civichatch92

i have a 92 civic h/b si, as of yet no exhaust well aftermarket one anyways. i was juts wondering why my friends that ever drive z24, which is a chev , why can he stay in first gear and go up to 40 km b4 shifting into 2? his only redlines at 5 or 6 and mine goes to 7 or 8, i don't knwo if that makes a differnece but i have to shift gears from 1st to 2second soon as i hit like 20km. should i be shifting when i hit 3 rmp? or when is it best to and it it possible to buy sumthign to make my rpm extend more? anyone understand me or was that just a dumb question

ryuujin

the Z24 most probably has a longer gear ratio than you That's why they can wait longer to shift

imported_MY SiR

Hey CivicHatch92,

That wasn't really a dumb question at all but it is a matter of gears. Actually, I think what ryuujin meant to say is: "the Z24 most probably has a TALLER gear ratio than you" From the way you worded your question, I doubt you really understand Ryuujin's answer.

Here's a better description. Remember, it's all in the gears.
First, there are 3 types of "gears" you have to think about.
First is the transmission, second is the differential and third is the wheel/tire size.
For argument's sake,
let's say 1st gear in your transmission has a gear ratio of 3:1. That means if the engine spins 3 times, the output of the transmission will spin once.
Next, let's say your differential has a ratio of 4:1. That means if the input (which is the same as the out of the transmission), spins 4 times, the drive shaft/wheel will turn once. Now if we combine the first two, if the engine spins 12 times (3x4), the wheels/tires will spin once.

So, if your engine is spinning at 2,400 rpm, that means the wheels are spinning at 200 rpm (12:1). If you have a 185/70R14 tire, the circumference ((14 inch x 0.0254 m/inch + 0.185m x 70% x 2) x pi) would be 1.93 m x 200 rpm = 386 m/minute x 60 minute/hour = 23,160 metres/hour or about 23 kph.

These numbers are just examples but could be close to your friend's Z24. Your honda probably has a shorter (numerically higher) first gear ratio i.e. 4:1 instead of 3:1.

Regarding the question of when to shift, well, it depends. If you want to maximize fuel economy and engine life, I would say shift around 3,000 rpm. If you want to go fast, shift at red line and let the VTEC kick in! Don't expect good fuel economy though.

About "extending rpm", I wouldn't bother if I were you. If you were to change them so, you don't have to shift so quickly in first, you would be really slow off the line. Have you ever tried to start to drive in 2nd gear instead of 1st? What happens? Well, in a sense you would be doing the same thing to what you asking about "extend rpm".

make sense?

Mark

civicrydah

this may not be answering ur question...but personally i tend to think of transmissions like an 18 speed bicycle. first off, u know what the gears look like on a bike rite? its the circles with teeth on them on the back tire. but of course u knew that!!!

the first gear is like the smallest gear on a bike (the one that is really easy to start off with, and the one smallest in size). once u get to a point where u gotta pedal really really fast and u get tired, u switch to a bigger gear which has a bigger diameter...thus causing u to lower ur RPM's. this process repeats itself exactly the same in other gears too.

say u wanted to go uphill on a bike. u would probably use a small gear....same applies to car when u downshift juss b4 u are about to ascend on a hill to get more power. (it wouldnt make sense to go up a hill on a bike in like the 18th gear! dido with a car in 5th gear)

now about the gear ratios....i think to change ur gear ratios u gotta upgrade a lotta parts if u keep stock tranny/engine (i think)....and its expensive.


btw for hondas at least....i know that the shorter the gear the better...cuz of vtec. thats why u see all the vtec engines with smaller gear ratios so they can get into the vtec powerband faster and stay there....

longer gear ratios on civics like the cx, dx, vx are meant for economical purposes. its so they wont waste as much gas. but an si or sir engine will have smaller gear ratios cuz ppl want that extra power faster. i know this cuz i had a dx si and sir civic....and the dx model went up to 60km/h in 1st gear b4 fuel cut off, never really paid attention to my si...but i think the sir is around 40 km/h (havent really paid too much attention to that either)

juss trying to make it easier to grasp.