4:10 or 4:30 gears for me

[82 GT]

I'm ready to order gears but I want to find out which set would be better for my setup.(signature below)
My cams powerband is between 2500-6000 rpms
I "might" be running a 28 inch tall slick.

What rpms are some of you guys turning that have either 4:10 or 4:30 gears
I don't want to "run out of gear" before the traps.
I'm at about 4500rpms now through the traps with 3:73's

[88fivepointoh]

4.30's all the way, You'll be happy with the performance probably doing about 2800 at 60mph.. Not to bad for highway but awsome at the track!

[Ieatcamaros]

What size tire were you running when you ran the other night? With a 28" tire and 4.30 gears, you should cross the line in the 5200-5600 range. The 4.30's get my vote as the minimum gear to use.

And with a 26" street tire, you would be doing 3300 at 60 mph.

[82 GT]

I was using 225/60/15 tires. I may as well have been using my daughter's 10 speed tires with the traction I had.

[Ieatcamaros]

That is a 25.629" tire, and with that on the street (driving to the track) you would be running 3383 RPM @ 60MPH. There are to many variables to give an exact finish line RPM, but the above figures are ballpark. I like the analogy with the 10 speed bike tire. That was funny.

[88fivepointoh]

Man thats a bit high, I mean I am a 5spd guy myself so i was wrong on the RPM guess.. sorry.. but still, 4.30's!

[I8URZ282]

If your not gonna run any spray on this motor I'd go 4:30's I ran them on my 351w too and I liked them. Personaly I'd keep the 3:73's and save the money from the gears and install and buy some juice for that thing and some tires. If you have traction problems with the gears you have now it aint gonna get better with 4:30's. Bill

[Ieatcamaros]

He has a C4, no overdrive. 3rd gear is 1:1. I love the c4 and all, but give me a 5 speed.

[I8URZ282]

I like my c4 at the track , but I wouldn't want to drive down the interstate with it

[82 GT]

Hey, ieatcamaros , where are you getting the math formulas to calculate engine speed/MPH? I couldn't find any for a C-4, they were all for the T-5

Anyway, what would be my RPMs at 65-70mph using the same 225/60/15 tire with a 4:10 gear?
Those 4:30's seem a bit much for the street. I really think I would run out of gear before I hit the traps though shifting at 6000rpms.

i8urz282 , I am getting slicks as well.

[crazypete]

Go to the link below and solve your rpm/gear/tiresize questions definitively. It's for trucks but it uses the standard ford transmissions. It's got fields for c4(auto), AOD, manual (4 spd) and 5 spd (t-5).

http://www.4x4cyberstore.com/website/rpmchart.html

On 15 inch tires with a stick, 4.30's is a bit much if you have any intention of streeting the car at all. I pull 3k at 75 and it feels like an awful lot. I couldnt IMAGINE running 3.3k at 60 mph!

Do this:

1. pick your maximum cruising rpm that you would want to maintain for hours at end
2. pick your average cruising speed that you find yourself drifting to
3. Match the 2 using the calculator and you have your gear ratio. I think you will end up with 3.73's

with 4.10's, a c4 and 225/60/15's you'll be doing 4150 at 75 and 3592 at 65 with a c4. Ouch...

I know the aod "sucks" but you might consider switching to an automatic with an OD (and beefing it up with a lentech, a hardened lockup shaft...etc) and then you can jump up almost 2 gear sizes and gain the acceleration through the first 3 gears and use your OD for cruising when you're driving it "like just a car". For comparison, the same setup with an aod only does 2800 at 75mph. Running at high rpms for a long period of time has strange side effects like the oil heating up and the oil pressure dropping and I dont even want to think about the transmission fluid temperatures. Just my thoughts....

[red82gt]

Keep the 373's and run a 26 inch slick instead. The formulas work well for street tires or drag radials but slicks grow down track and by the end of the run, your 28" tire is probably more like a 29.5" tire at the finish line. My RPM at the finish line and MPH on 26" slicks was always about 500rpm lower than what it should have been according to the calculators.
What did you run at the track? if you were only at 4500 on a 25.7" street tire then you probably would be best with 4.10's and a 26"slick. I don't think you'd run out of gear with 4.30's and 28" tires (slicks anyways).

[I8URZ282]

The difference in your 1/4 mile times isnt going to be much from a 3:73 to a 4:10 . I think you'd be better off spending your hard earned $ elsewhere.
Do you have good axles and posi yet for those slicks?

[Ieatcamaros]

I don't use any of the formulas online, I have my own. I have it on a spreadsheet if anyone is interested in it. I got 100 rpm difference in what crazypete posted. At 65, I got 3495. At 75, I got 4032 RPM. Not enough difference to matter, but it is the sole reason I use my own formula. Your rpm's at 68 mph(65-70) with a 4.10 gear is 3656. If you want to drive the car on the street but optimize at the track, I would go with 4.10's since you are going to be putting in an 8.8 anyway. Me, I would put 4.30's in and trailer it to the track. You got your 88gt for the street. IMO, your only other option (besides the high rpm's on the highway) would be to get a 4.56'd 8.8 and put a lentech aod in. That would be the SH1T!

[82 GT]

Originally posted by I8URZ282
The difference in your 1/4 mile times isnt going to be much from a 3:73 to a 4:10 . I think you'd be better off spending your hard earned $ elsewhere.
Do you have good axles and posi yet for those slicks?

I have an 8.8 I'm getting ready to buy and install soon. I don't really think I need 31 spline axles at this point in time.

[82 GT]

Originally posted by Ieatcamaros
I don't use any of the formulas online, I have my own. I have it on a spreadsheet if anyone is interested in it. I got 100 rpm difference in what crazypete posted. At 65, I got 3495. At 75, I got 4032 RPM. Not enough difference to matter, but it is the sole reason I use my own formula. Your rpm's at 68 mph(65-70) with a 4.10 gear is 3656. If you want to drive the car on the street but optimize at the track, I would go with 4.10's since you are going to be putting in an 8.8 anyway. Me, I would put 4.30's in and trailer it to the track. You got your 88gt for the street. IMO, your only other option (besides the high rpm's on the highway) would be to get a 4.56'd 8.8 and put a lentech aod in. That would be the SH1T!

I went to the analyzer on here and used the TOP SPEED calculator to find my rpm/mph but I only used the 4th gear column since that is a 1:1 ratio I need for my C-4 calculations.

With a 4:10 gear and 25.6" tire(225/60) I would be at 3500rpm at 65mph and I would be at 111mph in 3rd at 6000 which is my shift point.
With a 4:30 gear and same tires I would be at 3700 at 65 and 106 at 6000 in 3rd gear.
Using a 26' slick is only 200rpms less.

Ok, here is what I discovered which kind of changes things a bit for me.
Judging from that calculator, I don't have 3:73 gears like I thought I had or was told I had at one time. Instead, I have 3:27 gears!!
My best time on street tires is 13.78 at 105mph with traction problems.
When I get slicks, that's only going to get better. So I guess I need either 3:73's or 4:10's

[red82gt]

With 26" slicks and a 5 speed, I would cross the line in 3rd @6400 at 107+ MPH, according to the analyser, this should have been only 100mph so do remember to factor in tire growth. I think 373's and 26" slicks will be your best combo. If you get the 28" slicks, you'll need at least 410's but your freeway crusing will suck.

[Ieatcamaros]

I would get the 4.10's cause it is easier to change tires than gears. Or maybe it is just me, I love 4.10's on the street. But since you are going to be inside that 8.8, why not go ahead and put those 31 spline axles in there? With slicks and good 60ft times, you will want them in there.

[82 GT]

I went ahead and ordered the 4:10''s. I don't have enough cash to do an axle swap right now. Besides, this will see more street than the track.
I'm hoping that the gears and slicks will put me into the 12's now.

[Ieatcamaros]

I'm hoping that the gears and slicks will put me into the 12's now.

You won't be disappointed.