[25stevem]

To me it goes like this.

Are these motors with there low compression power houses.no!
But with a 4 bbl carb and in factory stock form they would still haul around a 4400 lb Grand Prix ok as a
daily driver, which is all that the OP wants out of it at this point!

Now if he chose’s to reuse his 4X-4 heads and it needs a valve job ( very likely) and some new valves ( likely also ) then why not go with the bigger intake valves and get 1.5 CCs closer to having a gain of .5 of a compression increase?

A gain in compression is not a guarantee of more power across the given motors full power band because there are many factors involved, however a increase in compression will always provide more low end and a better idle due to increased vacuum, and better fuel mileage which is getting to be very important again since we are once again forced to unnecessarily but energy from the Middle East and Putin!

It’s a win win if you have to go that route due to not finding a plop on set of 75 to 78 CC heads.

[scott70]

I remember years back I had a 67 lemans I raced. Had a 400 with 4x heads. Raced it quite awhile like that so I knew what it would do in the 1/8th mile. Buddy of mine had some 670 heads so I swapped them out from the 4x and touched nothing else. First time out back at the track it went. 5 second quicker and 5 mph faster. People were asking me what the hell did you do to your car! It went from running the best of 8.3's to running 7.8s.

[25stevem]

That’s all fine and dandy and thanks for sharing your findings and the details, but once again the OPs post is getting hijacked once things go into taking about racing.
The OP just wants a reliable motor to take him the 22 miles to and from work 5 or whatever days a week!

If he can get a little more pep while in the mild clean up and rebuild process. Then that’s icing on the cake for him!

You can certainly rebuild a set of 4X heads for Less then the cost of a ready to drop on set of 670 heads, so I kinda don’t see your point here, although once again I do appreciate your info as I am sure others here do also!

[scott70]

My point is it does sound like performance is somewhat what he's asking about!! If he didnt care at all I'm sure he would just put the 4x heads on and be done with it. Just showing what can be had with bigger valves and a bump in compression only. Get it???

[Stan Weiss]

Using weight of 3875

60 Foot ET = 1.9353
330 Foot ET = 5.3758
1/8 Mile ET = 8.2896
1/8 Mile MPH = 83.5410


60 Foot ET = 1.8531
330 Foot ET = 5.0768
1/8 Mile ET = 7.8248
1/8 Mile MPH = 88.8247

needs 68 HP more

Just how much did that change increase your CR?

Stan

[scott70]

Probably around 1.5 to 2 points,,,guessing.

[70KGOLD]

Don't forget about 350 5c heads. These will work good for you.

[hurryinhoosier62]

Originally Posted by 25stevem

To me it goes like this.

Are these motors with there low compression power houses.no!
But with a 4 bbl carb and in factory stock form they would still haul around a 4400 lb Grand Prix ok as a
daily driver, which is all that the OP wants out of it at this point!

Now if he chose’s to reuse his 4X-4 heads and it needs a valve job ( very likely) and some new valves ( likely also ) then why not go with the bigger intake valves and get 1.5 CCs closer to having a gain of .5 of a compression increase?

A gain in compression is not a guarantee of more power across the given motors full power band because there are many factors involved, however a increase in compression will always provide more low end and a better idle due to increased vacuum, and better fuel mileage which is getting to be very important again since we are once again forced to unnecessarily but energy from the Middle East and Putin!

It’s a win win if you have to go that route due to not finding a plop on set of 75 to 78 CC heads.

WHY would you do that when 6X-4s would be a better choice over the 4x-4s?

4X-4: 99cc chamber
.030 milling would reduce chamber size by 5cc with a straight mill (.005-.006 per 1cc)
4X-4 after .030 milling: 94cc before the valve job(usually adds 1-3 cc)
6X-4: 93cc chamber
.030 milling would reduce chamber size by 5cc with a straight mill
6X-4 after .030 milling: 88cc before the valve job.

[25stevem]

Could it be because he does not have a set of 5C or 6X heads ready to plop on!!!

[hurryinhoosier62]

Originally Posted by 25stevem

Could it be because he does not have a set of 5C or 6X heads ready to plop on!!!

6X-4s are rather easy to obtain; I have two sets in the garage. Purchased them for $100 per set.. You seem to be forgetting about the 4X head's cracking problems. The 4X is not a core I would even consider using.

[MarkS57]

Originally Posted by hurryinhoosier62

6X-4s are rather easy to obtain; I have two sets in the garage. Purchased them for $100 per set.. You seem to be forgetting about the 4X head's cracking problems. The 4X is not a core I would even consider using.

I found a set of 6X-4's cheap by using car-part.com. Search for cylinder heads for a 1977 Firebird 350 P.

[25stevem]

Get real hear folks!!
If you find a set for 100 bucks that’s really great !, but are you just going plop on that 100 buck set of heads, no!

So now your into the the heads for 100 bucks, getting them gone thru by a shop to get at if your lucky a cost of 450 bucks to get them bearly usable again , and then if you had to get them into your hands by being shipped, that’s another 100 buck at a minimum!

Now your up to 650 bucks that could have been well applied into his 4X heads if they pass a mag test.

15 minutes of work with on the deck of each head rolling over the needed sharp edges will stop any future cracks from taking place as long as the motor does not over heat badly!

[hurryinhoosier62]

Originally Posted by 25stevem

Get real hear folks!!
If you find a set for 100 bucks that’s really great !, but are you just going plop on that 100 buck set of heads, no!

So now your into the the heads for 100 bucks, getting them gone thru by a shop to get at if your lucky a cost of 450 bucks to get them bearly usable again , and then if you had to get them into your hands by being shipped, that’s another 100 buck at a minimum!

Now your up to 650 bucks that could have been well applied into his 4X heads if they pass a mag test.

15 minutes of work with on the deck of each head rolling over the needed sharp edges will stop any future cracks from taking place as long as the motor does not over heat badly!

Not an engine machinist, are you? 4X heads are notorious for cracking, period. Doesn't matter if they've been overheated or not. BTW...it's YOU'RE, not your and barely not bearly. So, you are ASSUMING that the guides are all good, the head decks are straight and true, the valve springs all meet spec and the valve seats and valve margins are correct. What IF they're aren't? You will then be spending the same money on cores of dubious integrity. Most 4X heads crack in between the intake and exhaust seats. HOW will breaking casting edges stop this? Paul Carter and a couple of other Pontiac engine machinists and builders I know have surmised that this cracking occurs due to the 4X castings being too thin in this area of extreme heating. Cast iron "work hardens" just like aluminum does. Run a lean condition, you just magnified the problem. 6X castings don't have this problem.

[TAGTOboy]

Spelling lessons aside, I would make this suggestion. Why not build a street commuter engine with the best pieces available and within the budget today so that in the future all one would need to do would be upgrading the cam, heads and possibly ignition plus retuning for added performance? Yes, two-stepping the journey to performance can be more expensive by meeting today’s parameters now and a different set in the future. But, it may be the most reasonable way to having his cake now and eating it down the road.
Build as stout a short block as you can and top with inexpensive , reliable top side parts. Have faith that in the end you will enjoy the car now and again when you finish upgrading.

[25stevem]

Let me unpack a story for you!
I have seen all casting number Pontiac heads crack, for one.
In the shop I worked in that handled a large network of towns in the mid to late 70s I came across 4 sets of cracked 4X castings , and 3 of them had cracks inbetween the valves and one set did not.

As it turned out the 3 sets of the heads with the between seat cracks where off of a local Towns police department detective cars, yes they had 3 Catalina’s in the detective car pool, pretty cool!

This police department also had a piss poor mechanic on the pay roll who would see problems and let them fester until a issue , a major issue in fact came about.

He did this of his own words for job security, and of course this info only came out after he was fired for being this way.

Anyway back to the heads .
This mechanic let the rad hoses in these cars fall apart, then when they would break down on the road he would go out to the fetch the car, not with the town tow truck, but with with new upper and lower hoses and 4 or more gallons of water.

He would refill the cars cooling system while the motor was still overly hot and then start the motor!

This is what cracked 5 out of six these heads that came off of this towns detective cars, the thermal shock of being red hot and then having cold water pumped back in!

The 4th set of cracked heads that I saw while working there did not crack between seats, it cracked from the center head bolt boss across the deck and into the chamber of cylinder 6.

This head also came off of a known badly overheated motor.

I don’t think that 4X castings are as overly inclined to cracking as many have said and if the OP here wants to reuse his heads and they pass a mag test I would go ahead and use them after touching them up as I have posted before here.

[25stevem]

And allow me to argue this basic point as to why there seems to be so many cracked 4X heads, how about the simple fact that there where so many of them in use in 1973 and 74!

In 73 for example every 400 and 455 made had a 4X heads other then the California 400 that had 4C heads for emissions and of course the cast number 16 heads for the SD455.

When you look back to 74 you see the exact same thing, and when you add up the two production years that’s a hell of a lot of 4X castings !


In 74

[Formulabruce]

Couple points to the OP
1. Mid '73 they moved to screw in studs, 4X can have either.
2. I have and have run 4X heads and WITH-OUT the EGR set up, the 2bbl is a great DD engine.. Why?
They were built for low end Torque, which probably has 300 at a low rpm that you actually DRIVE in...
3. Will do better with the big factory 2bbl. Adding a secondary that the engine, which wasn't built to do high RPMs, is a waste with not much improvement, if any.
4. Clean and inspect the heads, lap the valves, install positive exhaust valve seals, ditch the EGR, keep the intake and carb. Put in a little better than stock cam, made for low end like a XE250H ( IMHO for a DD
This way you can AFFORD gas and it will set you back in your seat)

[tinindian646]

I ran a set of 11 casting # off a 69 350 heads on a 400 block. 10.5 to 1 compression . thats 80cc heads on stock bore an stroke from sd performance. ran 12:84 in a 64 Catalina

[Cliff R]

The main reason we see a lot of cracked cylinder heads (not just Pontiac) in 1973-74 is due to the hardening seat process the factory was implementing at that time. They actually started induction hardening seats late in the 1972 model year run for some engines. I've seen later production Chevy "487X" castings with obvious "raised" and hardened exhaust seats and all the "993" heads that replaced them in 1973 will have hardened seats. I suspect, and this is just a guess on my part supported by talking to a few foundry employees that worked at GM in that period is that they hadn't quite perfected the casting methods or hardening techniques used to protect the exhaust seats from the "new" unleaded fuel that was coming out at that time.

For sure they got better at it because by the mid-1970's it's not nearly as common (with some exceptions) to find GM heads with cracked seats. It didn't help either that the two center exhaust ports are cast together and put a LOT of heat on those seats, which is where in almost all cases where they will be cracked. My uncle, who worked as a tool & die maker for GM in one of those plants at that time told me that when they were made aware of the cracking exhaust seat issues they changed a few things with the casting and hardening process which pretty much solved those issues. He said that they added material in those areas to the molds, slight change to the "recipe" for the base material, and flipped them over during the casting process to concentrate more material in and around the exhaust seats. A quick change to the quenching process and good to go.

I was pretty young at that time but already bit by the bug to own, drive and build fast cars. When he came to visit we had long talks and I would remember stories like that. He had another one about the switch from forged cranks to "N" cranks and how the "N" cranks were and are incredibly strong. He told me that they increased nickle content to the base materials and those cranks were not only incredibly strong they could take constant "cycling" without cracking or failing. He told me that the cast "N" cranks were also better than forgings for "harmonics" or dampening and fine for high performance use and in some applications superior to the twist-forged units they replaced.

He was also there when they were asked to lighten up blocks, cranks, heads and other engine parts to save weight and material costs, which he was not fond of and said it was the beginning of the down-hill run for the excellent V-8 engines GM had been turning out for decades. Just some history on these things as I remember it, I'll take a disclaimer on the accuracy but it's not too far off what was going on with GM in that time period...........

[Sirrotica]

FWIW, I had a friend in my hometown that did valve jobs at his house, back in the late 70s early 80s. Many of the garages in town would send their heads to him because he was real quick on the turn around and may have the heads returned 1-2 days. this was at the height of the GM tune ups that usually consisted of a camshaft (went flat) lifters, timing gears, valve job and possibly some guides in the heads.

To further enhance his turnaround time he had some good used chevy 305, 350 heads on hand so if he found cracked heads, he would just sell them a good used core.

One of the local wrecking yards would pull cylinder heads for him off of the core engines, and give him a bunch at at time. He and the owner of the wrecking yard knew each other, and he would take them home, sort through them and pay for the good cores, then return the cracked, unusable cast iron back to the yard for scrapping.

One time he picked up a whole pickup truck load of cores, took them home to sort out the good heads. Out of at least 75 cylinder heads, he got 3 good heads. That is how poor the SBC heads were at the time, just as Cliff has said from the info he got from his relative that worked for GM.

I was working at a dealership at the time, and doing side work at home for extra income. I would do at least one of these jobs a month, and as many as three a month. If a SBC got 50,000 miles without going into the engine, you would be very lucky. As Cliff has said, the beginning of GM losing their market share by cheapening the process of making their engines that were known for running 100,000 miles with zero problems, before the accountants started calling the shots.

It was good for the mechanics at the time, but terrible for the owners that many times were still paying off car loans when their only form of transportation needed $600- $1200 worth of work to the engine. It turned a lot of GM loyal customers off, because GM wasn't warrantying any of the repairs. The off shore cars really started selling at this time, because they ran forever without any major engine repairs. Toyota, Nissan, etc. only problem was the bodies rusted out quickly, but their drivetrains were just fine. A car owner could sling some bondo to get another year or two out of the body, and not have a $1000 engine repair bill starring him in the face.