Built gearbox update page 3

[Froidas]

I built my gearbox couple years ago. After many days of calculations, comparison and thinking, I chose U2Q7 with 4.64 FD and 0.735 5th gear. My Prelude is NA and not high HP, so I was looking for short 4 gears and I wanted long 5th gear for cruising. And it works as expected.

So now I'm reading this thread and I don't understand why M2F5 or M2V5 are considered as good gearboxes. Maybe I understand something wrong and you could clarify it for me? I know there's some science under that, short gears doesn't mean fastest quarter mile. But still it's a bit strange to me.
I used M2V5 before my current box and it was awful. The main problem - hitting 2nd gear in VTEC range, which was at 5000 rpm, so quite low already.

In the image bellow it's very easy to see why. 1st gear top is lower than 2nd gear VTEC.
Left - M2V5, right - modified U2Q7. The blue bar is gear until 5000 rpm, red bar - 8000 rpm. Speeds are in km/h, tyres R17 215/40.

[Merlin]

So now I'm reading this thread and I don't understand why M2F5 or M2V5 are considered as good gearboxes. Maybe I understand something wrong and you could clarify it for me? I know there's some science under that, short gears doesn't mean fastest quarter mile. But still it's a bit strange to me.
I used M2V5 before my current box and it was awful. The main problem - hitting 2nd gear in VTEC range, which was at 5000 rpm, so quite low already.

It depends on what you want the car for and if you are after hard acceleration in 5th.

The reason why the M2F5 in its stock form are not as preferred as other gearboxes is that its uses the 4.062 FD Vs the 4.266 in the other gearboxes. Yeah I did not take into consideration the longer gears in 1st and 3rd in the M2V5, probably better for boosted cars

Because of the longer 4.062 FD 5th gear is shorter to offset the longer FD. So when you take out the 4.062 FD and put in an MFactory 4.64 FD you have a gearbox that accelerates faster/harder in 5th in comparison with another box, regardless if that other box has a MFactory 4.64 FD or not.

Yes the U2Q7 has the same 5th gear ratio as the M2F5 but it does have short 2nd and 3rd gears (can be classed as too short when using an MFactory 4.64 FD, but that is personal preference). But, like the M2p4, the U2Q7 suffers increased rev drop from 3th into 4th, key gear changes when you are on track.

If you are planning on using an aftermarket diff it makes no sense to use the U2Q7 as you would be wasting money on that box since you would be replacing the diff. For a fully built gearbox with aftermarket diff and FD the M2F5 is the one to go for.

[Froidas]

Thank you for explanation! My car is not used for track and won't be, so I didn't thought about 3-4 gear shift, good point.

Why would you need to replace the diff? FD, some gears, if you want - yes, but diff? When you buy U2Q7, you basically pay for diff I know that aftermarket FD doesn't fit on M2B4 diff, but it does for U2Q7, did that.

[Merlin]

It is reported that the "lock" of aftermarket diffs are a bit more aggressive than the U2Q7 diff. If you want a decent diff for the road the U2Q7 is fine and good value for money. However if you want a bit more performance a Torsen diff from MFactory / Quaife etc... are the ones to go for.

[Froidas]

That makes sense, now everything is clear.
I started to think I missed something with my gearbox build while reading this thread. But now I'm calm, I chose correct path for my needs.

[newkid]

Yea @merlins right. U2q7 was avoided as was going aftermarket diff

[newkid]

Update.

Been told the bearings supplied don't fit into the casing as there too large. Also been told the bearings are different. Tapered rolling bearings as standard If I've remembered correctly. And replacements are ball bearing type. Tbh cars really starting to annoy me to the point there could be a breaking thread going up soon!

[vanzep]

thats not going to happen

you need some input from @Buzzonion Vtec imo

-only someone who has built a gear box will know-

sounds to me like youve got the wrong bearings.....if im reading it right the question is what bearings do you need to fit the mfactory lsd....most people use the quaife lsd like @Merlin and @RattyMcClelland

[RattyMcClelland]

Oem bearings and the ones in the mfactory rebuild kits I got.

[4thgenphil]

You may need to replace the bearing cups on the gearbox which i would do with new bearing anyway. They also need to be shimmed correctly.