynamometer testing before and after each modification.

My good friend, it appears that you misinterpreted the purpose of the thread that I started about the "poor throttle response". The first error you made was to confuse rear wheel horse power with flywheel power. The factory RWHP was dynoed/measured to be less than 300 HP due to the 12% - 20% losses in the drive train; both the automatic transmission and differential.

http://www.allpar.com/images/chrysler/crossfire/srt-6.jpg

http://www.blogcdn.com/green.autoblog.com/media/2010/08/fig21sachstorqueconverter2.jpg

The poor throttle response of my AMG engine, as I stated in my request, was improved over the factory setting by the commercially available Greek Sprint Booster (SB), but even that is not sufficient for autocrossing. SB's are now produced for almost all brands of automobiles with the 'fly-by-wire' Throttle Body (TB) control systems. The original throttle delay was about 400+ milliseconds and it is now at about 300ms, a tiny gain. In autocrossing Iam negotiating about 50 or 60 course changes in less than a minute and 300ms of added throttle delay per turn is crippling.

http://www.sprintbooster.us/

As you said " A good engineer knows that no engineering change to any machine doesn't come without any drawbacks….." Well having said that I can only reply by saying that the engine torque and power band are flatter and materially improved. The deficiency that I previously identified was with the slow computer controlled throttle body (TB) rate of operation. The TB is driven by a +/- 12v PWM signal at about a 200microseconds square wave and can not be easily tricked, as the rate of opening the TB is monitored by the engine management computer thru a closed feedback signal provided by the TB's position.

I have explored the idea of modifying the differential feedback signals to induce the computer to drive the TB more swiftly to a wide open throttle setting. This approach may be possible but is Id rather investigate to see if there are other options first.

In starting this thread, I was hoping to gather information about other peoples experience with software changes to the operating code, to eliminate the factory delays built into the TB operation. My Hemi dodge has a similar TB design and its wide-open throttle response is greatly diminished in comparison. Factory performance vehicles can be driven as if their TB's were cable driven; the factory has no significant delays built in these vehicles.

Had you asked, I would have told you that the car has been dyno'ed to show the improvement of each design change. My demonstrated flywheel HP gain is up by about 70 HP and most of that is below 3000 revs because of improved breathing provided by revised dual air inlet manifolds, reduced intercooler temperatures, port matching, larger crank pulley and lower parasitic pulley losses. These design changes that I developed have each been dynoed and have gone to production and have been sold to the Crossfire community.

Woody

Did you really think that on an open forum like this you'd get somebody to discuss how to modify source code of a proprietary embedded system control.

Do you have any idea at all about control theory? Have you ever heard at all what can happen when the poles of a feedback system wander into the right hand plane? Do you know that a Routh test of the control system will show the limits of stability. If you just tinker with feedback systems without knowing these theories and analysis approaches you may get what you desire, or you may get a machine that briefly tears itself apart.