Engine Size

[Clay Pitkin]

Ok my engine builder asked me a question, and I did not have the answer.

I run a two stroke snowmobile engine 1000 CC. Lets say I use a 800 or 900 crank, but I keep the stock bore 1000 CC, pistons, etc. Does the length of the stroke make the engine a different size even if the pistons is stock bore?
How is the bore figured in tech?

TIA
Clay

[RICK]

You're kidding me ,right?  Somebody that claims to be an "engine builder" asked that question?

[Jonny Hotnuts]

Is the displacement of a 2 stroke measured from the top of the intake port?

I could see questions about displacement of a 2 stroke if the displacement is measured from the intake port.
In truth this wouldnt entirely be a bad way to measure displacement as anything below the port is not part of the compression cycle.

Imagine the differences in reading if done from the cylinder volume pump VS measured bore and stroke.

Interesting.....

[debgeo]

change engine builders. Engine displacement is figured based upon bore and stroke time number of cylinders. Are you sure this guy is a engine builder

[RichFox]

I believe the answer to this question can be found on page 15 of the 2010 rule book.

[Clay Pitkin]

Yes he is! In fact he is very reputable. When he asked me this question, I looked at him strange to......
But he said in Snowmobile drag racing, they actually measure the stroke and the bore, so I am running a 1000 CC, the bore and the stroke both have to be that of what is for a 1000 CC, so you cant de-stroke it etc, if you do, you are in a different class, or DQ'd. In addition, he said that I could swap my crank out for a 800 or 900 CC, they have stronger main journals. But it changes the stroke.....

And you thought your rules that you have to do is strict.......



TIA
Clay 

[panic]

Never mind, I'll just let the experts answer this one.

[Nortonist 592]

That was a joke question, right?   

[Clay Pitkin]

Oh no, I am serious as a heart attack. I have heard of that, and know of rules in other organizations that do get this involved.

[Milwaukee Midget]

Clay, this sounds like we're not getting the entire story, and I'm not blaming you.  He mentioned nothing about shortening up the jugs, perhaps?

Sometimes really knowledgeable tech guys can rattle off a scenario that makes perfect sense until they stop talking.  That's what happened to me back in third-year Statistics.

But this raises a question - The "I" break is at 1 litre.  Other then perhaps a stronger crank, is there a reason that you're considering de-stroking?

Chris

[Stainless1]

Clay, not the expert but if you shorten the stroke enough, it will put you in the 750 class as long as you are not talking production.  If the smaller motor makes more HP, then by all means, go there, but if it makes less, what have you gained?  Don't answer reliability, this is racing, there's no room for reliability unless you already own the record  

[Nortonist 592]

Just don't forget to move the ports too.  Still find it hard to believe its a "for real" question.

[RichFox]

SCTA also actually measures the stroke and bore. If you change the stroke it will be measured at the new stroke, not the original. Anything between 751cc and 1000cc runs in the same class, so if you now have an 800cc motor it will still run in "I" class.

[dw230]

Can't use the pump on a two stroke Nutz. Uncovers the ports and measures the world.

DW

[kiwi belly tank]

Now this is entertainment!