Highway speeds

[Perfect Obsession]

[quote author=burnt03 link=board=1;threadid=15679;start=msg149113#msg149113 date=1083520772]
'78 2F, stock aisin, stock 4spd, 31x10.5R15 tires
I have to have it down to the floor most of the time on the highway in order to keep it half ass near the speed limit. When I hit hills it's all over.
On a flat the other day I thought I'd see how fast I could get it going, had it pinned for a long time and never managed to get over 60.
What might be causing this or is it normal?
And no, it's not in low range
[/quote]
I agree with Idave and I would add specific knowledges:
1) Tire
- a) Stock tires have 28" diameter (i think) so speedo correction factor is: actual diameter / stock diameter than about 1.107 = 31/28 therefore actual speed is 10.7% more than the indicated speed.
- b) Low trail tire pressure generates high rolling drag which is power eating on highway.
2) Engine performance:
- a) Cylinder compression shall be checked
- b) Distributor/diaphragm adjustability check (upon rpm and vacuum, ...)
- c) Carburation/air feeding (fuel/air filters, ...)
Running at 60 mph, is cruising speed for my 2F. Running at 70 mph is fuel sucking speed.

 

[fj40crusher]

74 fj40 with a 3 speed and a ford 302...60mph and it's screaming at 3000rpm.

Honestly, I wouldn't want to go much faster then that in my 40 anyway.

 

[Rice]

Hit one of the online RPM calculators and plug in tire size, engine RPM and rear end ratio for the true measure of your speed. Then you'll know if it's the speedometer. That said, if it's right then go for the tune up option.

Here's a calculator:

http://www.4wheelerssupply.com/Tech/rpm_calculator.php

 

[IDave]

60 mph is comfortable in my FJ40 F stock engine, stock sized tires. 70 is not except on an extreme straightaway. I was able to push it to 74 mph on the freeway one day (speed checked by GPS) while pulling my 2200 lb travel trailer, 3400 RPM on the tach. I bet I can get it to 80-85 without the trailer, but I haven't tried.

The fuel efficiency curve is such that 45 mph is the best mpg, fairly flat from 35 mph to 55 mph. Drops off fairly steeply on either end after that.

 

[IDave]

[quote author=Rice link=board=1;threadid=15679;start=msg150460#msg150460 date=1083705344]
Here's a calculator:

http://www.4wheelerssupply.com/Tech/rpm_calculator.php
[/quote]

That's cool. I plugged in my numbers for 70 mph and came up with 3333. Is that about close to what I said above or what?

 

[65swb45]

I am going for the carb here, but from a different angle. I think you are running a one BBL carb cleverly disguised as a 2bbl! Intrigued? Read on.

All the 74 and newers run a series of bushed rod linkage from the pedal to the carb that is somewhat less than efficient (to put it nicely) Have somebody slowly push the pedal to the floor while you watch the linkage. First note how far the pedal has to go down before the carb even STARTS TO REACT! Then, when you get done cussing the thing out, pay attention to whether it ever gets to the point of kicking the arm on the secondary. You may only be running a one barrel!

Even if you do get a little kick, remember that the vacuum diaphram actually controls the secondaries, unlike the 70-74 vintage. If the diaphram is internally torn, or in any way recieving less than a perfect signal, guess what? BTW, that diaphram is NOT part of a standard rebuild ANYWHERE!

 

[wesb225]

when i first got my 40 it had a worn out engine and a carb that needed a lot of work. We just put a Weber 38/38 on it and i can easily get up to speed and accerlerate faster. I would highly recommend the Weber 38/38