sgarnett

iTrader: (1)

Not really. Maintaining an arbitrary speed on an arbitrary road requires the same amount of power at any given time regardless of which gear you are in. Yes, it takes more power to climb a hill, but that's true in both gears.

However, it still takes more power just to rev the engine higher. In other words, more power is wasted just to keep the engine spinning.

Remember, even with the throttle wide open, you just aren't pulling much air in at 1200 rpm or so.

Of course, that reasoning breaks down if you go into power enrichment, but at that point mileage is no longer the goal. However, if the engine is lugged down to the point that you're holding it in power enrichment just to maintain speed, then clearly you are in the wrong gear.

Even running rich, though, you simply can't burn that much fuel at 1200 rpm.

Short of that, though, I found (with real time air and fuel flow measurements) that less fuel is consumed at lower RPM, period, and the most economical operating point is NOT the most comfortable operating point.

My daily commute involves a long stretch of fairly hilly 55mph road. With my stock transmission and stock rear gears, I usually drove it in 5th simply because it was more enjoyable, but it still burned less gas in 6th. I generally only used 6th at 65 on the interstate or at 55 on very flat roads, but that was because economy wasn't the only goal.

Now that I've swapped in a GTO transmission with lower 5th and 6th gearing (still stock rear gears) I use most of the time at speeds above 50~55.

I'm not suggesting that lugging the engine down to the point it's struggling is a good idea, and like I said I prefer to cruise in the 1400~1700 rpm range, but 1200 or even less still burns less gas.

sgarnett

iTrader: (1)

That was actually what I was hoping to prove when I was measuring the fuel/air flow in different gears. I don't enjoy cruising along barely above idle any more than the next guy, and I really wanted to find that 1700~2000 or so was more efficient, especially on the hilly roads. It certainly FEELs better there, but it still burns more gas.

YoungGunLs1

thanks for all of this great information you guys! I guess i will keep driving in 6th as I have been. I just liked fifth because my exhaust was much louder

I really appreciate all the comments.

sgarnett

iTrader: (1)

Like I said though, if the engine is struggling (which it might on a hill at 55 with stock gears) you may still want to downshift. Sometimes it's worth burning a little more gas

YoungGunLs1

ya i always downshift when comming up on a hill, I ussually have my cruise set and then take the cruise off, shift to 5th get up the hill, shift back to 6th and resume the cruise control. When I have to give the car more than probably a 1/4 throttle I can tell it needs to be downshifted, which is why I always take the cruise off to see how much its gonna take to get up the incline, and then decide if it needs to be in a lower gear.

2kSnakeEater

iTrader: (5)

I noticed 6th gear is good from 900 rpms anything lower than that bogs the engine, I go up and down us19 maybe hitting 40 in 6

dylan24

Well I usually use 6th at 50 and above and it seems to work fine. My car even pulls up hills in 6th fine. So I'd say go for 6th, because I notice a negative difference in gas mileage when I use 5th. But don't listen to me, if you really want to know, just open up that wonderful book in the glove box, the owners manual. I think GM would know better than any of us what their cars need to be at. But also I'm running an LT1, I don't know if that makes any difference, the LT1s seem to rev a bit quicker, but the LS1 has more *****, so youd figure it could definitly pull up hills in 6th.

Anyway, I don't think gas mileage should be a HUGE worry. I mean, if you are wanting to get good gas mileage, then you bought the wrong car. But I understand where you are coming from, I used to wonder about this myself, but more or less for wear on the car not so much mileage.

Wicked94Z

iTrader: (26)

I'm an LT1, in our manual it says you should shift into 6th at 45! LOL yea right, but before cam I was putting it into 6th at 50 only on level or downhill roads. On the freeway usually not till 60 because traffic can slow down, and I hate just downshifting/upshifting all the time. After my cam (230/244) the car pretty much blows on the freeway with 3.42s. I try to keep the revs up above 2k if i'm going up a hill or trying to accelerate because the engine just falls on its face below that. My parents were excited about the new cam hindering my highway capabilities because I usually cruise at 80 going to school, but now it seems to like around 72 no more no less. I need 4.10s.

NHRAMAN

iTrader: (1)

flat road over 60 = 6 th gear.....

TARZAN

iTrader: (12)

3.42's make that 6th gear no problem IMHO

-Will

Silver 00 SS

iTrader: (7)

Anything after 53ish i go into 6th gear....

gun5l1ng3r

Maybe my car is getting old, but it seems like my car is bogging when I put in sixth below about 65 or so. When I am in 6th gear at 55, I can hardly accelerate without downshifting.

HotWhipT/A

iTrader: (31)

67RSCamaroVette

iTrader: (63)

LT1's have a lot more torque down below 2000 rpm, so naturally, they'd do better with a taller gear.
olly

espfuel815

okay...so instead of speeds, what about rpms.

For me, I have stock 3.42 gears and I usually dont shift to 6th until about 70mph.
at that speed in 6th, it sits at 1500rpm

according to the RPMs, does it put stress on the motor or not to sit lower than that?

sgarnett

iTrader: (1)

Well, yeah. Nobody ever said driving economically didn't suck If you are cruising in the most econmical gear, it will bog if you attempt to accelerate. You have to be gentle on the throttle, and if you need to acclerate faster than a Yugo, downshift.

If it's struggling just to smoothly maintain speed, you're in the wrong gear. However, if the engine is running smooth but throttle response is, well, there just isn't any at all, then you are probably in the most economical cruising gear Whether that's the best gear or not is up to you

If there's much traffic, even if it's averaging 55~60, you may not be able to maintain your speed smoothly enough for 6th to work.

Or, to put it another way, economy and throttle response simply don't go together. The great thing about these cars is that you are free to choose which you want at any time.

steveb1

I very rarely use sixth. I have to be pushing 80 + mph before I'll even consider it.

DragonsPhyre

OK lot of folks go to 6th gear, that's wierd to me. 5th gear and Im cruising at low 2500-3000 RPMs at 70MPH... hit the gas a little and I'm 85 fast for an overdrive gear.. I have had the car maybe a year and only hit 6th 3 or 4 times just to do it. I can cruise at 70-75 in 4th gear and be less then 4000 RPMs a little high for cruising but not too high.

1994Z28Lt1

iTrader: (1)

holy ***** are you serious?
wow you must burn an absolute ridiculous amount of gas and put so much extra unnecessary wear and tear on your motor cruising down the highway at 4000 rpms

anything 55 mph and higher im in 6th which at 60 is right at 1500 rpm and my motor doesn't have any problem holding speed and even accelerating going up some of the steepest hills we have around here if i want more power it doesn't take more than a second to drop down a cog or two

five0killr

iTrader: (2)

i have 373's and a 28" tire, and a 231/237 and my car gets kick-*** gas milage around town in 6th at about 1200rpm in cruise...below that the car chugs, ive been doing it since the car was new, and it makes for good gas milage, and it lowers the noise level on my lanes duals. if i can cruise 50-52mph with 450rwhp in 6th gear, than most of you can as well...even if it takes 5 mins to pass someone