No theres alot more to it than that. It has to do with motor spin up rates, gearing and internal friction of the motor, MOI(moment of inertia) of the rotating componets being spun up faster due to higher numerical gearing. The explanation is very involved. Alot more so than youd expect. Its not as simple as "the gears are heavier", or" The gears are not cut the same so theres more friction". Yes those come in to play but are minimal.

Ill attempt at a feeble explanation.
to make it easier to understand I use a trick. To explain some thing like HP and where its going its easiest to solve the problem in the simplest terms. Energy(in this case HP) and where its going. What is using and consuming the "energy" the motor is putting out?

Ok..say you floor your car in nuetral with no load. It takes 1.5 seconds for the motor to go from 800 rpm to 6200 rpm. Say we already know the motor puts out 320 flywheel hp from an engine dyno. So you can say it takes 100% or all of the 320 hp to accelerate the engines own components from 800 to 6200 rpm in that very short time of 1.5 seconds. Without doing more mods or lightening up the internals or reducing friction this is the maximum the engine can accelerate and it requires 100% of the power to do so. I call this the "Minumim no load spin up rate". Its an odd concept. We always think of the motor as in terms of power output. But fact is under certain curcumsatnces the motor uses much of its own HP(energy) to sustain or accelerate itself.

So lets go to the oppisite end of the spectrum to give a comparison. Now the car is on a dyno and in 4th gear. You spin it up from (for arguement sake)800rpm to 6200 again. Now it takes say 15 seconds to acclerate the exact same rpm range. Now where is the energy going? since the engine rpm is increasing at a much slower rate much less of the energy(HP) is being consumed to accelerate the engines own components. It is being transmitted to the wheels through gearing.

Ok now lets split some hairs an put in 4.10s in place of out 3.42s and if you timed the runs you would see that with 4.10s due to mechanical advantage would spin up from 800 to 6200 rpm at a slightly faster rate say 14.5 seconds. Since the time is closer(although slightly) to the "minimum no load spin up rate" there is more energy being consumed by the motor/drivetrain to spin up its own components.

Now to test this theory. Put a car on the dyno and dyno in 4th. See what you get. Then dyno in third and see what you get. Then second, then first. You would see that 4th gear dyno would be for arguement sake say 300 hp. In third you would see maybe 275. in second maybe 220 and in first it would be probably less than 200 hp to the wheels. And you would see that the acceleration times (800-6200rpm) would be less and less as you got into the lower gears. Again...the closer you get to the "Minimum no load spin up rate" the less HP youll see at the wheels and the more HP it takes for the engines own components to accelerate itself.

This is the simplified version. We could get into it further and compare acceleration times of RPMs VS mph in different gears. And see what work is being done at the wheels. The faster the motor spin up rate the less work at the wheels. Hence the lower dyno #s

None of these #s have been checked and they are just generalizations. So dont pick them apart please.

Al

[ November 24, 2001: Message edited by: 383LQ4SS ]

[ November 24, 2001: Message edited by: 383LQ4SS ]

[ November 26, 2001: Message edited by: 383LQ4SS ]</p>

 

whew!

The concept is a bit more clear to me now. Thanks for the explanation <img src="images/icons/smile.gif" border="0"> (something you dont usually get on the "other" boards)

 

No problemo! I did post it once over there but it was a long time ago. The new board rocks <img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" />

 

Good explanation. I went through this like ten times and stopped doing it for people. I should get together with several people and make an FAQ list of all these misunderstood deals like the HP vs TQ question which is easily the best of all time.

I have actually seen guys say this proves that dynojets don't work and stuff! Hopefully this site can help reduce the general ignorance of the aftermarket car modification public. Sometimes I have flat out given up. <img src="images/icons/rolleyes.gif" border="0">

 

Lol...I know. Everytime I see this question I usually run and hide. But sisnce its a new board and all.....But yeah...a FAQ page for these hard to grasp items would be good. I hate thinking about it to be honest...it hurst my head lol.

 

Yep, good response 383LQ4SS, and thanks for taking the time to type that out.


Chris

 

383, Great explanation!

 

I'm sure lots are tired of this topic but can someone explain to me if gears really do hurt on the dyno..I hear they do/don't from many people but majority of people say they do..can someone please explain why they do hurt dyno numbers if so cause I'm clueless on the topic and my friends would really like to know too..thanks a lot

 

They take away about 5rwhp...but make up for it on the street....they are harder to turn thats all...

 

they have more teeth...

 

thanks for the quick reply BIGBOS, but just harder to turn..what do you mean by that? thanks

 

Thanks for the replies to everyone..I'm understanding it now but does anybody else have anymore good info on it? I believe it's been explained perfectly already though <img src="images/icons/smile.gif" border="0">

 

BrianLS1, good question. 383LQ4SS, great explanation - now I know where to go for my tech. questions. <img src="images/icons/grin.gif" border="0">

 

Al can you break that down to me again <img src="images/icons/grin.gif" border="0">

 

One more reason I am over here instead of "The other Boards." Great explanation..

 

Yes...it feels like there is a renewed sense of interest here. Man the "other" board has tumbleweeds blowing through it. <img src="images/icons/tongue.gif" border="0">

 

[quote]Originally posted by 383LQ4SS:
<strong>Yes...it feels like there is a renewed sense of interest here. Man the "other" board has tumbleweeds blowing through it. <img src="images/icons/tongue.gif" border="0"> </strong><hr></blockquote>

You aint lying. Place is a ghost town to say the least. Good explanation BTW. <img src="images/icons/smile.gif" border="0"> Its great when someone takes the time to explain something that well in detail.

 

Great explanation! <img src="images/icons/cool.gif" border="0"> Very easy to understand.

 

Chris.....Oh I definately agree with you. Its what works at the strip that counts. This was just a discussion on how and why. Be sure to post the results.......Al

 

[quote]Originally posted by Visceral:
<strong>Interesting enough, today or tomorrow MTI is going to re-dyno the car.

Only change? 4.10s

So we shall see what the difference is on paper...

Would I rather have 4.10s or 5hp on the dyno?

If theres any question in your mind, you havent driven a MN6 F-body with 4.10s <img src="images/icons/grin.gif" border="0">

chris</strong><hr></blockquote>


I'm real interesting in seeing those results, as I always wondered what my dyno numbers would have been on my 98 without the 4.10s. With the 4.10s the car dynoed 320rwhp.