This is my first build what are the pros and cons of going with a lower compression piston I really wanna get this thing put together but I wanna make sure I’m using the right parts
higher compression = better thermal efficiency
lower compression = better knock protecting and more timing.
A lot of turbocharged engines are knock limited on pump gas, which means as you advance ignition timing, you get knock before you hit MBT. That's one reason why e85 (or E30-E50 in our case) can make so much more power on a turbocharged engine, you can hit MBT or get very close to it on an engine that's normally limited by knock.
Low static compression lowers peak cylinder pressure, so it lets you get closer to MBT at high boost. You can run high compression, high boost on pump gas, you'll just be so knock-limited that you won't be able to run much timing, thus low power and poor efficiency. Timing is what makes so much more power. Most OTS tunes may add a bit more boost, but real kick comes from running more aggressive timing. The ticket these days is running a high compression turbo engine with e85 only, so you get quick spool and can still run aggressive timing. We find a lot of customer getting bent up on having low/moderate boost but higher timing, which other tuners are pushing crazy boost but low timing. Having a good balance leads to better fuel economy and power when you need it. Variable Cam Timing helps, but you can't overcome your
High compression, low boost is all about response and low rpm manners. This lets oems make a 4 cylinder with the torque curve near a 6's. Modern knock control has made this possible.
Back in the day, knock control was more of a damage control thing. If your knock algorithm kicked in, your engine was already getting f-ed, the algorithm just stopped the f-ing. Now, the systems are so responsive that timing can be adjusted on the fly to maximize power without risk to the engine. That's why many engines have a different power rating for different fuel grades.
DSport Magazine actually had a pretty good article on this about 7 years ago that is a good source of information when trying to decide whether to go high compression with less boost versus lower compression with more boost.
Come find the answers to high boost or a high compression ratios for street and race engines. We break it all down right here at DSPORT Garage.
dsportmag.com
This is also a good calculator for determining your effective CR based on your static CR and boost/elevation inputs.
If you really want a good read, you can get into how Variable Valve Timing can further affect the Effective Compression Ratio of the Ecoboost Engine here:
While the Ecoboost engine still uses a standard Otto cycle combustion system, its VCT capabilities can allow it to also operate very similarly to the Atkinson model, which helps greatly to both make power and retain fuel economy.
