[998Robbie]

Would increasing the compression on otherwise stock 999 yield anything worthwhile without a cam swap? Also, has anyone milled 999 heads to increase compression? I'm think that the heads can not be milled that much and higher compression pistons would be the better route.

What's the maximum that they could be milled physically and also what is the amount that they would need to be milled to get say 13:1 or even 14:1 compression. At that high compression would 98 octane be enough (92 m+r with 30% toluene mixed as octane booster)?

 

[tye1138]

It really depends on what you are looking to do. Substantially higher compression usually leads to higher running temps and the expense of keeping those down AND the added wear, can be costly. Obviously we're talking major changes like 14:1. You can easily run that motor a tad bit above 999R spec: http://ducshop.com/product_view.php?cat=6&pid=272

If you're seeking power the best route isn't necessarily to just change compression but to change the cams, lower the squish a bit and lighten the bottom end in conjunction with a slightly higher compression piston kit.

OR

You could just by a used 999R motor and be done with it... Thats my favorite option!



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[Reformedducnut]

Would increasing the compression on otherwise stock 999 yield anything worthwhile without a cam swap? Also, has anyone milled 999 heads to increase compression? I'm think that the heads can not be milled that much and higher compression pistons would be the better route.

What's the maximum that they could be milled physically and also what is the amount that they would need to be milled to get say 13:1 or even 14:1 compression. At that high compression would 98 octane be enough (92 m+r with 30% toluene mixed as octane booster)?

Compression gives you nice increase in power, but the downside is that your going to have to run race gas. Something with atleast 106 octane. You can't really depend on a "octane booster" They make claims that they can't live up to. I wold port the heads and polish the combustion chambers. Don't smooth out the intake runner that much becuase it needs tobe a little rough so you can get good atomization. But you can port and polish the exhaust port and polish the combustion chambers. This will help out, but unless your going to bump up the bore size................ Make sure you have the cams degreed. This can free up some extra free HP.

I've built tons of motors......tons. I haven't built a Duc motor yet, but all the same principles aply to any interal combustion motor.

 

[headstud]

I have built 2 999 base style engines with 4" bore custom domed pistons. One engine had just a cleanup cut on the head and cc'd out to 12.54 / 1. The 2nd engine had the heads milled more significantly and cc'd out to 13.54 to 1. Some changes to the porting on the second set of heads netted slightly over 150 h.p. at the tire. The first attempt with the lower c.r was in the low to mid 140's at the tire.
Both engines run fine on pump fuel, either 91 or 93. The higher compression engine runs where only the 91 is available and has been problem free with maybe 40-50 trackdays on it. Neither engine had the cases apart as I had the pistons, pins and rings weight matched when built. I don't believe you will get much past 12 to 1 measured with milling alone but someone else may know more about that. Also bear in mind that you will need larger pulleys (available from BCM) if significant milling is done. I had to use them on engine #2.
Hope that helps.