Author Topic: question about 8" rear end gears  (Read 7664 times)

Giddyupv8

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question about 8" rear end gears
« on: March 28, 2010, 08:24:56 AM »
Hi guys, first off I wanna say I'm liking this site. Navigation is relatively easy- even for a computer  illiterate  guy like me lol. Any how, now that my motor is finally done, I am planning on changing the gears on the rear end. I currently have stock gears. What would you recommend for a street and strip gear. I don't plan on doing a lot of strip racing- just want to see how she will do in the qtr. I also would like her to be capable for highway use and not scream like a banshee @ 4 gran. Just looking for a good gear to make her jump off the start.
Thanks,
John

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Re: question about 8" rear end gears
« Reply #1 on: March 28, 2010, 10:30:09 AM »
well if you have plenty of power stick with the lower ratios, like 3.23 or 3.55

66GTKFB

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Re: question about 8" rear end gears
« Reply #2 on: March 28, 2010, 12:12:41 PM »
First - welcome. That's a lot of engine in such a light car - not a criticism, an observation. I've seen only two other Mustang IIs set up for racing, an injected 302 (5.0?) and a 351W with a 4150 Holley. Both ran well at Laguna Seca.
As to the rear axle, get rid of the 8 inch setup and replace it with a 9 inch. This will require some customizing of axle tubes and shafts but it will hold together. A 3:25 set of gears will be your best bet for street but that also depends on the transmission type.
Jim

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Re: question about 8" rear end gears
« Reply #3 on: March 28, 2010, 12:43:31 PM »
Since you say you aren't going to be doing a lot of racing,  Jim is right.  Anywhere from 325's to 355's.  I have 355's in my Mach, and the launch is incredible.  373 to 410's will be too much for highway driving.  However, that 8 inch rear is a tough rear, and will stand up to 450 horses in most cases.  Any more ponies than that will cause you to have to go to the 9 incher and some serious mods to the undercarriage, especially the suspension and transmission.   You'll also have to tie that fox body together with some frame rails otherwise she will twist like a mofo. 

Giddyupv8

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Re: question about 8" rear end gears
« Reply #4 on: March 28, 2010, 03:08:56 PM »
Well the 8" rear is a stout rear end I defiantly agree, Ill probably keep it for now since I have no money left to spend on her now:(. I'll check into the gears you guys mentioned and decide . I already have a TCI Streetfighter C-4 tranny rated well over my new hp. So the trannys fine. I also bought sub- frame connectors to tie the frame together, the motors got brand new custom motor mounts, so Im not worried about that end either. My ultimate goal is to pull the front wheels off the ground, I think I will have that chance with this build. Thanks for the suggestions, John

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Re: question about 8" rear end gears
« Reply #5 on: March 28, 2010, 03:33:35 PM »
OK, sounds like you have your shit together.  Keep us posted. 

66GTKFB

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Re: question about 8" rear end gears
« Reply #6 on: March 28, 2010, 04:55:26 PM »
Well the 8" rear is a stout rear end I defiantly agree, Ill probably keep it for now since I have no money left to spend on her now:(. I'll check into the gears you guys mentioned and decide . I already have a TCI Streetfighter C-4 tranny rated well over my new hp. So the trannys fine. I also bought sub- frame connectors to tie the frame together, the motors got brand new custom motor mounts, so Im not worried about that end either. My ultimate goal is to pull the front wheels off the ground, I think I will have that chance with this build. Thanks for the suggestions, John
Stout? Possibly, but I don't think so, especially at your anticipated horsepower goal. I'll pose a question then, if an 8 inch is strong enough for your engine, why does my "K" car have a 9 inch rear axle? Why did all 390CID (and up) engines in Mustangs get 9 inch rear axles? You better do some more thinking.
Jim

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Re: question about 8" rear end gears
« Reply #7 on: March 28, 2010, 07:34:44 PM »
Jim, its not a matter of thinking , its a matter of funds or lack of. Sure Id love to have a 9" rear and I will- someday, I spent all my "car money" on the 363 short block, so for now, the 8" is fine.

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Re: question about 8" rear end gears
« Reply #8 on: March 28, 2010, 07:51:24 PM »
That 8" will be just fine.  Jim is lucky to have a 9" in his K car, but that is overkill IMO.  Sure, it would be nice to have one, but not necessary yet. 

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Re: question about 8" rear end gears
« Reply #9 on: March 28, 2010, 07:53:20 PM »
if you weld the axle tubes and brace the rear diff to the tubes your 8" is fine. however if you want the wheels off the ground you will need a stall converter with a flash stall speed of probably  3000 rpm  and slicks or drag radials........ but the most important thing in your case is the gears. the only reason my car gets the tires off the ground  with 2.73 gears is because of nitrous (250hp shot) and a stall converter.   so i think 4.10 plus is what you need in your case. 

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Re: question about 8" rear end gears
« Reply #10 on: March 28, 2010, 08:00:31 PM »
4.10's will be too much gears for the street.  3.73's would be the highest I would go for street use. 

Giddyupv8

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Re: question about 8" rear end gears
« Reply #11 on: March 28, 2010, 08:02:07 PM »
I have M/T drag radials on the car already, and went with a TCI 2500 stall. If I go with  4.10s , no more highway for me. Good idea on bracing that will help.

Giddyupv8

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Re: question about 8" rear end gears
« Reply #12 on: March 28, 2010, 08:03:08 PM »
Im thinking 3.55s

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Re: question about 8" rear end gears
« Reply #13 on: March 28, 2010, 08:04:53 PM »
Good choice. 

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Re: question about 8" rear end gears
« Reply #14 on: March 28, 2010, 08:15:43 PM »
ya but i do not think you have enough power to meet your "ultimate goal" of pulling your wheels up.  i've got a little over 650 at the wheels and can only get them up about 14 inches.  and thats with 250 instant extra horsepower at the loww end.  you dont have that power right away with a supercharger. a 2500 stall converter only has a flash of about 1800 rpm just an fyi.  a looser converter will do it for you with 3.55. but good luck regradless of how you go!  i cant wait to seee it in action either way

Giddyupv8

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Re: question about 8" rear end gears
« Reply #15 on: March 28, 2010, 08:22:07 PM »
I think you will see me on divorce court if I spend any more money on my II, or my wife might just plain shoot me lol

ol dirty doug

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Re: question about 8" rear end gears
« Reply #16 on: March 28, 2010, 08:26:18 PM »
ya but will it be worth it....is the question!  (i think so)

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Re: question about 8" rear end gears
« Reply #17 on: March 28, 2010, 09:08:47 PM »
Women should stay out of the race car discussions.  If you really want a race car, then  neither the 8" or the 9" will serve you well.  I thought we were talking about a street car. 

66GTKFB

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Re: question about 8" rear end gears
« Reply #18 on: March 28, 2010, 10:00:05 PM »
I got a 65 GT Fastback (225hp rated "A" code) with a 3.00:1 rear axle ratio and a 66 GT Fastback (271hp rated"K" code) with a 3.50:1 ratio. They both top out at around 115mph (shakes). 3.25 is enough. Also having blown an axle on a 9 inch (1964 289HP Fairlane, 4.11:1, D-gas NHRA) I can tell you that an 8 inch is too small, too weak.
Remember - "Speed costs money, how fast can you afford to go?"
Jim

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Re: question about 8" rear end gears
« Reply #19 on: March 29, 2010, 04:04:49 AM »
Then, there must have been something wrong with that 9 incher Jim.   You can't blow a 9 incher with that little engine if it is good condition.. 

 

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