Manifold Crack - Need New S2MS Intake

[pbf777]

Torque wrench? OK. What are the recommended values for the aluminum manifold vs. iron?

     The use of a torque wrench does not dictate a torque value, just aids in executing and the consistency fastener to fastener of the torque value chosen!     

     Scott.

[S7MS427]

Doug,

OK, point taken.  However, the proper use of a torque wrench will allow for the equal application of clamping force on all the intake bolts.  If done in small increments, any warping of the manifold will be non-existent or minimal and allow the manifold and heads to seal optimally (isn't that what we are looking for?).  I don't think you can apply a consistent 15-20 ft-lb with a 6 inch box wrench unless you have a calibrated wrist.  Looking at my copy of "Road Racing the Ford 289 High Performance Engine", "Special Components & Specifications, Group 2 Sedan & GT 40", the recommended torque is 12-15 ft-lb (read aluminum intake here).  So, that's a bit lower than your 15-20.  The cast iron manifold recommended torque is something like 23-25 ft-lb.  If the torque wrench is set properly and used properly, the installer risks very little.  Of course if you whale away on the intake bolts, you're going to break something for sure, especially at the corners which are essentially unsupported.

People disregarding the differences in material strength is why we see lots of helicoils in aluminum parts.  They treat those parts as if they were cast iron, crank on the fasteners "just to make sure they are tight" and end up stripping out the threads.  The lesson here is be careful and know what you are doing before you do it, get help if you need it.

[S7MS427]

Torque wrench? OK. What are the recommended values for the aluminum manifold vs. iron?

     The use of a torque wrench does not dictate a torque value, just aids in executing and the consistency fastener to fastener of the torque value chosen!     

     Scott.

+1

[s2ms]

What are the recommended values for the aluminum manifold vs. iron?

Published intake manifold torque limits:

Cobra aluminum intake: 14-16 ft-lb according to the 66 GT350 Owner's Manual, I assume 65 GT350 manual is the same.
Stock cast iron intake: 20-22 ft-lb, according to the 66 Shop Manual.

For the Cobra intake I've always followed the recommended limits on the inner bolts but only use 12-13 ft-lb on the LF, RF, and LR bolts, and 8 ft-lb on the RR bolt since it seems to be the most problematic

[Greg]

Just as equally important is the torque limit is the sequence, make sure you follow it and you will be okay.

[greekz]

Back to my original post, I checked another 66 manifold today and it has the same "crack" pattern as mine.  I now believe this is a casting flaw as others have stated.  Still going to check with liquid, and if no leaks, install.

Thanks again for all the input to my original question.

Greek