Merlin's 4G Time Attack Lude

[Merlin]

Time to bore/confuse more with the desicion on what gearbox to use, the standard gears in the M2F5 or the low ratio 2nd and 3rd gears found in the 5th gen 99+ M2P4 The M2P4 uses the same ratios as the U2Q7 found in the Accord Type-R, and those guys use the exact same 4.64 final drive.

The ratios in 4th and 5th are the same for both gearboxes.



M2F5 with MF FD on the left (Red), M2P4 with MF FD on the right (Blue).







What all this shows is that I would get a further 8.9% increase in effective torque using the M2P4 over the M2F5. The change in the gearing results in the estimated top speed in 3rd falling from 94mph to 86mph.

One interesting stat is that with the M2P4 in 3rd using the MF FD I would achive an estimated 24.4% increase in effective torque over the stock M2F5 (which is what I have been using up untill now).

After doing this analysis I am very tempted to use the M2P4 over the M2F5 as 2nd and 3rd acceleration will incease while 4th and 5th are the same. The only downfall with the M2P4 is that rev drop between 3rd and 4th will be a bit more. In my stock 5th gen with the M2P4 it is possible to keep it in VTEC between 3rd and 4th but you need to rag it.

[vtectom]

Any idea what max speed will be in fourth?
Will you need 5th at Knockhill?

[Merlin]

I have added the other speed graph to the previous page. Top speed in 4th for either gearbox is estimated at 120mph. At Knockhill I dont use 5th, but other tracks I will need to.

[Merlin]

At knockhill there is only one point where that may become a problem (hence why I have tried to work out the numbers), the strech between the chicane and Clark. In my stock 5th I hit the limit in 3rd before braking, the track car has a little more legs so I dont approcah the limiter. That is not to say I wouldnt run into the same problem with the M2F5 with the MF FD as the overall gearing is shorter. If I need to short shift into 4th at that point it makes no difference if I am using the M2F5 or M2P4. The M2P4 would give better acceleration out of the harpin (2nd gear), and give more torque though the entire first 3rd of the circuit (entry into Duffus to the exit of Clark) where I would be in 3rd the whole time.

[Donald]

Going on what you've said I'd go M2P4. Saying in your 5th gen you have to rag it, will it be the same with your new engine? I'm sure the change between 3 and 4 in my 5th is around 7k or 85-90mph (guessing at revs) to stay in VTEC, would've thought the beast engine wouldn't scream too much at that?

But then I am biased to an extent

[vanzep]

Another small factor in the equation would be that your M2P4 is a younger lower mileage gearbox - at least id expect it to be

Nice piece of kit the M factory final drive - beautifully machined

[Donald]

I found a nice private road on my way home from work and watched the rev counter a bit.

Changing at 7200rpm in 3rd drops you to ~5500rpm in 4th, so you'll stay in VTEC. Changing at bang on 7000rpm dropped out of VTEC momentarily, at a guess it was around ~5100rpm. This is all around 80mph.

[Merlin]

Thanks, yeah that is roughly what I found as well. I had this 5th for 3 years and didnt notice before Dino mentioned it.

The new ECU for the track car has it's shift light set to 8200rpm and VTEC is at 6K. Hopefully it would stay in VTEC with the M2P4.

At knockhill there is only one point where that may become a problem (hence why I have tried to work out the numbers), the strech between the chicane and Clark. In my stock 5th I hit the limit in 3rd before braking.

Also the straight I am on about is this http://www.youtube.com/watch?v=OcZ5_zvhVT8&t=0m36s

[Merlin]

Dilemma number 3 now, they are racking up, how much to replace during the gearbox rebuild?

I decided that the work that needs to be done to the gearbox is beyond the expertise and tools available free to me. As such the gearbox is going to be built and setup by a professional gearbox builder (currently tring to decide between http://ajkanegearboxrepairs.co.uk and http://www.alpinetransmissions.co.uk).

The problem is that now is the time to replace the seals and bearings, which come to a total of £630 in parts . That is a bit hard to swallow

So now the dilemmas are:

1. What gearbox to use, M2F5 or M2P4?
2. What gearbox oil / transmission fluid to use, and in what ratios?
3. How far do I go when replacing seals and bearings?

[NafemanNathan]

This better be worth the trouble once you've figured all this out!