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: 4,309 Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,309
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: 5,442 Indiana
YO7_A66
master
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master
Joined: Jan 2003
Posts: 5,442
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: 4,679 Florida
BDW
master
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master
Joined: May 2005
Posts: 4,679
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: 15,193 Omaha Ne
TJP
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 15,193
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: 4,309 Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,309
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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Re: Highway RPMs
[Re: MoparJ]
#1773456
03/07/15 05:42 PM
03/07/15 05:42 PM
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Joined: Jan 2006
Posts: 704 USA
rftroy
super stock
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super stock
Joined: Jan 2006
Posts: 704
USA
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Quote:
The A-833 with OD swap will take place sometime before the year is out.
You may not like the OD4 behind that engine. It will cruise nicely, yes, but the ratios are such that it is no fun getting going. The ratios are 3.09, 1.67, 1.00, 0.73. 1st to 2nd is getting very close to a 2 to 1 ratio change. I had a 318 with 360 heads, thermoquad, and a DC hyd. with specs right between the stock 318 and 340 cams, and an OD4. It was miserable to drive because of the torque curve. It winds out fast due to the low first, but then 2nd gear puts you way down on the torque curve, and you just lug for a while. If you shift at 4500 from 1st, you start 2nd at 2432. It was especially no fun in stop and go traffic, and you know what that's like here in SoCal.
I ended up pulling the OD4 after just a few months and put the std 4 speed back in.
I have the OD4 behind my slant 6, and it runs great. But that's when you find that the stock slant 6 has a really wide torque curve, and it can pull comfortably at low rpm. A warmed over 318 is going to be more "peaky", and that's where the wide gear spread works against you.
Not saying it won't be right for you, but keep in mind that acceleration runs aren't going to be as much fun.
Robert
AAR 4-speed 3.91, Tor-Red; 70 440 6 pack Roadrunner 4-speed 3.54, Plum Crazy; 68 Formula S conv 383 4-speed 3.23, Electric Blue; 69 Barracuda conv Slant 6 OD4 2.94, 71 B5 Blue; 78 Lil' Red Truck, Red; 70 Challenger S/E. 505 6 pack, Passon 5-speed, 3.55, B7 Blue
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Re: Highway RPMs
[Re: Von]
#1773465
03/10/15 04:32 PM
03/10/15 04:32 PM
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Joined: Jun 2006
Posts: 5,155 CT
GTX MATT
master
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master
Joined: Jun 2006
Posts: 5,155
CT
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Quote:
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....
The gear ratio helps but is probably one of the least important factors. Harder bores, moly rings, oil technology, and fuel injection have helped to make big strides.
Also theres lots of 4 banger cars that turn 3000-3500 @ 70 in overdrive.
Last edited by GTX MATT; 03/10/15 04:36 PM.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
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Re: Highway RPMs
[Re: Magnum]
#1773468
03/10/15 11:33 PM
03/10/15 11:33 PM
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Joined: Aug 2005
Posts: 5,993 Salem
Grizzly
Moparts Proctologist
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Moparts Proctologist
Joined: Aug 2005
Posts: 5,993
Salem
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A Member who I have not seen on here for quite some time, had an 833od in an A-body with a 360. I asked him about it and he said he never noticed any drastic difference: the 360 pulled the wide-ratios with ease and still did low 13's in the 1/4. 340Shorty had the same set-up in his truck and he liked his as well. I just got one in an '84 Ram with a 318 2bbl. With 2.94 gears, 30" tires, and at 4000 pounds that 833od is fun as heck to drive. I got back into one of my close-ratio ratio cars and it felt like you had to shift all the time. It seemed like it was wasting power. The 1st to 2nd is not an issue at all, 2nd to 3rd is a little much but nothing you can't get used to.
Mo' Farts
Moderated by "tbagger".
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Re: Highway RPMs
[Re: 70Cuda383]
#1773474
03/16/15 04:04 AM
03/16/15 04:04 AM
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Joined: Dec 2010
Posts: 12,375 SoCal
MuuMuu101
I got lucky at Woodward!
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I got lucky at Woodward!
Joined: Dec 2010
Posts: 12,375
SoCal
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Quote:
Quote:
I think there is a huge difference between a 4 banger and a big block spinning well over 3 grand for hours at a time.
Yes and no
Smaller engines usually have shorter strokes which is conducive to high rpm cruising. But, 3000 rpm is 3000 rpm... The piston sweeps the bore just as many times regardless of the bore/stroke, and rings/pistons sweeping up and down is what adds to engine wear.
Again, yes and no. With the smaller bores and stroke, there's less moving mass that doesn't move as far and that allows the engine to have a higher natural frequency (otherwise known as red line). But I don't really see a difference from a wear standpoint. Also, 4 bangers need to spin at a higher rpm at higher speeds in order to keep the car moving. It's actually a little wasteful for a v8 to be cruising at 3000 rpms (all depending on the vehicle's weight and aerodynamics).
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Re: Highway RPMs
[Re: MuuMuu101]
#1773475
03/16/15 11:47 AM
03/16/15 11:47 AM
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Joined: Jan 2003
Posts: 11,886 Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 11,886
Benton, IL.
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I was thinking of the weight stopping and starting with each stroke in the 8, especially big blocks. Our stuff is usually bigger and heavier inside and really wasn't designed to spin that high that long. Which is at least part of the reason why anything but a performance car got 2.76s or so. Of course, newer, lighter reciprocating assemblies lessen the impact. And doesn't the load increase exponentially with RPM? I just think that after a certain point, the higher the RPM and the longer it is held there, the more impact it has on our engines. So I don't cruise my big blocks over 3,500 for any length of time and usually try to keep it closer to 3,000. Too old school?
Master, again and still
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Re: Highway RPMs
[Re: DaveRS23]
#1773476
03/16/15 12:20 PM
03/16/15 12:20 PM
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Joined: Jun 2006
Posts: 5,155 CT
GTX MATT
master
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master
Joined: Jun 2006
Posts: 5,155
CT
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The point was that wear is essentially the same, and plenty of late model stuff buzzes down the highway around 3K even with OD.
Of course the connecting rods and pistons will see more stress on a bigger engine, that's obvious.
I personally try to keep it to 3K or less as well.
Last edited by GTX MATT; 03/16/15 12:21 PM.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
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Re: Highway RPMs
[Re: DaveRS23]
#1773478
03/16/15 03:01 PM
03/16/15 03:01 PM
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Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,376
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Actually............. 1. If properly designed, the parts of a V8 DO NOT see more stress than those of a properly designed 4. Stress is defined as force / area. Sure the forces are higher, but so is the area. Mechanical things are designed either to a maximum stress or a factor of safety.
2. If the 4-cylinder is more than 2 liters, chances are it has a pretty long stroke. Strokes of 3.7 to 3.9 are not uncommon in the 2.4 - 2.5 liter range.
3. Running the "big V8" at 3500 rpm for hours isn't outside what the designers built into these engines. The same basic engines were used for industrial purposes and many ran at 3000 or 3600 rpm for their entire existence. Trucks also run at that speed, at least they used to. If your engine comes apart after 100 hours of 3500rpm speeds you did something wrong.
4. No, the engine's natural frequency is not the same as the redline. The redline is the maximum safe speed for the engine based on the design stresses. I don't believe there is an identifiable natural frequency for the complete engine. There are natural frequencies for crankshaft, camshaft, rods, pushrods and valvesprings. There is a natural frequency for cylinders, and as they aren't all the same configuration, every cylinder could have its own. But as an assembly it would be very hard to identify a natural frequency for the engine.
5. There are two problems with running high rpm: wear and noise. Running the engine more rpm per mph (gear ratio) increases wear on the moving parts in the engine. This cannot be ignored. It is up to the owner to decide how much to tolerate. Higher driveshaft rpm with lower gears mean the driveshaft is closer to its natural frequency and stresses the universal joints more. The same is true of noise. Noise increases with rpm, and noise causes fatigue in the driver. It doesn't matter so much to the passengers, they can take a nap. But the driver needs to stay alert.
I changed from 3.91s to 3.23s in my '64Dog and surprisingly saw no difference in gas mileage. But, after a 600 mile trip I was not so worn out with the 3.23s. I did notice a considerable dropoff in acceleration ability around town, and so that part of driving became less fun. I also did not want to invest thousands in an overdrive, although that would have solved both problems.
R.
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Re: Highway RPMs
[Re: MoparJ]
#1773479
03/18/15 10:49 PM
03/18/15 10:49 PM
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Joined: Apr 2012
Posts: 76 South East Ontario, Canada
Ramtough
member
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member
Joined: Apr 2012
Posts: 76
South East Ontario, Canada
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High rpms on a Mopar not a problem in my option. The main reason I run them is when I was young dad had a 66 Chrysler 361 cid, most driving at 100 mph plus, rpms at 3500 plus. We put 660,000 miles on this car over 20 years like this, oil and filter changers every 2,000, the only work on it the was a couple of timing chain and gear sets, and at 380,000 miles new rod bearings rings and oil pump, no re-bore or other parts, oil would be down 1/2 quart at oil change when car was parked, pulled engine and put in my 70 Coronet for another 35,000 miles still ran good when I parked that. 74 - 318 truck drove the same for 230.000 miles no problems there either till the timing chain chain broke and bent valves( at the track with engine near red line ready to shift from 2ed to drive ), could have fixer easy most likely but gave a good reason to install a 440 in the truck.
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