I rebuilt a top end using a JE 10.5-1 101 mm and stage one Hotcam. It runs so much better than stock, on 85 octane pump gas at 5500 feet altitude. There is no down side.

Talked to a shop today they said the 100mm would probably be fine but if I wanted they have a machine shop they could send it out to get bored out.

So now i wonder what the power difference would be between 101mm and 102mm...
102 is only 664 cc, 20 over stock doesn't seem like it would be any difference at all. Any thoughts on that?

Leardriver, on 25 May 2012 - 10:14 AM, said:

Hearing this is what makes me want to get the 11:1... I've heard the same thing said by other people. If that's the case then it leaves me asking why wouldn't 11:1 run on 91 octane?
Especially since everyone says the compression is never actually as high as they claim. Not only that but 11:1 seems like a normal compression to me for most bikes, I'm pretty sure thats the stock compression of the drz400

I didn't want that bike to require premium, and at high altitude, it doesn't.

It makes the bike so much more fun to ride, for not much more $$

With the proper cam you can run a true 11:1 engine on 91 octane pump with the correct mods and part choices.

The cam is the heart of the engine.  Degreeing the camshaft in during installation should be done.  This is important.

Getting your engine to run at it's best on pump gas is all about having the proper duration, centerline, overlap and lift specifications.

The longer duration, increased overlap and centerline of a performance or race cam effectively lowers the length of time(amount of degrees) the piston has to compress the fuel charge. This reduces the the cylinder pressure which is what the higher compression ratio piston corrects.  Matching the two together properly will keep the cylinder pressure at the correct level for the fuel available.

Two cams with the same specs can perform differently due to  ramp angles the cam grinder choses also.

These changes can altered to adjust/determine the engines rpm range and overall performance and volumetric efficiency.

This is why the money for the custom cam is well worth it.  A good engine builder knows how to grind a cam for your needs and desired engine performance.

If you are going to do it, do it right and be happy or deal with the end results.

Page Mohler, on 25 May 2012 - 05:29 AM, said:

YES, they do!

cyclewizard, on 25 May 2012 - 04:28 AM, said:

If your hotcam holds up you're leaving a good amount of money in your pocket too. I've used Harmon/Collins, Webcam, Megacycle, HRC, Mugen and a few others. Some grinders put too steep ramp rates on the lobes for good rocker life. I've seen more than a few name brand regrinds trash topends too. Higher hp demands higher precision and maintenance so don't overbuild unless you plan to keep up with that. Big cams are hell fun but can be destroyed easily by a less experienced rider. CW can fix you up if you need the big dog stuff.

valvesrule, on 25 May 2012 - 06:12 PM, said:

Well you're spot on about high lift and steep ramp angles and wear on the valve train, in order to cure this problem a set of roller rockers are needed like the Rotax engines have incorperated into there valve train.
what happens with huge cams is the rockers ride of the cam and wear out prematurely.
I can grind a less agressive cam similar to a hotcam if someone wants that. But with the motors I built a hotcam is not up to the task..
Take a big block 750L motor and put a hot cam in it and you would think your riding a stock motored L.
Like TNT said the cam is the brain and heart of the motor..

I do have tiny winy cams but nobody seems to want them..
When I grind a cam the first thing I check for, are the rockers riding off the cam, if they are I change the RA's and lift..
I try to keep the lift no more than .400 for this reason.
CW

TNTsXLR, on 25 May 2012 - 04:33 PM, said:

........