Hello,

I just noticed, when not in gear and I try to rev the engine, when the tach hits 4000 rpm, the engine hesitates and the needle falls again, almost as if it were shifting gears while driving (which of course is not possible since I'm just sitting in the driveway). While driving and stomping on the pedal, it'* a smooth delivery all the way up to 5000 rpm'* without any complaints. Does anybody know if this is a safety feature to not allow it to rev high while not in gear, or possibly there might be another problem that I need to figure out? Thanks for any help!

Yep... in park, the 4000 RPM load that you are putting on the engine doesn't have any torque on it. When you are driving, the torque is transferred properly to the wheels, effectively putting a "load" on the engine. An engine without a load can blow up easily, since there is no place to transfer the power!! Essentially it'* Newton'* second(?) law. At least, this is an electrical engineer'* explanation

Revving your engine when not under load is a bad thing. The PCM knows this, and retards the timing to prevent it. Rev limit is done by timing retard, top speed limit is done by cutting off fuel delivery. That'* where some guys with NOS get into trouble. Straight NOS after the top end cutoff makes things go BOOM!

Your car is working as it should. Even revving in park or neutral to 4000 is bad. Don't do it.

It never fails to astound me how fast you guys are. Thanks for the info.

Yup. Been there a couple times. Remember, the Jet raised my redline, too. I shift higher in both normal and performance mode. Can't remember what it changed to, maybe I'll have to run it again!

Yeah, from what I've always understood is that redline (or peak horsepower, or both) occurs around 5500 rpm, then the PCM will cut off fuel at 6000 rpm. I don't think I've ever hit the red while actually driving, but I was revving just to test if the engine would stutter, which it did, but at least it'* not a problem - in fact a good thing.

Will, for what purpose does the jet chip raise your redline? I thought that the redline was determined based on the measured tolerances of the parts of the engine, not on timing or a/f ratio (which I presume the chip modifies), so raising the redline could be destructive to the engine unless the innards have actually been modified.

They raised the physical redline limit based on dyno data for the adjusted torque/hp curves. Didn't raise much, but they're making better use of the improved horsepower that way. I don't hit it often, and when I do, I don't stay in it for long.