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Author Topic: Engine Size  (Read 6358 times)

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Offline Clay Pitkin

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Engine Size
« on: January 07, 2011, 05:38:50 PM »
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
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Offline RICK

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Re: Engine Size
« Reply #1 on: January 07, 2011, 05:45:48 PM »
You're kidding me ,right?  Somebody that claims to be an "engine builder" asked that question?
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Offline Jonny Hotnuts

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Re: Engine Size
« Reply #2 on: January 07, 2011, 06:13:58 PM »
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.....

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Offline debgeo

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Re: Engine Size
« Reply #3 on: January 07, 2011, 06:14:39 PM »
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 :? :? :? :?
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Offline RichFox

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Re: Engine Size
« Reply #4 on: January 07, 2011, 06:52:10 PM »
I believe the answer to this question can be found on page 15 of the 2010 rule book.
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Offline Clay Pitkin

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Re: Engine Size
« Reply #5 on: January 07, 2011, 07:32:16 PM »
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.......

 :-D

TIA
Clay 
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Offline panic

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Re: Engine Size
« Reply #6 on: January 07, 2011, 07:50:44 PM »
Never mind, I'll just let the experts answer this one.
« Last Edit: January 07, 2011, 11:23:08 PM by panic »
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Offline Nortonist 592

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Re: Engine Size
« Reply #7 on: January 07, 2011, 08:12:14 PM »
That was a joke question, right?   
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Offline Clay Pitkin

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Re: Engine Size
« Reply #8 on: January 07, 2011, 09:47:13 PM »
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.
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Offline Milwaukee Midget

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Re: Engine Size
« Reply #9 on: January 07, 2011, 10:15:06 PM »
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
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Offline Stainless1

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Re: Engine Size
« Reply #10 on: January 08, 2011, 12:30:03 AM »
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  :-o
« Last Edit: January 08, 2011, 10:28:13 AM by Stainless1 »
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Offline Nortonist 592

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Re: Engine Size
« Reply #11 on: January 08, 2011, 01:43:15 AM »
Just don't forget to move the ports too.  Still find it hard to believe its a "for real" question.
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Offline RichFox

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Re: Engine Size
« Reply #12 on: January 08, 2011, 11:04:00 AM »
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.
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Offline dw230

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Re: Engine Size
« Reply #13 on: January 08, 2011, 12:56:16 PM »
Can't use the pump on a two stroke Nutz. Uncovers the ports and measures the world.

DW
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Offline kiwi belly tank

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Re: Engine Size
« Reply #14 on: January 13, 2011, 11:16:59 PM »
Now this is entertainment!
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