short shift, how short?
 

How far short should I try to shift? My manual has a min speed per gear listed:

1st = 3 mph (idle)
2nd = 7 mph (idle)
3rd = 22 mph ~1250 rpms
4th = 33 mph ~1500 rpms
5th = 48 mph ~1750 rpms

I always keep a bit above these #s. and I can still shift at 2500 or so for all shifts It doesn't like much less. Honda motors like to be revved, or well my foot likes it. Torque peak is 4500 on my engine. I saw some chart for a car doing various speeds in 5th gear, and it went down to like 38mph or so. That would definitely not make my motor happy. I am sure this was different gearing, weight etc. I bet if I somehow magically lost 500 lbs from my curb weight, that would change. My numbers for this current tank are looking good tho, and I've very rarely pushed it over 2500 rpm. Any thoughts on this?

It depends if you are driving uphill, downhill, or on level. If you are driving on a level surface or downhill you can shift very short (just use a light throttle and you will be able to pull out of the low rpm zone).

Yup...just depends on the car and how and where you are driving. My 190e will do just fine in 4th at about 30mph if I am not attacking a hill. I did have a 1981 camaro a long time ago that would easily start in 3rd and be in 4th at 15mph...but was a LOT faster starting in 1st. :D

I can be in 5th at 20mph in the xB and did a rolling start in second at 500 rpm . . . now that was pretty low and I get concerned with the oil pressure at that speed - at least with Synlube there is lubrication even at 0 rpm but I don't like to push it that low - good minimums are 1000 rpm for slow acceleration and brisk is 1500-2000 rpm usually I am in 5th at 25 or 30 with good acceleration - 30mph is about 1500 rpm in 5th. I notice a little bogging if the engine is not fully warmed up probably due to the VVTi and igniton timing moving around if the load is too high and the rpm too low then it will skip a little so higher rpm with light throttle works more consistantly. But for hill pulls at contant throttle any low rpm will do nicely.

Be careful with short shifting in regard to trying to save gas, and increase MPG.

The mistake most make is that low RPM's mean high MPG, and this is not necessarily true. In general it is, but not always.

Often, short shifting actually can use more gas and decrease MPG. Often a car needs to stay in it's "sweet spot" to get optimum MPG, which often means not shifting too short.

There are many factors here, such as where peak torque is in the RPG range, the speed the car is at and in what gear.

When I had my manual tranny V6 Mustang, and using a ScanGauge II, I noticed that my milage actually got worse if I short shifte, even though the engine didn't lug. And if I shifte later, it got worse too, so for your vehicle you need to find the sweet spot for a given circumstance (flat, hilly, etc).

We need to divorce ourselves from the absolute that low RPG means better MPG....often it does, but there are times it does not.

In my auto 2007 Yaris, if I use the gas peddle to shift short, I often see a decrease in MPG over just allowing the car to shift on it's own. Not to say this is true 100% of the time, but often it is. It took me a few weeks, but I did find the sweet spot with my Yaris and if I short shift under this sweet spot or over it, MPG decreases.

Using the tach to "judge" fuel consumption is deceptive, and for this reason you need a ScanGauge II which shows Load, and GPH and other factors which will better help you fine-tune your driving technique...this is much better then relying solely on the tach, to be sure.

Also and back to manual trannies, skipping gears will often not increase MPG...better to use them all to help the engine bring the car up to the required speed.

I agree. I just wish I had an option (short of converting my car to EFI) to get ANY performance data that is better than miles/gallons at fill up time. :) I suppose I could get a vacuum gauge, but that is only going to tell me that I am using a light or heavy foot on the throttle. ;)

When in creep-n-beep, I shift at idle.

One thing that the SuperMID showed me was that I wasn't getting good FE at low RPM's. Also that the throttle's effect on FE was MUCH more sensitive when the motor was lightly loaded at a low RPM than it was when it had a heavier load at a somewhat higher RPM. Its much easier to maintain an indicated 40km/l) on the SuperMID at 65mph with a injector pulse width of 4.0 than it is at 35mph with a pulse width of 2.4 (barely over the idle pulse of 2.3).

:p Again, I am jealous. :) Dang ol' mechanical FI.

Hmm...maybe for the next fill up, I will try running at higher RPMs, but with a light throttle.

Might be interesting to see what happens.

I get better in town mileage when shifting at very low rpms.

1-2 700-1000rpms
2-3 1100
3-4 1300
4-5 1500

level ground, downhill slightly less rpm, uphill slightly more rpm. The saturn pulls cleanly off idle in most situations

I guess it really depends on the vehicle! Theres no way I shift into 5th at 1500 rpms, no way. In 5th at 1500, it has a hard time accelerating on flat ground at all. But it is a jap car. they are more upper rpm HP, and not mucch bottom end. Its gutless below 2000 in any gear. Prefers 3000+. I will have to try a tank shifting at 3000, instead of my now usual 2500.

Hey, byobbq, say something intelligent about what this graph says about where to shift.
https://www.fuelly.com/attachments/fo...e15f6050e6.gif
To me it seems to say that you would want to be asking for nearly the maximum torque, and shifting at about 2600 rpm, trying to keep the revs and the torque demand right on that region of the best BSFC.

However the 'previous engine' had the most efficient areas not so tightly concentrated.

On my car with SuperMID, I have found that keeping the revs low does help fuel economy - seeming a lot more important than most other things!

And it is a 1.8 japanese engine!

Bill...does that mean I would be better keeping my car near it's torque peak...or just keeping it at the lowest % throttle that I can?

From the graph, it looks like you want to be pretty close to the peak, meaning stepping on it pretty hard... Still hoping for BBQ (or someone else) to confirm my understanding of the graph...

What kinda toyota do you have that motor in? :)

Do you know if you can find that kinda graph for a Mercedes 103.940 motor, or did you get this from a dyno?

Ya, exactly. BYOBBQ posted it. He has (or had) a Camry. I have not been able to find one for the K24 engine in my car. It seems to me that if the engine in every Accord, Element, RSX and TSX for the last 5 years doesn't have a BSFC chart that is findable on the internet, finding one for the Mer will be difficult...

Remember your gear ratios will make the biggest change between cars. A 3.5 versus a 4.1 will have to spread the shifts out further to get the same results. Also your trans ratios have much to do with it. I can right now be in 3rd gear in about 3 car lengths of the geo, it will be interesting to see what will change when the 14s are installed. Experiment and see it's the only real way to see. Japenese or European cars like to rev. american cars usually have lots of torque. Thats why in cars equiped with skip shift under 30% throttle will go 1st to 4th.

My car is pretty gutless all over. Especially in 5th gear. Sometimes I shift and wait for the acceleration to happen. la la la, anyday now! That sort of thing. I tried the short shifting in an altima and it just wasn't compatible. Too much weight and not enough low end torque.

Thing biggest thing that will help you decide which method is a supermid or an SG2.

good luck

lol i loose like 2-3 mpg if i shift at 2000rpm vs 2500rpm. i have a 5speed 4 banger s-10. if i shift somewhere around 2500 rpm i get 25mpg if i go lower than that (liek at 2K or under it only gets like 21-22mpg) course its an underpowered 4banger for that heavy of a truck...



im gonna try at 3K and see what happens. all i know is i HATE the speed limit of 30 mph.. its too high for 3rd gear and too low for 4th... 4th kidna labors and doesnt sound good at all. 3rd sounds high and the upshift light comes on...but i barely press the gas pedal(liek the weight of my shoe could drive it perfectly...

somehting else ive noiced is the wider tires(noticeably liek 1-2" wider with more agressive tread) and rims i put on for summer dont seem to affect mpg at all (maybe liek .3mpg or so) but it is a truck that has a buttload of torque for a 4 banger cuz its geared that way so maybe on trucks it doesnt make a difference.