How much less would you dyno with 3.55 or 3.73

[ElDiablo Viper]

First why the cars dyno less and also how much less?

 

[Newport Viper]

When my car was done www.superiorautomotive.com They said there is no difference with different gears call them.

 

[ElDiablo Viper]

That is strange.

 

[Daffy Duck Viper]

But isn't it true that different gears don't change the power of the engine, only how the wheels receive that power? Based on that, gears would not change a dyno reading. Seems logical to me. Of course, often logic is not reality. *chuckle*
-Daffy

 

[J DAWG]

http://vca2.viperclub.org/forums/showflat.php?Cat=&Board=UBB14&Number=111093&Forum=All_Forums&Words=Dyno%20results&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=6months&Main=111093&Search=true#Post111093

 

[Speedstyle]

As long as you dyno with the same ratio....i.e. 1 to 1 gearing, it shouldn't make a difference. It makes a difference on the street because the power is multiplied to the wheels more. Remember, your engine isnt gaining power, just gaining how its put to the wheels.

 

[Martin D]

Experience tells me you will lose 3% with the gear change....
Maybe your results will be different!

Regards,

 

[Jack B]

An observation - I had a viper t56 on the bench and turned the input shaft by hand in all the gears. There is a substantial difference in the amount of force required to rotate the shaft between the different gears. At higher rpm's the those differences have to show up on the dyno. Although not the differential, there should be some correlation to changing the rear-end ratio and a comparison between different transmission gears.

On the dyno there is no doubt that there would be a recordable difference if you dyno'ed with a transmission gear numerically lower than fourth. On the other hand using a gear higher than fourth would put undue stress on the driveline. For those that start their dyno runs at much lower than 3000 make sure you don't stand to close to the car.

Losses of 15% are real world in a car with half-shafts. If you a assume a max loss of 4% beyond the rear-end, that leaves 11% losses in the transmission, drive shaft and rear end. The 3.55 gears require a 14% increase in rpm's to offset the change in ratio to obtain the same speed. There are going to be some fixed losses that do not change with rpm, therefore, the max additional losses would be 14% of 11%, or 7 hp. Understanding that there are fixed losses the net change on a dyno should result in something less than 7 hp, probably in the 3-5 hp range.

 

[ElDiablo Viper]

Jack, great info! THANKS!