heres a link to my mods:

http://www.lvfbody.com/whoismember.asp?memberID=86


I am having a new rearend built, and was planning to install somemore 4.10s.

with my previous 4.10's, on 255/16 BFG DR's...I go thru the traps at 4500 in 4th gear. I shift @ 5800 rpm.

I was thinking about going with 4.30's to get a little closer to 5800 when I go thru the traps.

but I'm concernd that I may not have the power or RPM's to pull the 4.30's.....

I also would like to find an gear ratio calculator to see what my revs will be in 6th on the freeway with the 4.30s and stock 245/16 street tires.

 

From your numbers, it sounds about right. Going from 4.10 to 4.30 should mean you'll cross the finish line closer to your shift point. You already know you've run out of track before you run out of rpm so the 4.30's should help. When I had a 383 and 3.27 gears I was doing the same thing. Shifting at 6700 and crossing the finish line at 5500. I needed something like 3.90 gears.

The other option is to put shorter tires on the car. If those tires you have are 28" tall, going to a 26" tall would be similar to changing the gears. I never like suggesting a shorter tire though. The taller, the better, then adjust the gearing to match the tall tires.

I'm assuming this is for a 10 bolt? I didn't know they made 4.30 gears for the 7 1/2, 7 5/8" 10 bolt. The only deep ratios I've seen are 3.73, 4.10 and 4.56. The 4.56 needs a special cross pin.

A 9" or 12 bolt will have 4.30 ratios or something very close to it depending on the gear manufacturer. I wanted 4.30's for a spare center section and only Strange Gears makes 4.30's for a 9". Everyone else makes 4.33.

 

thanks for the reply...thats the info I was lookin for...

and the gears will be for a Ford 8.8/F Body conversion that I am going to have built here very shortly.

 

Stephens reply brings up another question.....what size ET Streets to run......they will be mounted on factory 16" salad shooters.

I will definitely be running a 255/50/16 BFG DR on the street as well as the track.

I had planned on using the 26x10.5/16 ET Street or the equivelent Hoosier Quick Time Pros's if I decide to go with a DOT Slick.

I'd also like a few more opinions on the gear ration question as well.....thanks.

 

Sounds like the problem that was happening with my father's challenger he built when he owned his machine shop in the 70s.

It would run 12.40s@118mph on street tires on all motor(built 340) going through the traps at around 6600rpms. He shifted it at 8300 rpms. He definately would have went faster in that car with a better gear, if he could get decent traction with his street tires.

 

First, let's give you some very useful calculations:

Tire diameter (in inches) = ((width x ratio x2) / (25.4)) + rim diameter. Where ratio is the second number, in a decimal (so for a 245/50/16 tire, you enter ((245 x .50 x 2) / (25.4)) + 16

Speed in MPH = (RPM x Tire diameter in inches) / (gear ratio x tranny ratio x 336)

Now I'll calculate out some things for you. Of course 4th gear is 1:1 ratio, while 3rd is a 1.30 ratio. Since it is a manul, there is no converter slip, but tire diameter can be affected by wear, inflation, manufactured diameter outside the exact calculated diameter, and growth under speed....but it won't be off THAT much.

255/50/16 BFG DR's = 26.04"
245/50/16 stock tires = 25.65"
26x10.5x16 ET Streets = 25.9"
26x11.5.x16 ET Streets = 26.3"
26x9.5x16 Hoosier QTP = 26.1"

With the 4.10 gear and stock tires, at 5800 you are good for 108 MPH.

5800 on your BFG DR's would be 109.63. But there is no way you are going through the traps in 4th at 4500 w/ a 4.10 and those tires; that = 85.06 MPH.

With a 4.30 gear, 5800 on your BFG's = 104.53. Errr...that's VERY marginal at best. Add any mods, and you'll be screwed. Your other problem; if you want to stick with a 16" rim, the biggest diameter you are going to be able to get is a 26x11.5x16 ET Street (26.3"), which at 5800 would only give you 105.58 MPH with a 4.30. There are no 28" tall tires for a 16" rim, so you are SOL there.

Another question is your future plans. If you plan on stick w/ a stock heads/cam motor and no power adder, then IMO your best bet would be to stick with 4.10's and running any of the tires mentioned above other than the stockers. OR, you could run say, a 28" tall tire on a 15" rims, at 5800 and a 4.30 that would give you 112.4 MPH, which should be plenty for you.

But if you want to add nitrous or forced induction, even on stock heads/cam, 4.30's will screw you. With 4.10's, you'll at least be able to run a 28" tall tire on a 15" rim and have enough room to at least have marginal gearing at 5800. Of course, you get a cam in there with some more RPM ability, and everything changes. Just depends on what you plan to do in the reasonable future.

 

WOW!!!!....now thats the response I was lookin for!!!!!!


"With a 4.30 gear, 5800 on your BFG's = 104.53. Errr...that's VERY marginal at best"

I pulled 104.2mph with 3.42 gears, spinnin a 2.4 60ft on kumho street tires...and that was goin thru the traps in third, hittin the factory 6200 limiter just as I pass the lights.

I shift @5800 rpm.

whats gonn happen when I install the 4.30's(or even 4.10's) and start cuttin, say, 1.9 60fts???

now for my plans:

1. There may be a SC in my future, but not for a few years probably( all depending on $$). but I will go Heads?cam before I install an SC.

2. eventually, there will be heads and cam, but also, probably not for atleast a year to 2 years(again, all depending on $$)

I have considered running a 28" tire, but I am unsure of 2 things:

1. will a 15" rim fit on stock rear brakes??
2. any other mods neccassary to fit a 28" tire??

as far as the 4500 in 4th issue..its what I remember, but its been almost 1 and 1/2 years since the 4.10's where in the car.

my best time in vegas with the 4.10's, on the BFG's, was a 13.69 @ 102.28, w/ a 2.01 60ft...and the next pass the stock carrier went to lunch.
now, I am 2000ft lower in elevation, and I run the time in my sig, with 3.42's, on street tires(stock size) cuttin crappy 2.4-2.6 60fts.


again Joe...thanks for the awesome info.....

 

A 15" rim will fit but you will need to grind the cooling fins and probably cut the pad clips.

A 28" tall tire will fit but you will need to cut the lower outside edges of your wheelwells. I just used a hacksaw on mine to trim the plastic and about 1/2 inch of metal that was in the way. Steep gears and a taller tire is generally the preferred way to increase traction and performance at the starting line.