Nitro-C5

Is there an actual formula that shows the Dyno difference when going from the Stock 3.32 gears (on a M6) to going to 4.10 rear?

Stock M6 is pretty well considered 15% loss, while an auto is 20% loss. Where would these gears land? I've heard 17 and 18% does this sound about right?

2thDr

There should be absolutely zero difference in HP on the dyno.

Nitro-C5

:iagree: There "should be" absolutely no difference...but there is. How and why I'm not quite sure, but WAY to many people and tuners have reported HP fluctuations when changing gears.

FRC21

There WILL be a difference because you are no longer at a 1:1 ratio in 4th gear.

chuckster

The transmission is ALWAYS at 1:1 in 4th gear. It's the rear end that is being changed.


So that being said and with a 4.10 rear.. ...For every 4.1 rotations of the Engine... the rear wheels turn one full rotation.

There is a minimal HP loss that show up on the Dyno but it is Bogus.. I don't understand the details but don't worry about it..

Mike Mercury

huh ???? :confused:

kh24

So if for every 4.1 roataions of the engine, the rear wheels turn one full rotation wouldnt that mean that a gear like 3.42s would be better. I mean with that logic it would only take the engine to turn over 3.42 times to rotate the rear wheel instead of 4.1 times. I dont fully understand how gears work but i thought the point of switching to a 4.10 was so the wheels rotate faster. From what your saying it looks like it would make them rotate slower

As for the hp loss, I figure about 17-18% instead of 15% sounds good.


[Modified by kh24, 7:27 PM 4/15/2003]

chuckster

4.10 Gears make the motor turn faster and the wheels slower but more powerfully. The gears are doing most of the work. That is why they make you feel like you added 70hp...

Think of a 10 Speed bike...In first gear you can pull a wheelie by just pedaling.. But... you can't go very fast...
You give up speed for Power..
Think of the 4.10's like 1st gear on the bike.. and say the 2.75 gear is like being in 10th gear on the bike... :lolg: :lolg:
http://science.howstuffworks.com/gear.htm




[Modified by chuckster, 8:05 PM 4/15/2003]

Nitro-C5

Chuckster,
Excellent explaination! I've had the 4.10's for over 6 months now and believe me the SOTP difference is awesome. Not worried about the dyno being lower I'm just trying to find some type of formula that would easily equate...does the 17 to 18% sound about right ot you?

The main reason I'm asking is that I'm having some very extensive motor work done in the next few weeks and I'm trying to hit the magical # of 800hp (at the crank of course) and the few % points with the different rear may effect my ultimate goal.

kh24

If your trying to hit 800hp and your keeping 4.10s, i guess its safe to say that this isnt going to be a car your gonna run at the drag strip.

NEPTUNEBILL

There have been many explanations of this on previous post I don't really understand it myself and will experiment shortly with my 390s, the dyno is set to calculate hp at the wheels based on a 1 to 1 ratio, the 1 to 1 is there in the c5 and the zo6 in 4th gear though the trans gear ratios are dif in the other gears, as a test if you dyno in 3rd gear you will get less hp because of the lower final drive ratio, try to dyno in 5th gear and you will have more hp because in 3rd you are more than 1 to 1 and in 5th you are less than 1 to 1, so the hp is the same of course the dyno just reads it diff. any additional drive train loss would be minimal I would think I wish I could remember the post where this was explained by a member who seems to understand this, I was told by a friend a couple of nights ago that from 3.42 to 3.73 was between 8 and 11 hp based on percentages you would think that the 410s would cost you in the 15 to 20rwhp. It would seem that to 373s it about 2%, 390s a little over 3% and the 410s in the 4% range. I will post after I re-dyno with the 390s.

Mitch C

:iagree:

If I remember correctly Wallst Al said his car lost 9 RWHP on the dyno when he went from 3.42s to 3.73s. Another forum member reported losing 10 RWHP on the dyno when he went from 3.15s to 3.42s.





[Modified by Mitch C, 12:38 AM 4/16/2003]

rwj383

Nitro-C5- you shooting for 800hp?!?! Please tell us how you get there!! If this is true, you will not like your tall gears anymore. you'll never be able to use first gear, maybe get some traction in 2nd and so on. People really benefit from tall gears in a <500hp car at the strip because the taller gear converts the available tq to the rear wheels faster (the 10 speed bike is a good analogy). But the bigger motor you build and the more available power you have, the less need for all that help out back at the gears. eventually your power will overcome the rear wheels too fast with tall gears. One answer is to put a bigger (taller) drag tire on to realign your ratio. this is fine, but what about the street? if you are like me, you will be driving your car around on street tires. I am currently challenged with a decision since i am having an even bigger motor built. Do i want to go from 3.42 to 3.90 gears with a nitrous fed 436? No, i dont want to do this. However, since i roll around town with tall 345/30/19 Pilots, I would definitely benefit from a slightly taller gear. So, do i buy the 3.73 or 3.90 then have tall drag tires for the strip?? we'll see. anyway, point being is that your 4.10's wont work too well for you with an 800hp motor.

Tell us more about this motor....sounds great.

Scissors

Simply put, divide 4.1 by 3.42, then take the result and multiply it with the RWTQ. Then chop a bit off. Going to the 4.1 rear gear will increase rear wheel torque, but not affect HP mathematically speaking. In reality, the further any ratio gets from 1:1, the more drivetrain losses you see. So the formula isn't exact, but it's close.

:lolg: That's funny!

Seriously, though, as dyno after dyno have shown, the A4 in the C5 loses only about 12%. The manual is even better.

STAGED

I would not even pay attention to leverage difference since the speed & torque tradeoff is a linear relation. Theoretically if you neglect lubricant friction (not realistic), power should never increase or decrease with a gear change.

I like to say in real life, the losses may be due to the smaller area of contact at higher numerical ratios cause a thinner film thickness of lubricant for given load. For given sliding speed of the gears in contact a thinner layer of lubricant means higher VELOCITY GRADIENTS. Higher velocity gradients mean higher shear (viscous) stress. Higher shear stress in turn means greater heat generation that cannot be recovered. This increased heat generation rate is offset by power loss.

To verify this one could run a 3.42 diff'l gear C5 and a 3.73 or 4.10 geared C5 in strict climate controlled dyno room environment. Make measurements on the vehicle at same ENGINE RPMS and GEAR SELECTED, not wheel rpm (with the realization that wheel speed for given engine rpms and gear selected on the higher numerical ratio car will be slower). Then measure the temperatures of the casing until it reaches steady state. If the higher diff'l ratio setup has higher temps, then my test and explanation is correct. If not, then I will have to rethink where my logic went wrong with the test procedure.

NEPTUNEBILL

Assuming wallst al has an m6, which going from a 3.42 to a 3.73 would seem to indicate, the diff in the 3.42 and the 3.73 is 9% and he lost 9hp or 1hp for each %point he has altered the 1 to 1 final drive ratio, the other member went from a 3.15 to a 3.42 (obviously an a4) which is 8.5% diff in final drive and he lost 10hp which would seem about right as the a4 tend to dyno diff at the wheels. Based on this the 390 is 14% diff than the 342 and it would indicated a 14hp loss at the wheels, the 410s are just under 20% diff and would indicate a 20hp drop at the wheels, this seems to be concurrent with the info so far, so to 373s =10hp loss, 390s=14hp loss, and 410s = 20hp loss, it will be interesting to see how close this comes as time goes on, with more info we should be able to come up with a similar formula for the a4, I also wonder if this figure varies with the amount of hp one has, for instance I don't know what hp wallst al is running but is there a diff % of loss if you have a 600rwhp car compared to a 400rwhp car.

CJS

The reason that a dyno reads lower HP with 4.10's compared to 3.42's is in the way the dyno works and calculates HP. There is no true loss of HP on the car. The only loss is in the innaccurate way the dyno reads the HP.

Mitch C

:iagree:

Nitro-C5

Currently having a forged 383 built that will withstand heavy doses of N20. Really trying to see MAX engine HP can be. Will shoot for dyno number with around a 250 - 300 shot. Will NOT run this shot all the time, for durability issues will probably use a 175 to 200 shot mostly. Once again just seeing the Max output on the engine. Going with a TT before winter so I would like to know the limitations before then. Also I had the 4.10's installed awhile ago, I know not ideal for this set-up but still fun on the street.

Nitro-C5

12% :confused: Never heard that before. All info i have read shows numbers from 19-20% for auto's and around 15% for M6. These are based on totally stock car. Could you please show me some information about the 12% number for autos, and using that theroy I guess M6 would be closer to only a 7-8% loss.