I am about to shave the heads on my 89 200. I want about 140 psi. I was just wondering what the best way to know how much to step up in jet size is? Should I just read my plugs after a WOT shut down and try going up a couple sizes at a time untill the plugs look good?
It's going to be trial and error...
Shaving the heads to increase compression does not mean you will see higher performance.
The difference in higher compression heads(after-market or factory XP/GT, etc) is also the swirl pattern created by the shape of the combustion chambers, hence the better the swirl pattern, the more complete the combustion process is, creating better performance.
Your engine will last longer with the lower compression.Really depends on how much $$$$$$ you really want to get into. I get a whole lot of engines here that should have been left low compression, some only last 25-30 hours.
rudetech1...another face of places in the past..Good to see ya again!
Ok, This is how you do high speed jetting.
First start out by changing your high speed jets out to new ones that are 10 sizes larger. If you do a high speed run with your original jets it won't run long enough for you to shut it down.
Second, do your high speed run with your trim tucked all the way in for each run unless it is unsafe at high speed all the way in, in that case only go out as much as is needed to make it safe. Each run must be run the same way each time.
Shut the motor off at high speed with the kill switch. Tie up to a buddies boat and pull your spark plugs. ALL OF THEM. Each cylinder may need a different jet size. Go up or down in jet size until the plugs are coffe tan/brown. Any lighter and it will melt.
As far as shaving your heads. Don't. Find a set of 86/87 looper heads and send them to Monty or Al Stoker and have them cut for a 3.0ltr. This will put you right about 145 lbs. They can open them up a bit to make 140. You will need to run 93 octane and more oil.
You will see a performance increase but you are also going to lose some reliability. If you ever get a load of bad fuel you can kiss that motor goodbye. You really should mix Av-Gas or race fuel with it at 50/50.
Is all this really worth the 3 or 4 mph you are going to gain in top end?
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