zeliggusgus

this is my first MT so my knowledge of shifting is pretty limited. my 8 is only a few months old and only has 1300 miles on it. i'm still breaking it in the long way and haven't broken 6K RPMs. but i figured the optimal range for shifting for better gas mileage is below 6K RPMs.

conceptually, i look at it like this: higher RPMs means more gas consumption. so shifting to a higher gear lowers the RPMs. but you can't shift too early because even though the RPMs are low, the engine is being worked too hard. i'm always afraid of working the engine too hard, especially in the break-in period. on the other hand, red-lining can't be fuel efficient either. do i have it right?

can someone explain it to me conceptually, and can someone actually give me actual numbers on when to shift to optimize gas mileage? thanks.

NgoRX8

iTrader: (1)

Shift before the 2nd fuel injection opens. which is at 3750 rpms.

yiksing

Not confirmed yet.

Cruise control is effective though.

vectorwolf

Yeah, you have it right. You have to balance the low rpms with the proper gear for the conditions. If you're driving on a flat surface, and not accelerating, go ahead and drop it down. If you're gaining speed, or on any sort of incline, you may want to shift down briefly to avoid wasting fuel in too high a gear.

I kind of look at it like being on a 10-speed bicycle. If you're in too high a gear at a low speed, or on an incline, you expend a lot of energy without getting a lot of work done (ever tried climbing a hill in top gear? lol), but if you're coasting along at a brisk pace, it's almost effortless to keep yourself going. On the other hand, if you're on flat ground, you waste just as much energy pedaling like crazy in a low gear, yet you can climb hills with very little effort at the proper speed. But yeah, you've got the idea.

therm8

Transient rpm has little effect on your mpg. For example: winding out 1-3 then shifting to 6th to cruise will net you almost identical mileage as shifting below 3750 on your way to 6th. 95% of driving will be under cruising conditions (my number, made it up, but you get the idea). Cruising rpm will have the most effect on mpg. Don't cruise in 4th when 5th or 6th will do. The 8 will never get great mileage, but you can get low to mid 20's on the highway, assuming all mechanicals and electronics are working properly and your cruising rpm is relatively low (best I've had was at 70mph (4AT), 26mpg over 340 miles, but it's hard to go that slow for that long ). Reving to 6 or 7k rpm or even redline won't kill your mileage as long as you don't cruise around up there.

I have long stretches of 20-35mph roads on the way to work. So one tank I drove it in 2nd and 3rd, while the next tank I drove it in 4th. Both tanks I drove normal (for me) every where else. Redline multiple times a trip. I got 17mpg on the 2-3 tank, and 19 on the 4 tank. I even tried a tank where I never exceeded 5k rpm with no change in mpg, and alot less fun.

The moral of this post is, if you're trying to maximize mileage, get to your cruising gear as fast as possible, and have fun on the way.

NgoRX8

iTrader: (1)

lol, i still get pretty bad mileage cuz of trying to get up to 6th gear fast.

Ophitoxaemia

i got the best mileage, especially in city driving, by shifting at 2500rpm. crawling around the streets of san francisco and stop sign to stop sign driving in the east bay still netted 18 mpg.

at the track i got 6 mpg =)

james

zeliggusgus

what about skipping gears? sometimes when i'm on a street with a 35 limit, and i feel like taking off, i can get to 35 in 2nd even without going over 6K RPMs, and then i throw it in to 4th to start cruising. is that bad for the car? good/bad for MPGs? that's one way to "get to your cruising gear as fast as possible, and have fun on the way." i've heard that accelorating can affect gas mileage too. in the summer days here in ok, they tell you to not accelorate so fast because it saves gas. does that only apply to automatics? old wives tale?

another thing i do is when i know i have to stop soon, i throw it into neutral until i have to stop. is that bad?

and while we're on the subject of cruising...i know that when i'm cruising on the highway, i should be in the highest gear possible. but when i'm cruising on city streets, i have a hard time knowing what gear i should be in. what's a good RPM to cruise at when i'm not on the highway?

icyur2

Try this:

1 - Change your oil to 5w20 (best oil for maximum mpg)
2 - Warm car up no longer than 2 min. @1st drive (longer warm-up will EAT your mpg)
3 - Any other warm up after 1st, keep it less to 1 min.
4 - Do NOT take RPM over 3k until your temp gauge reaches middle
5 - Keep rev low between 3700-3500rpm
6 - Try to cruise between 5/6 gear (depending on street speed)

Other than this, I've been getting between 17-20mpg with most city driving!! I would redline it once/wk or have some spontaneous fun with the higher revs...

icyur2

To answer your questions:

1 - Nothing wrong with skipping gears, as long as you "tap" your gas to keep the rpm up as you downshift (going from 6th to 4th - depending on speed will yank you hard if you don't keep your rpm ratio to what gear you are switching). Don't think it is "bad" but if you do it often, it might eat your mpg since you are going to be over 3750rpm (more fuel dumped in).

2 - I throw it in neutral if I see a redlight ahead..keep in mind of the traffic though..because if the street is set up in a way where an idiot can suddenly get in your way, being in neutral, you won't be able to react fast enough to evade..so..pros & con to this..it will save gas though..

3 - In the city, I cruise @5th gear if I go no faster than 40mph on a flat surface. I'll switch to 6th if I go over 40mph. I find I get more of a response if I need to suddenly speed up @5th gear than at 6th while in the city...if you fall between 20-30mph, I would switch to 4th gear. Keep in mind that this only applies to a flat surface..this will change when you are going up a steep hill...

Anybody have comments on this? I'm no expert, but I'm getting good mpg with this...

Georgia8er

This will not save you fuel. I used to think so too until I read something about it here, then confirmed it with my Canscan. If you go to nuetral the engine idles and uses fuel BUT if you are coming to a redlight and leave it in gear, little if any fuel is dumped into the combustion chamber. If you watch the air fuel ratio when you let off the accelerator the AFR will go high, i.e. way more air than fuel. A forum member reported that his coolant temperature actually went low on a long drive down a mountain.

Otherwise sounds pretty good.

tuj

The above posters are correct about putting the engine into neutral. Keeping the engine in gear will allow the ECU to go into fuel cut strategy and actually turn off the injectors if it can. Putting the car in neutral will use more gas than keeping it in gear.

As far as skipping gears goes, in theory you are always supposed to move the shifter in sequence, even if you don't let out the clutch. So if you do a 2->4 shift, the shifter should actually move into the 3rd gear gate before it goes to 4th. The reason for this is that the syncros are designed to move better sequentially. In practical terms, it doesn't really matter unless you have having a hard time with the shift. A better example might be a 4->2 downshift when you don't have time to use 3rd.

Chrisbert

The biggest thing I've found is 5th and 6th are my friend for MPG improvements. 5th actually works pretty well around town above 40mph. My gas warning light came on this morning right at 260 miles and it takes ~13 gallons to refill it from there. 20MPG ain't bad in my book.

icyur2

Whoah..didn't know that about the neutral gear. Thanks guys!! I might bump it up an additional 1 mpg