To shim or not to shim; that is the question....

[sheetwright]

Shimmed mine right off the bat. Only way to go if you want to run 91 octane safe or a touch of torco. I was running 11.5 lbs safely from ulmer. Then he changed timing, and added the ignition module to bump it up to 13.5lbs. Still ran thousands of miles with no flaws. If I found 87 octane I just added torco, and off I went. 248 hp on the dyno with over 2200 trouble free miles with Allen's setup.

 

[snoprof6]

Coming from a newbie, i would say the head shim has the vote. Sorry to rob the thread but what are pros/cons of each option? Or can someone explain why they like one over the other. Have a 2011 apex out back that is taunting me with a 290 kit

 

[sheetwright]

If I recall the 290 mcx kit is a shimmed kit. The whole idea is to lower compression to allow lower grade gas, decrease the option of detonation, and allow you to increase boost. Can be done with pistons or shims. Shims are a less expensive option over pistons. Call ulmer. He is an ace from,what I hear withy the 290mcx kit

 

[Riceburner]

Coming from a newbie, i would say the head shim has the vote. Sorry to rob the thread but what are pros/cons of each option? Or can someone explain why they like one over the other. Have a 2011 apex out back that is taunting me with a 290 kit

If you want to make big power with the 290 kit, go with the low compresssion pistons.
The pistons in the 2011's & up are lighter than those on the older Ape's & prone to cracking according to Robbie if you are wicked up to 19 lbs ish which can easily be done at Sea Level or close to it.

If you want to run the MCX 290 stock at 14 ish psi you are fine with the shim in my experience.
I have no personal experience running one vs the other but collective wisdom says the low comp pistons engines have a little less lag.

Head shim a lot less money in parts and labour time. It works just fine IMHO.