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Discussion Starter · #1 ·
Most of us know that the MPH tells us a good estimate at what the car is making power wise. As Ive been looking at some time slips and setups lately Ive noticed some tend to have more MPH than others even though they dyno'd very close at the wheels and also weigh pretty similar weights. Anyone have input as to what would cause that? To give an example, my current car (a street car not set up for drag racing at all) will make about 770 at the wheels on lower boost, it weighs about 3300 and on the street with no traction through first and at the beginning of second will still get up to 141 on a dragy. But then I see this other local guy, foxbody weighs 50lbs less and his car is running in the high 140's (usually 148ish) and deep into the 9's with only 30 more rwhp than mine (798rwhp). I cant imagine if I gave my car another lbs of boost which gets me Another 20 at the wheels that my car would trap 7-8mph higher.
Just got me thinking what else plays a big part in MPH?

Usually Ive heard tire spin wont effect top end that much. Does tire spin in first take that big of a number off the top end?
 

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Torque converter. Gear ratio. 4 speed vs. 3 speed vs. 2 speed vs. High gear only. And then there are throttle stops and ignition retards, etc. Take care. Tom Worthington
 

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Most of us know that the MPH tells us a good estimate at what the car is making power wise. As Ive been looking at some time slips and setups lately Ive noticed some tend to have more MPH than others even though they dyno'd very close at the wheels and also weigh pretty similar weights. Anyone have input as to what would cause that? To give an example, my current car (a street car not set up for drag racing at all) will make about 770 at the wheels on lower boost, it weighs about 3300 and on the street with no traction through first and at the beginning of second will still get up to 141 on a dragy. But then I see this other local guy, foxbody weighs 50lbs less and his car is running in the high 140's (usually 148ish) and deep into the 9's with only 30 more rwhp than mine (798rwhp). I cant imagine if I gave my car another lbs of boost which gets me Another 20 at the wheels that my car would trap 7-8mph higher.
Just got me thinking what else plays a big part in MPH?

Usually Ive heard tire spin wont effect top end that much. Does tire spin in first take that big of a number off the top end?
Ever time I spun a little taking off, I ran bigger speed.
 

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Discussion Starter · #4 ·
Ever time I spun a little taking off, I ran bigger speed.
Thats exactly it, I dont understand how some traps are so much higher. I went looking in another thread on here and there were a few people making considerably less power (50-75rwhp) in cars that have similar weight trapping 8-10mph faster. It just isnt correlating to me, and the thing is, they have the time slips to prove it so its not bench racing. Im just not seeing where Im
Going wrong here but trying to figure it out.
 

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Discussion Starter · #5 ·
Torque converter. Gear ratio. 4 speed vs. 3 speed vs. 2 speed vs. High gear only. And then there are throttle stops and ignition retards, etc. Take care. Tom Worthington
I should of mentioned, the cars Im discussing and my car and manual trans cars. Gear ratio I know plays a part but our gear ratios are real far off. Guy I know running 148 has a 3:73 rear, my car is a 3.91
 

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Weather, power, weight, aero, converter, and gearing for the proper rpm of your combo.
Doug
 

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It looks like most of the possible scenarios have been answered.

Gearing, weather, aerodynamics all play a part. Look at the time slips and compare the 60 ft, 330, 1/8 etc. and you find some cars leave harder but mph less while others with the same rwhp will really come on top end.

Typically a turbo car will out mph a nitrous car if they are both at the same power level.
 

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Discussion Starter · #11 ·
It looks like most of the possible scenarios have been answered.

Gearing, weather, aerodynamics all play a part. Look at the time slips and compare the 60 ft, 330, 1/8 etc. and you find some cars leave harder but mph less while others with the same rwhp will really come on top end.

Typically a turbo car will out mph a nitrous car if they are both at the same power level.
The only difference in the time slips was the first half of the track, and thats why Im only asking about MPH, because of your exact statement. Whats happening is the exact opposite of whats always said. For example, because of the tires on my car and the excessive wheel spin my car 60' is way less than these other cars, up to .5 in some cases. But there lies the issue, they dead hook on a slick and have 7-8mph on me at the end, when everyone always says wheel spin doesnt effect mph. That has to be untrue by these examples. My time time to the 1/8 is slower as well because of spin, yet Im gaining more mph the back half of the track then they are and still coming up way short.
 

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The only difference in the time slips was the first half of the track, and thats why Im only asking about MPH, because of your exact statement. Whats happening is the exact opposite of whats always said. For example, because of the tires on my car and the excessive wheel spin my car 60' is way less than these other cars, up to .5 in some cases. But there lies the issue, they dead hook on a slick and have 7-8mph on me at the end, when everyone always says wheel spin doesnt effect mph. That has to be untrue by these examples. My time time to the 1/8 is slower as well because of spin, yet Im gaining more mph the back half of the track then they are and still coming up way short.
Some cars will run faster with a little bit of wheel speed (tire spin) now if you are blowing the tires off and 60 ft times are way off the the tire spin will have a big effect on performance. A half second in the 60 ft is huge.
 

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Discussion Starter · #13 ·
Some cars will run faster with a little bit of wheel speed (tire spin) now if you are blowing the tires off and 60 ft times are way off the the tire spin will have a big effect on performance. A half second in the 60 ft is huge.
The best one of the 60' on the other car was a 1.51, the worst on my car was a 2.1. Im on street tires, good street tires but still street tires none the less. With almost 800rwhp I dont think Ill ever be able to hook in first, Ive tried slipping the clutch, rolling out and hammering it, rolling out and easing into it. It spins regardless and the 60' times dont hardly change with any of those methods. I will be putting a slick on here within the next couple weeks. Ive had a hard time find the wheel for the back with the size and backspacing I need. And since its not a race car, Im not wanting to spend $2k on rear wheels I use 3-4 times a year.
 

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Discussion Starter · #16 ·
How do you even know the dyno numbers are right for each car ?
I cant answer that, all I know is what each car made on the dyno, to get in to where one dyno read more or less than the other I dont think really makes a difference, I cant imagine one dyno would be off by 100hp or more which is what it would have to be to have that discussion about the change in mph. Sure I understand there may be small factors but none of those account for huge horsepower that it would take to run so much faster
 

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You can't compare drag strip mph to the mph on computers. They are calculated differently. The computer will typically read higher.

You can't really compare rwhp numbers from different cars on different machines. There are too many variables that can change the final number.
 

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Discussion Starter · #19 ·
You can't compare drag strip mph to the mph on computers. They are calculated differently. The computer will typically read higher.

You can't really compare rwhp numbers from different cars on different machines. There are too many variables that can change the final number.
I dont think anyone is reading whats happening. We all know what everyone always says, and you said the same thing thats always said to be true. The computer will read higher. Then why is mine reading 8mph lower? And Im not splitting hairs here on dynod and variables. I get it different machine read different numbers, but Im not talking about another mph and 10-20hp differences here. We are talking almost 10mph. Sorry but I have yet to see a dyno that reads 100+ hp differences from another, regardless of brand. If that were happening that company is out of business.

So the question remains, everyone keeps saying the statements "wheel spin will create a higher mph" and "the computer will read higher than the track" (which also btw has been checked several times and the dragy has been within a half mph at the most on most passes). So if all these variables would give me a higher mph then why is it so much lower on a car that weighs close to the same and has close to the same power. They are both Centri supercharged and The only difference is tire.

I guess what Im trying to disspell is that there is more to the story thanthe statements of wheel spin will create higher mph. I guess its not the case on all cars is all. Now obviously Im not talking about spining for 300', obviously thats going to lower mph at the stripe. Im talking spinning during the 60'. So that begs the question, if I lowered my 60' to the same 1.5 they were running, would my mph go up to around theirs? The internet tells me my mph would be even slower. Thats the point of this thread.
 

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I dont think anyone is reading whats happening. We all know what everyone always says, and you said the same thing thats always said to be true. The computer will read higher. Then why is mine reading 8mph lower? And Im not splitting hairs here on dynod and variables. I get it different machine read different numbers, but Im not talking about another mph and 10-20hp differences here. We are talking almost 10mph. Sorry but I have yet to see a dyno that reads 100+ hp differences from another, regardless of brand. If that were happening that company is out of business.

So the question remains, everyone keeps saying the statements "wheel spin will create a higher mph" and "the computer will read higher than the track" (which also btw has been checked several times and the dragy has been within a half mph at the most on most passes). So if all these variables would give me a higher mph then why is it so much lower on a car that weighs close to the same and has close to the same power. They are both Centri supercharged and The only difference is tire.

I guess what Im trying to disspell is that there is more to the story thanthe statements of wheel spin will create higher mph. I guess its not the case on all cars is all. Now obviously Im not talking about spining for 300', obviously thats going to lower mph at the stripe. Im talking spinning during the 60'. So that begs the question, if I lowered my 60' to the same 1.5 they were running, would my mph go up to around theirs? The internet tells me my mph would be even slower. Thats the point of this thread.
Yes if you could drop your 60 ft time a half of a second your MPH would be faster at the stripe. While your car is spinning the tires you are not accelerating as fast as a car that is not spinning the tires . More acceleration equals more MPH.
 
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