[Supras] Head Gasket Choice For N/A

[Christian, Skip]

Jim,
	I really hope you're right because I do not want to remove the
head !!!!!  The issue is - does "non-interference" mean that I can
disconnect the cam belt, turn the cam so the #1 intake valve is
completely open, crank the engine, and have no damage.  This is what
went through my mind right after it happened.  I will pull the plugs &
check for possible liquid in the cylinders.
	Here's one for you guys - how much crank resistance would a bent
valve cause ?  Could I turn through it with a breaker bar & socket after
the engine had been cranked ?
	Agree with you on degreeing for turbo cars.  The benefit is not
worth the dyno cost, unless you have dyno time remaining from testing
something else & have the sprockets installed.  But, for N/A cars, it
seems to be a well kept secret along with the factory cam timing specs
:-)

Skip

P.S.  Anyone in Washington DC area want a '88 N/A automatic parts car
with an almost perfect body and a perfect interior ??  White, blue
cloth, targa, TEMS, LSD.

-----Original Message-----
From: Jim Jobe [mailto:jjobe2 at supratech.org] 
Sent: Friday, March 02, 2007 12:16
To: Christian, Skip
Cc: supraman88; supras at supras.com
Subject: Re: [Supras] Head Gasket Choice For N/A


The term non-interference suggests that at peak lift and TDC the pistons
and valves do not intersect.  So if the belt breaks and there are valves
open at peak lift, the pistons will not hit them at any point.  Thus cam
timing is irrelevant.

Seems to me the stock valve springs coil bind fairly quickly too, so I'm
not sure that floating the valves fully open would cause them to hit.

Not many have degreed the cams.  My local group has and we experiment
with valve timing quite a bit on our big turbo cars.
However the rest of the group tends not to worry about it because most
of the cars in this group are turbocharged and there are far easier and
simpler ways for the average owner to increase hp than learning how to
properly degree cams.

On Fri, Mar 02, 2007 at 11:50:52AM -0500, 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