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Highway RPMs
#1773436
03/06/15 05:05 PM
03/06/15 05:05 PM
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Joined: Feb 2008
Posts: 992
Simi Valley, CA
MoparJ
OP
super stock
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OP
super stock
Joined: Feb 2008
Posts: 992
Simi Valley, CA
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My Duster with 3.91s runs about 3500-3600 rpm at 68-70 mph. Usually I will run around 3300-3400 rpm on the highway, but sometimes you need to run a little quicker to keep up. Eventually a 4 speed will be going in. Tires are 255/60/15s. Motor is a warmed over stock compression 318 (with XE268 cam) with 45K since the last rebuild. Doesn’t use a drop of 15w40 Delo oil between changes. The engine buzzing doesn’t bother my ears, but with regular oil changes (every 1500 miles), am I flirting with danger at the revs mentioned? I don’t think so, but just wanted to hear some opinions!
2016 Ram 1500 Crew Cab: 5.7, 65RFE, 4.56 gears with locker, Hemifever tuned, AFE intake, 87mm throttle body, JBA headers, 3" Flowmaster exhaust, split to dual 2.5" exits. 13.57 best ET so far.
Searching for new A or B Body Project!
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Re: Highway RPMs
[Re: stumpy]
#1773438
03/06/15 05:35 PM
03/06/15 05:35 PM
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Joined: Mar 2005
Posts: 1,373
Rancho Cucamonga, CA
D_C
pro stock
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pro stock
Joined: Mar 2005
Posts: 1,373
Rancho Cucamonga, CA
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If you plan to swap in a Standard 4-Speed Transmission, fourth gear is Direct, as in no different than Third Gear in a 3-Speed manual transmission, or Drive/Third Gear in a 727 or 904 Automatic Torqueflite.
You would need a an Overdrive Transmission to bring the RPM down at freeway speeds. Higher continuous RPM does accelerate engine wear, though you may be able to live with that.
Swapping to Taller tires works similar to swapping in, say, 3.54 or 3.23 rear axle gear ratio, but off-the-line performance would suffer a bit as well, and there are practical limits on how tall a tire you can fit in your wheel wells.
There are lots of great Gear Ratio calculator applications available, wherein you input rear-axle ratio, transmission ratio (1-to-1 in high gear for a Standard, non-overdrive transmission) along with Tire Diameter which will calculate Engine RPM based on Speed in MPH.
You can run the numbers to determine what combination would produce your desired results, though it is always a compromise.
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Re: Highway RPMs
[Re: D_C]
#1773439
03/06/15 05:38 PM
03/06/15 05:38 PM
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Joined: Feb 2008
Posts: 992
Simi Valley, CA
MoparJ
OP
super stock
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OP
super stock
Joined: Feb 2008
Posts: 992
Simi Valley, CA
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Quote:
If it is a Standard 4-Speed Transmission, fourth gear is Direct, no different than Third Gear in a 3-Speed manual transmission, or Drive, Third Gear in a 727 or 904 Torqueflite.
You would need a an Overdrive Transmission to bring the RPM down at freeway speeds. Higher continuous RPM does accelerate engine wear, though you may be able to live with that.
Swapping to Taller tires works similar to swapping in, say, 3.54 or 3.23 rear axle gear ratio, but off-the-line performance would suffer a bit as well.
There are lots of great Gear Ratio calculator applications available, wherein you input rear-axle ratio, transmission ratio (1-to-1 in high gear for a Standard, non-overdrive transmission) along with Tire Diameter which will calculate Engine RPM based on Speed in MPH.
You can run the numbers to determine what combination would produce your desired results, though it is always a compromise.
904, with TF-2 kit, 2800 stall.
Moved away from 3.23s a while ago, so the 91's are here to stay.
2016 Ram 1500 Crew Cab: 5.7, 65RFE, 4.56 gears with locker, Hemifever tuned, AFE intake, 87mm throttle body, JBA headers, 3" Flowmaster exhaust, split to dual 2.5" exits. 13.57 best ET so far.
Searching for new A or B Body Project!
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Re: Highway RPMs
[Re: D_C]
#1773442
03/06/15 05:50 PM
03/06/15 05:50 PM
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Joined: Feb 2005
Posts: 4,311
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,311
Prospect, PA
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Quote:
If you plan to swap in a Standard 4-Speed Transmission, fourth gear is Direct, as in no different than Third Gear in a 3-Speed manual transmission, or Drive/Third Gear in a 727 or 904 Automatic Torqueflite.
You would need a an Overdrive Transmission to bring the RPM down at freeway speeds. Higher continuous RPM does accelerate engine wear, though you may be able to live with that.
Swapping to Taller tires works similar to swapping in, say, 3.54 or 3.23 rear axle gear ratio, but off-the-line performance would suffer a bit as well, and there are practical limits on how tall a tire you can fit in your wheel wells.
There are lots of great Gear Ratio calculator applications available, wherein you input rear-axle ratio, transmission ratio (1-to-1 in high gear for a Standard, non-overdrive transmission) along with Tire Diameter which will calculate Engine RPM based on Speed in MPH.
You can run the numbers to determine what combination would produce your desired results, though it is always a compromise.
The manual transmission will lower by 200 rpm his highway cruise rpm.
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Re: Highway RPMs
[Re: D_C]
#1773444
03/06/15 06:06 PM
03/06/15 06:06 PM
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Joined: Feb 2008
Posts: 992
Simi Valley, CA
MoparJ
OP
super stock
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OP
super stock
Joined: Feb 2008
Posts: 992
Simi Valley, CA
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The A-833 with OD swap will take place sometime before the year is out. I drive one or two days a week, with maybe 30-40 of the 110 or so mile I may drive being at those engine speeds. All variables such as coolant temp and oil pressure have not changed in the past year. I am also in Southern California.
2016 Ram 1500 Crew Cab: 5.7, 65RFE, 4.56 gears with locker, Hemifever tuned, AFE intake, 87mm throttle body, JBA headers, 3" Flowmaster exhaust, split to dual 2.5" exits. 13.57 best ET so far.
Searching for new A or B Body Project!
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Re: Highway RPMs
[Re: MoparJ]
#1773445
03/06/15 06:34 PM
03/06/15 06:34 PM
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Joined: Jan 2003
Posts: 5,443
Indiana
YO7_A66
master
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master
Joined: Jan 2003
Posts: 5,443
Indiana
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My 340 Challenger runs 3500rpms at 70mph (255/60/15's & 3:91's) and I never sweat it!
1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
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Re: Highway RPMs
[Re: Paul_Fancsali]
#1773447
03/06/15 07:25 PM
03/06/15 07:25 PM
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Joined: May 2005
Posts: 4,707
Florida
BDW
master
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master
Joined: May 2005
Posts: 4,707
Florida
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Couldn't take my 340 screaming as everyone passéd me on the highway. Car is much funner to drive with the 518 w/LU. 3.73 gears, 26.7 inch tires. 
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Re: Highway RPMs
[Re: DaytonaTurbo]
#1773449
03/07/15 12:21 AM
03/07/15 12:21 AM
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Joined: Jan 2003
Posts: 27,421
Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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I drive the 90 mile run to Carlise at 60 mph in my 63 with 4.30's. I use a 30" tall tire and it runs about 3200 at 60 mph. Its no problem for me to run the 90 miles at 3200 rpm as it usually takes me about an hr and a half. Ron
Last edited by 383man; 03/07/15 12:22 AM.
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Re: Highway RPMs
[Re: stumpy]
#1773450
03/07/15 01:18 AM
03/07/15 01:18 AM
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Joined: Jan 2003
Posts: 15,311
Omaha Ne
TJP
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 15,311
Omaha Ne
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Quote:
Nothing wrong with that. Cars did that for years before OverDrive became a standard item.
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Re: Highway RPMs
[Re: Grizzly]
#1773452
03/07/15 03:14 AM
03/07/15 03:14 AM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
master
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master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Quote:
As far as will high rpm on the highway hurt it? Eventually, yes: there's a reason why new vehicles with overdrive are hitting 300,000 miles and the old girls barely made 100,000.
No offense, but considerably more involved than just final drive ratio....
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: Highway RPMs
[Re: DaveRS23]
#1773454
03/07/15 04:51 PM
03/07/15 04:51 PM
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Joined: Feb 2005
Posts: 4,311
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,311
Prospect, PA
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Quote:
3.91s have been our gear of choice forever. So hiway RPMs has always been something we keep an eye on. 3,000 has been the dividing line so to speak. Staying there abouts or under is preferable and the farther over that you get and the longer you stay there, then the more pounding you are doing to the engine.
I've always used 3,000 rpm as the dividing line as well. No testing, data, or science, just feels about right.
Last edited by BSB67; 03/07/15 07:25 PM.
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Re: Highway RPMs
[Re: BSB67]
#1773455
03/07/15 05:36 PM
03/07/15 05:36 PM
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Joined: Jan 2003
Posts: 27,421
Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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Quote:
Quote:
3.91s have been our gear of choice forever. So hiway RPMs has always been something we keep an eye on. 3,000 has been the dividing line so to speak. Staying there abouts or under is preferable and the farther over that you get and the longer you stay there, then the more pounding you are doing to the engine.
I've always used 3,000 rpm as the didviding line as well. No testing, data, or science, just feels about right.
Thats not a bad idea. But I will say with the solid flat tappet cam I use my eng sounds real nice singing along about 3200 RPM with my cam. Ron
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