It does if his "double the RPM/double the speed" value is only 120MPH.
That would be a "best case" value which will only get slower with wind resistance.
CK5
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stock vehicle...over 100 mph
- Thread starter blazin_blazer
- Start date
It does if his "double the RPM/double the speed" value is only 120MPH.
That would be a "best case" value which will only get slower with wind resistance.
cegusman
3/4 ton status
Went 110-115mph in my old k5 6.2/700r4/np208/4.11/39.5 boggers. Had a friend next to me in his car.
Don't bother risking your life to show us how inaccurate your speedo is...
Here's a simpler way:
If the redline of your engine is 6000RPM, take the truck up to highway speed in top gear and then get the RPMs to 3000RPM (or 1/2 of whatever redline actually is).
Read the speedometer.
Your top speed (not accounting for massive wind drag) is going to be double whatever speed you are reading at 3000RPM.
"Double the RPM, Double the speed"....it's a simple mathematical truth, and you don't have to kill yourself to get the number.
Caveat:
If your speedometer is way off even at 3000RPM, your top speed will also be wrong.
Works for me....
50mph, 2000rpm to 100mph and 4000rpm. I've maxed my truck out and about 100mph is all i can get out of it before I run out of gear
I have to admit to being rather skeptical that a sub-300 h.p. SUV is capable of going that fast. The above idea to check to see if the gearing of the vehicle at least makes it theortically able to go that fast likely won't prove anything either as most newer cars are at well under half of the red-line rpm while cruising at 70 mph...my truck only runs about 2,500 rpm and my wife's car around 2,000 at 70 mph. My truck redlines at 5,800 rpm and I'm pretty sure it is not capable of running 150 mph +.
Hopefully your wife will be fine, so don't take this the wrong way........but going that fast on public roads is both stupid and dangerous. I know you were in a hurry to see your wife but getting killed or arrested on the way to the hospital is not going to help anybody.
Hopefully your wife will be fine, so don't take this the wrong way........but going that fast on public roads is both stupid and dangerous. I know you were in a hurry to see your wife but getting killed or arrested on the way to the hospital is not going to help anybody.
Here's a homework exercise for anyone interested....
Greg is traveling across Utah on a wide open (and empty) highway and is traveling 100MPH in top gear. To alleviate the boredom, he snaps a photograph of his progress.
Based on the photograph below, what is the vehicle's calculated top speed?
Hint: This vehicle has much less wind resistance than a Nissan Pathfinder!
Greg is traveling across Utah on a wide open (and empty) highway and is traveling 100MPH in top gear. To alleviate the boredom, he snaps a photograph of his progress.
Based on the photograph below, what is the vehicle's calculated top speed?
Hint: This vehicle has much less wind resistance than a Nissan Pathfinder!
Xtremegmc80
1/2 ton status
actually it looks like u were doing 99 mphHere's a homework exercise for anyone interested....
Greg is traveling across Utah on a wide open (and empty) highway and is traveling 100MPH in top gear. To alleviate the boredom, he snaps a photograph of his progress.
Based on the photograph below, what is the vehicle's calculated top speed?
Hint: This vehicle has much less wind resistance than a Nissan Pathfinder!
had my 2001 camaro z28 at 150 plus, and the front end started to float lightly at around 140 i was around 22 at the time my 80 gmc prolly 115, and 03 silverado gov out at 98 mphEDIT** found the pic that was taken with my sidekick 2 pager. 2001 z28..
Id say the answer would be 157.5 mph. Anyhow my 96 z28 doesn't have a speed limiter, i had it up to 145mph before i ran out of road. it shifts into 4th at 135mph (4l60e stock gears) My blazer (see below) i had to 115mph, was racing my buddies volvo suv. kept even with him till bout 115 then he started pullin.
In all reality it is very posibble to get a suv over 150mph. (im not sayin that a stock nissan could do it) even with a (4cyl) now you have to keep in mind that hp only makes it faster. gearing is what will get you to go! Heck you could make a box van go 150mph if you had enough road/gearing. (wish we had drylake beds here in the east coast!
In all reality it is very posibble to get a suv over 150mph. (im not sayin that a stock nissan could do it) even with a (4cyl) now you have to keep in mind that hp only makes it faster. gearing is what will get you to go! Heck you could make a box van go 150mph if you had enough road/gearing. (wish we had drylake beds here in the east coast!
Well........not exactly. Sure, you can optimize the top speed of a vehicle if you match the gearing but it will only get you going so fast. Simply matter of fact that it requires a certain amount of power to go certain speeds. I have personally set up vehicles at work for durability tests where you can easily knock 5-10 mph off the top speed by placing a little more aerodynamic drag on them...in fact aerodynamics affect the top speed much more than additional weight does.
EXACTLY. Just because a vehicle can on 170 on paper doesnt mean it will do it. Wind/ road resistance play a huge factor. The said vehicle needs to have enough power to over come all the forces acting upon it, then still have energy left over to accelerate.
In a vacum, with no resistance this would not be the case.
Disregard if you don't like math, facts, or critical thought:
1) Basic Drag is an exponential function - as speed (V) increases the drag force increases proportionally to V squared. The force required to push a car at 150mph will be 225% of the force required to push the car at 100mph.
2) You would have to turn at the peak RPM to theoretically max out speed according to Greg's model (assuming manual trans or lockup). Most consumer cars have their horsepower peak somewhere below the redline, however. This being the case (and considering an auto trans would unlock the torque converter at WOT), you would simply stop accelerating and plateau the speed somewhere short of redline at max power. More RPM's and you'd actually start losing power.
3) Driving a Nissan PFinder at anything above, say, 120 would likely be accompanied by a stench due to soiled drawers...especially if you twitched or there was a crosswind.
4) Factory governors on OBDII vehicles are based on the speed ratings of the tires they were sold with originally.
5) I'm glad your wife is OK.
1) Basic Drag is an exponential function - as speed (V) increases the drag force increases proportionally to V squared. The force required to push a car at 150mph will be 225% of the force required to push the car at 100mph.
2) You would have to turn at the peak RPM to theoretically max out speed according to Greg's model (assuming manual trans or lockup). Most consumer cars have their horsepower peak somewhere below the redline, however. This being the case (and considering an auto trans would unlock the torque converter at WOT), you would simply stop accelerating and plateau the speed somewhere short of redline at max power. More RPM's and you'd actually start losing power.
3) Driving a Nissan PFinder at anything above, say, 120 would likely be accompanied by a stench due to soiled drawers...especially if you twitched or there was a crosswind.
4) Factory governors on OBDII vehicles are based on the speed ratings of the tires they were sold with originally.
5) I'm glad your wife is OK.
When i still had the mild 355 in my K5 I once managed just over 100 mph. That motor revved to 5500 rpm easily...yet in top gear and WOT it didn't have the power to get over 3900 rpm. At that point there was more wind resistance than there was power to overcome it, so the rev's stopped climbing. Co-efficient of drag is the most important 'stat' when talking top speed.
In my case when I realized 102 or 103 was it, I took my foot off the gas...and almost ate the steering wheel it slowed down so suddenly.
Rene
In my case when I realized 102 or 103 was it, I took my foot off the gas...and almost ate the steering wheel it slowed down so suddenly.
Rene
blazin_blazer
1/2 ton status
1/2 my redline
ok, this method not real accurate...my redline is 6250... and at 3000 rpm i'm going 105 mph, i know this thing is fast, but by this method, my top speed would be over 200 mph
sorry its so blurry, its a phone...+i was going over 100 takin the pic, but you can make it out 3000rpm=105mph
i had to see if i saw what i saw, was spooked to try and take a pic @ 140, i found out that in overdrive i peak at @ 3700 rpm at 122 mph....hit the button turn off od and it will climb to 4600-4750 rpm w/speedo buried @ 140. no more testing...its fast, thats enuff for me!
It does if his "double the RPM/double the speed" value is only 120MPH.
That would be a "best case" value which will only get slower with wind resistance.
ok, this method not real accurate...my redline is 6250... and at 3000 rpm i'm going 105 mph, i know this thing is fast, but by this method, my top speed would be over 200 mph
sorry its so blurry, its a phone...+i was going over 100 takin the pic, but you can make it out 3000rpm=105mph
i had to see if i saw what i saw, was spooked to try and take a pic @ 140, i found out that in overdrive i peak at @ 3700 rpm at 122 mph....hit the button turn off od and it will climb to 4600-4750 rpm w/speedo buried @ 140. no more testing...its fast, thats enuff for me!
The calculation is accurate....especially with a manual transmission with no slippage. Gearing is not a "fuzzy" thing, it ALWAYS works the way I described.
What is NOT accurate is the assumption that because the gearing numerically allows for 200MPH, you could really expect to ever GO that fast.
As you seemed to be experiencing, you ran out of horsepower before you ran out of gear / engine RPM. The tach eventually just stops climbing in top gear because the amount of wind resistance (drag) is 100% identical to the amount of power produced by the engine at that RPM. You reached a perfect point of equilibrium between the two forces.....HP pushing vs. wind resistance.
What is NOT accurate is the assumption that because the gearing numerically allows for 200MPH, you could really expect to ever GO that fast.
As you seemed to be experiencing, you ran out of horsepower before you ran out of gear / engine RPM. The tach eventually just stops climbing in top gear because the amount of wind resistance (drag) is 100% identical to the amount of power produced by the engine at that RPM. You reached a perfect point of equilibrium between the two forces.....HP pushing vs. wind resistance.
BlazerBud
1/2 ton status
The problem with doubling the MPH and doubling the RPM is that we are skeptical of the accuracy of the SPeedo in the first place. There is no way in Hell that he went 140 MPH in that vehicle. There is the truth that the Speedo can register 140 MPH, without actually going that fast. This just means that the guage is not linear, almost no instrument (car gauge, lab instrument, scale) is truely linear. They only operate accurately within their intended range.
I bet if he got a ticket while he thought he was doing 140 MPH, it would be for something like 102 MPH in a 65 MPH zone.
I bet if he got a ticket while he thought he was doing 140 MPH, it would be for something like 102 MPH in a 65 MPH zone.
Alright then....
All we really need is an accurate reading of RPM at a speed that everyone agrees should be accurate on the speedo. I'd suggest that something around 55 - 60MPH would be accurate, since that is what the manufacturer is expecting us to be driving at most of the time.
With any combination of speed vs RPM in top gear, the rest of the values can easily be calculated....and we can put this whole stupid arguement to rest.
All we really need is an accurate reading of RPM at a speed that everyone agrees should be accurate on the speedo. I'd suggest that something around 55 - 60MPH would be accurate, since that is what the manufacturer is expecting us to be driving at most of the time.
With any combination of speed vs RPM in top gear, the rest of the values can easily be calculated....and we can put this whole stupid arguement to rest.
tiny2085
1/2 ton status
the whole double the rpm doubles the speed thing is not even close. it takes 8* times as much power to go 200 as it does to go 100. just becasue you double the rpm, doesn't mean you double the power of the motor, like someone stated earlier rpm to speed is not a linear rate. And the 8 times as much power figure is from hot rod when they were building a salt flat car and figurd out they needed 1,000 horse to go 200 in a 3,200lb camaro. I"m not trying to put you down brother, just trying to help you understand how it works. and i'm not saying it won't do 140 either.
I think YOU are missing it....
- The guy hit an aerodynamic wall well before his top-gear redline. That's obvious to everyone...
- With one accurate speedometer and RPM reading (at a lower speed) we can easily show what is theoretically possible in top gear.
- We can also demonstrate how far off his speedometer is at speeds above 100MPH.
tiny2085
1/2 ton status
no you are missing it.... I'm just kidding. I understand what your saying, I didn't want him to think i was bashing on him, so i was trying to show him how it works so HE can figure it out. how do we know maybe its a factory supercharged model that only had one ever produced ya know?
1967k10
1/2 ton status
I'll add my .02 cause I too am looking for the accurate way to figure this.
My 01 D-Max runs 2000rpm @ 77mph and 2700rpm @ 100mph with 33" tires,3.73 gears, 6spd manual,and the speedo recalibrated for the 33"s.
We were out one night in BFE and pegged 100 and punched it. took it all the way to 3700rpm
. My buddys GPS couldn't keep up but we figured it was in the neighborhood of 140. I know D-Max's with 5spd Ally's are capable of 140mph and I have a higher OD. Any thgoughts that will help us both figure accurate speeds.
My 01 D-Max runs 2000rpm @ 77mph and 2700rpm @ 100mph with 33" tires,3.73 gears, 6spd manual,and the speedo recalibrated for the 33"s.
We were out one night in BFE and pegged 100 and punched it. took it all the way to 3700rpm
. My buddys GPS couldn't keep up but we figured it was in the neighborhood of 140. I know D-Max's with 5spd Ally's are capable of 140mph and I have a higher OD. Any thgoughts that will help us both figure accurate speeds.
1967K10,
If nobody responds to your question by the time I get back from lunch, I'll run your numbers and post them up.
If nobody responds to your question by the time I get back from lunch, I'll run your numbers and post them up.
