Thread: first 390 build

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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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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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Originally Posted by DennyW

4.56 gears, 2500 rpm's, at 55 mph, with a final transmission ratio of 1.00, tires would be 33.708...Does that make you happy ? hahaha

Looks right to me Denny. Thanks.

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Ok I took it to my friend he knows about rear ends he just pulled the differential out and counted the teeth he said it was a 3.70 open rear end
Which I figure is a pretty good set of gears

Originally Posted by DennyW

Well, your speedo gear is off then...

Yea verily.

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Originally Posted by DennyW

Well, your speedo gear is off then...

Denny speaketh truth!! If you were on 33's, running 2500rpm (not "About"), with no OD you were turning 66.5mph, not 55. Maybe that explains the string of tickets.....

You guy may very well be right the Speedo cable bounces pretty hard

Time for a new cable, its been spun pretty hard I think I had my engine spun around 120 after that the cable just bounces

Riley-------a question for you ----did the guy remove the whole center section? had to raise truck, take off wheels, brakes and pull axles?

On a nine inch ford you can just remove the pinion to count the teeth-only a few "non-hunting" ratios that matter about where they are tooth matched on re install.

I honestly don't know, I dropped my truck off at his place for a while to let him do it,

Are you doing any of this yourself??????? or just completely farming it out?????

If you are farming it out---the people doing it won't be very receptive to any thing you pass on to them from the "net--------

Yes I put my heads together my self I will be putting the engine together I built my truck from the ground up and im more of a paint and body man not a mechanic, so I needed one of my good friends to see what my gear ratio so I'm not guessing

that was an era of classic looking trucks-have you posted any pics of it?


Is your gas tank behind the seat?

Originally Posted by riley1996

Yes I put my heads together my self I will be putting the engine together I built my truck from the ground up and im more of a paint and body man not a mechanic, so I needed one of my good friends to see what my gear ratio so I'm not guessing

It's good not to be guessing when the facts make huge differences in the approach. One thing to consider, you mentioned in an earlier post,

Originally Posted by riley1996:550437

....I'll be running a trans cooler...

Noble, OK sees large seasonal swings in ambient temperature with winter highs below freezing. An uncontrolled tranny cooler piped into your line will likely keep your tranny well below it's design operating temp. The reason that the cooler is in the radiator is to both heat & cool the fluid, not just cool. Loading it when cold can be worse than letting it get a little hot. You're much better off with no external cooler, or if one is needed, using a cooler with a thermostatic fan so that it only pulls air when the fluid is over temp. Just some gray hair advice, and you may choose to ignore it.

Best of luck with your build.