Bfenty

84 4+3

I've found most cars tend to be in the 1600 to 2300 range at cruise. 55-60 without od isn't bad. 1300 in mine in town feels too low.

Joe C

just think of the days before overdrive was common. used to cruise the interstate in my 69 350/4-speed (w/ 3.36 gears), at 70 mph in the low 3K RPM range. ran like that for hours at a time - pretty much never gave it any thought -

84 4+3

This is also true. I personally don't like it but it's more than likely fine. Actually it is...

Bfenty

84 4+3

The only issue is you'll be using a lot more fuel lol.

Bfenty

Yeah but I mean I drive it to work 15 miles on a sunny day, all on two lane highway. I really don't do any interstate driving in it and I don't put that many miles on it-it's my nice day, fun car. That said I don't want to tear up my engine or anything-fuel consumption isn't so much a concern because, like I said, the miles are so low that a few less MPG doesn't make a huge difference.

QCVette

Both of these post nailed it.

Joe C

, but back in the day, if I was getting 15-16 MPG highway, I was happy. still, never gave it much thought....

Tom400CFI

I agree. Cruise at what ever RPM you want.

The 351w in my boat "cruises" at ~2800-3200 RPM....been doing that for 26 years without any complaints.

Bfenty

wow ok so I guess I was way over-estimating how much impact RPM has on an engine. Sounds like as long as you're not red-lining it constantly, you're fine, right?

Tom400CFI

Well....*I* personally feel that you can redline it constantly, and still be fine. Not that I would...but you could.

Another example I have for that is my previous truck; a '96 Silverado 1500 with a Vortec 350/5 speed. I used that truck to tow the previously mentioned boat to Lake Powell and back, through the rocky mountains...100's of times. There are mountain passes and canyons where I'd have it in 3rd gear, WOT, 4500-5500 RPM for minutes at a time. 10 minutes. I sold that truck at 296,000 miles still running as it did new.

These engines (designs -not each individual engine) pass a validation test where they're rung at WOT, being cycled from peak torque to peak hp RPM's back and forth for 200 hours. They can take it.

Joe C

right - it's all about the dynamic stress caused by rapid acceleration or deceleration of internal components. pretty much any steady-state engine speed will generate far less internal stress.

cv67

Had a Camaro that cruised at 3500 rpm for hours on the fwy it didnt wear anything out.

The OD was out on my Silverado for a long time. Leaving it in D the mileage was exactly the same vs OD til I hit 70 or more . Think lugging it put more wear on it than where it was "happy".

Look up a random list of cams, even smallish ones will say ideal cruise rpm range is higher than youd think. Lots of old trucks out there with 4.10 gears that have 200k on them think what rpm they cruise at

Some act like these are made out of tissue paper, 350s last practically forever. Most failures are lack of maintenance or an idiot behind the wheel. Never busted one yet!

81c3

Had a 71 & 2 72 C-10 2WD pickups... all had 4 speeds with 4:10 gears... 3200 rpm at 65 ish.... never an issue...

Bfenty

Ok, thanks guys. So don't floor it constantly, smooth acceleration/deceleration, and I'm good.

I'm actually pretty careful with my car because I know it's old. Until I can rebuild the engine I will continue to baby it, but it's good to know that I'm not destroying the engine if I go to 55-60mph.

84 4+3

If I had to guess, you have an omc drive too. If so how is that treating you? The diesel in our boat also cruises around 2800. Whole different ball game with those though lol.

I lost overdrive in my 3500 today. 4300 for 7 miles on a 383. I may have watched the gas gauge go down but... Sounded fantastic and scared the crap out of me when I jumped up a grand without pushing the pedal... #racetruck

Paul Workman

The simple answer for any given situation (load variance) is told by your accelerator...which ultimately relates to engine wear and MPG in the long run.

Engine wear is the result of friction and speed. And, breaking these down involves lots of differential type analyses to determine the best compromise in any given situation...which ultimately gets us back to the "simple answer".

Need proof? Climb onto a 10 or (better yet) a 21 speed bicycle and go for a long ride with some hills along the way. Then you'll feel first hand about engine torque and speed and what trade-offs work best to provide the POWER necessary to negotiate the various loads (hills).

Think of it this way: Think of fuel consumption as a wear indication. Suddenly what cuisinartvette experienced makes sense - another excellent illustration of the (gear ratio vs. RPM) dynamics at work!

Tom400CFI

Right?

I have never, and will never own an OMC product. My brother has a Cobra drive in his boat.

Direct drive, here. It's treats me great. Had it 18 years now and changed engine oil and trans fluid once a year. Best boat drive system made (from a maintenance perspective). I do miss having power trim and a jack plate from a performance perspective....but those things wouldn't help much on this boat.

ddahlgren

There is more than 1 train of thought of this as far as the engine is concerned. No matter what RPM it takes the same HP to go any given speed with the same car. HP is a function of torque and rpm. Lower the RPM and it takes more torque to make the same HP. The torque exerts force on the bearings loading them down harder trying to break the oil film. If the RPM goes up torque needed goes down so bearing load goes down especially at the very modest engine speeds we are talking about. For the most part fuel is needed vs. HP required and RPM to some extent. Personally I don't run under 1800 to 2300 rpm even if the engine seems to pull it ok. To each their own I guess.