Shift timing/patterns

[extragoode]

What effect exactly does goofy shift patterns have on FE? Things like starting in 2nd and 1-3-5 shifting. My problem is I have a '00 Frontier Crew Cab 4x4 170hp 3.3L V6. It idles high while it's cold, like 1700rpm, so I've been starting in 2nd because even without any gas at all it's ready to hit 2nd as soon as the clutch is up. As soon as it warms up it settles down to idle around 600 and I go back to starting in 1st. Sometimes I do the 1-3-5 pattern because all these gears are so close together. I think this truck is geared for towing, all other driving be damned. I feel like skipping 2nd and 4th allows me to shift smother while accerating and minimize the time the clutch is down. The literature for the truck says this thing produces 90% of it's torque at 1500rpm, so it's got no trouble moving just itself and me at 900rpm and I usually shift up around 1500. When I skip a gear I'll shift around 2k. Does any or this make any sense to anyone? It's just something I've been thinking about.

[basjoos]

Use whatever shifting pattern fits your transmission's gear ratios, your engines' torque, and keeps the RPM's below 2000 for normal acceleration. On my car, its usually 1-2-3-5, except when accellerating on a hill, where it will be 1-2-3-4-5. If I am merging into heavy fast-moving traffic where I need full accelerationg and have to run it up close to redline, it will be 1-2-5.

[H4MM3R]

I rule I like to remember is The faster you put your trans in OD the better the FE. Short shifting, starting out in 2nd and skip shifting all work at getting to OD the soonest.

[LostCause]

I'd find your engine's BSFC and accelerate to cruising speed as quickly as possible staying in that rpm range. It is important to stay closed loop, though.

Accelerating quickly cuts down on pumping losses by opening the throttle plate. High rpm's create a lot of friction, so it is important to keep engine speed low. Essentially, you are trying to drive with a lot of load.

SVOboy's website has a section on the topic that covers it well. Accelerate quickly, shift early, cruise slow. Use whatever gear pattern allows you to do so.

- LostCause

[extragoode]

That's kind of what I was thinking and was hoping was correct. Have you tested these at all? I don't have any instrumentation, yet. I was wondering if anyone had any numbers. Is it exactly the same/marginally better/worse?

[LostCause]

SVOboy's website has numbers. 3.3% increase.

- LostCause

[extragoode]

Originally Posted by LostCause

SVOboy's website has numbers. 3.3% increase.

- LostCause

Awesome! That's what I was wondering. Thanks!

[tasdrouille]

Originally Posted by LostCause

I'd find your engine's BSFC and accelerate to cruising speed as quickly as possible staying in that rpm range. It is important to stay closed loop, though.

Accelerating quickly cuts down on pumping losses by opening the throttle plate. High rpm's create a lot of friction, so it is important to keep engine speed low. Essentially, you are trying to drive with a lot of load.

SVOboy's website has a section on the topic that covers it well. Accelerate quickly, shift early, cruise slow. Use whatever gear pattern allows you to do so.

- LostCause

I mostly agree with your post but would like to make the following comment in regards to friction.

I was reading some SAE papers today (again!!), and as I was educating myself on friction modifiers I found out the difference between cruising at 1250 rpm vs 2500 rpm is roughly a 10% increase in engine friction. Chances are you are much closer to the BSFC island at 2500 rpm with the added friction load. Is that movement towards the BSFC island worth it? It depends of what the BFSC map for your engine look like.

Those maps should come with the owner manual (sorry I'm just really mad I can't find one for my engine)

[Straight-3]

I go through all the gears, with wide open throttle and low mph shift points during acceleration. I use piston speed as my guideline which it think is about 1000 to 1200 fpm. for max economy. Basically for my car (91metro) with a 77mm stroke that translates to about 2000 to 2400 rpm as my target range. Since I dont have a tachometer I had to calcualte the shift points in mph so thats like 11, 20, 30, and 41mph from shifting into 2nd through 5th. I think if you skip gears you might end up outside of the most efficient rpm range for your engine.

[Daox]

If you can get a dyno graph for your car (search online, use gtech or similar device, or dyno) you should be able to tell when you achieve maximum torque. At WOT plus at peak torque is going to be where your optimal BSFC is. With the dynometer graph of torque you can see what rpms you should be keeping the engine in for peak efficiency (still in WOT). I did this with the Paseo recently and it seemed to return roughly 4% increase in fuel economy (48 to 50 mpg). In my case I actually had to increase the rpm range in which I had been driving.