IMHO.. any change in mpg post re-gear is more due to change in driving style than change in hardware
Worse MPG after re-gear. Any soloutions?
- Thread starter Lunch Patterson
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I have to agree completely. I had a 99' auto Jeep with 32s and 3,07s. Regeared to 4.56. MPGs got so much worse. I started driving it like a sports car. I hated it and gas was only $2.13 a gallon back in the old "pre Biden" days.
I am running this plugs. Installed them last year.
Autolite Iridium XP Automotive Replacement Spark Plug, XP985
Autolite XP985 Iridium XP Spark... https://www.amazon.com/dp/B000ET5TLM/?tag=wranglerorg-20
They need to be gapped I think to 0.35 or something (there is a sticker under the hood).
W/o proper gapping, they will not work fine.
Did you gap yours?
Vtx531
TJ Addict
Hey, the Y scales on this chart are totally irrelevent. If the scales were the same numbers, torque and hp always cross at 5250 on every engine. Even that is meaningless though as far as "crossing" because they are different units of measurement.
Actually 5252. But correct, it is the result of how horse power is calculated.
I agree that I should have stated it differently.
The value in 2750RPM is in that the maximum torque starts there. Decreasing RPM will reduce the torque and hp, increasing RPM will increase hp only.
This is why 2750RPM should be the best RPM for highway cruising if the idea is to optimize for power, not MPG.
The only relevant mechanical change was the gear swap. It's the catalyst, not the culprit.
The moment the foot hits the loud pedal the number of relevant variables goes through the roof.
I just did a gear swap.. my driving style is totally different. Up-shift and down-shift points are different. Cruising rpm's are different both on highway and around town. Rate of acceleration is different (and more fun).
Fellers, turn on your geek filter if you're triggered by engineer-speak!
Yes, the engineering definition of power is the time rate of performing work. In equation form, it's:
power = work / time
Work is synonymous with both energy and torque (all three can be measured in ft-lb). When engine dynamometers are used to generate power and torque curves, they measure brake force and crank speed. The brake force is multiplied by the distance from the load cell to the brake shaft centerline to get a brake torque and then, if the engine is connected to the dyno through any gear reduction (usually only with motorcycle engines where the transmission is integral with the engine cases), that number is multiplied by the gear ratio to arrive at torque in ft-lb at the crank. So that's the "work" term in the equation. The time term comes from measuring crankshaft speed (or measuring brake speed and using the same gear reduction to get crankshaft speed), but it's in the denominator (rev/min). So, the division switches to multiplication, and the equation becomes:
power = shaft torque x shaft speed
However, with power in units of hp, torque in units of ft-lb, and engine speed in units of revolutions per minute, the units require conversion factors. The three basic units for all of those are force, distance, and time, but it's a bit complicated by shaft speed also including the unit of revolutions. Revolutions can be removed from the equation by converting it to radians because radians, a measure of angle like degrees, are actually a unitless measurement, unlike degrees or revolutions (yes, that concept is confusing). One revolution, which is 360°, is 2*pi radians.
Any way, in order for all the units to work out, you have to convert each unit in the equation to the basic units of feet, pounds, and seconds (along with turning revolutions into a unitless number by multiplying by 2*pi):
- 1 hp equals 550 ft-lb/sec
- 1 revolution per minute equals 2*pi/60 radians/sec (but remember that radians isn't really a unit, so it drops out, and the units become 1/sec)
550 x hp = ft-lb x RPM x 2*pi/60
If you then do the math, it becomes:
5,252 x hp = ft-lb x RPM
And if you look at that equation, no matter what value you use, if hp equals ft-lb, the RPM has to be 5,252. So, that's the long way for an engineer to say:
"what Vtx531 and NashvilleTJ said"
The other cool thing about knowing this equation is that, if you have a torque curve only, you can generate a power curve, and vice versa!
That’s a lot of words just to say we were right - thanks!
Seriously, I enjoyed the detail. Is it fair to say that torque is measured, but horse power is calculated?
That’s a lot of words just to say we were right - thanks!
Seriously, I enjoyed the detail. Is it fair to say that torque is measured, but horse power is calculated?
He lost my attention at "Fellers".
I’m curious to see how it turns out for you. I still stomp the pedal to shift down to third even with FRP’s stock tune.
For the most part, yes. Horsepower is always calculated from torque and engine speed (there's no other practical way to do it). However, in strict terms, all three (power, torque, and engine speed) are calculated values. Torque is determined by measuring a strain in a load cell, calculating a force from that, and multiplying by a measured distance. Speed is usually determined by timing a rotational event (how long to complete a revolution or portion of a revolution) and calculating a speed. The accuracy of measuring speed is usually pretty good. The accuracy of measuring torque is substantially less so.
OP
I replaced all the o2 sensors today. Yes, I checked 5 times that I put the right ones in the right places. I now have no data from either downstream / sensor 2s. It was just one not working before, now both are not working. I saw disconnecting the battery for a while might get them to go. It is odd that I didn't get a check engine light, until both of them were out, not with just one sending no data.
Yup. If you're accelerating more quickly, you're using more fuel.
I find generally the change is temporary, at least for me. Once the novelty wears off I'm back to driving like a grandpa.
Vtx531
TJ Addict
Make sure you're looking at the appropriate OBD2 channels. I'm not sure you are - O2 sensor channels usually read in volts, not %. Trims in % are usually calculated channels that represent what the PCM is using to determine injector pulse widths (how long the injectors are open for each combustion event, which is how the air/fuel ratio is adjusted). Also, be aware that default channels are often listed by the diagnostic scan tool, even when your PCM doesn't use them.