Quote:
Originally Posted by ANTI_LAG
While variable cam angle helps with spool, the reason why a higher CR motor will usually spool a turbo up quicker is simple. Most cases a higher cr motor will make more power na. More power= better spool up. We have ran motors all kinds of ways, on our Honda stuff we usually don't go lower than 11:1, this allows us to run a much bigger turbo to keep it spooling quickly. We have also ran 12:1 many times, this is where we run a class limited 72mm running around 44-47psi, helps to get us in the power band. Now take this for thought, go take a low cr boxer and see if you can put the large turbos we are running on these FRS and see if they spool the same, I'll tell you right now they won't. And I saw in a earlier post someone mentioned about the 2JZs couldn't make the power they do if they had high cr, most the big boys are not running that low of cr. I might add though camshaft plays an important role in this, we always run all motor camshafts in our turbo setups, no "turbo specific" camshafts. This might not work for everyone but has worked for us.
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Cams and pressures! NA cams work amazingly well when the operating pressures of the engine are similar to NA environments. Get intake pressures and exhaust pressures to be similar to how an NA engine operates and you can get great scavenging and improve VE over 100% to a pretty large extent!
High compression also works well when VE is low. They intentionally lower VE on the Prius engine and run 13.5:1 compression for better mileage. The lower VE prevents detonation, even though 13.5:1 is way high for pump 85 octane.
This is a very deep subject and there are a lot of variables at play! But it is one of the things that fascinates me most about engines!