2fastfu

I just added E85 to my 403ci stoker motor last month to get every little bit of HP squeezed out of it and I gained 13 RWHP and 11TQ I'm now @ (485\485).

Now to make a long story short, yesterday I was changing over spark plugs from TR5's to Stock LS9 iridium plugs and I couldn't get one of the plugs to seat all the way and might of messed up the threads by forcing it in and it's still short by seating all the way down by a 1/8 inch or so. now i'm just going to pull the heads to fix it just for ease of mind even though it's still running fine.

So finally to my question. How small can I go on gasket and how much can I mill heads to bump compression a point or more? I want a 12:1 compression min. I have srp pistons that are -10cc, the pistons come out of the block by +10, my cam is 586\588 234\242 on 112 LSA, and I have TF 225 cnc heads that were cut 1cc just for inperfections. Current compression is at 11:0 now. I was thinking of doing .30-.40 cometics, and milling heads .30 to get as close to the 12:1 I want. Can I mill the heads even more say .45-.60 and not have clearnace issues? I want to bump compression as high as i can without changing the pistons out and to able to go back to pump gas some day if i wanted to.

The engine builder that built my motor here in Tucson said not to use smaller gaskets and just have heads milled .30 and be done with it and if I wanted a higher compression motor i should just change out the pistons. He was stuck on selling me new pistons even though I said I wanted to do it the other way and heard of other people using smaller gaskets and milling as much as .60. He said well you would just be looking for problems when you start doing stuff like that. I don't know what to think so please give me some facts please!

also can I order new pushrods by the amount of milling done to the heads done?

2fastfu

Will I have to mill my fast intake bottom to match up with the heads if i mill my heads?

Gering

Ragtop 99

I've never heard of that. You are not changing the mating surface between the heads and the Intake Manifold.

I would have the builder port match the IM and heads while everything is apart.

briancb1

By milling .XXX or using .XXX thinner gaskets, you are changing the location of the intake ports and bolt holes by just that much. A good machine shop will clean up the intake port side depending on how much you sink the heads down to make those corrections for you.

There's enough slop so the bolts will line up and be able to tighten down, but it doesn't mean the port alignment will be great.

Ragtop 99

I understand how the valve train geometry can change, but I'm having a hard time visualizing the impact on an IM since that since the neither the port surface that mates to the IM nor the IM bolt holes are touched when the heads are milled. Any chance you have a diagram or something that shows how that works?

briancb1

Okay well first off, trust me and secondly bring it up to whoever mills your heads. They will probably shave off whatever necessary based on how much you want to mill.


Measure the distance from the top of one head to the other head, at the top. What's the distance?

Measure the bottom of one head to the other bottom? Notice how the bottom of the heads are closer? It's because they are not parallel but at an angle from one another.

Now measure one head .030" from the top to the other head .030" from the top? Notice how its a shorter distance? To allows your intake manifold to "sink in further into the valley" (if you will) some material has to be removed because the to faces are closer together where the intake bolts onto the heads.

Ragtop 99

Good description. Thank you!