taller tranny

[MetroMPG]

Originally Posted by 95metro

So it's just the torque difference between the 3 and 4 cylinder that makes it bearable with the 4? Any possibility of keeping the 3-cylinder final drive and just changing the 3rd, 4th, and 5th gears to smaller sizes?

It's all about the torque.

[SVOboy]

If you took all the other crap out of my swap it would've only take a few hours with jared's help. The biggest thing I think is experience. Now that I've done it I don't have to fool with all the stuff that went wrong,

EDIT: Just saw I was the motivation, yay. When I get home from this graduation party I'll post my gear ratios for you to drool at.

[95metro]

Originally Posted by MetroMPG

Also, that would mean taking the tranny apart, which is slightly scarier and requires special tools, I think.

Yeah, I know. I tend to make projects more difficult then they generally have to be, but I'm also generally happier with the final results. Of course, in our case maybe the slower 0-60 time is a good thing. We're hardly trying to break any speed records.

A perfect solution would be to fabricate a custom six-speed. I'm always reaching for the shifter and suddenly realizing I'm already in 5th. But, there I go making it even more difficult again.

Still, a full custom gear set would be really cool. 1st to 4th for town and a cruising gear for the highway. Perhaps one of these days when I have a garage...

[95metro]

You got my brain scheming, Darin. Here's some good, general info on transmission gears (copied from http://www.innerauto.com/Automotive_...mission_Gears/):

Most cars have from three to five forward gears, and one reverse gear. The transmission changes the ratio of the engine speed and the wheels by connecting gears in various combinations. If a gear with 10 teeth is driving a gear with 20 teeth, the drive would be said to have a 2:1 ratio. First gear connects the engine power to the drive wheels via a pair of reduction gear sets, which gives increased power and reduced wheelspeed when the car is beginning to move. This means the engine is turning much faster than the output shaft, typically around a 4:1 ratio. Intermediate speeds are delivered by changing the gear ratio closer to 1:1. Final drive is usually accomplished by directly linking the input and output shafts, giving a 1:1 gear ratio. Using a moveable set of different sized gears, it's possible to get several degrees of torque output. The differential pinion, driven by the drive shaft, turns the ring gear, which acts like a single speed transmission. This further reduces RPM's and increases torque by a set ratio.

Gears work exactly like levers. A small gear driving a larger one gives an increase in torque, and a decrease in speed, and vise-versa.

Transmission gears are heat-treated, high quality steel. They have smooth, hard teeth, cut on precision machinery while red hot. There are many types of gear teeth, but most transmissions use spur and helical gears. Most of the gears are the helical type, because they last longer and are more quiet than spur gears. There has to be enough room (a few thousandths of an inch) between the gear teeth for lubrication, expansion, and any irregularities in size.

[MetroMPG]

Originally Posted by 95metro

Any possibility of keeping the 3-cylinder final drive and just changing the 3rd, 4th, and 5th gears to smaller sizes?

Sounds like the "nerd gear" option that my brother in law and I talked about. As in - why wouldn't the manufacturers offer a taller that stock top gear for the hard-core FE nuts?

[95metro]

Just pondering some more and I was wondering if those two older Swiftclones you have actually do have the same gear ratios as the Blackfly. The late 80s early 90s clones certainly seemed to get better FE than the mid 90s to 2000 3-cylinders.

They were lighter, maybe even more underpowered, but were the gears identical? Maybe look at putting the old Firefly tranny in the blackfly? I thought I read somewhere that there were some slight transmission variations besides final drive.

[MetroMPG]

Originally Posted by 95metro

They were lighter, maybe even more underpowered, but were the gears identical? Maybe look at putting the old Firefly tranny in the blackfly? I thought I read somewhere that there were some slight transmission variations besides final drive.

Lighter, less rotating mass (12 in wheels & tires); also the pre-86 cars EPA ratings were higher, even though they used the same test method (they introduced a "fudge factor" and changed the ratings even though the cars didn't change).

[GeoMetry]

I think I am accomplishing basicly the same thing but doing it a completely different way. The whole point of switching out the transmission is to get further down the road for each revolution of the engine. I opted to just swap out the wheels and tires. Going from 155/70-R12 to 155/80-R13 has the same effect as putting in a transmission from an XFi. In addition it only cost me $50 for the wheels and tires. I have ordered the proper lug nuts for another $20 and I am expecting them this week. In my case this has the added benefit of greatly simplifying the task of getting replacement tires as the 12" tires are getting hard to find.

I already swapped out the camshaft for the camshaft from an XFi. I was told that the XFi camshaft gives the engine better low end torque. So I hope to be reporting some excellent numbers when the Gas logs come back.

[95metro]

Originally Posted by MetroMPG

(they introduced a "fudge factor" and changed the ratings even though the cars didn't change)

Oh right, I totally forgot about that. The "decreased percentages" from everyone whining that they couldn't attain the numbers the EPA posted.

Thanks for the bedtime reading - but I'll have to do it now. I'm busier at home than at work lately...

GeoMetry - That's very cool about your cam swap. What's the major difference between the standard and XFi cams?

[MetroMPG]

Originally Posted by GeoMetry

I opted to just swap out the wheels and tires. Going from 155/70-R12 to 155/80-R13 has the same effect as putting in a transmission from an XFi. In addition it only cost me $50 for the wheels and tires.

You're right - same effect. And truth be told, if I knew someone with a big honking set of 14 or 15 inch wheels that would fit our odd-ball bolt pattern, I would like to try them first and do some calculations to see whether or not I'd be happy with the transmission swap.

I probably wouldn't be doing any of this if I didn't have the transmission. It was essentially free.

I'm eager to see your gaslog results too. FYI, I helped Matt with the gaslog a little bit today, running through the new setup looking for bugs/improvements. I think he's close to switching the new garage/gaslog back on.