From: Lehanover@aol.com
Message-ID: <10e.26030873.2c97ed41@aol.com>
Date: Tue, 16 Sep 2003 00:36:17 EDT
Subject: Re: [FlyRotary] Re: Good news, Bad news
To: flyrotary@lancaironline.net
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit

In a message dated 9/15/2003 9:34:53 AM Eastern Daylight Time, 
13brv3@bellsouth.net writes:

>  I'm starting to believe that I could just retard the timing
>  a few degrees, and make sure I'm slightly on the rich side with fuel, and
>  let-er rip to 6-7 psi.  Maybe I'm making too much of this 2-3 psi that 
Bruce
>  suggested as a maximum.  Gotta think about this some more.
>  
    As I said before I no not about turbos. I have been up to my eyes in 
Mazdas all day, as this is the first day of the SCCA national championship race 
week. The fastest Mazda is 8th on the grid so far. We get three more qualifying 
sessions before the race. My car was 20th of 29 cars today. The Toyotas have 
more power and are lighter. I got to talk to Daryl Drummond the Mazda engine 
builder for a while. Got the word on sagging oil pressure. I feel much better. 

Some observations about turbo engines. The intake and exhaust manifolds are 
not works of art. Nothing you could get away with on a NA engine. So some value 
of boost (intake manifold above ambient in pounds) is used just to get back 
to what you would have had from the same size NA engine. Turbo engines have 
lower compression rotors than NA engines. So here again, some of the boost is 
used to make up for the lost compression. So, before the boost comes in, the 
turbo engine is a dog. 

Here is why they work.

When we raced a Fiat, I angle cut the heads until I was touching both valve 
seats with the cutter. Then I relieved the head so that the pistons just 
cleared with the head gasket missing. So, we would have about 245 pounds of 
compression while 
 cranking. Now nobody should run that much compression and expect to make one 
lap. But it runs just fine, because static or calculated compression ratio 
doesn't mean squat. One dare not load the engine at low speed at all. Once 
moving, you don't dare lug the engine below say 6,000 RPM. So it is a pain to move 
the car to the false grid, and to get it going for the parade lap. But once up 
to speed and the revs kept in the power band, there is music. So the 15:1 
compression must run no advance at all right? No, 35 degrees all the time. Crank 
triggered for accuracy. A similar pickup in the distributor with the advance 
weight range widened to go from 5 degrees at idle to 35 degrees wide open. 

The answer is that the effective compression goes down as revs increase, 
because cylinder filling time is reduced per cycle. So at speed we don't have 16:1 
we have maybe 10:1 depending on how much inlet tract restriction the rules 
stipulate. So what is the effective compression ratio of my competition with the 
same engine but who installs 10:1 pistons?  Maybe 8:1? 

So to start with, the turbo starts with lower compression so that you can 
turn the screw in and make boost without hurting the engine. Then you turn the 
screw in some more to make up for the intake with no tuned lengths. Then you 
turn the screw in some more to make up for the dreadful restrictive exhaust 
header and turbine. Then you turn the screw in some more because this pig is 
supposed to be stronger than the NA engine. Then you turn the screw in just a bit 
more to account for the extra 47 pounds the turbo adds to the plane. So how much 
boost is that exactly? 
I have no Idea. A guess might be 8 to 10 pounds. I would watch the EGT and 
keep it rich enough to always be 100 degrees rich of peak EGT. Add a knock 
sensor. I would split the timing and add a retard system for the highest boost. I 
would over cool the oil. I would buy the ceramic seals for boost over 10 
pounds. I would hire a turbo expert before I melted something expensive. 

So the answer is cylinder filling at high cyclic rates. The cylinder filling 
of a well done NA engine at sea level can be replicated at any RPM and any 
altitude with the turbo. 

Lynn E. Hanover