I have a iron block 408ci motor that I'm having built. The engine will have -2cc reliefs in the flat top pistons. I want a compression ratio around 11.7-11.8:1 and run on pump gas. What i'm running into is knowing how far to mill the 70cc chambers to achieve the compression ratio desired. I will be using a standard MLS gasket. I'll have to look up the thickness of the gasket. I'm being told they will need to be milled down to a 66cc chamber by one builder and 64cc by another. I would obviously need to figure this out in thousands to tell them at the machine shop. I called a machine shop and they said they can flat mill the heads down but asked me about the intake fitting after milling. Anyone have a answer to what i do about making sure the intake fits after the heads are milled. Do the valves have to come out to be milled? I"m sure theres alot here I dont know so please ask and inform me the best you's can. I dont want to get the heads over milled or under and I dont want fitment issues with the intake later. Thanks for your help and input.

Bruce

 

.006 for every cc. You also need to know har far out the piston comes out of the hole. Typically .005-.007

 

I think I was told in the hole -.006 for the piston

 

Anyone know about the concern of milling the heads and intake fitment concerns later on? Are all heads flat milled or angle milled? Do they take the heads apart to perform the milling or do they stay together?

 

Pretty sure they need to come apart to mill so they can be cleaned as well. I do not think you are going to mill the heads enough to make any difference on the intake unless you are going with a tight tolerance of maybe a sheetmetal but I still feel you will be fine. As far as the angle they mill the heads that I do not know.

Is the .006 in or out of the hole? I am going to assume out of the hole but want to make sure.

 

Also, get me your stroke and bore size along with your rod length and I can figure out what you need and your head gasket thickness as well.

 

I'm told thats in the hole, the bore 4.040 Diamond Custom pistons flat top -2cc valve relief, compstar rod length 6.125 and 4in stroke callies dragon slayer crank. I'm actually told its a 410ci by those #'s but close enough to call it a 408 IMO I can't locate anywhere that says a 4.040 headgasket. I see headgaskets that say range from 4.030 to 4.125 bore. Is that the style gasket i need? Looking at just regular GM performance MLS gaskets but I see a varied thickness from .023-.051 i think.
The piston is in the hole .006 and I think thats cause the motor is technically set up for nitrous. And theres a big chance I can be wrong in that assumption. Hence why i'm asking so much. THank you for your input 03 BUSA and anyone else.

Bruce

 

You are not trying to find a gasket with the same bore size because the head gasket squishes. I am not sure what the 4040 guys rune but for my 427 with 4.125 bore I use a 4.130 gasket. I will run the numbers at both positive and negative .006 but I really think it should be out of the hole??

 

With using the piston in the hole and a .051 gasket I come up with 11.0 with the heads at 70cc. With the piston out of the hole and those same figures I come up with 11.3.

 

With milling the heads down to 65cc which would be .030 milled off the heads I come up with 11.65 compression with the piston in the hole and 11.9 with the piston out of the hole. You really need to know for sure that piston figure but this will get you close with a .051 gasket. If you choose to use a thinner or thicker gasket these values will change. Personally I would run a Cometic MLS type gasket.

 

Once again thanks for the great information 03 BUSA. I'll dedicate the first low 10second slip to you if i can get this to all come together. Looking to have around 550rwhp/500rwtq NA in my 2000 C5 FRC 6spd and run low 10's with the extra 100rwhp/115rwtq. This being based on my 10.81 at 130mph run with the NA 346ci motor with heads/cam/intake at 444rwhp/385rwtq

 

So far as the intake fitting. on my forged 347 i had my TSP 5.3l heads milled down from a 64cc to a 59cc. when installing my Ls6 intake the guide pins would not sit down in the guides in the heads. when the heads are milled they bring these holes closer together than i thought they would. many guys say they never had to do any modifications but in my case i did. What i did was get the old trust dremel tool out and started cutting on my Ls1 intake first to make sure i could get the result that i wanted. then began shaving the guides on my ls6. once cut enough i installed the intake and torqued to specs and looked at the impressions left by the seals on the intake to make sure the ports where completly sealed. so there is my story. oh yea by the way i also had to remove the two brass pins at the corner holes on the intake to be able to shave the guides enough. worked like a champ hope this helps

 

No problem, glad I was able to help.

 

the trick flow 235 is advertized at a 4.100 bore.
a 4.125 gasket is recommended.

my 235's were in the 4.08x range, and i wanted to use a stock gasket, so i went with a l92 version. its advertised at 4.09x.
most of the ones i put a mic on were over 4.09x. some of them were 4.1x.