# What Block do I Have?



## redhorse719 (Jan 9, 2019)

Today I was looking through my stash of blocks for one suitable for rebuild for my 68 GTO. It is not numbers matching so I'm not concerned with engine codes, I just don't want to use a thin wall (late 75 & up) block. I found this std bore block and need to know if it is a thin wall block. The engine code is X7, the casting date looks like H227, the block casting, although sloppy, looks like 481988, and it has XX in the lifter valley instead of 00. Any help to determine what I have would be greatly appreciated.


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## PontiacJim (Dec 29, 2012)

"XX" typically means it is a late 1970's 6.6 Trans-Am engine - or even a cop car. Looking at the cast date code, looks to be a 1978 engine. These are good.

The bad engines, "557" will have the main cap area on the block side milled down to save weight and the main cap bolt holes going into the mains on the block will go clear through. Problems with these blocks brought out a run of the 481988 just like the early ones, but are identified by the "XX" in the lifter valley. The earlier cast blocks would have had the "00" for 400CI.


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## redhorse719 (Jan 9, 2019)

PontiacJim said:


> "XX" typically means it is a late 1970's 6.6 Trans-Am engine - or even a cop car. Looking at the cast date code, looks to be a 1978 engine. These are good.
> 
> The bad engines, "557" will have the main cap area on the block side milled down to save weight and the main cap bolt holes going into the mains on the block will go clear through. Problems with these blocks brought out a run of the 481988 just like the early ones, but are identified by the "XX" in the lifter valley. The earlier cast blocks would have had the "00" for 400CI.


Thanks PJ for the quick response. what I found confusing was the Wallace Racing website shows 481988 is a 1974 casting number but the casting date of H227 doesn't agree nor the X7 engine code. Notice that there is no EUN on the block, is that unusual? Thanks again


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## O52 (Jan 27, 2019)

From the Wallace site

400, Manual Trans, 402 cam, 6x heads, 17058266 Carb. 
From a 78 Firebird with W72 option.
The same casting number can be used over different years


8​400​220 HP​X7​M​8.1​402​6X​1-4​17058266​FB W72​


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## redhorse719 (Jan 9, 2019)

O52 said:


> From the Wallace site
> 
> 400, Manual Trans, 402 cam, 6x heads, 17058266 Carb.
> From a 78 Firebird with W72 option.
> ...


Cool thanks. That means Pontiac cast some blocks in 77-78 using an earlier mold. The chart I used on WR website only listed the 557 block cast after late 75. Pontiac Block ID Numbers. That's why I was a little confused by the casting date and the 481988 being cast 71-74 by the chart I was looking at. Am I safe to assume that this is not a thin wall casting? Thanks again 052.


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## O52 (Jan 27, 2019)

Like Jim said earlier, they brought out the old 988 casting but replaced the OO with XX to differentiate from the older 71-74 casting.
The W72 option added another 20 or so HP to the standard 400 which IIRC was on the 77 Can Am too. It was considered the last of the High Performance Pontiac engines


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## Montreux (Mar 8, 2009)

Hmm. Live and learn! Saw the cast 74 and the casting number, and thought 1974 400!


Pontiac Block ID Numbers



But then there's that pesky late '77 casting date, and the X7 code that didn't exist in 74 !?!

Looks like PontiacJim and O52 nailed it.


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## redhorse719 (Jan 9, 2019)

Montreux said:


> Hmm. Live and learn! Saw the cast 74 and the casting number, and thought 1974 400!
> 
> 
> Pontiac Block ID Numbers
> ...


They were much more help that the Wallace Racing site.


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