droping rpms

[Destroyer000]

i first had 3.27s and 28.9inch tires on my ranger. super cab 4x4 5spd with a 4.0. i used to tach about 2k. then i went to 3.73s and 31s and my rpms went up just a little. about 22,2300 now iam at 4.10s and 33s and iam taching about 2700 doing 65. whats the best way to get my rpms back down. lower gears, bigger tires?

 

[kimcrwbr1]

Are you changing the gear in the tranny transfer so your speedo is correct have someone follow you and compare actual speed on a stock vehicle. Vehicle speed is a unknown in your calculations.

 

[Destroyer000]

yes i did swap the speedo gear. i stared with a white which was a 17 tooth then with the 3.73s i went to a 19 and with the 4.10s i went to a 21 an it was way off and i put a 20 in and its off about a mile.. my odometer is off about a tenth of a mile. so for every 10 miles you add a mile.

 

[kimcrwbr1]

So at 65 mph your actually going about 72 if you add that 10%

 

[kimcrwbr1]

What I would be looking at is the skinny pedal the less you have to push on it the better the gas mileage. say you have the pedal 1/4 the way down at 2700 rpm at 72mph change that to 1/3 the way down at 2200 rpm at 72mph you are gettin less mpg and less torque at the wheels when you need the power. It all depends on the skinny pedal and what your trying to achieve.

 

[kimcrwbr1]

A vacuum guage to do your calcs will help I had mine ran into the cab off the manifold while I was dialing my carb in to see how it responds to foot feed, different jets and timing.

 

[Destroyer000]

iam not doing 72 iam definitely doing 65. i even had my gf follow me with her civic and she said i was doing 65mph. when i plug my scanner in it tells me my speed as well and its dead on along with the gps unit i used once. as far as the skinny pedal, once its up to speed i barely push on it to stay at my speed.

 

[holyford86]

iam not doing 72 iam definitely doing 65. i even had my gf follow me with her civic and she said i was doing 65mph. when i plug my scanner in it tells me my speed as well and its dead on along with the gps unit i used once. as far as the skinny pedal, once its up to speed i barely push on it to stay at my speed.

something just doesn't seem right there, I'm running 4.56 gears and 33 inch tires and @65 mph I'm taching ~2600. Verified by GPS and a follower. Perhaps try having another vehicle follow you just for a little bit of extra verification?

 

[adsm08]

How old is your clutch? With a setup like that I could see maybe some clutch slippage without you noticing.

 

[naford]

Using this chart, on this TRS link it looks like after every tire and gear change you are going up in RPM. But it looks like it's only 300 hundred rpm difference. You didn't say if it is and auto or manual. If it's an auto it could be the overdrive isn't working. If it's a manual it could be the clutch is slipping. I think the bigger tires put more stress on the clutch just becuase of their weight than smaller tire and thats why the clutch is slipping.

http://www.therangerstation.com/tech_library/gearandtirechart.html

 

[adsm08]

He did say. It's a manual.

 

[exbass94]

Either your speedometer is off, the tach is wrong, or the clutch is slipping. Those are the ONLY possibilities, period. According to my calculations, with 33s, 4.10s and an OD gear ratio of 0.79 (you ARE in OD right??) 2700 rpm = 81 mph.

EDIT: just did the calculations again, this time using 4th gear 1:1 ratio. 2700 rpm = 64.56 mph. If you want lower rpm's why don't you use 5th gear??

 

[Destroyer000]

i always use 5th gear.. the clutch isnt slipping. it was just put in last year. only thing i can think of is my tach is off a little.

Holyford86.. before you went to 4.56s, you had 4.10s and you said your speedo was accurate.. now your at 4.56s and its still accurate? something doesnt add up

naford, thanks for posting that i tried to find that and couldn't.