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Re: to much free-flow bad?!?



In a message dated 11/19/1999 11:57:36 AM Pacific Standard Time, 
scirocc09@yahoo.com writes:

> Back to my friend. When i keep reminding him that i have no mufflers,
>  he tells me that im gonna burn out my valves. something about needing
>  backpressure and the heat builds up causing valve failure. ive been
>  thinking about it and wondering how could leaving hot gas around make
>  things any cooler. then it hurt and i decided to ask the list. anyone
>  got any answers?

Free flow is not bad if your engine is designed and tuned for it.  Take a 
look 1/4 mile funny cars and dragsters.  These cars are basically made to run 
at WOT.  And their exhaust are very free-flow.

For our cars, too much free flow IS bad.  I believe TT has tests showing 
that.  Some backpressure is needed to help scavenge the exhaust gases at the 
low and midrange.  This in turn helps with torque.  It's always a tradeoff of 
low end vs. high end power.

The myth about burned valves on a freeflow system I think came from when 
people tried to run there engines without any exhaust manifold or very short 
pipes. When the engine was shutdown, the exhaust valves are exposed to 
ambient air and therefore were chilled compared to the hot exhaust gases.  
This chilling caused the valves to warp and over time caused poor seating.  
Well you know what happens when valves are adjusted too tight or the valve 
head is warped...  exhaust gases leak by and you get burnt valves.

This may have been an urban legend that's been past down through the years, I 
don't know, but it makes sense to me.

-Dick-
78 Scirocco
Original Owner
<A HREF="http://member.aol.com/sailingfc/">http://member.aol.com/sailingfc/</A
>

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