Well, got my head back from the engine shop on Thurs of last week. They had to plane it .035 to take the warp out, one intake valve was burned and all my exhaust seats were warped and not sealing. After some heavy math I found that it wasn't going to affect my timing as bad as I thought, only about 1 - 2 degrees retarded. Compression is a little higher, somewhere around 8.5 or so... not too bad. After reinstalling the head I took the car out for a test drive. Everything seems to work great, with no noticeable effect from the cams being retarded. Maybe a little more low end and a little less top end(compression increase has something to do with the increase in bottom end as well I imagine). Didn't have any issues with timing belt tension, still have lots of adjustment on the tensioner pulley. Drove into town and bagged on it all night with no probs, but that's not to say nothings going to happen.

Just though I'd share the info just in case someone ever is in the same situation and needs to rebuild the head they have rather than finding a new core(which I would still recommend if possible).

did you actual measure the cylinder volume ? and check cam timing ?

I just calculated how many degrees the cams would be out by taking the .035 that the head was planed, the radius of the cam gear itself, the circumferance of the cam gear divided by 360 and figured it out from there. The final answer is multiplied by 2 I think since the cams rotate once for every 2 rotation of the engine. Not exactly a degree wheel, but I think my math was sound. The timing marks on the cams were only very slightly out of align, and if they were out almost 10 degrees like you had implied they would be(you said 5 degrees for .020) I don't think it would work as well as it does. Not that I doubt your experience, but it seems "my mileage did vary" As for compression, since the combustion chamber isn't the same diameter as the bore, the amount of space removed would be less than say removing the same amount from the deck. It ended up being very little. Since the engine has 7.8:1 compression stock, removing a small amount of combustion chamber makes a lot less difference than removing the same amount from say, a 10:1 compression engine. You had originally said .004 of planing would increase my compression by .2(which would put me at about 9.7:1 now), I believe it to be a lot less than that.

If you would like to compare math I can get all the info I have and sit down and work it out again, but I am not trying to say I know more about it. If anything I would like to see where I went wrong if I did. You probably have a lot more experience with DSM's than I do, but I do have experience with motors and had a mustang with 11:1 compression.

Please feel free to counterpoint anything I have said, I wish only to learn.

So you just did the math on paper and didnt measure anything..

I have tested everything using the right tools and no paper work. if by taking .035 off and only seeing 2 degrees off, then your math or paperwork is wrong (sorry) but no way will that much taking off .035/.8mm and the cams vs.crank timing will only 2 agrees. And for CR, by decking the head and using your math, (this I would like to know) since you didn't say you measure the orignal combustion chamber volume before cutting & afterwords. How did you figure out

now this is also base on using a stock head gasket. you never said which gasket was installed.

I beleive in doing things right. second-hand guessing and thinking it should be okay is like using a ass dyno.

they dont give concerte facts & proof & spreads mis information.

double post

I'll admit that my guesswork on the cam timing isn't the recommended way of figuring it out, and I wouldn't use it normally but it gives a rough approximation which was all I was after. My only point is my car wouldn't run as well as it does if the cams were out 10 degrees... don't you agree that 10 degrees is a lot? But having little experience with degreeing cams, I will digress. And as for compression ratio, there is no tool to measure it(other than the tools used to measure the factors involved), it is all done with math.

I will post my figures here for your scrutiny and will leave you to prove/disprove them. I don't have a combustion chamber volume but working backwards from the stock CR we can get close. My numbers may not be spot on, but I think they will illustrate that planing .004" off a head does not equate to a .2 increase in CR(Not on a 7.8:1 CR motor anyway, a higher CR motor may eventually approach that ratio since the smaller the combustion area is, the more drastically it is affected by a small change)

Displacement:
Bore: 3.346"
Stroke: 3.39"

formula for finding cylinder volume: Pi*r^2*H
3.14 * ((3.346/2)^2) * 3.39 =
3.14 * 2.789 * 3.39 =
29.808 cubic inches (*16.387 to convert to CC's)

488.47 CC's of displacement per cylinder.

Now since I didn't have a combustion chamber volume, I worked backward from the stock compression ratio. Assuming 7.8:1, this yields a combustion chamber size of 72cc(note that the combustion chamber in this case includes head gasket thickness and piston dish when calculated this way)

Compression ratio = (displacement + combustion chamber volume) / combustion chamber volume

(488.47 + 72) / 72 =
7.784:1 compression ratio.

Now... take the .035 I planed off my head. We will assume the combustion chamber is perfectly round for this and the same size as the bore(using the actual size would further prove my point as the area removed would work out to be even less due to the shape of the combustion chamber).

(3.14 * 2.789) * .035
=.306 cubic inches * 16.387
=5.022 CC's

Do you agree that we have removed 5cc of combustion chamber volume? If we had 72 to begin with and now have 67 then we can now calculate our new CR.

(488.47 + 67)/67 =
8.29:1 Compression ratio.

Please feel free to tell me how I obtained a figure of 8.29:1 and you obtained a figure of 9.8:1.

Peace.

oh boy I havent done this in a long time on paper but I will go back to my books from the last few motor build up & when I get home later on tomorrow. But here are the correct specs for a 4G63 motor is

bore 3.366
stroke 3.465
or 1997 cc


since I noticed your numbers are out. And thanks for making me lookup sh!t up again from the past few motor buildup logs

I will help clear the air out tomorrow.

but right now, booty calls man!

Yes, the stroke should have been 3.46, I accidentally read the 1.8 stroke length from the book. Even with the .070 difference the end CR still works out to 8.3. My numbers from the Haynes book too, not actual measurements I realize, but I think I am in the ballpark.