Intake manifold angle

[afret]

Felpro makes angles gauges to check the angles of the heads on the block and the angles of the intake manifold faces that sit on heads for chebbies (no surprise).  I read somewhere that these gauges have a built in bias so the bottom part of the intake gasket would get .005 more crush than the top rather than to have the mating surfaces perfectly parallel from top to bottom.    Does that sound reasonable since it seems like intake gasket leaks are more common near the bottom of the gasket?

[jayb]

Sounds reasonable in theory, but the FE block and head measurements I've seen don't show any bias like that.  Block decks are exactly 45 degrees off horizontal, and the intake surface is 90 degrees to the deck of the head.  This is based on how they are machined at my local shop, R&R Performance.  I won't be putting any kind of a bias like that into my intake adapter...

[afret]

Yeah, I guess parallel mating surfaces should be the best seal.

[ScotiaFE]

Interesting subject though.
When I had the 428 running with the RPM intake and Felpro print o seal gasket the gasket failed at the bottom of the intake port.
It was like it was over crushed. But the top was still in good shape.
If anything I think a small taper to the top would have solved the problem. Meaning the bottom being wider than the top so as put put less crush
on the bottom of the gasket.
I put a tougher gasket in and it ran for a few more years without a gasket issue.

On a side note, over on the other side you had commented you might toss them Hookers in the trash.
One mans trash is another mans Hookers or headers if you must.
Just in case.

[lovehamr]

It seems like the print-o-fails are designed to do things just like that.  It's just that water normally gets in on the act as well. 

[afret]

Talked to the tech guy at BHJ that also makes intake angle checkers.  He confirmed that their gauge is also designed to have a bit more crush on the lower part of the gasket than the upper.  Makes you wonder.........

[jayb]

That is interesting, since BHJ is one of the standards.  I have one of those upright rotary table setups on my CNC machine now, and it is supposedly accurate to 0.001 degrees.  I'm also working on a "trunnion table" that bolts to the rotary table face.  I plan to mount the FE intake adapters on the trunnion table, and then rotate them around like they are on a spit for machining all the different angles.  I'll bet that if I took an Edelbrock Performer RPM and put it on there, I could measure the manifold to see if it is really 90 degrees or not between the intake faces.  I think I'll give that a try when I get the trunnion table finished...

[ScotiaFE]

Hmmm.
I have a NIB RPM and a very accurate protractor.
I must dig them out and have a look see.

[afret]

Got one of those digital protractors with a 0.1* accuracy.  My victor measures 134.9* measuring the angle made by the bottom that seals against the block china wall and the face that seals against the intake gasket.  That would give the angle of the intake face a 45.1* angle from the horizontal.  That would make it about .005 tighter toward the lower part of the intake gasket, I think.

[ScotiaFE]

So I got around to digging out some stuff to have a look at this.
I also had a look through the FE drawings I have captured on the spider web.
The intake drawing I have says the angle is 44* 55' to 45* 7'
The RPM measured 44* 50'
The TW measured 44* 35'.
If I was going to cut a surface I would be shooting for 45*.
I guess the moral of this story is if your close to 45* and you use a good gasket with a bit of goo on it you should be good.

[jer427]

Something else to keep in mind also. I have seen the front and rear cork end gaskets prevent the sides from sealing properly if you have too much crush. Better to have no crush at all and a little silicone. Rather than machine the bottom of the intake, I would throw those end gaskets away and just use silicone. 90 degree surfaces should work fine. Proper intake manifold fit is one of the hardest things to get accomplished on an FE.

[jayb]

Something else to keep in mind also. I have seen the front and rear cork end gaskets prevent the sides from sealing properly if you have too much crush. Better to have no crush at all and a little silicone. Rather than machine the bottom of the intake, I would throw those end gaskets away and just use silicone. 90 degree surfaces should work fine. Proper intake manifold fit is one of the hardest things to get accomplished on an FE.

I encountered that very problem with my brother's 428, and gave a brief description of the issue in my book, in the Dyno Mules chapter.  I've been using silicone only on the end rails for many years, and that is one of the reasons why...