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Old 05-08-2007, 03:43 PM   #21
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It's kind of a PITA, but googling has helped me find two out of three engines I was looking for. To give you an idea of how much engines haven't changed, a ~30 year old passenger diesel engine will be most efficient at ~2400rpm/80% throttle, a twenty year old gasoline engine is ~2200rpm/80% throttle, the Prius' engine is at ~2700rpm/80% throttle iirc. It's pretty much in between 2000-3000rpm, and near full throttle. However, gearing the car like this would result in crappy gradability/acceleration in top gear, so imo, about half throttle at whatever speed you want to cruise at is generally a good compromise. For my Camry, dropping engine speed by 25% would increase mileage by ~10mpg at 55mph and I'm guessing you'll see something similar for your element. I like to use a ratio of engine displacement to speed at ~55mph, so my 3L engine should be turning at 1500rpm there, a 1.5L engine can turn at 3000rpm, and a 6L engine should be idling down the road for pretty good mileage. For your engine, I'd guess ~1900rpm (edited for error) is good, but... I wouldn't actually recommend it until I had some more info on SFC.

Edit- Your gearing should be .825/5th and 4.765/r+p, so with 215/70R16s you should be o.k. at ~2600. Of course, the automatic is at ~2175rpm at the same speed, so I'm guessing you can safely go down to there, or even 2k rpm, since the automatic gets the same highway mileage as the manual because of it's lower ratio, a manual w/ that ratio should break 30mpg np. A transmission out of a 5spd accord should put you at 34mpg EPA highway, if it'll fit.
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Originally Posted by FormulaTwo
I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 05-08-2007, 06:34 PM   #22
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When people go from big rims to really really big rims, especially on an auto, it can increase the amount of time spent downshifting and keep the tc unlocked which can hurt mileage.
What's tc?
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Old 05-08-2007, 06:47 PM   #23
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Torque converter clutch. Normally automatics are connected to the engine all the time through a fluid coupling called the torque converter, which is why when stopped, they can idle in gear w/o stopping. The engine just spins the fluid around w/o stopping. If it were a manual transmission, the car being stopped would make the engine stop because there's a direct manual connection. In an automatic, the tc is a mechanical connection that will engage/lock up when certain speed/engine temp/etc... conditions are met to improve efficiency. It's better to drive w/ it locked up as often as possible because you get an extra ~10% (or more) boost in efficiency compared to normal operation w/ the torque converter.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 05-08-2007, 07:29 PM   #24
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It's kind of a PITA, but googling has helped me find two out of three engines I was looking for.<snip>.
Thanks bbq. I'll keep looking. There's gotta be one out there.

Here in the flatlands, I could bump up the final drive AND add a sixth gear, and I think it would work wonders. But I don't think there's a payout, since I am not able to do it myself... But I think the E would gladly do 60 mph at 2000 rpm. It's a pretty grunty engine. I will keep scanning the horizon and looking for opportunities to make it happen...
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Old 05-08-2007, 08:27 PM   #25
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Tire size calculator:
http://www.wickedbodies.net/Tire-Size-Calculator.htm

Tire's overall outer diameter is what will affect engine rpms at any give ACTUAL road speed and thus your FE.

You can change the rim size and get the same overall diameter or not, that depends on the actual tire size you use.

IF you change the overall diameter (which is the only way to change engine rpms using the tires/wheels) then your speedometer will be a liar and you'll need to compensate with different speedo components etc. That may or may not be possible to do. If not, you risk speeding tickets. Not worth it in my book, ymmv as usual.

Rims also have a flange width dimension which affects the range of tire sizes it will accept. See tire specs at tirerack.com for details on flange width.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

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Old 05-08-2007, 08:43 PM   #26
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hm i did that tire size calc to the tires i have and the tires i want.

turns out that my spedo would be off by 3.5 miles(it reads high anyways and this would line it up perfectly)

there would be 45 revolutions of the wheel less per mile with the new size

the tire height diameter would be 1.26 larger

which isnt all that much bigger but i belive it would help. (still only $32 a tire)
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Old 05-09-2007, 03:45 AM   #27
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Quote:
Originally Posted by VetteOwner View Post
hm i did that tire size calc to the tires i have and the tires i want.
turns out that my spedo would be off by 3.5 miles(it reads high anyways and this would line it up perfectly)
there would be 45 revolutions of the wheel less per mile with the new size
the tire height diameter would be 1.26 larger
which isnt all that much bigger but i belive it would help. (still only $32 a tire)
VetteOwner,
Good work.
Did you check the door sticker to check if you're running OEM size tires now? Could be that speedo is off due to a different tire size on car now.
Or maybe rear end or tranny was changed at some point??
Anyway if car is set up as originally, I'd check proposed tire size vs. OEM size and see how that comes up on the calculator.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 05-09-2007, 11:50 AM   #28
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no i broke the origional spedo that used read correctly but i had to ge one out of a different yeared vette. it has the stock tire sized on it now. (maybe the origional tires who knows, cuz thier pretty bald with low miles)

it is and should be set up as factory. i havent seen any evidence of repairs anywhere on it.

so im guessing that the tire diameter being only different by 1.26" would make a bit of a difference (this would accualy correct my spedo being off) since i gotta get new tires anyways i might as well go a bit bigger since i drive 60-75&#37; highway (45-55mph)
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Old 05-09-2007, 07:50 PM   #29
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I did it with my Metro, went from stock to bigger wheel/tire combo and it KILLED my mileage. Check my garage and you can see pics of the wheels. Went back to stock 13's w/racing discs. IMO, the optimum choice. Only thing better would be to get a set of RE92's to roll on. In time, I'll do that.
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Old 05-09-2007, 09:41 PM   #30
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[QUOTE=Wazabi Owner;50807]I did it with my Metro, went from stock to bigger wheel/tire combo and it KILLED my mileage.QUOTE]

What size were the new wheels(rims)?

What size and type of tires did your 13" setup have?

What size and type of tires did your larger setup have?

Did you happen to wiegh the complete unit and compare it to the 13" setup?
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