RPM's V.S. MPH
11-07-2006, 07:31 PM
#1
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Thread Starter
Join Date: Oct 2006
Location: Fort Worth, Texas
Posts: 322
RPM's V.S. MPH
Hey im getting gears and would like someone to do a little research for me if you dont mind. I need to know what RPM's the motors are running at different speeds w/ different gears. Ect. 3.73, 3.90, & 4.10. Thanks it is a daily driver and most are on the Hwy. thanks again.
11-07-2006, 07:35 PM
#2
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Join Date: Oct 2006
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Posts: 609
RE: RPM's V.S. MPH
Ok before this gets started.. easy numbers...
70 MPH
3.55 2300 rpms
3.73
3.90
4.10 2500 rpms
Obviously the other gears are insignificant in between ..
You can debate it all day ..
Unless you have plans for a 500 Hp plus Daily Driver... 4.10 is the way to go ..
70 MPH
3.55 2300 rpms
3.73
3.90
4.10 2500 rpms
Obviously the other gears are insignificant in between ..
You can debate it all day ..
Unless you have plans for a 500 Hp plus Daily Driver... 4.10 is the way to go ..
11-07-2006, 07:44 PM
#4
4th Gear Member
Join Date: Oct 2006
Location: Durham, NC
Posts: 1,541
RE: RPM's V.S. MPH
ahem...i did this once before...but for the basics, for every tenth you go up in gear ratio, you gain 75 rpm on the tach, i did this for someone else askin specifically about 3.90 vs 4.10
it basically says any of the gears can be fine for you, depends on your choice of mods (n/a, f/i, nitrous) and personal feel/choice...use the first set of equations to figure your speeds, theres a calc somewhere i know
alright im about to sound smart...and i took a good portion of my night just to get this strait
alright lets get a few things strait first...rpm is determined by: mph x ring/pinion ratio x tranny ratio x 336 / tire diameter
now your tire diameter for a completly stock gt is 18.7 in according to tire rack
you have 15 gal tank
60x3.90x.67x336/18.7
now at 60mph in 5th gear your running 2817 rpm with 3.90
60x4.10x.67x336/18.7
now at 60mph in 5th gear your running 2961 rpm with 4.10
so for a rule of thumb, you gain about 75 rpm per tenth you go up in gear ratio
now....
lets look at injectors!
alright 19lb injectors flow 19lbs of fuel per hour of use at 44 psi fuel pressure (which your probably running) at 100% (your not running, probably bout 80%)
19x.8= 15.2lb/hour
now gasoline weighs in at 6.25 lb/gal...so your using approx 2.5 gal of gas after going 60 miles with 3.27
average this out and your getting approx 24 mpg
NOW!!
your increasing your rpm by 450 rpm (75 rpm rule of thumb x approx 6 tenths) with 3.90 and 600rpm (75 rpm rule of thumb x approx 8 tenths) with 4.10
3.90
#x3.90x.67x336/18.7=450
#= 9.58mph
4.10
#x4.10x.67x336/18.7=600
#= 12.16mph
with 19 lb injectors at 80% running the same rpm...
3.90 you are now running 50.42 mph at the same rpm which is a mpg loss of 3.832 mpg
4.10 you are now runnning 47.84 mph at te same rpm which is a mpg loss of 4.464 mpg
....ahhhh....if im wrong or u want to dispute sig figs...screw you...naw but if im wrong...correct me...i tried...other than that...go with 4.10's
alright lets get a few things strait first...rpm is determined by: mph x ring/pinion ratio x tranny ratio x 336 / tire diameter
now your tire diameter for a completly stock gt is 18.7 in according to tire rack
you have 15 gal tank
60x3.90x.67x336/18.7
now at 60mph in 5th gear your running 2817 rpm with 3.90
60x4.10x.67x336/18.7
now at 60mph in 5th gear your running 2961 rpm with 4.10
so for a rule of thumb, you gain about 75 rpm per tenth you go up in gear ratio
now....
lets look at injectors!
alright 19lb injectors flow 19lbs of fuel per hour of use at 44 psi fuel pressure (which your probably running) at 100% (your not running, probably bout 80%)
19x.8= 15.2lb/hour
now gasoline weighs in at 6.25 lb/gal...so your using approx 2.5 gal of gas after going 60 miles with 3.27
average this out and your getting approx 24 mpg
NOW!!
your increasing your rpm by 450 rpm (75 rpm rule of thumb x approx 6 tenths) with 3.90 and 600rpm (75 rpm rule of thumb x approx 8 tenths) with 4.10
3.90
#x3.90x.67x336/18.7=450
#= 9.58mph
4.10
#x4.10x.67x336/18.7=600
#= 12.16mph
with 19 lb injectors at 80% running the same rpm...
3.90 you are now running 50.42 mph at the same rpm which is a mpg loss of 3.832 mpg
4.10 you are now runnning 47.84 mph at te same rpm which is a mpg loss of 4.464 mpg
....ahhhh....if im wrong or u want to dispute sig figs...screw you...naw but if im wrong...correct me...i tried...other than that...go with 4.10's
11-07-2006, 07:57 PM
#6
4th Gear Member
Join Date: Oct 2006
Location: Durham, NC
Posts: 1,541
RE: RPM's V.S. MPH
max hp for injectors is measured by number of injectors x injector size) / BSFC = Max safe hp
BSFC= the brake specific fuel consumption (dont worry too much about it)
so for the basics, here's a chart from motorsport digest where they discuss this:
Injector Size
Supercharged
19 lb. 276 hp
24 lb. 349 hp
30 lb. 436 hp
36 lb. 553 hp
42 lb. 611 hp
55 lb. 800 hp
Naturally
Asperated
19 lb. 338 hp
24 lb. 427 hp
30 lb. 533 hp
36 lb. 640 hp
42 lb. 747 hp
55 lb. 978 hp
however i would not recommend running 19 lb injectors at 100% duty cycle to support 276 hp...they wont last too long...best get 24 lb even if they run 70% its still better
BSFC= the brake specific fuel consumption (dont worry too much about it)
so for the basics, here's a chart from motorsport digest where they discuss this:
Injector Size
Supercharged
19 lb. 276 hp
24 lb. 349 hp
30 lb. 436 hp
36 lb. 553 hp
42 lb. 611 hp
55 lb. 800 hp
Naturally
Asperated
19 lb. 338 hp
24 lb. 427 hp
30 lb. 533 hp
36 lb. 640 hp
42 lb. 747 hp
55 lb. 978 hp
however i would not recommend running 19 lb injectors at 100% duty cycle to support 276 hp...they wont last too long...best get 24 lb even if they run 70% its still better
11-07-2006, 07:59 PM
#7
I ♥ Acer
Join Date: Oct 2006
Location:
Posts: 609
RE: RPM's V.S. MPH
ORIGINAL: ponysnake99
ahem...i did this once before...but for the basics, for every tenth you go up in gear ratio, you gain 75 rpm on the tach, i did this for someone else askin specifically about 3.90 vs 4.10
it basically says any of the gears can be fine for you, depends on your choice of mods (n/a, f/i, nitrous) and personal feel/choice...use the first set of equations to figure your speeds, theres a calc somewhere i know
ahem...i did this once before...but for the basics, for every tenth you go up in gear ratio, you gain 75 rpm on the tach, i did this for someone else askin specifically about 3.90 vs 4.10
alright im about to sound smart...and i took a good portion of my night just to get this strait
alright lets get a few things strait first...rpm is determined by: mph x ring/pinion ratio x tranny ratio x 336 / tire diameter
now your tire diameter for a completly stock gt is 18.7 in according to tire rack
you have 15 gal tank
60x3.90x.67x336/18.7
now at 60mph in 5th gear your running 2817 rpm with 3.90
60x4.10x.67x336/18.7
now at 60mph in 5th gear your running 2961 rpm with 4.10
so for a rule of thumb, you gain about 75 rpm per tenth you go up in gear ratio
now....
lets look at injectors!
alright 19lb injectors flow 19lbs of fuel per hour of use at 44 psi fuel pressure (which your probably running) at 100% (your not running, probably bout 80%)
19x.8= 15.2lb/hour
now gasoline weighs in at 6.25 lb/gal...so your using approx 2.5 gal of gas after going 60 miles with 3.27
average this out and your getting approx 24 mpg
NOW!!
your increasing your rpm by 450 rpm (75 rpm rule of thumb x approx 6 tenths) with 3.90 and 600rpm (75 rpm rule of thumb x approx 8 tenths) with 4.10
3.90
#x3.90x.67x336/18.7=450
#= 9.58mph
4.10
#x4.10x.67x336/18.7=600
#= 12.16mph
with 19 lb injectors at 80% running the same rpm...
3.90 you are now running 50.42 mph at the same rpm which is a mpg loss of 3.832 mpg
4.10 you are now runnning 47.84 mph at te same rpm which is a mpg loss of 4.464 mpg
....ahhhh....if im wrong or u want to dispute sig figs...screw you...naw but if im wrong...correct me...i tried...other than that...go with 4.10's
alright lets get a few things strait first...rpm is determined by: mph x ring/pinion ratio x tranny ratio x 336 / tire diameter
now your tire diameter for a completly stock gt is 18.7 in according to tire rack
you have 15 gal tank
60x3.90x.67x336/18.7
now at 60mph in 5th gear your running 2817 rpm with 3.90
60x4.10x.67x336/18.7
now at 60mph in 5th gear your running 2961 rpm with 4.10
so for a rule of thumb, you gain about 75 rpm per tenth you go up in gear ratio
now....
lets look at injectors!
alright 19lb injectors flow 19lbs of fuel per hour of use at 44 psi fuel pressure (which your probably running) at 100% (your not running, probably bout 80%)
19x.8= 15.2lb/hour
now gasoline weighs in at 6.25 lb/gal...so your using approx 2.5 gal of gas after going 60 miles with 3.27
average this out and your getting approx 24 mpg
NOW!!
your increasing your rpm by 450 rpm (75 rpm rule of thumb x approx 6 tenths) with 3.90 and 600rpm (75 rpm rule of thumb x approx 8 tenths) with 4.10
3.90
#x3.90x.67x336/18.7=450
#= 9.58mph
4.10
#x4.10x.67x336/18.7=600
#= 12.16mph
with 19 lb injectors at 80% running the same rpm...
3.90 you are now running 50.42 mph at the same rpm which is a mpg loss of 3.832 mpg
4.10 you are now runnning 47.84 mph at te same rpm which is a mpg loss of 4.464 mpg
....ahhhh....if im wrong or u want to dispute sig figs...screw you...naw but if im wrong...correct me...i tried...other than that...go with 4.10's
Ok ... don't listen to that mess of crap ...
I have had 3.55 and 4.10 .. and of course stock 3.23 and I have driven about every type of car with about everytype of gear ratio ...
I know for a fact .. 3.55 at 80 mph is 2450-2500 rpms .. and at 70 mph about 2250-2300
I also know for a fact .. at 70 mph 4.10 are running 2500 rpms ...
Listen to people who have the gears and drive them .. not to the number game !!!
11-07-2006, 08:05 PM
#8
2nd Gear Member
Join Date: Jun 2006
Location:
Posts: 410
RE: RPM's V.S. MPH
I know @ 70 MPH i am running 1700-1800 rpm, but i am running 2.73's with 18 inch wheels and its an auto
gawd talk about no low end torque
here i come 4.10's
you guys are forgetting wheel and tire size affect the end ratio, someone running 16's vs 18's if the 18's over all tire diameter is larger then it changes the gear ratio also
when i had stock 15's on the v6 i did like 70 @ 2500rpm then with the 18's i did 70 @ 2300-2350rpm
gawd talk about no low end torque
here i come 4.10's
you guys are forgetting wheel and tire size affect the end ratio, someone running 16's vs 18's if the 18's over all tire diameter is larger then it changes the gear ratio also
when i had stock 15's on the v6 i did like 70 @ 2500rpm then with the 18's i did 70 @ 2300-2350rpm
11-07-2006, 08:40 PM
#9
4th Gear Member
Join Date: Oct 2006
Location: Durham, NC
Posts: 1,541
RE: RPM's V.S. MPH
Ok ... don't listen to that mess of crap ...
I have had 3.55 and 4.10 .. and of course stock 3.23 and I have driven about every type of car with about everytype of gear ratio ...
I know for a fact .. 3.55 at 80 mph is 2450-2500 rpms .. and at 70 mph about 2250-2300
I also know for a fact .. at 70 mph 4.10 are running 2500 rpms ...
Listen to people who have the gears and drive them .. not to the number game !!!
I have had 3.55 and 4.10 .. and of course stock 3.23 and I have driven about every type of car with about everytype of gear ratio ...
I know for a fact .. 3.55 at 80 mph is 2450-2500 rpms .. and at 70 mph about 2250-2300
I also know for a fact .. at 70 mph 4.10 are running 2500 rpms ...
Listen to people who have the gears and drive them .. not to the number game !!!
Now if he has to listen to people who know gears, my friend has a GT with 3.73's and i own a cobra with 4.10's, and i must say myself that if i had the choice i would drop my gears .2 atleast to 3.90 or even 3.73 because its better to have traction than slip the clutch or just spin tires...and ppl will tell you its not just picking gears, its picking gears to match your car
11-07-2006, 09:32 PM
#10
4th Gear Member
Join Date: Jun 2006
Location: New York
Posts: 1,178
RE: RPM's V.S. MPH
I have a '99 automatic with 4.10's and at 65 MPH it is turning 2500 RPM's, at 75 MPH it is turning 2950 RPM's, basically 26.5 MPH/1000 RPM's. If you have some numbers for the gears you have now the rpm's can be calculated. Mark