[geeteeohguy]

As an auto tech in the industry working at a shop that worked on all makes in the 1980 era, my experience mirrors what Brad stated. We were doing major engine repairs on 1-2 year old domestic cars and the sales of Hondas and Toyotas and Datsuns was really starting to take off. For good reason. All those cars seemed to need were brake jobs and oil changes. The domestics? Cranks, cams, heads, you name it. On top of all the electrical problems. 1980-1990 was indeed the nadir of American auto manufacturing.

[hurryinhoosier62]

Originally Posted by 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...........

Cliff, your explanation makes perfect sense. Cast iron that has been overhardened would be more prone to cracking, especially in the hellish conditions of the combustion chamber. I remember attempting to locate mid 1970s SBC heads that weren't cracked when I was going through tech school in the early 1980s. It wasn't an easy task.

[eodcoduto]

I didn't know that my question would stir up so many emotions! I appreciate the responses and advice, especially since it comes from long standing SME's in the field. My plan for now is to do a basic re-ring and deck the heads to 90cc then run it. The car is a 455 factory car so I will patiently be on the hunt for a 455 while I drive the 400 and keep working on the rest of the car. I'd love to daily drive a 12 second T/A but that's not realistic in my opinion, and I don't mean just cruise a few miles but as the only car, all weather every day driving.

[F ROCK]

FWIW: in 1971 The YS 400 engine found in the GTO was rated at 250 or 300hp with 96cc heads and the 067 cam.
It does have the larger exhaust valve; not sure how much that matters at this level.
I had one for 20 years. It burned rubber on demand with 3.08 posi; and ran great.
So if you could mill your heads to 96 cc or less, you'd give your engine a pretty respectable bump in power, and stay very budget friendly.

[eodcoduto]

That sounds like a solid solution to what I am trying to get done. I need a new cam anyway and from what I can find the torque is around 400 on the '71 GTO so I could live with 375 with my smaller valves.

Originally Posted by F ROCK

FWIW: in 1971 The YS 400 engine found in the GTO was rated at 250 or 300hp with 96cc heads and the 067 cam.
It does have the larger exhaust valve; not sure how much that matters at this level.
I had one for 20 years. It burned rubber on demand with 3.08 posi; and ran great.
So if you could mill your heads to 96 cc or less, you'd give your engine a pretty respectable bump in power, and stay very budget friendly.

[F ROCK]

I dont think the smaller exhaust valve is going to make a bit of difference at this level, but i'm not an expert.
I've got a 464 with 041 clone cam, and 6X-4's with the smaller, 1.66 exhaust valve. Runs great. I dont race it so I cant say when it runs out of breath, but it will burn tires all the way down the street.
As Brad or someone has mentioned, the '64, '65, (and maybe '66?) GTO's all had smaller valves, and 300+ HP.

I dont disagree with Steve; the bigger valve would be nice; but if you're hoping to someday upgrade the heads; i'd just do the minimum.
Agree with the others who said build the best bottom end that fits the budget.
I've only owned one pair of 4x heads. Mine weren't cracked but the other members have seen more heads than me.

[unruhjonny]

I have somewhat compressed the OP's initial post;

Originally Posted by eodcoduto

...here is my situation. ... my (car is a) '74 T/A ... I swapped him for his 1973 Y4 400 with 4x-4 heads and some other parts. This was done because ... it is ... closer engine to factory ...
So this sweet Y4 400 is the 180hp 2bbl version, 55K miles with a stock bore, crank, rods and a ton of crud from the little old lady driver. But there isn't a ridge in the engine and the bearings are good.

I know that I can shave the heads to my goal of 9.2 compression, but I am looking for other options as well. I am keeping the 8 valve relief pistons so my math says I can run 72cc heads and hit close to my goal, but I always ask for other options first. ... There is a set of 7k3, and I won't run headers so that may work. This is a super cheap build, gaskets and bearings and make it run is all I'm after now. Any advice is appreciated.

When I first read this I figured that this would get somewhat derailed by well intended members about making more power - and I wasn't terribly surprised by the conversation that followed.

There is a member here who constantly makes great post that seem to go against the flow - for good reason;

Originally Posted by Cliff R

For those of you worried about not having big valve heads it's not really holding things back anyplace on a build like this. ...

BINGO - NAILED IT!!

Originally Posted by F ROCK

I dont think the smaller exhaust valve is going to make a bit of difference at this level, but i'm not an expert.
...

Again, nailed it.

honestly, these engines make great torque, even in the low hp configurations.

Back to the OP;
I have found that searching for cylinder head cc ratings can be confusing - because they are often wrong.
It has seemed to me that PMD when in two year cycles - that is they essentially made the same drive trains for two years;
Generally 1971-1972 motors are rated at 8.4:1 compression
Whereas 1973-1974 are rated at 8.2:1 compression
I say this because you are considering 1973 vs 1972 heads;
Those 7k3 heads will probably make a smidge more compression than the 4X heads, and as pointed out they do have large valves.
According to the Wallace racing head page, the 4x-4 (350/400) heads are 99cc, while the 7K3 are 96cc.

I have run like a couple others here have, small valve heads on my car's motor, and was surprised with how little difference it made;
My take away was that engine compression and camshaft play much bigger roles than valve size.

If I was you (eodcoduto), I'd run the 4x heads, because those are the correct castings for your Trans Am.
I'd be sure to at the very least clean them up well with what ever tools you have available, and inspect for cracking - not because you have any reason for concern, but because you have the engine apart, and this is a good time to find if you have any potential issue.

That engine picture to me looked like factory cast slugs, and even though some (more or less) scoffed at them, they are great parts and were used in nearly all the pre-smog engines including the RAIII - so I'd take any scoffing at the idea of using cast slugs with a grain of salt.
If you decide to get new slugs, stay away from the ones with more valve reliefs - only because those will lower your compression.
If you decide to clean up the engine, and leave the short block alone, I wouldn't fault you - it is after all only a 55k mile engine that ran fine (I understood that correctly - right?)

You can play with deck height (if the block will see any machining);
You can play with cylinder head milling (if the heads will be resurfaced);
You can play with head gasket thickness.

All three of those will help you bump compression - if you want to do that.

If you will humour it, I'd suggest leaving pretty much everything as-is, and replacing that '255 cam with something slightly bigger like a 066 or a 067 - but don't go too big.
It reads as though same year 066 cammed 400/4bbl motors were rated at 200hp (+20), while 067 cammed 400/4bbl motors were rated at 230hp (+50hp).

Please let us know what you do, and the results.

[SD455DJ]

Originally Posted by eodcoduto

I didn't know that my question would stir up so many emotions! I appreciate the responses and advice, especially since it comes from long standing SME's in the field. My plan for now is to do a basic re-ring and deck the heads to 90cc then run it. The car is a 455 factory car so I will patiently be on the hunt for a 455 while I drive the 400 and keep working on the rest of the car. I'd love to daily drive a 12 second T/A but that's not realistic in my opinion, and I don't mean just cruise a few miles but as the only car, all weather every day driving.

Eodcoduto, That sounds like a good plan. I know I'll get flamed for this, but we used to 'shade-tree' rebuild engines when we were young and poor all the time. We would tear the short block down, dingle-berry ball hone the cylinders, install new rings (cast iron Hastings IIRC) on the old pistons, new bearings with a hand polished crank (emery cloth - shoe shine style), get the rod big ends checked at NAPA machine shop (reuse the rod bolts!), and degrease and power wash the bare block & heads at the quarter car wash. Then put it all back together. We had a friend that was in school for becoming an auto tech, so we used tools he could borrow for the shop. They always seemed to run really good and made a lot more power than before the rebuild! Throw in a new Summit 2800 cam and you'll be making 250 hp no problem.

Dennis

[unruhjonny]

Originally Posted by SD455DJ

Eodcoduto, That sounds like a good plan. I know I'll get flamed for this, but we used to 'shade-tree' rebuild engines when we were young and poor all the time. We would tear the short block down, dingle-berry ball hone the cylinders, install new rings (cast iron Hastings IIRC) on the old pistons, new bearings with a hand polished crank (emery cloth - shoe shine style), get the rod big ends checked at NAPA machine shop (reuse the rod bolts!), and degrease and power wash the bare block & heads at the quarter car wash. Then put it all back together. We had a friend that was in school for becoming an auto tech, so we used tools he could borrow for the shop. They always seemed to run really good and made a lot more power than before the rebuild! Throw in a new Summit 2800 cam and you'll be making 250 hp no problem.

Dennis

I've done less than that many times over;
if the engine didn't seem to have any short block issues, I"d just clean up the gasket surfaces, and swap top ends.
I've never had a problem from doing that;
If you take you're time, and don't rush things, it's pretty straight forward.

[eodcoduto]

I’ve done that a few times as well, and have a Chevy 366 I’m doing the same to now for my C/60. As long as the tolerances can be kept it a great way to keep an engine going. Buying all new top of the line everything sound cool, but isn’t realistic for the majority of rebuilds.

[SD455DJ]

Originally Posted by unruhjonny

I've done less than that many times over;
if the engine didn't seem to have any short block issues, I"d just clean up the gasket surfaces, and swap top ends.
I've never had a problem from doing that;
If you take you're time, and don't rush things, it's pretty straight forward.

Yeah, you could just leave well enough alone (the shortblock), other than I would carefully degrease it with by hand with a degreaser spray and scraper, taking care to regularly wipe out the cylinders as you go and keep any goo out of the bottom end...done that too...lol!

Dennis