1972 400 with 6x4 heads

[DirtyWhite77]

Hi guys I need to pull the engine out of my 1977 trans am. It’s a 1972 Pontiac 400 with 7j2 heads. The dipstick is broke in the pan, the rear main seal is leaking, the trans is messed up, and a motor mount is torn up. And I have the hood front fenders and front bumper off right for a repaint. So before I install the body back on I figure it be smart to pull the motor/trans and fix the little stuff wrong with it. I plan on pulling the heads off the engine and a couple of main caps to check everything out. The engine runs and turns over really good now, I don’t want to rebuild it now. I’ll probably clean the block up and paint it. I’ll remove the cam and inspect all the lifters as well.

Recently I’ve bought a set of ready to run 6x4 heads from a guy in town. He removed them from his 77 motor for a set of new aluminum heads. He says they’ve never been milled but they have web rebuilt with new valve springs and seals before. The head to block surface doesn’t seem to have been killed, and I can’t find any machinist markings anywhere, the head to intake side also doesn’t look to have been machines. There doesn’t seem to evidence anywhere of a leak when they were being used.
I trust the guy, I know other people around town that have dealt with him before and I don’t think he’s INTENTIONALLY trying to pull a fast on me. 
I also have a 1977 4 barrel iron intake. I’d like to install the heads  the intake and a more torquey but still very mild cam before I reinstall the engine in the car.

Assuming that my short block hasn’t been modified or decked should I run into any problems installing the 6x4 heads onto my 72 block? I’m gonna have machine shop cc the heads and make sure they’re not warped or in need of milling. I  might have them do a 3 angle valve job. I’d also like install a more torquey but still very mild cam. I think maybe an reproduction “041” cam might fit the bill for what I’m wanting? If I did install a new cam, I’d buy a new set of valve springs to match the cam,  since I don’t know 100% what condition these are in. If my heads still need the pushrods holes elongated for 1.65 rockers would it be worth i machining them and installing different rockers?

I don’t want to go through the bottom end of the engine yet, I bought the heads and intake to use later down the line when I can put in better rods and do something with the compression ratio. But I figure while I have the engine apart the 6x4 heads are much better than my 7j2 heads, and a cam swap would give me good excuse to install new lifters and springs. I am open to any or all good modifications to the oil or cooling system while I have the car apart. I’ll install a crank-scraper upon reassembly. I’m looking into baffled oil pans, or possibly baffling my own. My motor has a little 5 blade. Instead of investing in a 7 blade fan and a fan clutch im gonna find a quality electric fan setup.

[b_hill_86]

Don’t see why you’d have an issue. I run a set of 6x4 heads that are milled on my ‘69 400. Can’t definitively answer your other questions though, sorry.

[5th T/A]

DirtyWhite, I am hesitant to comment on this. It sure is easier to Remove and Replace an engine with the front clip off. Replacing motor mounts on a 2nd Gen F-body is not easy with the engine installed either, so I understand that as well. Specifying a camshaft is beyond my expertise. Besides heads you need to consider static compression, exhaust system and rear end gearing. I would be concerned about putting much time and money into a 50 year old engine. The last thing you want is to put it back together only to find out it’s needs more work and have to do it all over again. If you are replacing the cam you need new lifters. More than likely the timing set needs to be replaced. You will get sucked down the rabbit hole as to where do you stop.

You are kind of caught between a rock and a hard spot. Assuming the car is running OK and you just want a little more power. I would suggest doing nothing other than tending to any oil leak problems. If you have the time and money consider at least a refresh or a complete rebuild. Why go through all the work twice.

Also the wrong cam can do more harm than good. Be cautious about your choice.

[ws6formula]

For sure you could get sucked down the rabbit hole

Pontiac used the 6x-400 heads on 77 TA W72 motor to increase compression slightly from 7.6:1 to 8.4:1 (thats per Rocky Rotella's TA book). I had a set of 6x-4's that cc'd at 97cc. Using the Wallace CR calculator
(http://www.wallaceracing.com/cr_test2.php), your CR would be around 8.5:1 with a 95cc head.

Id likely want to verify the springs in the head and take them apart to check they are ok. Of course , you could magnaflux them to check for cracks.

For cams , I ran summit 2801 cam in 78 W72 motor -I used new valve springs and had 6x-4 heads heads milled .030 - plus 1 3/4 headers and dual exhaust (otherwise pretty stock) - ran 14.30s in quarter at maybe 97/98mph? 
.
The Summit 2801 is 214 int./224 exh. at .050.,  Lobe Separation 112 and  0.444 int./0.466 exh. lift.
Another alternative could be the Pontiac 068 cam.
The 068 cam specs 212 int./225 exh at .050, Lobe Separation 116 and  0.444 int./0.466 exh. lift.
There are other cams with similar specs from Lunati , Ultradyne etc.
This page has good list comparing pontiac cam specs http://www.pontiacpower.org/PontiacCams.htm
I am guessing you have a rear gear ratio around 3.08s to 3.42s? I would think the 041 cam is too much for your
current combo.

[gstrandfarm9420]

Depending on the pistons and CR your 72 currently has, probably around 8.5:1, the different heads could lower your ratio and performance unless you take cc measurements and have them milled. I would talk to a knowledgeable engine machine shop before you do anything drastic.

[firebirdparts]

it's curious, to me, that the old 2-barrel heads had a bigger exhaust valve than a 6X has.  But I am sure that the 6X would do better.  Getting exhaust out is the easy part, I guess.

[Wallington]

On many GM heads, and  others, of the era, the exhaust was the limiting side of the head for performance. Sounds like these may be no different, only that not all models require as much intake and can benefit from it.

[tajoe]

I'm with the posters above, in that, if you don't wanna take the short-block apart to bore and install new pistons, I'ld have a hard time convincing myself a set of heads and a performance cam is the right approach. If the eng. is high mileage, and worn out, then adding more top end is a recipe for disaster. Especially if you plan on opening the secondarys. Have seen too many spun brgs in my day, when attempting this. but we all like bench racing motor builds, when the time comes to rebuild. Hope your body panels and paint work out for ya. I'ld concentrate on that 1st, unless you care to spend a few grand on a motor rebuild too.