[Supras] Head Gasket Choice For N/A

[Christian, Skip]

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


-----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 :-)
>
>