Two questions.

YNOT · March 24th, 2007, 03:19 AM

Anyone know the formula to figure out engine rpm at 65mph with 3:73 gears and 25.6" tires in a 1989 GT 5.0 5-speed?

Also does anyone hate there 3:73's? It's not my daily but it'll never be a track car and once in a blue moon, I will be driving 65mph for 1.5hrs to my cabin on the weekends. (134,000 on the motor)

I also don't want 1st gear to be useless, so I've been researching like crazy for opinions and I'm still trying to decide 3:55 or 3:73. (yes i know beating a dead horse topic)

HMUSN · March 24th, 2007, 03:26 AM

the horse has been dead for a while.
3:73's man.

i prefer 4:10's myself though..

i drive 110 miles a day on them

at 75 i am at 2300 in fifth

wraitherx · March 24th, 2007, 06:39 AM

Originally Posted by HMUSN

the horse has been dead for a while.
3:73's man.

i prefer 4:10's myself though..

i drive 110 miles a day on them

at 75 i am at 2300 in fifth

+1

95opal · March 24th, 2007, 09:26 AM

Check this it should help ya. http://www.csgnetwork.com/multirpmcalc.html

Stangzilla · March 24th, 2007, 09:27 AM

The 3.73's are just perfect for the highway...And have good performance also...

nolife · March 24th, 2007, 10:48 AM

RPM = transmission_ratio x 1056 x mph x axle_ratio / wheel_circumference

T5 with .68 5th gear and the circumference of a 25.6 tire being 80.42 would put you at 2165 RPM @ 65MPH.

RPM = .68 x 1056 x 65 x 3.73 / 80.42 = 2165 RPM

Stangzilla · March 24th, 2007, 02:37 PM

Originally Posted by wraitherlx

Originally Posted by HMUSN

the horse has been dead for a while.
3:73's man.

i prefer 4:10's myself though..

i drive 110 miles a day on them

at 75 i am at 2300 in fifth

+1

What size tires do you have?

stang94 · March 24th, 2007, 06:29 PM

3.73, well rounded gear for highway and street car.

nolife · March 24th, 2007, 07:34 PM

Originally Posted by Stangzilla

What size tires do you have?

With those quoted numbers (4.10s right?), mathmatically he would have 30.56 tall tires. That's big.

Evil Intent · March 24th, 2007, 11:50 PM

Stupid question......

that conversion chart is pretty cool, I decided on 3.73..... (4500rpm@150mph theoretical)

why have I read that 3.55 is the best choice for a manual trans, 3.73 for an auto?

according to the formula the difference is like 275rpm

YNOT · March 25th, 2007, 02:10 AM

i know i hear 3.55 manual 3.73 auto and i hear 3.73 manual 4.10 auto. that's why i posted this.

1slo5.0 · March 25th, 2007, 04:07 AM

The best choice for gearing is what your car needs, not what people "think" is best. For a street car a 3.73 is a good all around gear that will still get decent fuel economy. If you are serious about racing the car you need to do some mathematical formulas to figure out what gear will put you in the proper rpm range at the end of the track.

shawn91stang · March 25th, 2007, 10:16 AM

Originally Posted by Darrell

The best choice for gearing is what your car needs, not what people "think" is best. For a street car a 3.73 is a good all around gear that will still get decent fuel economy. If you are serious about racing the car you need to do some mathematical formulas to figure out what gear will put you in the proper rpm range at the end of the track.

What formulas do you use to figure these up?

50COUP332 · March 25th, 2007, 11:17 AM

3.73 for a 5-speed and 4.10 for an auto

1slo5.0 · March 25th, 2007, 01:28 PM

Originally Posted by shawn91stang

What formulas do you use to figure these up?

95opal posted a calculator that will do the trick.

Darrellx14 · March 25th, 2007, 04:13 PM

convert MPH to Feet Per Minute. Divide it by tire rollout. Multiply it by
the effective gear ratio. That's it, your RPM!!!

cali 5.0 · March 26th, 2007, 12:20 AM

i've got 3.73 gears in my 89gt with a stock t5 and i can only get about 90mph out of 4th gear at 5000rpm... wish i would have went with the 3.55. and racing on the top end, 4get about it... my brother has 3.73 in his 00gt and by the time i get to the top of 4th gear he's in low 3rd and when i do go to 5th he jus smokes me...

1slo5.0 · March 26th, 2007, 10:52 AM

Originally Posted by cali 5.0

i've got 3.73 gears in my 89gt with a stock t5 and i can only get about 90mph out of 4th gear at 5000rpm... wish i would have went with the 3.55. and racing on the top end, 4get about it... my brother has 3.73 in his 00gt and by the time i get to the top of 4th gear he's in low 3rd and when i do go to 5th he jus smokes me...

If you can't get more than 90mph out of your car with 3.73 gears, you have major issues somewhere. Assuming your car is bone stock with the exception of the gears it should have no problem seeing 115-120mph in 4th gear.

cali 5.0 · March 26th, 2007, 11:43 AM

thts wht i thought.... the clutch is fair,, i think i might need a new tho but do u think it could be slipping tht bad,, bkuz tha car feels strong in the low rpm range but on the top end it doesnt hav it...

HMUSN · March 26th, 2007, 11:46 AM

Originally Posted by Stangzilla

Originally Posted by wraitherlx

Originally Posted by HMUSN

the horse has been dead for a while.
3:73's man.

i prefer 4:10's myself though..

i drive 110 miles a day on them

at 75 i am at 2300 in fifth

+1

What size tires do you have?

i run 275/40/17's all the way around.

my speedo is jacked right now though.. i run about 6mph faster than i am going.

March 24th, 2007, 03:19 AM	#1
YNOT Regular 1989 GT Hatch Join Date: Mar 2007 Posts: 227 iTrader: 0 reviews	Two questions. Anyone know the formula to figure out engine rpm at 65mph with 3:73 gears and 25.6" tires in a 1989 GT 5.0 5-speed? Also does anyone hate there 3:73's? It's not my daily but it'll never be a track car and once in a blue moon, I will be driving 65mph for 1.5hrs to my cabin on the weekends. (134,000 on the motor) I also don't want 1st gear to be useless, so I've been researching like crazy for opinions and I'm still trying to decide 3:55 or 3:73. (yes i know beating a dead horse topic)

March 24th, 2007, 03:26 AM	#2
HMUSN Doc 1986 SVO 48.47@ 12.58 Join Date: Nov 2006 Posts: 37,050 iTrader: 11 reviews	the horse has been dead for a while. 3:73's man. i prefer 4:10's myself though.. i drive 110 miles a day on them at 75 i am at 2300 in fifth __________________

March 24th, 2007, 09:26 AM	#4
95opal Hardcore Enthusiast 95 opalfrost gt Join Date: Nov 2006 Location: Connecticut Posts: 1,516 iTrader: 0 reviews	Check this it should help ya. http://www.csgnetwork.com/multirpmcalc.html __________________ 5.0 magazines 94-04 performance mustangs feature car! Fall 2010

March 24th, 2007, 09:27 AM	#5
Stangzilla MM Fanatic Join Date: Aug 2006 Location: On my way to Baines's house!! Posts: 3,298 iTrader: 0 reviews	The 3.73's are just perfect for the highway...And have good performance also... __________________ Rotating The Earth 1320 Feet At A Time!! Today, I found out that when I masturbate at night while watching internet porn I cast a huge shadow on the curtain and the entire street is able to see it.

March 24th, 2007, 10:48 AM	#6
nolife MM Fanatic 91GT, 88GT, 02GT Join Date: Dec 2006 Posts: 3,057 Blog Entries: 3 iTrader: 0 reviews	RPM = transmission_ratio x 1056 x mph x axle_ratio / wheel_circumference T5 with .68 5th gear and the circumference of a 25.6 tire being 80.42 would put you at 2165 RPM @ 65MPH. RPM = .68 x 1056 x 65 x 3.73 / 80.42 = 2165 RPM __________________

March 24th, 2007, 06:29 PM	#8
stang94 Hardcore Enthusiast Join Date: Oct 2006 Location: Jamaica, NY Posts: 1,071 iTrader: 1 reviews	3.73, well rounded gear for highway and street car. __________________ Giving Away For FREE PM ME. FREE 351 Block, 90,xxx miles (Non roller block) FREE 94-98 GT Hood (red)

March 24th, 2007, 11:50 PM	#10
Evil Intent Regular 1991 GT Vert w/stuff Join Date: Mar 2007 Location: Southern California Posts: 69 iTrader: 0 reviews	Stupid question...... that conversion chart is pretty cool, I decided on 3.73..... (4500rpm@150mph theoretical) why have I read that 3.55 is the best choice for a manual trans, 3.73 for an auto? according to the formula the difference is like 275rpm __________________ 91' Convertible, T-56, Cage, Aluminum Flywheel, Passes Smog on 87 Octane

March 25th, 2007, 02:10 AM	#11
YNOT Regular 1989 GT Hatch Join Date: Mar 2007 Posts: 227 iTrader: 0 reviews	i know i hear 3.55 manual 3.73 auto and i hear 3.73 manual 4.10 auto. that's why i posted this.

March 25th, 2007, 04:07 AM	#12
1slo5.0 MM Ninjas! 1990 Mustang LX 9.36@143 mph Join Date: Jan 2006 Location: North Fond du Lac, Wisconsin Posts: 11,375 iTrader: 1 reviews	The best choice for gearing is what your car needs, not what people "think" is best. For a street car a 3.73 is a good all around gear that will still get decent fuel economy. If you are serious about racing the car you need to do some mathematical formulas to figure out what gear will put you in the proper rpm range at the end of the track. __________________ My daily driver has 16 cylinders and 4400hp @ 1000 rpm.... ***1988 Mustang GT - Stock....almost

March 25th, 2007, 11:17 AM	#14
50COUP332 Newbie Join Date: Mar 2007 Location: DELTONA ,FL Posts: 29 iTrader: 0 reviews	3.73 for a 5-speed and 4.10 for an auto __________________ 86 NOTCHBACK

March 25th, 2007, 04:13 PM	#16
Darrellx14 Regular Join Date: Jul 2006 Posts: 82 iTrader: 0 reviews	convert MPH to Feet Per Minute. Divide it by tire rollout. Multiply it by the effective gear ratio. That's it, your RPM!!! __________________ '87 Mustang 5.0 T5 Coupe New motor I/P: stock shortblock Edelbrock heads Typhoon Intake 70mm TB 80mm MAF 24lbers 1.7 rr B303 cam. Shooting for 300rwhp?

March 26th, 2007, 12:20 AM	#17
cali 5.0 Regular Join Date: May 2006 Location: grand prairie tx Posts: 383 iTrader: 0 reviews	i've got 3.73 gears in my 89gt with a stock t5 and i can only get about 90mph out of 4th gear at 5000rpm... wish i would have went with the 3.55. and racing on the top end, 4get about it... my brother has 3.73 in his 00gt and by the time i get to the top of 4th gear he's in low 3rd and when i do go to 5th he jus smokes me... __________________ 89 gt 3.73 gears, full exhaust, holley system max2 intake manifold, 70mm throttle body, jet chip

March 26th, 2007, 11:43 AM	#19
cali 5.0 Regular Join Date: May 2006 Location: grand prairie tx Posts: 383 iTrader: 0 reviews	thts wht i thought.... the clutch is fair,, i think i might need a new tho but do u think it could be slipping tht bad,, bkuz tha car feels strong in the low rpm range but on the top end it doesnt hav it... __________________ 89 gt 3.73 gears, full exhaust, holley system max2 intake manifold, 70mm throttle body, jet chip

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