Have an 88 with a cam, going 95, need to know correct comp

[Samsquanch]

Hey guys, I've got a 2003 fatboy, fi, Andrew's 37 cam, white bros 2:1 pipe, SE air filter, 21t front sprocket. Bike is fun to ride but you know how things go...

I'm going to eventually want to make it faster. Big bore and head work are next.

I found a guy selling some SE 95 jugs and wiseco flat tops (9:1) for a good price. (All new in boxes).

Using the big boys comp calculator it seems I'll need to shave the heads down to get me to an ideal compression ratio, which I'm fine with as I'll be having heads done if I go big bore.

Am I barking up the wrong tree? Are the flat top pistons a good choice for my Andrew's 37 cams or do I need to be going with a stronger compression ratio set of domed pistons?

I dont imagine I'll run into valve and piston contact with a 510 lift cam, these pistons have .180 depth valve pockets.

Thank you in advance.

[838]

TDC lift is the factor for valve to piston. Not total lift. I had to go to 78cc with flat tops to achieve 10:1 at 95". Different cam though.

HD Street Performance did all the work for my 95". You should talk to him (Don). That little 95" was a powerhouse!

[Don D]

Well you can mill the heads, it will be a hefty cut with flat top pistons. I did that many years ago, I no longer go there. Using a small dome (KB907C) is the way to go. Others will mill them .070+ and now the intake fit is in play. Some would just short the build and move on. It won't run terrible, it just won't be up to the potential.
A 95" motor with that cam, heads ported with a 1.9" intake, at 10:1 will make 100+ hp and 105 TQ all other things being ideal, and run well.

[Samsquanch]

Sounds like buying 9:1 pistons and playing around trying to massage the bike to 9.5 or 10:1 is kinda silly when i could just get some appropriate pistons and not cut the heads down so far that it creates other trouble...

Thanks guys. I had not considered what other dimensions change when cutting heads down so far.

[04rkryder]

"Using a small dome (KB907C) is the way to go."

The KB907C is a 4 3/8 stroke piston according to my catalog. Maybe you meant the KB905C 6.7 cc piston. 10.0:1 compression w 85cc heads.

To the OP, don't waste money buying SE cylinders, just bore your stock ones.

Don can do it all for you.

[838]

To the OP, don't waste money buying SE cylinders, just bore your stock ones.

Don can do it all for you.

[Hillside Motorcycle]

We would bore that to 98", and we can/do taylor piston dome volume if required, to attend to compression needs.

[Don D]

 The KB907C is a 4 3/8 stroke piston according to my catalog. Maybe you meant the KB905C 6.7 cc piston. 10.0:1 compression w 85cc heads.

Absolutely, good catch.

[turboprop]

We would bore that to 98", and we can/do taylor piston dome volume if required, to attend to compression needs.

To the OP:

This. And he is across the lake from you.