[Tom Vaught]

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.

[Steve C.]

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.


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[mgarblik]

Originally Posted by Steve C.

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.


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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?

[Steve C.]

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


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[goatwgn]

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.

[Steve C.]

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

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[goatwgn]

Originally Posted by Steve C.

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

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Good advice.

[Tom Vaught]

Originally Posted by goatwgn

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.

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.

[mgarblik]

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.

[Tom Vaught]

Originally Posted by mgarblik

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.

Marty had a NA block 455 HO I believe, that was run at Norwalk, 740 HP range, just prior to the Turbo project. He decided to stop racing the engine 'one pass before the engine failed' (He drove the car on the trailer and we saw the failures when the engine was torn down).

All three center 4 bolt main caps were cracked. #3 was starting to crack up the inside bolt hole in the main cap. #4 was cracked about 1/3-1/2 of the way up the inside bolt hole, and the #2 main cap was cracked all the way up the hole on one side.
The outer bolt and the center stud and nut/washer were the only things keeping the cap in place. It was now a 2 piece cap.

So my visual inspection of the block/main cap failure said: that the #2 main failed first, then the #4 main, then the #3 main was soon to follow.

That fits exactly with your failures in the "#2 oil feed drilling from the main saddle" with your 455 engine blocks, Mike.

Tom V.

[johnta1]

My 70 Trans Am Ram Air III was also this way. It was a WS block

Mike, would you have any block info on the WS?
(the engine unit number, cast date code, etc?)

Never heard or seen a WS with 2 bolt caps.


Steve's YZ maybe, but I would think that would be an anomaly also?

Steve any block info on it?

Were these late year TA's?

1970 generally was the only years I have seen the 4 bolt drilled blocks, with 2 bolt caps.
(but doesn't mean much either )

[Steve C.]

According to old records from 1982 my '70 Trans Am is vin 228870N115457, motor number 0518873, 9799914 YZ block. On cowl tag 22387NOR729068 BDY

And now looking at these records I think I was incorrect about the main caps in my previous post. These old notes say 4-bolt main. It came with a TH400 trans.


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