# Question on Pontiac 400 Blocks



## mrvandermey (Jun 15, 2011)

Hi guys. I have question on Pontiac 400 blocks. I picked up a second hand Pontiac 400 YS code last year. The plus side is that it is a complete engine and allegedly runs. Down side is that it is a 1972 block, and I have a 1968 car. 

Here is what I am confused about, I was under the impression that the YS code 400 blocks were essentially the same over the years and it was just the heads that were different (not withstanding the Ram Air blocks). However, a buddy has told me that the blocks were different, especially after 1971. So, is a 1972 YS 400 block essentially the same as a 1968 YS 400 block?

The engine I have is likely in need of rebuilding, especially for peace of mind if nothing else. But before I spend any money on a rebuild kit, I just want to make sure that with the proper heads, a '72 YS 400 block will perform as well if not better than a '68 YS 400 block. On ebay, I see rebuild kits for the 400, some same it is for '68-'79, while others say '72-'79. So I am a little confused here.


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## Instg8ter (Sep 28, 2010)

The blocks are essentially the same, 72 is when the emmision standards went into effect and they de-tuned the motors with larger volume heads but yoru 68 heads will work on the 72 block. The 75 and later blocks had less meat in them and are not recommended for builds approaching 500 HP.


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## mrvandermey (Jun 15, 2011)

How much better is a Pontiac 428 than a 400? Is it like the 455 where it is the same block as a 400 with a bigger bore? Will parts off a 400 fit a 428? There is one for sale around here. It is a bare block, 4-bolt main, been cleaned, magna fluxed, bored .030 over and is ready to be built. Is it worth $1,900?


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## BearGFR (Aug 25, 2008)

You can't go by the 2-character block code (YS in this case) at all. Pontiac reused the same code in different model years on completely different engines. The correct way to identify any block is to start FIRST with the 4-character date code (top rear next to the distributor) and with the casting code (passenger side rear, down low "behind" the head, on top right next to where the transmission bolts up.

And no, not all 400's are alike - not by a long shot. The ones to avoid for high performance builds carry casting number 500557. They don't have nearly as much meat/strength in the main webs as the earlier 400's do, making them iffy for anything much over 400 hp and definitely out of the question for a stroker motor.

The answer to the question, "how much better is a 428 than a 400", is zero. A 428 is not as good as a 400. Neither is a 455. Both the 428 and the 455 have 3.25" mains, the 400's have 3.00" mains. That extra 0.25" translates into a weaker block (less material in the webs) and oiling problems (more centripedal force trying to sling the oil out). That's why stroking a 400 will make you as much if not more power than a comparable displacement 428 or 455 and will also live longer.

Bear


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## mrvandermey (Jun 15, 2011)

BearGFR said:


> You can't go by the 2-character block code (YS in this case) at all. Pontiac reused the same code in different model years on completely different engines. The correct way to identify any block is to start FIRST with the 4-character date code (top rear next to the distributor) and with the casting code (passenger side rear, down low "behind" the head, on top right next to where the transmission bolts up.
> 
> And no, not all 400's are alike - not by a long shot. The ones to avoid for high performance builds carry casting number 500557. They don't have nearly as much meat/strength in the main webs as the earlier 400's do, making them iffy for anything much over 400 hp and definitely out of the question for a stroker motor.
> 
> ...


Now this is the kind of information I need to know. THANK YOU BEAR! 

I currently have a full complete 1972 Pontiac 400 (offhand I do not know the casting numbers, but do remember seeing the date code near distributor showing a '72). The engine and heads are matching. When I bought, it came out of a '68 GTO (seller went with a LS6 resto mod) and seller claimed it ran before removal, but I have not seen or heard it run. 

Since I have not seen the engine run, and do not know for sure if it runs, I plan on at the very least, overhauling the engine....might even rebuild it. But I wanted to make sure that I was not wasting my time or money with it. I would prefer a '68 block, just to be year correct, but if I rebuild the motor I have and put better heads (likely aluminum) on it, and can have a strong reliable engine, then I am good. I was just worried for someone with more knowledge than me said '71 and newer are lower compression and have lower horsepower ratings. Plus when I looked at rebuild kits on eBay, they vary, some saying from '67-'79 while others say '72-'79. So I just want to be sure I am doing it right.

On the 428, it is a '67 date code and a "SR" block. For a moment, I thought it might be interesting to have a 428. But as a bare block and crank only, I wanted to know if I could some of the parts (bolts on like intake, oil pan, starter, timing cover, etc) off my current 400 to build it up. I appreciate BEAR for telling me what the differences are.


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## geeteeohguy (Feb 2, 2008)

What Bear said. Also, a '72 block is a great block. No difference between it and a '68 block in nickel content or quality and measurements. The 'bad' blocks are the 557's, which are mid/late '70's blocks. I would much rather run a 3 inch main block over a 3.25 main block for the reasons Bear stated. Back in the old days, the 421/428/455 was sought after as a way of gaining cubes. It was the only way to do it. Stroker cranks for the smaller 3 inch main engines have made that school of thought totally obsolete. A stroked 400 will be stronger, run harder, and last longer at sustained higher rpm than a big-journal engine will. Build the '72 block with confidence.


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## mrvandermey (Jun 15, 2011)

Okay, I think I understand. A Pontiac 400 is a better choice to go with, especially with today's technology. It also appears that not withstanding the heads, there is little to no difference between a '68 400 block and a '72 400 block. Since my car is not now, nor ever will be a "numbers matching" then I should be able to use this '72 block with no problems. I think I got that much.

Next question, looking at engine rebuild kits or even rebuilt engines, I always see the piston size to be STD, .030, .040, etc ......what does this mean? When and for what purpose would I have to use over sized pistons over a standard size? Do I get more power with oversized pistons? If so, at what cost (what I am giving up or risking)?


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## the65gto (Oct 9, 2008)

mrvandermey said:


> Okay, I think I understand. A Pontiac 400 is a better choice to go with, especially with today's technology. It also appears that not withstanding the heads, there is little to no difference between a '68 400 block and a '72 400 block. Since my car is not now, nor ever will be a "numbers matching" then I should be able to use this '72 block with no problems. I think I got that much.
> 
> Next question, looking at engine rebuild kits or even rebuilt engines, I always see the piston size to be STD, .030, .040, etc ......what does this mean? When and for what purpose would I have to use over sized pistons over a standard size? Do I get more power with oversized pistons? If so, at what cost (what I am giving up or risking)?


Simply put, if your engine rebuild does not require any boring during clean up, you keep the standard size. If you have to bore it 10 over, then you need to match the pistons with the increased size of the bore.


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## mrvandermey (Jun 15, 2011)

the65gto said:


> Simply put, if your engine rebuild does not require any boring during clean up, you keep the standard size. If you have to bore it 10 over, then you need to match the pistons with the increased size of the bore.


I understand that you have to match the size of the piston to the size of the boring. But what I do not understand is when and why would you bore the cylinders in first place?


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## geeteeohguy (Feb 2, 2008)

Cylinders get worn. They get tapered, out of round, and sometimes scuffed or pitted. During an engine overhaul, the cylinder gets measured, and then bored just enough to restore the cylinder walls to manufacturer's specs. Most standard bore (never been rebuilt) engines will get a .030" overbore. Oversized pistons are commonly made in .030, .040, and .060 sizes. Generally, .060" is the maximum size for an overbore, due to cylinder wall thickness limitations. The LEAST amount of overbore is the best. An engine overhauled with an .030" overbore can be rebuilt 2 more times. Once you go past .060", cylinder sleeves must be installed, which is an expensive proposition. Sometimes one gets lucky, and the original cylinders are roughly in specification. In that case, a light hone and the re-use of standard size pistons can be accomplished.


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## BearGFR (Aug 25, 2008)

Yep - two reasons to bore a block are:
1) To get a surface that's round, clean, and straight
2) To increase displacement

(or both)

As far as bore sizes, a .030 over 400 is the same as a standard 455. About the only things what won't directly interchange between a 400 and a 428/455 are the crank and pistons - everything else is interchangeable. The crank because of the main journal size, the pistons because of the pin location. All stock Pontiac rods are 6.625" long, all the deck heights are the same too, so in order to also keep the pistons to fit in the block the difference is in the pin bore height in the pistons. If you bore a 400 + 0.030 and try to run standard 455 pistons in it, you'll find that at TDC the pistons are about a quarter of an inch down from the top of the cylinders whereas in a 455 (with a stroke that's almost a half inch longer than a 400) they'll be "just right".

The stroker set up I'm running in my car also uses longer, 6.800" rods for a more favorable rod/stroke ratio, and uses pistons that have the pin height in the correct spot so that they're near the top of the bores (I didn't zero-deck it - I needed all the help I could get to make the engine live with the iron heads I was running) at TDC. The pistons I'm running are +0.035 over standard 400. It just happened to work out that a "standard replacement" piston for "another brand of engine" had all the right dimensions and measurements to fit just right. That saved me from having to pop for custom pistons.

Bear


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## kdzee (Nov 4, 2013)

*Thanks for this info*



BearGFR said:


> You can't go by the 2-character block code (YS in this case) at all. Pontiac reused the same code in different model years on completely different engines. The correct way to identify any block is to start FIRST with the 4-character date code (top rear next to the distributor) and with the casting code (passenger side rear, down low "behind" the head, on top right next to where the transmission bolts up.
> 
> And no, not all 400's are alike - not by a long shot. The ones to avoid for high performance builds carry casting number 500557. They don't have nearly as much meat/strength in the main webs as the earlier 400's do, making them iffy for anything much over 400 hp and definitely out of the question for a stroker motor.
> 
> ...


I've been checking out the numbers on my 70 Lemans Sport which I thought had a 400 in it. I bought the car just for the engine to put in my 68 GTO. It has a YU code which is a 350. I found the engine numbers match the car so that's the good news. I have the casting code on the back of the engine 9799916 Like you said, I need to find the year next to the dist. first. Each year has different codes.


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## BearGFR (Aug 25, 2008)

There were a few engines that were one year only. Yours, 9799916, is one of them and it's a 350. It was only made for model year 1970. The YU further identifies it as originally being in an A-body (Lemans/Tempest) with an automatic transmission, single 2bbl, probably with casting number 11 heads.

Bear


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## rexs73gto (Nov 25, 2012)

I have to say I don't agree with the statement that the 455 won't live a long life. I run a 462 thats a 455 + .30 over sized. It's been in the car for about 10 years & the car runs 11:50's all day long consistant. Also remember that the 350 never came in a GTO , except the 74 which is the Ventura body which is the last GTO made. But in 68 there was still a rule in force made by John Deloeren that stated that no engine smaller then the 389-400 inch engine would be put into the GTO. But also the 428 & 455 are very good engines to use . Also be careful to watch out for the 557 blocks, they came out in late 76& were used to mid year 77 until Pontiac found out they were junk because they had taken so much material out to save weight that they went back to the original castings for the last few years the 400 was built. A 557 block is only good for stock builds of 350HP or less , otherwise there just boat anchors. The 428 & 455 give great low end torque & if your wanting to fry some tires & beat most all off the line go with the big cubes. Said then & now there no replacement for displacement.


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