Gearbox build

Froidas · Post by **Froidas** » Sun Feb 05, 2012 8:53 pm

Blue bar - before VTEC zone. So in my case it shows speed (top speed of it it is written) from 0 to 5000 rpm.
Red bar - show full gear. From 0 to 8000 rpm in my case.

So lets take 1st gear of my second chart. Redline (top of red bar, at 8000rpm) speed is 36,05 mph. And we see, that second gear blue bar top is 35,42 mph (lower when 1st red bar top, you can draw a line), so that means, that when you shift from 1st to 2nd, it would be more than 5000 rpm, so it means, it would be VTEC zone

I hope I explained it and didn't make it more confusing

littlefeller · Post by **littlefeller** » Sun Feb 05, 2012 10:52 pm

explained very well. also if you compare the red (max rpm speed) bar to the next blue bar for the next gear (min speed for vtec crossover) you can figure at what rpm you can shift and still be in vtec, you will notice that @ higher gears you could shift lower than max rpm for this to accure.
after going through all of the gearboxes for the lude there are none that will stay in vtec between 1st and 2nd without adjusting either the vtec point or max rpm. at first i thought this must be wrong, but then remembered a conversation with tramroadmotors (he was using bagoshit for compatition) he says wheel spin was a major issue in the lower gears so maybe this is why the gearboxes are this way (designed this way). there were also some boxes that fall out of vtec between 2 to 3rd too.

Froidas · Post by **Froidas** » Mon Feb 06, 2012 5:38 am

Never thought of that... Just noticed, that with my current M2V5 gearbox you must rev to the top to hit 2nd gear in VTEC. Thought that was my fault, if I didn't reach VTEC zone in 2nd

I can't wait to try my new gearbox with LSD. I wonder, how much less wheel spin i will have in 1st and 2nd gears.

littlefeller · Post by **littlefeller** » Mon Feb 06, 2012 10:57 am

after looking at these graphs, it would seem to be great if you could have different vtec crossover points in different gears and have a different rev limit for different gears too. if you could lower vtec in 1 and 2, then lower rpm limit in 3,4 and 5 now this would be great. there doesnt seem to be much point in reving too high on a std motor as the torque is already falling away before 8000 rpm. wonder what the 0-60 times would be with vtec after 1-2 shift, or would it just spin the wheels even more

Froidas · Post by **Froidas** » Mon Feb 06, 2012 11:40 am

Maybe it would, but you started to think too complicated, to my mind

First of all, VTEC crossover point impact final power and curve.
The easiest solution is to rev until 8000 with standard engine (above is not safe and no purpose, as you said), and rev more (it matters, what modification and how goes the torque curve, etc.) with more or less build engine bottom. As I remember, with my first H22A2 engine and it's box, it was possible to hit 2nd in VTEC range. If I remember correctly..

I think it's no big deal, that spin between 1st and 2nd. Of course it's a loss, but small one. Main thing is to control your launch in 1st gear. So as I think now, what you can do with gearbox to improve performance, is short gears (and 5th long for cruising, if you need) + LSD. Also good tires and dry road

judderod · Post by **judderod** » Fri Mar 30, 2012 10:46 am

8K on a standard engine

I wouldn't risk it. Torque at that RPM will be falling off rapidly.

I'm at 8250 on a fully built forged and balanced bottom end

Can probably go higher tho...

h10ndr · Post by **h10ndr** » Sat Feb 23, 2013 10:54 am

This brings in another thought about the accuracy of the standard rev counter. It over reads, so changing at 8k indicated is actually more like 7,600. You can see the difference in rpm if you have something which displays the rpm from the distributor wire. i.e. VAFCII or laptop datalog from ecu (Hondata, Neptune RTP).

edit: its more accurate in the lower rev range but goes further and further out the higher you rev

littlefeller · Post by **littlefeller** » Sun Mar 31, 2013 7:28 am

the rpm in the graph is taken from the ratios and not the rev counter, this may be why some say the graphs are incorect, it is right , its your rev counters that are wrong

eDaniel · Post by **eDaniel** » Mon Aug 19, 2013 8:25 pm

Has anyone tried to install a Prelude 5th gear into ATR one (U2Q7) as from what I heard this is not possible out-of-the-box? I have an ATR box and I'd like to replace the stupid original 5th gear with a longer one from M2A4/M2K4/M2J4.

mercutio · Post by **mercutio** » Mon Aug 19, 2013 8:43 pm

why wouldn't it be possible I thought all the H boxes were compatible