I got my head back from the local machine shop today; they said they took off .005" on top of .006" that was taken off in a previous resurface. They also measured it from the top of the head rather than the 3 indicator "cups" so I don't know if I believe there was even a resurface done previously.

Squish band=good and head resurfacing indirectly messes with the squish band when a spacer/thicker HG is used to make up for the material taken off. I'm tempted not to use any spacer or thicker HG to retain the squish band, hoping the cam timing isn't very affected from the head being a little closer to the block. Do the pros outweigh the cons? My block needs to be decked as well, although I'm guessing less than .005"; so lets say .015 worst case total.

Any risk of valve interference or enough cam timing off from using non-adjustable cam gears? I'm trying to figure out the lesser of the evils.

Stock rebuild although looking to push its limits.

Thanks

-Matt

Run it by me one more time why you dont want to use a thicker headgasket.

Example:
Tuning the LET - Ignition

Less chance of knock, more efficient combustion. In that particular article it states only off boost gains but I would venture to guess it would decrease BSFC(a good thing) similar to higher compression. aka getting more out of a given setup.

IMO .015" would make a much larger impact on an already tight squish band than cam timing, but I don't have any experience to back that up. And, cam timing can be fixed with adjustable cam gears, although I'd like to spend my money elsewhere.

Matt, it's not worth running the head spacer, IMHO. The one "modern" design left in the 4g63 is the head CC design. That squish shape in the head is good and the stock piston shape is already BAD at making it work. Look at the much better magnus piston. So don't make it worse by screwing with the quench pad with a fat head gasket.

Since you're looking for a budget build, cam gears may actually be for you. You can gain alot with a little more exhaust cam retard. But put it together and check it first. You may have already dialed in a little more overlap .

Push the limits of a 6 bolt? PPPSHT Good to see you're getting ready to bolt the head on!

IIRC the stock HG is .035" while the standard Cometic is .051" Coincidence?
If you're worried about clearances, test fit the head on the block and place a small ammount of silly putty in a plastic bag inside the combustion chamber.

Thanks for the replies, guys. They are very appreciated!


Ahhh I can't wait to drive my car again.... It's been so long I can't even imagine it running again, no matter how many hours I spend making engine noises in it.

I think I'll grab an OEM gasket and see where it puts me.

Mr Peepers said:

It's been so long I can't even imagine it running again, no matter how many hours I spend making engine noises in it.

Click to expand...

Too funny!

Pneumo has a good point about the Cometic HG. And the silly puddy trick really works. You can get an oem style HG from partsdinosaur.com for $16 plus shipping (USPS Priority under $7). It would be a gamble in my book because I don't know how much .015" shave will affect the timing marks. But, your compression will be higher with a stock gasket .

I took a few measurements to see how much timing would be affected by a change in deck height. Naturally I'll show my work so people who are smarter than me can correct my mistakes.

camgear diameter= 5.68"
circumference = 17.835"
Since there's 360 degrees in a circle, every degree = .0495" at the cam. (that's 17.835 divided by 360)

But since we want to know timing degrees at the crank lets halve that number.
.0495 divided by 2 = .0248" per degree of movement at the crank sprocket.
.015 divided by .0248 = .605.
So shaving the head/deck by .015" will retard timing by 0.6 degree. Less than one degree.
Who wants to split hairs?

dsm-onster said:

Too funny!

Pneumo has a good point about the Cometic HG. And the silly puddy trick really works. You can get an oem style HG from partsdinosaur.com for $16 plus shipping (USPS Priority under $7). It would be a gamble in my book because I don't know how much .015" shave will affect the timing marks. But, your compression will be higher with a stock gasket .

Click to expand...

You know, I've been meaning to ask that. It's an OEM "style," and I have probably 2-3 of them laying around from there, not to mention the one coming in the current gasket set. I'm really really leery about putting one on the car, though. It's not ALL that hard to swap if it blows, and it wouldn't be bad to make a point, either. Really though, how much is there to skimp out on a gasket? Thinner sealing ring material wouldn't even be that cost effective etc. Yes, OEM, OEM, OEM but in my opinion it often seems to be said so blindly. What if something IS the exact same as OEM yet 1/3 the price. But I digress..

If it doesn't get to piston too close to the head, I think I'll go stock. What is a good clearance? With the gasket in place(it will squish when tightened a bit)? I don't know how much the rod will stretch at rpm. I have many questions feel free to link me to a page/resource and tell me to search.

I can always throw cam gears on and take care of the timing "issue." Retarding the cam timing will shift the curve up a little anyway; not a bad thing.

pneumo said:

I took a few measurements to see how much timing would be affected by a change in deck height. Naturally I'll show my work so people who are smarter than me can correct my mistakes.

camgear diameter= 5.68"
circumference = 17.835"
Since there's 360 degrees in a circle, every degree = .0495" at the cam. (that's 17.835 divided by 360)
At the crank one degree = .0248" (half of .0495)
So shaving the head/deck by .015" will retard timing by 0.6 degree.

Click to expand...

Good stuff 0.6 camshaft degrees is 1.2 crank degrees. That will move up your powerband SLIGHTLY. There's far more difference between stock automatic turbo cams and manual turbo cams than 1 degree of retard.

Buying OEM (Mitsu products) insures the quality. But if you can see the same traits or identical product in another brand then I consider it foolish to pay for a logo. I've paid $20 for a Fel-pro head gasket and it has taken the worst beating of all and still not blow. I learned, albeit the hardway, to do head gasket swaps the right way and now how to tune some the right way. THAT is what makes it last.

I don't know how much the rods stretch. I do know that, yes, it mostly a function of rpm as you mention. And Stock cams die before redline. Though they are more advanced than aftermarket cams, thus lifting more during the dwell time around TDC, they have a much lower lift. That 1.2 degrees of cam retard may come in handy .

I just edited my post to clarify the timing change would be 0.6 degrees at the crank.

Sources I've read recommend .030" clearance in the squish band. If you're on stock cams I don't think you'll have to worry about valves hitting since many aftermarket cams use greater lift and duration without contact between the piston and valves. Just don't get too radical with the cam gears. IMHO the squish band clearance is there to give a loose fitting, slapping piston enough room to flop around without hitting the head on the front/back.

You should be fine, my car has about .050 cut off the head. slightly O/T but i am building a vintage motocross bike, and i just got .130" cut from the head and jug, it took it from about 9:1 to about 14.5:1, big difference in power. But now it pings even on 110oct VP race fuel. shit.

4g63's really don't have much of an effective quench(squish) area to begin with. I've seen stock engine's with almost .080". Most guys that really know what they're doing with 4g63 engine's will take a virgin head and resurface it to meet the finish requirements of the gasket(.005 or less), put the piston at 0 deck and run a .030 gasket.

Of course you would need to check piston to valve clearance. Rod's don't really stretch unless they are about to fail, it's called thermo-elastohydrodynamic deformation. With a steel rod, valve clearance should be about .080 on the intake side and .100 on the exhaust side. If you're using aluminum rods, you absolutely have to call and talk to the rod manufacturer about clearances.