What shift points yield better times at the track?

evo77 · Aug 30, 2003

Going to add a few posts here from another thread that I thought was very informative regarding this. Would like to hear everyones thoughts. The last time I went to the track I was shifting at 6200 rpms every run. Dissapointing time is in my sig. Although I've tried shifting at 5500 on the street, I just feel that the 700 rpm that I'm losing out on is still somewhat usable. But I guess that might not actually be the case.

Dalite said:
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 than 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.

Direct Connection said:
Analyzing dyno charts is an excellent starting point to determine optimal shift points, but you have to also consider the equally important of transmission gear ratios. Torque output from the cranshaft is multiplied several-fold (depending the gear) before it reaches the ground, so holding out a gear -- even if the power is observed to drop off on a dyno chart -- can often result in greater torque due to this gear multiplication. I find that by comparing the drive-wheel torque at various engine speeds in a lower gear to the resulting drive-wheel torque that accompanies a shift change to new, lower engine speeds, I can precisely determine the optimum shift points (i.e., the engine speed at which the least amount of wheel torque is lost following a shift). This, of course, requires either an engine or chassis dyno graph from which to obtain the exact torque values at specific engine speeds. Using a chassis dyno chart that I have from when my SRT-4 was stock, I quickly calculated that shifting as close to fuel cut as possible (say, around 6,200 rpm) will result in the least amount of wheel torque lost following the 1-2, 2-3, and 3-4 shifts. Due to the larger gear spacing between the lower gears, this is most important at the 1st and 2nd gear shifts and less so in the higher gears. In drag racing, you also need to consider traction issues, turbo spooling issues, etc ..., so this is hardly an infallible rule, but it is a good starting point. Let me know if you'd like to me explain this a bit more -- I can give you the formulas so you can calculate these figures yourself.

radguy · Aug 30, 2003

All my best times were shifting at 6000rpms.

guhfluh · Sep 1, 2003

I side with Direct Connection. Even though torque falls off at higher rpms, the actual whee torque applied will (almost)always be greater in the lower gear. Riding the gear out as long as possible should give better times, as long as the power is useable without wheelspin.

It's just my visualization in my head. I haven't seen any writeups or factual data supporting either yet.

Redracer · Sep 5, 2003

5700 has been my optimal shift points

evo77 · Sep 5, 2003

The fall off in power is probably due to the loss in boost as the rpm reaches redline.

Now that I installed my WGA (finally!), this thing holds boost all the way to redline. So I'm shifting this biatch to 6100 through all the gears!

I'm hitting the track tomorrow so we will see.

SRT4finally · Sep 5, 2003

When stock I shifted as soon as boost dropped, whether it be 5200rpm I KNOW I didn't take it to redline, I could only pull 14.4 shifting at 6k, and pulled consistent 14.1 short shifting so-to-speak at about 5200.

avtomat · Sep 5, 2003

i think it definately makes sense to shift way before redline because you have you hit 4 anyway pretty close to the last second. so its not gonna make a difference in how many times you shift.

avtomat · Sep 5, 2003

evo77 said:
The fall off in power is probably due to the loss in boost as the rpm reaches redline.

Now that I installed my WGA (finally!), this thing holds boost all the way to redline. So I'm shifting this biatch to 6100 through all the gears!

I'm hitting the track tomorrow so we will see.

the fall in power isn't due only to losing boost. the smartest move is to stay in your power band which i believe drops off at 5300

especially in higher gears

SiCkTwiSTeDsRt4 · Sep 5, 2003

i guess it depends on just how you drive and the driver as well...i mean if you cant shift that good as it is what does it matter to anyone???or...i mean it all can fall down to the mods as well...diff mods different rpm ranges...

DJ_SRT-4 · Sep 6, 2003

I shift at 5800rpms.

14.34 @ 98mph in 3600ft elevation.

What shift points yield better times at the track?

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