[Supras] Head Gasket Choice For N/A

[Christian, Skip]

Jim,
 
    Sorry for the late response.  My POS CC internet at home doesn't
work so I only have E-Mail at work.
    Increasing the amount of charge in the cylinders.  As the piston
comes up on the exhaust stroke and the exhaust valve begins to close,
the next part of the four cycle engine is the intake valve opening.  I
set my intake cam advanced, thereby opening the intake valve sooner.
So, its beginning to open before the exhaust valve closes.  The exhaust
traveling down the manifold/pipe, sucks in more intake charge than would
have happened if the intake valve had opened after the exhaust valve was
completely closed.
    In order for this to produce more power, there has to be minimal
restriction in the head, and intake & exhaust manifolds.
    The factory Alfa cam sprockets are infinitely adjustable (up to
1979).  Don't know about 1980 & on intake as it had variable valve
timing.

Skip 
 
________________________________

From: Supraman [mailto:supraman88 at verizon.net] 
Sent: Sunday, March 04, 2007 18:06
To: Christian, Skip
Cc: supras at supras.com
Subject: Re: [Supras] Head Gasket Choice For N/A


Christian, Skip wrote: 

	Jim,
	
		When the lobe centers are decreased, either by design or
by
	adjustable sprockets, the minimum piston to valve distance is
reduced.
	This combined with my tight clearances is what, I think, caused
my
	problem.
		Lobe center is the halfway point between valve opening
and
	closing.  I have not been able to find anyone, and site, or any
book
	that lists the cam timing specs for the 7M Supras.  No one seems
to want
	to understand these days......  For the Alfa, optimum lobe
center for
	street (broadest power curve) was about 102 degrees for both
intake and
	exhaust valves.  When the intake was retarded 12 degrees in '72
(sorry,
	I was wrong before - it was 12 degrees, not 14), this changed
the lobe
	center from 102 to 114.  When the exhaust was retarded, the new
exhaust
	lobe center became 114 degrees.  Less overlap, less chance of
unburnt
	gas in the exhaust.  Alfa went to variable valve timing in 1980.
On my
	'73, I re-set the intake to 102 and, on a 2 lane highway, no
longer had
	to downshift to fourth to pass :-)
		The cam setting for best peak HP (in the Alfa) is 108
degrees,
	but the gain in top end comes with a big loss in low RPM power.
About
	108 is the narrowest new car can do and still pass emissions
without a
	big exhaust restriction.  That is why new cars (without variable
valve
	timing) all seem to have good power but no bottom end.
Manufacturer's
	have figured out (FINALLY) that with the cams set for best peak
HP, the
	exhaust flow restriction can be reduced & still pass emissions.
		I use the Alfa because it is a true hemi and similar to
the 7M.
	
	Sorry For The Rambling,  Skip
	  


Not at all! I understood...er, MOST of it. I'm not really a Gearhead, so
you kinda lost me a bit, but I can somewhat follow the logic behind it.
>From what I get, I guess you're increasing the burn time (from the time
the Intake valve closes to the time the Exhaust valve open) and burning
more of the fuel getting into the engine. Interesting. And, you used
stock Alfa sprockets? 





	
	-----Original Message-----
	From: supraman88 [mailto:supraman88 at verizon.net] 
	Sent: Friday, March 02, 2007 10:59
	To: Christian, Skip; supras at supras.com
	Subject: Re: [Supras] Head Gasket Choice For N/A
	
	Ooops...missed this part. Thought it was awful hard to damage
the valves
	on one of these engines. Yes, please tell us more!
	
	
	Christian, Skip wrote:
	  

			Unfortunately, I used a "Gates" timing
belt....... Because I was
		    

	in a 
	  

		hurry...  It shredded itself at 82K miles and I ended up
with bent 
		valves.  Intakes were set at .0004 because dealer had no
shims and cam
		    

	
	  

		timing was changed to increase overlap (big power
difference - more 
		than all the aftermarket parts combined & still passed
emissions).
			So, here I am.  Planning to buy a "rebuilt head"
& install.
		Maybe, I just don't learn :-)