perfect time to shift?
 

I shift below 2000 rpm on my 94 civic dx, since i drive 100% city. im wondering if it would save more gas if i shifted at 3000 rpm would be more efficient, since it takes more time to get up to speed with shifting at 2000 rpm, the time wasted might consume more gas since shifting at 3000 will make me get up to speed faster and coast

Well I know on my VX, which has a shift-light to tell you where to shift, it keeps pretty much all of the city shifting under 2200rpm. The VX does have more tq lower in the RPM band than the DX motor, so you might want to go up to 3k...not sure really. I would try shifting higher and compare tank mpg results to shifting at a lower RPM.

My untested hunch is that you want to shift at as low RPM as possible without having it lug after you shift. Sometimes when driving a Prius I feel that fast bursts of acceleration are just as efficient as slow acceleration because of the car's predisposition for P&G. But the Prius has the continuously variable transmission that makes it easier to do fast bursts while maintaining optimum RPM. I think most people would tell you to get a SuperMID and do some testing. I find it hard to believe you get 28mpg shifting at below 2000rpm. I'm pretty sure the general consensus early shifting is better. As long as the engine isn't lugging.

but shifting isn't always the answer. In my insight I've found that some times its easier to hold a higher FE average in a lower gear. I think alot depends on your speed. I can travel 45mph in 4th and maintain the same mpg as I can in 5th. It really depends on several other variables other than RPM.

I had a supermid before but i sold it since i drive 100% city now, with tons of stop and go, so i dont want to concentrate on looking at it when theres alot of people and cars around me, can be dangerous

1993civicvx : i think if you had my route and lived where i live, getting 28mpg is normal haha. i used to get 44 mpg on my car before i moved to philly

When I had my 2000 ZX2 with a 2.0 DOHC motor, I found better fuel mileage shifting at 2 1/2 grand

I shift no higher than 1500rpm. Usually around 1300-1400 rpm.

My understanding is that shifting lower and keeping a larger throttle opening reduces pumping losses. Less fuel/air mixture also goes through an engine at lower RPM. That's not to say that it's good to throw it in a low gear and stomp on it. Heavy throttle (more than 70-80%) will cause enrichment. This is how I heard it explained. Hopefully someone can confirm or correct this, as I am still a relative novice.

I generally shift around 1500 RPM unless traffic conditions require a little more umph. Then I might let it go to 2000 and skip a gear somewhere when my speed is where I want it to be.

So is it better to be at 1500RPM and 60% throttle or 1250RPM and 100% throttle? Which uses less fuel? It seems to me 1500 would, but I never do it. I always opt for the lower gear if I can. I need a SuperMID super bad.

Just to throw a wrench into everything..... I, for the life of me, CAN NOT get my car out of closed loop while in gear and stomping on the throttle... Otherwise, ideal would be closer to as much throttle as possible while keeping it out of open loop while also considering load (constant = better) :thumbup:

Blanket statements like 'an engine operates most efficiently at such and such RPM' won't necssarily get you the best fuel economy. All engines are somewhat different. To think that, say, an old-school carbureted two-valver is going to have the same efficiency curve as a fuel injected four-valver is simply absurd. So, in order to determine the best shifting RPM for fuel economy, experiment.

i can't experiment without a supermid, hence why I want one, unless I drive consistently one way on an entire tank, and then another on another tank.

clencher: so you think then that it's prolly better to leave it in 4th and go for not full enrichment rather than puttering up in 5th with barely enough power?

I think you don't have to watch the SuperMID display all the time.

It tells you the fuel efficiency results among different driving styles, then you will be able to find your best technique to get the best results on your own route.

Yoshi

If I get in top gear goign up the hill, i have to hold the pedal down as much as it will go in order to make it up without lugging. If I leave it in fourth, I don't hvae to go full enrichment (maybe 80% instead, prolly not 60%) and fourth gear is only about 20-25% faster revs. Prolly bout the same either way.

Just shift without fuel, from a standstill with ice on idle get up to 20mph's or so then shift back to 4th and slowly get up there. If you have a light that might be helpful, but I usually give it just a tee bit of fuel after I get up to some kind of speed. However, the clutch is the only pedal in use until that car is idling in 5th, then after I drop to 4th I give it a notch.

My 1.8 litre does fine if from a standstill I let out the clutch easy and wait until the rpm's are at 800... First gear is the only gear I let out the clutch easy, once the car gets going that clutch comes out quick. First gear hardly takes a few seconds, second is almost as easy, third works the ice some and 4th tests it, but a high compression ice will get up to idle rpm's even in 5th.
So once idling in 1st then I shift to 2nd the rpm's drop to 5-600 and the engine's idle power gets it back up to idle speed, then shift again into the next gear, repeat until idling in 5th.
Once at 750-800 rpm's in 5th, take back down to 4th and give it just a tee bit of fuel, this should get it up to 30-35mph then back to 5th and once again a wee bit of pedal, voila.

The technique is a little bit like a ice OFF rolling start down hill, except this works best on level ground.

Notes: Doesn't work going up a hill :p
> Depending on ice compression some cars may not do well past 4th gear, the higher the compression the better the highest gears work, also 5th should be no real problem on a 6 or 7-speed transmission thou into and past 6th might not work on any.
> You could probably give it a go, when idling in 5th don't down shift but instead use 5th with an ultra light foot on the throttle, I find this tests my patience too far thou theoretically it should work.
> Yes you need a manual trans :p

Car used for the above technique: 1991 bmw 318is.
My mpg: 25 - 28, worst 22 best 30
EPA mpg: 17 - 23

Thank you.

I found that a takeoff from a stop at 500 rpm and shifting at 1000 into the next gears to get back up to 30mph impacted the trip MPG the lease with light throttle - which lugs it anyway at that low an rpm. Lubrication does a weird thing at low RPM - here is a graph of Synlube vs Regular lubricants.
Attachment 1065
So you want to stay in the mid-rpm range for reduced friction whereas with Synlube I can go really low on the RPM and still have only a little friction.

Oh I'm sorry, yeah I do run synth in everything, I like that chart.

Amazing, I discovered most of these things on my own, never knew there was a world of like-minded folks.