BEST RPM SHIFT POINTS

[MEXICANPT]

WHAT'S BEST TO SHIFT AT REDLINE OR TO SHORT SHIFT @5,200 RPM, HP PEAK'S THERE WITH THE STAGE I. I FEEL LIKE AFTER THAT IT'S JUST A LOT OF NOISE AND NO REAL PULLING POWER. ANY INPUT?[8)]

[GLH_TC 16V]

General rule of thumb is 10% past the HP peak. So when you shift, you will fall back into your HP range to maximize the area under the curve. So if your peak is at 5200RPM, then you should be shifting a tick over 5700RPM.

Are you going by the dyno chart that Mopar gave you for peak HP? Dyno testing is the best way to determine peak HP and thus optimum shifting points.

[MEXICANPT]

YES, I'M USING THE CHART FROM MOPAR, THANKS FOR THE INPUT, SOUNDS ABOUT RIGHT TO ME.

[THier]

GLH is right on, think about it, if you shift right at peak hp, you drop below it, shift past peak and you fall much closer to peak hp.
Tom

[Dalite]

I don't know if this makes much sense, but here is an interpretation of the torq/hp curves that was posted in the SRT-4 forum to a similar question:

quote:
Try shifting between 4800, and below 5000 instead of taking it to the top. Look at the torque curves for the stock and Stage I engine performance, and you will understand why I make this suggestion.

The SRT-4 may be different from the PT-GT, but the SAE paper that outlines the 2.4L Turbo build and control design shows the torque to peak around 3800 RPM, with a gradual decline to around 5000 RPM, where it starts really going south.

What the graph shows is the Stock Turbo 2.4L building around 180 ft-lb torque near 1700 RPM, a sharp rise to around 230 ft-lb near 2000 RPM, slow rise to a small notched peak at 2300 where the turbo begins to make boost, a rise to max torque of 245 ft-lb around 3750 RPM, gradual decline to near 230 ft-lb around 4800 RPM then sharp decline to near 160 ft-lb around 6000 RPM.

To put this in perspective, the graph shows torque to be about the same (~180 ft-lb) around 1700 RPM that it is around 5700 RPM. Between that point and 6000 RPM, it falls sharply to near 160 ft-lb at 6000 RPM.

The HP equivalents show a fairly steady rise from around 60 HP near 1700 RPM to 215 near 4800 RPM. From there, a slow decline to around 200 HP near 5600 then a sharper decline to around 180 HP at 6000 RPM.

If the SRT-4 Torque and HP curves are similar, there is a sharp loss of torque at HP beyond 5500 RPM ( a basic carry over of the 2.4L design), with peak Torque and HP around the 4800 RPM Mark.

Based on this, shifts before 5000 RPM are definately suggested.

If you are holding until 6000 RPM, even though the butt dyno still shows it pulling strong, you have already started loosing momentum and time.

I don't know about the SRT-4 PCM programming, but do know the on the PT Turbo side, the PCM is tuned for "torque-based" boost control.

This equates to the PCM program designed to give the same engine torque output for any given throttle input, regardless of ambient conditions (temperature, barometric pressure, etc.).

Since it is a forced air induction system, altitude compensation is not as big an issue as in NA engines. Also, since the system is torqued based boost control, the PCM will command the engine to produce the same torque output (based on throttle position) no matter what the ambient (weather) conditions are.

This will take a little getting used to.

That was a discussion about the Stock 2.4L Turbo Torque/HP curves.

On the Stage I 2.4L on the PT, Torque peaks at 260 ft/lbs from 3600 - 4400 RPM. HP peaks at the 5200 RPM mark.

I also agree that the 10% past the HP peak is a good rule of thumb.

Dyno testing will be the way to go in determining whether to use the HP peak + 10%, the torque peak or somewhere between the two.

With the PCM programed for Torque based boost management, and the brick wall inherit 5500 RPM in the 2.4L engine; it is a safe bet that there isn't much reason to go to redline.

If graphs and charts can be trusted, a shift much past 5500 RPM would be a toss up between loosing momentum due to the engine past it's peaks or the effects of the rev limiter sneaking in. Either way, it amounts to loss of momentum.

[3BarBoost]

If you have reduced backpressure, you can make good power up to fuel shut-off. I touch it top of third in the quarter, bout twenty yards from the lights.

[MEXICANPT]

VERY USEFUL INFO, I'M STILL TORNED BETWEEN 4800 AND 5700 RPM.

[COP TZER]

This is a GOOD thread... i've been wondering this same thing. I'll usually hold till very close to redline before shifting. I've found that shifting around 5000 tends to have a bit of a bog going in to second gear. But when shifting just before redline you land smack in the middle of the power range. Also, if you are power shifting you'll know there is a big problem with wheel spin in second gear. I've gotten much better results by quick shifting into second and slipping the clutch; while still powershifting into third.

[Steve03GT]

quote:Originally posted by MEXICANPT

WHAT'S BEST TO SHIFT AT REDLINE OR TO SHORT SHIFT @5,200 RPM, HP PEAK'S THERE WITH THE STAGE I. I FEEL LIKE AFTER THAT IT'S JUST A LOT OF NOISE AND NO REAL PULLING POWER. ANY INPUT?[8)]

Another question for those interested in accelerating from a stop is what rpm to launch at for best results? Us A4 guys are somewhat limited, but the M5 guys have great latitude here. On my 1/4 drag race program, it appears a good starting point is between 3500 and 4000 rpms or up to a point where traction can be had, whichever comes first.