So I always read the gear ratios and compression ratios, but what exactly are these measuring?

I'm pretty sure the compression ratio measures the air:fuel mixture in the cylinders?? Am I wrong?

What does the gear ratios tell you about how the car will perform?

Long vs. Short Gear Ratios?

I realize one gets you to a higher speed in a certain gear, but TELL ME MORE!

Thanks for any info you got!

Ian

 

10 views and no responses? apparently NO ONE knows about gear ratios or compression ratios!!! hahahaha

 

for some reason, that makes me feel better...I mean I always read the numbers..."final drive ratio" and all that...but I have NO idea what it really means!

 

IF ANYONE HAS ANY IDEA>>>PLEASE POST A RESPONSE!!!

I will buy you a

 

www.howstuffworks.com

 

Compression Ratio tells us the ratio of the volume of the cylinder between its peak expansion versus its peak compression. Basically, you are dealing with the piston compressing the air-fuel mixture in the cylinder.
An engine with a high compression ratio is compacting the air-fuel in the cylinder more than one with low compression. The more you compress the air-fuel, the more it resists being compacted. Basically, you are generating a lot more force and power if you have a higher compression ratio (and the two cylinders we are comparing are equal size).
Easy answer: Higher compression, higher performance.
Gear ratios deal with how your wheel rpms and engine rpms correspond. If the ratio is 1:1, then every engine rpm is equal to every wheel rpm. Different gear sizes are used to reduce strain on the engine or maybe increase HP or torque for a given wheel speed. I can do 80 mph in 5th gear at 2200 engine rpm. The engine isn't working very hard or using much fuel at this engine rpm. But what if I encounter a steep hill and want to maintain my speed? I need to downshift to another gear so I maintain wheel speed up the incline by increasing power output from the engine. It takes more energy and work to go up an incline than just travelling with no incline. I downshift and the engine gets more power (which I need to maintain my speed up the hill) because it is able to produce more power at higher RPMs.
More power means more fuel consumed and more wear on the engine. We need gearing to achieve a good balance of power when we need it without constant wear on the engine.
Hope this helps.

 

example on my mustang cobra the stock gear radio for 99 cobra is 3.28. let said when i doing 80mph on a highway. the rpm is read 2500rpm at 80mph with 3.28 gear radio. now let say i change my gear from 3.28 to 4.10 gear radio. intead of doing 80mpg at 2500rpm is more likely 3500rpm.
can u see the different the higher the gear radio goes up the faster the engine rep.

 

CC...I get it, I get it, Higher Ratio = Higher RPM at a certain speed...which is used to get the engine in your ideal power band i'm assuming? So...if you did go up to a higher gear ratio, you would "essentially" gain acceleration because the engine would now be spinning faster, however....your shift points would be lower in mph??

right?

 

so what exactly is final drive?

 

this is what I'm SAYING!!!??

 

There's the transmission gear ratios, which are the multiplier for each gear that is the ratio between the engine crankshaft and the driveshaft.

The "final drive" ratio is the ratio of the differential itself which splits the driveshaft into powering both wheels -- that differential also has gears, and has one constant ratio which is the ratio between the speed of the wheel half-shafts and the drive shaft.

Engine CrankShaft ==> [TRANSMISSION] ==> Drive Shaft ==> [DIFFERENTIAL] ==> Half-Shaft ==> Wheel

[Transmission] Has a gear ratio (diff. for each gear)
[DIFFERENTIAL] Has final drive ratio

The total ratio between each engine RPM and one wheel RPM can be obtained by multiplying those out.

 

I Get it...

I feel sooo much better...