[Half-Inch Stud]

Main Caps get the solid match-drill pins.

Block-head can have rollpins, But I've only seen solid dowels.

I've only seen solid dowels on any Poncho engine.

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Paul Spotts]

I've only seen solid pins or dowls myself - but I'm not sure if any were 1977's.

Also the 220 HP (W72) are thick web blocks. Thin web blocks have the main cap threaded bolt holes go completely through (lack of material) and the thick web blocks do not - they are blind tapped holes. All 79 blocks (PWH) were the 220 hp thick web blocks`

on my website: http://www.spottsperformance.com/engineid.htm

I show the casting #'s of the 77-79 blocks as:

77 to 79 568557
78 to 79 (TA 6.6) 481988 xx

the 78-9 TA 6.6 220 HP blocks are completly different from the 180 HP blocks - even the 5 motor mount lugs are there (not drilled and tapped though) the "XX" is casted several places on the block and even in the center lifter valley web (like the 55 for 455, and 28 for the 428) the kicker is, the casting #481988 is the casting number for the 71-74 400 blocks - Pontiac brought back the early thick web casting in 78-9 for the W72 - maybe the roll pin dowl was used in 77 and it wasn't going to cut the mustard, hence the reborn thick web blocks? that makes sense to me.

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www.spottsperformance.com

[PONTIAC DUDE]

Paul. I have 2 77 or 78 blocks with the spring pins. Hardly any support across the main webbing area under the main bolts holes.

But they both had over 100,000 miles and the mains and rod bearings looked good when pulled apart.

First one I saw I though maybe someone changed them. But it had the factory bearings.

************************************************** ***************************

Build it fast, build it right, build a Pontiac.


http://PontiacDude.cc

[Bermuda Blue]

74Grandville:

you are wise to be concerned about your main caps. loose caps due to cracked, elongated or simply oversize dowel holes is one of the most overlooked problems when building a pontiac. I do not reccomend the "special spring pins" or roll pins. the following is an exerpt from a manufacturer's roll pin catalog

"Slotted spring dowel pins, also known
as roll, expansion, or tension pins are
a low-cost alternative to dowel pins in
applications that do not require the
strength or accuracy of a solid pin."

if your caps are loose, install oversize dowels and used main studs. if you plan to make big power (> 550) go for steel main caps. regarding the stress placed on the block by solid dowels, there is no way a correctly installed solid dowel will put stress on the block. the stress imposed on the block by the main bolts will be orders of magnitude greater than the stress imposed by a dowel pin. and if you think that because you have a later block that it is thinner and susceptible to stress, think again. contrary to what you may have heard, every 400 & 455 block i have seen (so the sample size is admittedly small) cast after 72 has a thicker main web area when compared to earlier blocks. they do have thinner cylinder walls though. this includes a 77 400 block. Odds are your main web area is nice a thick, so if you have loose caps, install those oversize solid dowels and don't worry about dowel induced block stress.

[John Witzke]

Paul the engine block casting number used for the 1977 W72 (T/A 6.6) block was 500557. My untouched factory original 11,300 mile 1977 W72 code Y6 Trans Am has the 500557 block.

I can share with you that Pontiac had problems with the 1978-79 400-cid engines including the W72 with rod bearings spun and burnt and broken crankshafts as what appears to be the result of loose main bearing caps. Pontiac was unable to provide a clear reason why because at the time the problems surfaced 400-cid build out had been completed at the plant. This is from a Pontiac memo.

John Witzke

[Rob]

Good thread discussion, I call stuff junk sometimes and people get offended. Usually it doesn't mean really bad junk. I suppose we all need to improve our language skills.

John sounds like the final authority on the production of that year 400 and his research and documention are probably unparalleled.

I've rebuilt a roll-pin main Pontiac for daily-driving type use worked fine. I was shocked a bit that they were in there & thought maybe some rebuilder replaced them, but this engine was one that you know your the first person looking at the inside since the person that put it together. Given the choice it's obvious a thicker main web and solid pin makes a stronger block. Like "Half-Inch" said they were doing it to save money and weight. Also I don't think anyone brought up the point that using main studs is a really good idea too.

The guy that invented the rev limiter could have saved a lot of those early Pontiac engines.

-Rob

[Paul Spotts]

[QUOTE]Originally posted by John Witzke:
Paul the engine block casting number used for the 1977 W72 (T/A 6.6) block was 500557. My untouched factory original 11,300 mile 1977 W72 code Y6 Trans Am has the 500557 block.

----------------------

John - thanks for that info - I'll update my web site. I only listed the 78-9 W72 blocks as the 481988 casting - From my info and research the 500557 block is a thin web block - they are the blocks my machine shop curses out.

my info on the 78-9 481988 W72 castings is from actual inspection of blocks. I haven't seen that info published anywhere - its definetly not in Pete McCarthy's book. A few years back, I had several blocks baked, shot peened and checked for cracks. I had 2 "XX" (a 78 "WC" and 79 "PWH") and a 76 400 (I think it was a 500557). The 76 was definetly thin web like Ken described - every one of those blocks had main caps that needed to be realigned - but I never noticed the roll pins since my machine shop performed the work and re-dowled those blocks. Last year, I built a 76 400 and I did get to see how bad the caps were misaligned. I will still stick to my educated guess that Pontiac, for their last "good" 400 brought back or revamped the tooling of the older 71-74 casting for the W72 cars. Makes sense that the 40 more HP cars would need a stronger block - especially because the earlier one was not up to par. Not saying the 77 and earlier 400's are junk - just the 78-9 w72 220 hp "XX casting" is better - I have some pics I'll post. I've had this info to write about in HPP as well, but forgot about it. Glad you got to John nice job. 11,000 W72 TA! - WOW that's pretty rare and quite valuable.


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www.spottsperformance.com

[John Witzke]

Thanks for your info Paul. Actually on the street there was very little difference between the 1977 W72's vs. the 1978-79 W72, maybe a .10-.20 sec and 2 mph through the quarter-mile. Probably the best all around W72 car would be the 1978 4-speed as it benefited from the use of 3.42:1 gears. All 1977 auto and 4-speed, 1978 automatic and 1979 W72 cars used 3.23:1 gears. The 1977-78 automatic cars did have a higher stall torque converter and other transmission tweaks. The 1978-79 cars benefited with the dual resonator exhaust. Basically there is no difference in the specific parts used with the 1977-79 W72 engines. In fact based on the information I have it appears the so called camshaft change for the 1978 W72 engine did not account for a 20hp increase over the 1977 W72 . Advertised output of the 1977 version and the 1978-79 versions are measured at two different rpm points. Based on the information provided by Pontiac Motor Division to the MVMA and the part numbers listed in the master parts catalog, it looks as if camshaft part numbers 549112 (1977 Automatic) and 10003402 (1978-79) may have the same specifications. (However McCarthy’s book list specifications for the 10003402 that I have never seen published anywhere else.) So in theory, it appears that Pontiac made a camshaft revision, but only in the usage and not in specifications. If Pontiac did change the camshaft specifications used in the 1978-79 T/A 6.6 engines, why didn’t they report the change to the MVMA? Remember, Pontiac supplied the information and specifications to the MVMA. It is very possible that a change may never have been recorded and or reported to the MVMA. My research on the camshaft issue is an on going process as I am recording all stamped markings as well as paint codes from each of the original camshafts.

John Witzke

[Paul Spotts]

John - the only statement, ("Basically there is no difference in the specific parts used with the 1977-79 W72 engines") I would disagree on is the blocks. The 77 recieved the std thin wall 400 block, the 78-9 recieved the thick web 71-74 version block - to me, that is a big difference in parts and probably why you see more 78's then 77's - plus I'm sure they made a bunch more 78's. After reading Rocky Rotella's article with the balancer change in 76 its all starting to make sense. As for why Pontiac had problems with the newer blocks(burnt or spun bearings, cranks etc as John mentioned) is quite easy to figure out from all the newer blocks I've built, its the main cap alignments - its like they skipped a major step in the production machining - I'm absolutely sure it was a "cost reduction" factor that came back and bit them(doesn't it always??). EVERY newer 400 I built has needed the caps realigned. I align hone every block, but hardly does an earlier block need caps realigned with larger dowls

Thanks for the info John and everyone else - you have answered many of my questions on why the newer blocks had changes and issues.

another excellent thread

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www.spottsperformance.com

[Paul Spotts]

here is the "XX" block - I think it was a 79 PWH block I had and sold.

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www.spottsperformance.com

[Bermuda Blue]

the thick-web 77 block i inspected was cast in 1977 but could have been cast in late 77 for the 78 model year since i don't recall the month of the casting. if i get amibitious maybe i'll get the casting #. very interesting how pontiac brought back the older thick-web casting. wonder who got fired for releasing the thin-web design. this info will also allow people to identify thin-web blocks - don't beat on them.

Now if we only had data on nickel content.

[John Witzke]

Paul - thanks for clarifying the thicker webs in the XX481988 blocks. This helps greatly with my research. But one question remains as to why Pontiac, knowing the 400-cid was going to be phased out, elected to go back using the thicker web blocks for such a very short period of time (only for four months of casting production).

Bermuda Blue - My research indicates all 400-cid including the XX481988 used for the W72 were only cast through November 1977. Talking to Pontiac employees who were there during that time, it appears the final casting for the 400-cid engine occurred just after Thanksgiving 1977. Those raw cast blocks were then stored, machined and assembled as needed for the 1978 orders. The orders ran fairly strong for the W72 engine in 1978 as 34,886 Firebirds (Trans Am & Formula) were built, the most popular year of the 1977-79 W72 program. By July 1978 Pontiac only had 8,690 XX481988 400-cid blocks left for use in the 1979 cars. The best information I have been able to uncover so far shows these final blocks used in the 1979 cars were machined at engine plant 9 around July 1978. Here is an example of the casting dates that I have recorded, a 1978 Trans Am produced on March 23rd 1978 with block code X7 and cast date K077 (November 7th 1977), and a 1979 Tenth Anniversary Trans Am produced on February 18th 1979 with block code PWH and cast date K187 (November 18th 1977). What is interesting is the block in the 1979 car was produced November 18th 1977, just 11 days after the block in the 1978 car while both cars were produced nearly one year apart. To date, no factory original W72 Firebirds have been documented with block cast dates later than November 1977.

John Witzke
Member Society of Automotive Historians
POCI Tech Advisor
1977-79 W72 Performance Package Historian

[Paul Spotts]

figured I'd bring this topic back up. just had a customer requesting info on engine adapters. I explained how some newer blocks have the lugs - they just need to be drilled and tapped. He ends up having a W72 block from a 78 TA 4 speed car. here is the numbers:

engine code: WC
unit number: 28N119887
date code H227 (august 22nd 1977)
casting: 481988XX

Also, there is a big 74 near the distibutor area. That is the 1974 block id - the last year of that casting. That makes me think that Pontiac realizing the issues with the thin web blocks brought back the latest tooling in thick web blocks for their "last hoo-rah" or it may be better said as to have something hold up for their performance offerings. Makes perfect sense, why put out weak castings in an engine producing more power that the factory knows will be thrashed. Smart business and a major headache eliminated for recall reasons. Good job Pontiac - way to end the 400 in style.

[Held for Ransom]

I looked at my 1978 Trans Am X7 block (K037) and saw no 74. And it also has spring pins for dowels.

[Paul Spotts]

Held - what is your block casting number? Maybe the only thick web castings were on the 4 speed motors or maybe its a random thing. Pontiacs have such interesting mysteries

[pippintook]

I recently purchased a 1978 TA W72 4spd with WS6. I am doing a full engine rebuild. What I have observed about my engine is as follows:
1. engine ID = WC
2. block casting number = 481988
3. block casting date = K077
4. block has 5 engine mount points
5. block was cast at GM5
6. all main cap dowels are solid
7. xx in valley pan
.
I purchased this TA from the original owner and the engine was all original before I took it apart. I am uploading pics.

[pippintook]

Here are some engine pics

[pippintook]

more 72 engine pics

[pippintook]

w72 block casting date

[pippintook]

w72 engine