TheHeadFL

I was having a discussion with my friend about when he ought to be shifting at. I tried to graph out the torque curve across the gears, and plot the shift points, and from what I can gather, he ought to be shifting at ~6700rpm, but hes shifting at 6300rpm now. His traps in the 1/4 are between 112 and 114 and I think they should be much higher than that based on his dyno chart.

What do you guys think? I am figuring peak HP happens right about 6200rpm, and he should be shifting 500rpm or so later. Opinions? (No, this is not an LT1, by the way, its an LS1)

http://www.mangucha.com/~drewb85/mattdyno.jpg

Cmr0z28

hey man, MattZ28 here from ws6zxr.com......I'd say right around 6600 or 6650 RPM's.

94formulabz

Dats a nice dyno. Whats his setup?

Your right on the 6700 where the dyno stopped. I guess he's not comfotable spinning it past 6700. He should be shifting somewhere past that probably, like 7k HP wise but for longevity of the motor it makes sense to keep it down unless it's built to spin that high. Do you have the actuall data numbers that they used to make the graph? If you do that would be helpfull, i'll make you a real nice excell spreadsheet cuz i'm bored, haha.

-brent

94formulabz

The 500 rpm later thing works if there is vavle float or something going on that makes the power really drop off. Yes it peaks at 6200, but it's pretty darn flat through there. There si a tiny blip at the end, but nothing major. If that curve continues the way it is gradually tapering off then it looks like he'd still be making ~360 at 7k rpm. a 7k shift will take him back to 4.9k rpm where he's making about the same HP. Having the same HP before and after the shift will guarentee that through that gear you have maximized the area under the curve.

Basically he needs to shift as late as he's comfortable with so your 6700 suggestion is much better than 6300.

TheHeadFL

Actually I have already built a little excel spreadsheet to try to compare various shift points and their effects. Unfortunately, he hasn't been able to get the data points yet so we've just been doing estimates based on a few dyno sheets.

My method of calculation was basically... I have the gear ratios for each gear.... and he has 3.73s out back... so I multiply Tranny Gear x Rear Gear x Torque at that specific RPM. I do this across the range of every gear. Where these curves intersect in my mind is the optimal shift point of every gear, in other words, through gear multiplication and the torque at the shift point, going to the next gear will net exactly the same torque figures at the wheels. Opinions on this?

By the way, the setup is stock bottom end with Stage 2 CNC heads and 220/220 Comp Cams grind.

94formulabz

I'm not so sure that is a valid method for determineing shift points. You do want your HP to be the same before and after shifts though, because that will maximize the area under the HP curve. Your method of looking at torque would have me shifting down around 2.5k operating around the torque peak if i understand it correctly.

Hp is just a function of torque and RPM, thats what you want to use for an acceleration calculation. Your interested in power (forcexdistance/sec), not just torque (force) or work (forcexdistance).

http://www.personal.psu.edu/users/b/...alculators.xls

94formulabz

This is an M6 correct? we are talking about shifting, not auto shift points.

TheHeadFL

EDIT: Yes, T56

I'm not sure how it would come out to be 2.5K.

The reason I am using TQ instead of HP to calculate is because HP is constant and not affected by gearing. TQ is affected by gearing.

Basically, my method is this.... start with the assumption that we always want to *maximize* torque multiplication through gearing. This means that whenever possible, we want to be in the gear with the most multiplication. The only time we want to go to the next lower gear is when it becomes advantageous, either for power or reliability reasons. (ie. valve float)

[I found these ratios on the net, not sure if they are LS1 or LT1]
Therefore, in 1st gear, if at 6000rpm I am making (corrected for gearing) 300rwtq (342hp) I am actually putting down to the wheels 300 x 2.66 (1st gear) x 3.42 (rear gear) = 2729 pound feet of torque to the rear axles (wheels change this even further). In the next gear, at 1.78:1 reduction, I would be turning approx 4015 (say 4000) rpm. At this RPM, say I am producing around 290rwtq. So, 290 x 1.78 x 3.42 would give me 1756 pound feet of torque at the axles. Lets say I could rev my motor out to 7k safely, but it only made 180rwtq all the way out there. Shifting from 1st to 2nd gear at 7k rpm would put me at 4700rpm in 2nd gear, where I might be making an arbitrary 300rwtq or so. 180 x 2.66 x 3.42 = 1637 rwtq. 300 x 2.66 x 3.42 = 1826rwtq. In other words, I have revved too long, and I actually am gaining torque at the wheels by going to the next gear.

I am not sure if I am explaining my ideas adequately. Basically, my point is that you always want to use the lower gears as much as possible, which means shifting as late as possible, except where the engine can't handle it, or isn't making power up there.

By my way of thinking, at least, you only want to go to the next gear when it is advantageous to do so, in other words, the optimum shift point is the point at which the torque curves from the two gears intersect. (When charted along a graph of wheel RPM [mph])

TheHeadFL

This is what I managed to come up with:

http://www.mangucha.com/~drewb85/points.jpg

94formulabz

Ok, i understand where your coming from now, makes sense. Mine optimizes the HP t.

Your method gives shift points within 100 rpm of mine.

I'm trying to think about this and figure if we've just calculated the same thing using slightly different methods or if these are two idependent methods that give similar results.

TheHeadFL

Partly my graphs are flawed by the granularity of the dyno information we received. This graph is months old, and we're trying to dig up the original files so we can get a true RPM by RPM printout of the data points....

But I think all I've done is attack the problem differently. I think all I've done is ignore HP and calculate torque directly, but it seems like it would be equally feasible to do it the other way around.

toegead93

94formulabz:
This is off subject a little, but I went your web link and noticed the 93 gears. the 93's had the M28 and M29 geared transmissions. The M28 came with a 3.36 first gear while the M29 came with a 2.97 first gear. Just a note Interesting site though.

94formulabz

Being that I have a 94 and your the one with the 93, i'll trust you on that one. Was first the only difference from the ratios I had listed? Was there any method to their madness determineing which 93s got which transmissions? I got my ratios from sallee chevrolet replacement T56 listings. Could you clear this up a lil more, i like knowing trivial stuff like this

-brent

toegead93

I don't know about replacements, but two manual transmission choices were available in 93.
Year Model/Optn 1st 2nd 3rd 4th 5th 6th Final
---- ------------- ---- ---- ---- ---- ---- ---- -----
1993 Manual/M28 3.36 2.07 1.35 1.00 0.80 0.62 2.73 (GU2)
1993 Manual/M29 2.97 2.07 1.43 1.00 0.80 0.62 3.23 (GU4)

check this site out
http://www.angelfire.com/ga/cincity/...on.html#ch4_3a