Revving over 7K a bad thing?

[Nd4SpdSe]

Originally posted by stang67fb:
little off topic here but...how many of you actually like the very close ratio 5 speed tranny we got in the mx3? Cause now that i got my ZE i ******* hate it.

ACtually i like it, its quick, 1st to 2nd can be tricky when racing, but i love the quickness...with my ze i dont need to shift as much anymore either, i can pass cars easilly in 5th. I can almost start from a dead stop in 3rd, so a rolling stop i can stay in 3rd easy, so in town i ncan pretty much use only 3rd and 4th

5th revs a little high, like at 4200 at 120km/h, but the gas milleage it good and cant complain, its WAY better than it was with the k8

<small>[ December 14, 2003, 12:17 PM: Message edited by: Nd4SpdSe ]</small>

[killerpickle]

Im no racing expert, but shifting after 7k can help bring the next gear up to a higher power band sooner, or even right away say, first and second. I go to 7300 or more in first and a little less in second, maybe 7000-7200. In the later gears it might not be an advantage In third I rarely go past 7000 and forth if I ever get that fast I shift about the same..

[Nd4SpdSe]

it depends, i havent played around with it, but the Millenia ZE, its max torque is a 4800rpms i belive, but when redlining and shifting, it seems to start the next gear in the mid-5k range...i dont know the powerband, but if the torque levels off after 4800, that not bad, but if you loose torque after 4800rpms, that prolly not what we want...

getting mx-6 or performance cams should sort it out, i think the max torque on the mx-6 is like 5500-5800rpms

[IanL]

I do agree with that. Its the torque that makes the car accelerate, so you need to operate the engine over the middle of the torque band peak to get the best performance. I worked out a set of shift points for the stock K8:

1st to 2nd - 6200
2nd to 3rd - 5900
3rd to 4th - 5600 (optimum!)
4th to 5th - 5700

The Redline is the shift point for maximum wear and maximum fuel consumption, its not the shift point for maximum acceleration.

The full post is here, its the post dated 26 August.

If someone has a link to the KLZE torque curve, it would be interesting to compare the shift points.

<small>[ December 15, 2003, 04:07 AM: Message edited by: IanL ]</small>

[killerpickle]

I disagree with the 1st to 2nd shift point very strongly, especially for the k8. I was extremely hard on my old engine. I would rev it to 7500 in first and would very nicely engage to second with out feeling bogged down, if I was to shift from 6200 rpm in first, second would start way to low, I believe even before vris kicks. The Ze's torque may peak at 4800 but does not drop off till much later. I wish I had a dyno handy...

[IanL]

You have to look at the torque curve - unfortunately its no longer available online. If you change from first to second at 6,200, you hit 3,400. The value of torque at 3,400 is available until 6,000 rpm, but no higher. There's no point in hanging on in first beyond 6,200 - there's more torque lower down.

In fact, beyond 6,200, when both VRIS valves close, the torque drops below the value at 2,600, so you would accelerate better from 2,600 up than from 6,200 up. It may not feel like it, because of the noise

Yes, you will get more torque after your change to 2nd, if you wait till 7,500 in first - but you will have taken longer to get there than if you had changed earlier - its the overall time that counts.

[HFStuart]

Ian,

By using those change points from 1st to 2nd you will drop to revs where the engine will produce more torque. BUT it is torque at the wheels that makes the car accelerate not torque at the flywheel.

The jump in gear ratios between 1st and 2nd is so much bigger than any of the other gears that you can probably run to the limiter before the torque drops such that more as available in 2nd.

I found this link SHO Link

That shows that in some cars you should always use max revs to change up - I don't know if this is the case on an MX-3

Stuart

<small>[ December 15, 2003, 04:51 PM: Message edited by: HFStuart ]</small>

[Custommx3]

Just be careful going to high RPMS. KLZEs have a known problem with breaking vavle retainers @ high RPMS.

[Nd4SpdSe]

Originally posted by Custommx3:
Just be careful going to high RPMS. KLZEs have a known problem with breaking vavle retainers @ high RPMS.

Funny how must ZE'ers are racers too...so its quite the ironic issue

[IanL]

Originally posted by HFStuart:
By using those change points from 1st to 2nd you will drop to revs where the engine will produce more torque. BUT it is torque at the wheels that makes the car accelerate not torque at the flywheel.

Stuart,
****! You're absolutely right. I forgot the gearbox is a torque multiplier. Completely changes the picture.
Profuse apologies, guys. I was wrong.

[mazdubber]

in some cars you should always use max revs to change up - I don't know if this is the case on an MX-3

This is definitely not the case in the mx3, as in most mass produced vehicles. Most vehicle manufacturers set the gear ratios and final drive ratios for what the average buyer will use it for (fuel econemy). Unfortunetely this means that the ratios will be way off when it comes to 'performance' driving. Some vehicles ratios are so far off that you have to max out the revs in order to stop the motor from dropping below the power band.

For racing applications, the ratios are set so that the motor will always be in the power band. This means that if the power band is between 4 and 5 thousand rpm, under hard acceleration you would shift at 5 thousand every time. The next gear up would drop the motor down to 4 thousand rpm. The gears would essentially make the most of the available power.

Anyways, back to the mx3. Unfortunateley these are fitted with our grocery getter gears (great for the fuel econemy but not for the racing). The ideal solution to this is to install a custom set of gears with dog ring engagement (non synchro). It's not all that hard to figure out the ratios if you know the acceleration and speed you want. The other solution is to figure out what the power band is, be it via a dyno or just the feel of it, and keep your shifting so that you will always start a new gear at the bottom of the power band. My stock k8 feels like it's bottom is around 4300 to 4500. However thats with over 200k.

Sorry in advace about this long, possibly off topic speech.

[HFStuart]

I suspect you have missed the point of my post- I was talking about driving for maximum performance, not day to day driving.

The gear ratios in an MX-3 are not designed for economy (18.something mph/000rpm in top) They are designed to give a low torque engine the best performance compromise.

The torque produced by the motor at gearchage is not very relevant, only the torque that reaches the wheels is. I don't have the plots but I would suggest that you need to rev to at least 7k in 1st 2nd and possibly 3rd before changing up to get the best performance precisely because the gaps between the gears are so large.

While I'm on bear in mind that the rev counter on the car ALWAYS over-reads. It's calibration is such that it can read up to 7400rpm at a genuine 7000rpm. Jap and European (not UK) cars were redlined at 7500rpm with the stock K8 (not ZE)

Does anyone fancy doing the wheel torque/speed graph to help sort this out ? - a rolling road torque plot would from a std car would help !

Stuart

<small>[ December 17, 2003, 05:08 PM: Message edited by: HFStuart ]</small>

[superslacker]

in daily driving to work and school i find myself shifting @ 6500 to 7000 rpms constantly, and almost always heel toeing or double clutching in any bends or coming to a stop. i also have the car at WOT pretty often, but i don't go mashing the gas to the floor from a stand still or while the clutch isn't fully engaged. what kind of trouble am i asking for from my mx-3?

my poor car... i love driving too much haha

[Steeb]

Originally posted by superslacker:
in daily driving to work and school i find myself shifting @ 6500 to 7000 rpms constantly, and almost always heel toeing or double clutching in any bends or coming to a stop. i also have the car at WOT pretty often, but i don't go mashing the gas to the floor from a stand still or while the clutch isn't fully engaged. what kind of trouble am i asking for from my mx-3?

my poor car... i love driving too much haha

poor gas mileage. u should be ok if u take good care of it. but soon enuf, if u drive it like that all the time its more likely to go. yah right..... just take care of it. i drove the crap outta my k8 some times and it refused to kick the bucket.

<small>[ December 18, 2003, 04:59 AM: Message edited by: Steeb ]</small>

[MX3KL08]

What do you guys mean by double clutching? I thought that was only for non syncro gearboxes.

<small>[ December 18, 2003, 05:47 PM: Message edited by: MX3KL08 ]</small>