when to shift

[madwilly814]

should I ...

a) shift at redline
b) shift at 4400 (peak torque)
c) shift at 5600 (peak HP)

[MorganS13]

i asked this question about a week ago and the answer i got was this:

1st-2nd at 6500
2nd-3rd at 6200
3rd-4th at 5800 (or u can stay in third if you're more concerned about E/T than MPH)

Basically u shift where it puts u in your optimum power range in the next gear.  I never got a clean run to try this out...

[ca18guy]

Pretty much you need to goto the track and find whats best for your car. I would shift alittle after peak HP so you could land in the best part of your power curve.  Goto a track and mess with launch and shift points to really improve your time.

[uiuc240]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (MorganS13 @ Oct. 15 2002,11:37)</td></tr><tr><td id="QUOTE">i asked this question about a week ago and the answer i got was this:

1st-2nd at 6500
2nd-3rd at 6200
3rd-4th at 5800 (or u can stay in third if you're more concerned about E/T than MPH)

Basically u shift where it puts u in your optimum power range in the next gear. I never got a clean run to try this out...</td></tr></table><span id='postcolor'>
Morgan, you should find my old post and quote it <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>

Eric

[MorganS13]

Here you go:

"i'm assuming you have 195/60-15 tires for this calculation. &nbsp;if you don't, the numbers change slightly (mph goes up), but that's not a big deal.

if you shift from first at 6200 rpm, your rear tires are rolling at approximately 33 mph. &nbsp;when you shift into second, that same tire speed equates to only about 3600 rpm.

i realize that your momentum (acceleration) will cause you to be traveling FASTER than 33 mph when you engage second gear. &nbsp;so let's say for the sake of argument, that you're now going 38 mph. &nbsp;that still only puts you at about 4100 rpm when you grab second.

the hp peak on the 240 is at 5600 and torque is at 4400, right?

so now let's say you shift at 6500 rpm.

that puts you at 35 mph when you start the shift. &nbsp;then add that same 5 mph. &nbsp;now you're at 40. &nbsp;40 is good for just under 4400 rpm in second.

so in my opinion, you should be shifting from first to second at 6500 rpm.

in the same fashion, the 2-3 shift should occur at:

about 6100 rpm. &nbsp;that's ~56 mph, and after you grab 3 and engage the clutch, you might be at 59 mph, which would put you *just* under 4400 rpm.

i realize this isn't exactly scientific. &nbsp;for instance, we should really be looking at the rate of acceleration and the mass of your car to find out how much more speed you'll be gaining between the shifts.

but this is a good starting point.

cliff's notes:

1-2 shift is better at 6500 rpm
2-3 shift is good at 6100 rpm
3-4 shift should be at about 5800 rpm (but if you're drag racing in a KA24DE without a turbo, you should just leave it in 3rd and go the distance, IMHO)

that was a fun post....

Eric"

[AKADriver]

If anybody has a clean dyno plot of a typical KA, it's pretty easy to figure out from that, and scientifically (though the estimation in Eric's post isn't too bad, it's a roundabout way to get an answer that's only mostly correct).

Don't worry about where the torque and power peaks are. &nbsp;Only worry about waiting to shift until there's no more torque available in your current gear than the next one.

For a good explanation of how to properly derive shift points, see this section of the Neons.org FAQ (http://neons.org/faq/FAQ_LE.html#Power). &nbsp;The numbers are all wrong for our engines but the derivation is the same. &nbsp;And with a 240SX, unlike the Neon the result is going to be an engine speed below redline.

[uiuc240]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (AKADriver @ Oct. 15 2002,2:53)</td></tr><tr><td id="QUOTE">If anybody has a clean dyno plot of a typical KA, it's pretty easy to figure out from that, and scientifically (though the estimation in Eric's post isn't too bad, it's a roundabout way to get an answer that's only mostly correct).

Don't worry about where the torque and power peaks are. Only worry about waiting to shift until there's no more torque available in your current gear than the next one.

For a good explanation of how to properly derive shift points, see this section of the Neons.org FAQ (http://neons.org/faq/FAQ_LE.html#Power). The numbers are all wrong for our engines but the derivation is the same. And with a 240SX, unlike the Neon the result is going to be an engine speed below redline.</td></tr></table><span id='postcolor'>
Good point about the dyno stuff. &nbsp;However, there are two caveats with that:

1. &nbsp;I doubt he has dyno numbers of his particular setup.

2. &nbsp;Dyno runs are done in 3rd or 4th...so what do you do about the 1-2 and 2-3 shift?

I still stand by my estimation and think it's a good starting point for anyone trying to get the most out of their powerband. &nbsp;Now, obviously, if you're running a set of cams, the torque curve will be way off...but with just intake and exhaust, this should work just fine.

Eric

[sykikchimp]

your power isn't going to be that far off with the different gears.. &nbsp;you may be able to lay down a bit more torque but they curves should still peak and fall at the same points..

here is my shitty dyno from last week:
I would guess this is fairly a typical peaks, and dives.. (except for the crap at 4k)
http://charles.sykikchimp.org/images/dynosmall.jpg
(blue was 4th gear, red was 3rd)


By looking at that dyno, shifting at around 5800 rpm would be right after peak hp starts to drop off, and should land me at a good place on the torque curve to take advantage of the torque thats available for the longest time period I can. &nbsp;If I waited to shift until 6500 rpm then I would land near peak torque but it would almost immediately drop off and I would loose any power I might have just had.

[xLSTONEx]

morgan and uiuc have it exactly right. I even have a computer program that tells me thouse exact marks. And it works for me.

[DuffMan]

You do want to shift arround 6500 on the 1-2 shift even higher if you have basic mods like exhast and intake because they open up the top end.

An important thing to consider is that even though your torque and power is falling off at the top end the mechanical advantage of gearing plays a huge role in acceleration and shifting up to 2nd gear will cause you to have only 57% acceleration assuming equal torque as you would in 1st.