Edge Hawk

Ok, The theory for better ET is shifting at HP peak or at the point where you will have the best Avg. HP under the curve right?

So, my question is would a car with say a 4000 stall 2.5-3.0 STR and 3.23s do better if I brought the shift points down from 6000 to 5500 (hp peak) THAN if I had say a 3500 with same STR but left shift points alone and went with 3.73.

Data:
dyno

curent 1/4 time = 12.70 @ 108.7

with out adding HP my ending MPH should stay the same.

shift rpms
stock shift points

rear end 1st start 2nd end 2nd start 3rd end 3rd
3.23 6000 3660 6000 3200 4600
3.73 6000 3660 6000 3200 5600 (<- mph at shifts will be different)

now with modified shift points
rear end 1st start 2nd end 2nd start 3rd end 3rd
3.23 5500 3360 5500 2925 4600
3.73 5500 3360 5500 2925 5600

So, how much of a torque multiplication differnce would there be with:

A Higher stall and stock shift points with the 3.23s
Vs.
B Lower Stall & stock shift points & 3.23s
Vs.
C Higher stall and stock shift points with the 3.73s
Vs.
D Lower Stall & stock shift points & 3.73s
Vs.
E Higher stall and lower shift points with the 3.23s
Vs.
F Lower Stall & lower shift points & 3.23s
Vs.
G Higher stall and lower shift points with the 3.73s
Vs.
H Lower Stall & lower shift points & 3.73s

I'm thinking the best ET would be G
and the slowest would be B

how would you rate them?
reason for this post
TC = $750 + $200 = $900
lower shift points (HPP3) = $250
3.73s = $250 + $200 + $250(you'll need the HPP3) = $700

(assume stock TC,lower stall but not stock, high stall)


A=$900
B=$0 or $900
C=$1600
D=$700-1600
E=$1150
F=$250-1150
G=$1600
H=$700-1600

CHRISPY

Personally I would go with a TP4200 stall minimum, and shift about 6200rpms. As for gears you could stay with the 3.23's but I would probably not bother doing gears till you can afford a 12 bolt.
The ultimate combo is TP4200-4600 converter with 4.11 gears in a 12 bolt on slicks. It is INSANE off the line and the shift extension is unbelievable.
Chris

Ragtop 99

iTrader: (7)

[quote] Ok, The theory for better ET is shifting at HP peak or at the point where you will have the best Avg. HP under the curve right? <hr></blockquote>

Let's start by correcting that. ET is a function of highest average torque to the rear wheels, so gearing comes into play. A4s have very wide gear ratio spacing, so you are almost always better off spinning the motor higher (within its normal operating range) rather than shifting to the next gear.

[quote] So, my question is would a car with say a 4000 stall 2.5-3.0 STR and 3.23s do better if I brought the shift points down from 6000 to 5500 (hp peak) THAN if I had say a 3500 with same STR but left shift points alone and went with 3.73.
<hr></blockquote>

The increase in midrange torque multiplication from the 4000 stall will not compensate for short shifting it. 3.73s will make the 4000 stall faster, just like it will make the 3500 faster.
Your fastest combination will be "R" (Ragtop Special <img src="images/icons/wink.gif" border="0"> ): higher stall, higher shift points, and 3.73s

Conclusion:

1) Buy tires first; you need them for any combo.
2) Buy the 4000 stall and a tranny cooler.
3) Buy the HPP3 if you need to fix shiftpoints after installing the converter or if you're willing to raise shiftpoints to 6200 - 6400. Otherwise use the money elsewhere, like for a pulley.
4) Buy the gears if the 4000 stall is too loose; otherwise put the money into headers.

[ November 20, 2001: Message edited by: Ragtop 99 ]</p>

ONYXSS

Edge Hawk - as far as converters go, it doesn't matter. Your choice of converter shouldn't affect your shift point decisions. Rule of thumb is to shift about 6 % above your peak hp. And converters don't change your peak hp and they don't change your shift points. They just keep the rpm's closer to the peak hp. So your targeted shift points should work with any of your converter choices.

[ November 20, 2001: Message edited by: ONYXSS ]</p>

Edge Hawk

Hmm, thanks guys, but I think you missed one question....

Ok, let's say you have a 4000 stall and your shifting at 6000.

so on the 1-2 shift you drop to 3660 RPMs and it'll flash up to 4000 right away. so you get flash for about 300 RPMs.

now with a 5500 shift point
the 1-2 shift then will drop you down to 3360 RPMs and it'll flash up to 4000. so you get flash for about 600 RPMs.

I think this is what Chris meant by shift extension.

You see even If I shift at 5500, I'll be right back up to 4000. So it seems to me that the torq. multiplication will be more if you shift at the HP peak.

CHRISPY

Nope that isnt correct. With a TP4200-4400 stall if you shift at 6300 say your shift will come back around 5000 rpms. That is the benefit of shift extension. you are comparing shift extension to a stock or near stock converter with the large rpm drop between gears. It is totally different with a TP4200+ converter.
Chris

RyanJ

chris is right. the shift extension is different for any converter. my 3800 stall drops to ~4600 i think with stock shift points. I might be wrong on that exact rpm, havnt atapped in a while. also, your mph will not me the same on the big end with a converter. too many things will change to predict, but depending on efficiency, 60' time, tires, and finishing rpm, it could be higher.


BUY TIRES! AT LEAST 26x10.5-16 ET Streets. Theres no point in going half way on this.

If i were you id wait for another GP on the ST3500. and im a vig guy, so thats saying something.


oh and BTW, i kinda liked the hawk without the spoiler. <img src="images/icons/smile.gif" border="0">


Ryan

Pro Stock John

iTrader: (34)

[quote]Originally posted by Edge Hawk:
<strong>Okay, let's say you have a 4000 stall and your shifting at 6000. So on the 1-2 shift you drop to 3660 RPMs and it'll flash up to 4000 right away. so you get flash for about 300 RPMs.
</strong><hr></blockquote>

No, that is not accurate. In your scenario it will drop to 3660 RPMs and still have to accelerate from there. There is no flash. It will NOT flash up to 4000 right away.

We are always looking for the balance between overreving past peak HP and dropping too much below our peak tq. And Nick @ ARE also says we want like 1500-2000 rpms to run through each gear.

Our shift points might end up being higher on 1-2 than you would have with say a 200R4, only because of the gearing of the 4L60E.

[ November 20, 2001: Message edited by: Pro Stock John ]</p>

Ragtop 99

iTrader: (7)

Lee: How did you come up with 3660 rpm?

On the converter output shaft, 1-2 shift at 6000 rpm:

1.62/3.06 * 6000 rpms = 3,176 rpms, not counting the fact that the car may have gained 1 - 2 mph during the time it took to shift, thus raising the rpms by 100 - 200 during that instance.

The converter input shaft side is engine rpm and where it lands is a function of shift extension and converter slip.

Terry Burger

iTrader: (4)

Get the car on a dyno and do a 1-3rd gear run, that will allow you to calculate where your shift points should be set. Anything else is pissing in the wind, but I must say higher shift points usually work better than stock ones.

Edge Hawk

oh, my bad joel. I thought 2nd gear was 1.88:1.

well $hit. <img src="images/icons/smile.gif" border="0">
thanks.

ONYXSS

Terry, don't agree with that one. Generally a dyno is not the best place to set your shift points. The track is, cause the car will shift differently under different loads. In fact, I recently had to re-set mine and found that the car can shift significantly different at the track (WOT from the start) than it does at WOT from a roll. The dyno may give you a starting point, but don't be surprised if the car doesn't shift the same at the track. Some guys dyno their shiftpoints and then hit the limiter at the track.