real HP

[NWRQC]

Contact Dodge

Go there and they will email you your build sheet.
Otherwise I believe that there is a sticker in your glove box that should tell you. Mine didn't so I just emailed them.

 

[BigSloth]

Or record your rpm while cruising at 70 in OD , then figure out your tire size in inches, input that into any gear ratio final drive rpm calculator using 0.67 as the transmission ratio, and that will give you your approximate gear ratio. Then just round to the nearest ratio.

 

[garner]

Crawl under the truck and look at the sticker on the axle

 

[truckin151]

go with the 4.56's, the rpm at 75mph is only 21-2200 rpm, which is right in the sweet spot for really good mpg.

 

[PCA4208]

go with the 4.56's, the rpm at 75mph is only 21-2200 rpm, which is right in the sweet spot for really good mpg.

Really? I'm at 2200 at barely 65-70.. At 75 it's like 23-2400.

 

[Davy120]

Im at 2100 at 75....and i have 3.92s

Camo Ram

 

[BigSloth]

Yeah my calculations with 305/50/20 (32") tires for 3.92 it's 2068 and 4.56 is 2407 rpm at 75mph. Still very well low enough to maintain half decent fuel economy on the highway. But your in town mileage will increase substantially.

 

[truckin151]

mine are 305/50/20 and measure out to 31" tall with a tape. took it for a quick check. @ 70mph I'm at 2100rpm, @ 75mph I'm sitting right on 2250 ( both on rpm gauge and digital datalog gauge) & @ 80mph it jumps to 2400rpm.

Part of it may be due to my custom trans tune as well

 

[ST-8]

My truck on a 275/60/20 would be at 2100 or so but on my 265/70/17 its more around 2300-2400.

 

[Davy120]

Im on 315/70/17s...2100 all day long (at cruise) at 75

Camo Ram

 

[BigSloth]

mine are 305/50/20 and measure out to 31" tall with a tape. took it for a quick check. @ 70mph I'm at 2100rpm, @ 75mph I'm sitting right on 2250 ( both on rpm gauge and digital datalog gauge) & @ 80mph it jumps to 2400rpm.

Part of it may be due to my custom trans tune as well

I'm not doubting what you are running, but that just does not add up. At 70mph a 31" tire with 4.56 gears through the 545RFE's 0.67:1 ratio in 5th gear with TC locked, should be 2318rpm. at a 4.10 ratio with the same tire size the rpm is 2084, which is mighty close to your 2100. No amount of trans tuning can change the ratios, that requires hard parts. You can modify shift points, line pressure, and anything hydraulic to an extent, but ratios are decided by the planetary set.

Like I said, im not calling you a liar or anything, the math just isnt there. Did you buy the truck with the gears installed or did you physically handle a set of known 4.56 gears prior to install? Because I think you either were lied to during the sale, or received 4.10 gears by accident.

 

[PCA4208]

Can I suggest we make another thread about ratios, speed and rpm's? All this is doing is cluttering up an engine performance thread.

I'd be more than happy to post like mad on another thread, because I'm interested to know why my rpm's are so high, and truckin's are so low.

 

[truckin151]

I'm not doubting what you are running, but that just does not add up. At 70mph a 31" tire with 4.56 gears through the 545RFE's 0.67:1 ratio in 5th gear with TC locked, should be 2318rpm. at a 4.10 ratio with the same tire size the rpm is 2084, which is mighty close to your 2100. No amount of trans tuning can change the ratios, that requires hard parts. You can modify shift points, line pressure, and anything hydraulic to an extent, but ratios are decided by the planetary set.

Like I said, im not calling you a liar or anything, the math just isnt there. Did you buy the truck with the gears installed or did you physically handle a set of known 4.56 gears prior to install? Because I think you either were lied to during the sale, or received 4.10 gears by accident.

Edit: My bad, went back and checked my log, got my numbers swapped,

@ 65mph = 2100rpm
@ 70mph = 2250rpm
@ 75mph = 2400rpm

Those numbers are consistent with the 4.56 gearing.

SPEED x OGR x 336 / TIRE HEIGHT = RPM

Btw, the tune also affects tc lockup. rpm can also be affected by street incline as well. there are outside factors that go into it as well.

 

[TheMaddog]

go with the 4.56's, the rpm at 75mph is only 21-2200 rpm, which is right in the sweet spot for really good mpg.

Really? I'm at 2200 at barely 65-70.. At 75 it's like 23-2400.

Im at 2100 at 75....and i have 3.92s

Camo Ram

My truck on a 275/60/20 would be at 2100 or so but on my 265/70/17 its more around 2300-2400.

damn!!!! I think I'm at 2300 rpm at 70.

 

[PCA4208]

Yeah so this morning on cruise at 70 mph I was at 2350 rpms. So idk what's going in with my truck.

 

[TheMaddog]

Yeah so this morning on cruise at 70 mph I was at 2350 rpms. So idk what's going in with my truck.

You also have gears lol

 

[PCA4208]

You also have gears lol

Haha yes but I'm a full 1k above of what truckin was doing. But whatever, I only drive highway speed for about a minute or two to get to school. Other than that its all city for me.

 

[truckin151]

your about 100rpm higher..... 1k higher would be an issue

 

[ST-8]

When I had 3.55 on my 17s I think I was at 17-1800 rpm

 

[PCA4208]

your about 100rpm higher..... 1k higher would be an issue

Oh yea haha I meant 100 more haha yea 1k more would be pretty weird.