Mini Moto / Pocket Bike Exhaust Port Mods - Part 2

This post is a follow up to an earlier one which detailed some of the issues with port shape mismatch between mini moto / pocket bike cylinder heads and racing exhaust pipes.
The earler post is here:  Mini Moto / Pocket Bike Exhaust Port Mods .

Port matching, which consists of reshaping port outlets to be size and shape matched for better flow, is all but standard practice in all forms of motorsport and is often done at home by enthusiasts who are looking to extract all the performance possible from their engines.

Mini motos / pocket bikes are almost always tuned to varying degrees and indeed, the internet is full of articles and websites dedicated towards helping you make your moto faster.  There are many articles which point towards 'opening up' the exhaust port on these bikes, but for all the time and effort being put into opening them up, there's almost always a huge port mismatch between the cylinder head and the exhaust pipe.

As I showed in the initial post, this is the typical 'view' the exhaust has as it exits the cylinder head towards the exhaust pipe:

Head To Pipe Exhaust Port Mismatch

There's much more detail, along with a couple of crude flow models in the initial post, however as I'd touched upon when writing that, it's not only the area in red here, representing the inlet to the racing exhaust which is the problem, it's the turbulence caused by the exhaust being deflected around this mismatch that has a much greater impact than what is illustrated. Obviously any more 'opening up' of the exhaust port on the head is going to exacerbate this effect instead of serving to resolve it, meaning that another solution was due.

I've also touched upon in the initial post the options of welding the port up and re-machining it to a shape which would match up better to the pipe, or even of possibly using JBWeld as has been suggested. (Note: do NOT use JBWeld to rehape your exhaust port - it will quickly break down under those conditions and you'll have much larger problems than just port mismatch)

The ideal to all of the above would be something which could be bolted on in just a few minutes, requiring an absolute minimum of prep to either of the mating surfaces and ideally requiring no welding or machining  whilst offering great flow improvements.

Following on now to the CAD and flow models of the original post, here are some images of a test-fit piece which I've machined from wood. There's a slightly more revised version I've now prototyped in bronze and have working in practice /being tested, but I'd prefer to keep that version under wraps until its' for sale. To the naked eye, there's not much difference at all between that one and this, but there are subtle refinements which manage to extract another couple of  CFM of flow.

Finally, after that lengthly introduction, here's the wood model of the 'FlangeFlow' port adapter.

Wood Prototype FlangeFlow Port Adapter

I've done a few of these from hardwood as they were quite quick to knock out on the CNC and yet were rigid enough to survive being mocked up and flow tested on several head/pipe combinations.

Unfortunately the available equipment for the flow testing was less than ideal and was rather 'mad scientist / high school science fair' in appearance, but the purpose was served and we were able to reaffirm that the slight changes we were making were in the right direction. We do have formal flow-testing scheduled for the near future.

How much of a difference do the FlangeFlow adapters make? In simulations, >15% was common to see, in the real world, we'll be backing all this up with some extended dyno testing in the near future, but I can tell you this for the moment:  You can hear the difference, certainly feel the difference in acceleration/top speed, and it required stepping up one jet size on one 'stage 2' motor, and two jet sizes on a 'stage 3' motor to maintain the air/fuel ratio.  Both the motors tested were 49cc air cooled (the initial target platform for these adapters), and both had been initially built with off-the-shelf available components which were then race prepped and the rotating assembly carefully balanced.
The 3x test riders (two very accomplished racers and one amateur) all indicated they felt a 'big improvement' in midrange and especially top end. Acceleration out of corners was improved and straightline speed increased so that one rider commented on having to 'hit the brakes a little earlier to scrub off more speed' before the corner.

These are a couple of images showing the FlowFlange situated against a couple of different cylinder heads and against 2x different race pipes. Note that all the misalignment is addressed and that although kept to under 6mm thick so as not to cause exhaust fitment issues, the flow transition from one shape to the other is radically improved.

FlangeFlow / Port  View 1

On these two heads (by different manufacturers with different markings, having had only the ports smoothed but not hogged out, you can clearly see how linearly the FlangeFlow mates to the port shape for a seamless, uninterrupted exhaust flow.


Also, in the reverse direction, with the exhaust pulse pushing the extra air/fuel back from the pipe into the head to be burned, there's a much improved flowpath. This contributes to better cylinder filling, higher cylinder pressures, and more power all the way through the RPM range.

FlangeFlow / Port View 2

 

 

 

 

 

 

 

 

 

 

Additionally, these pictures show the FlowFlange positioned against a typical race pipe. As indicated in the previous post, of the several exhaust I had access to, all had an inlet diameter within 1mm or so of each other. I've matched the exhaust side up to the proper racing pipes but matching to more mainstream aftermarket pipes is also excellent. 

Exhaust Pipe Match View 1

Again, the clear, uninterrupted flow path can clearly be seen as it's presented to the exhaust flow from the head into the pipe.

Exhaust Pipe Match View 2

Though not specifically related to the workings or benefits of the FlowFlange itself, 

Below are several images of the FlowFlange wood model as it was being cut on the CNC machine. 

Beginning of first top side CNC cut

1/3 of of the first top side cut done

Approaching full depth now

External profile CNC machinig

CNC shaping the internal port contour

A bit more port clean up

Perimeter milling

Milling away the fixture supports

The FlangeFlow will soon be available as part of an easy, 5 minute bolt-on kit which in most circumstances will aid in exhaust port flow by a minimum of 15%, in many cases, much higher.  The kit will come with new, spring loaded mounting hardware, custom gaskets - one for each side of the FlowFlange, the bronze FlowFlange itself, stickers, and an instruction sheet. 

The FlowFlange is 100% designed, manufactured, and packaged in the UK.

enquiries can be sent to me or to info@mgdesignlondon.com

New Mini Moto / Pocket Bike Cylinder Barrel / Head Design for Maximum Performance

This post is going to be a sneak preview of a new cylinder head design I'm working on for 39/49cc  aircooled engines typically used in Pocket Bikes.

An initial design parameter of this design is full backwards compatibility with existing engine cases and engine internals, as such, I've stayed with a fairly conventional appearing external shape.
Ultimately these heads will be available paired with the billet engine cases which are in the works, but for the near future, the barrels and a custom cylinder head with a selection of compression dome inserts will be available.

The following images are WIP CAD models. There's revisions being done and lots of flow modelling at various piston positions (every 10 degrees of crank rotation.).

Cylinder Barrel Without Fins

You can see from these images that the cooling fins haven't been modeled yet. They're going to be positioned and their density determined by thermodynamic modelling in an effort to gain some level of control over the conditions in the combustion chamber.


Of note is the round exhaust port which has been shaped and sized to match up seamlessly to the best race pipes for these heads. This alone makes a significant difference in the amount of flow the heads will sustain.

Exhaust Port View

The interior or the exhaust port has been carefully shaped, and although the bottom 10% or so isn't really visible in this view because of the port floor contour, the overall shape can be seen.

The ceiling of the port has been raised 2.25 mm from stock on the 39CC variant, and 2.85 mm from stock on the 49CC version when compared to standard 'High Performance Heads'. Also, much work has been done refining the shape of the port transition and ensuring that flow is optimised  from the very moment the port is opened, through the piston being all the way to BDC.

Thought has been given too towards the air/fuel charge being pulse returned from the exhaust pipe with the floor of the port being shaped to direct this flow precisely where it's most desirable for the custom shape of the combustion chamber.

Quarter View Into The Top Of The Barrel

Lastly, using very carefully shaped and flow tuned contours for all the ports has yielded great results. The ports all have semi-angular domed 'ceilings' with multiple internal angles which direct the incoming air/fuel charge precisely yielding a very desirable swirl which works in careful conjunction with the small returning air/fuel charge from the pipe.

When I have achieved precisely what I intend to with this modelling, I shall post some video of the flow modelling during the compression phase of the engine operation but suffice to say for now that this barrel / head combo is going to make more power, more reliably, and allow for a wider range of tuning options whilst offering a complete intake charge burn than anything else on the market available for the air-cooled engines.

Lastly, provision has been made during the design of these heads for a 6mm thick thermal insulating layer between the base of the barrel and the engine cases. This should serve to not only allow the bearings to run cooler and longer, but to keep the air/fuel charge cooler and denser as it enters the combustion chamber for further improved power.

These heads will NOT need to be ported, smoothed or modded in any way to offer outstanding performance. In all actuality, these heads are tuned to the point that any modifications will likely be detrimental to performance.

More info to follow shortly.

Currently, on my lathe bench

This is what happens to your workshop when you have a motorcycle/mini moto crazy 8-year old in the house.
Mind you, this on top of all the running motors he has already...and yet he started the day by telling me that he has a list of parts he 'needs' to order...

The lathe bench this morning.

I suppose the one redeem in all of this is that he now knows how to build a motor, how to use all the tools properly, and actually insists upon using a torque wrench when he tightens anything..

First Post - This is where it all begins

A few quick notes about this blog;

This is going to be a bit of a gathering place where I record ideas and developments related to my son and his aspiring career as a motorcycle racer.

Having a fair workshop setup at home, including a CNC, lathe, pillar drill, 3D printer, two CAD workstations and a plethora of measuring tools, I've been unable to leave many of the engine components from his mini-motos alone and in all this, have developed and am developing further, a few unique high performance parts.

Content here will include blueprinting, measuring, testing, assembly, modification, and tuning of small race motors - everything from 39cc pocket bike/mini moto engines on up.

Regarding myself, I currently own a small mechanical engineering/design firm in London and being a designer, I'm always looking for ways to improve upon existing ideas and coming up with new, innovative solutions to problems I encounter.

I'll add this as a bit of a disclaimer right from day 1.  I'll include much information here, and provide pictures and suitable evidence as to the success or failure of the ideas and concepts presented here, but obviously, I will not and cannot guarantee you'll get the exact same results should you attempt some of these modifications at home.
Additionally, some of the ideas presented here have led to the development of products which I now sell. Though I promise not to overtly advertise products I sell, I will walk the reader through the development of the product, it's manufacture, and any subsequent testing performed upon it and may or may not note that the product might be available for purchase through the company.

All opinions expressed are my own.

Much more to follow soon...