Thread: first 390 build

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Return the converter and get some rear gears

what do you have for a dist

Originally Posted by jerry clayton

Return the converter and get some rear gears

what do you have for a dist

Msd 8595 pro billet
And If I get lower gears with 295/60r15 wheels and tire ill be turning 3000+ 55 and up wont I?

why not just use a stock ford dist and spend those dollars somewhere else?
I haven't run any numbers on the revs but IIRC some of my earlier trucks did cruise at 33oo at 75mph with the trailer 373 gear and the 16.5 truck wheels/tires

just driving around with 3.25 gears you won't get in into a hp range on the street at the speeds you'll get to so you need to do gears and cubes
that 110 octane will cost you about $15 per gallon plus shipping unless you have a dirt track near you that has it

Originally Posted by jerry clayton

why not just use a stock ford dist and spend those dollars somewhere else?
I haven't run any numbers on the revs but IIRC some of my earlier trucks did cruise at 33oo at 75mph with the trailer 373 gear and the 16.5 truck wheels/tires

just driving around with 3.25 gears you won't get in into a hp range on the street at the speeds you'll get to so you need to do gears and cubes
that 110 octane will cost you about $15 per gallon plus shipping unless you have a dirt track near you that has it

My truck ran at 2200rpm at 32 mph with pretty tall tires then I was gonna put some 15x10s with 295/60s and sure I was gonna run 2200+ around 25mph so I was pretty confident it would work out and the msd distributer was new in the box as a bday gift and the race fuel is 5.99 a gallon for 102 octane

Originally Posted by jerry clayton

why not just use a stock ford dist and spend those dollars somewhere else?

Jerry, I suggested that he should run a very strong ignition system because the motor will have high cylinder pressure with 11.19:1 SCR and a short cam, closing the intake valve sooner. He can get by with it without detonation because of the quality of the fuel he will use. I would even suggest tightening up the spark plug gap a little. I figured his DCR at 9.78:1....

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post number 6 you said 110 octane

if you were 2200rpm at 32 mph it hadn't shifted into high or converter/clutch slippage----my 1999 truck with 16inch wheels runs 75mph at 2200

if you turn 2200 at 25mph, you'll only run 75mph at 6600rpm!!!!!!!!

I'm goin to bed---------i suggest you take a clean sheet of paper and re plan this build

I'm not goin to replan this build, I think techinspector was right I should keep my stall, I will run a trans cooler,I have confidence in my builder that he wont let me build something that will be a turd, I'm confident it will be a damn good motor

And yes I admit I messed up I got a little comfused on the rpm, I misprinted I ment 102 not 110, I will figure this out

I couldn't find a 295/60r15 tire listed, but a 275 is a 28" tire. Assuming that diameter, the C6 with no OD and 3.25's you'll turn 2730rpm at 70mph.

I just did some research, I turn around 2500rpm at 55mph with a 33 tire I think I actually might have 3.73 4.10 4.11s, there ain't no slippage it shifts into 3rd so I might actually have a pretty low ratio

Originally Posted by riley1996

I just did some research, I turn around 2500rpm at 55mph with a 33 tire I think I actually might have 3.73 4.10 4.11s, there ain't no slippage it shifts into 3rd so I might actually have a pretty low ratio

Riley,
You're "around 2500rpm" is troubling, but let's run the numbers. You mentioned your 2500 @ 55mph again, and Denny assumed 28" tires, but you've said that your running 33's with those numbers. If we run the numbers, 1.0 final drive ratio, 33" OD rear tires, 55mph then you'll be spinning 2,554rpm with 4.56 gears; but you'll be at 2,302rpm with 4.11's. Not sure which "around" is closer for you, but if you were cheating a little above you've probably got 4.56 rear gears, of if you were below by a bit more margin then I'd say 4.11's. If you still had the 33" tires then it's a surety that you don't have 3.73's.

I agree that you need to get your hands around reality on this truck, and quit dealing with estimates, abouts, and guesses and start tossing out facts. It's not that hard to lift the rear wheels, chalk mark the tire and driveshaft and count the turns of the driveshaft with ten turns of the wheel.....

duplicate post

Originally Posted by rspears

Riley,
You're "around 2500rpm" is troubling, but let's run the numbers. You mentioned your 2500 @ 55mph again, and Denny assumed 28" tires, but you've said that your running 33's with those numbers. If we run the numbers, 1.0 final drive ratio, 33" OD rear tires, 55mph then you'll be spinning 2,554rpm with 4.56 gears; but you'll be at 2,302rpm with 4.11's. Not sure which "around" is closer for you, but if you were cheating a little above you've probably got 4.56 rear gears, of if you were below by a bit more margin then I'd say 4.11's. If you still had the 33" tires then it's a surety that you don't have 3.73's.

I agree that you need to get your hands around reality on this truck, and quit dealing with estimates, abouts, and guesses and start tossing out facts. It's not that hard to lift the rear wheels, chalk mark the tire and driveshaft and count the turns of the driveshaft with ten turns of the wheel.....

Roger and I are on the same page.
I plugged 2500, 55 and 33 into an online calculator and it spit out 4.46:1 gears.
Here's a list of available gears for a 9"...
Ford 9" Differential Parts | West Coast Differentials

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68 F100-------was the truck a 390 from the factory? Do you have a 9inch ford or Dana rear end? They should have a tag showing the ratio and whether its a locker.
Did you ever see the movie-Funny Car Summer with Jim Dunn? My 1970 truck was in it .

This is what gets me the truck was a 390 from factory, now the rear end is a 9 ford rear end, but no tag I spun the drive shaft one time and the tire was already a half a quarter to one revolution but it pulls to hard off the line to be a really tall gear and turns 2500rpm at 55mp but their ain't no slippage and the its shifting info 3rd, so I'm lost checked my tack changed it and it was dead on so I'm at a loss

Originally Posted by DennyW

That would make the gear ratio about 3.78 with 28" tires

Well DennyW I'm gonna take your word for it, I think my setup will work a whole lot better than I thought, but i appreciate the help you guys have givin me, I mean yall don't have to sit here a help me with my problems yall do it because yall want to so I really appreciate it guys thanks