Does Lower Final Drive Change Dyno Numbers?

**WhiteAP1** · 21-09-2006 06:12 PM

A different ratio will increase the amount of times ure drive shaft turns per revolution of the wheels.(obviously)I wouldnt put ure 10 extra kw down to FD. It MAY do something for ure torque figures, but ive never heard of any dyno gains showing due to FD. Perhaps if u put ure car on the dyno before and after the different FD, u would see what Dyno Dave means by a "small margin", practically nothing. Many S2000 owners have changed their FD and apart from a shit load more response and shorter gears, there are no reports of increased dyno figure, then again they're different cars with a different layout. Any advantage ure FD has over ure mates car wouldnt really be evident on the dyno. Thats my 2c in my experience.

**barefootbonzai** · 21-09-2006 06:28 PM

it's no biggy, was just asking if it affected it or not, and if it did it would increase the number not decrease. But string was saying the opposite...

**barefootbonzai** · 21-09-2006 06:32 PM

first post

Originally Posted by string

incuring a greater (engine) torque loss.

2nd post

Originally Posted by string

a final drive will increase wheel torque

WTF is that shit!

**WhiteAP1** · 21-09-2006 06:42 PM

Ure new ratio has shortened every gear. Hence shorter run time, and due to that, a smaller read out/plot.

**string** · 21-09-2006 06:43 PM

A torque on an object causes angular acceleration. The ammount of energy needed to accelerate an object to a given rate of rotation is a constant, regardless of the time taken to get it there. Power is defined as energy over time.

Wheel torque, is defined as the ammount of torque acting at the wheels, i.e. engine torque * gearing ratios. As you increase the final drive multiplier, you increase wheel torque, which is what accelerates the car.

Doing a 1000->8000rpm run for example; two otherwise identical engines, one with a shorter final drive, i.e. higher wheel torque, will run through the RPM range FASTER. In this shorter ammount of time, the same drive-line components must be accelerated at a greater rate. Greater rates of angular acceleration = greater torque required to do so = less engine torque available to spin the rollers of the dyno = less 'read-out'.

Now chances are, that this incured loss may be so small (due to any number of factors specific to the setup) that individual result variations may be greater, so testing for this in the real world is difficult.

Realistically the best test of real, usable power is the drag strip. Dyno numbers are a wank.

**barefootbonzai** · 21-09-2006 06:46 PM

my bad. you're way too technical for this brother. but yeah i think i know what you're saying.

**string** · 21-09-2006 06:59 PM

It's hard to believe theory, when real world results sometimes say the opposite. The problem is there is so many variables in the real world, that it's so difficult to attribute a single cause to a single effect.

The problem I have with dyno figures is that they are similar to, for example, the BMI way of measuring obesity. The general public require a non-technical way to measure a car's performance, and "at the wheels" figures are the common place measure. I think they are a great measure (inertial dyno's anyway) of performance, and you can get pretty close estimates of quater mile times, just from simple rules of thumb. The problem occurs when people start to take the numbers seriously, and compare them as if dyno figures are the word of god.

**fatboyz39** · 21-09-2006 07:24 PM

barefoot, FD does effect dyno number. Don't think there will be a BIG difference, but numbers will change.

**Encor3** · 21-09-2006 09:07 PM

read what string wrote and +1 rep point for you because i learnt alot from it good on ya

**barefootbonzai** · 22-09-2006 01:10 AM

I'll tell you what, String was getting wat too technical to really benifit me. Fatboyz and Dyno Dave have pretty much answered what i wanted to know. Theory doesn't mean much to me, i'm more of a do it sort of guy.