Building a “racer”

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Ulwembu1
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Joined: Thu Nov 05, 2020 8:00 pm
Location: Netherlands

Building a “racer”

Post by Ulwembu1 »

Hi everyone!

Took me a bit to register due to some issues.
I’m currently building a “racer”. Donor is a Silver Century Plus. Talked a bunch with Brian from Bermuda and taking his advice to change out parts and remodify some bits. Currently done:
- High compression cylinder head
- 40 Featherweight gearbox
- Shim made from another gearbox to accommodate a Yamaha propellor
- 102 prop shaft to accommodate the Yamaha prop (still need to be reworked)
- Bought several Yamaha props in different pitches to test
- Amal 420

I’m debating wether or not I need to install a expansion exhaust.

Plan is to build a Minimax hydroplane which would weigh around 70 lbs. It will be just for fun since we don’t have a race class in the Netherlands (yet!).

Any other recommendations would be very welcome!
never-outbored
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Re: Building a “racer”

Post by never-outbored »

I’m doing a similar thing at the moment. I suggest reading up on all the forum posts discussing this previously, reams of information there. Those with “race” centurys that run well have got there through extensive r&d, there’s no silver bullet, and if someone had found one they’d keep it close to their chest!
Good luck, Ed
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Collector Inspector
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Re: Building a “racer”

Post by Collector Inspector »

Ulwembu1 wrote: Fri Nov 06, 2020 1:31 pm Hi everyone!

Took me a bit to register due to some issues.
I’m currently building a “racer”. Donor is a Silver Century Plus. Talked a bunch with Brian from Bermuda and taking his advice to change out parts and remodify some bits. Currently done:
- High compression cylinder head
- 40 Featherweight gearbox
- Shim made from another gearbox to accommodate a Yamaha propellor
- 102 prop shaft to accommodate the Yamaha prop (still need to be reworked)
- Bought several Yamaha props in different pitches to test
- Amal 420

I’m debating wether or not I need to install a expansion exhaust.

Plan is to build a Minimax hydroplane which would weigh around 70 lbs. It will be just for fun since we don’t have a race class in the Netherlands (yet!).

Any other recommendations would be very welcome!
Good on you!

A simple cross flow two stroke always gets some juices flowing.

May as well document what you are doing for us as there should never ever be any embarrassment for giving something a right royal try...EVER

You have information to proceed with confidence so far. All good in that aye.

My question is weather (Ahem) you are going for power from high revs or the other way....maximum torque below 5000rpm?

Power can be the same when applied to the water...so different approach but satisfying results either way.

Look forward to the flying spanners@midnight with some pics along the way

Regards

BnC.
A chicken is one egg's way of becoming others
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Charles uk
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Re: Building a “racer”

Post by Charles uk »

Before you start on your Minimax, have a look on the New Zealand Seagull racing web sites , they race in water conditions similar to yours which are very different to the open sea in Bermuda.

In NZ only Pirate Pete uses a Minimax & he uses a 5R on the back, but he does post films.

Have a look at your carb & the inlet port geometry & let us know where the venturi is going to be located .

Read all the books, all you can find on two-stroke performance tuning.
Make it idiot proof and someone will make a better idiot.
Ulwembu1
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Joined: Thu Nov 05, 2020 8:00 pm
Location: Netherlands

Re: Building a “racer”

Post by Ulwembu1 »

The similarity in conditions is exactly why the Minimax appeals to me: flat water, light weight, fairly flat bottom and no depth. On top of that: it will be the first ever boat I’ll built so it’s a good oppurtunity to dip my toes in the water for future projects.

At first I’ll put it tigether with the idea given to me by the Bermudan guy. I did order several props though with different pitches to see what works best in our waters.

Must admit that I’ve been checking out other carbs and reed valves and such...
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Charles uk
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Re: Building a “racer”

Post by Charles uk »

Your weigh will also make a difference.

Look on the Kiwi sites for a boat called Microgull a shallow V bottomed speed boat with a windscreen, black hull yellow deck, that weighted less than 40 lbs before painting, 6mm ply below waterline 4mm above.

The carb has to suit the complete inlet tract!

Brian is very good!
Make it idiot proof and someone will make a better idiot.
Ulwembu1
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Location: Netherlands

Re: Building a “racer”

Post by Ulwembu1 »

70 lbs is including the engine on the Minimax. Just received a book on 2 stroke tuning to get me further. Plan is to make sure the setup I have now runs and go from there.
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Charles uk
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Re: Building a “racer”

Post by Charles uk »

I've never seen a Minimax that weighted less than 60 lbs, you might get one down to 35 lbs if you use carbon composite but that could be 3000 euro plus, if you did all the work.

See if you can find somebody with one that you can test drive in Holland.

Whose the author of your two stroke book?
Make it idiot proof and someone will make a better idiot.
Ulwembu1
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Location: Netherlands

Re: Building a “racer”

Post by Ulwembu1 »

A. Graham Bell. Publisher is Haynes.
Horsley-Anarak
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Re: Building a “racer”

Post by Horsley-Anarak »

try this one

http://www.vintagebikebuilder.com/jenni ... dbook.html

see how long your tuned pipe needs to be.
Ulwembu1
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Location: Netherlands

Re: Building a “racer”

Post by Ulwembu1 »

Cool! Thanks!
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Charles uk
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Re: Building a “racer”

Post by Charles uk »

Jennings is considered better than Bell even though it's earlier.

Or try Motorcycle Tuning two stroke, John Robinson.

Two-stroke Tuning, Roy Bacon.

The Two Stroke Engine it's design & tuning, K. G. Draper.

Two-stroke High Performance Engine Design & Tuning, Cesare Bossaglia.

The High Performance Two-stroke Engine, Dr John C Dixon.

& the most difficult read Two-stroke Engines, Professor Gordon Blair.

I thought Dixon was better than Bell from a beginner's & technical viewpoint.
Make it idiot proof and someone will make a better idiot.
Ulwembu1
Posts: 6
Joined: Thu Nov 05, 2020 8:00 pm
Location: Netherlands

Re: Building a “racer”

Post by Ulwembu1 »

Thank you!
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