Shaunbo13

Heys guys! I want some more info. You guys are great with your advice, so here it is. Im putting on an intake, carb, valve covers, while i have it off, new water pump, timing chain(double or single-question #1), should i take the heads off and have them milled, for better compression? If so, what should i have them milled to? I heard this from a friend, wondering if it would give horsepower. I need to replace the head gasket anyways, leaking both inside and out. I'm going to put new headers on, its already got a dual exhaust. If I do get them milled, what kind of gasket do I use, and do I need to do anything else if I get the heads milled, maybe I shouldn't get them milled? I just don't know. 1968 Cutlass holiday coupe 60,000 og miles. I've almost got them off...so any info would really help out. What Im after is a mild rebuild, more horsepower, and chroming it a little..Thx guys!

Fun71

The factory '68 head gaskets are thin steel shim gaskets that are 1/2 the thickness of aftermarket replacement composition gaskets (.020" or so vs. Fel Pros at .040"), so replacing them will reduce the compression ratio. Milling the heads can make up the difference to bring it back to factory or above.

There were different compression ratios in '68: 10.25:1 for the 4bbl engines and 9.0:1 for the 2bbl engines. Which is yours? This would help determine how much you might mill the heads (if you even need to) to raise the compression or keep it at factory levels.

Shaunbo13

I want more horsepower, I would like to raise compression right? It was a 2bbl and Im putting a 4bbl on it. my compression is 9:0:1, i think I want 10:0:1, if I am right..lol. If I do raise compression, would i have to do anything else to the block or heads, or can i mill the heads and be good to go? yes I have no idea as to what i would need them milled to, Im lost. Thanks for helping! This is a rebuild in the works as we speak, so the info everyone post is greatly appreciated! and how do i even know if i need to mill my heads, im trying to do a mild rebuild with out messing with the cams and pulling the motor

DoubleV

Bumping the CR up a little and nothing more isn't really going to get you much performance, at least not what you may be expecting. There are however other things you can do with your heads that would make a bigger difference in power such as bigger valves, 3 angle valve job, blending bowls, grinding down the A.I.R. bumps in the exhaust ports, filling heat crossovers, welding center divider ( if using headers ), and other things I'm sure. These things may not net you huge gains if you're sticking with the crappy stock cam, but performance will definately be improved.

P.S. The advertised CR of 9:1 for your engine is actually very likely to be lower than that. Measuring is the only way to know for sure exactly what it is but I've heard they're usually more around 8.5:1.

Lars

get a comp double roller chane, when the head are off fill the crossovers and pour or clip the center devider, mill the heads 20 thou, get some thin cometics gaskets, 5 angle valve job. you NEED to do this!!! theres a thred in "racing and high performance called home porting teqnics, read it all!

Fun71

Be aware that the factory camshaft is really, really small so doing things like increasing CR and head porting won't make a huge difference in performance. These things will go very well with a camshaft change, though.

Kennybill

Upgrade the camshaft & new lifters & valve job (new springs & dust the heads for flat sealing surface). Dual exhaust, I hope already. Don't go to big on the cam, more like a rv cam. Comp cams has a couple single pattern cams that will "wake up" your engine. Jmo, Ken

olds 307 and 403

I say mill your heads .010-.020" and get .011" shim head gaskets from Smitty275 on here. What DoubleV suggested will definitely give more power with a mild cam swap. You will need a new timing set anyways. I have seen too many pictures of the plastic coated cam gear broke apart and ending up in the oil pump pick up. I have had good luck in that department but my 350's were 8 years newer and maybe they had more durable plastic by then?

jfb

check what your clearance should be first and do the homework and call mondello for it. I say cut them and bump the new cam a few degrees and get the info needed from mondello,clearance,gasket thickness etc plus how many degrees and have all areas of info in front of you when calling.

DoubleV

Have you not heard the countless horror stories of dealing with Mondello Performance Products by now? Everybody should stay away from those clowns at all costs.

Lars

Megaoldsfreak?

brownbomber77

Corteco head gaskets from Rock Auto I thought were at .028? They're less than $20 a piece shipped. There's a lot of "while you're in there's" while you have the timing cover off and interested in making horsepower. A better cam and new lifters with that timing chain change, milling the heads .020 will make up only for the added girth of the head gasket.

olds 307 and 403

Corteco come in two thickness, .028" and. 040". I got the .028" in my 330-455 and 403 overhaul sets. Supposedly the overhaul sets come with .040", mine didn't.

jag1886

Just be careful trying to jack the compression to 10, the only real problem is you will have to worry about every tank full of gas you put it because it may be the one that makes it ping like hell. I found this out the hard way. I'd try and stay at 9-9.5 at the most if you want to have worry free driving.
Horsepower has a lot to more to do with combo than just cranking up the compression. You might want to consider adding a gear or a 3-4 speed auto (I'm just guessing that car has a 2 speed auto).