I have recently built a 300 for my f150, before i new anything about cam shafts i slide a 270 clifford cam in it, and now that its in my truck, im running 2.75 in the rear end with a stock c-6 and i can hit 45mph in first gear and it screams, but it doesnt start screaming till around 30-35 mph, should i put a high stall torque converter in it? and if so which brands are good?, or should i stick with a shift kit that would shift later and harder, or should i throw both parts at it? does anyone have any experience with big cam 300s bolted to automatics? any thoughts? thanks!

1981 2wd F150 Custom
clifford 6=8
EFI exhaust
walker y-pipe
Holley 390 CFM 4brl
Clifford 270 cam kit
C-6 Auto
MSD rev limiter Ignition (not installed yet)

 

from Clifford's website:

This camshaft creates a strong torque curve just off idle until 3,400 RPM, then Peak horsepower is seen around 4,500 RPM

i wouldn't throw a high-stall torque converter at it. if you want it to shift harder, sure- you could install a shift kit.

i'm not sure i understand your problem- what's wrong?

 

the problem is i hit power band at 30 miles an hour, its like a stock motor until then, and to even reach powerband i have to shift it manualy, the automatic shifts at way to low of speed, i shift from 1st to second at top end powerband around 45mph and i have to wait till 60mph to hit powerband again, its kindof annoying, im just seeing if anyone has messed around with torque converters or different gearing or shift kits, and what there findings have been

 

Your problem isn't with needing a higher stall converter or shift kit or anything like that.

What you need is a different set of rear end gears. 2.75 gears is too tall for the way your motor is built. Try a set of 3.27 or 3.50 gears to really wake your truck up. The motor will rev up to a higher RPM faster, which means it'll get into it's power band quicker as well. Beware though, the lower rear end gears will cause your cruising speed to change and will impact your gas mileage.

 

we probably need to know more about your setup.

what size tires?
what rpm do you want to be running at a specified speed?
what rpm are you running at that speed currently?

as far as the auto shifting too early- you can just adjust the vacuum modulator.

 

agreed. what you've done is build a motor for higher rpm, but you've got rear end gears designed for lower rpm. its a mis-matched setup.

if you're running huge tires, you may be able to move to a smaller size- but if not- then as '83 said, you may be looking at a gearing change.

 

thanks guys! i forgot to mention i was thinking of re gearing as well, i need to throw a tach on it,, i have no clue what my rpms are, 235x75 r15s for tires my summer tires are a little larger in hight on the rear im just not sure the exact size. i think i will look into the gears before anything maybe a shift kit too just cause the 40 bucks,

 

With 235/75/R15 tires (which equates to about 30.5x9.5x15) and 2.75 gears with a C6 automatic, you're turning about 1711 RPM at 55 mph. Good for gas mileage.

With 3.27 gears, the same tires, and the same transmission and speed, at 55 MPH you're turning 2034 RPM. Much better cruising RPM for the way the motor is built. You can step on the gas and it'll immediately be in it's power-band if it kicks down. Where the big difference is, is in gears 1 and 2.

In 1st gear, 30 MPH, with the same tires and 2.75 gears:

2.46 x 2.75 = 6.76 final drive ratio.

2294 RPM at 30 MPH with 235/75/R15 tires.

With 3.25 gears:

2.46 x 3.25 = 7.99 final drive ratio.

2711 RPM at 30 MPH with 235/75/R15 tires.

That's quite a difference.

If you have a 9'' rear end, you'll probably have to get 3.25 gears, as I don't think they make 3.27 for the 9'', only the 8.8. You'll also have to change your speedometer gear so your speedometer reads correctly.

I'd definitely go with 3.25 gears. If I remember right, you can also change the modulator valve to control how HARD the transmission shifts. I wasn't aware that you could adjust them to change the shift points, but if you can, go for it.