Hi all, I'm adding a fuelmoto power pack which includes TW-555 cams, PCV, pushrods, etc, etc.... I talked with my mechanic this morning about bumping up the compression without doing a big bore and he suggested milling the heads to increase compression. Just wondering if anyone here has any experience with this and if so how did it work out? I'll also have to run this by Jamie to ensure he has a map to accomodate this mod.

 

Your going to have to raise the comp to run that cam.Raising comp can be achieved a number of ways.My heads where done on my build.Im running about 11.2 static.The bike will have a nice heathy sound to it.You have to watch how much you raise it in different parts of the country,due to the gas, & heat!!!

 

It's done all the time. Your heads are measured to determine exactly how big your combustion chambers are, and then the mating surface is milled to reduce the size of the chambers until they are at the correct size for the static compression you want.

Your pistons will also need to be measured to determine how far down the bore they are at TDC. This affects your compression calculations and your squish zone. Ideally, the pistons would be flush with the cylinder bore (zero deck). You could deck the bottom of the cylinder bores to acheive this, but if your heads are being milled, you can have the machine shop spin drop your heads. This puts a little shoulder on the heads where it mates with the cylinder bore that would match the amount of distance the pistons are in the hole.

As long as you have the heads off, it's not that much more time to swap pistons, so if you are considering going to a larger bore, now is the time.

This is how one thing leads to another.

 

This is not true. I've seen a lot of people say that to run the 555's and the 6-6's you need to raise the compression and it's just not true. They do run great with raised compression (matter of fact, Jamie from fuelmoto, runs 10.25-1 in his kit), but you don't need higher compression to run that cam.

 

So can I change the pistons without boring the cylinders? Is there pistons for a 96" that will increase compression or are you talking about better ones?

 

I thought about this also, I want to stick with HD parts and do not want to add the adjustable pushrods. So like the OP I am looking for the details on how much milling I would have to do in order to get 10.5:1 and from there I would be able to match my push rods and head gaskets. I have SE255 cams and think this is a good ratio for this cam but will take input on a better setup.

 

I havent found any yet, I wanted to go with a raised piston and keep my 96". The only thing i have found is the 3 7/8" (103c.i.) piston and cylinder kit from Harley. I guess if you go that far into the engine might as well up the cubic inches while your there. I would love to see what a 96" would do with higher compression vs a factory 103 c.i.

 

If he is running a stock motor the static(9 ish) is already low.Adding a bigger cam with a 41 intake close will make the dynamic comp even lower(due to the bleed off).The bottom end will suck.The bike will be a pig!! If you want it to run right you better add some comp(Cams & comp must match).Call Mr.Woods & ask him what he thinks your comp should be at.I bet he will tell you to raise it.His cams love comp ,& boy due they hit hard!!! Ask me how I know!!! I have had other cams & they don't compare to his!!! I junked my T-Man 662-2 in favor of his TW 68 ,& it was the best thing i ever did!!!!

 

The 96ci with the higher comp will run right by it!!! no question!!!

 

so my next question is what comp should we land on?? My builder is thinking a little over 10.... I'm definately not the sharpest knife in the drawer when it comes to this!! Maybe I'll give Bobby a call. I wanted to avoid a big bore but maybe I'll just pull the cylinders and get them bored and add bigger pistons. I absolutely don't want to get into the bottom end, so what bore/pistons would accomodate the headwork?