Got a question for all you engine guru guys. got a 09 classic, 96inch with some performance stuff done works great. thinking of going 106 or 107 but don't want the problems with hard starting and expense. can i run low comp. pistons to help solve this problem and still get good performance. thanks.

 

You can run upwards of 10.5:1 with a proper tune, but with the fuel quality you are getting today, the engines are very tune dependent. Last couple of engines I have built have been in the 10:1 range and although not making quite the power of a higher compression engine, they perform well. It is all in what you want, and how and where you ride.

 

Yesterday I tuned a 103 we built. 10.1 compression (flat top pistons) and it made 115 HP and 115 TRQ. Higher compression builds are great, but with the crappy fuel we have now and worse fuel coming, it'll be very difficult to get rid of spark knock.

 

Don't try to design your build around a compression ratio value, choose your cam first based on your intended use, and then design your build around it and set your compression to what ever the cam needs.

 

GMR Performance has built many 107 at 9.8 static with great results using the Andrews 54 cams. Start easy with nice flat Tq lines that are very stout IMO.