Theoretical Top Speed Increase Question - TCCoA Forums
 
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post #1 of 14 (permalink) Old 06-16-2004, 02:03 PM Thread Starter
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Theoretical Top Speed Increase Question

I am still trying to figure out how you can ever go faster than stock without changing stock gearing. Let's say a 97 4.6 with 3.27:1 has a top speed of ~145-150 at 5250 rpm in OD(not good for tranny). Now that's with 205hp and 280tq. If you upgraded and had 410hp and 560tq(hypothetically), how would you be able to go faster than 145-150 in top gear at 5250? Assuming no slip losses from either the drivetrain nor from the tires, in either the modified or unmodified tests, how would the car achieve a greater speed?

This is all theoretical. Do not misconstrue this as questions for the open road. It is only about gearing and acceleration.

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post #2 of 14 (permalink) Old 06-16-2004, 02:23 PM
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if the only thing you changed was the power output of the motor you would still be going the same speed at any given RPM. Although, if you had 410hp, you could turn more than 5250 rpm's in top gear, so you would go faster.

If you changed the rear end to something lower numerically, though, then you could put that power to use and achieve higher speeds.
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post #3 of 14 (permalink) Old 06-16-2004, 03:19 PM Thread Starter
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So I am correct in thinking that with the same gearing you can never go faster speeds at the same RPM in the same gear, you just accelerate to your top speed quicker (assuming same RPM limit) ?

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post #4 of 14 (permalink) Old 06-16-2004, 03:28 PM
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post #5 of 14 (permalink) Old 06-16-2004, 03:43 PM
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HP does have a significant part in being able to obtain the top speed. Just because you have the gearing to do it, does not mean the car can or will for any significant time hold that top speed, you still need the power to do so.

I could put 2.73's in my car and say it would go up to 180 mph but without the power to do so it still is not going to do it. (These numbers are just arbitrary and theoretical to demonstrate the idea of HP being important to top speed.)

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post #6 of 14 (permalink) Old 06-16-2004, 04:06 PM
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Check the math... I believe that 150mph would have less than 5000rpm with 3.27 rear end. I can state for the record though, that the theoretical top speed is greater than 152mph. At less than 5000rpm.

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post #7 of 14 (permalink) Old 06-16-2004, 06:41 PM
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There is gear limited top speed, and power limited top speed. The latter is our limitation.




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post #8 of 14 (permalink) Old 06-18-2004, 01:02 AM Thread Starter
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power limited top speed will soon not be the issue, as I am upgrading(for Texas World Speedway or a sanctioned track). Now, assuming a stock 26.9" diameter tire, 3.27:1 gears, stock 4R70W overdrive gear, at 5250rpm, what is the non-wind corrected top speed(theoretically)? Peter M, PM me about how you came to your findings.

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post #9 of 14 (permalink) Old 06-18-2004, 01:45 AM
 
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Quote:
Originally posted by Peter M
Check the math... I believe that 150mph would have less than 5000rpm with 3.27 rear end. I can state for the record though, that the theoretical top speed is greater than 152mph. At less than 5000rpm.

Don't ask.




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You said don't ask but I have to sorry... You've gone over 152 miles an hour? How do you know, do you have an aftermarket speedometer that reads that high. I hit 135 to 140 and almost pissed my pants, I cant imagine 150+.....Hope you dont have stock brakes.

And I hope I never get a MMX Driveshaft or I may have to do some experiments.

Please PM me if you don't wanna reply out here.
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post #10 of 14 (permalink) Old 06-18-2004, 10:20 AM
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Quote:
Originally posted by 46cougrrr
power limited top speed will soon not be the issue, as I am upgrading(for Texas World Speedway or a sanctioned track). Now, assuming a stock 26.9" diameter tire, 3.27:1 gears, stock 4R70W overdrive gear, at 5250rpm, what is the non-wind corrected top speed(theoretically)? Peter M, PM me about how you came to your findings.
Then your going to have downforce isses. you won't be able to go over 160-something without it becoming very dangerous. You'll need a splitter, and a spoiler (one that actually works), suspension work, and adequate tires.




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post #11 of 14 (permalink) Old 06-18-2004, 10:56 AM
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If you want real world answers check out this article J wrote on taking a Marc VIII to the salt flats

http://mark8.org/lod/bonneville.htm

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post #12 of 14 (permalink) Old 06-18-2004, 05:51 PM
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3.73's work out to ~148mph @ 5000rpm in OD, I figured the math on that some time ago.
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post #13 of 14 (permalink) Old 06-19-2004, 04:35 AM
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With 3.27 gears, the car will be going near 180 mph at 5300 rpm. I calculated it by checking the rpm at, say, 70 mph and then multiplying the speed by redline rpm (5300) divided by current rpm.

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post #14 of 14 (permalink) Old 06-19-2004, 09:01 AM
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If you guys read the article J says it's best to make the run in third rather than OD because there are no gears involved it's 1 -1 and the most efficient. Also notice that after their 3 mile run the trans temp was 250 *

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