I’m in the process of upgrading the engine in my 07 Street Glide from a 96” to a 103” with heads and cams. I have the SE Pro Twin Cam 103+ Cylinder Heads, SE Big Bore Stage II Kit with flat top pistons, and Head-Quarters Hurricane HQ-TC-500-HC cams. I calculated the the static compression ratio with flat top pistons at about 9.5:1 with the standard head gasket but I'm getting some conflicting information. I'm being told that the actual compression ratio will be more like 8.5:1. I really like the performance and crisp sound of a high compression engine but also realize the negative aspects, e.g. heat etc. I'm thinking about using the SE Pro Twin Cam Stroker forged Pistons for “103+” Cylinder Heads (10.5:1 compression ratio) and hope someone can give me some feedback on this setup.

 

Although i cannot give you any help with this, I would like to hear to outcome an performance report if you will, of the bike when finished, I have been thinking of doing the same thing.

 

I figure 8.7 compression with those heads and flattop pistons...you could either mill the heads to bring compression up or use high comp pistons and a longer cam...maybe HQ would let you exchange for 575 cams?

edit: or use .030" head gaskets for a little more comp

2nd edit: 10.5 comp with 500 cams is doable, but a thorough tune will be needed

 

help is here first of all if you are using SE 103+ heads
part number 17071-03B black or17072-03B silver
then you need to use the SE 103+ pistons
part number 22483-04 whitch will give you around 10.5:1.
If you try to use flat top pistons you will be shooting your self
in the foot, just like i did "the first time, before i learned better. "
The set up that i used is the cvo 103 heads which is almost the
same as the SE 103+ heads, my intake and exhaust valves are a
hair smaller than the 103+ heads but that is the only diferance
then i used the 103+ pistons, SE 258 cams and SE quick install
push rods with SE air breather and cobra speedsters exhaust,
on a 2007 RKC that now runs like a Harley Davidson should run
If I ever do anything diferent I I would use the SE 255 cams
or put my stock cams back in I hope that I could be of help to you
good luck with your build..........................kev

 

Thanks for the input. I did some more reading on this subject and realized I could not use the flat top pistons. I talked to Kevin at Head-Quarters and said with the 98cc combustion chamber and larger valves, the 500 cam would be better for low end torque. He also said that the 575 would give me a little more HP on the top end but it would raise the torque curve to a higher RPM on the bottom end. I'd rather have more torque at a lower RPM than more HP on the top end. Kevin, it sounds like you're speaking from experience regarding this subject. Are you running these pistons and heads? If so, can you give me some specifics on your build and some info on the torque, HP, rideability, etc. Any information would be appreciated.

 

yes I am using that set up and i love it ! It runs good enough that
I see no need to have it dyno tested.
The only testing that i have done to it is that it will run 117mph
and still be pulling it also hit 70 mph before I shifted into 3rd gear
I do not recomend these test, But !, I had to know .....kev

 

If you mostly ride one up, get the .575 cams, they are pulling at 2200 rpms and the torque dose come on quick and hard.

 

I like Branch Heads. Great porting polishing job along with reworking the combustion chamber to give you a really good power and torque and will work with flat top pistons

 

GAstreetglide: Seems like you are buying parts without a plan, then trying to design an engine on the internet for the mismatched parts you have. Much too adventurous for me. My suggestion is to use complimentary components, and one way to do that is to check-out the HD SE parts catalog on-line which includes a build for your current heads, cylinders, the pistons you don't yet have, and an SE cam.

Here's a link to the '09 SE parts catalog that has the build you are close to having (you need the pistons mentioned above and SE 257 cams):

http://www.harley-davidson.com/en_US...SE_001_031.pdf

(See page 10 of the catalog for the "103CI Super High Output" chart and the components use.)

Alternatively, sell the stuff you have now and start over with a respected vendor; buy their package; and, follow their recommendations.

Kevin, from HQ, is a very good friend of mine and I have the earlier 88" version of the 500 cams--they're a great cam. But I wouldn't try to use HQ cams in what you are building. There's a good chance you'll be chasing problems with the mix and match components.

Lastly, I am not a tech. But if you couldn't figure out that by using 98 cc heads (the ones you bought) your static compression with flat-top pistons was going to be well-below 9:1, you have a great deal more to learn about HD motors and should be very skeptical about receiving internet engine design advice, mine included.

Edit: I apologize if my remarks seem unfair or harsh; it's not a personal attack, merely noting you are probably in over your head and don't have a plan of what you are trying to do. And the same folks who told you that the CR with the flat-tops is 9.5:1 may also be the same folks that will now offer advice. Whatever "contradictory" information you received about CR, I'll bet my bike that Kevin told you your CR would be well-below 9:1.

 

I would sell the heads and have your stock heads worked. 98 cc heads and flat top pistons only make 9:1. your stock 75 cc heads will make around 10:1 and can be ported anyway you wallet wants and somewhat milled to make 10:5.