Me and my friend are in a little spat here at work. Is there any visual differences between a 350, and 400? Will 350 parts fit a 400? And lastly, how many teeth would a 400ci flexpate have? Anyhelp is appreciated.

Yes,
There are visual differences externally to tell a stock 400 SBC, and also a 400 block...

A stock 400 has a balancer with a "cutout" area for the external balance. it is not uncommon now to build one internally balanced using a neutral balance damper...

The front of most 400 blocks have little cating "circles" all around the front freeze plug area...

Also,
they all had 168 tooth flexplate/flywheels, and only have a staggered bolt pattern.

The little known identifying method is that the external block walls are swelled slightly at each cylinder to make room for coolant flow, so the blocks outer sides are not flat.

Wow ... I have one on the stand now and thought I knew them pretty good. I never noticed the extra width for the water jacket! I take a look at those "casting?" circles around the front frost plugs as well... Its likely I haven't noticed because I don't have any 350s kicking around to compare it too.

If you can see the casting #s on the back you can of course ID them that way as well.

all factory 400s (except the 509 casting) have 3 freeze plugs on each side instead of two...
But, as Jake said, the quickest tip off with a factory engine is to look at the balancer.

You've got me scratching my head though Jake. I'll have to look this evening at the 511 block I just bought. I could have sworn that it uses a straight pattern starter??

[This message has been edited by HEAVYchev (edited October 07, 2005).]

the 400 main journals are bigger also. but i think you can run 350 rods (5.7" long) with the right piston (wrist pin location).

<font face="Arial,Verdana" size="2">Originally posted by HEAVYchev:
all factory 400s (except the 509 casting) have 3 freeze plugs on each side instead of two... </font>

That is only correct for 4 bolt main 400's The early blocks had 4 bolt mains and 3 freeze plugs. Later blocks were 2 bolt main and had only two freeze plugs.

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Mike T. 71 RS/SS

Alright... Now things appear to be getting REALLY confusing.

I just walked out in the garage and looked at my bare block sitting on the stand. The numbers cast in the block at near the oil pressure port are " 3951511 ".

This indicates it is a 511 block. It is definately a two bolt main, and it definately has three freeze plugs on each side.
The starter pad, has 3 tapped bolt holes, kinda triangular pattern?

Definately 400 bore, definately has steam holes.

Not trying to argue with anyone, but what gives? Seems like there must be many variations, and few sure fire ways of telling besides the balancer, casting #s, or measuring the bore.

front tires off the ground at launch!

I think the 73 year engines were two bolt with the three freeze plugs and still the high alloy iron. Later engines had only the two freeze plugs but you'll see a pad or swelled area where it would have been as I recall.

<font face="Arial,Verdana" size="2">Originally posted by XxWickeds10xX:
Me and my friend are in a little spat here at work. Is there any visual differences between a 350, and 400? Will 350 parts fit a 400? And lastly, how many teeth would a 400ci flexpate have? Anyhelp is appreciated.</font>

Look for a Small Block Chevy that has "509 "511" or "817" as the last 3 digits of the engine ID on the back on top

Hijack in progress!
What's the deal with the 817 blocks? Good, bad?

I work at a machine shop and we have pretty much seen all the variation of 400 with 2 or 3 freeze plugs. however the quickest ID is that even if there is not a 3rd freze plug there is a raised par of the casting where that freeze plug should be.

Hope this helps. James

Yup, the freeze plug count isn't a positive ID. And Jake neither is the starter bolt patern,, I have a 509 and just built a 511 for a buddy and both are drilled for both (straight and staggared) starter bolt paterns.

The one positive thing I've seen here is what badazz said...

the 400's casting numbers ended with "509', '511', or '817' There wern't no others, and there were no other sbc's that ended with those 3 digits.

Getmore... here's the general consensus: Some fact, some fiction, some just rumor

3951509 cast between 70-71 was a 4bolt main block, cvast from 74-80 was a 2bolt main block.
The best of the best is a '509' casting with the 010/020 identifiers on the back of the block and under the timing cover. Any '509' casting with 2bolt mains is the most sought after and is reputed to be the strongest main web, thickes cast core of the 400's We have a member that works at one of the GM foundarys and he says the 010/020 is not really a true indicator of the casting material. I have heard reputable stories that in the 70's it was, but how long that carried who knows. A 010/020 indicates the percentage of added tin and nickle to the iron casting. (allows some flexability wothout cracking and adds strength) Many sbc's had the 010/020 indicating the 'full treatment' of alloy additives, others have just "010" indicating less additions,, those with no identifiers being a GM spec material casting,, which isn't a bad deal at all.

3951511 cast from 70-73 was a 4bolt main, but some replacement blocks had 2-bolt main caps. The 511 2bolt main is another of the more desired castings.

The '511' casting is the second favorite. Rumor is it has more tendancy of core shift and thinner cylinder walls than a '509', some improvements that came with the '509' (most notably in the main web area) were not present in the '511'.

330817 cast from 72-80, all are 2bolt mains

The '817' had the worst reputation of the 400's. It is said to be sorely lacking in the metalurgy department. "Soft as Butter" is how I heard one machinist describe the 817. Even this is one the the desired 2bolt main castings, it has a poor reputation and is notorious for cracks in the main web and cracks across the deck between the bolt hole and the cylinder,, and . With that said, this 'least desired' 400 casting is alive and well in many HP applications.

All of the history, rumor and old wives tales aside. A word of asvice. If your considering doing the 'splayed main in a production 2bolt casting' Here's a little fact for ya. I just had a 509 casting short filled with hardblock, bored and honed with a deck plate, zero decked, I supplied a set of splayed main caps and had them fitted to the block, then the main bore align bored and honed. Add baking the block, jet washing, installing cam bearings.... Cost me $1370. For $500 more I could have had a brand new Motown block, add $200 to that and it could have been a Dart block. There is simply NO COMPARISON between a GM production casting and the strength, material, priority main oiling, billet main caps, cylinder thickness (most can be safely bored to 4.200) and rigidity of an aftermarket block. If you are looking for a serious block, don't waste your time with the GM production 400 castings,,, none of them. Go straight to a Bowtie, Motown, Dart,, etc. In the long run you will be WAY ahead of the game. If your needs don't take you to high side or 400 or 500 HP, most any of the GM productions castings will generally tolerate that just fine. Nothing says it will survive and nothing says it WILL fail. It's just a matter of rationality. You don't want to put an expensive rotating assembly, high HP combination in a production casting that has a reputation of problems. Be it fact or rumor,, it's not worth the risk IMO

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Yep to what Marv said. In the Seattle area, I just had all the aforementioned work done on a 511 4 bolt block. I had the cylinder walls sonic checked and they were all in a range of .23 to .25 inches thick with minimal core shift. The machinist was very surprised at the thickness. However, while this should be a good block, I should have went with an aftermarket block for what I have invested in this monster.