Re: Claims vs. Claims - getting them straight

[DeWitt Harrison <de@aztek-eng.com>]

On Tue, 28 Oct 1997 14:11:17 -0700, Bruce Bell wrote:

>I think that 1.5 CFM to HP rule of thumb has some factor
>for VE already built in. If not, then the max. hp for a
>1781 cc 4cyl VW would be around 115 hp @ 5500 rpm.
>Tectonics has built too many of these with more power.  
>
>Also, I don't think VE is a constant for a given motor.
>i.e. I expect it goes down as boost pressure goes up
>because of the increasing back pressure. 

Of course you are right about VE being a variable. Otherwise
all the stuff builders do to tune intake and exhaust plumbing,
timing, etc., would be wasted. Your back pressure example is
a good one too. Without a dyno or a good engine simulation
software, we have to be content with a best guess for VE
at the operating point of interest. In our discussions, the
operating point of interest always seems to be WOT +
full boost + max rpm.  (If we could get Dave to work
backwards from stock MC specs to stock VE, we might
then at least have a good starting point for VE.)

It is probably beyond the scope of the figuring that has
been posted here so far to characterize the behavior or feel
of the motor across the rpm band let alone to consider part
throttle responses. At a minimum, in addition to a variable
VE, it would necessary to plot various paths through the turbo
map. But we need not let that stop us from improving our
basic understanding of what engine parameters need to be
improved to get more seat-of-the-pants satisfaction. Trading
numbers is one way to do that.

DeWitt Harrison    de@aztek-eng.com
Boulder, CO
88 5kcstq