NA6CE / BP-VE swap

The engine of NA6CE produced after 1989 is a 1.6L-B6 type.

Itfs going to be 23 years from the beginning of its production. Depending on the possibility of obtaining the needed parts, its service is possible. Though, in this case we could think of a BP-VE swap too.

We have overhauled many B6 engines but the biggest barrier was the crankshaft. Mainly the crank tipfs abrasion is severe and because of this in some cases its reuse can be difficult. This means that reviving a B6 engine might have its costs.

If we compare the B6 (1.6L) to BP (1.8L) we can see, that its cubic capacity is small and the torque is less, but it has its pleasures thanks to its short stroke, thatfs why therefs no need to disapprove of it.

However, in the case of the actual O/H we can also think of setting it up in one go with NB8fs (later model) BP-VE with VVT.

VVT function

In the case of Miata/Mx-5 models later to NB8 (later model) we equip the camshaft with hydraulic variable valve timing system (VVT).

This is the down-sizing of each company earlier and these days too. The demand is a highly efficient compact engine that has small cubic capacity with low fuel consumption and is easy and fun to ride. The main method for this is the VVT. The VVT is installed in most of the light vehicles too. You can understand how typical this system is by knowing that it is installed in light trucks too.

It is possible to enjoy tuning by using VVT skillfully.

Equipping NA6 with BP-VE

Wire processing

The case of swapping BP-VE to NA8 and NB8 (early model) and the case of swapping to NA6 are not the same.

The ignition system and the signals of each part differ, thatfs why it is important to consider it properly.

For example the igniter

It is a type that is being built-in to the NA8 ignition coil. In the case of NA6 it is an external type. Wire processing is needed if we want to turn it into a BP-VE direct coil. Of course it is necessary to remove the terminal from each coupler, but by replacing them with a special connector (housing) we can think about the possibility of wire processing.

A very easy and reliable wire processing is possible by using Maruhafs special relay harness.


It is a special method for NA6 with Freedom ECU base.

Basically it is just connected. (the pin on the connector side is replaced)

The Freedom ECU is a full computer system, thatfs why combined with different engines an individual setting is possible.

If it is a basic BP-VE swap, even our companyfs original program (mail order) can fit the requirements.

Modification of the peripheral parts accompanying swapping

Following the engine swapping the other peripheral parts have to be altered too.


The NA6EB6 engines are normal 120 PS powerless engines. The power up of these engines has its costs. And this is where the BP-VE comes into picture. Letfs see the performance differences of NB8fs (later model) genuine normal and our companyfs BP-VE (air flow-less, Freedom control).

The graph below is not an extract published by the maker but our companyfs measurement results.

C: NB8C VVT genuine engine + (Freedom ECU)
B: NB8C VVT genuine engine + (genuine ECU)
A: NA8C genuine engine + (genuine ECU)
The NA6C genuine enginefs torque and power too are inferior to the others.

There is a power and torque difference even in the middle area. It is the result of thoroughly provided setting using Freedom and making use of the "no-air-flow-meter" changefs benefits.

BMC air cleaner BOX

In the case of this timefs swap we use BMCfs DIA air cleaner BOX.

Except making the change to no-air-flow-meter easy and securing the fresh air, the other thing that stands out, is the typical BMC filter design that uses the direct intake system.

Ferrarifs F1 constructorfs championship victory was many times supported by filters made by the company BMC.


Maruha Motors Co., Ltd.
Ushizuma 2095-6, Aoi-Ward
421- 2106 Shizuoka city, Shizuoka prefecture
TEL: 0081-54-294-0076
FAX: 0081-54-294-1312