Cam questions on turbo and N/A

[JShadzi at aol.com]

Ya, but overlap in a turbo car is not that bad, expecially wrt high RPM 
power.  Remember, it is gas flowing through the turbine that makes power, 
whether it comes from combustion or from the intake charge.  A little overlap 
means that some of the boost goes through the comb. chamber and, you guessed 
it, right back through the exh. turbine which turns the intake impeller, and 
more pressure results.  Granted, this can soften low RPM response, but the 
increased flow will ultimately result in spinning the exh. turbine, a good 
thing at higher RPM.  

The TA cars had some major lift AND overlap, sure, they were race cars, but 
they also made about 600hp, and you can't do that on a low overlap cam like 
the stock cars use.  

It is kind of a misnomer that turbo cars should not have overlap, on a 
supercharged car, however, low overlap is more necessary becuase exh. energy 
is just going out the exh, not back through the device doubling the hp of the 
car like in a turbo application.  I had a lengthy conversation with the owner 
of Magnuson Superchargers(the importer of all Eaton Superchargers in the US) 
recently about the difference in cam design in turbo vs supercharged 
applications, he agreed that a little overlap in higer output turbo cars was 
a good thing.

Javad
80tq.com

In a message dated 10/1/2001 10:33:15 PM Pacific Daylight Time, 
audi at mediaone.net writes:

<< Um, where the heck did you hear that?  It sure *sounds* loony!  As you
 say, overlap issues going that way could be serious. >>