im in first gear, and when im going and shift at 2000 rpm to 2nd gear, it drops 500 rpm to 1500 rpm..... when im in 1st and go to 3000 rpm and shift to 2nd, it drops 1000 rpm, when i shift at redline from 1st to second, it drops 2500 rpm..... how does this work, im totally confused....

 

Uhmm... doesn't it depend on how quickly YOU shift?

And while I don't study the tach while shifting, your numbers do seem a bit off.

 

no, i shift as quickly as the next guy

 

Because they're gear ratios.

For example, the first gear ratio is 3.267:1. So, when the engine is turning 2000 rpm the transmission output shaft is turning 612 rpm (2000/3.267=612). Second gear is 1.88:1, so the same 612 rpm of the output shaft now equals 1150 engine rpm (612*1.88=1150), a drop of 850 erpm.

If, instead, you shift from 1st to 2nd at 3000 erpm, you'd drop to about 1700 erpm (3000/3.267*1.88=1726), a difference of 1300 erpm.

When you make a 1-2 shift at redline, say 7000 erpm, you'd go to about 4000 erpm. And so on. The RPM change from gear A to gear B (upshift or downshift) is ERPM / gear ratio A x gear ratio B. (Forgetting that the car decelerates a little between shifts.)

Hope that helps!

 

I think that what Un-Kut is making reference to is the revs in one gear vs. the previous gear, and not the revs dropping between shifts.

If I understand correctly your question, you want to know why revs drop more rpms at higher rpms than at lower rpms. Essentially, it's all about the ratios of the transmission. Essentially, then ratios depict the relationship between the number of revs of the output of the transmission, vs. the input shaft. In our TSXs, the ratios are as follows:
Gear / Ratio
1st / 3.27
2nd / 1.88
3rd / 1.36
4th / 1.03
5th / 0.83
6th / 0.66

What I believe you're asking is: when shifting from 1st to 2nd, revs drop from 2000 to 1500 (-500), or from 3000 to 2000 rpm (-1000), or from 7100 rpm to 4600 rpm (-2500). The key to understanding that is to understand that the difference in rpms will be the result in the difference between your input and output shafts. Since at a given speed your output shaft spins at the same speed, the difference when shifting gears is dictated by the ratio of 2nd gear to 1st gear ratios. Another way of saying this is that the relationship between the two rpm values is not a difference (one minus the other), but a division (one into the other)

That number would be derived as the quotient of your 2nd gear ratio divided into your 1st gear ratio, or 1.88/3.27 = 0.575. That is to say that, for a given speed, your engine will spin in second gear at 57.5% of the revs that it would in first gear. Using your example, you would find the following relationship:
Revs in 1st / Revs in 2nd / Absolute Difference
2000 / 1150 / -850
3000 / 1725 / -1275
7100 / 4082 / -3018

As you can see, the absolute difference in rpms increases as engine speed increases, more than 3000 at redline, and less than 1000 at 2000 rpm.

I hope this helps.
Chris

 

thanks guys

 

Nice answer... wish I had seen it before working on mine!

 

Hmm... I shift at 7500 rpm to second gear and the rpm is above 5000 rpm.

 

I'll have to go try it out, but I got the gear ratios from the Acura TSX specs on the Acura web site. Unless the ratios listed are wrong, or if earlier TSXs had different ratios, this should be impossible. :weird:

 

Here you go.

 

Jtso, in your video...is it safe to go up that high once in a while? Or have you upgraded your internals? I never let my car go above 7050 RPM's...

And I guess the ECU doesn't log that in unless it's a mis-shift and you go beyond 8k right?

 

The ECU has been reflashed by Hondata and the upper rpm limit is now 7600. The internal is stock. I don't think there is any problem with running the rpm that high once in a while. I did mis-shift once and the rpm went way up.

 

i've bounced off the rev limiter once, on purpose, in 2nd gear

 

That's weird....when I shift at 7000 to 2nd gear I land above 5000 RPM.

 

^ If you HAD a second gear!

(sorry, that was mean... just too easy)

 

LOL. My second was there all along. It was the mainshaft that gave out.

Either way, she's back in commission right now and I hope it'll stay that way!

 

Yeah, when I was going through those calculations I thought the same thing. When I 1-2 shift at 7500, I stay on the high cam. Do you know what gives? I must be missing something in my calculations (the nature of my answer is correct, but the math doesn't match reality). Is that 2nd gear ratio wrong? If 1st is really 3.267, and 7500 to 5000 is what we're getting, that means 2nd has to be around 2.18, doesn't it? The rpm observations of the OP bear that math out, too.

The Acura site says 1.88, though. What are we missing?

 

Holy Crap, your tach flys up soooooo fast!! What are you engine mods again JTso??
DC headers, UR Pulleys, Ran High flow CAT, Hondata, which intake & exhaust?

 

That video was taken over a year ago. It was equipped with Hondata reflash, K&N CAI, DC header, Carsound cat, Tanabe SMH and big bored TB.

 

WOW, so its even better now then. I haven't been around long enough to follow all of that but sheesh man, your tach flies up really fast! I need to really start saving up for some engine mods. Thanks!

 

lol you luv the blinking red light...

Wish we had 11,000 rpms, I hate it when I run out of rpms

 

6.33 sec, not bad at all. I need to work on my launch. You did that with VSA on, too. Do you find it better with or without VSA on?

 

You're missing the fact that in between shift, the car still accelerates rather than deccelerate like you mentioned earlier. Unless you take 2 seconds to shift from 1st to 2nd, then your car will deccelerate in between shift. But if you're shifting very quickly (like fraction of a second), then the car continues to accelerate but at a slower rate than when it was in gear.

 

I don't think that's it. I tried it out today, not accelerating but simply holding 1st for a second at 7000 rpm, shifting to 2nd, and the rpms going into 2nd were about 5000. Hmmm...

 

I've tested with and without VSA and it makes no difference. Remember the movie "Initial D"? The guy was trained driving with a cup of water in the car, and try not to spill it. Well, the VSA is my "cup of water" . So, I try to launch without wheel hops or tire spins, as either one will kill time. VSA gives me the feedback I need to make the necessary corrections.

 

You know, that's an excellent point. I noticed that you only flashed the VSA light for a moment, in the middle of a shift. Good idea, try to get to the edge where you don't set off the VSA.

Any ideas on the gear ratio dilemma?

 

Not a clue.

 

You're right.. the car continues to accelerate despite that the rate of acceleration is decreasing between shifts. But I don't think that this would account for anything remotely close to what we're seeing here. In order to show a difference of 1000 rpms in 2nd gear (25% difference), the speed differential between the release of 1st gear and the engagement of 2nd gear would have to be very high.

I'm with Peter thinking that the ratios we obtained are wrong. either the 1st gear ratio is too high, or the 2nd gear ratio is too low... any more info anyone?

 

Are you being facetious? Is it obvious and I'm just not getting it?

 

That makes two of us...

I tested it tonight, and if I shift at 7400 rpm, i end up in 2nd around 5400 rpm, which gives me a .730 ratio differential between 1st and 2nd gear, instead of the .575 we originally calculated.

 

Nah, I'm not sure why either and can only speculate. There might be a slight amount of slippage (split second) during the initial clutch surface contact to fully engage that allows the engine rpm to stay up instead of a complete drop in rpm.

 

Another possibility is the stored flywheel momentum keeping the rpm up. The faster it spins, the less rpm it drops. On the other hand, the rpm in between shifts tend to drop faster for light weight flywheels which might be closer to the math calculation earlier.

 

good read... ifl

 

FWIW, I think I've figured it out. Watching JTso's video, the speedo as he shifts from 1-2 does continues to rise from around 36 to around 41 mph by the time 2nd is fully engaged. Doing some quick math, at 41 in 2nd you'd be around 4970 rpm with stock-size tires. Allowing for some imprecision in the tach, speedo, etc, that accounts for the difference in rpms. Vwong's explanation was right on! (So, basically, that means vwong figured it out and I'm just confirming it.)

The car continues to accelerate, albeit at a much lower rate, between shifts -- unless, like he said, you take too long to shift. My G-Tech actually shows it on the acceleration curve. It's less steep at each shift but still sloped up -- accelerating, but at a lower rate than when in gear.

I know what you're thinking: I'm a genius. Probably smarter than JTso. Fortunately, what I lack in automotive knowledge I make up for in humility...

 

= JTso

vwong

peter

 

While on the subject of shifting...

At what RPM do you all typicall upshift in everyday, around town driving? Is there an optimal or recommended RPM for general upshift? I don't figure it's good to drive around redlining all day.

 

3-3.5K seems to work for me.

 

That's what I was always generally taught growing up, learning to drive, etc. But every now and then I wondered if an auto like ours had a higher optimal range for everyday shifting. Just a curiosity issue.

 

I do the same in day-to-day driving, about 3500 -- nice and relaxed, gives the rod bolts a rest.