10 July

Ex Rod Millen Pikes Peak RX-7 4WD Rebuild

20b motor 005 Ex Rod Millen Pikes Peak RX 7 4WD Rebuild

Ok, so we tried to keep it a secret until the car was ready to be unveiled, but the story leaked out and the phone started ringing.

The answer to most callers was No, but after much thought and consideration, we agreed to allow Brad Lord from Speedhunters.com to profile the car for us.

This car ain’t no copy or imitation, it’s the Real Deal, the Full Monty.

You can read his article here: Resurrecting An Iconic RX-7


20b motor 009 Ex Rod Millen Pikes Peak RX 7 4WD Rebuild


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28 June

13B Peripheral Port Build – A Very Happy Customer!

John is a very happy customer!

He’s so happy, he can’t wait for us to build the engine for his next project.

Here’s what we did for this build:

-13B Engine with Peripheral Porting

-New Rotor Housings (complete with old style Mazda logo)

-Our ‘Secret Sauce’ Rotorsport Racing Porting

Lightened and Balanced RX4 N/A Rotors

-Special Oil Gallery Modifications

-Race Grade 3mm Carbon Apex Seals

-Specifically Lightened Flywheel To Match This Engine

-A Few Other Tricks To Improve Performance We Can’t Tell You About!


The install was carried out on John’s late 70’s Mazda 323.

John says:

‘It Goes hard and Pulses Loud’.

‘I’m real happy with this engine and the work Grant has done’.

-John Hollows

(Click on the images to enlarge)

Image 300x225 13B Peripheral Port Build   A Very Happy Customer!

Image 2 300x225 13B Peripheral Port Build   A Very Happy Customer!

Image 1 300x225 13B Peripheral Port Build   A Very Happy Customer!

15 June

Racing Beat – Authorised Dealer Approved !

racing beat logo1 300x45 Racing Beat   Authorised Dealer Approved !

Racing Beat Inc, the most famous name in rotary performance products, based in California, has granted approval to Rotorsport Racing & Engine Balancing Ltd to be their Authorised Dealer for New Zealand and the South Pacific.

fc bonn 1024 300x225 Racing Beat   Authorised Dealer Approved !


Check out our Racing Beat Page to learn more.


FD Bonn.10241 300x225 Racing Beat   Authorised Dealer Approved !

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14 June

20B Engine (Sorry, Sold)

(Sorry, but the 20B engine has now sold)


0550a925249430a 20B Engine (Sorry, Sold)

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2 January

Rotary Engine Balancing – Balance In Action

Explaining how we balance a rotary engine can be difficult as it’s a very skilled procedure and an area where no shortcuts can be made.

Hopefully this post will give you a better appreciation of what’s involved.

Firstly, the rotors are weighed, then the heavier rotor is lightened so both rotor weights are identical (less than 0.1 of a gram difference)

During this process, both rotors are also balanced to remove any rotational imbalance.

d93aeb0f6ec0035 Rotary Engine Balancing   Balance In Action

Rotor weight matched at 4452.3

a127dd89c65c954 Rotary Engine Balancing   Balance In Action

Spun on balancer to check and identify any imbalance

4786a13c4f43cd6 Rotary Engine Balancing   Balance In Action

Note: Rotor mounted on special spindle, not the eccentric shaft.

1c006672916fdcf Rotary Engine Balancing   Balance In Action

Results displayed on computer screen, Balanced To Tolerance!

Secondly, each rotor is reconstructed as a rotor manderal with bob weights attached.

These are matched identically to replicate each rotor so the weight and balance is the same.

66817e6daaf2262 Rotary Engine Balancing   Balance In Action

Each rotor manderal checked to ensure it is identical in weight and balance to the rotor it is replicating.

06c880d72c303cf Rotary Engine Balancing   Balance In Action

Thirdly, the rotor manderals are assembled onto the eccentric shaft along with front and rear counterweights.

3be00aafa2ca927 Rotary Engine Balancing   Balance In Action

This full assembly is then spun and checked for imbalances in the counterweights.

db97cf2208966bf Rotary Engine Balancing   Balance In Action

This spin showed there was a 6.51 g imbalance from one counterweight and a 6.5 g imbalance from the other.

Note: this engine had been previously “balanced” using a long outdated method that is prone to error.  As shown on the screen, both counterweights were out of tolerance and would have produced significant vibration potentially damaging the engine.

5db09fc4377f313 Rotary Engine Balancing   Balance In Action

The counterweights had 6.51g and 6.5g removed by drilling.

Finally, after the imbalance is removed (or added as extra weight in some cases), the rotating assembly should be well within tolerance!

On this assembly, the imbalance was corrected to within 0.02 of a gram.

We provide you with a full printout of all data for your information.

Contact Us now or phone Grant on 021-298 5146 for your rotary engine balancing requirements using state of the art equipment from CWT.

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13 November

13B Rebuild – Your Rotary Engine Built To Your Requirements!

Many of our clients like to have their engine customised, especially if it is for a car restoration project.

There are two main things to consider for your 13B rebuild.

What happens inside the engine and, what happens on the outside!

On the inside, we will talk with you about any porting work you may wish to have carried out.

Most popular porting is the ‘bridgeport’ which you can see more about in our 12a rebuild section.  This is a high performance modification providing a significant power increase over standard.

f1a9998053b9e4e 13B Rebuild   Your Rotary Engine Built To Your Requirements!

Mild porting is also a popular alternative which provides smoother operation at lower rpm and probably better driveability in low speed situations.

The ‘Peripheral Port’ rotary modification produces the highest power and designed specifically for race and rally use.  Not recommended for street use because of low rpm roughness, they come into their own once the throttle is opened wide!

Once you have decided to either have the engine ported to some degree or leave it unmodified, we strip the engine down to inspect for wear in any of the components.  All parts are cleaned thoroughly before reassembly.

We use genuine Mazda parts for your 13b rebuild, including all gaskets, housings, seals and bearings, although for high performance applications we sometimes use special ‘unbreakable’ apex seals from the US.

We highly recommend our rotary engine balancing service which eliminates any imbalance in the rotor assembly.  One of the biggest cause of engine failure in rotary engines is because of poor balance which places excessive stress on the bearings and other components.  Not only is significant power lost or consumed by the imbalance, the engine performance can be seriously degraded, so let us balance it for you.  It will be the best investment you can make in your engine!

2d1350e4caa11d7 13B Rebuild   Your Rotary Engine Built To Your Requirements!

On the outside, we can provide any finish you require.  From the standard factory look, to full custom spec, you ask for it and we will achieve the look you want.

Colour matched housings to the vehicle?  No problem!

Polished alloy housings?  No problem!

All nuts and bolts zinc plated?  No problem, your choice of gold or silver finish.

Call Grant on 021-298 5146 to discuss your 13b rebuild or contact us.

Need a rotary engine for your project?  We have a selection of cores and complete 13b engines for sale.

b8bf373e929b3c4 13B Rebuild   Your Rotary Engine Built To Your Requirements!

13b bridgeport with Weber IDA48 carburetor and manifold.

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4 November

Rotary Engine Balancing – Before And After Balancing Data

Each time we balance an engine, we provide a printout of the rotor imbalance at various speeds from 1000 rpm  to 10,000 rpm.

The printout also shows the final balance figures after we correct any imbalance.

This is done after we make sure both rotors are identical weights, in this case 4611.6.

For this assembly, the initial imbalance was 745.44 inch/lbs at 10,000 rpm.

After correction this was reduced to 0.43 inch/lbs at 10,000 rpm.

The imbalance of 745.44 inch/lbs is quite common because the rotors are never finely balanced by the factory.

However, with high performance engines in particular, it places significant load on the engine and bearings, causing greater fuel consumption and decreasing power output.

This engine will now operate more freely, have less vibration and produce more power than the same engine in an unbalanced state.

Contact us or call Grant on 021 -298 5146 to discuss having your rotary engine balanced.

fde17446629f8a0 Rotary Engine Balancing   Before And After Balancing Data

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2 November

12a Rebuild – Reassembly

With this 12a engine, it has been set up as a ‘Bridgeport’ with modified inlet and exhaust ports.

As you can see, we want your engine to look as great as it runs, so all misc items zinc electroplated, this makes them not only look brand new, but protects them from surface rust and corrosion.

All external steel engine surfaces have been painted (to the colour of your choice).

b7bf2dd80a7cf3e 12a Rebuild   Reassembly

Parts ready to be reassembled.

693aacb7edeab22 12a Rebuild   Reassembly

Bridgeport inlet can be seen in the side housing.

b9e670b2d69e715 12a Rebuild   Reassembly

Exhaust port modified, sleeve widened.

5a972a8c74e2599 12a Rebuild   Reassembly

Looking good!

697c04c4ef1100b 12a Rebuild   Reassembly

Assembly almost complete.

74b400e7bc60cc6 12a Rebuild   Reassembly

Behind the front cover.

254f89627a554be 12a Rebuild   Reassembly

Front cover installed.

e0ffbb092b346d0 12a Rebuild   Reassembly

Just the final finishing touches needed.

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27 October

12a Rebuild – Bridgeport Cut – Hand Finished Perfection

In a previous post you will see the initial bridgeport cut made above the standard intake port.

Once this has been completed, it’s back to the workshop to enlarge and smooth the ports with a special grinding tool.

This provides an unrestricted airflow into the engine, with a massive reduction in drag and turbulence, it also provides a significant power increase!

46dad7f8c3acb45 12a Rebuild   Bridgeport Cut   Hand Finished Perfection

3de17f0fb33fac5 12a Rebuild   Bridgeport Cut   Hand Finished Perfection

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8 October

Rotary Engine Balancing – We Have The Latest Engine Balancing Equipment

** Stop Press **

We can now provide a full engine balance carried out on the latest fully computerised CWT engine balancer, with custom rotor mandrels and bob weights that are individually made for each model of rotor from X-treme Rotaries in Australia.

A computer printout is given with the assembly with before and after balancing plus individual rotor weights. This is extremely important if a rotor is damaged in an engine as we can balance up another rotor to suit your assembly without the need of rebalancing the complete assembly again.

Don’t forget that we can build your rotary engine to any specification you require as well as supply genuine Mazda or aftermarket parts at competitive prices.

So deal with the experts for your rotary engine balancing, you won’t regret it!

Phone Grant today on 021 298 5146.

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