Milling your intake manifold for short deck motors

[FreddieWilliams]

How does one determine the exact amount to shave off the intake manifold?

Is it a 1 to 1 ratio???????

For example:
If your deck has been cut by 0.040" then one should remove 0.040" from each side of the manifold to mantain propery bolt and port alignment.

Or put another way, shaving 0.040" off of each side will allow the manifold to drop 0.040" into the valley pocket?

I have no idea how much my deck has been cut but it has. Without any intake gasket in place, my bolt and port alignment are way off.

I have heard 0.030" to 0.060" needs to be shaved off.
Just how does one determine the proper amount?

TIA

 

[KendallF]

If the head/manifold face is at 45 degrees to vertical, the manifold should drop down 1.4 x whatever you mill from each face (equilateral triangle, square root of 2). It should move "down" the mating face of the head approximately the same distance as the amount you remove. So if the bolt holes and ports look like they're .020" off, try .020" first and see (remember to measure with intake gaskets in place).

Good luck and remember, it's a lot easier to take more off than to put some back on! (Not that I have ever done that )

 

[FreddieWilliams]

Kendall,

The deck on the block has been cut quit a bit apparently.

I figured I need to move the intake bolt hole down about .070".
This is with stock valley pan intake gasket too. More if I plan to use a thicker intake gasket.

Here are some measurements I took of different intake gasket thicknesses:

Gasket / Uncompressed / Compressed
Stock (Metal) / .035" / .020"

Felpro (96033)(Coated metal) / .060" / ?

Felpro (1200) (Composite)/ .060" / ?

 

[FreddieWilliams]

For the sake of other searching this topic in the future, I will comment on what I found.
I talked to Kenny Duttwelier the other day about milling the intake to correct port alignment due to deck height reduction.

I was in fact wrong in assuming you needed to remove the amount you wanted the intake to drop from both side. It is not a 1 to 1 relation. In my case, I needed the bolt hole to drop 0.070”. This means that you need to remove ~0.035” from each side of the manifold to achieve this.

Donald L. Webb explains it this way:

Once you have the amount shaved from the heads, block, head gasket, etc, you also need to know the angle between the deck and the inlet face on the head. If the angle is 90 degrees, it's an easy problem. 0.7 is the number to remember. Multiply the amount shaved from the deck and multiply it times 0.7. This is the amount to remove from the bottom of the inlet manifold to bring it into the proper relationship again. But now the gap for the intake gasket is too tight, so you need to remove stock off the intake face. Multiply the amount removed from the bottom of the manifold (end seal) by .07 and this is the amount to remove from the intake face.

In your example: .070" removed from head, block, head gasket, etc. X 0.7=0.049" off bottom manifold (end seal area) X 0.7=0.034" off intake face.

Since I had about 0.140" of end seal clearance, and the intake was going to drop ~0.050" leaving me with 0.090", I opted to forgo the end seal milling and use RTV in place of the stock rubber end seals. I figure the smaller gap would allow for an easier seal with RTV. Make sure to check your clearance. At some point it may be a necessity to mill this area or it will hit the block.

 

[KendallF]

Yep, I screwed up above...for some reason I was thinking that milling both faces resulted in double the drop..doh.

The face is 45 degrees to the vertical, so it drops down .707 (cos(45) or 1/sqrt(2)) of whatever's milled off of the face. Then the amount that it slides "down" the manifold/head face is another 45 degrees from that, so it slides .5 of the face mill amount. Tell Donald Webb to post next time.

 

[Jerryl]

Good thread.
I am continuesly amazed how much info there is on this board!
Be sure to account for head gasket compression.

PS:
How do you in fact measure and ensure alignment of the intake ports to the intake ports? Play-Doh?

 

[Nashty]

:smile:

Yep, I screwed up above...for some reason I was thinking that milling both faces resulted in double the drop..doh.

The face is 45 degrees to the vertical, so it drops down .707 (cos(45) or 1/sqrt(2)) of whatever's milled off of the face. Then the amount that it slides "down" the manifold/head face is another 45 degrees from that, so it slides .5 of the face mill amount. Tell Donald Webb to post next time.

Get your Trig straight soldier !!! :smile: :smile:

 

[stagemonster]

how much can you deck the block down and it still be ok to use

 

[KendallF]

how much can you deck the block down and it still be ok to use

Holy resurrected thread, Batman! I have seen a bunch of blocks decked at least .035" (to a 9.500" deck height). If you have doubts, have the block sonic checked.