This is a comparison of a CRX Si Transmission with the stock 4.2 FD in blue, a 4.7 FD in red, and the 4.9 FD in green(? I didn't bother with the colors when I made the graph).

I used a BS dyno plot of 80 ft-lbs throughout the RPM band so obviously it's not real HP numbers, but the fact of the matter is, the final drives give you more HP.

On top of the pretty picture, I've got the math.

Tranny's are just torque multipliers. Engine Torque x gear x final drive.
IE 100ft-lbs on a 3.250 (CRX 1st gear) x 4.2 (CRX SI final drive) = 1,365 ft-lbs.
Now, compare that to the 4.7 and the 4.9 FDs and you get the following:

100 x 3.25 x 4.2 = 1,365 ft-lbs
100 x 3.25 x 4.7 = 1,527 ft-lbs 11% increase over stock
100 x 3.25 x 4.9 = 1,592 ft-lbs 14% increase over stock

Something for all of you to consider.

 

Final Drive...what is the final drive?

EDIT: this is a serious question. I want to know what it is and what it does.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JayKayNidas &raquo;</TD></TR><TR><TD CLASS="quote">Final Drive...what is the final drive?

EDIT: this is a serious question. I want to know what it is and what it does. </TD></TR></TABLE>

The final drive is the "big gear" in your tranny/differential that transmits the power to the axles from the tranny gear set.


This is a RWD FD but it's the same function.

 

I loved my 4.9 final drive with my all motor D16Z6....it's the downfall of all D series.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Spade &raquo;</TD></TR><TR><TD CLASS="quote">I used a BS dyno plot of 80 ft-lbs throughout the RPM band so obviously it's not real HP numbers, but the fact of the matter is, the final drives give you more HP.</TD></TR></TABLE>

I'm aware of the benefits that shorter FD's offer, but is this really the most accurate way to describe that effect?

The FD does act as a multiplier of the engine's torque, but the amount of power that the engine actually generates is finite.

 

you "lose" hp if you run taller tires due to making a larger gearing..

isnt it the same concept?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LowTEC-Derbo &raquo;</TD></TR><TR><TD CLASS="quote">you "lose" hp if you run taller tires due to making a larger gearing..</TD></TR></TABLE>

No, you lose mechanical advantage.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Padawan &raquo;</TD></TR><TR><TD CLASS="quote">No, you lose mechanical advantage. </TD></TR></TABLE>

true. You don't pick up power...think of it as leverage.

Higher final drive=quicker acceleration=lower top speed

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Padawan &raquo;</TD></TR><TR><TD CLASS="quote">

I'm aware of the benefits that shorter FD's offer, but it this really the most accurate way to describe that effect?

The FD does act as a multiplier of the engine's torque, but the amount of power that the engine actually generates is finite. </TD></TR></TABLE>

Ah crap. That's not what I wanted to mean. I meant, you have a higher horsepower curve/area than a stock FD.

CRAP! This is exactly what I didn't want the thread to turn into. LoL Guess I shouldn't have rushed the post.