Landracing Forum
Tech Information => Steering - Suspension - Rear End => Topic started by: CGoodson on March 30, 2013, 06:00:00 PM
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I'm trying to figure out what rear end I should run other than a quick change. What would be the best rear end to run under roadster that fits without narrowing. Also trying to figure out what rear end that you can find tall gears for 2.25 to 2.50 gear ratio. Having a hard time finding anything here in Colorado.
Thank you :cheers:
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There is no free ride---to get what you want you will need to go to a GM 7.5" rear end
available gear sets:
2.14 2.28 2.42 2.56 2.73 2.92 3.08 you will have to put Ford housing ends to eliminate the c-clips and have axles made
the GM 10-12 can get you to a 2.28,( 2.41 and 2.52 I THINK) gear sets in the 8 7/8" ring gear
These 7.5" are easily found out of camaros, m vans motes s10s ect---they also have THORSEN lockers---the best- cheap on ebay for the 2.14>-3.08 gearsets
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Thank you for the info Sparky. Does anyone know what the tallest gear you can get for 9" or 8.8" ford rear ends. I have 9" and 8.8" and where is the best place to find them. Also I found a 8.25 chrysler rear end and found 2.26 gears for it. Would that be a way to go?
Corey :cheers:
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What kind/class roadster are you running and what is your expected speed?
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Small motor around the 200mph range.
Corey :cheers:
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9-inch Ford: 2.47:1 - there are rumors of a 2.29:1 ratio out of a seventies Lincoln, but I have never been able to confirm with any "rear end professional" that it really exists.
Good luck!
Willi
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X2 on the 10 bolt.
If you're running a Small motor around the 200mph range.Corey :cheers:[/i]
then you don't want a nine inch. They use too much power. Get the 10 bolt and you have a nice spread of ratios as Sparky points out above....he put 800hp through one,and ran 300, we just ran 215mph with our set up with just over 300hp.
Makes for a slower ratio change than a QC but when you're running 199.xxx you want something that frees up, not gobbles up power :cheers:
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Anybody out there have any rear ends for sale that are ready for Bonneville?
Corey :cheers:
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Your information's a little vague to get accurate advise. With a small engine you will need ratio options & it's common knowledge the GM 7-1/2 10 bolt covers it well.
It takes less HP to turn a big tire than it does to turn a big gear & keep high gear in the trans as 1-1.
There's an easy to use gearing calculator on this site in the side bar.
Sid.
http://www.squirrelpf.com/turbocalc/
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Okay - I am a bit stumped here.... You say a small motor and 200 mph range..... Would we be talking a small LOW revving motor or a HIGH revving motor?
My "dreamwheel" says that, with a 28" diameter tire and a direct drive top gear in the transmission, assuming NO tire slippage, in order to go 210mph, you would want a 3.00 - 1 gear ratio at 7563 rpm.... or a 3.07 - 1 gear ratio at 7740 rpm.... or a 2.56 - 1 gear ratio at 6454 rpm.....
My turbocharged 2 liter Dodge engine was an 8000 rpm engine..... it never actually got run in the lakester but it was my expectation that I would have been using a 2.80 - 1 or a 2.86 to 1 rear end ratio to go 235 mph (which was the record at that time)...
So, if possible, please provide us with a few more specifics on engines, expected rpms, transmission to be used etc and we could be a bit more specific with (potentially highly opinionated) advice.... :-D
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The GM 10-12 has a 2.28 ratio available---they MAY fit a 8.8 ford I put Ford 9" brgs ends when I ran one the Gm 8.5 has a 2.41 ratio
on a Roadster I would opt for the smallest tires possible as---- they stick out in the WIND
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As a newbie when it comes to gear calculations I have a question or two. I plugged in some random numbers into the squirrel deal. Im basing thse calcs on running a powerglide with no converter with a 1.76 low and high gear of 1.0. Plugging in an 8000 redline, 29 in tall tire, final drive ration of 2.42 its coming up with max rpm of 162 in low and 285 in high. Does that sound right? I understand that its not taking into consideration vehicle weight, frontal area or any of that. Just seemd kinda high
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285 and 163 are correct. The formula is: mph=rpm x tire dia(inches)/gear ration x 336. Running this set up means you need an engine that will pull from 4500 rpm through 8000. Can you say "Big Block Chevy"? or equals and if you had a turbo even better.
Rex
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lol BBC :-D
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Thanks Rex for the info and input. As for the BBC route, yeah I would agree. The more time I spend around Sparky, the more that route makes sense :-D ( Ill hold off on turboing for a while though LOL )
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there are lots and lots of ways to skin a slow cat ---the faster the cat goes- :roll: - the fewer options!
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As a newbie when it comes to gear calculations I have a question or two. I plugged in some random numbers into the squirrel deal. Im basing thse calcs on running a powerglide with no converter with a 1.76 low and high gear of 1.0. Plugging in an 8000 redline, 29 in tall tire, final drive ration of 2.42 its coming up with max rpm of 162 in low and 285 in high. Does that sound right? I understand that its not taking into consideration vehicle weight, frontal area or any of that. Just seemd kinda high
The calculations are a series of equations that not everyone understand some of the "whys" of.....
You will first have to know some data about your running gear combination - or, at least, the one you are "wishing for".... The engine's maximum horsepower and at what RPM is important as the ultimate top speed of the vehicle will be in the vicinity of 3% to 10% beyond that..... The transmission's top gear - is it direct or overdrive?...... The tire diameter (don't worry about growth factors until you are getting past 250mph)
Starting with the tire diameter - you multiply 29" X 3.1416 (this number is designated by the Greek letter Pi - a mathematical "constant" which is the ratio of a circle's diameter to its circumference).... You will arrive at the amount of 91.1064". Divide this by 12 (making the amount into feet) - You will get 7.5922'... Then divide a mile - 5280' - by the tire's circumference... 5280 / 7.5922 = 695.45 - Tire revolutions in a mile. This is the amount of tire revolutions per minute that will be required to go 60 MPH.
Now, in your case, Frankie, my way of structuring the equation to determine top speed will be like this.
285 mph is 4.75 times faster than 60 MPH. So, 695.45 X 4.75 = 3303.39 Tire revolutions per minute. Now, multiply that amount by the gear ratio - 2.42 - 1.... Like this - 3303.39 X 2.42 = 7994.2 RPM.
This gets interesting when you "play" with it.... You can divide the end result by any one of several of the variable and then remultiply by other variable and come up with multiple determinations.... For instance - 7994.2 / 2.42 = 3303.39 X 2.75 = 9084.3 RPM...ooops! way past the redline! So, take 9084.2 / 4.75 = 1912.04 X 4.2 = 8030.6 RPM... 4.2 (60 x 4.2 =) 252 MPH
In order to factor in lower transmission gear ratios, you need to multiply the transmission gear ratio by the rear end ratio and then recalculate as if that is the overall ratio (which, while in that gear, it is)... so, with your powerglide, 2.42 X 1.76 = 4.2592 overall ratio... 162 MPH is 60 X 2.7....So, 695.45 X 2.7 = 1877.72 Tire revolutions... 1877.72 X 4.2592 = 7997.6 RPM....
I hope that explains it clearly enough....
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Fastman, thanks for the explanation, I appreciate it!
Didnt mean to hijack the thread, carry on folks :-)
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Go to our section on formulas and you will find gear calc. It's a way to see what you may need. You can set it for torque and HP and RPM. I happen to use a Pontiac and have all the ratios from 2.56 up. I have 4 different tire sizes from 26 to 32. I also have trans with a .96 overdrive. Not much I can't do with a pumpkin and tire change.......best to be prepared.....good luck
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JD :cheers: :cheers: :cheers: