LS head milling and plastic intakes
Posted: Tue Jan 10, 2012 8:31 pm
I hate to ask a basic question but since I've not done it, I have no experience to pull on for this question.
On any engine, if you mill X amount off the deck, you mill the same off the intake face or off the manifold itself. Since LS engines use a plastic manifold that cannot be milled, it has to come off the head.
My first question is, since the LS heads don't have the intake side 90 degrees to the deck, how much does milling the deck (A) equate to milling off the intake flange (B) because if its 90 degrees, Its a 1 to 1 relationship, but when the angle changes, so does the relationship.
Second question- since the bolt holes are like the ford bolt holes, I assume the intake holes need to be elongated towards the inside. How much can you mill off a head before runnning into manifold bolt hole fitment issues or just manifold fitment issues period? I can't mill the chinawall of the block, so I can only play with the heads pretty much.
In case anyone is curious, im trying to just tweak my 6.0 truck motor.(4.00 x 3.622). I have a set of 317 castings that I've ported that are 210cc's and flow 308cfm @ .600 lift. I intentionally kept them small to keep port velocity high since I only have 364 cubic inches and its a truck. I had originally thought of opening them up to 230cc's and just narrowing the lobe seperation as a crutch but instead I figured it would be much better to keep the port smaller, sacrifice some top end flow numbers and widen the cam instead. Its a 5,000lb 4x4 truck that does see occasional towing and daily driven. I was thinking with some 1 7/8 ARH headers, a 226/228 @ .050 cam and 11:1 compression that I should be able to come close to 500hp at the crank and still make most of my power below 6500 rpm.
I ask the milling question because the stock chamber is 71cc's and to bring the compression that high, I need to remove 12cc's which is around .070 off the deck. (going off the standard asumption of .006 per cc) but I would mill them .050 and check the chambers before going any further.
Input?
On any engine, if you mill X amount off the deck, you mill the same off the intake face or off the manifold itself. Since LS engines use a plastic manifold that cannot be milled, it has to come off the head.
My first question is, since the LS heads don't have the intake side 90 degrees to the deck, how much does milling the deck (A) equate to milling off the intake flange (B) because if its 90 degrees, Its a 1 to 1 relationship, but when the angle changes, so does the relationship.
Second question- since the bolt holes are like the ford bolt holes, I assume the intake holes need to be elongated towards the inside. How much can you mill off a head before runnning into manifold bolt hole fitment issues or just manifold fitment issues period? I can't mill the chinawall of the block, so I can only play with the heads pretty much.
In case anyone is curious, im trying to just tweak my 6.0 truck motor.(4.00 x 3.622). I have a set of 317 castings that I've ported that are 210cc's and flow 308cfm @ .600 lift. I intentionally kept them small to keep port velocity high since I only have 364 cubic inches and its a truck. I had originally thought of opening them up to 230cc's and just narrowing the lobe seperation as a crutch but instead I figured it would be much better to keep the port smaller, sacrifice some top end flow numbers and widen the cam instead. Its a 5,000lb 4x4 truck that does see occasional towing and daily driven. I was thinking with some 1 7/8 ARH headers, a 226/228 @ .050 cam and 11:1 compression that I should be able to come close to 500hp at the crank and still make most of my power below 6500 rpm.
I ask the milling question because the stock chamber is 71cc's and to bring the compression that high, I need to remove 12cc's which is around .070 off the deck. (going off the standard asumption of .006 per cc) but I would mill them .050 and check the chambers before going any further.
Input?