C5JONNY

Hear are my most recent dyno #'s 306 RWHP 341.9 RWT Gears definitely make the #'s a little wacky. Cant see what the new mods produce!


[Modified by C5JONNY, 3:46 PM 1/19/2004]

runamuk

Horsepower is actually measured using a formula at 5252 RPM (this is why HP and torque always cross at 5252 on your dyno sheets) I don't have the formula in front of me but I can get it when I go home which is why the numbers are distorted on a dyno with different gear ratios

STAGED

Taking friction out of the game, hp should not change regardless of gear ratio as there's a linear and direct tradeoff between rotational speed and torque. But add real world friction, then for higher ratio gearsets, then that's where I believe we have hp losses as I explained above.

For the moment, one should ignore the itemization of the torque and rpm components of the hp eqn. since it doesn't add any ammunition toward explaining the hp change with gear ratio changes. One should merely look at it from the standpoint of the rate of energy/work "budget" and the possible differences in friction when changing gearsets. :flag


[Modified by STAGED, 10:07 PM 1/19/2004]

Tree

Doesn't anyone speak English? There must be an understandable way to explain this to non-engineers that is accurate. I don't believe that's yet been accomplished in this thread.

JJ in FL

Id still LOVE to see a stock 3.42 car race a stock 4.10 car from a stop, from 30mph and from 60mph. I still think a 3.42 car would pull from a roll, they do trap higher, if thats the case I dont understand the love affair w/ 4.10s for the street :confused:

camiv

[QUOTE]Id still LOVE to see a stock 3.42 car race a stock 4.10 car from a stop, from 30mph and from 60mph. I still think a 3.42 car would pull from a roll, they do trap higher, if thats the case I dont understand the love affair w/ 4.10s for the street :confused: I think you need to figure out the type pf tranny and reasoning why one choses one set-up over another. A A4 with 3.73's or 4.10's from a stop, roll, or 30mph is much quicker. I agree that an mn6 with higher gears is not as important or desirable but higher gears in an a4 seems like a must. Just my.02

Midwayman

That because the 4.10 delivers almost 20% more actual torque at the wheels. (This is zero'd out on a dyno because they are trying to give a engine reading based on measurement at the wheels) Its kinda like taking all your gears down a gear. you all know that 2nd accelerates faster than 3rd, right?

Mike Mercury

if you're big into running the 1/4 mile; the problems that more radical gearing can inflict would be ading an additional shift before crossing the timing line.

Once you induce an additional shift (especially that close to the finish line) it takes the rpm back down. On an A4, there is no other gear to use other than OD... and it's useless; especially at the now lower rpm just after a shift.

I remember reading somewhere that those with the 3.73 in the A4 are at or near redline in 3rd gear at the end of a 1/4 mile run. ???????




[Modified by Mike Mercury, 7:05 PM 1/19/2004]

JJ in FL

"you all know that 2nd accelerates faster than 3rd, right?"

True, but while a 4.10 geared car is in 3rd a 3.42 geared car is still in 2nd and will therefore be pulling harder at that mph. This has been discussed before somewhere on here with lots of different opinions. thats why I said Id love to see or read about a race with two vettes where the only difference between the two is the gearing. :)

NIGHTMARE...2001

:lol: :lol: :lol: Thank God they're explaining this, and not me!! :nonod:
Wow...lot's of intellect here! :yesnod:

When I changed my rearend gearing from 3:15's to 3:73's at 21MC, I was told that the change was good for a 7% HP loss(on the dyno)at the rear wheels!!! :( Much more than that was lost through the torque convertor!!! :eek:

CJS

"Doesn't anyone speak English?"

I'll try. Changing the rear gears does NOT change the horsepower that the engine produces at the engine itself.

The dynometer MACHINE that measures the horsepower produced, measures the horsepower wrong if the gears are changed.

This is because the dyno machine is not really measuring the horsepower directly, but it is Calculating it from measurements made on how fast the car can rotate a big heavy drum up to speed using a 1:1 gear ratio.

It seems odd but the dynos in general use in shops DO NOT compensate for rear end gear changes, so unless you are running the stock rear ratio, the dyno is giving a wrong number. The dyno is set up to calculate horsepower using the stock ratio only.

Thats why so many people say the only true test is the track. The track is a true measurement of time and distance and weight (mass). The track is not a calculated number.

Midwayman

CJS, if the dyno didnt allow for compension in gear between a 4.10 and a 3.43 rear end, you would see VASTLY different dyno results between the two cars, with the 4.10 posting better numbers. Engine HP hasnt changed, but mechanical advantage has. In any given gear, the 4.10 rear will post greater measured torque (and therefore HP) at every engine rpm. If the shop cant compensate for a different rear end to give an accurate dyno, you should be looking for a different shop.

And BTW dyno's dont measure HP. They measure torque and calculate HP. There are a number of factors that make a dyno different than a street run. Mostly heat, airflow and traction, but the physics behind turning that rotating drum into a HP measurement are accurate assuming the dyno operator got all the settings right.

knewblewkorvette

you guys are getting me so confused :confused:
I have two simple questions.
1st Will the 4.10s make my mostly stock vette faster from 0 to 60?
2nd Will the 4.10s be bad if I go for more HP, say 600 HP?

Midwayman

1) Yes, you already have to shift once, assuming you have traction.
2) Well at a certain point 1st will become useless..... dont know quite when that is though. My last car had that problem. 1st gear was so short is only made it to 30mph and had enough hp that you barely got the clutch in before having to shift.

Dan_the_C5_Man

I've tried to stay out of this, because I don't want to come off as a know-it-all! :smash:

Yes, 4.10's will improve acceleration in every gear, no question.

No, 4.10's would NOT be a good idea in anything above 450HP. I'm going w/ 3.90's myself, as I feel that is a good "compromise", and I've got a bone-stock motor.

Just for reference, an MN6 w/ 3.90's is roughly the equivalent to a stock Z06 set up w/ a 3.42 diff. (Z06's have different ratio's in the trans.)

Hope this helps.. :D

And for the last time, gears do NOT "add" or "subtract" HP or Torque! The motor is still doing the same amount of work in the same amount of time; it's just that w/ the gear change it has an easier job of moving the mass, so the car will accelerate quicker, but "lose" top speed. (As if the stock gearing had any basis in reality; I don't think anyone here is making enough HP to redline in 6th gear!) :jester


[Modified by Dan_the_C5_Man, 1:00 PM 1/20/2004]


[Modified by Dan_the_C5_Man, 11:02 PM 1/20/2004]

ArKay99

It seems to me that there is some confusion regarding the differences between horsepower and torque.
Horesepower: Horsepower is the imperial (British) unit of power, now replaced by the watt - the new SI unit. One horsepower is the work done at the rate of 550 foot-pounds per second and it is equivalent to 745.7 watts. Horsepower was first used by James Watt, who employed it to compare the power of steam engines with that of horses.

Torque: The measure of the force applied to produce rotational motion usually measured in foot-pounds. Torque is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied.

As can be seen by the definitions. HP is a measure of work done over time, 1 second, whereas torque is a measurement of the force that work is producing at any given instant.

More HP + More torque = Faster. :cool:

Izover4u

:iagree:

Tree

Maybe that's not the case, in which case you could understand the love affair with numerically lower gears. What do you base your assumptions on? I have 4:10's, and it's one modification you can immediately appreciate.

JJ in FL

"Maybe that's not the case, in which case you could understand the love affair with numerically lower gears. What do you base your assumptions on? I have 4:10's, and it's one modification you can immediately appreciate"

If its not the case, I will go buy some 4.10s. I baseing this on some past experience w/ other cars. And the fact that a 4.10 car is in 3rd while a 3.42 car is still in second, and a 4.10car is in 4th, when a 3.42 car is still in 3rd. I think 4.10s are great if you are looking to race in only 1-2 gear, or if you drag alot. I just cant see a 4.10 car hanging w/ a 3.42 car from a roll. I wish someone would prove me wrong, its the last mod I can buy and keep my warranty. :thumbs:

CJS

Quote "if the dyno didnt allow for compension in gear between a 4.10 and a 3.43 rear end, you would see VASTLY different dyno results between the two cars, with the 4.10 posting better numbers"

Sorry, but the real world is different than this above view. Many on this forum have dyno tested before and after gear chage of 3.42's going to 4.10's and the TESTED horsepower always goes DOWN about 15hp at the rear wheels.
Ask any dyno operater on the forum if his dyno has an adjustment for different gear ratios, lets see who has that feature on his dyno.
The problem is that current dyno machines are far from perfect in measuring true HP, they are a great tuning device though.