Hello,

Sorry for bombarding the forum with a lot of questions, but this is my first performance build so I do need some advice.

Bike is a 2002 FXD with TC88" engine.

I have new S&S 79 cc heads, 1.940" intake and 1,575" exhaust valves, .650" lift springs. I think these heads flow better than stock but maybe not as good as professionaly ported heads.

I have also bought a set of JE 3.927" pistons, that will give 98 cui displacement. I misunderstood the specs when I ordered them, I thought they were +1.2 cc but it turns out they are -1.2. Basically flat tops.

According to the big boyz calculator this will give a compression ratio of 9.95:1 with 0.045" head gaskets and 10.25:1 with 0.030" gaskets.

I also have S&S 2-1-2 pipes and Dynatek TC88 ignition. I was hoping to still be able to run the stock CV40 carb to keep the budget from going completely off the rails.

So, here comes the million dollar question. What cams to use?

I am primarily looking at S&S cams since I want the easy start option, but I could consider other brands as well, I would then need to install compression releases I guess.

The cams I'm choosing between are 570, 583, 585 or MR103. All gear drive.

S&S tech support have recommended one of the four but I will not reveal which one, to avoid bias in your suggestions.

I am very thankful for any input on this

 

I’d do the 570 at 10.25:1

S&S tend to be conservative in what they recommend re compression

 

"For what it`s worth" ( nothing )
98" / + 3cc pistons / Stage 2 heads / 570 gear drive / Twin tec ign. / CV carb / 2-1 exhaust
Well pleased with how it runs from "top to bottom"
This is on a heavier bike ( RK ) with taller 2:88 primary gearing

 

This sounds quite similar to my setup. It's good to know you can run the stock carb. Do you happen to know what jets are in your carb?

 

48 / 190
the N95 Sportster needle with no shims
43 MPG at 65-70 MPH

 

The 583 are going to bump your dynamic compression up to much and the 585 is probably going to be too much cam just my opinion on the 585. I’m going through something similar except my compression is a tad lower. I’ve got the S&S 510s now so I’m going to stick with them since I just spent my cam money on an oil pump and cam plate. The 585 may be ok but I’ve always heard go with a smaller cam than you think you need. I also know for a fact that the 570 is a proven performer in similar builds. That’s my free advice. Keep in mind what you paid for it lol
edit I’m not sure if you have compression releases but you would probably want them. I don’t know much about the MR103 but I thought it was another that would bump your dynamic compression to high.

 

Thanks, this is great info

 

The MR103 has intake closing at 33 degrees so not as early as the 583. S&S actually recommended the MR103 but I think I will go for the 570, it's seems like a proven and popular cam.

I will buy the easy start version so I will not have to bother with compression releases.

The S&S heads have a complicated provision for releases but I think I have figured out a way to use oem Harley electric releases if I can't find any ez start 570's.

Thanks for your reply, good info

 

S&S has a kit for manual compression releases for their heads. Cable operated. Releases will fit under stock harley rocker boxes. I have used them before. Don't have to worry about burnt fingers. Pull **** mounted to left side top of rear head. Harley ACR's will not fit to S&S heads. Different smaller thread size.

 

Also, if using Harley rocker boxes on S&S heads, You MUST use special S&S lower rocker box gaskets. Harley gasket will NOT work. S&S heads do not have a breather channel in them like Harley does. So they use a thicker gasket and cut a channel in the gasket. Actually breaths out from Harley breather assemblies, through the gasket and then down hole and out through outside breather port at stock location