Hi all, I lurk here quite often, but rarely post. I just had to share this, though.

This past Sunday afternoon I was in my shop when there came a knock on the door - fairly unusual. Lo and behold it was a friend of mine that I used to work with. He was looking for some truck parts that I had. We talked a bit and I mentioned that I was in the planning stage of an engine for my hot rod truck. In the corner of my shop I had a 1970 vintage, standard bore (but needing boring), 400 small block. It was a solid 4-bolt main block - probably the only thing that I wasn't overly comfortable about with building that engine.

Hearing this, my friend speaks up to inform me that he had been looking for just such an engine for another friend of his. That friend wanted a 400, 4-bolt main block, but all my friend had was a 2-bolt main block.

Now, from reading previous threads, I know that there are people that have strong feelings, one way or the other, about 400 engines in general and 2-bolt mains versus 4-bolt mains in particular. It's not my intention to re-ignite the flames of those previous discussions, but I would like to put my 2-cents in. I have studied the 400 engine for some time now and feel that I am qualified to do so.

The 400 engine has 2.65" diameter main bearings (large-journal) from the factory versus 2.45 for the medium-journal 350 blocks. What doesn't seem to be widely understood is that this increase in bearing journal diameter required that the main bearing cap bolts be moved outward from the crank centerline a corresponding amount. When 4-bolt main caps were used on the 400 engine, this meant that the outer bolt holes in the block come very close to - and in some cases intersect with - the lower cylinder wall. This can be detrimental when the engine is being built for high performance.

This is NOT to say that a 400 4-bolt main block cannot reliably be used for a performance application, but it does place limits on the overall power production that can reliably be obtained from such an engine.

This, in short, is the reason that I 'prefer' the 2-bolt main 400 blocks over the 4-bolt main 400 blocks - although I won't ordinarily turn down the offer of a solid 4-bolt main block. The 2-bolt main blocks just more readily lend themselves to having splayed 4-bolt caps installed - if wanted/required.

The deal: I was able to trade my 4-bolt main 400 engine straight across for a 2-bolt main engine from my friend. He got what he wanted and I got what I wanted: a win-win situation.

Just for the record, though, I think that I got the better part of the deal for a couple of reasons. The 4-bolt block I had needed to be bored, whereas the 2-bolt block that I acquired has already had the ridge at the top of the cylinders removed (slight though it apparently was) and been dingle-ball honed. I measured the bore size, taper and out of round and all are well within spec. The crankshaft looks great too. Also, this block is one of the reported few 400 blocks that doesn't have 3 freeze plugs on the side. It has a slightly raised pad where the center freeze plug would have been.

Does anyone have a good idea about how many "2 freeze plug" blocks were built? How scarce is this block.

It's a 330817 casting with T1127CTX embossed on the deck. The guy that my friend got the engine from told him that it was from a '74 Monte Carlo and had less than 20,000 miles on it.

I have big plans for this engine. I'm taking my time and doing it right. Wish me luck.

 

Wow, sorry for the looong post. I just wanted to share.

 

Congrats on your score! FWIW, I agree with your thoughts on the 2 bolt 400s. Take a look at my photos......the engine in my buildup is also an "817" block. They're pretty much a dime a dozen.... nothing unusual or scarce about them more so than any other good 400 block.

The only thing I'd recommend is making sure you have it sonic checked if you plan to bore it very much, as these siamesed cylinders will have more core shift than other blocks. A real good preliminary check for that is to look at the rear cam boss for concentricity (wow, that's a mouthfull ). If the cam bore is out of center relative to the boss, you can bet there's been a good deal of core shift! There's also a shot of my rear cam boss in my photos

 

Thanks for the comments. I'm sure that not everyone here will agree, however.

The "817" blocks are pretty common, but are all of them "2 freeze plug" blocks? That's something that I've only seen referenced in books (Lingenfelter's comes to mind). Supposedly, these blocks are "highly sought after by street racers that are trying to fool the competition into thinking that the block is a common 350.

The rear cam bearing (and front, for that matter) is a little off center toward the top end, but still pretty well centered. I already plan on having it sonic checked. I appreciate the direction, though.

Good pictures of your engine! I'm looking forward to the day when I can get mine looking that good. I've spent the last couple of evenings checking it out and cleaning it up. I want it smooth as a baby's butt inside and out (casting flash free).

What paint did you use on your block?

 

I used to own a big old Caprice Station wagon with a SB400 in it.

I'm killing myself for not pulling that engine before I scrapped the car.

Ah, the errors of youth!

 

817 that's the same block I have, I put ARP main studs in it

 

817 that's the same block I have, I put ARP main studs in it. I had a 4 bolt main too and sold it and bought a 2 bolt

 

Motorhead: Cool! Does it have 2 freeze plugs per side or 3? What did yours come out of - just out of curiosity?

 

The 400 that have 2 freeze plugs and the raised center boss are pretty common. However there are 400's (built in 1980 only I belive) that have only 2 freeze plugs and have no raised boss in the middle at all (identical to the 305/350), they are very rare (as if stock 400 blocks are not hard enough to find anyway) and much desired in the oval track racing arena as well as street scene, I have never seen a 4 bolt one, I will have to look at mine and see for sure but I think it has "509" cast in it on the side. If you do get one be aware the rear cam bearing bores are know for being a bit oversized in these blocks and most cam bearings just slide right in with very little press so pay attention to this. I've had quite a few 400's in my time and only found 2 of theses 2 freeze plug blocks with no boss. Most all of the 3 freeze plug blocks I have had are all 4 bolt main, where as the 2 bolt main are 2 freeze plug with the center "boss". I've built quite a few motors both racing quality and street quality with both 2 and 4 bolt mains and on the 4 bolt mains they do tend to crack near the lower part of the cyl wall where the outer bolts are. I built 663hp with a 23* 434 about 6 years ago that ran with a stock 2 bolt block for over a year until it cracked the main caps themselves (the customer didn't want to spend anymore money at the time), a set of splayed billet caps fixed it and its still being run every weekend to this day.
I've had a few idots try and pull the "it just a 350" on me street racing with a "raised boss block" and of course I just told the either you have a 400+ inch motor or thats a bow tie block since they are the only 2 blocks Chev made like that, and no one in his right mind would make only a 350 with the expense of a bowtie block.
Of the 2 "regular 350 looking" blocks I have one I built into a very strong 406 and sold to my best friend for his Monte Carlo it currently is on its way back up to me for freshining and a little "further inprovement". The second one is sitting in the corner of my shop awaiting a special project some day.
Will

 

I got the pleasure of riding and then getting offered the keys to Caboboy's 3.875 stroker 400 block. So it's actually a 421 ci. It's just a torque monster compared to a wimpy 350.

If that's not enough motor he also has the 100 hp or so N2O system all in place just waiting for the correct chip.

 

It's always cool to hook up with you George

We shoulda gave those gals in the parking lot a shot at the title when we left the restaurant

 

Thanks, rklessdriver (Will) That's the most complete answer that I've heard on this subject.

Mine has the center, raised "boss". It's not that I'm trying to play street racer. I was just curious about the 2-vs-3 freeze plug story. I have also heard that the lack of a middle hole/freeze plug made for a stiffer block - a plus on an engine destined to be stressed a little more than the average engine.

I also appreciate your comments on the splayed-vs-standard 4-bolt main caps, or 2-bolt w/ studs (that 663hp 434 engine 'did' have studs, no?). I'll probably end up going the splayed-main route - just for piece of mind.

Thanks again!