I've got 1 head on my 3/4 ton truck that has a rocker stud pulling out, and a very mangled valve tip. I also noticed for the 1st time (shows how observant I am when I'm in a hurry) that this engine has 2 very different heads on it...a 624 (lightweight smog head) on 1 side and a 882 (heavy smog head with better ports) on the other :rolleyes: The engine in this truck is the one that came in my nova when I bought it. It is a low mileage rebuilt 355 4 bolt with cast flat tops averaging .053 in the hole (yuck). I was just going to get the one head fixed before I noticed the difference between heads, but now knowing the heads are so different I wouldn't be able to sleep at night. I also have a set of 882 truck castings with the 1.72 intake valves but 1 ended up being cracked BAD (came off of a free 350 that froze and busted the block). I dug thru my piles of heads, and about all I have left now are either single good, rebuildable heads, or matched sets of heads in need of some $$$'s to rebuild, or some very small chambered 305 heads. But, I do have a set of brand new vortecs that I was going to put on my 388 (before I changed my mind) with screw in studs, guideplates, heavier springs, and 60cc chambers (milled to remove some surface rust). Problem is, even with a standard .041" head gasket, I'm going to end up with around 9.3 to 9.4-1 compression, with nearly .100 quench graemlins/sad.gif The cam in there now is a comp cams 260ah-8. 260/268@.006, 212/218@.050, 108 lca, installed on a 104 ica. I think with a tight quench this would work ok, but with the mile long quench, who knows? Since this is a fairly heavy truck application, and since I have 3.23 gears, 31" tall tires, and a 700r4 tranny, I suspect the vortec heads would cause all sorts of pinging problems...the efficient chamber design can only do so much. With the current 76cc heads, compression is only about 8-1, but it runs quite strong as is. Do you think I could get away with the vortecs, or should I see about swapping some of my mismatched heads for a set of rebuilt 76cc smogger's?

Yes you will only be at 9 to 1 maybe 9.2 to 1 with the vortecs that is O.K. for pump gas.you can get away with 9 1/2 comp with super or mid grade pump gas.It gets my vote,do it.Voretcs are 40 horsepower bolt on.Im pretty sure thats right its 1:30 am here and I'm sleepy,but I think I'm right.

[ 02-12-2005, 10:42 PM: Message edited by: georgia 69 ]

The thing with quench is that once you get real wide there effectively is no more quench area. That's pretty much what you would have with .100".

You won't hear me say this very often (like never LOL) but you might just consider using a thick head gasket to lower the compression a tad and open the quench up from .100" to about .120".

At .120" the "area formerly known as quench" just becomes part of the combustion chamber with enough room for a more-less normal burn (according to KB pistons) across the entire cylinder and your compression ratio will drop about a half point.

When quench is between .060 and .120" the quench area (again according to KB pistons) becomes prone to abnormal combustion in the quench area. It is almost like the quench area starts to act like its own combustion chamber with the mixture lighting off from hot spots (like carbon buildup).

Hope that helps.

Travis,

I think Eric is on to something..

Some of the old smog MOPAR motors didn't have any quench b/c their chambers were wide open. And if I recall right, some of them were even down in the hole like .100" too??

I think HR or CC mag.(??) did a compression/hp test using, (I want to say), a 360 but it might have been a 440 with the open smog heads and flat-top pistons and all they did was record the dyno hp and power numbers as they went from 12 to 1 down to 8 to 1 CR. Or something like this?

They started with a shim and then backed the compression off using .040 copper headgaskets until they got to the bottom CR. number. They just stacked them and compensated for the intake fit!!

The motor ran fine with a .160"(??) headgasket stack if I recall right at 8 to 1, but it felt lazy, even though it still made GOOD power.

Now they might have used .060" headgaskets up to .180"(???) It's been too long since I've read the article..

Anyway, the mag. said that they only did this type of test to prove the old adage that a number in CR. is about equal to 4 percent one way or the other and they verified that it is true.

Just food for thought.

And it's raining here, looks like for all day. I will be glad to help you unhook your Trailer if you want if you haven't done it yet?

pdq67

Here's the "mental" situation I am running into. The engine in my '78 1/2 ton isn't that much different than this one would be with the vortecs. It also has cast flat tops, but "only" .040 in the hole, with .041" thick felpro head gaskets (.081 quench). It also has 9.4-1 compression, but it has a larger xe268 cam in it, and it runs just fine on 89 octane and has run on 87 octane in a pinch without problems. I could, in theory, run something like a victor .026" composite head gasket (block has apparently never been decked, so I don't want to use a shim type gasket) to end up with around .079" quench, which would bump the compression slightly to around 9.5-1 or so. I know this would work with a larger cam like the xe268, but i suspect the 260ah-8, with its shorter duration and tighter lsa, will be a problem. I do, however, have a brand new edelbrock performer 400 cam (not the same as the regular 350 204/214@.050 performer cam) that is a single pattern 214/214@.050, .443/.443 lift, 112 lsa/107 ica. It is an old school grind with somewhere around 280*@.006 IIRC. I know this cam would work ok with the stock torque convertor...I just wonder if the duration is long enough to allow me to run pump gas ok. I also have a 272 energizer cam (216/216@.050, 110lsa/105ica) that is already broke in that I pulled out of the engine when I swapped in the smaller comp cam.

Paul, the trailer is ready to haul short of just pulling the hitch lock off of it. I just need something to pull it with. I've got 3 trucks...and all of them are down right now graemlins/sad.gif

Wouldnt the 272 energizer work ok with the vortec heads. And do you have the means of cleaning up the chambers on the vortecs? I think that would be the way to do with comp below 9.5

I'll vote for the vortecs woth the energizer. Trucl will run like a (quote) " "scalded dog!" (unquote) might hafta run hi-test gas tho.

xe262 ?

As long as you aren't pushing the DCR envelope, bad quench won't cause huge problems IMO. Now I can't define exactly what pushing the limits is . . . but if your DCR is 8.0:1 with iron heads then you will probably have "issues" with a .080" quench -- .080" is probably about the worst place possible to be ;)

PS. and PDQ is right about them small block Mopars -- I spent some time playing with some '70 SB 340 heads and the quench pad is recessed into the head with a slight angle making it slope toward the center of the chamber. It was closest near the outside of the cylinder and widest near the center of the chamber. The "quench pad" was far enough away from the piston that it wasn't even machined -- just an "as cast" finish.