kenkaru

I am running a Hotcam (I know I know) and I am almost done with my home ported heads. I'm doing a medium aggressive job on the heads; working all of the recommended areas and not messing with the swirl ramps too much.

Anyway, I don't plan on changing the cam until it's time for a new shortblock so would it be worthwhile to mill the heads? They are the '98 castings.

How much power could I expect to gain?

How much should I pay to have them milled?

Another consideration is I only have access to 90 octane maximum over here in Germany but I will be getting EFI Live so I can do a little tuning to help that situation right?

Any input would be appreciated!

GuitsBoy

iTrader: (4)

I would definately mill the heads and run a thinner gasket. You need to crunch some numbers and shoot for around an 8.25 DCR to work with 90 octane. Miliing the heads may only be worth a handful of HP up top, but it will boost low end torque and make tehc ar feel more peppy when not at WOT.

kenkaru

Thanks!
Any advice on how much I should get scraped off? .030?

How much should it cost me to get a machine shop to do this?

BTW, I'm new to tuning; what's DCR?

GuitsBoy

iTrader: (4)

DCR = dynamic compression ratio. To calculate it, i need to know the intake valve closing point of your cam.

Shooting for a good DCR will tell you how much youve gotta mill.

TchargedLS1TA

iTrader: (9)

I got mine milled for $80. .030" seems to be the norm, and is a good safe number to run and avoid P to V issues, just make sure you run shorter pushrods..

kenkaru

Well, with the help of my wife I decided I'm not going to put any money into these heads since I'm trying to only spend money on things that will go on my next engine. ie intake manifold, TB, etc Thanks for all of the responses though!
Hence the reason why I'm doing a home port on a set of heads I picked up for 100 bucks. I'll post up some pics in a few days.

GuitsBoy

iTrader: (4)

Then just go with as thin a head gasket as you can. Summit has some MR gaskets that my friend is using on his motor. Theyre a .042 if I recall.

kenkaru

EDITED... realized about the whole "compressed thickness" gasket thing

How thick are the stock gaskets compressed?

I already have a set so I don't know if it would be worth it to get the thin ones.?

Thanks again! This is really helping me out

GuitsBoy

iTrader: (4)

If theyre GM 5.7L MLS gaskets, theyre .060 compressed thickness. If theyre graphite, theyre .052 compressed. If theyre 6.0L MLS truck gaskets, theyre .054.

Tri5Nerd

iTrader: (3)

You need to have them check the chamber CC after the mill, these heads can have varying thickness, I had my heads milled to 60CC and the shop took .037" of or one and .042" off the other - These were 5.7 heads.
So have the shop mill then check chamber CC which did cost more for me to have both heads to 60CC.

kenkaru

Ok so it looks like I need a 62cc chamber. I have a place that will mill my heads for 100 bucks.
I already have the gm head gaskets (gm# 12558810) so how much should I have taken off?
I started another thread... can I cc my heads with h20, a pipet, and graduated cylinder?
I know it sounds funny but I'm actually serious!

(ya I changed my mind I think I'm gonna do it)

kenkaru

here's my calculation

GuitsBoy

iTrader: (4)

You can CC your heads with a burette, which is a graduated cylinder with a petcock on the bottom. RTV a piece of lexan to the bottom of the head with a hole drilled at the highest point of the combustion chamber... Measure how much water comes out of the burette.