How fast is a 2F supposed to be

[fireflyr]

I put a tach on my F.5 to see what kind of RPM it was doing on the freeway. With 4.11 gears and 33 inch tires it spins at 2600 rpm at 60 indicated (uncorrected speedo). Vibration and noise keeps me from doing much more.
Like it was said above, you don't want to drive too fast; you'd deprive too many people from seeing your fine vehicle.

Anyone know what redline is? 3500? 4000? Not that I want to test it.

 

[Roboosfj40s]

Sold the Hot Rod years ago. Been scrapped of of the road and trees too many times ha ha. 50-55 is plenty fast enough for me and I get 9.5 mph in the city. Highways around here are so full of traffic I cant actually check highway mileage because it moves so slow. Stock 2F, 3 speed tranny on 33 x 12.5's, 4" lift, stock carb, stock points dizzy. Not sure what recorded red line is supposed to be. After 42+ years of legal driving I kinda go by engine sound. I do however have a tach.

 

[1911]

Anyone know what redline is? 3500? 4000? Not that I want to test it.

The consensus here on Mud is 4,000 rpm or a little more, depending on how well it is balanced.

I run mine up to 3000 to shift going up a hill, but much prefer to keep it at 2500 or less. With my stock 3.7 diffs and a rubber overdrive (33") mine will cruise at 65 mph turning 2500 rpm. Plenty for my road trips to go wheeling.

 

[ken_79-fj40]

I've got 3.70's and 33" tires on mine. It cruises with traffic at 70 no problem. Even uphill. But having the engine balanced makes all the difference in the world. Before the rebuild it felt like it was going to fly to pieces at anything above 3800 rpm. I've spun it to 5 grand a few times and it's smooth as can be. But I rarely take it above 4000. It may be a forklift motor but built right they work really well. Mileage still sucks though. I get 12-14.

 

[Cruzer_89]

Nice Trollhole

 

[AlexJet]

Anyone know what redline is? 3500? 4000? Not that I want to test it.

I'm not sure about Red Line start point, but when I looked at specs for 2F, it gave me max HP at 3'600 RPM. I'd consider Red Line from somewhere around 3'800-4'000. I'd agree with several above mentioned post that it should stay under 3'000-3'200 for motor safety and lifespan.

 

[MicahMan]

no tach

So I don't have a tach but I have checked it at my buddy's shop. Sounds like I cruise around 2800 on the freeway with 4.11s original 73 f motor and 33s. With my gps speedomoter I am right at 65. On the freeway at this speed I get 14mpgs. Around town slightly less, but not much. In 4low noone checks right!

 

[DenCo40]

My 2f will go all day at 3K. I'm at 4.11 on 35's. Not sure of the speed cause the speedo is way off. The motor will go faster, but it seems like it's going to explode if I go past 4k.

 

[NIKNITE]

OK

I'm sure you checked for cracked V lines & possible manifold leaks flat spots in excel. are not a gear issue It is a tank but they even run good If you look for leaks you might also find that it runs better cold but makes more power it's a good place to start! There are also issues with fuel pressure & the thing is I don't care if it's a dam lawnmower make sure the motor is right first it makes all the difference in the world !

 

[Roboosfj40s]

My 2f will go all day at 3K. I'm at 4.11 on 35's. Not sure of the speed cause the speedo is way off. The motor will go faster, but it seems like it's going to explode if I go past 4k.

Compared to stock tires and rims i found a calculation on this. When running 33" with 4:11 gearing it increases your speedometer by 8 mph and reduces the gearing to around 3:70 ish. I think this is way some call bigger tires their OD. So at 50 mph you are actually going 58. Anyway I checked mine with other vehicles and it seems to be about right. I don't know what 35's would do.

 

[FJsnoozer]

That Change in mph is not straight across the board, it is proportionate..

While 62 might = 70
45 might only be +6
30 might be +4
And so on.

:Cheers:

 

[Sea Knight]

The consensus here on Mud is 4,000 rpm or a little more, depending on how well it is balanced.

I run mine up to 3000 to shift going up a hill, but much prefer to keep it at 2500 or less. With my stock 3.7 diffs and a rubber overdrive (33") mine will cruise at 65 mph turning 2500 rpm.

Similar setup on my '82 with stock CA smogged 2F/H41/33's. On flat highway stretches I've squeezed out 18-19 mpg at ~62mph. I don't care to drive any faster than 60ish in the 40, even though it'll run at 80+ without complaining. Seems to defeat the purpose.

 

[duffontap]

That Change in mph is not straight across the board, it is proportionate..

While 62 might = 70
45 might only be +6
30 might be +4
And so on.

:Cheers:

Someone should check my math because I was a philosophy major, but this is how I do it: I divide 28.75 by aftermarket tire size (31, 33, 35, etc.) and subtract the quotient from 1 to get the percentage. 28.75/33 = .8712; 1-.8712 = (approximately) 13%; So, the corrected speed for 33" tires is 13% faster than the stock tires, and the travel speed is 113% of what the speedo says (60mph x 1.13 = 67.8 mph).

31" tires travel 7% faster (60 on the speedo = 64.4mph)
33" tires travel 13% faster (60 on the speedo = 67.8mph)
35" tires travel 18% faster (60 on the speedo = 70.8mph)
37" tires travel 22% faster (60 on the speedo = 73.2mph)

Additionally, you are traveling, 13% farther on 33" tires so 100,000 miles on your odometer represent 113,000 miles actually traveled. This helps with gas mileage calculations.

 

[Mace]

Stock 2F that someone was throwing away for a V8 conversion.
SM420/dual minitruck tcases/14 bolt (4.11 gearing)/39.5" Irocks, Propane and a turbo.


142 hp 221 ft lbs torque at the rear wheels. Lots of parasitic loss in the drivetrain..

 

[DenCo40]

That Change in mph is not straight across the board, it is proportionate..

While 62 might = 70
45 might only be +6
30 might be +4
And so on.

:Cheers:

Thanks that helps me put it in perspective! I always thought my speedo was 10 under whatever I was doing.

 

[FJsnoozer]

Also, there is a member on here selling a gauge face that corrects for 33s! So you won't have to do math at every speed. He ha effectively shifted the dashes 13%

 

[duffontap]

Also, there is a member on here selling a gauge face that corrects for 33s! So you won't have to do math at every speed. He ha effectively shifted the dashes 13%

That's a great option. Similarly, replacing your 18 tooth speedometer drive gear with 16 tooth speedometer gear (from a vehicle equipped with 3.73 gears) will speed your speedo up 12.5%--almost perfect for 33" tires (and it corrects your odometer). SOR sells used 16 tooth gears for $13 and installation takes about 30 minutes.

 

[FJsnoozer]

Good to know. We always did that with the mustang gear change. My gauges need refurbishing, so two birds one stone. Kit is 35 bucks. I am also going to add the EL lighting to the gauge for night driving.

 

[DSRTRDR]

Also, there is a member on here selling a gauge face that corrects for 33s! So you won't have to do math at every speed. He ha effectively shifted the dashes 13%

one can also get a different gear for the speedo that corrects for 33s and shows correct speed on the stock instrument cluster - like this:

That's a great option. Similarly, replacing your 18 tooth speedometer drive gear with 16 tooth speedometer gear (from a vehicle equipped with 3.73 gears) will speed your speedo up 12.5%--almost perfect for 33" tires (and it corrects your odometer).