# Static Vs Dynamic Compression, What's the Difference? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [January 31, 2017, 4:06am UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267 "2017-01-31T04:06:58Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [January 31, 2017, 4:06am UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267/1 "2017-01-31T04:06:59Z")
I’ve heard those terms but don’t understand the difference between the two. This terminology tends to come up in discussions about cam profiles. So what does it all mean? ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [January 31, 2017, 5:16am UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267/2 "2017-01-31T05:16:48Z")
This can probably explain it better than I can. Note the first paragraph. Dynamic starts getting complicated and variable; and especially if you’re not familiar with cam overlap, cam timing, and so on… [http://www.enginebasics.com/Advanced%20Engine%20Tuning/Static%20vs%20Dynamic.html](http://www.enginebasics.com/Advanced%20Engine%20Tuning/Static%20vs%20Dynamic.html) Dynamic doesn’t really come into play for DIYers and mechanics in the field. That’s mostly something for automotive engineers and performance engine builders to be involved with. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [January 31, 2017, 5:59am UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267/3 "2017-01-31T05:59:43Z")
I’m not sure I agree that dynamic compression test does NOT come into play for “mechanics in the field” Granted, it isn’t a test that is performed very often, but occasionally it does come in handy ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [January 31, 2017, 12:17pm UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267/4 "2017-01-31T12:17:23Z")
That link is a pretty good description of the concept. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 31, 2017, 3:30pm UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267/5 "2017-01-31T15:30:33Z")
Excellent link, my friend. It explains the concept better than I ever could! 😝 Thank you. ---
**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\ **Post date:** [February 1, 2017, 12:26am UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267/6 "2017-02-01T00:26:14Z")
When the intake valve closes later, not only is the dynamic compression reduced, you could also say the dynamic displacement is reduced, since only the cylinder volume above the intake valve closing point counts as displacement. The so-called Atkinson cycle engines used in the Toyota Prius uses intake cam timing to control power output, effectively making it a variable displacement engine. Need more power? Increase the displacement of the engine by closing the intake valve sooner, need less power? reduce the displacement of the engine by closing the intake valves later. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 1, 2017, 2:33am UTC](https://community.cartalk.com/t/static-vs-dynamic-compression-whats-the-difference/99267/7 "2017-02-01T02:33:12Z")
Thanks, excellent link provided by OK and informative discussion by the other posters. I understand conceptually at least the difference between static & dynamic compression now.