3.73's and highway speeds

Michael Yount said:

Dbeck - what kind of tach? And did you adjust the speedo correctly after the gear change?

Click to expand...

Autometer tach with 100 RPM increments.

I did install a new speedo gear for the 3.73s.

I always try to keep revs ~ 2100

'91 5.0' -

3.73's aren't my preference either with stock engine and tires at highway cruising (70) ... for that I prefer 3.55's with the T-5Z and 3.27's with the factory T5

These two are a better all around gear and torque can make a world of difference as well for street use.

Why rev the car more than you have to

hell i spin my diesel more than 2400 on the highway.......especially at 90-95mph.....for hours on end.


i would not worry about it..........in fact, your stop and go milage will go up, dramatically if you do alot of it. when i lived in socal, and drove about 60 miles a day in bumper to bumper, going from a 2.73 to a 3.73 (in a 3600lb convert) ganed me about 40 miles to a tank.......and on the highway, i do not remember any loss........but, back then gas was only a buck twenty, who payed attention ????

I'm at around 2000-2100 rpm at 105-110 kph....That's around 65 mph or so.

Several of us have been pointing at the same thing - the wear/tear factor is negligible plain and simple.

If you want to think of it in terms of mileage - it's pretty simple math. If you're turning 3000 instead of 2500, the pistons travel 20% further. That makes a 300,000k mile engine a 240,000 mile engine - that's one way to think about it. Let's face it - that's simply a non-issue for 99.9% of us.

Now, if you've got gas mileage issues, or noise issues - that's a different reason to slow down. But if you're worried about hurting the engine -- well, that's kind of like worrying about being struck by lightning while surfing naked off the coast of New Zealand. Odds are, it ain't gonna happen.

Michael Yount said:

Several of us have been pointing at the same thing - the wear/tear factor is negligible plain and simple. ....................

Click to expand...

I agree with most of what you're saying, but to add, most people experience added vibration with lower gears and vibration creates more wear overall. Not to mention the annoyance of shimmies/vibration.

The longevity of the cylinder rings and bearings alone are not a huge issue as most of these engines deserve a rebuild at 100K anyways, but the added revolutions on the accesories and transmission add up. The added force that gears create in the tranny can reduce it's service life as well.

You're right in saying the difference isn't great, but it is noticeable to me. I think a lot of gear selection has to do with user preference and the use of the car.

My preference is a street car and moderate gear selection, that is why I prefer 3.55's to say a 4.10. It's best to build the drivetrain and chassis around an rpm and driving style (race/street) that is preferable to the individual and need.

We will always have 3.55 guys saying 4.10 people are nuts and 4.10 people that think the 3.55's are a waste of time ...

I think stating that 10-20% more wear is negligible is not entirely accurate though.

"...most people experience added vibration with lower gears..."

??? Fix the problem -- it shouldn't vibrate; if it does, a repair is in order. The car ought to cruise just as smoothly at 100 mph as it does at 50. If it doesn't, there's a problem that needs to be addressed.

"...most of these engines deserve a rebuild at 100K anyways...." You are joking, right? There are many examples out there of 200K+ mile 5.0L's; many get the piss beat out of them non-stop and they last well over 100K. There's no reason that a well maintained 5.0 shouldn't go a 1/4 million miles with no major problems.

This thread wasn't about what gear to select. It was about whether you're gonna hurt the car running at higher speeds/higher revs. The simple answer is no -- you're not gonna make a noticeable difference in the longevity of the car running at 85 vs. 70.

It doesn't hurt my car... I just had them put in this summer and my car has 110K miles on the odometer. The car drives better now than it did before and it makes highway on ramps really fun....

srothfuss said:

It doesn't hurt my car... I just had them put in this summer and my car has 110K miles on the odometer. The car drives better now than it did before and it makes highway on ramps really fun....

Click to expand...

damn right-lots of fun-great pick up at just about any speed-potentially lowers top speed if staying with the same engine...I agree with Michael, it won't make a huge difference in longevity-provided that your vehicle is in good repair...

Michael Yount said:

It was about whether you're gonna hurt the car running at higher speeds/higher revs. The simple answer is no -- you're not gonna make a noticeable difference in the longevity of the car running at 85 vs. 70.

Click to expand...

That appears to contradict itself.

A higher rev will hurt engine longevity. Assuming all variables were the same on a 250k 5.0L. Would you rather have one cruising at 2,000rpm or one at 3,000rpm their entire life. Yeah, that is what I thought

3,000 rpm (per example) is over half the efficeint revving capabilities of the 5.0L and that is at cruise Umm...yeah, no thanks...

Edit: Let me point out that a few in this thread have cars that don't have that much mileage or have a car that isn't a "daily driver" or took on longer trips. Or have money to afford "wear"...sooo.....

Michael Yount said:

??? Fix the problem -- it shouldn't vibrate; if it does, a repair is in order. The car ought to cruise just as smoothly at 100 mph as it does at 50. If it doesn't, there's a problem that needs to be addressed.

Click to expand...

Agree, but a factory balanced drivetrain does vibrate 90%+ of the time when switching from 2.73's to 3.73's ....
It's just a fact, as numerous here will testify how wonderful the aluminum dampening driveline is. I realize you have had a fair share of wrench time and know the difficulties in isolating chassis vibrations ... it's a time consuming process that 90% of the guys on here will fail to do ... right?

Michael Yount said:

... You are joking, right? There are many examples out there of 200K+ mile 5.0L's; many get the piss beat out of them non-stop and they last well over 100K. There's no reason that a well maintained 5.0 shouldn't go a 1/4 million miles with no major problems.

Click to expand...

Yes a 5.0 can run for a long time, but I would rather turn a crank .010" at 100K (if needed) than grenade it entirely at 200K when a bearing spins. Plus the benefits of closer tolerances for a street engine are nice too.

Michael Yount said:

This thread wasn't about what gear to select. It was about whether you're gonna hurt the car running at higher speeds/higher revs. The simple answer is no -- you're not gonna make a noticeable difference in the longevity of the car running at 85 vs. 70.

Click to expand...

If you run the car for 250K+ ... or even 150K, for that matter, you would notice wear more so with low ratio gear sets. It's a fact. Yes oil lubricates wonderfully, but all the factors of physics come in to play.

I'm not trying to argue with you Yount, but if I was an uninformed moron and took gear selection 'A' as granted fact, I would be upset when my stock 5.0 cost me my McDonald's paychecks just to eliminate NVH or other unsatisfied issues caused by selecting a personal non ideal ratio ...

... But to agree, it is not that great of a difference for some, but for guys like me and the original poster we notice and it is a different preference.

That's all.

I think, I am pushin 4200 at 70 w/my 3.90 (But my car is rarely ran on the hwy, nor ever ran on the street lol, only a few times I took it out for a long spin w/o my trailer, ok ok call me a trailer queen! but im the 1320 trailer queen!

C6, 3.73's and 3000 rpm stall, turnin 3000+ at around 50 mph, freeway would be too much for me at constant rpm around probably 3500-4000, need to find some 3.27s or 2.73s

The Mustang I have is my first Ford. I can not believe the beating a 302 can take. I dont think any highway mileage can kill it.

Don't confuse the issue guys -- this thread wasn't about personal preference regarding gear choice -- it was about whether running at a little higher rpm was bad for the car. That's simply one piece of the data one needs to make an informed gear choice. (And as I recall, the original poster had already made his gear choice)

Most of you are too young to remember what it used to be like. Overdrive tranny's and really low cruising engine revs are largely a product of the EPA. As CAFE requirements got tighter, manufacturers achieved their highway mileage numbers largely with long rear gears. The fox bodies are a classic example -- a 2.73 gear with a .675:1 overdriven 5th. Not to save wear and tear on the engine - but to achieve a certain highway mileage number. Drop on back to the 60's when all the domestic cars were running 3 speed automatics (the vast majority) or 4 speeds -- top gear was 1:1. And a pretty standard rearend ratio was 3.00:1 or 3.23:1. The tires were a bit taller - but not much. (to compare that rear gear number to the Fox number - multiply 2.73X.675) The engines routinely saw MUCH higher revs under cruise. And they were aerodynamic slugs that weighed more which made the engine work harder to push them through the air at a given speed. And even with poorer oil, poorer machining and assembly, carbs/points (tuneups pretty much required every 6000 miles just to keep them from missing) -- cars routinely lasted 100K. Our 65 Olds Vista Cruiser had 156K miles on it when Dad sold it - still in very good working order. Many, many of those miles were put on loaded with 5 kids and luggage and spinning along at about 3000 rpm at 70-75 mph on the highway. And we weren't the only ones -- millions of other high mileage cars out there under similar conditions during that time period.

Let's add another one in -- most of the smaller engined cars out there today are turning significantly more revs at cruise than the stock 5.0's. Even though some are lighter, most need the torque multiplication that comes with more gear to make performance targets. So most of those 4 and 6 cyl. powered vehicles are zipping along at revs more like what we're seeing with 3.73 gears. And the majority of them are capable of about the same revs as the 5.0L -- they're good for about 6000 rpm -- it's not like we have 9000 rpm engines turning at 3000 rpm. Do you have any idea how many 100K+ mile Civic/Accord/Camry/Corollas there are out there still running just fine?

The point isn't whether there's more wear/tear -- the point is whether the additional amount is SIGNIFICANT -- remember the post -- between 70-80 mph. It's not significant. You do A LOT MORE to shorten the life of the motor/car/driveline every time you take it to the track, or run it hard through the gears, or play burn-out king, than you will cruising it at 500 rpm higher. So if less wear /tear is what you're after - there are a lot of more impactful driving behaviors that should be focused on than simply cruising with 500 more rpm. And for those of you that seem really paranoid about it (5 spd) -- perhaps you should just idle it around. That way there's no more wear and tear than absolutely possible.

As for the youngster spending his hard earned pay from MickeyD's on his ride, I couldn't agree more Couped -- the best thing we can do is coach him to mod the car correctly -- including fixing any vibrations that come along with his mods and understanding the implications of his choices. But he'd get his biggest bang for the buck (in terms of longevity) laying off the Friday night burnouts and attempted ricer kills.

Should they worry about driveline integrity from spinning the shaft faster? Yes - they should pay attention to that. Should they worry about hurting a good running, well maintained engine by spinning it 500 rpm higher on the highway? No - they don't have to worry about that.

Lastly - on the 100K mile rebuild front - if you've got a well maintained engine with a few accurate gauges, there's no need for pre-emptory rebuilds. Your oil pressure gauge and a periodic examination of your used oil filter will tell you if you've got a bearing issue rearing it's head. You should be cutting a filter open every 4th or 5th change -- cut them all open if you like. It's easy to do. With a little common sense, you can run very high miles without any needless worry about blowing it up unexpectedly.

The simple fact remains...more engine wear will occur with a steeper gear when mileage starts to rack up. That is all that needs to be said. Whether or not you like some more miles out of your car or not...it's up to you. It really isn't debatable...

"old cars" didn't last as long as cars today. Reason being for several reason and I'm sure a lower rev and valvetrain's are a couple bigger factors in that. There is a difference between turning 8 cylinders at 3,000rpm and a 4 cylinder at 3,000 rpm.

Michael Yount said:

My wife's Bimmer turns over about 3700-3800 rpm cruising up around 75-80. Been doing it for 80K miles now - car runs even better now than it did new.

Click to expand...

Same deal with my parents BMW's.. 4spd auto's.. they carry about 3000rpm+ at 65mph IIRC.

"There is a difference between turning 8 cylinders at 3,000rpm and a 4 cylinder at 3,000 rpm."

So tell us - exactly what do you think that difference is?

Michael Yount said:

"There is a difference between turning 8 cylinders at 3,000rpm and a 4 cylinder at 3,000 rpm."

So tell us - exactly what do you think that difference is?

Click to expand...

Your "average" 4 cylinder'd car (per your examples) rev higher than 6k before redline and the 5.0L don't even do that. It is around 5,600 rpm or so right...but starts cutting off even before then. Those toyota's usually are around the 6,500 rpm mark or so on "average". Plus the cars your talking about...they are usually newer and do they have the same rotating weight as a 5.0L for example? same valvetrain? same car weight? same need? same piston rings? same pistons? etc. Just a few...

I wouldn't idle my car around (not enough oil coverage). Bad example there