I did a little research on different gears for my car, trying to decide which one' s to go with. This is what I found for my particular setup.
IN 5th gear @ 55mph
2.73 gears = 1358rpm's
3.55 gears = 1607rpm's
3.73 gears = 1856rpm's
4.10 gears = 2040rpm's
4.56 gears = 2269rpm's
only 911 rpm's more @ 55 mph in 5th gear with 4.56's compared-the stock 2.73's. This goes to show you that a gear swap does not decrease your fuel mileage that much at all. BUT if I go with 3.73's I will be running 101 mph in 4th @ 5500 rpm's and i would rather not have to hit 5th gear so I think the 3.55's are a better choice for me, unless I go with a taller tire. Such as a 28 inch slick which will put me at 111.7 mph at 5500rpm's.BUt the 3.55 will take me to 117mph at 5500.Decisions decisions DECISIONS!!!!
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1992 LX hatchback, with 93' Cobra Motor and 5 speed,cobra intake(ported lower),GT-40 iron heads,FMS 65mm TB,F-303 cam,C&L 73mm mass, 24lb inj.,walbro 155fp,adj. reg,12" K&N cone,BBK short headers,BBK H-pipe, Flowmaster 2 chamber cat back,Eibach pro springs,17" cobra R rep. wheels, 245/45 front, 275/40 rear, goodyear eagle GSC's.
You wont need to shift to 5th with 3.73's. How often do you run at a track? Is it your daily driver? take those things into consideration also. Also, check the RPM's for 65 and 70mph. Highways here in Missouri we tend to drive at least the speed limit on them.
I am running a 150 shot of NOS on top of all the other mods, so I won't be able to run the 3.73's because they top out at 110 mph in 4th at 6000 rpm's. I don't want to rap the engine that high with NOS. There is a track less than 20 miles away from me. As of now it is only 1/8th mile, but they are extending it to a 1/4 this year some time.( so they say) There is also a road course that I can run on, that's where HPMotorsports Paul Brown practices if you have ever heard of him.The police also use it for training.well, with 3.73's in 4th going 65 would be around 3600rpm and in 5th it would be a little under 2400. 75 mph in 4th around 4500 and 5th 2600 rpm's. I also have a truck, so I could drive it more often, but I have been driving my car alot lately since it's summer.But I don't drive it in snow or rain.
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1992 LX hatchback, with 93' Cobra Motor and 5 speed,cobra intake(ported lower),GT-40 iron heads,FMS 65mm TB,F-303 cam,C&L 73mm mass, 24lb inj.,walbro 155fp,adj. reg,12" K&N cone,BBK short headers,BBK H-pipe, Flowmaster 2 chamber cat back,Eibach pro springs,17" cobra R rep. wheels, 245/45 front, 275/40 rear, goodyear eagle GSC's.
For one, I didn't know about the link on this site. And the one I used is more accurate. Just because a tire says it is a 275/40/17 doesn't mean it is the same diameter. the site i used uses actual tire diameter not size, which is more accurate to me.
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1992 LX hatchback, with 93' Cobra Motor and 5 speed,cobra intake(ported lower),GT-40 iron heads,FMS 65mm TB,F-303 cam,C&L 73mm mass, 24lb inj.,walbro 155fp,adj. reg,12" K&N cone,BBK short headers,BBK H-pipe, Flowmaster 2 chamber cat back,Eibach pro springs,17" cobra R rep. wheels, 245/45 front, 275/40 rear, goodyear eagle GSC's.
I mean tire diameter equals wheel diameter plus two multiplied by the product of the width (in inches) and the aspect ratio. Seems like a pretty tight equation to me.
So for you 275/45/17 tire, you would first convert the width to inches (10.8267717). Google does conversions, BTW. Then you would multiply that by the aspect ratio, 45%. That gives you the height of the tire. There are two hights of the tire, top and bottem (of left and right if you prefer), in the diameter of the tire. So add two tire heights to the diameter of the tire, and there's your number.
I don't see the wiggle room you speak of in that equation.
(Not to call you out or anything, I just have never heard anyone say that two tires with the same dimension can have a different total height.)
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Current Mods: FRPP 4.10 gears, MGW shifter, MM sub. conn., Am. Th. cat back, K&N, Miglia wheels, wheel spacers (1 3/16" rear).
(basically stock)
Soon to be installed: Street Heat intake, Twisted Wedge heads, Anderson Ford B-31 cam, BBK LT headers, BBK mid pipe w/ cats, BBK 75mm throttle body, AFM power pipe, Pro M-80 MAF, FRPP 30 lb. injectors, BBK 255 lb./hr. fuel pump, H&R race springs, Bilstein shocks/struts, FRPP FR500 steering wheel.
(not so stock)
WTF??? Is it gang up on stimp day. Happy 4th to all of you too!! I'm just trying to figure out what gear will get me to the end of the 1/4 without overreving 4th gear. Everyone's telling me to go with 3.73's but with a 4th gear ratio of 1.1 and a 25.250 diameter tire, I will be topped out at 110 mph at 6000 rpm's which is a little too high for my comfort running 150 shot of nos. This is why I mentioned the taller tire, to bring the rps's down at the end, I think the motor will handle it as long as I can keep the rev's down at the end.
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1992 LX hatchback, with 93' Cobra Motor and 5 speed,cobra intake(ported lower),GT-40 iron heads,FMS 65mm TB,F-303 cam,C&L 73mm mass, 24lb inj.,walbro 155fp,adj. reg,12" K&N cone,BBK short headers,BBK H-pipe, Flowmaster 2 chamber cat back,Eibach pro springs,17" cobra R rep. wheels, 245/45 front, 275/40 rear, goodyear eagle GSC's.
Hey man chill out...I don't think any person is trying to insult you here..remenber; you can't see emotions thru a screen...
I run the 373 gears and have a 26.5 x 8 slick and i go thru the traps at about 5200 rpm...Which is about where i need to be...I would always go with experience before i trusted a computer formula....Goodluck..
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91 LX...Motor is out and waiting for 347 to be finished for next season..All bolt-ons with Nitrous...100% dragster...
For what it is worth, experience tells me you put your combo together to just hit the end of your power curve of your cam and intake manifold at the traps. you don't always want to be redlining unless you want to always be rebuilding your motor. Mistakes happen at redline.
NO JESS, That is what I don't want to do is redline the engine, That is why I don't want to go with the 3.73's like everyone is telling me to do. I want to go with the 3.55's so I DON'T go through the traps at 6000. with the cobra spec T-5, the 3.73's and a 25 1/4 diameter tire ,I will have a max speed of 109.9 mph in 4th gear. NOT GOING TO WORK FOR ME!!!! I know mistakes happen, especially when your running a 150 shot of laughing gas.
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1992 LX hatchback, with 93' Cobra Motor and 5 speed,cobra intake(ported lower),GT-40 iron heads,FMS 65mm TB,F-303 cam,C&L 73mm mass, 24lb inj.,walbro 155fp,adj. reg,12" K&N cone,BBK short headers,BBK H-pipe, Flowmaster 2 chamber cat back,Eibach pro springs,17" cobra R rep. wheels, 245/45 front, 275/40 rear, goodyear eagle GSC's.
Some info on gears 
