Off-topic Talk Where overpaid, underworked S2000 owners waste the worst part of their days before the drive home. This forum is for general chit chat and discussions not covered by the other off-topic forums.

Stupid Question About RPMs...

Thread Tools
 
Old Sep 5, 2007 | 11:28 AM
  #31  
Saki GT's Avatar
Moderator
20 Year Member
Liked
Loved
Community Favorite
 
Joined: Jul 2004
Posts: 36,017
Likes: 226
From: Queen City, NC
Default

Originally Posted by rustywave,Sep 5 2007, 03:12 PM
edit: nevermind, didn't mean enclosed system. air in, air out. i meant like, drag works on the car, not on the engine...right?
Yes, people are muddling the work the engine does with the overall forces of a car in the real world. 4k rpm is 4krpm, period. You have to realize that as long as there is friction on the car, it will not stay at 4k rpm unless you are constantly accelerating. You need an opposite force to offset friction. That's either the engine accelerating, or another outside force countering friction, like gravity. Its basic physics.
Reply
Old Sep 5, 2007 | 12:14 PM
  #32  
justblazesticky's Avatar
Registered User
 
Joined: Mar 2007
Posts: 81
Likes: 0
Default

when a gear is in a higher gear at a given rpm, it produces more load on an engine. i have proven this with my previous car.

it was a crx with turbo, boost was maintained at a steady level by the wastegate spring in my ext. wg. due to more load in higher gears, the boost level would peak higher than in the previous gear even though the only thing regulating the boost is the wg spring.

there is without a doubt more load on the motor in a higher gear because of the gear ratio. now, in the instance of my turbo car, it resulted in a leaner condition. the load led to the turbo making more pressure, and the leanness is due to more boost for a given a/f ratio. it may be that the extra load added to the leaner condition on its own (for example, leaner conditions for n/a), but i am not certain.

now, dynos read torque as engine output, but i remember reading once that the gear ratio multiplies the engine torque, and real torque at the wheels differs between gears. that's why the s2000 feels as if it accelerates harder in 1st gear vs 2nd gear, and i mention those gears since air resistance is not as great as in higher gears.

the question as to whether more gas is being burnt, i can't tell you. but i know for certain that engine load is a measurement that comes into play for stand alone computers, for example the AEM EMS gives you load outputs.
Reply
Old Sep 5, 2007 | 02:17 PM
  #33  
Austblue's Avatar
Registered User
 
Joined: Sep 2002
Posts: 8,085
Likes: 0
From: 3rd bedroom on the right
Default

Originally Posted by S2020,Sep 6 2007, 04:53 AM
baring friction? what? we live in an imaginary world?

My friend asked me if I can slam dunk from the free throw line. I told him I could, baring gravity.
This is my point you can't make an argument that ignores basic principles.

Here's another tricky one for you guys that think that the tranny is outside the engine therefore not affected. Why does a car with 19" steel chromz accelerate slower than a car with forged lightweights?

And here's one for the 4krpm is 4krpm in any gear, when you're rolling down a hill with no accelerator input and the gravity allows your car to get up to 4krpm, is the engine working as hard?

So now that we've quashed that theorem lets use our melons to reverse that principle and realise that the amount of effort/work required is not independent of the external forces that are applied to the engine and car.
Reply
Old Sep 5, 2007 | 02:23 PM
  #34  
Austblue's Avatar
Registered User
 
Joined: Sep 2002
Posts: 8,085
Likes: 0
From: 3rd bedroom on the right
Default

Another way of looking at it is the by-product of more work done, mileage. Add lots of weight and your car will use more fuel to do the same work right? Well being in 4th gear @4krpm means travelling faster than 4krpm in 1st therefore the effective weight of the car is greater.

If this last bit gets you read up about why ricer wings only work at XXXmph and then take those principles of downforce and chuck in a little coefficient of friction and you'll see the light.
Reply
Old Sep 5, 2007 | 02:25 PM
  #35  
Austblue's Avatar
Registered User
 
Joined: Sep 2002
Posts: 8,085
Likes: 0
From: 3rd bedroom on the right
Default

Originally Posted by Elistan,Sep 5 2007, 11:48 PM
"working as hard" = "making as much power" in my opinion. Perhaps wantone meant it differently than that, dunno, I'm not a mind reader. I also threw in the assumption that we're talking about full throttle. Because if we're at 10% throttle in 1st gear, and 50% throttle in 6th gear, obviously the engine will be making more power (ie, working harder) with the larger throttle opening.
That's why you should always state your assumptions! Why would you assume full throttle? @ full throttle unless we're taking a snap shot the car wont maintain 4krpm w/o an external force keeping it there. Which highlights that external forces need to be taken into account. Now see my previous arguement for a closing statement
Reply
Old Sep 5, 2007 | 02:48 PM
  #36  
GT_2003's Avatar
Registered User
 
Joined: Jan 2007
Posts: 1,135
Likes: 0
Default

the problem with assuming "4000 rpm is 4000 rpms" is the fact that a gasoline engine has a throttle that controls the amount of air ingested, and the amount of fuel by association. More air needs more fuel. More air and fuel makes more power. Running at a constant 4000 rpms demands a different mount of throttle depending on the gear, the slope of the road, the wind direction, and the density of the air.

It's easy to test, however. In an S2000, cruising at 7000 rpms in first versus 7000 rpms in 6th will show an obvious difference in throttle position. By the same token, cruising at 4000 rpms in second going uphill and then going downhill will show that the throttle position is different depending on the load on the engine, even if the rpms are the same. More throttle equals more power. The load on the engine is obviously greater when more throttle is needed to maintain speed in the same gear.
Reply
Old Sep 5, 2007 | 03:36 PM
  #37  
Austblue's Avatar
Registered User
 
Joined: Sep 2002
Posts: 8,085
Likes: 0
From: 3rd bedroom on the right
Default

Break out the champagne!!!
Reply
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
blacks2k
Aus & NZ Off Topic
28
Apr 17, 2008 02:25 AM
nightcrawler7188
Off-topic Talk
0
Mar 14, 2006 05:56 AM
gabedude
Off-topic Talk
0
Jul 20, 2001 07:47 PM




All times are GMT -8. The time now is 08:59 PM.