hi compression gaskets

[procircuit21]

I am about to put a top end in my '91 KDX and I was considering going with one of those high compression gasket kits. i heard a couple of complaints about them but I thought i would check here before I did anything. Also i am putting a Pro-X piston in and the place i bought it from (local shop) said that it was a little bigger than standard but didnt require any overbore. has anyone heard of this?

 

[canyncarvr]

I heard of this! ;)

Go here to see a pro-x chart that shows sizes of the different alpha designations (about the 9th post down).


They are all 'standard' sizes. Your bike will be marked with its alpha spec on the cylinder and the head.

The correct fit is the one that fits correctly.

The size difference isn't huge. You aren't going to stick your bike with a 'B' piston in an 'A' engine due to the size difference.

You've heard complaints and you are going to use 'em anyway? That doesn't make a whole lot of sense, does it?

Spend the $40 or so to get the head machined (by someone that knows what they are doing!!) complete with attention to squish angle change, and use a real gasket.

...imo

 

[dthoms]

Think it through before you up the compression on your bike. You might gain a little power but it will cost you. Depending on how high you up the compression you might find your bike will not run right without high octane fuel. In fact it might run worse on pump gas then it did previously. I have went down that road before and it gets costly and can be a pain finding high octane gas in the middle of nowhere.
I would suggest other mods if you are looking for a boost. Like new reeds, better pipe, power now. In fact I would have my bike ported before I would raise the compression.
I have seen a lot of people bike that would just run better if the tuned it correctly and cleaned the air filter more often. I'm not saying that is your problem but theres a lot of people that modify their machines and then can never get them tuned right afterward.

 

[beefking]

Don't go with high compression, the gains are minimal! Unless you ride at high elevations (above 2k feet) where you are already at a downset because of lower oxygen/air pressure levels. I had porting done by Eric Gorr (more power everywhere type), and I already had +2mm Wiseco kit. The bike rips! (89 200 BTW). It's running a little down right now b/c the jetting is off a bit and the pipe is smashed up, but it's still VERY fast.

So in my opinion, there are much more effective ways to get mo' power that will end up costing much less in the long run...say, 3 or 4 tanks of gas! Such as reeds, pipe, porting, etc. etc....Good luck. :thumb:

 

[canyncarvr]

The two above posts from BK and dt make my point perfectly.

Head machining that is done properly is more a matter of squish band adjustment than it is simply higher compression ratio. And someone that knows what they are doing will not cause a fuel problem (won't run on pump gas) if that is the desired effect.

It is indeed the 'knows what they are doing' part that's sticky. I've had engine work done by a mech that was renown for his abilities and knowledge. I made it very clear what I wanted.

My engine was ruined for its intended purpose.

The original question was, as long as the thing is apart why not bump the compression a little?

Because several that have used them have found them to be junk.

Live and learn. Experience is indeed the best teacher. Also the worst. Best to learn from someone else's mistakes.