I am going to be rebuilding the engine in my 2005 Civic VTEC within a few months, as it is not healthy. I really would like to install high compression D17A7 pistons while it is apart and would greatly appreciate whatever information anyone can give me about high compression pistons. If you do not know the answers to some of these questions, that is fine. Just answer the ones you can and I will appreciate that. Thank you very much to anyone who contributes information. Here are my questions:

1. What exactly are the benefits of high compression pistons? Better fuel efficiency and more power?
2. How many HP, torque and MPG could I gain by upgrading from 9.9:1 to 12.5:1 pistons on an engine with all the basic bolt ons? Could I feel it?
3.What would happen if I install high compression pistons and use 93 octane fuel without tuning? Would I still gain power or would my engine explode?
4. Where would the power improvement be in the RPM range, or would it be through the whole RPM range?

 

Waste of money to only upgrade pistons. It will give u slight top end. 12.5 is high compression for 93 pump gas, expect knock. Id go E85. You have to have it tuned to be run safe and reliable and at that time you can see where the power is made on the dyno graph.

 

The D17Ax is NOT a performance engine and you would have to spend thousands to get much usable gain. If you really want more power, swap in a K20/K24. If you do go K, you might also find that the suspension is now inadequate for the higher speeds. Just a thought.