'79 3peed
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Junior User
Joined: Jan 2005
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From: knoxville
'79 3peed
hey i just bought a '79 f100 a few months ago, and would like to know what the shift rpm's are on it. i dont have a tach so i dont know. also what is the rev limiter set to?
Elder User
Joined: Jul 2004
Posts: 911
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From: Northern Virginia, USA
There is no rev limiter, but you're gonna run out of steam at about 3500-4000RPM. You'll feel it in the seat of your pants. You're in no danger of hurting the motor at those RPM, unless something is really wrong with it (which I doubt). What's your rear end ratio and tire size? Is this the 3-speed column shift?
Elder User
Joined: Jul 2004
Posts: 911
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From: Northern Virginia, USA
I don't have the exact ratios for your 3.03 tranny, but 3.03, 1.79, 1.00 oughta be about right.
You're gonna want to shift at about 18mph and 30mph for normal driving conditions. That puts your RPM's in the 1500-2500 range. You really don't want to go much lower than about 1500 for daily driving. Shift later when carrying loads, going uphill, or having fun.
Max MPH in each gear (assuming 4000RPM rev limit):
1st 25mph
2nd 45mph
3rd 80mph
If all you do is putt around town, you're OK, but with any sort of speed, you're going to rev the snot out of the engine. A 3.08 rear with your 3 speed is a classic combination, gets good mileage (20mpg on a good truck), runs well on the highway , and is well suited to the torque band of the 300ci six. Or you could go with larger diameter tires. But you have a low-speed truck right now. I'd recommend swapping the rear-end gear to a 3.08. $200 in parts, and a garage or a friend oughta do it easily.
You're gonna want to shift at about 18mph and 30mph for normal driving conditions. That puts your RPM's in the 1500-2500 range. You really don't want to go much lower than about 1500 for daily driving. Shift later when carrying loads, going uphill, or having fun.
Max MPH in each gear (assuming 4000RPM rev limit):
1st 25mph
2nd 45mph
3rd 80mph
If all you do is putt around town, you're OK, but with any sort of speed, you're going to rev the snot out of the engine. A 3.08 rear with your 3 speed is a classic combination, gets good mileage (20mpg on a good truck), runs well on the highway , and is well suited to the torque band of the 300ci six. Or you could go with larger diameter tires. But you have a low-speed truck right now. I'd recommend swapping the rear-end gear to a 3.08. $200 in parts, and a garage or a friend oughta do it easily.
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Junior User
Joined: Jan 2005
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From: knoxville
alrighty thanx. since me havin a 3.42, you say go to a 3.08. isnt the higher the last number, the higher top end you'll have? im not sure if im correct on this one. i was thinkin about runnin 3.55's. i mostly use it to drive around town, but i like to have fun at the red lgihts, so...any ideas?...
Elder User
Joined: Jul 2004
Posts: 911
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From: Northern Virginia, USA
Nope, other way around. Gear ratios are #input turns to #output turns. So your driveshaft turns 3.42 revs for every 1 rev of the rear axle. 3.55's would make you rev higher to turn the same axle speed.
The 300 doesn't like to rev (unless you do lots of work on it); it does best doing torquey-things, and you're revving the snot out of it on the highway. You'd find the truck would be quite happy with a 3.08 (I think); smooth acceleration with less frequent shifting.
You'll get much better performance gains by doing the standard carbed 300 upgrades- EFI exhaust manifolds (or headers), Offenhauser or Clifford dual-plane intake and a 390-450CFM carburetor. Search the Inline board; there's TONS of information about the aforementioned upgrades.
But that all depends on how much you want to spend on this truck.
The 300 doesn't like to rev (unless you do lots of work on it); it does best doing torquey-things, and you're revving the snot out of it on the highway. You'd find the truck would be quite happy with a 3.08 (I think); smooth acceleration with less frequent shifting.
You'll get much better performance gains by doing the standard carbed 300 upgrades- EFI exhaust manifolds (or headers), Offenhauser or Clifford dual-plane intake and a 390-450CFM carburetor. Search the Inline board; there's TONS of information about the aforementioned upgrades.
But that all depends on how much you want to spend on this truck.
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Junior User
Joined: Jan 2005
Posts: 94
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From: knoxville
alrighty, well i was told wrong then about the gear ratio. thanks for clearin that up for me. all i have done to it is a brand new 1barrel carb, and open straight pipes, no cats, no mufflers, nada. so...i was thinkin about the offensauser (3) 1 bl. carb set up, but dunno about the power output, plus keepin all three tuned would be a pain, but..any suggestions would help..
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Elder User
Joined: Jul 2004
Posts: 911
Likes: 2
From: Northern Virginia, USA
For drag racing, higher gears are often better, because you get better acceleration.
I bet your truck sounds awesome...
Most anything is better than the Ford YF carburetor. Carb, intake, headers/manifolds, and you'll grin from ear to ear.
I bet your truck sounds awesome...
Most anything is better than the Ford YF carburetor. Carb, intake, headers/manifolds, and you'll grin from ear to ear.
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Elder User
Joined: Jul 2004
Posts: 911
Likes: 2
From: Northern Virginia, USA
Yup. And with a top-end of 80mph, you're already at serious drag-race gearing. :-)
I wouldn't go with any higher gearing unless you're gonna swap in an overdrive transmission or put on large tires.
I wouldn't go with any higher gearing unless you're gonna swap in an overdrive transmission or put on large tires.
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