Datsun Dreaming
Doesnt see what you did
Joined: Sep 2007
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lower gear generally means better gas mileage, but slower acceleration. The j30 is like what 3.89? Not bad for someone making more power than a stock KA that wants some extra penny savings.
But then again, I have been told that Chris (epstein) made like 30mpg with a 4.36. =\
But then again, I have been told that Chris (epstein) made like 30mpg with a 4.36. =\
I made 30 with my 3.91 (J30) and no tuning ...
Please hold...
Joined: Jul 2004
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IIRC you can get good gas milage with a 4.36 because the engine dosnt have to work as hard to move the car since the gearing is taller. It does put you at higher rev's but its negated by the less work the engine has to perform. I'm sure if you went to a 4.6 your gas milage wouldnt be as great though.
Its the same as if you went to a 3.54 on a low powered car. Your rev's would be super low but it makes the motor work alot harder to rotate the drivetrain.
Its the same as if you went to a 3.54 on a low powered car. Your rev's would be super low but it makes the motor work alot harder to rotate the drivetrain.
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Team White Car 2010
Team White Car 2010
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Drove it. Saw a few drops of fluid under it after it being parked at work a few hours. I think its leaking power steering fluid. Saw a CLEAN ass R33 at advance in spring hill. Shit was nice as hell.
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Formerly Earlkel OG join date 8-14-2003
Formerly Earlkel OG join date 8-14-2003
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IIRC you can get good gas milage with a 4.36 because the engine dosnt have to work as hard to move the car since the gearing is taller. It does put you at higher rev's but its negated by the less work the engine has to perform. I'm sure if you went to a 4.6 your gas milage wouldnt be as great though.
Its the same as if you went to a 3.54 on a low powered car. Your rev's would be super low but it makes the motor work alot harder to rotate the drivetrain.
Its the same as if you went to a 3.54 on a low powered car. Your rev's would be super low but it makes the motor work alot harder to rotate the drivetrain.
No.
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Gonna elaborate on this a bit.
Above is a BSFC curve for a DOHC 1.9L Saturn engine. Close enough to our KAs and out of boost SRs.
You want to minimize BSFC, as it is a measure of fuel consumed per unit of power. In this case, maximum efficiency is 2500RPM and 124N-m of torque. At this engine speed and power output, 250 grams per kw of fuel are consumed per hour.
For reference:
250 grams ~= 1/10 of a gallon
124n-m ~= 90lb-ft
1kw ~= 1.3hp
and, 90lb-ft at 2500RPM is about 45hp. Which is about where you'd require in cruise at 70mph. Funny how that works. Good job, auto engineers.
Anyway, moving on. Downshifting is like moving along a line parallel to the two i drew above. Those lines may not be exact, they're pretty arbitrary, and their actual slope is dependent on the transmission ratios.
Anyway. You'll see that downshifting ALWAYS puts you in a worse BSFC category, given that you're over like 2500rshared_pm.
FYI, part of why this is:
Gasoline engines thermodynamically are not very efficient at partial throttle. The engine experiences signifigant pumping losses from a partially closed throttle. Diesel engines don't have this problem, and so their torque peak is typically right at best BSFC. Which is why the euro guys have gotten such good city MPG out of diesels.
95% of TR probably doesn't care about anything I just said. Here's a sweet S-chassis dropped on its nuts:
Above is a BSFC curve for a DOHC 1.9L Saturn engine. Close enough to our KAs and out of boost SRs.
You want to minimize BSFC, as it is a measure of fuel consumed per unit of power. In this case, maximum efficiency is 2500RPM and 124N-m of torque. At this engine speed and power output, 250 grams per kw of fuel are consumed per hour.
For reference:
250 grams ~= 1/10 of a gallon
124n-m ~= 90lb-ft
1kw ~= 1.3hp
and, 90lb-ft at 2500RPM is about 45hp. Which is about where you'd require in cruise at 70mph. Funny how that works. Good job, auto engineers.
Anyway, moving on. Downshifting is like moving along a line parallel to the two i drew above. Those lines may not be exact, they're pretty arbitrary, and their actual slope is dependent on the transmission ratios.
Anyway. You'll see that downshifting ALWAYS puts you in a worse BSFC category, given that you're over like 2500rshared_pm.
FYI, part of why this is:
Gasoline engines thermodynamically are not very efficient at partial throttle. The engine experiences signifigant pumping losses from a partially closed throttle. Diesel engines don't have this problem, and so their torque peak is typically right at best BSFC. Which is why the euro guys have gotten such good city MPG out of diesels.
95% of TR probably doesn't care about anything I just said. Here's a sweet S-chassis dropped on its nuts:
I <3 usdm
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I'm not gonna lie. I read the first sentence, got bored, read the last sentence, and then I looked at the pretty picture.
