compression?

[fulltiltboogie]

For you 95-up 200 owners. What kind of compression numbers do you get with your motor?

[canyncarvr]

I've got mine written down someplace...don't remember the number exactly.

It's largely a waste of time to ask, though. The way the test is done is critical to the outcome..so is the guage used and how it's used. The 'waste' part is that responses may well mislead you to some erroneous conclusion of what your numbers mean.

When a compression number is of most use is when it's from YOUR bike, taken at a previous time so you can compare it to another test done..on YOUR bike.

My bike is ported, so any answer from me is a waste of time anyway!


...because of the porting I mean...

BTW...engine should be at operating temperature, throttle held wide open. Note not only the maximum pressure obtained, but the number of kicks to get it there (whatever a 'kick' is..part of the issue of meaninglessness) and what the 'average' gain per kick/stroke is.

[fulltiltboogie]

I realize that pretty much any measurements not taken with a Snap On guage are useless. I would have figured all the responses into my conclusions. I was just curious to see what others were getting. I guess nobody checks. I would have thought maybe some at least checked their comp every once in a while. I know mine has always read higher than Kaw specs. (190 lbs) That always seemed high to me and even high enough to require higher octane fuel. What surprises me is that my bike is on its 5th season of hard riding/racing and it still has the same comp as it did the day I got it. CC-what does porting have to do with the engine compression? Thats a new one on me. You changed the intake, transfer and exhaust ports but what in the world does that have to do with comp besides that your head has been changed? And this number of kicks thing.....I never heard of that. I always just thought you kicked it until it topped out.

[Matt-itude]

how hard some one kicks it affects it also. on porting, the amount of air that enters and is trapped in the cylinder to be compressed, will affect the pressure more air trapped higher pres. etc so that being said reeds if someone moves the throttle at all while they kick and like how many times it is kicked. for me I use my same gauge hold the throttle wide open kick it half heartedly 5 times. after 150 miles on my 03 200 and bone stock at the time (pipe reeds etc all stock) I had 145#.

[canyncarvr]

re: how hard some one kicks it ....


Which is what I meant by:

whatever a 'kick' is


re: what does porting have to do with the engine compression?

You didn't ask about compression ratios, but combustion pressures. Actually both of those may change with porting.

How well an engine breathes matters. IF you start out with 1.0 atmospheres in the cylinder before you start squeezing it, you end up with XXlbs of pressure.

Start with 1.1 atmospheres...you get a different reading.


Porting a 2-stroke is similar to camming a 4-stroke. Soooo....a 108º centerline cam with 72º of overlap will give you the same compression readings as the OEM cam you took out?

You had better hope not!

Given the same piston/head configuration the aftermarket cam noted above will give you squat for compression numbers..ratio AND pressure! Heck..you end up with a pressurized intake manifold a whole lot of the time!!!

So much for vacuum boosted brakes!


Look at the mechanical compresson ratios of a KDX with the KIPS on/off. Changes a whole lot, 'eh? Certainly, the actual combustion pressure numbers vary also. What does the KIPS do? Raises the exhuast port. What do a lot of porting jobs also do? Raise the exhaust port (not mine).

Sorry, I'm kind'a repeating myself here..... a few times. I sense some incredulity in the 'tone' of your question. If I wasn't clear the first time, maybe the second or third time will help. Not harping or anything...just want to answer the question.

Cheers!


BTW...I have a Craftsman gauge...so there's another reason any answer from me regarding my bike would be a waste of time!!



If you have the same compression numbers now that you had five years ago, that is a good thing...probably.

Well...it is possible to have wear (a bad thing) in some places subtracting from the number and deposits (another bad thing) in other places adding to the number. Something else to think about!


re: And this number of kicks thing...

The absolute number obtained and the number of 'breaths' it takes to get there are not the same thing.

Consider an air compressor. What is an engine anyway?...it's an air pump. It's apples and oranges to say, 'This compressor puts out 200psi!' and, 'This compressor puts out 10 SCFM!'

The former doesn't mean much at all. The latter means you have a pretty much kick-a$$ unit for home use!!

If you get your 190psi with one kick...or six...not the same thing. If you USED to get it with one...and now it takes six....not the same thing.