Bye bye 2 strokes!

[lilredmachine]

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[lilredmachine]

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[lilredmachine]

How did we get onto karts? We were talking about a sidecar in a four stroke class that topped 110 MPH with an MZ 125 4t motor in it. I don't care that a lighter 2 stroke kart is 15 MPH faster (Weight does make a difference to top speed, lighter weight allows longer gearing to be run whilst still remaining competitive on acceleration)

I reckon the MZ motor in that sidecar is producing a decent amount of power. Thats all. If you want to get antsy over capacity, a tiny hydrogen peroxide rocket will produce 1500 HP, and they have been put into loads of karts.
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Bikes: too many, too much for one man to maintain anyway.

[Kickstart]

Hi

Right, so now we get to the truth that the 125 side car class is limited to 4 strokes. If so that is why they are limited to the slower 4 strokes rather than the faster 2 stroke. So if "They want more, if it is possible, it is assumable that they have done it".

What is the point of using a class restricted to 4 strokes to try and show that they are better than 2 strokes?

The kart was merely mentioned as being something with a similar drag to the 4 stroke you mentioned but with massively more power due to its 2 stroke engine. Rather destroys your comment that "There is no physical reason for 4 stroke 125s to be less powerful than 2 strokes", especially when there has been one hell of a lot more development in 4 stroke engines than in 2 strokes.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[lilredmachine]

[Kickstart]

No. You started out with the comments that there is no reason why 4 strokes should be less powerful (there are reasons). You have then gone one to try and show how powerful 4 strokes are with an example of a sidecar 4 stroke, which is pretty slow compared to a rough 2 stroke equivalent.

While development may make 4 strokes more powerful, they have got a hell of a long way to go to catch up with 2 strokes, and that is despite far more development resources having gone on the 4 strokes over the years.

Chances of a 30hp 125 4 stroke in a road bike is nil in any reasonable timeframe.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[lilredmachine]

[Kickstart]

Fair enough, but you did try to say that they can be as good as 2 strokes for power which is a long way from the truth, when a good Moto GP 4 stroke engine requiring very regular rebuilds manages about the same specific horse power as a 2 stroke road bike.

Only way that 4 strokes come out OK in racing is because the rule books are (now) written to favour 4 strokes. When in the GPs the rules just specified the engine capacity nobody had bothered to race a 4 stroke since the early 80s when Honda tried and failed to compete with the hideously complicated but still slow NR500.

If they could get competitive power from a 4 stroke then they would have raced them.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Nath]

[NC30UK]

very true but i was compairing a mass production bike of the 60's (CB750) against something modern (sports 750). The modern 750 makes twice the power of something from the 60's. With 30 years of development bikes are making twice the power they used to, so give it another 20 years and 4 stroke bikes could be making more power per cc than current 2 strokes do.

But as keith rightly said, this is more as a result of the massive investment that goes into modern 4 stroke engine design and a complete lack of investment in 2 stroke design.

The RC165 refference was a response to gsxrmik saying:

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[Jack_Cheese]

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[NSR Mick]

[Nath]

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[stinkwheel]

Dare I bring up the subject of wet-sump 2-stroke twins with a 180 degree crank and transfer ports between the two cylinders which effectively do not need oil in with the fuel? (Didn't Ariel make one back in the 1950's?)

Yamaha currently make a V6 high pressure direct injection 2-stroke with a capacity of 3.3 litres producing 300hp. Unfortunately they are only fitted to outboard motors as yet. Had one on the boat we hired in Florida last year. An 18 foot boat with a fully planing hull and anything over half throttle would have flipped it.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[LUXY DJ]

you seen how much these NEW! diesels spit out BLACK sortty smoke......(&this is a improvement )
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GSXR750
(FAR FAR from standard) www.gixerjunkies.net

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[stinkwheel]

Another point worth dropping into the discussion is that race engine designs are not driven by what is fastest/most powerful. They introduce regulations to encourage development in the direction the manufacturers would like to see their road bikes go.

It was done back in the 70's when people were making ludicrous engines like a 4-valve per cylinder, 250cc inline six. The use of multiple, tiny pistons made for a very fast bike but had no chance of transferring to a saleable machine. So they brought in a minimum single cylinder capacity rule.

They did the same with 2-strokes, mainly by allowing the 4-stroke machines much more leeway on weight than the 2-smokes, effectively giving the 4-strokes an artificial advantage.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[stinkwheel]