dtorc4

What are the pros and cons of using a 400 block rather than a 350 block? I know about the steam holes, but what else? I have AFR 190 heads, I assume these would work for a 400. I will still keep the TPI setup. Please help! :confused: :cheers:


[Modified by dtorc4, 9:52 PM 12/27/2001]

danno85

Here are some thoughts for you.

First of all, finding one these days is a problem. I think they were last used
in production vehicles around 1975. The 2-bolt block was more desirable than
the 4-bolt main block because it was thought that the outside main cap bolt
holes weakened the block somewhat. The 2-bolt main caps have large angled
sides kinda like the 2-bolt big block caps, and the 2-bolt block is a good candidate for fitting with splayed main caps (which strengthens the block
because the outside bolts are pulling at an angle).

The cylinder walls are not very heavy even though they are siamesed, so you
definitely do not want to go more the .030 over. Even still, depending on your
application, if you really want to make alot of horsepower then you might be
hampered by some cyl wall flexing which will allow for some blow-by and oil
control problems. If you really want to use a 400 sbc block, the best thing to
do would be to have a dozen to choose from and have the cylinder walls all
sonic checked for thickness, and choose the best of the group based on that.

With a bore that big, the head bolts are getting pretty close to the cylinders
and so it is even more critical that the cylinders be honed with a torque plate.

The main cap bolts are spaced a little farther apart because of the larger main
journal size, so if you want to run a windage tray mounted on main bolt studs
you will have to slot the holes in the windage tray to get it to fit.

All 400 sbc blocks will be left hand (drivers side) dipstick. Not a problem if
you are running long tube headers, but won't work with factory exhaust. Just
something to keep in mind. (the oil pan will have to be for a left hand tube
as well).

I don't know much about aftermarket cranks, but the main journal size on
the 400 is larger and thus the main bores in the block are larger. So, you
would either need a crank with "400" style main journals, or buy special
expensive spacers to go in the block to allow using "350" size main bearings
and crank.

If you do go with the larger bore 400 block, you can (and should) open up
the combustion chamber of the head around the valves to match the cylinder.
This un-shrouds the valve and allows the engine to breath a little better.

Hope that helps some.

Dan

Nathan Plemons

Not that I'm an expert on the matter, but it seems like it would be a lot less grief to just build a stroker out of a 350 block. If you get the right block you can go all the way up to a 427, and everything would still fit together just fine.

That's what I would do, but the 400 would be an interesting project.

CFI-EFI

I agree with most of what Danno85 says. However, it isn't that the outer bolts weaken the block. The two bolt block has thicker main journal webbing, that is thicker, stronger hulkheads. I think Danno85 is a little too critical of the cylinder wall strength, but better safe than sorry. There are a lot of 406's powering various forms of race cars, so I think cylinder wall flex must not be too big a problem. I would reccommend that you have your heads drilled for the steam holes. Personally, I don't understand all the 383 hype. They definitly are an improvement over the 350, but why would you want to cut 0.200 off of your main bearings and give up a eight inch of bore? BTW, Chevy produced the 400 from 1970 to 1980. That's MY take on the subject.

dtorc4

Building the engine is not a problem, as I have found a short block already w/ brand new lunati I beam rods, speedpro forged pistions with coated skirts, and a steel crank (don't know the brand). As far as installation, will all the accessories work in the serpentine style setup?

CFI-EFI

YES

MrJay

All stock 400 engines are Externaly balanced and because of that they had to have a special balancer and flex plate but some people have had internaly balanced there engines so they can use the old stuff that they have.
You nead to as this guy that has that engine if it is internaly or externaly balanced because if it is Int. then you can use most of your stuff (maybe you have to get a different flex plate) but if it is Ext. then you have to get a 400 balancer and a 400 flex plate, I think the 400 balancer is 8 inc so Im not sure if it will fit but they may make a Ext. balancer that is smaller.
The 400 will run a little hotter then a 350 so you will have to have the cooling system good and clean.
I hope this helped a little.

Jay

The Green Rocket

How the 400 sbc could end up being so misunderstood by Chevy lovers is a mystery that's sure not to be answered soon. Perhaps it is because some enthusiasts wrongly built them while ignoring the differences from the 350; steam holes, external vs internal balance (aftermarket has complete availability of internal balance 400 components), etc. A more common mistake would be to undercam the engine; add 50 cubes and the engine will want a larger cam all things held equal.

Want to see what these 400's can do, just go down to the drags where they can often be found. On two different trips to the California Hot Rod Reunion held at Famosa i have had the pleasure of seeing a "nostalgia" front engine dragster trip the light to a track record high 5 second 1/4 mile (remember, I'm talking about a record for a front engine nostalgia style dragster) - the engine in both instances was a 406 (400 + .030 overbore) smallblock in typical supercharged nitro burning configuration.

Just a note, a 427 cube smallblock is usually based off a 400 style engine with a 1/4" stroke, not usual to build a 427 cube smallblock from a 350 block.

Here is why many racers like the 400: the larger 4.125" cylinder bore size allows the use of larger valve diameters without the same valve shrouding problems associated with a 4" bore 350 block. An engine is just an air pump, anything that enhances airflow potential like larger valve sizes and less valve shrouding will lead to larger power numbers.

Oh yeah, for those who haven't noticed, you will be seeing more of these 400 smallblocks, rather than less. Because both Dart and World products have their own versions of the 400 block. Bill Mitchell Hard Core Racing is also offering "crate" 415 or 427 cube engines based off the World casting (Bill Mitchell IS World Products).

Thomas

black bart

Congratulations Green Rocket after reading so much misimformation it's good to see that someone has some knowledge of the 400. When deciding what size engine to build remember what Smokey Yunick said about it.
NO SUBSTITUTE FOR CUBIC INCHES

Monty

"NO SUBSTITUTE FOR CUBIC INCHES" except for BOOST. Even better is CUBIC INCHES AND BOOST! ;)

Anyway. I would definitely recommend stepping up to an aftermarket block like the Dart or GM Rocket block if you're going to build a serious 400+ Sbc stroker. The cylinder walls, decks, main webs, bulkheads, etc are all thicker and offer increased strength and stability compared to any production block. While their initial purchasr price is higher, consider that all they need is to be honed to size to fit your pistons, all other dimensions are within .001" already. Included is splayed steel 4 bolt main caps. Also the option of a taller 9.325" deck is something that should be strongly considered. I went with the 9.325" deck, 400 main, Big blcok cam bearing, Dart block. The 9.325" deck height will allow you to run a 6.125" rod, even with a 4.0" stroke, yielding a respectable 1.53 rod/stroke ratio. For comparison purposes, a 5.7" rodded 383 has a 1.52 r/s ratio. Other features like a raised camshaft position allow you to run a stronger standard base-circle camshaft, and you don't have to worry about rod/cam intereference or grinding rod bolts. Also with the .800" spread pan rails, you can run up to a 4.125" stroke without needing to clearance the pan or the pan rails. With a 4.00" stroke, all I had to do was notch the bottom of the bores with a small 1/4" diameter notch, didn't touch the rails at all.

Contrary to what World and Bill Mitchell imply in their Motown block advertising, spread pan rails and raised cam locations do not add significant costs to your engine build up. Summit sells a pan that fits in their catalog for less than $250 with alot of the tricks. You can get a custom aluminum pan with all the tricks for about $300. A Cloyes tru-roller timing chain for the raised cam is less than $100, about $10 more than a standard timing chain, and a standard timing cover fits perfectly fine. Dart, GM and Edelbrock sell intake manifolds that fit the tall deck blocks for just a few $ more than a standard deck intake manifold.

By the time you find a production SBC 400 that hasn't already been overbored, doesn't have cracks, and go through the expense of sonic checking, magnafluxing, boring/honing and any other machining like decking or align honing, you will rapidly approach the cost of these blocks. Add in the cost of converting it over to splayed main caps and you're right there. Then consider that the aftermarket blocks can be bored out to 4.200" and still have cylinder walls over .300" thick, and it becomes the logical choice. Once a SBC400 block is overbored .030" to 4.155", most of them cannot be overbored again.

dtorc4

What if it is already bored .060" over? Is this too much? Is the block still reliable w/ this much bore, assuming everything is ok?

The Green Rocket

dtorc4, I take it that the engine that is available to you is bored .060 over? Usually the 400 production blocks that have been bored out .060 are best used in a drag racing application where they can have the block cooling passages partially filled with hard block for better cylinder bore stability. Now the aftermarket blocks can take much larger overbores and still have good cylinder wall thickness.

I would not yet be in a hurry to pass on that +.060 400 engine. The big issue is cylinder wall thickness, or as a less obvious issue, cylinder bore casting shift. Since it is a short block assembly I am going to ask you to take a look at the lifter bore area (as a proxy for the actual cylinder bore core shift, if any). As you look at the lifter bores, see if they look like they are off center in relation to the casting - if so then you are virtually certain to have a block with core shift. So, if the lifter bores appear to be shifted in some direction in relation to the casting, then the same is likely to be true of the cylinder bores in relation to the casting. Not as accurate as a sonic wall thickness check, just a quick way to wade through a pile of potential core engines for a performance buildup.

Thomas

Monty

Like Green Rocket said, you can get an idea by looking for evidence of core shift, but a sonic check is really the only way. If the bores are already .060" over, I'd focus on sonic checking the thrust sides of each bore. I've seen some that were as thin as .090" or less. That's pretty thin and would probably lead to some cylinder wall movement which would negatively affect piston ring seal.

I'd recommend discussing it with your machinist or engine builder and see what they think with regards to the power level you want and the application. You could fill it up to the bottom of the freeze plugs and that would certainly stabilize the bores. However, keep in mind that the block is on it's last rebuild. It definitely can not be overbored again if it is already .060" over. If the block requires any significant machine work, that might be something to consider.h