As you well know changing gears correctly while accelerating hard is very important. So i took into consideration 2 very different types of engines. A turbo-diesel and a NA gas engine (e46 m3, s4 v8 or whatever). The turbo-diesel first of all is a diesel :)) and it has another rev range and it is turbocharged aswell. So let's just say the diesel has it's peak power at 4100 rpm and a redline at 4500 rpm. the max torque is achieved somewhere around 2000 rmp (i think). The E46 M3 has a totaly different engine. It is very sport oriented indeed and it is an otto engine. It's peak power is achieved at 7900rpm and has a readline at 8000rpm if i'm not mistaking and a peak torque at 4900 rpm. My question is for best performance and to explore the engine potential, where do you have to change gears (at what rpm)?
For each type of engines. I think it's best to change a little over the power peak because then (in the next gear) the engine is closer to the peak power. Where is the best power band on both cars? I drove a turbodiesel and i saw the best performance from 2100-2300 rpm where the turbo kicks in till 4300 rpm where the turbo already lost boost. Anyway i haven't driven an m3:)) . yet :P to talk about the power band. But i'm just curious what do you guys think of those things? Power band? Optimum time to change gears? How important is when the peak torque occurs? How important is the type of induction on the engine? How would you handle a turboed engine? and so on... Thank you.

My opinion is that in gas engines you should change gears where the red line starts so when you change to the next gear you will have a lot of rpm and the engine will not "stall". Now in diesel engines i don't know, because here the peak power is much lower from the redline and it's known that in diesel engines after the peak power there is no power. So, after the peak power and until the red line the engine will just rev producing no hp and torque. I hope i explained it right. . .

I know that the turn counter in the M3 goes to 9000 (I think:-k ) and it goes into red at 7000, so I think the best time to change gear in the M3 is at 5000, I own a BMW 318IS and there the best time to change gear is at 4000 rpm and in my car the turn counter goes to 8000 and is in red at 6000 rpm, now I know you can't compare the 318IS with a E46 M3, but it's to get an idea.

If you wana go fast you should change gear close to redline, because when you release clutch in that gear, you will be in the power band. Its more important in a turbo than in a NA, you know that before turbo kicks on, there is poor torque.
So its more important at wich RPM will the engine be when you release clutch that if you have +10lbs after redline.

When racing, you change gears probably 100 rpm before the fuel cut-off, that's simple.

When you're driving normally, that's another story. In a car with a 6500 rpm redline, I normally shift at 3000-4000 rpm, depending on the engine. I might as well shift even at 2500 rpm sometimes, or maybe at 5000. But normally 3000-3500-4000 should be ok.

I have a uncle that owns a 1.6 astra. He changes gears way before 2000 so he goes in 5th gear at around 60km/h. He makes me SICK! LOL

EDIT: He also starts in second gear... When he let me drive his car I think he was scared a lot of me reving it up to 5000 before changing gears hahaha.

A friend of mine changes gears like that. He believes he's saving fuel this way. It's soooo irritating!

A friend of mine changes gears like that. He believes he's saving fuel this way. It's soooo irritating!

If the tests are right, it does save fuel. My dad read it in the newspaper, and he tried it once. But only once, and after that he went back to the normal shifting, because he also hated it.

Yes, it does save fuel, but only if you don't depress the gas too much, which means that you will do 0-100 km/h in like 20+ seconds. I can't stand that!!

If you floor the throttle at low rpms fuel consumption is way worse that doing it in the power band.

"A friend of mine changes gears like that. He believes he's saving fuel this way. It's soooo irritating!"
"If you floor the throttle at low rpms fuel consumption is way worse that doing it in the power band"

It's true that it saves fuel. Even alot. The thing is you have to be very gently with the throttle. At all speeds. Even at start off. And to really save fuel reach some speed 60-70 km/h and then move the stick to neutral. Do this as often as you can. I have a TDI that in normal driving in city take 7-8l /100km in averege. The smallest figure i ever reached was 4.1L/100km in city but the traffic was lighter indeed.
The second statement is very true.

It was said by me, it has to be true.

And not only is bad for milleages, is bad for the engine itself too. If you wana raise your speed quickly, downshift and floor it.

Yeah...i drove an rx-8 and in 6 at 1800-2000 rpm i had to serve the 3rd to really put the engine at work. And about changing 100rpms before fuel cut off i think that goes well only on NA high rev engines (eg M3 or s2000). if we're talking about a turbo engine like the 1.8L 20v turbo Audi S3 i don't quite think that's the best approach. I don't know the power band from the S3 but i don't think it is so near the red line. Because if you change 100rpm before fcutoff you might find yourself on the red line again after 2 or 3 second after the shift and i don't think that the turbo works at so high rpms. Not stock turbos anyway

That may be cause because the transmision is aceleration-oriented (please someone tell this in correct english :P)
I dont think that a turbo dont works at high rpms, there is where it runs !!

let me ask what are you guys tryinhg to achieve here?? you lost me!!

You should change a turbo diesle just as late so the turbo can kick in, the end, go home.

And to really save fuel reach some speed 60-70 km/h and then move the stick to neutral. Do this as often as you can.
Why???? :confused:

When racing, you change gears probably 100 rpm before the fuel cut-off, that's simple.

Depends of the car, engine size etc....

Why???? :confused:
Engaging the transmission in Neutral disengages the engine to the wheels. Doing so while you drive saves gas because the engine is at idle speed. As long as you don't use the gas in Neutral, you're saving fuel. If your engine is overheated, try doing it. Just don't go too slow.

Nope, you don't save gas, because when you roll (with a gear engaged) without pressing the gas, no fuel in injected at all!

Nope, you don't save gas, because when you roll (with a gear engaged) without pressing the gas, no fuel in injected at all!
Yeah. And going in neutral isn't a good idea. For example you don't have total control of the car and if you need to accelerate you will loose time and a little concentration thinking what is the correct gear to go with. Not a good idea.

Also, going in neutral overheats the gearbox, ALOT.

thats all an oil thing, keep it moving and it doesnt happen. Happens a bit in my dads auto.

"Nope, you don't save gas, because when you roll (with a gear engaged) without pressing the gas, no fuel in injected at all!"

Really? I don't quite think so. Just because the momental fuel consumption on the computer shows little figures i don't think the engine doesn't need fuel to run. what does it keep reved? cheese?

and why "Also, going in neutral overheats the gearbox, ALOT." ???
i thought the gearbox heats up from the movment of the pinions (don't know if it's the right term)

I used to wonder why the car bruns alot of fuel at idle revs (especially when the engine is cold but that's another story) being stationary and why does it burn so little fuel when being in movement at similar rev (let's say with no gear engaged)?
I think it might have smth to do with the force that is needed to push the piston...i mean when stationary the engine needs alot more fuel to create the force needed to push the piston...when in movement the amont of fuel needed is way less because the wheels are in motion. Don't know if i made myself clear but anyway i tryed. Don't know also if my theory is right....

You're bang on both counts. When the engine idles fuel is still injected you will see because the tacho still shows the engine reving which means fuel must be being inject. The gearbox doesn't overheat unless it sits ideling in heavy traffic

"Nope, you don't save gas, because when you roll (with a gear engaged) without pressing the gas, no fuel in injected at all!"

Really? I don't quite think so. Just because the momental fuel consumption on the computer shows little figures i don't think the engine doesn't need fuel to run. what does it keep reved? cheese?
My computer shows zero when I'm not pushing the gas (i.e. at a downhill) with a gear engaged, and it is true that no fuel is injected at all. (I'm talking about manual gearboxes)
The engine keeps revving because you're rolling and movement is transferred from the wheels to the engine, via the gearbox. Fuel starts getting injected again when you push the gas.

And 12 inch, I'm positive that manuals get some kind of damage when you roll with neutral at high speeds for a long time.

Jim, go to your car, put you feet out the door and start it up and sit there and it will empty out slowly but surely.

I'm not sure I understood what you said, but I said rolling, which means shifting into neutral while the car is running with a high speed. I know that neutral is not bad if you're on a standstill.

Whoa! You guys are all over the map on this one. With so many types/tunes of engines, shift points depend on the power curve. You need to stay on top of it.

When you go downhill on your power curve (hp decreasing with rpm), you should shift at the point where the next gear will put you on the curve at the rpm where you have the same hp going uphill (hp increasing with rpm).

Normal N/A mods like intake, porting, cam, and exhaust increase airflow at high rpm at a huge cost in flow and torque at low and midrange rpm. If you have to shift at a mechanical redline, your next (stock) gear ratio could put you so far down the power curve that you might average a slower acceleration than stock in that gear.