F Engine Max Operating RPM (1 Viewer)

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If I missed this in my preliminary searching Please just point me in the way I should go.....:)

What is the max Operating rpm my f engine (stock w/1bbl aisin plus a header) should be capable of?

The reason I ask (in case i asked the question wrong):
When i drive on the highway (stock 3 speed tranny - 30.5 tires) The engine seems to run up to about 2800 rpm and that seems like its all in.....I can hold it to the floor and squeak out another couple hun for 3k rpm but that seems like flirting with disaster from the sound of it......

It idles lovely at 650 and runs like a champ - solid - no worries.....just curious about the max operating rpm I guess.......
 
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Depending on where you look, max HP is rated at 3600 rpms or 4000 rpms. The 3600 rpms is from the CruiserFAQs (link at the top) and 4000 rpms is straight out of my owners manual for my 71.

With that said, I wouldn't stay much above 3000 rpms for any length of time on a stock motor. I did a 6 hour highway drive at about 3000 for most of the way (up to about 3400 at times), but I was a little nervous. But, my engine ran fine with no problems. I guess bottom line, the engines are rated at 3600 +. Take it to where you feel comfortable.

:cheers:
 
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Thanks, I was thinking it should be above 3k - I just don't know how I could get mine there!

Do I need to check my throttle linkage perhaps? I thought at one time the addition of the header (po stuff) was inhibiting the linkage but with my son pushing the gas pedal I saw the carb throttle go to its max.....Its been a while since i've looked though......

It just sounds so strained at 2800-3000....It'd be like entering the earths atmosphere from space if I could even get it to 3600.....
 

RockDoc

I'll take Bruce Vilanch for the block.
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How's your exhaust? When I first got my 62, it seems to crap out around 3000, after replacing the muffler, it turned into a new beast that had much more power at the top end, and sounded a lot better when up there. Have you checked your compression to see if it's tired in that sense?
 
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The exhaust from the header outlet on is new.....new generic turbo muffler....new exhaust pipe ... tight - no leaks

I havent checked the compression yet.....I'll do that this weekend....

After reading this I feel like I need to find whats keeping it from going over 3K for sure.....
 
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What may be limiting you is the poor beast's inability to horsepower it's flying brick profile faster that the speed you see at 3k, due to wind drag and internal drag.

One of my early cruisers was a '66 like yours, stock, and I put 32" tires on it (sucked MORE hp). Ran beautifully, but I was ashamed whan an old college girlfriend was in town and I proudly picked her up with the top off and could barely chug up the steep highway on-ramp near her house (this was in the mountains north of LA).

But it performed flawlessly off-road! And it was EASY to rev that thing to 4k when in 4-lo.

So try it off-road in 4-lo, I'll bet that thing will rev easily past 3k.
If not, you've probably got a rev-limiter somewhere in your ignition.
 
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I wonder if it's the one barrel. I don't know the cfm of your Aisin, but someone replaced mine with a 1 barrel Rochester and it runs good, but it's pretty much all in around 55, maybe 60 on a good day(I don't know the rpm's).
 
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Assuming all is in nominal condition, that engine will cruise at 3000 happily... but I would not ask it to sustain much more than that for long term. for short term (running through the gears) 4000 is fine... it should take 5000 rpm spike with no problem... I would not be comfortable with a stock bottom end any higher than that though.


Mark...
 

Living in the Past

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Oiling of these old F engines was not a strong point with the partial flow filter. My old 68 never like all the freeway miles I put on it. I don't like to cruise any faster more than 2300 RPM now. But it long been retired from being a daily driver. But how high I coud get the RPMs was never a problem. Besides compression how about the plugs, points, wires, rotor and cap. Is the timing dead on? The spark and timing can limit your top end too.
 
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With no headwind on a flat road, at 3,000 RPMS I am going 63.4 mph (GPS) with stock gearing and 35s in my 73. This being said, when I was coming back from SnT, at one point I had such a strong head wind (like gusts up to 60 mph . . . major wind warnings), I could only go about 40 mps. It is a giant brick and an old engine. I sat back and didn't press the enigne. It is about the drive, not getting there in a Cruiser.

But, I was very happy to let a big rig pass me and got close enough to draft an easily got up to 55 (speed the truck was going)
 
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I'm not overly concerned about going faster or running higher rpms....just wondering why it won't/cant.......I'm probably the slowest dude on the street

The plugs/wires/contacts/timing is all new within the last couple months and I rebuilt the carb and recently adjusted it when I installed a nice vac gauge....

So lets forget highway driving for an instance......

When I start from a standstill going through first and second,,,If I let 'er rev I'm still limited at around 2800-3000 rpm........
I certainly don't rev that much going through the gears, I just did it today to see if it would jump up over 3K......
 
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"Ran beautifully, but I was ashamed whan an old college girlfriend was in town and I proudly picked her up with the top off and could barely chug up the steep highway on-ramp near her house (this was in the mountains north of LA)."
-That's when you do that butt-scootching-back-and-forth movement to help your cruiser up a hill!
 
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Its a tractor motor, Man!
I know....and thats fine as long as its doing what its suppose to do....I'm just concerned that only going to 3k while either through the gears or on the highway isnt "normal".....

There are no vacuum leaks and the timing is correct but I'll check it all again today when I check compression......
 
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Well check these two clips out...not my cup of tea, but yet still impressive. Also not a 40, but still an argument as to driving a brick in the wind.

YouTube - Ferrari vs Jeep Cj-7 0-156mph

YouTube - 785hp Corvette vs Jeep Cj-7

BTW...I am really not as good a resource as these other guys here on MUD, and these two clips are not only fun to watch, but I posted them to show that the over all body shape should not be the cause of your concerns. Have you looked over all your lines yet? Have you tried keeping it in low just to see if you can top 3000? What about when in neutral...can you rev higher than 3000?
 
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I know....and thats fine as long as its doing what its suppose to do....I'm just concerned that only going to 3k while either through the gears or on the highway isnt "normal".....

There are no vacuum leaks and the timing is correct but I'll check it all again today when I check compression......
You're right. Your motor should have no trouble going faster than 3000 RPM.
 
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GA
Thanks, I was thinking it should be above 3k - I just don't know how I could get mine there!

Do I need to check my throttle linkage perhaps? I thought at one time the addition of the header (po stuff) was inhibiting the linkage but with my son pushing the gas pedal I saw the carb throttle go to its max.....Its been a while since i've looked though......

It just sounds so strained at 2800-3000....It'd be like entering the earths atmosphere from space if I could even get it to 3600.....
can you work the throttle with you hand? are you sure it goes to the max?

how's your fuel filter?
 
Last edited:
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Jsut got back from a snow run with near wet cement snow around 2 in the afternoon. OF course my 40 was doing double duty as a tow truck and I seldmom if ever, reveved past 3000 RPMS. ANy more than that and I feel I am jsut asking for trouble. I was able to cruise home at 2800 RPMS going just under 60. IF you go above 3000, don't do it for long and up to what you eel YOUR engine likes. EVeryone has an idea of RPMS with thier own engine after years of driving them. LEarn yours and do what you feel i right.
 
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My 74 F.5 did exactly what yours is doing. I did a compression check and found a dead cylinder. Fixed that via a valve job and it ran better but still not exactly right. Sent my stock carb to FJ40Jim and now it runs the way it was supposed to. Be sure and check your timing advance and compression, if all OK then:

Whether you are in first gear or low range or whatever, you should be able to exceed 2800-3000 rpm on flat ground holding your foot to the floor. If not, when you hit 2800-3000 does the engine miss or stumble or just stop revving? If it misses I would suspect it's an issue related to ignition. It could be something hosed up with the vacuum or centrifugal advance in your distributor. If it runs smooth and just loses power, it sounds more like a carb issue like its running out of fuel. It could be running out of fuel due to many issues up to and including something inside your carb not being right. I'm not a carb expert so you might want to ask someone like FJ40Jim for his input on your issue.
 

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