Rule change submissions close 1 March 2016 - be in to win.

[TZ350]

No one has explained why all of a sudden all the other bikes CC need to get bigger but not the 100cc 2 strokes.

The 100cc 2T's have the 110cc re bore allowance so are now effectively 110's, a 10% increase.

If the restriction is so unimportant there thus should be no issue leaving it in place then is there............... that old silly rule was designed to be a restriction.

That is my angle too.

That silly old rule does not work as a restriction. And if it is going to be left in place I think it needs to be better defined to cover a wider range of carburettor types and EFI.

[TZ350]

But that's the kicker if it is truly irrelevant why the need to get rid of it, I am pretty sure if a bit of development time was spent optimising for a larger carb the HP would go up.

Probably the hp may go up but the kicker is that aircooled 125 2T engines are limited to something less than 30rwhp by the thermal limitations of their engines cooling system. It does not matter how big a carb you have and power you make on the dyno, it looks like, that in reality 125 air cooleds are limited to something less than 30hp out on the track if they want to finish a race without melting.

The thought for the day:-

The carburettor is only a small part of a 2T's "transfer efficiency"

If you want to really improve a 2T's performance then concentrate on the "trapping efficiency"

Improving the "trapping efficiency" can improve power and power spread. One way of improving power spread is to improve the "trapping efficiency" by lowering the internal pressure in the pipe when the engine is below peak torque rpm.

Less standing pressure in the pipe means less incoming charge is pushed back down the transfers after BDC and "trapping efficiency" is improved in the lower rpm range.

You will get more low end toque from less standing pressure in the pipe than by fitting any sort of big carburettor.

[jasonu]

I think it is nothing to do with the carb, thermal melt down will be due to the air cooling being unable to shed the waste heat generated from 30+hp.

Attachment 319579

I once did a back to back test between a std 24mm OKO carb red line, and another OKO 24 bored out to 30mm, blue line. Both carbs were identical in style and layout and both with jetting optimized. Not as big a difference as I expected.

The 24mm carb restriction does not stop tuners from making 30hp or more but a 30+hp 125 seems to have gone beyond what air cooling can handle reliably. Even the air cooled factory race bikes of the 60's and 70's only made mid twenties power.

The legitimacy of my carburettor tuning has been questioned because I can make a tuned 24 flow as well as a factory 30. How to do it is no secret.

People have questioned the legitimacy of improving 24mm carbs so they flow better. The same people have never stopped to question the legitimacy of improving 2T cylinders, clearly they are both a legitimate Bucket thing to do.

Personally I would mourn the loss of the 24 rule because I have had so much fun with it. I have found and published so many ways to defeat it (if it was ever a real restriction on power???) that it is now irrelevant.

If the 24 thing makes people feel better and they want to continue with the comfortable illusion of a 24mm restriction, then sure, that is my first choice but the rule probably needs to be better defined to also cover EFI and throttle plate carbs like the Tillotson pumper as well as the usual motorcycle slide carbs.

The next best thing is to get rid of both carb restriction rules and cut two complicated unnecessary sentences out of the F4 F5 rule book wording.

In broad terms, carb restrictions are irrelevant in limiting power, but cooling ability is everything and air cooling does not cut it.

Mate I have no issue with the way you or anyone else has gone about improving the 24mm carb.

IMO to comply with the 24mm carb rule as long as, somewhere in the throat of the carb or carbs, there is a restriction that has a CSA of no more than 452 sq mm (ie3.14x144) AND MUST BE ABLE TO PROVE IT I'm good with it. It doesn't matter if it is a small carb(s) that has been bored out or a big carb(s) with a restrictor installed or if the throat(s) is round or oval.
I know stuff all about FI so cannot comment as to if a 24mm throttle body is comparable to a 24mm carb.

[husaberg]

The 100cc 2T's have the 110cc re bore allowance so are now effectively 110's, a 10% increase.



That silly old rule does not work as a restriction. And if it is going to be left in place I think it needs to be better defined to cover a wider range of carburettor types and EFI.

Re the 110cc, That is not what was written and what you thought was a great idea though. Go back and have a look a page or two back
PS still no one has explained how a 170cc is a rebore allowance for a 148cc bike

In order to not completely obsolete some of the existing buckets my 11pm at night half pissed idea for buckets would be:

4T - 200cc 2 valve Air cooled Non Competition
4T - 170cc 4 valve Air cooled Non Competition
4T - 160cc 4 valve Water cooled Non Competition
4T - 150cc Competition Engine

2T - 125cc Air Cooled Non Competition
2T - 105cc Water Cooled Non Competition
2T - 85cc Competition Engine
Again - Less rules means less bullshit!!!!!!

Love it .... now if only someone would put in a reduced rules submission.

Hint there was a valid reason for the 110cc to do with pistons not being available
Re the carb the rule seems to be working no protests etc what you did with the venturi is perfectly legit.
I have never seen anyone question it, Plenty of people think the restriction works, otherwise why get rid of it.
I am pretty sure the spread of power would be far wider with a larger carb likely more over rev as well.

[jasonu]

The 100cc 2T's have the 110cc re bore allowance so are now effectively 110's, a 10% increase.

.

Did I read correctly that 104cc to 110cc water cooled 2T will have a 24mm carb restriction?????

[husaberg]

Did I read correctly that 104cc to 110cc water cooled 2T will have a 24mm carb restriction?????

When it was introduced a few guys were very adamant that this was in place as a restriction.

did someone say 110cc 2 strokes

Go back and have a look at the post I quoted.

while you are at it explain how the carb is a restriction that has to be in place one year but is totally irrelevant the next when it suits you.

I think the restricted carb would have been a deliberate decision, 110cc water cooled, open carb would make everything else obsolete.

I may well be proved wrong but I think we have pretty much found the limit for power production from the 24mm carb without the aid of a plenum or the like
A reliable 30hp out of a 110cc water cooler would be a piece of cake, its f##k all work and easily the winning option. This rule change is the nail in the air cooler coffin. Next year lets clear the way for an open carb size and finally push the 125 air coolers to the back of the sheds

Up to 110cc can be water cooled, but if greater than 104cc then restricted to 24mm carb.

[TZ350]

Did I read correctly that 104cc to 110cc water cooled 2T will have a 24mm carb restriction?????

Currently, Yes.

[TZ350]

Probably the hp may go up but the kicker is that aircooled 125 2T engines are limited to something less than 30rwhp by the thermal limitations of their engines cooling system. It does not matter how big a carb you have and power you make on the dyno, it looks like, that in reality 125 air cooleds are limited to something less than 30hp out on the track if they want to finish a race without melting.

The thought for the day:-

The carburettor is only a small part of a 2T's "transfer efficiency"

If you want to really improve a 2T's performance then concentrate on the "trapping efficiency"

Improving the "trapping efficiency" can improve power and power spread. One way of improving power spread is to improve the "trapping efficiency" by lowering the internal pressure in the pipe when the engine is below peak torque rpm.

Less standing pressure in the pipe means less incoming charge is pushed back down the transfers after BDC and "trapping efficiency" is improved in the lower rpm range.

You will get more low end toque from less standing pressure in the pipe than by fitting any sort of big carburettor.

Did anybody see this about improving power and power spread by improving the trapping efficiency????

[jasonu]

Currently, Yes.

Was this a rule put in place or was it an unintended consequence of allowing water cooled 2t's 110cc?

[TZ350]

When it was introduced a few guys were very adamant that this was in place as a restriction.

They can be as adamant as they like, but they are wrong about it being an effective restriction. And I am adamant about that because I have tested the idea and have posted the back to back dyno results.

[TZ350]

Was this a rule put in place or was it an unintended consequence of allowing water cooled 2t's 110cc?

Looks like an unintended consequence.

[husaberg]

They can be as adamant as they like, but they are wrong about it being an effective restriction. I am adamant about that because I have tested the idea and have posted the back to back dyno results.

Correct, you did post the results of a one off test on a bike that had been optimised over a number of years for a 24mm carb. i certainly never expected an imediate huge increase in power from a one off test with a bike optimised for a smaller carb . Did you?
I was surprised at the time how little it was initially, but then again your bike ihas been developed fror a long time all arround this one restriction.

[TZ350]

Chapter 16 – Road Racing – Miniature

16.2 - Engines must be derived from non-competition motorcycles. Motocross, Road Racing, Enduro
and Go Kart motor and transmission parts are not permitted.

There shall be no restriction on the make, type or design of carburettor, ignition, exhaust, piston, cam, valve springs or cooling system except for class eligibility.

All engines must be normally aspirated except F4 4 stroke engines of less than 100cc capacity and F4 2 stroke engines of less than 70cc capacity, which may be turbo or supercharged.

Plus...

4T - 200cc 2 valve Air cooled Non Competition
4T - 170cc 4 valve Air cooled Non Competition
4T - 160cc 4 valve Water cooled Non Competition
4T - 150cc Competition Engine

2T - 125cc Air Cooled Non Competition
2T - 105cc Water Cooled Non Competition
2T - 85cc Competition Engine

These are maximum capacities, there is no overbore allowance.

- Less rules means less bullshit!!!!!!

It is not perfect but something like this is a whole lot simpler than the Ausie rules.

[TZ350]

Correct, you did post the results of a one off test on a bike

Show me their tests on any bike ....... ... I back what I say with evidence, let us see their evidence, I bet there is none other than group think blindly clinging to an old wives tale.

[kel]

while you are at it explain how the carb is a restriction that has to be in place one year but is totally irrelevant the next when it suits you.

Read the quote and try again