4 bolt main small journal block with 2 bolt caps
 

While helping this good friend of mine with rebuilding the engine in his 1970 GTO, I ran across something I had never seen on a small journal block before. It has the outer holes for 4 bolt main caps drilled and tapped, but only has 2 bolt main caps. I have seen this dozens of times on the 3.25 inch main blocks (my own '73 455 engine in my '66 is like this), but I don't recall ever seeing it on a 3 inch journal block. The engine is a 1970 400, with number 48 heads on it. Block casting 979914. Running across a lot of interesting Pontiac stuff lately. A few weeks ago it was a '73 455 that had 4 bolt mains installed on it out of a Grandville, now this.:)

I have seen both ways on the 400 blocks starting around late 1968-1969 time frame.

Personally my favorite 400 block is the 'lowly' 67 2 bolt main (non drilled for 4 bolt mains) block as you can add splayed caps fairly easily but $$$.
The other benefit is that the 2 bolt mains will be fine for many levels of street cars and the main webs are a lot stronger without the extra holes drilled in the block webs.

You have run across some interesting stuff like the '73 455 that had 4 bolt mains installed on it out of a Grandville. When the cars were going down the line and the 2-bolt main 455 block engine was not right there at the moment, the 4 bolt main block engine got installed.

Tom V.

Same on my numbers matching RAIII 400 block in my '70 Trans Am (automatic car). Outer holes for 4 bolt main caps but only had 2 bolt main caps.


.

I have heard that the '67 2 bolt block is the best out there in terms of overall strength for an engine that bolts into the newer cars with Turbo hydramatics without issue. :)Just curious your opinion on this. Would installing short bolts with loctite in those open holes help the durability of the block? Never had an issue with my 2 bolt larger main 455 in my own car, but it is only at about 450 hp level. This person plans on adding a stroker kit to make a 461 out of it. He has a two bolt '69 grand Prix 400. I told him that would be a little bit better choice for a stroker kit. (The GPs engine did not have the outer bolt holes). He is also considering line boring it and adding Milodon main caps. The car has a 4 speed and drives it pretty hard. Thanks Tom for any input you may have.

Use ARP main stud kit. Pro-Gram Engineering main bearing caps are also popular.

.

Good advice.

my '70 YD 2bbl engine with 16 heads is drilled and taped for 4 bolts, but only 2 bolt caps.

funny you mention the '73. my buddy got a 455 out of a '73 Grandville with 4 bolt caps on it.

All 400 blocks from 68-73 or 74[somewhere around there] that I have seen have 4 bolts drilled and tapped but only use 2 bolt caps. Very common, nothing special.

My 70 Trans Am Ram Air III was also this way. It was a WS block. Back in the day, I questioned whether someone had changed the caps for some reason. Later found out this was quite common. Saved Pontiac the cost of 6 bolts, and a tiny bit of iron to make the larger caps. Possibly $1.00-2.00 per car. That was a big savings at the time. Kinda makes you sick doesn't it?

Ford did a similar thing using four bolts on the wheels instead of five.


.

very very common in 1970 blocks, I have not seen a 1970 400 block that did not have the extra holes.

Guess I haven't seen it before because most of the 400s I have messed with were either 1967-68 models or later mid to late '70s 400s. As well as 326s, 389s, a 421 and 455s.

My '72 YS block(GP) is drilled and tapped for 4 bolt mains, but my '72 YX block(Catalina) isn't. Has anyone ever heard an explanation as to why PMD did this?

I have info that states that all 1970 ra3 motors with a 4 speed in back should have been 4 bolt main.

This. I've disassembled a number of 400s from the late '60s and early '70s and all but one have been drilled for 4-bolt caps.

The one I have that is not drilled is a '74 block and it also appears to have the thickest main webbing I've seen. Should make an excellent foundation for my next 4" stroke build.

I read that same information. That's why I was so surprised when my WS stick Ram Air III had 2 bolt caps. My friends 69 Judge Ram Air III stick had 4 bolt caps. Go figure.
Almost feel they threw whatever caps they had lying around in the bins when the block came down the line. Seems to be very random. Years ago I disassembled a 400 2 bbl. and was stunned to find 4 bolt caps on it. Just weird.

I have a spare 400 (XH code) engine out of a 1970 Grand Prix that only has 5 of the 6 extra drilled and tapped holes. The 6th hole is only partially drilled. Drill bit must have broke during the drilling operation and because it was to have 2-bolt caps it wasn't worth reprocessing the block to complete the drilling and tapping of that 6th hole.

We (Marty, Bill Klausing, and I) located a 67 2 bolt main block in the late 1994 time frame.
Marty added splayed 4 bolt main caps from ProGram. (Think Marty had it 'vibra-shaken' to remove stresses in the block before the main caps and machining (caps installed).

The engine with a 250 cfm head (closer to 240) ran 6.96 et at 206 mph and lived for 3 years under high boost. It did have my old RA-IV SD forged crankshaft (prepared by Moldex). Old design Diesel Turbos and no head gaskets. Special sealing rings were installed.

At the time Donavan was the fastest pontiac out there and on the first full pass at Norwalk (with the trans skipping 1st gear and running 2nd and third gears) the car went 7.40s at 194-196 mph. With a JUNKY 2 bolt main production factory pontiac block casting.

I have a lot of respect for those 67 2-bolt main blocks as that was a real durability test on that thing.

So that is why I say it is the best common block out there.

Tom V.

We brought the Grocery Getter out in 1996 with three 1972-1974 455 stock blocks. Using Program Engineering caps. The crankshafts were stock Pontiac N cranks, carefully prepared by me with no surface treatments, just nice oil holes and large radius. Lots of tuning errors with the nitrous. Lots of time spent learning the ignition timing the engine really wanted. Even a quarter mile run starting in 2nd. gear with all that nitrous when a shift linkage part failed. Never made the kind of power Marty made, but I would argue, we may have been just as abusive to the block. We were right at 1000 HP which was allot in those days. All three blocks did eventually fail and they all failed in the same area. Right up the oil passage at the #2 oil feed drilling from the main saddle to the cam bearing. At least for us, that was the weak spot in the 455's. Overall, the Pontiac block is very tough. By the way, no lifter brace in any of the blocks. Roller cam though with .850 lift and 260 lbs. on the seat back in those old days. We also ran our blocks unfilled. Didn't want the weight, didn't want the bore distortion, did want the cooling.

70 RA III and RAIV blocks were 4 bolt mains.Tom