You guys know who you are,... the fastest ones. At what RPM is your trucks shifting? After my little dyno experience I'm looking at a reburn to lower my shift points.

I have never looked at the tach at WOT before but the dyno told the tale. 5,820 RPM seems just too high. Am I right, what RPM's are you shifting at?

From my dyno graph, I see that my torque and horsepower lines are crossing at 5200 RPM's. From there on it's downhill loosing TQ and HP. It seems,to me, that lowering shift points from 5,820 would keep me in the powerband longer resulting in quicker E T's, right?

All comments are welcomed. Tuner's comments are extremely welcomed.

Tim

 

Tim,

I believe my chip was setup for 5550 with it shifting around 5600. I think anything less than 5500 would give you some lag after shifts. You want to keep it alittle above the peak power range to help keep the truck pulling and not let it fall on its face. Thats what I understand.....

Maybe Sal will jump in and give you his thoughts....

 

Depends on your pulley size. I started shifting a little lower when I went with larger pulleys. I would stay 5650 or less depending on your mods.

 

You're shifting at 5800 rpms? Holy moley.

I usually set trucks to shift no higher than 5600, anything over that, and you hurt ET.

Just FYI, every power graph will cross hp and torque at 5250 (will only show on a graph if the scaling is equal for hp and tq), it's a scientific fact.

The normal practice is to shift a tad higher than max hp, so that you are closer to that power range when the rpms drop on the shift.

Hope this helps.

 

What Richard said, You don't want to bog down on the upshifts, but your numbers are a tad high, maybe a reburn is what you need, but don't go too low, somewhere around what Richards numbers were, after all, he cracked into the 11's and that's real good, just don't push it too much 'cause you wanna keep that thing in one piece, John H.

 

Tim,

Every dyno sheet you look at will have the hp and torque cross at the same point. All the dyno does is measure horsepower, and then calculate torque. It does this by:

Power = Torque X RPM / 5252

Therefor, they should all cross at 5252 rpms if you think about it. As far as finding your optimal shift points, do this math (this is a writeup for finding it on a 300ZXTT):

1. Get a dynochart w/ torque & hp vs. RPM

2. Know the gear ratios, these are the same for NA & TT 5spd:


1st: 3.21:1
2nd: 1.93:1
3rd: 1.30:1
4th: 1.00:1
5th: 0.75:1

3. Gearing is a multiplier for torque, so even if the torque isn't as high chart wise towards the end, the gearing makes the mechanical difference & results in maximum acceleration. I'm just going to run down my chart so you can see how the process works, oh, here's the dyno chart again:



Here's how it works out in a chart:




gear rpm tq output rpm tq output difference
3.21 0000(000)000.00 7200(220)706.20 34.57
1.93 4327(348)671.64 6850(237)457.41 01.11
1.30 4613(351)456.30 6625(255)331.50 00.50
1.00 5096(331)331.00 6650(250)250.00 00.50
0.75 4987(334)250.50 7200(220)165.00 00.00

4. 3.21 0000(000)000.00 is nothing, literally, but the next chunk is the first shift point: 3.21 7200(220)706.20 -> 1.93 4327(348)671.64 at 7200rpm, the chart shows 220ft-lbs of torque. OK, I know, it really doesn't... think interpolation for a sec. :-) I'm going to multiply the torque value by the gear ratio:

220 ft-lbs * 3.21 gear ratio = 706.2 ft-lbs of output shaft torque

5. Now we use the gear ratio finder from above to determine where this shift point will land us in the next gear:

nextRPM = shiftRPM (gear2/gear1)
nextRPM = 7200(1.93/1.30)
nextRPM = 7200(.601)
nextRPM = 4327RPM

6. At 4327 RPM we see the torque is 348ft-lbs. Multiply this by the gearing:

348 ft-lbs * 1.93 gear ratio = 671.64 ft-lbs of output shaft torque

This is significantly less (34.57ft-lbs) than the amount of power we shifted from. Why shift when the ground is still feeling more force then in the next gear? But, we ran out of RPM to work with, forcing a shift into the next gear.

For the next gears there's a lot of trial & error. I wrote a script to do most of the math for me, but it can be done on paper with a little more time. :-) The easy way is to start graphing the torque from redline back in 50 RPM measurements. These numbers can be used through all gear readings, just use different multipliers for gearing. Keep doing the math until you find a shift point where the output shaft torque is the same or slightly less in the next gear or as close as possible. The first shift had a 34.57ft-lbs difference, the rest you can hit very close in the next gear. The shape of the torque curve will determine how close you can get.

Hope this helps,

 

DamonH,

You are in violation of making my brain work too hard!

torque = john(me)*(1/scratching head) + (10(confused)

Never was any good with algebra...

I have a headache now... thanks alot...

If everything you said is accurate, well then hats off.

If not, well it sure sounded cool.

 

LOL, all I asked for was shift RPM's. I know I'm shifting at too high an RPM range, and I'm not splitting hairs here, I just want to know what an optimum RPM would be so I can have my chip tuned for better E T's. That is, if I keep my chip. I find it unsettling that my shift points were set that high, agree?

Tim

 

Thanks Sal,

Can you think of any scenario that would dictate shift points being set so high by a tuner, considering the limitations of a Lightning's internal parts?

I want to go fast, not blow up. I will not run my truck again until I feel safe with my tune. I find this unbelievable.

Tim

 

Dislexia ???



Capt. Smartass to the rescue

 

The more boost the quicker the HP comes on, the sooner you can shift. I run 13.5 psi and shift at 54-5500.

 

Man I had something right!!! LOL

 

Richard,

I was going to thank you later. Just waiting on more replies.

Thanks,

Tim

 

Damon

Dynojets and other dynomometers measure torque, ( twisting force on the drum ) and calculate horespower. Your equation is the exact equation the Dyno does...

http://www.vettenet.org/torquehp.html

Doug

 

Im just glad my head still has something worth while in it!! I have been so busy and confused lately!! I hope you can get that baby straight man, I wana see you hit 7's soon!!!