Hello, guys. I'm sorry for having to ask a silly question like this. I know the Slant Six gurus are on here, so this is the best option I have.

I have a 1985 D100 Ram 3 speed automatic and I believe 3.23s that was handed to me by my Grandad. 62,000 miles, all original truck. In all of the time he owned it, it never saw above 65 mph.

For the first time today, I took it out on the highway. I was afraid of how gutless it seemed down low that it wouldn't run highway speed. BOY WAS I DEAD WRONG, lol. I decided to dust it some and punched it and ran it up to 91 mph before I backed out of it and it was still climbing like no problem. I was afraid of over revving it and cruised at 80 for about 20 miles before I got off the freeway. Never knew it had this kinda guts in it.

I don't have a tach, but at 80, it sounds somewhere around 3,000 RPMs. Is it safe with a Slant 6 to run at that RPM on the highway for good distances without hurting anything? Anyone else here with a truck similar to mine that cruises around that speed on the interstate? Thanks for any help!

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2007 F-150 5.4L

1985 D100 225 Slant 6

I cant speak as a slant 6 guru....I am not....a mere newbie , since my son and I just got our first last summer.....but I might be able to share my perspective to help a little...

We have gotten spoiled with overdrive, 6-8 gears etc these days....modern vehicles cruise at 80 mph at 2k rpms or so and are QUIET......

Back in the day, it was common to run at those RPMs at highway speed so I am told.

When I drive my 72 Barracuda to shows, I am on the highway doing 65-70 and about 3k RPMs....that's a 318 but same point......when I first started driving the Barracuda, I felt for sure that the engine was gonna blow up....LOL...its loud and sucks the gas down.....but blow up?

It hasnt in about 9 years of regular cruising.

If the engine is in good condition - good cooling sytem, good oil pressure etc and the rest of the vehicle is as well to handle the sustained driving at that speed, cant see why 3k would hurt a slant 6.

I am sure the more experienced here will chime in with more info.

Yes.... as long as the engine is in good shape and has been maintained correctly (with the proper oil level), 3000 rpm is not unheard of depending
on the tire size, rear ratio and transmission option....

You will find that the stock engine runs out of steam about 4000 rpm, FYI.

I have a 1976 D100 with factory 3.9 rear axle gears and a stock 727 transmission. I can drive at 65-75 mph for extended periods on the highway with no problems. I don't have a tach either, but I run 235/75/15 tires which works out to 3480 engine rpm. I can almost watch the gas gauge drop, but it still pulls up to 80 and beyond, but I don't have nerve to hold it that fast for long. It made a four hour drive home at those speeds when I bought it and didn't complain. I would love to get some kind of overdrive installed, but for now I can just cruise at 55 if I want to keep rpms down.

The engine has about 130,000 orriginal miles and is doing ok, but oil pressure does seem a bit low when it is hot and the original vibration damper separated.

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Casually looking for a Clifford hyperpak intake for cheap.

If the engine is in good shape, three grand on the tach is fine.

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If it was easy, everybody would be doing it.

With original 3.55 gears, 205/60-14 tires and non-lockup 904 I have kept cruising rpm in between 3300 and 4000 rpm depending of road type. More than 4000 is too noisy but I can go there for a while above after installing a large aluminum radiator.

For next season I am getting 4.10 SG rearend so the 4000 rpm will become more common. 15MPG.

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1966 Dart. 170 cu.in. 200 rwhp.

Thanks for the replies everyone! Much appreciated.

Another question I have; can anyone tell me how to check to see what gear ratio I have?

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2007 F-150 5.4L

1985 D100 225 Slant 6

If there is still the factory tag under one of rear axle cover bolt read it there. Othervise you can lift both rear tires and if there is SG then just rotate wheel exact on turn and calculate how many turns the drive shaft makes. With open differential it is bit more difficult to test.

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1966 Dart. 170 cu.in. 200 rwhp.

I had a 87 D150 slant six.with automatic trans. I ran it 75 on the interstate and never thought anything about it. Still ran great when I sold it. Craig

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I'm going to attempt to fix this project and not make it any worse.

Sticky under transmission section; how to ejaculate rea rend ratio:

http://www.slantsix.org/forum/viewtopic.php?t=36418

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Dang WJAJR! What do you get up to under your car?!

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Casually looking for a Clifford hyperpak intake for cheap.

If you can get 15 MPG at 4000 rpm then you are a lot smarter than me!!

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Remember the speed is still quite low and the engine has almost no load and deep vacuum. Its about 70 miles per hour. Fuel injection of course helps a bit.

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1966 Dart. 170 cu.in. 200 rwhp.

Thanks for your help, everyone!!

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2007 F-150 5.4L

1985 D100 225 Slant 6

Hummm...

Must have brewed up a red lined word, clicked on the wrong selection and never looked back.

For those wondering just what I was thinking; calculate was what I though got clicked on.

For S & G's spell check caculate within this site's word processor; see missed it by one.

Reed: MYOB there buddy. LOL

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC