[Supras] Head Gasket Choice For N/A

[Christian, Skip]

Jim,

	I have adjustable sprockets.  Alfa Romeo used the same engine w/
same cams from 1972 until 1995. All Alfa cam specs are common knowledge
(no silly secrets).  As emissions rules got tighter, '72-'74 cars had
intake cam retarded 14 degrees, then from '75-'77 the exhaust was
advanced 14 degrees.  Cat was added in '78 and cam timing was restored
to pre-emissions settings.  However, exhaust restriction kept power
down.  In the Alfas, when overlap was reduced, bottom end power went
down.  Longer durations disappeared in 1969 - possible as a result of
the mechanical fuel injection.
	So, for the Supra, I started by advancing the intake cam 2
degrees and retarding the exhaust 2 degrees.  Drove & check power &
response.   Bottom line is if cams are set at intake advanced 4 degrees
and exhaust retarded 4 degrees whole power band is improved.  Since my
car is an automatic, I set all eight in the intake to produce the best
bottom end power.  Only problem is power now runs out at around 5200 RPM
and the blasted automatic cannot be re-programmed to shift when I want
it to under full throttle :-)  Anyway, (when the car was running) if the
throttle is punched (about 1/4 throttle) at 2000-2500  RPM, the nose
comes up.  Just what an N/A automatic needed.  FYI - I tried 6 retarded
for the exhaust and 2 advanced for the intake and the engine power was
still increasing when it hit the 6500 RPM redline.  The magic number
seems to be eight degrees (if the valve clearances are within spec).  If
I went higher than eight, power dropped off due to a flow restriction.
For all this, car had no CAT, HKS sport exhaust, K&N open filter, and 3"
intake pipe (in place of the plastic noise canceller).
	Car always got 20-22 MPG before adjustments.  After, its 20-21.
Not much change.  Also, easily passed emissions (with CAT installed :-)
	If you but the adjustable sprockets, try to find the ones with
the degree markings (if the government still allows them).  Finally, if
I remember correctly, each tooth slot on the cam sprockets corresponds
to eight cam degrees (but please check this first).  All the above is in
CAM degrees.
	I tried to keep this short, but, sorry, I'm an engineer.......

Have Fun, Skip


-----Original Message-----
From: Jim Wooden [mailto:Jim at WoodenU.com] 
Sent: Friday, March 02, 2007 10:52
To: Supras at supras.com; Christian, Skip
Subject: Re: [Supras] Head Gasket Choice For N/A

Skip:

If you have a second, tell me about that increased overlap on the cam?
;-)
Did you use custom gears on the cams or move the dowel pins?

I have MkIII 86.5 NA and am due for a new timing belt soon....

Along with the increase in performance, did you notice any dramatic
decline in gas mileage?

Thanks,
Jim
Original owner 86.5 MkIII NA




>Bob,
>
>         Thanks. I've done the head gasket once already.  Stuck on a 
>stock gasket, torqued to 54/58 (?) ft-lbs (from TSRM).  Lasted two 
>weeks & I started hearing the tell tale bubbles in the heater.  I 
>figured the engine was trash, so I got out the torque wrench and 
>torqued all of them to 85 ft-lbs.  FYI - Block deck is trashed from 
>acid damage.  After the
>85 ft-lbs, as long as the car was COMPLETELY warmed up before touching 
>the accelerator pedal, the car used NO coolant no matter how hard it 
>was driven.  But, touch the gas before and gurgling from the heater.  
>Gasket would seal with head expansion at 85 ft-lbs !
>         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 :-)
>
>Thanks, Skip
>
>P.S.  Wonder if those 85 ft-lbs stock bolts are going to come off.  My
>'88 had one of the Allen heads crack...