The title sounds ominous. The thought of doing this task was daunting, but I finally got off my duff and did it.
what is it that i have done?
I have created Frankenstein's transmission.
I took a 4spd from a Civic Hatchback and a 5spd from a CRX HF, and created a 5spd with a different final gear... or more accurately, I added a 5th gear to the 4spd.
"what is all this fuss about final gear?" you ask
you'll be sorry you asked, but at least I have pictures.... you could just skip to them.
Final gear (or final drive) is the gear by which all others are multiplied. Remember this for when you look at the tables below... FINAL.... All gears, 1-5+R are multiplied by this gear. Also Pay attention to the individual gear ratios' differences.
FINAL is very important. It's the last gear in the equation. Each gear is actually a pair of sprockets to find the ratio -dividing #of driven teeth by drive teeth- like gears on a bike, but autos use two pairs for each gear, the final pair's ratio being multiplied by every gear on the stick.
For example, if your 1st gear ratio is 3:1, and your final gear ratio is 3:1, your actual 1st ratio is 9:1 (3:1*3:1=9:1).
Now your 4th gear ratio may only be 1:1
but the final drive is still the same gear @ 3:1, so actual 4th is still only 3:1 (1:1*3:1=3:1).
My final is going from 3.25:1 to 3.88:1... it doesn't sound like much, but it's about a 20% increase in tire spinnin' fun off the line versus the HF trans. ALL GEARS get this 20% increase.
blah,blah and so on
So, here are my "4" transmissions. all numbers are ratios x:1.
_______Si__________________HF _____________4spd ______Franky
1st_____3.25______________3.25______________3.25_______3.25
2nd____1.894_____________1.65_____________ 1.65________1.65
3rd____1.259_____________1.033_____________1.033_______1.033
4th____0.937 ____________ 0.823_____________0.823_______ .823
5th____0.771 ____________0.694 _____________X____________ .694
FINAL___4.25______________2.95______________3.888_______3.888
The Si trans is way too low geared for the engine I'm about to use. The HF trans belongs with the engine, but went in a slightly lighter car and has zero torque off the line. So basically I took the 5th gear out of the HF trans and put it in the trans with the 3.888 final drive.
I get the long distance between gears vs the Si trans(lower#=lower RPM), plus a little more oomph where I want it I hope. The engine I'm using makes slightly less torque than the one I'm removing, but it makes it all at a much lower RPM. Horsepower is a function of torque, so the horsepower on this engine is low, but thankfully the fuel economy is high.
I don't believe I'll be sacrificing much economy with Franky, but I'm sure he'll put a little fun into this 70hp engine. Jump for pics.
OK! and HOORAY!
it took me a little while to figure out that the reverse fork bracket from the four speed was keeping me from shifting to 5th, but once I put the other bracket on, it was fine. I forgot to take a pic of that.
Now all I have to do is give the guts a thorough cleaning and lube, and seal the case back up. I'll probably put the other trans back together too, giving me the "bride of Franky 4spd"
BTW, the big ass gear which stayed in the trans is part of the final drive gear which drives the axles.
Update... I do have pics of that bracket. These two pics are best if compared. You can click on any of these pics for larger views as usual.
For more ratio understanding, you can visit this gear ratio calculator and plug in the #s from the chart above, a tire size of 185/70/13, and any speed to see the difference in engine RPM@speed.
http://www.chevellestuff.com/tools/rpm_calculator.htm
