chuson

Since the 05/06 AT Hondata ECU Reflash is still in not release yet, I'm wondering if Hondata can "re-tune" the Rev-Limitor or the Torque Convertor (Sorry I don't know which word is right)

Here's the issue: When I ran on the Hwy in SS mode, I found that @ 6K rpm in 3rd gear, my speed is around 160km/h. If I red-line (7300 rpm) it, the top speed in 3rd will be very close to 180km/h before I need to shift to 4th. However, if I'm cruising @ around 160km/h in 5th or 4th gear(I tested both), when I need to accelerate faster, and would like to downshift to 3rd, it won't let me do it. Not until the speed is down to 140ish or else I would be stuck in 4th gear for a very slow acceleration.

So here's my question? Can the Rev-Limitor delay by ECU control or if a Hondata reflash can fix this problem?? I guess this is a main reason why the AT is always behind the MT

narci

How many times you plan to be cruising at 160km/hr and then accelerate to 180km/hr?

remind me to be off the higheway when your on it hehehe

dingobiatch

no, i agree with him. this problem spans across all gears - seems that you can't downshift until you would only be doing doing ~4500rpms in the gear you downshift into. hopefully that makes sense... like, you can't go into second from third unless your RPM's would be 4500 or so when you go into second.

narci

ahhhh...so it;s througout the gears..didn't know that. I don't use the SS mode all that often.

CGTSX2004

iTrader: (1)

My assumption is that Hondata isn't going to touch this. There is too much potential for something going wrong, over-revving the engine, or damage to the transmission. If you don't like way the SS limits your ability to shift, then you're gonna have to trade it in for a MT.

hondata

Correct. We will not be altering shift points.

chuson

Can someone tell me what's control the "shift point"?? Is it the ECU, or a separate unit in the tranny or something??? Can a professional shop do it??

The 5th gear is excellent for saving gas, and I used it the most in normal driving. But I don't like how's the tranny depends on the lower 4 gears for acceleration. I was thinking if...
1st: 0 - 45km/h
2nd: 20 - 100km/h
3rd: 40 -150km/h
4th: 60 - 200km/h
5th: 90 - highest possible speed...

Will this setup benefit the 5AT TSXers??? Maybe a faster acceleration???

Benz_05_TSX

iTrader: (1)

what the hell?? my 1st gear went up to 90km/h and second is at 120km/h...

chuson

WHAT??? I think my 1st gear red-line @ around 60km/h~ 2nd gear red line @ around 118km/h I think. Above is what I thought as an ideal shift point.

swirlie

I bounced off my rev limiter at about 60km/h in 1st. But then I've got a 6MT.

chuson

How would his 1st gear went up to 90?

EuroAccord2.4AT

second gear for AT is till about 120 or 140 km/h...don't know it exactly. First gear is NOT 90km/h ... it's lower.. bad that I don't know, must do some speeding tomorow and go to germany test the top speed

Dan Martin

I plotted the gearing in Excel to make these graphs:

chuson

Hey Dan~
Thx for plotting the graph. On the AT, I thought the 4th gear reaches the same top speed as the 5th gear, also 5th gear does not pass 3500rpm on my car ( I guess everyone is the same.)

While compare to 6MT, the MT does have 2 EXTRA gears to help acceleration. Each gear takes the load efficently and equally. My question is if there's ANY chance that a 5AT can change its gear ratio and makes it closer to a MT??

I don't drive MT, I can't have a MT, but I'm willing to get a MT if it's my own car~!

jlukja

Top speed is limited to 143mph (some say its drag limited, others say its a speed governor). It can be reached both in 4th gear and in 5th gear in an AT. Not sure why you can't go over 3500 rpm in 5th gear. Isn't that somewhere near only 105mph?

Dan Martin

Sorry, you can't re-gear the 5AT to make the ratios similar to the 6MT.

I realized after I posted the graphs that they might be hard to read, so I revised them:






You'll never switch into 5th gear if you're going for top speed in the AT TSX. It's too tall. The shift point is beyond the drag limits of the car. Perhaps with forced induction it would be used, but certainly not on a stock engine.

observer

According to this dyno of the stock 5AT (green line)



doesn't it imply that there is no reason for you to go beyond 5000RPM if you're going for maximum acceleration? If this graph is correct, it seems to me that VTEC is useless in the 5AT.

Dan Martin

You shift for max horsepower, not max torque.

If you did a 1-2 shift at 5000 rpm, you'd be down to ~2700 rpm and making somewhere around 80hp. If you shifted at 7300rpm, you'd drop to ~4200rpm and be making 115hp.

observer

What I care isn't shifting for max hp or max torque, what I care is shifting for maximum *acceleration*. Based on that dyno graph, I think it's obvious that you'll be accelerating faster shifting at 5000RPM compared to shifting at redline.

What's wrong with doing a 1-2 shift at 5000RPM down to ~2700RPM? At 2700RPM you have 145 ft-lb of torque and that torque stays pretty much constant for the next 2000RPM. In contrast, at 5000RPM you only have 140 ft-lb., but worse yet, the torque number will drop to <120 ft-lb when you reach 7100RPM. This means in those RPM ranges you will accelerate faster in 2nd gear compared to 1st gear.

observer

btw, my belief and assumption is that instantaneous acceleration is proportional to torque, not hp.

EDIT: okay, I read more about the issue of hp vs. torque in this article: http://www.allpar.com/eek/hp-vs-torque.html

so I found out given the exact same torque number, you would be accelerating faster in 1st compared to 2nd. So let me think about this more and try to figure out the optimal shift point from 1st to 2nd based on that dyno.

observer

These are the 5AT gear ratios:

1st - 2.652
2nd - 1.517
3rd - 1.082
4th - 0.773
5th - 0.566

This means 1st gear torque is 1.75 times as good as 2nd gear torque, 2nd gear is 1.40 times as good as 3rd gear, etc.

115 (@7100RPM) *1.75 = 201 > 145 (@2700RPM)
115 (@7100RPM) * 1.40 = 161 > 147 (@3500RPM)

This means that shifting at redline is indeed optimal for acceleration, which is actually a relief for me.

chuson

Hey observer~
Grab a stop-watch, and try to time your 0-60 or 0-100 when shifting @ both 5000rpm or redline, you will feel the differences.

Exactly~ the 5th gear is sooooo tall that it's almost useless for acceleration, shouldn't we call it a 4AT? If the gear ratio or shift point can be change, then the AT will be at least smoother and has power on tap, no more waiting~

jlukja

I've heard it said that torque gets you moving and horsepower keeps you moving.

dingobiatch

would shifting at 7100 be optimal or would 7600 be better? (for those with hondata)

JTso

iTrader: (2)

^^ You need to shift at higher rpm in order to keep the next gear in high cam mode. Hondata makes the task easy.

Tsx536

Would it even be possible to get the gear ratios changed?
Wouldn't this be a mechanical change? I'm confused as to how this is related to Hondata and the ECU.

Dan Martin

I think initially this thread was about changing the shift points, but it has since turned into a gearing thread. Gearing would definitely be a mechanical change, but the shift points are controlled by a computer somewhere.

chuson

Like Dan mentioned, I think the shift points are controlled by the ECU. But what about the gear ratio? Thus I'm not an expert on car parts, so I posted my thought and want some feedback on how it can be done.

If I want to make the gear shorter (5th) or more efficient in acceleration, that's involve Gear ratio right??? And if YES, does it also controlled by ECU?? or it's the tranny itself??

rmpage

No. Gear ratios are determined by the mechanical design of the transmission, as in how many teeth each set of gears uses, and its final ratio.

Think of your 27 speed mountain bike and the relationship of cog sizes for each gear combination, and how you would change cog sizes.

This has nothing to do with engine management. As Dan said, the ECU controls at what RPM and TPS combination the transmission shifts into different gears, but it does not control the gear sizes themselves, as is easil understood.

Tsx536

Would it be possible to change the gear ratio on our AT transmission?

I know some of the S2K guys change their gear ratios. This on a manual though, and I've never heard of anyone doing it on an AT.

Dan Martin

You'd be more likely to be able to change the final drive ratio than the actual gear ratios in the tranny.

JTso

iTrader: (2)

There is one gear ratio you can change ---> tire size.

chuson

so I gUess tHat's a NO then. Well, got my Injen installed today, and I'm picking up my Header and RSB tomorrow. soooo Excited.