Who's big bore raised the compression?

 

Personally I would run the #55 grind from Webb with the ACR installed on the camshaft.It would in theory give a good power hit from 4500-9200 rpm.
I only know this by running the numbers in the same way i would for my kart motors. (briggs animal class) now yes all motors are different but if you just calculate displacement to intake size you can get these numbers...don't ask me the numbers as my father helps me out with final numbers as he is good in algebra and math and i just know how to weld and fab and build things......
Either way the TM33 carb ( i think that was what was mentioned for the 292-331 size would work great in theory on this cam grind....I'm actually slightly tempted to try the cams in my 250 to see what they would do actually.....Higher airflower velocity = more torque so it should work very well if you are carbbed right.either way my displacement or jug is not being changed until it warrants it....My 250 size runs just fine and wheelies just fine too.
I also think that polishing the intake ports is a waste of money as well as there is no "swirl" for the intake....

 

Yes, they are drop-in, but only available in Japan. I was thinking that one could provide the grind info to Web Cams and they could build to spec. These grind numbers arerace proven on the motardcircuits here inJapan.

I really like the rush of acceleration with these cams. Had it up in the mountains once already, right before the first major snow. They also counteract rounding-off of the HP curve from about 8500 RPM and above as you increase displacement. You can hear an ever-so-slight 'lumpety, lump' sound -for lack of a proper word- at idle Dealer's dyno is broke, so I need to search-out another machine in Spring.

 

By keeping the same combustion chamber size and increasing piston displacement, the compression ratio is increased. Only by increasing the combustion chamber size an equal percentage will the ratio remain the same. I had not thought of this until Luke Heaney at Luke's Racing pointed it out. He also agrees that polishing intake ports is not benificial, however he does clean up the rough castings where they need it. Slicker exhaust ports arguably do help with outflow though. While releaving the head, he removes the eyebrows around the valves and polishes the chamber too. Nice work all in all.

Bill

 

Thanks Bill, I can understand that but yougot me thinking now.

Were the figures you posted actual figures or just your engine guy's estimate?

At what displacement?

The thing is since the piston does not actually contact the head I would think when you big bore you do gain a little bit of cylinder head volume because like I said, there has to be a little space left between the new increaded bore area & the head---this space was not there before so the volume would be slightly bigger than before. Yes this space is very small but it would not take much to effect compression ratio.

I'm not preaching here I'm asking questions. I wish I would have looked at this when I had my engine all apart.

Ignoring what I mentioned above lets see here, stock bore is 72mm& a 11.0:1 compression rario. If head volume was truley a constant that would mean with the KLX 300 cyllinder(292 cc 78 mm bore) I am at 12.91 compression ratio. But I have to believe that cyclinder head volume has to increase some---anyone have any experience?

 

nm

 

Very astute observations and questions for sure. Luke CC'd the head and ran the math on the displacement. I told him I was using a J&E piston from Kustom Kraft, but I'm not sure if or how that fit into his calculations. He seemed locked onto the problem, but anyone is fallible. I'm sure he would welcome a call if you wanted to ring him and see how he came up with his numbers. His work was art. I hated to put it all back together and mess it up with combustion hydrocarbons. Well, not for long. It's a blast to ride.

Bill

 

You are correct, Sir! 21.5 to be exact. That number makes a lot more sense. I corrected my earlier post. It seems that I was thinking in terms of headings rather thanbearing from true North.

 

You guys have piqued my interest. Let's see who is first to geta compression check. I will get the numbers for 300cc and Wiseco piston. I will have to bring a thermometer to get delta T for the density altitude comp.It'scold over here!

 

nm