short version: it drops the top speed, but the car doesn't have the HP to get to it anyway so it doesn't matter.

i set this up when i was trying to see what a 4.88 would do to my cruising speed.

http://calc.teammfactory.com/gearcal...ission+1+%26+2


you can put in other Final drive ratios to see the changes. or you can put in the manual gear ratios and play with that.

Attachment 124496


Sent from my iPhone using Tapatalk

And I was wrong!
60mph at 2,200rpms.
That pic is with the 4.88 FD


Sent from my iPhone using Tapatalk

Knock is pre-ignition of the air-fuel mixture... based on too much compression.

Octane number is a relative measure of knock resistance. Many formulations can be called 95RON... but they all have a the same knock resistance. This is equivalent to a mixture of 95% iso-octane and 5% n-heptane.

Some chemicals resist knock better than either of the above chemicals. Ethanol is one of them... which makes it great for turbocharged applications that generate high cylinder pressures.

Real knock resistance is a function of cylinder pressures and temperatures:
http://www.rx7club.com/attachments/a..._pressure4.jpg

Maybe i missed it skimming through... How does 4.88fd affect gas mileage? Im not too familiar with how each gear scales and stuff.

The big difference on MPGs is with right foot, no the FD or FI alone will make a huge difference.


Sent from my iPhone using Tapatalk

For all the hassle, cost and expense I'd honestly just get another car!
Esp if the 0-60 goals etc are high priority

While changing from 4.10 to 4.88 FD reduces the load on the engine, in theory this should give better mileage, but in reality you'll waste so much more gas having fun with the new FD that it usually reduces MPG. In the AT, the traction control comes on almost immediately with a 4.10 FD. With the 4.88 FD though, I was able to spin tires in 3 gears before the traction control kicked in. An example of bad MPG while having fun. There are websites that have gear/speed calculators to tell you what your engine speed change is, but the bottom line is the way you drive, AND the way your car is tuned will affect MPG a lot more than a 4.88 FD.