RPM at 70MPH

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Thanks to all who have commented. This helps me with the decision to make sure I don't get embarrassed by a rustang or such and keeping the rpm low-ish on the freeway.

Wow, very low rpm for the 6 speeds! I don't plan on going that low. I think I will stick to 3.55 or 3.23 for my set up.
 
You can get a T56 with a different 6th, or it's updated version the TR6060 (what's found in Challengers and newer Vipers). I believe the 6th on those is more like 0.65. I think some older GM T56s were also more like a 0.76 for top gear. I wanted the low rpms, so I sought out a 0.5 overdrive as 6th is only ever really used for cruising on the highway. I figured the lower I could go the better.
 
Already set up with my 46rh. My floors are perfect and I don't want to cut it. Which is funny, because I have no issue going genIII etc or most other changes deviating from stock..............

Part of the equation is I have the 46rh, crossmember etc for the swap.
 
I have a stock 5.7 and 545RFE. With 3.23 gears it cruises great at 70 mph around 2000 RPM. I would have gone with 3.55 or 3.91 gears, but the 3.00 1st gear in the 545RFE trans made me change my mind. For comparison my cruise RPM is higher than my 04 Durango with the same engine and trans.
 
Well Im a little bit 'out there'...I run 4.11s and a 27" tyre...no overdrive.

Car sits quite happily on our state limit of 64mph.....on 3500rpm. :burnout:

In fact..the car felt happier at 70mph.

Have done this on a couple of three hour trips....I measured my mileage once - got around 21 mpg .
 
Rat,

Interesting. I am trying to avoid the "drone" or "unhappy rpm" thing. My 360 sits around 3600 or so and is irritating at speed.

Decisions decisions...
 
1973Barracuda said:
Rat,

Interesting. I am trying to avoid the "drone" or "unhappy rpm" thing. My 360 sits around 3600 or so and is irritating at speed.

Decisions decisions...
Click to expand...

I know exactly what you mean. Before the 6 speed my car would zing around 3000 rpm at highway speeds, but never seemed to care much. The noise would get to me though. My old motorcycle had overdrive which did a nice job of lowering the pitch of the exhaust even though the rpm didn't change much compared to my new bike. The new one winds 5000 on the highway and just kinda gets to me on longer trips.

Like Rat my car was actually rather peppy with the non-OD setup as it was already wound up and ready to go. And the mileage thing is really more a function of load compared to rpm. Yes, you'll have some more parasitic drag from friction and stuff at higher rpm, but ultimately if you make the same power at 50% throttle and 1500 rpm or 10% throttle and 3000 rpm you're burning roughly the same amount of fuel. Engines are more efficient at certain speeds over others though, so some might show larger variances between speeds. I know mine has pretty much been stuck at 16 mpg through it's entire life. 318 with a 4 speed and 3.07 gears? 16 mpg. Carb'd 5.7 hemi with 4 speed? 16 mpg. Fuel injected 5.7 hemi with 4 speed? 16 mpg. Fuel injected 5.7 hemi with 6 speed overdrive? 16 mpg... I know my issue is in the tune now though. I think I've squeaked another 1-2 mpg with some massaging and bet I can get close to 20 with some more time and logging.
 
Re the 'drone' - Thats why Im a BIG fan of Magnaflows...

Im sure the constant 'frap frap' of Flowmasters or the fart of a Borla would drive me crazy in no time....
 
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