Highway RPM's

oldsproject
Old Fart

65 Post Sport Coupe/425 - 65 Lansing Holiday Coupe 442/400 - 65 Fremont Holiday Coupe 442

Posts: 1,522

Highway RPM's Jul 6, 2011 0:35:44 GMT -5

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Post by oldsproject on Jul 6, 2011 0:35:44 GMT -5

What's the ideal RPM range for good fuel economy at highway speeds on these big blocks (425 in my case). Realize lots of opinions and contributing factors but looking for thoughts for fuel economy as I match up tranny, tires and rear gears. Currently looking at a stage 2 700R4 matched up with 3:55s or 3.70's maybe steeper? The 3.06:1 1st gear should provide pretty decent tire speed at take off and the .7:1 overdrive runs the RPMs down pretty good (2000-2100) with a 26" tire. Anyway, a ways off before my wife let's me spend that kinda cash but in the planning stage and appreciate any insight.

442scotty
Senior Member

Posts: 537

Highway RPM's Jul 7, 2011 9:07:42 GMT -5

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Post by 442scotty on Jul 7, 2011 9:07:42 GMT -5

Would that bring it down to the range of 323's ? I get about 15mpg on my car...In my other car, the cutlass I have 256 gears? I believe with the 2004R trans...Built for low end use so it still pulls pretty good and Im hoping for 20-25 mpg hiway...1500 rpm at 65 mph...should find out the mileage on the 16 th when I take it on a 150 mille cruise

oldsproject Old Fart 65 Post Sport Coupe/425 - 65 Lansing Holiday Coupe 442/400 - 65 Fremont Holiday Coupe 442 Posts: 1,522	Highway RPM's Jul 7, 2011 13:34:45 GMT -5 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by oldsproject on Jul 7, 2011 13:34:45 GMT -5 Thanks Scotty, let me know how that works out.

442scotty
Senior Member

Posts: 537

Highway RPM's Jul 29, 2011 8:51:37 GMT -5

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Post by 442scotty on Jul 29, 2011 8:51:37 GMT -5

Ok so I took the Cutlass out for a 300 mile run.. btwn 70-75 mph ..mostly 75...(around 1650 rpm on my tach) with about a half hour of crawling in traffic at idle. Mileage came in at 26 MPG (Imperial gallons) which would be less in US gallons. I used a lot more gas at 75 mph. if I had stayed between 65-70 I probably would have been better off but no one drives 65 anymore.
Still had pretty good pulling power up steep hills with the gearing the way it is. All in all I was pretty happy with it. At $5 bucks a gallon it all adds up...

oldsproject Old Fart 65 Post Sport Coupe/425 - 65 Lansing Holiday Coupe 442/400 - 65 Fremont Holiday Coupe 442 Posts: 1,522	Highway RPM's Jul 29, 2011 11:28:28 GMT -5 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by oldsproject on Jul 29, 2011 11:28:28 GMT -5 Sounds pretty good to me.

Post by oldsproject on Jul 6, 2011 0:35:44 GMT -5

Post by 442scotty on Jul 7, 2011 9:07:42 GMT -5

Post by oldsproject on Jul 7, 2011 13:34:45 GMT -5

Post by 442scotty on Jul 29, 2011 8:51:37 GMT -5

Post by oldsproject on Jul 29, 2011 11:28:28 GMT -5