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Discussion Starter #1
Video here.

I recently swapped in a new transmission to replace my old one that was in dire need of new synchros.

The old transmission was a stock M2Y4 with an open differential and stock final drive. The 2nd gear synchro was so worn that shifting into 2nd was only possible if the revs droped down to about 1k and then shifting slowly. That or just rev 1st a little high and jump right into 3rd. Both were not much fun to do. 3rd gear was starting to go under high RPM quick shifting as well.

So, it was time to either replace the synchros or just buy a race transmission from a former world challenge racecar. After thinking it about it for a few long seconds, I decided on the race transmission.

New Transmission
This new transmission is a M2F4 that comes from the 4th gen H22A1 VTEC model, although this one was installed on a 5th gen, as pictured above. It features a Quaife Limited Slip Differential and a 4.85 custom Houseman Final Drive.

The M2Y4 and M2F4 have nearly the same gear ratios with the exception of the 5th gear on the M2F4 being slightly shorter.

By shorter I mean for example: At 80mph in 5th gear, the 4th gen tranny will be at a slightly higher RPM than the 5th gen. The 4th gen tranny will also have a slightly lower top speed.

LSD - All about the Quaife Limited Slip Differential
The purpose of a limited slip differential is to power both drive wheels instead of just one. With an open differential, power shifts to the wheel with less grip. The LSD, on the other hand, senses which wheel has the better grip and biases the power to that wheel.

The real world indications of this include:
Wheelspin is reduced under acceleration and turning. Just launch the car and it pulls away flawlessly.

Hard launches create a nearly 50/50 power split to both drive wheels, resulting in essentially twice the grip of an open differential. This completely eliminates the peglegging effect that open diffs are infamous for.

LSD also improves handling by transmitting more power to the outside front wheel while turning causing the car to achieve much higher cornering speeds. This is similar to the effects ATTS produces, however ATTS is electronic and doesn't work as productively or seamlessly. ATTS is also only prevalent under spirited turning situations and not straight driving or launching. This makes LSD far superior.

A LSD greatly helps a FWD car handle much less FWD like. By that I mean much less understeer, with oversteer ability even, and ultimately a greatly enchanced automotible handling experience.

Driving Impressions
The Final Drive
The purpose of a larger final drive is to make the gears shorter. Shorter gears make the car faster, but also give the car a lower topspeed. As expected, this Final Drive does just that.

The gears are very very short. 5th gear is about the same speed as maxing out a stock transmission's 4th gear. In effect, each gear feels about as powerful as one down from it. 5th feels like stock 4th would. 4th feels like stock 3rd would, etc.

1st, well, 1st is just amazingly fast revving. VTEC engages and the RPMs shoot to reline before you can even have time to react.

I was plesantly surpised by how close these gears are. It feels like a completely different car now. It's as if there are no dry spots of power. You are always in the power band and/or very close to engaging VTEC, if not already there.

At 70mph in 5th gear I'm at about 4100 RPM. At 80mph that raises to about 4850. Mind you a stock transmission's final drive would yield about 4k RPM at 80mph in 5th. So this is quite a difference. It's almost motorcycle-like, well, not that high. It is considerably higher, as you be cruising along as 4k RPM and only going ~67mph. Driving along in the neigbhorhood, 3rd or 4th gear both have enough power to pull the car around at 25-35mph at about 2000 RPM.

There are some bad things about a shorter final drive. With shorter gearing comes a higher revving engine. Gas milage will suffer from the engine having to rev more to go the same amount of speed as before. Just how much more, I'm not quite sure yet. I'll update this review with gas milage once I get some more results.

Also, top speed goes down. The stock top speed on a 5th gen is somewhere around 140-150, which is always debatable because the stock speedo is inaccurate at such a high speed. Nevertheless, that is the assumed top speed.

With this new Final Drive, the top speed has been reduced to about 130. I haven't maxed out 5th gear yet, but I am speculating it to be around this speed.

This isn't neccessaraly a bad thing, because when do you really need to go 140 mph? Most Honda club race cars don't even get up to this speed. Fortunately, I could run say a 225/50/16 tire and slighly increase the overall wheel/tire diameter to create a little bit of extra gearing for a higher top speed. This would be particually helpful at TWS with that famous long front straight. Plus any other track with a long straight.

More LSD
The LSD is just wonderful. It's very seamless. Just turn as you normally would and you'll notice you can lay a bit more throttle on than before and the car just rotates around perfectly. It surprised me at first as I oversteered.

Launching, as I said earlier, is much simplified. Hardly any wheel spin is present as the car comes alive from a stop.

I currently have worn crappy Kumho 711 tires, so any attempt to push the car and really test the lsd tends to just make them slide around. I'll be able to give a better review of all the effects the lsd has after geting a better set of tires.

More to come later....

Lots and Lots of Numbers
Transmission Gear Ratios
Here are the different gear ratios.

1st is the stock 4th gen VTEC Transmission
2nd is the stock 5th gen Transmission.
3rd is my Transmission.

4th Gen M2F4:
1 - 3.307
2 - 1.950
3 - 1.360
4 - 1.071
5 - 0.870
FD - 4.266

5th Gen M2Y4:
1 - 3.285
2 - 1.956
3 - 1.344
4 - 1.034
5 - 0.812
FD - 4.266

New Transmission:
1 - 3.307
2 - 1.950
3 - 1.360
4 - 1.071
5 - 0.870
FD - 4.85
Final Drive
Stock / New
4.266 / 4.85
Below are the speeds at which each gear would max out at:
Old Redline Speeds
~ = approx
Gear / MPH
1 - 40
2 - 65
3 - 95
4 - 125
5 - ~145

New Redline Speeds
Gear / MPH
1 - 35
2 - 58
3 - 83
4 - 100
5 - ~130

A picture form for you visual learners:

Redline MPH Graph
Blue = Stock
Red = New
Each subsequent colored line represents a gear.

Note: Don't mind the redlining tachometer and excessively toped out speedometer. The car wasn't even on.
These are the approximate VTEC crossover points with a stock ECU:
Old VTEC Engagment Speed
Note: Stock VTEC Crossover
Gear / MPH
1 - 20
2 - 40
3 - 60
4 - 80
5 - 100

New VTEC Engagment Speed
Gear / MPH
1 - 20
2 - 35
3 - 58
4 - 73
5 - 85

And another picture for the visual people:
VTEC Engagment Graph
Blue = Stock
Red = New
Each subsequent colored line represents a gear.

New Cruising RPM in 5th Gear
70 - 4100
80 - 4850
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