Weight, where is the loss?

[Dr. Jerryrigger]

Originally Posted by brucey

With the auto in the subie, I've found that accelerating quickly (at least to 30 mph or so) is no more harmful than accelerating slowly. It gets you into the wonderful top gear much quicker that at least according to the scan gauge, it makes no real difference.

interesting, I'll have to try that. I don't have a scan gauge, so I'll take your word for it. You do get better mileage than me.

[brucey]

I'd also only recommend it if you know it's clear up ahead, of course.

For city driving (where I can only do 24 or so during daytime traffic.. at night I can get 30 assuming I can catch the lights right) my usual method is:

From a stop, make sure it's clear, accelerate somewhat briskly (The trans will shift about 3000~3500 rpm) to about 32 mph and let the transmission shift into 4th and lock the torque converter. Try to hold that as gently as possible if it's a long stretch... OR Put it in neutral if I know I can coast to the next stop, if there is traffic I'll try not to get too low under the limit for courtesy sake.

If you give it too much gas (nearly floored) it will change the fuel trim and go into a more rich burn for about a minute before going back to its normal mixture.

We've both got the 4EAT, so I assume yours is very similar. The gearing (Mine is 4.444) is probably the only difference. So just try and find out how low you can get the torque converter to lock up in 4th. (The rpms will stop varying with throttle and the car will buck a bit more while accelerating, like in a manual car)

RobertSmalls: Yeah, I know what you mean. At my normal cruising speed (55~60) I'm around 2500 rpm, so between that and the 4.444 final drive I think I have plenty of power to make up a few extra pounds.

[texanidiot25]

Originally Posted by RobertSmalls

Lucky you; that looks like the better torque curve.

It's always frustrating to see how high most dyno plots start. I used to upshift my Subaru at 2000RPM, so this plot captures none of what I care about.

Well, when you look at the average intent when dynoing a car, you can see why such low RPM is never looked at. But one reason simply is setup, trying to not "bog" the motor from such a low RPM to read a very small amount of power.

However, there are other ways to measure HP off a dyno.

[TheEnemy]

Originally Posted by Old Tele man

...here's an equation for vehicles in the 3,000-lb. range, attributed to Detroit, that's used to estimate weight changes upon fuel economy:

(MPG2 / MPG1) = (WT1 / WT2)^(0.72)

...where: suffix-"1" is old and suffix-"2" is new.

MPG2 = MPG1*(WT1/WT2)^(0.72)

MPG2 = 26*(3000/4000)^(0.72) = 21

Not even close to what I observed. If I had dropped below 24mpg I would have to get gas at both ends of the trip. Only once did I have to get gas midway in the trip, and that was when I had beds hanging out the sides and over the top.

[RobertSmalls]

Originally Posted by Old Tele man

(MPG2 / MPG1) = (WT1 / WT2)^(0.72)

If this applies to weight of the car at the design level, it includes an upsized engine as well. So 3000lb becomes 4000lb, 26mpg becomes 21mpg, your 2.2L becomes a 3.0L, and the car is no peppier.

[TheEnemy]

Originally Posted by RobertSmalls

If this applies to weight of the car at the design level, it includes an upsized engine as well. So 3000lb becomes 4000lb, 26mpg becomes 21mpg, your 2.2L becomes a 3.0L, and the car is no peppier.

Ok that makes better sense, in fact it fits pretty well with if I had gotten the 4X4 version with the V6.

It wouldn't relate well to whats being discussed here though because we are compairing loaded/unloaded weight.

[Fr3AkAzOiD]

This topic came up in another forum (sorry, no link) and one of the things that was brought up is how much torque the vehicle produces.

Vehicles that produce more torque seem to be effected less by a weight increase then one with less torque.

[Dr. Jerryrigger]

I just got my best tank ever, and I had the car loaded with about 500lbs of stuff on the return trip (tank was for both ways). Granted, everything when really well as far as driving conditions. But I also had the CEL on the whole trip (O2 and knock).
I have found it almost pointless to P&G at 60 with my car. It has to be one heck of a hill, and then to get it back into gear, and get the torque converter to lock seems like it balances out most of the benefit. But with a heavy load it drives like a aerodynamic Legacy!

[Dr. Jerryrigger]

Originally Posted by brucey

From a stop, make sure it's clear, accelerate somewhat briskly (The trans will shift about 3000~3500 rpm) to about 32 mph and let the transmission shift into 4th and lock the torque converter.

I have found it nearly impossible to get it to lock under 41, but when it does I can holed it down to 30.

[Olympiadis]

Originally Posted by Dr. Jerryrigger

I have found it nearly impossible to get it to lock under 41, but when it does I can holed it down to 30.

That's the hysteresis for the TCC logic. There is often a minimum vehicle speed, RPM, coolant temp, max engine load, max TPS %, and a couple of qualifications timers for the lock function.

To unlock, basically the reverse is true with some additional factors such as delta-TPS, brake-pedal switch, park-neutral switch, delta-MAP, and of course the MPH hysteresis which gives the delay so you don't have constant locking and unlocking.

You can get better mileage by adjusting most of these calibrations.