LS head milling and plastic intakes

[quicksilver]

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?

[JoePorting]

I've milled heads before to get compression and found it to be more trouble then it's worth. I'd either live with the lower compression or get new pistons for the compression you want.

[quicksilver]

Also- the 317 head has a 71cc chamber whereas the 243 castings have a 64cc chamber. Did Chevrolet just cast the chamber deeper for the other heads or what?

I think I may need to grab a set of 243 heads and start there to hit my targeted compression number since .078 would be a large amount off the other heads.

[airflowdevelop]

If you can get a set of A-B-C quality 243's...start there.

If not... .070" off of 317's you will need to cut the intake flange .015-.020". It is hard to tell as the plastic manifolds normally sit high on the head from factory. Cutting .030" off of stockers normally makes the manifolds fit perfectly. When you cut more then .040" it starts going the other way.

[quicksilver]

I'd really like to use the heads even with knowing I would have to mill the intake flange. It doesn't seem like a big deal to me, and the heads have a pretty thick deck so I wouldn't be in trouble.

That, and im only shooting for 500hp which is nothing new for a properly done LS engine.

I would love to just swap out the pistons, however if I pull the pistons out, I will HAVE to hone it since I wouldn't put the same rings back in the same holes with new pistons which means the whole motor would have to come out. I could pull the pan and rods/pistons out without pulling the motor out of the truck. Gotta love how GM made almost everything accessible.

I am thinking about it though, but If I did and didn't rough up the cylinders, I dont' even think the factory style phosphate coated rings would seat in well. :/

[3pedals]

Also worth noting is that with that much of a cut(.050"-.070"), you are probably going to need to flycut the pistons. I flat cut .050" from my L92 heads, and used a .040" cometic gasket and my intake fits fine with NO extra work, but it is a VicJr. I had to flycut too.

[quicksilver]

Also worth noting is that with that much of a cut(.050"-.070"), you are probably going to need to flycut the pistons. I flat cut .050" from my L92 heads, and used a .040" cometic gasket and my intake fits fine with NO extra work, but it is a VicJr. I had to flycut too.

I had thought of that, but with as small of a cam as im using, I don't think the valves are in danger of hitting the piston.

[quicksilver]

Even though the LS heads have the 15 degree valve angle. I come from the SBF world, so im used to the 20 degree stuff that has a mile of P2V clearance.

[Bossman]

I angled cut a pair of LS 5.3 heads for a customer .125 that's 1/8 inch of his heads, he said he had no problem putting the engine back together and claims in runs like a scared rabbit. and didn't cut the intake face of the heads