i put a tach in my 1984 f150 and it's topping at 2,000 rpm thru the gears and goes to 2500 under no load. i know they make max tq at like 1200 rpm but i thought it would rev 3-4k. is this normal? it has a stock carb from a 1980 and a long tube header w/ true duals, msd coil, electric fan, new plugs wires and dizzy cap.

 

Do you have the tach set to the 6 cylinder setting? Stock they should freely rev to about 4500-5200rpm, the built one in my 84 F250 saw 5500-6000 often.

 

Is it an automatic or a manual?

By topping at, do you mean that you can't rev it any more? What's limiting you?


You should be able to rev to at least 3500 stock. Peak horsepower for the carb'd 300 is 3000 RPMs, so you should be capable of least that.

I'm assuming that since you have headers and duals, you don't have cats (was gonna suggest a plugged cat). With headers, you should be able to rev over 4000 RPMs easy.

 

its a manual trans and i got it to 2500 in first but all others lost acceleration at 2k. and no no cats and this is an older tach and it does not have the 4/6/8 option. (maybe its made for v8's only?) it does sound like your reving the hell out of it when its at 2500. (to me it sounds like 3500-4000 but thats not what the tach says)

 

abandonedbronco thats a nice bronco you got im helping a buddy build his 78 back up w/ a built 460 and 40in tires with lockers front and rear. its a beast

 

Most tachs have a removeable back cover, the switch is inside there. There should be a screw or on some the thumb screw the wires pass through is what holds it all together.

 

Thanks!
I've had a lot of fun with it. Broncos are the best. Especially those 78/79s. You and your friend should have a great time building one of those up.

 

yeah his father built it 25 years ago and sold it after a few years and lost track of it and he found it a few months ago but it was a bit rough so he is saving it / making it a little better. they have like 5 or 6 78 79 broncos.

 

thanks i will remove it and take it apart some and try to find the switch. its an old sun super tach II

 

bingo i found a white switch for a screw driver and now things look much better. 4k with a quick rev. thanks for the help!!

 

Cap on a 300 stock is about 3600. The stock valvetrain aint there for 4500. Do that and you will be replacing the cam and lifters.

I have seen this done several times by morons. A built engine with the propper camshaft and lifters can touch up into the 5k range safely. There is no power in them above 3200 in a stock carbed engine anyways.

That is some realy bad advice six. This guy is going to ruin an engine trying to see if his tach works?

 

2000 RPM is where my stock 300 would start to choke out, my shift point was between 1800 and 2000. At this point the motor was screaming. I think you guys who are seeing 4-5000 RPM out of a stocker have some calibration issues, I can get to 3000 RPM+ now, but only after a Clifford intake and EFI manifold install. Check your cruise speed at say 55mph, and punch your info into a gearing calculator. My tach is calibrated correctly, and I was seeing the RPM range indicated in the first post.

Thinking you had it set right the first time, anyone seeing above 3000 RPM from one of these motors under normal conditions has something set wrong.

 

Well, I must have unknowingly ruined all the 300-6 engines I have owned then- Except that all of them left my ownership under their own power, typically in much better condition than I received them in. I would accept your statement with proof. Show me a properly maintained engine that has valve float issues before the stock carb runs out, or bent pushrods or anything else people say these things do, and I'll accept it. Until then, I will maintain that the engines I have had (aside from the built one that would turn 6k and the current high compression one) are your average 300, and demonstrate typical capabilities of one of these engines.
Spreading rumors like this is why people yank these engines for a 302, they read in forums that they can't spin fast, they'll flatten the cam if you take them on the freeway, or that there isn't any potential power to be had, and those are lies. This is a superb engine solidly reliable and capable of being built into a very reliable performance engine as well.

 

Do you know for a FACT that you had a properly calibrated tach? Did you even run a tach, or are these just estimates? Seeing just how hard I had to push my 300 to get even 2200 RPM in 3rd before shifting, I have a hard time believing the numbers you're claiming.
And my numbers are based on an accurate aftermarket tach, properly set and double-checked using a gearing calculator.

 

i changed the adjustment on the back but i cant read what it said because the wrighting is so small. it came from v8 and that was the reading from the start then was the current reading and the next click was reading nothing. i have a better tach i got for my mustang and maybe i will hook it up and try it.( i can see the wrighting for the cylinders on it,i just hate redoing the wiring side of it)