1978 L78 T/A 6.6 Original Block?

[tom420]

Okay. I've been up, down, and around, this 1978 Pontiac 400 4BBL Trans Am issue for three weeks now and I still have no idea what block is supposed to be in my dad's 1978 Trans Am bought new from the dealership.

My dad died a few years ago and left a 1978 Trans Am, which he bought brand new from the dealership to my brother. Just before my dad died, my brother managed to blow up the original engine. My sister, worrying that my dad would find out and do unspeakable things to my brother, took the car to a "backyard" mechanic to get it back on the road before my dad found out.

The "backyard" mechanic pulled the original motor and slapped in a worn out Pontiac 301 with an adapter to bolt up the TH 350 auto which my brother promptly blew two years later, thankfully after my dad died.

Now, I've been tasked to return the car to the original numbers matching beast it was.

Unfortunately, the original block/motor is long gone so I don't have original casting numbers etc.

I need help identifying what exact block was in the original car.

The build sheet lists the motor as "L78" which some sites say was the 500557 block. Other sites say it was a 568557 block. To throw massive confusion into the mix the car has the T/A 6.6 decals on the hood scoop which I have been told ONLY came on the W72 1978 T/As. Granted my dad could have added the decals after he re-painted the car in the late '80s but I don't remember. My sister is trying to find some original pics from the '70s when he bought it.It also has the "WS6" performance package.

I'll attach the original build sheet. I need to return the car to numbers matching so I would appreciate if an expert could guide me in the right "block" direction at least.

[aussieta]

the L78 is the 400 engine,
W72 is the improved engine, which does not appear on your build sheet
someone else should know more about casting numbers

[5th T/A]

Referring back to Rocky Rotella's book, page 175. Your car with a L78 400 as noted on the build sheet would have had a block number of 500557. Mid year 1975 Pontiac switched the 400CI block number from a 481988 to a slightly lighter weight 500557. In 1977 they used the 500557 block with the W72 engine but experienced problems with main journal bulkhead failures, so for 1978 Pontiac switched back to the stronger 481988 casting.

You should be able to fin a 557 block, but unless you find the original block, it will not be a matching numbers car because the original block has the sequence number of the Cars VIN stamped on it.


A couple of other things worth mentioning.

The Turbo 350 trans that came in your 1978 TA will bolt up to a Pontiac 301 without any adapter. Both engines have the same BOP Buick/Olds/Pontiac bolt Pattern.

Why someone would go through all the work to install a Ponitac 301 is beyond me. While engine mounts are the same and the trans will bolt up. The Power steering and alternator brackets are different. Most the AC compressor brackets are different. The 301 engine has a lower deck height and intake manifold requiring a much taller shaker baseplate. All these items will have to be changed back if you wish to install a Pontiac 400. The reason I know all thois is I swaped the stock 301 out of my 1980 TA and replaced it with a Pontiac 400.

[FormTA]

Tons of valuable information there. I have unfortunately always had 301 cars so my knowledge is very limited on the 400 cars. Very interesting!

[Wallington]

I think Tom is also asking about the differences between the 500557 and 568557 blocks used on base 400's.  I don't have anything definitive, just side notes and from what John's W72 write-up said.

[stros]

I had the L78 before replacing it with an LS3.  It was the 500557 block.  While I understand your desire to return it to original, the L78 is a dog of an engine.  It has very little power and at least mine had a multitude of problems.  I couldn't save it.

If I were you I'd find an engine that you'll enjoy driving the car with.  The L78 will not be it, just to be frank. 

[langss]

Why someone would go through all the work to install a Ponitac 301 is beyond me. While engine mounts are the same and the trans will bolt up. The Power steering and alternator brackets are different. Most the AC compressor brackets are different. The 301 engine has a lower deck height and intake manifold requiring a much taller shaker baseplate. All these items will have to be changed back if you wish to install a Pontiac 400. The reason I know all thois is I swaped the stock 301 out of my 1980 TA and replaced it with a Pontiac 400.

I think I can provide a little insight into what may have happened...I didn't know it at the time... But the 78 TA that is my project, was bought as a parts car... It was hit hard on the rt front side. The guy that bought it from the Insurance Company, Thought he was buying a car that was compatible with the 78 he already had...Just because you own a Wrecking Yard...Doesn't mean you know MODEL SPECIFIC... So his Out Of California Model which he thought had the lesser engine(400) was in know way compatible with the California Model with the (403)...He was only going on the assumption that a 78 is a 78 and when he found out that nothing was usable from one car to the next...He decided to sell it. The guy that removed that Questionable Blown Up 400 and replaced it with the 301...probably thought he was cutting a fat hog... Whether the engine is any good or not...It was a 400...as compared to a 301, that may or may not have been on its last legs... In my case, the only thing the guy managed to swap from car to car, was the Speedometer and the original installed radio and speakers...And I only found that out after contacting the original owner. People do shady stuff when they think they wont get caught....

[Wallington]

Why? Because it was their quick and easy way out of adding another engine, one easily obtained and cheap and they likely had it already. Not every car is a 100 point restoration candidate, some are simply cars.

[roadking77]

Whether or not an L78, or a 557 block which most will put down, the 400 can be built with plenty of power to move the car up and down the road. Yes, new (1977/79sh) these cars are anemic compared to new (20--) cars today. However in the day just about the only car that had more power and performance was the corvette. I would think if you are looking for a Pontiac motor you will most likely have it rebuilt. The 557 block (I have one in my 77) is quite capable of more than stock h/p. This motor is fine and will run great. Would I stroke and run it on the drag strip, NO! But to cruise around its more than fine. Same can be said of an L78 motor. Stock configuration means ZIP if your doing a rebuild. Would an LS swap be cheaper maybe, as its not cheap to have a Pontiac motor built.

[5th T/A]

Why someone would go through all the work to install a Ponitac 301 is beyond me. While engine mounts are the same and the trans will bolt up. The Power steering and alternator brackets are different. Most the AC compressor brackets are different. The 301 engine has a lower deck height and intake manifold requiring a much taller shaker baseplate. All these items will have to be changed back if you wish to install a Pontiac 400. The reason I know all this is I swapped the stock 301 out of my 1980 TA and replaced it with a Pontiac 400.

I think I can provide a little insight into what may have happened...I didn't know it at the time... But the 78 TA that is my project, was bought as a parts car... It was hit hard on the rt front side. The guy that bought it from the Insurance Company, Thought he was buying a car that was compatible with the 78 he already had...Just because you own a Wrecking Yard...Doesn't mean you know MODEL SPECIFIC... So his Out Of California Model which he thought had the lesser engine(400) was in know way compatible with the California Model with the (403)...He was only going on the assumption that a 78 is a 78 and when he found out that nothing was usable from one car to the next...He decided to sell it. The guy that removed that Questionable Blown Up 400 and replaced it with the 301...probably thought he was cutting a fat hog... Whether the engine is any good or not...It was a 400...as compared to a 301, that may or may not have been on its last legs... In my case, the only thing the guy managed to swap from car to car, was the Speedometer and the original installed radio and speakers...And I only found that out after contacting the original owner. People do shady stuff when they think they wont get caught....

I understand your point. Back in the day that the original engine was probably destroyed on this car, I hung around with a group of guys who tore up their TA's. I could get a running junk yard Pontiac 400 for $200.00. It was a quick easy way to get their cars back on the road again (they were used as daily drivers). I never did an Olds 403, but if one needed replacing, I would have used an Olds 350 that would go right in and the 403 air cleaner and shaker would have worked. I never did one with a small block Chevy either, but if it needed doing I would have put in another small block Chevy. These were usually one day engine swaps because everything was the same, nothing had to be modified. Occasionally I had to pull a two barrel intake from the junk yard engine in replace it with the blown engine's four-barrel manifold.

[5th T/A]

Whether or not an L78, or a 557 block which most will put down, the 400 can be built with plenty of power to move the car up and down the road. Yes, new (1977/79sh) these cars are anemic compared to new (20--) cars today. However in the day just about the only car that had more power and performance was the corvette. I would think if you are looking for a Pontiac motor you will most likely have it rebuilt. The 557 block (I have one in my 77) is quite capable of more than stock h/p. This motor is fine and will run great. Would I stroke and run it on the drag strip, NO! But to cruise around its more than fine. Same can be said of an L78 motor. Stock configuration means ZIP if your doing a rebuild. Would an LS swap be cheaper maybe, as its not cheap to have a Pontiac motor built.

Kerry, I agree, Engine block does not determine power. The W72 400 had a different cam and I think smaller chamber heads off a 350, slightly raising compression. They also had a better flowing exhaust system and a numerically higher axle ratio. These things together made the car a lot peppier.

I personally wanted to have a Pontiac engine in my car, today there are a lot of options out there, to each their own!

[Wallington]

I think anyone who jumps into a stock 400, basic or even W72, after driving newer cars will be deeply disappointed. Only the torque is doing its thing. A mild rebuild and upgrade does wonders, to any. The typical warmed-over rebuild of these for the street doesn't require a W72 block to do so, that's just bumper stickers to impress people.

[stros]

Whether or not an L78, or a 557 block which most will put down, the 400 can be built with plenty of power to move the car up and down the road.

Sorry but I don’t think that’s correct from all of the feedback I got back before the forum crashed.  My understanding was that the 557 was known to be a very weak block that could not be built
with more power well and was prone to cracking.  Here’s a mention of this on the PY forum.  My engine may have been just old and worn out but this advice was pretty consistent.

https://forums.maxperformanceinc.com/forums/showthread.php?t=826321&page=2

[firebirdparts]

Welcome to the forum, Tom.  Glad to hear your story.  The original block was 500557 like you already heard.  The heads would be 6X, and there are two different sizes of combustion chambers available for the two different compression ratios on that.  The 78-79 cars had a unique intake manifold that you can actually spot, if you're interested in making it look exactly right.  The intake and heads are actually pretty good as built.

I don't ever blow up anything, so I don't go around the internet telling people they will "always fail" whatever.  It is certainly possible to get heavier duty block if you wanted to.

Every late 70's Trans Am that's been repainted, pretty much all of them, have a T/A 6.6 sticker on the shaker.

[stros]

Welcome to the forum, Tom.  Glad to hear your story.  The original block was 500557 like you already heard.  The heads would be 6X, and there are two different sizes of combustion chambers available for the two different compression ratios on that.  The 78-79 cars had a unique intake manifold that you can actually spot, if you're interested in making it look exactly right.  The intake and heads are actually pretty good as built.

I don't ever blow up anything, so I don't go around the internet telling people they will "always fail" whatever.  It is certainly possible to get heavier duty block if you wanted to.

Every late 70's Trans Am that's been repainted, pretty much all of them, have a T/A 6.6 sticker on the shaker.

Understand the point, but back 10 years ago we had several experienced engine builders on this site.  They sure seemed to be in common agreement about the 557 L78 being one of the weakest blocks when I was trying to figure out if I should rebuild it.  Anyways, I wasted way too much money on that engine .  But obviously there's no way to tell if the issues I had were block specific issues or just the impacts of time/mileage.

I just think if you're on the verge of making a big investment in a new engine, best to pick one of the known stronger/ more dependable options that are available. 

[Wallington]

That's true. It buys reassurance, if nothing else.

Hopefully Tom returns, because he is still asking a different question than all that being the late casting change to 568557. It's a shame getting replies in a topic for a change and not being related to the question.

[5th T/A]

Welcome to the forum, Tom.  Glad to hear your story.  The original block was 500557 like you already heard.  The heads would be 6X, and there are two different sizes of combustion chambers available for the two different compression ratios on that.  The 78-79 cars had a unique intake manifold that you can actually spot, if you're interested in making it look exactly right.  The intake and heads are actually pretty good as built.

I don't ever blow up anything, so I don't go around the internet telling people they will "always fail" whatever.  It is certainly possible to get heavier duty block if you wanted to.

Every late 70's Trans Am that's been repainted, pretty much all of them, have a T/A 6.6 sticker on the shaker.

Understand the point, but back 10 years ago we had several experienced engine builders on this site.  They sure seemed to be in common agreement about the 557 L78 being one of the weakest blocks when I was trying to figure out if I should rebuild it.  Anyways, I wasted way too much money on that engine .  But obviously there's no way to tell if the issues I had were block specific issues or just the impacts of time/mileage.

I just think if you're on the verge of making a big investment in a new engine, best to pick one of the known stronger/ more dependable options that are available.

I agree with getting the best available unless trying to get the car back to Concours or original as possible. Keep in mind there were thousands of 500557 in full size cars, Grand Prix and station wagons that never had an issue. This might have something to do with the way they were driven than anything else. What's interesting Butler sells short block kits using the 500557 block. These are probably for lower horsepower builds. But I can't imagine they would want to sell something that isn't going to hold up.

IMG_3910 by Lawrence Alexander, on Flickr

[5th T/A]

That's true. It buys reassurance, if nothing else.

Hopefully Tom returns, because he is still asking a different question than all that being the late casting change to 568557. It's a shame getting replies in a topic for a change and not being related to the question.

Sorry Ben, I am guilty as charged.

Going back to the original question, the L78 400 would be a block number of 500557. Going back to Rocky's Firebird book on top of page 174. Rocky verified with GM that 568577 was never a Pontiac part number. That part number belongs to Oldsmobile for a non-engine part. This could maybe be verified by Firebirdparts.

From what I am reading the 500557 in a 1978 F body with automatic transmission would have had a two digit block code of YA or YU depending when the car was built.

[Wallington]

Well that's interesting to know. I know nothing of it except that it gets mentioned here and there online, copied and pasted by others. His build sheet says PYU, we already knew it was the base block.

[Maxthe222]

L78 and "T/A 6.6" are two different things, like what you mentioned later on. Yes this is a WS6 car, but in this case, the W72 engine did not come part of the bundle. Your shaker would have been blank from factory, as the standard L78/L80 cars did not get a shaker decal in 1978. So many people just buy the kit from Pheonix Graphics that just comes with the T/A 6.6 decal and just throw it on. It's getting a little harder to find original 78 engines as of late as the price has been going up for them, especially W72's. Another thing is, it'll never be numbers matching without the original engine, it will just have the "correct" engine. The numbers that match are the VIN number on the body and the partial VIN on the block. If that partial VIN is not on the block in the car, it's not numbers matching.

[stros]

L78 and "T/A 6.6" are two different things, like what you mentioned later on. Yes this is a WS6 car, but in this case, the W72 engine did not come part of the bundle. Your shaker would have been blank from factory, as the standard L78/L80 cars did not get a shaker decal in 1978. So many people just buy the kit from Pheonix Graphics that just comes with the T/A 6.6 decal and just throw it on. It's getting a little harder to find original 78 engines as of late as the price has been going up for them, especially W72's. Another thing is, it'll never be numbers matching without the original engine, it will just have the "correct" engine. The numbers that match are the VIN number on the body and the partial VIN on the block. If that partial VIN is not on the block in the car, it's not numbers matching.

Hmm that's interesting.  I know for my 1977 the L78 had the "6.6 Litre" decal on it instead of the T/A 6.6.  I thought the 1978 L78 was the same decal-wise.  Sorry we're probably back off topic again, but now this thread is becoming a good history of the not often mentioned Trans Am L78 engine 

[Maxthe222]

Hmm that's interesting.  I know for my 1977 the L78 had the "6.6 Litre" decal on it instead of the T/A 6.6.  I thought the 1978 L78 was the same decal-wise.  Sorry we're probably back off topic again, but now this thread is becoming a good history of the not often mentioned Trans Am L78 engine 

The SE's for example always had the shaker decal, but for whatever reason, in 1978 and 1980, the standard engines did not receive shaker decals, as well as some other misc decals like the front bumper "Trans Am" sticker. The shaker was just blank, unless the car came with the W72 performance package or was an SE. T/A 6.6 in 1978 and T/A 4.9 in 1980.

[Wallington]

I guess we just keep chatting until Tom returns. Anyone know any good jokes?

[b_hill_86]

Two engines walk into a bar…

[nUcLeArEnVoY]

He didn't respond to his same thread on PY, either. Lol

The block that would be in your car would be a 500557 block, either with a YA or YU code stamped on it for an auto trans. People give those things away, if you want to do a numbers-matching resto, then that's to your benefit. There's services out there that will stamp numbers into the blocks to make them appear fully numbers-matching... take that for how you will from an ethical standpoint. I wouldn't worry about the shaker decal. People just slap the T/A 6.6 stickers onto those shakers all the time without realizing that they're actually reserved for the W72 cars - most people, even to this day, don't really know about the ins and outs and fine subtleties of these car's production quirks. They're also the same people that pay absurd prices for them in the spirit of speculating.

The history of some of these cars is pretty fascinating. The PWH 481988 block that originally came in my '79 W72 is long gone and was replaced by some plain-azz XA 500557 block from late '76. I can only imagine how critical a failure it must've been to necessitate replacing the superior 481988 block with the XA block, since it's takes a lot to condemn an engine block these days but it is what it is. Interestingly, only the block is unoriginal - 6X-4 heads, correct 17059263 carb, intake, manifolds, emissions equipment, air cleaner, etc. from the W72 motor are still on the car. Oh well, I have a standard bore PWH block that has been magnafluxed literally sitting in a box in my sister's old bedroom, so I guess when the time comes I'll do a build on it.

As for the driveability of my car, yeah, it's a turd. It's literally just all torque with some rear gear mixed in. At least the car looks good getting passed by everyone else, haha.