# Worth upgrading for 2bbl 4X heads?



## AJFrechette (May 25, 2011)

Hi Folks,

Trying to figure out if it's worth upgrading from my 2 barrel 4x heads. When i built this engine years ago I didn't do the research on what i had on the long block. The car has a 3:23 rear end and i assumed it was anemic out of the hole for this reason. But I need to pull the engine to hunt down a mystery leak (probably rear seal) and to do some housekeeping. I was also thinking about going to FI to cure what i expect is a lean condition making run hot. 

Any tips are welcome. 

Allen


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## PontiacJim (Dec 29, 2012)

AJFrechette said:


> Hi Folks,
> 
> Trying to figure out if it's worth upgrading from my 2 barrel 4x heads. When i built this engine years ago I didn't do the research on what i had on the long block. The car has a 3:23 rear end and i assumed it was anemic out of the hole for this reason. But I need to pull the engine to hunt down a mystery leak (probably rear seal) and to do some housekeeping. I was also thinking about going to FI to cure what i expect is a lean condition making run hot.
> 
> ...


Need more info on the engine specs. :yesnod:


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## AJFrechette (May 25, 2011)

Thanks Jim,

It's a 1973 400 block that's .10 over. I think the previous owner put a mild cam in it and i can't imagine it's doing that much with the small valves and low compression. It's running a quadrajet. 

Not sure there's that much else to report on this one? 

There's a set of the smaller volume 6x's with the larger valves on craigs list locally for $400...


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## PontiacJim (Dec 29, 2012)

AJFrechette said:


> Thanks Jim,
> 
> It's a 1973 400 block that's .10 over. I think the previous owner put a mild cam in it and i can't imagine it's doing that much with the small valves and low compression. It's running a quadrajet.
> 
> ...



OK, more info. The 4x heads can either be pressed-in studs or screw-in studs depending on when they were cast. IF you have the screw-in studs, I would keep the heads and have the larger intake valves installed to save some money. Read this: 4X Racing Heads - Tech Articles - Hot Rod Network

The 6x's have different chamber volumes from 93cc to 124cc, so make sure you are getting the smaller chambers. Here is a guide to chamber size: Pontiac V8 Cylinder Heads

Keep in mind that I would not simply buy the heads and expect to bolt them on and go -unless advertised as being completely rebuilt. If you buy them, first thing I would do is have them disassembled and magnafluxed for cracks - make sure you get in writing from the seller a money back guarantee if the heads are cracked or unusable.

If they pass, then I would have them rebuilt, ie resurface the heads, new valves, 3-angle valve job, hardened exhaust seats if desired (I don't feel it is necessary if going stainless steel valves), new exhaust valves, springs, retainers, keepers, & seals. Install new 7/16" ARP rocker arm studs to replace the factory 3/8" screw-in bottle neck studs (which will require polylock rocker arm nuts), install a new water nipple outlet at this time and new welch plugs.

However, your 4X heads should have 98cc chambers which will match the chamber size of the 6X with 100cc's if that is what is being offered. If they are the 93cc chamber 6X heads, then I would go that route just for that reason alone. 

But if your 4X heads match the 6X 100cc heads, I might want to think on it a little. You can have 7/16" screw-in studs installed(polylock rocker arm nuts will be needed). Have the heads resurfaced. Install the bigger 2.11" intakes and have a 3 angle valve job, hardened valve seats on the exhaust side if desired, new exhaust valves, springs, retainers, keepers, and seals. New welch plugs & heater nipple(if yours looks at all rusty). 

So if you compare the work needed to upgrade the 4X heads versus purchasing the 6X heads - you will see much of the same parts are going to be needed. The difference I see is fitting the 2.11" intakes and adding the 7/16" screw-in rocker arm studs as being the extra cost items. That is where I would visit my local machine shop and get a price on the costs and measure them against the purchase price of the 6X heads. I would think you should find a few dollars being saved and I would use the savings to put back into the rebuild of the 4X heads.

Never hurts to pick up a backup set of heads either - I have a couple sets. You can have them worked until you are ready to install them.

Power gains? Probably more noticeable in the mid to upper RPM range providing you have a good flowing exhaust system. Screw-in rocker arm studs allow you to go with a more radical cam profile without worry of pulling up/out the press-in studs. With a low compression engine as yours, I like the Comp Cams Xtreme cams ground on the 110 LSA. This is what I would install to wake up the engine if I did not know what cam was in the engine now. It may very well be a Comp Cams cam as they are often used in Pontiac builds. Used one of these cam kits (matched valve springs with the cam/lifters) in my '72 400CI 7K3 head build with low compression and was real happy with the performance of the cam. The 110 LSA builds cylinder pressure so it helps the already low 8.0 compression ratio.

So a few things to consider. I think I covered it all, but use this as a guide rather than gospel. :thumbsup:


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## AJFrechette (May 25, 2011)

PontiacJim said:


> OK, more info. The 4x heads can either be pressed-in studs or screw-in studs depending on when they were cast. IF you have the screw-in studs, I would keep the heads and have the larger intake valves installed to save some money. Read this: 4X Racing Heads - Tech Articles - Hot Rod Network
> 
> The 6x's have different chamber volumes from 93cc to 124cc, so make sure you are getting the smaller chambers. Here is a guide to chamber size: Pontiac V8 Cylinder Heads
> 
> ...





Thanks for the guidance. Mine are pressed in studs, and the seller claims the heads are the smaller 92cc size. They apparently were rebuilt 5k ago with stainless valves and roller rockers. But you mentioned that the performance difference would only be noticeable in the higher RPM's, so it might not be worth the effort. It climbs out of the hole pretty well now, but it's definitely not putting out more than 300 horse. It has a comp cam in it, but i am not sure about the specs, and it has a 2.5" exhaust with factory exhaust manifolds. As you point out, it might be worth picking these up as insurance for "down the road"...

https://portland.craigslist.org/clc/pts/d/pontiac-trans-am-ta-66-headsx/6443266872.html



Allen


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## PontiacJim (Dec 29, 2012)

AJFrechette said:


> Thanks for the guidance. Mine are pressed in studs, and the seller claims the heads are the smaller 92cc size. They apparently were rebuilt 5k ago with stainless valves and roller rockers. But you mentioned that the performance difference would only be noticeable in the higher RPM's, so it might not be worth the effort. It climbs out of the hole pretty well now, but it's definitely not putting out more than 300 horse. It has a comp cam in it, but i am not sure about the specs, and it has a 2.5" exhaust with factory exhaust manifolds. As you point out, it might be worth picking these up as insurance for "down the road"...
> 
> https://portland.craigslist.org/clc/pts/d/pontiac-trans-am-ta-66-headsx/6443266872.html
> 
> ...



OK, checked out the ad. 1977 6X-4 heads 93cc's. For $400, I would say they are a deal and I think I would be hard pressed to pass on them myself with them being rebuilt & the roller rockers/poly locks. The smaller combustion chamber will bring you closer to an 8.25 compression, so not a big increase. However, if your budget allows, I would go with a pair of Cometic .027" thick gaskets (as opposed to the typical .039-.041" gaskets) to push the compression closer to 8.5 which is a good number. Cometic Gasket - Pontiac 400 428 & 455ci V8 .027" MLS Cylinder Head Gasket, 4.160" Gasket Bore. Each 

The bigger intakes will help as I stated earlier. Roller rockers free up some HP and the poly locks allow you to "zero-lash" the lifters to maximize their operation.

Work on the advance curve in the distributor to maximize your timing and you can most likely pick up some free HP there as well.

If nothing else, I think I'd grab them if only to sit on them for a future build of my engine. :thumbsup:


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## AJFrechette (May 25, 2011)

Update:

I picked up the heads for $300, and i am going to pull the engine and just walk through it to address the dreaded rear main seal leak. i will post another question in a new thread to see if anyone can comment on a nagging overheating problem i am experiencing. But the short version is, that the car runs excellent, all of the possible weak links have been addressed (water pump plate spacing, cast iron impeller, radiator, air flow, radiator fan, shroud spacing, timing cranked to max advance possible, thermostat working right, good top to bottom radiator temp delta T's, flow is excellent) and on and on. The only thing i can think of on this is that the vehicle might be running a bit lean, so i installed an AEM wide band sensor and ran the car across a broad range of conditions (freeway, hard acceleration, part throttle, up hills, over hill, over dale, you name it) and it's running at what appears to be excellent AFR's at all demand levels but perhaps just approaching 14.7 at cruise at highway speeds. One thing i have observed is that the car heats up amazingly fast. Like crazy fast. It can jump to 180 in just a minute or so. Might be exaggerating a but here but i will time it. The car will idle all day in the hottest weather at 180. Get it out on the highway and she gets hot. Question is, how lead does she need to be before she get hot because of a lean cruise mix? I am certainly not above 14.7 at cruise. Probably closer to 14. 

Also, probably important to note that it's .40 over and the PO put a cam in it (i will check to see if it's possibly too rowdy when i yank it) but do these blocks start to run hot when they get bored out this far? Thoughts?

Thanks! 

Allen


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