NC 2.5l engine swaps ?

[ozace]

What about putting a 4.1 diff in if you haven’t already?

maybe worth exploring further

IIRC, pcmx5 on here did it & loved it.

As a daily?

[hks_kansei]

from a quick google the factory NC ratio is a 3.7

Going to a 4.1 (from a 3.7) is about 10.8% shorter, so as a rough guide expect RPM at whatever speed to increase by about 11%
and in turn, it should feel roughly 11% quicker (really rough on this one since there's way more to factor in than just gearing)

Top speed in each gear will also be reduced by approx 11% as well.



I'd do the diff swap, for the $200 in labour for a shop to assemble the diff and set lash etc, plus the cost of the crown and pinion set it's a pretty cheap way to make a car feel quicker.

From memory the NC crown and pinion are shared with a few other cars, I think the Honda S2000 is one, and pretty sure the RX8 uses the same diff (hell, the NC and the RX8 are like inbred cousins and share a lot of stuff)

From memory the RX8 uses a 4.44 (20% shorter than a 3.7), and I THINK the S2000 used a 4.1.
If you can find a secondhand crown and pinion from either of those it will probably save a lot of cost in obtaining the ratio you want.

[ozace]

Thanks, what happens to the speedo? Is there a simple fix

[hks_kansei]

Speedo depends on how the NC gets the signal, if it's from the gearbox output (pretty sure this is the case) then the speedo will be off by 10% with a diff change.

If it uses wheel sensors (unlikely) the speedo will be accurate still.

Someone else will need to clarify which one the NC uses as I dont really have that much knowledge on specific models past the NB.



As far as fixing the speedo, being electronic, you will have two options.

1: use a speedo sender (the gear that sticks into the gearbox to pickup speed) that suits the diff you are using (I believe the USA NC had a 4.1 as standard, so that should be a direct fit)

2: purchase a speedo correcting device, which is wired in line to the current speed sender, and essentially just uses a circuit to change the speed of the pulses going to the speedo gauge to either increase or decrease the speed shown.


Using a new sender is the simplest, but relies on finding a 4.1 sender (as mentioned, pretty sure they're freely available from the US)
The circuit based adjuster is more flexible and allows for future changes etc, but usually costs a bit more, plus needs to be wired in.

[Dan]

The NC uses the ABS speed sensors for the speedometer so only wheel/Tyre changes can affect the speedometer.

[hks_kansei]

The NC uses the ABS speed sensors for the speedometer so only wheel/Tyre changes can affect the speedometer.

Perfect.

Wasnt sure it it was doing it that way, or still used the older gearbox method.

In that case Ozace, diff swap shouldn't affect speedo at all.

[ozace]

Thank you very much

[cwto24]

I've had both 2L with 3.7 diff and the 4.1 diff and the 2.5 with both diff's too.

Correct, downside is cost, but best bang for buck would be 4.1 after all the mods you've done. It'll change the car.

2.5L is very driveable but eats petrol as expected.

You can get a 4.1 crown and pinon from an auto diff and transplant that into your diff.

[ozace]

I've had both 2L with 3.7 diff and the 4.1 diff and the 2.5 with both diff's too.

Correct, downside is cost, but best bang for buck would be 4.1 after all the mods you've done. It'll change the car.

2.5L is very driveable but eats petrol as expected.

You can get a 4.1 crown and pinon from an auto diff and transplant that into your diff.

brilliant

[Regie]

yep to add on from what Trev said above

you can source a NC auto diff from here in Australia, but you will have to transfer the gear over to your current diff as the Aussie autos are NON LSD

or you can source a CW&pinion from overseas and get it sent over - this is the option I went for from memory it was around the $300 mark delivered from Spain I think it was. All USDM cars run the 4.1 ratio

or maybe Lou (boyracer on forum) may have a full 4.1 lsd assy ready to bolt in.

a ratio change is far cheaper than a 2.5 swap, especially if you have to pay a workshop to carry out the job.

my 3 best performance mods on my nc were, Headers, 4.1 FGR and lightweight flywheel. The flywheel could be another option for you, check out the Fidanza flywheel that Chris from MX5parts sells. Its awesome!

[93_Clubman]

What about putting a 4.1 diff in if you haven’t already?

maybe worth exploring further

IIRC, pcmx5 on here did it & loved it.

As a daily?

Don't think it was his daily as he had a couple of cars, but it wasn't a weekender either.

[ozace]

Brand new diff gears only from Mazda are 1800ish. I see why the need to come from is or a wrecker

[ozace]

Time to get organized for sandown track day tomorrow, more research is needed

[Custardtart]

Two 2.5l swap threads for the price of 1

I’m not sure why it should be an expensive swap? $750 for a motor, swap everything off your 2.0l.

A couple of hundred $$ for timing belt, fluids, odds and sods and job done. Probably a weekends work for a home mechanic and a mate.

You don’t need the Ecutek tune do you?

You could sell you 2.0l even minus the oil pan for $1000?

[NitroDann]

Im not trying to be a prick..but..

Come on man its clear you have no idea whats involved and yet you make posts like that with such conviction.. why?

Dann