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When to shift for most acceleration


This is a discussion on When to shift for most acceleration within the Ram Srt-10 Racing forums, part of the Viper Truck SRT-10 Discussion category!
In the past when im on it, or if I was racing someone, I would shift as close to redline ...




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Old 05-25-2006, 10:44 PM
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When to shift for most acceleration

In the past when im on it, or if I was racing someone, I would shift as close to redline as possible. Throttle closed between shifts. 2nd lightly spins but usually doesnt screech. Today I short shifted into second and the tires def broke loose. About 2000 Rpms from redline. Whats everyone else doing at the track/street for better times. I've been kinda worried since everyone says its soo easy to chirp 2nd, even 3rd. Feel a lil better now.

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Old 05-25-2006, 10:46 PM
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You want to keep it near the redline without getting so close that trq falls off....
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Old 05-25-2006, 11:24 PM
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There is a post on the NFF site .. somone should pull it.. its a silverback post shows shift points vs trq ... basicaly worked out for my truck..

shift 1 to 2 at 5900
shift 2 to 3 at 5600
shift 3 to 4 at 5400
shift 4 to 5 at 5700

and thoes shift points will provide max acceleration... for me anyway
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Old 05-25-2006, 11:54 PM
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I have my shift light set @ 5600 and just shift as fast as I can on the flash.No time to look at a tach with so much else going on.
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Old 05-26-2006, 12:07 AM
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I'll shift from 1st to second about 5500 rpm's yank second without letting off the throttle. Second to third is a little tricky but same method...5600 then palm the shifter straight up into the a/c controls with a slight lift of the throttle...same for third to fourth...5600 rpm's, slight lift of the throttle....open palm straight back. Good luck.
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Old 05-26-2006, 12:12 AM
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Quote:
Originally Posted by slow91
I'll shift from 1st to second about 5500 rpm's yank second without letting off the throttle. Second to third is a little tricky but same method...5600 then palm the shifter straight up into the a/c controls with a slight lift of the throttle...same for third to fourth...5600 rpm's, slight lift of the throttle....open palm straight back. Good luck.
That is about what I would do. I usually always shift a high HP car/Truck a little early 1st-2nd to avoid wheel spin. If the vehicle has enough TQ, it usually works well.
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Old 05-26-2006, 12:19 AM
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This is 3 posts that Silverback put up on the other site. Here Ya go...

Shift Points

--------------------------------------------------------------------------------

Okay, I promised to calculate the ratios so folks could plot out what is happening on their dyno graphs in regard to HP/Torque.

Here are the ratios to use.

1st to 2nd = .6758
2nd to 3rd = .7255
3rd to 4th = .7667
4th to 5th = .7425

I did not bother with 5th to 6th as you will not gain any speed by shifting to 6th.

Here's how it works. If you shift at redline, 6000 RPM's, just multiply 6000 by the ratio for that shift. For 1st to 2nd that would be 6000 X .6758. That equals 4055 RPM. If you shift at 5200 it would be 5200 X .6758 and that equals 3514 RPM.

Now you can take those RPM's, 4055 and 3514 and see where they drop you on your engines dyno chart for HP/Torque.

SRT10VENOMOUS was kind enough to provide his dyno graph so I plotted those points on his graph. Shifting at 6000 dropped into the 375HP/490LB-FT Torque range. Shift at 5200 and those numbers are 325/480. You also need to look at the HP/Torque numbers at the shift points. At 6000 RPM's the torque has dropped off considerably compared to 5200 RPM's. Also since the ratios are different for every gear change you may want to consider different shift points for 1st to 2nd compared to the rest of the gear changes as they are relatively close to each other.

Make sense? One thing to remember. These ratios are not affected by the rearend gearing

I guess I didn't do a very good job explaining it. Sorry.

There is no one answer to your question. It is affected by the mods you have done to your engine. If you shift to soon and the engine drops out of it's power curve you will lose time. It also goes the other direction. Shift to high in the RPM band where the HP/Torque is dropping off, you lose time also. That's why you need to take the ratios and plot them on your dyno chart.

I'm going by memory now, but I believe you want to shift at a point where the next gear drops you right at the peak of (or just slightly before) your torque curve. That torque is what's going to provide you with the fastest accelleration.

Make sense?

I'm going to use the dyno graph that was in the original post to explain this so that is where the numbers will be coming from.

It looks to me that the peak torque is right about 4200RPM's so I will use that number for this.

If you shift at 5600RPM's you will be at the following RPM's in the next gear.

1st to 2nd = 3785
2nd to 3rd = 4063
3rd to 4th = 4294
4th to 5th = 4158

You can see by the above numbers that shifting at the same point, in this case 5600, sees a difference of 500+ RPM's in the next gear depending on which gear is being selected. One of the really nice things about our motors is they have a big fat (and relatively flat) torque band. In this case it looks like the torque from 3785 to 4294 is in the 480 to 512 range. If anything you might benefit by shifting at an even lower RPM for the 3rd to 4th gear change as you are now on the downward side of the torque curve.

Not sure if I'm helping or confusing you, but I hope it does help you to understand a little better.

Last edited by UNIBOY; 05-26-2006 at 12:58 PM.
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Old 05-26-2006, 09:30 AM
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If you check with the RC guys who are running 12s they are shifting at around 5500 or 5600 rpms. I ran 13.07 last time out shifting near 6000. When you rev that high you get past the drop off point of the torque band.
Lesson learned for me last time out there.

I have since reset my shift light lower. 12s next time out shifting at 5500.
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Old 05-26-2006, 01:34 PM
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Quote:
Originally Posted by ViperTruck2933
If you check with the RC guys who are running 12s they are shifting at around 5500 or 5600 rpms. I ran 13.07 last time out shifting near 6000. When you rev that high you get past the drop off point of the torque band.
Lesson learned for me last time out there.
I have since reset my shift light lower. 12s next time out shifting at 5500.
Blaine (SVTFREAK) and I are pretty much dead even on the street. At the track...he ran a 12.79 @ 108....I have yet to time mine. I shift "almost exactly" like he does when we race.

Esh
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Old 05-26-2006, 02:59 PM
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Uni, thanks for posting Silverback's original post. That is great info. It would seem we have a freakin rokt scientist in our crazy group!!!!

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