How Important Is Dynamic Compression?

At LS Performance Racing we take great pride in providing you with the best setup possible for your vehicle's needs. When doing this several variables are taken into consideration especially when doing a camshaft swap, one of the main variables is your Static Compression Ratio and Dynamic Compression Ratio or better known as SCR and DCR. Most people don't understand how important this can be to improve the vehicle's 60 ft times, increasing low-end tq, and achieving better driveability even when using a big camshaft, this can help make more HP and TQ all across your camshaft power band.

By doing an aftermarket camshaft swap you can make a lot more HP and TQ but depending on your engine's SCR you might need to increase it to compensate for the loss in your DCR to get the best performance out of your engine's new setup. But what is DCR, and why is it so important? DCR is your Cylinder Compression Ratio after the camshaft has been taken into consideration. With a higher DCR, there is more force pushing the piston down on each firing stroke there for making more HP and TQ over the entire power band, increasing the driveability, and even fuel economy in some applications.

Engines running on 87 to 93 octane will perform great with a DCR of 8.00:1 to 8.50:1. Increasing your SCR after a camshaft swap can be very helpful due to the new longer closing point of the intake. For this example, let's use a stock LQ9 10.10:1 SCR 6.0L engine with the stock camshaft that has an intake closing point of 34.5° ABDC, which means when we do the math, the DCR will be 8.16:1, not bad at all on a pump gas street engine, but let's pick out a camshaft that will work great with any stock cathedral port cylinder head. The LSPR reverse split 230/224 camshaft has been one of the most commonly recommended and used camshaft for any street/strip car/truck application using factory cathedral port cylinder heads and will be the camshaft we use for this example. By giving it a closing point of 46° ABDC the DCR will drop to 7.51:1 which will hurt the low-end tq and driveability but there are several different ways to increase your DCR, 1st by milling the cylinder heads this will decrease the Combustion chamber volume and increase the DCR, 2nd by swapping out the factory 317 cylinder heads with a set that has a smaller combustion chamber like 243/799, this will increase the DCR. By swapping to the 243/799 cylinder heads we can raise the SCR to up 10.93:1 as seen In the picture below.

With the new 10.93:1 SCR the DCR is now 8.13:1 due to the smaller 64.5cc combustion chamber and given the fact that the only difference between these two factory cylinder heads is the combustion chamber size there should be no loss of power only power gained, which will almost raise the DCR back to the factory specs and will make the engine more responsive down low by giving it more TQ and increasing driveability. This is even more important in an engine that is equipped with a big camshaft that has a great deal of overlap. A higher DCR like 8.50:1 to 9.00:1 depending on the camshaft size and overlap will help to make up for some of the poor driveability and TQ loss down low and will help you to get the full performance out of the camshaft