Volumetric efficiency of VW heads

[Crawdad]

As anyone determined the VE of various typical performance heads, say for a given valve size and port volume? Or at least a ballpark number? I ask because it is a number that is called for in the calculations for sizing a turbo.

Is there a simple way to measure it on a flow bench? If not, one of you turbo gurus with deep experience might be able to work backwards from some known combination that has a given torque curve on the dyno chart, compare that to the compressor map for that turbo, and reverse-engineer the equations to arrive at the VE of the heads. Sorry, that sounds like a homework assignment. But it would be nice to know.

[miniman82]

Who cares about numbers, when it's all said and done the academics matter not so long as you get the result you're after. There's enough experience out there now for people to be able to tell if a given turbo will work or not, why not ask that question?

[Crawdad]

Fair enough. I'd never proceed on a build without first consulting you, and Shag, and Chip, and Stripped, and John C., but wanted to first get a handle on the fundamentals. Equations help me see the underlying logic of what I am trying to accomplish, and that is part of the pleasure.

Questions about particular turbos engine recipes to follow shortly.

[miniman82]

Like Keanu said in that movie Consrantine: "it's not always like it is in the books".

In other words theory is nice and all, but when you get down to it results are what matters. Useful as a guide sure, but frequently people find they are able to use different parts then they would expect and get similar results. More than one way to skin a cat, as they say.

[Kalle]

Interesting thread!

Yes, you will find knowledge and luckily you will also find people willing to share valuable info. And of course you also have the www where you can find both useless and useful information. Nevertheless, it is actually really interesting to "build" a engine on the paper/PC before you go ahead and buy expensive parts. I have used Engine Analyzer on most of my engines and I get a real kick when the theory and actual results matches. With EA you can easily see the effect of changing your cam, CR, intake length, exhaust, boost etc.

For example, below is a print out from EA of my 1641ccm engine as a NA engine with my current JPM vs a ordinary Engle TCS20;



And below you can see the EA curves of what will happen if I decide to increase the size to 1835ccm and do a little head work:



140hp NA at approx 6000 rpms. Add 1 bar/15psi of boost and I should have 280hp. 15 more psi and I should have 420hp.

Best rgs
-K-