One of my buddies recently got a 400 block.He just got the block.

It needs anew sleeve in it.So he is going to resleeve it and have all the machine work done.I have a good 350 crank.

Whenever you build a 400 with 350 crank do you use the 400's rods or the 350's.I know the 350 has a 5.7 inch rods.Does the 400 have a 6.0 inch or a 5.940?Also I believe I have a set of 400 heads.The thing is the casting # says they are either for a 350 or a 400.I know the 400's had steam holes in them.How can I tell if the heads I have the steams holes?

Also since the 350 is internal balanced and the 400 is external whenever you put the 350's crank in it.Does that make it internal?also are the main journal sizes the same or are there special main bearings?


Thanks

 

You want to use the longest rod you can. I can't really explain why, but in the magazine i was just reading (Hot Rod) it was something about compression height.

 

Is this going to be for a street car? If so I would leave it a 400. He is giving up un necesary cubic inches and torque. I believe the rods in a 400 are 5.65. The rods you use will depend on pistons also. I will not guarantee this, but if you use the stock 400 pistons I think you could use the 5.7 rods with the 350 crank if you went that route but I have never done this. If you use the 350 crank it would be intearnally balanced I believe, but the journal sizes are different but I dont know exactly what they are.

Ben

 

You can use the 350 crank and it will be an internally balanced assembly. You would use a 350 flywheel or flaxplate and a 350 balancer. It is also correct to use the longest rod you can. Mine uses a 6.0 rod. In order to install a 350 crank in a 400 block, you must use either main bearing spacers or special thick bearing made for this swap. Building a 377 this way is like having the good ole 327. You make great high end power and can rev it to the moon.

 

He is not sure yet what the motor is going into.He has a 1970 ford truck that he was going to build up.Then he decided it was to ugly to build.So now he wants to build a 67-72 chevy and put it in that.It will be street driven.But he wants to it be quick.He really wants to beat me.

I am building up a vortec headed 350.So he decided he wants to beat me.

Either that or he wants to build a tube chassis with dana 60 front and rear axles.Put it in that and go 4-wheelin with it.

 

I talked to him more about it last night.He says the 400 block is a 4 bolt main.Which I know is pretty rare.I read somewhere that the 400 2 bolt main was really stronger than the 4 bolt.How can this be true?I didn't understand it.

We where looking price wise at which would be cheaper.And with me having the crank and rods.(5.7 350 rods)It would be cheaper to build the 377.I found the correct pistons for this.I just couldn't find the right main bearings.

How much hp are guys making with 377's?And how high do you have to rev it to make power?He is buying a 1970 chevy with a 327 in it and he is trading me the 327 for my crank rods and helping him build the motor.So it looks like a 327 is going in my camaro.

 

There are no "right main bearings".

However, Comp and a couple of other sources have "bearing spacers" that you put in the block and then put regular 350 bearings into.

All you need then, is a stock 350 crank, stock 350 rods, and stock 400 pistons. It makes basically a 350 with 1/8" overbore.

 

400 2 bolt main stronger than a 400 4 bolt main?? Survey sayssss..Nope. Im not sure what type vehicles the 400 4 bolt main came in but I do know it came in the 74' chevy caprice wagon. Dear old pops owned one and it had the 400 4 bolt main with qudrajet carbie with faux wood paneling..jesus that thing was a beast...lol..later

 

400 2 bolt stronger than a 400 4 bolt??? YES they are correct. the 400's had fairly thin webbing where the mains bolted up to it, by drilling extra holes into the already thin webs all you do is weaken them. the caps are good and strong but the webs pay the price for it. 350's are different because they have much thicker webs from the get-go.

 

I thought the 2 bolt 400s had more webbing at the mains than the 4 bolt plain and simple, but i could be wrong. The factory 4 bolts were straight mains, instead of splayed too i think. This means that a 2 bolt that is machined for SPLAYED 4 bolt mains will be stronger. Thats just what i heard tho.
matt

 

The 4-bolt blocks were the early ones. They do in fact have less metal in the main web area. They can easily be identified by the 3 freeze plugs in each side. The later blocks, with only 2 freeze plugs like all other small blocks, have more metal, but were only fitted with 2-bolt main caps. Those make a better foundation for a high-HP stock block motor, by adding aftermarket splayed center main caps.

 

there was a post in the drag racing forum called "destroker questions" that i put up, it'll answer alot of your questions...

 

RB83L69 There are no "right main bearings".

However, Comp and a couple of other sources have "bearing spacers" that you put in the block and then put regular 350 bearings into.

All you need then, is a stock 350 crank, stock 350 rods, and stock 400 pistons. It makes basically a 350 with 1/8" overbore
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In theory, You need a special piston for a 377 to get the right compresson height. this will vary depending on rod legnth. Please let me explain.....

Longer rods are better as they let the piston exert more leverage on the crank thereby turning the crank with less effort, a longer rod also slows pistion travel at the top and bottom of the stroke. This helps the piston maintain cylender pressure during compression, and helps the cylnder fill on the intake stroke..... I can explain this in detail if you wish....

All SBC have a deck height of 9 inches. (9.025 to be exact). Lets say for discussion that the 400 with stock rods (5.565 inches) and stock pistons, and 400 crank (3.75 inches) has 0 deck height. If you switch to a 5.7 inch rod with the same pistons and crank the piston will now come .235 inches above the deck. Once you swap in the 350 crank (3.48 inches) the piston will move 1/2 the stroke diference back toward the crank. In this case .135'' (3.750-3.480= .270 270/2=.135) this will still leave the stock 400 piston .100" out of the block.

If you went to a 6.000 rod the piston would be .400' out of the block. A 377 piston will have the bore of a 400, but the wrist pin hole will be closer to the top of the piston (.100" with a 5.7 inch rod, .400" with a 6.0 rod etc) to keep the deck height at zero.

If you ran the 400 pistons on the 5.565 rods with the 350 crank the pistons would be below the deck .135". Therefore a piston with a taller compression height would be needed to maintain 0 deck height.

Hope this helps.

Bagz

 

Two bolt blocks are stronger that 4 bolt blocks because of the bolts going into the main webbing. You can have your engine builder splay the main caps and this makes the outer bolts go into the block webbing. The bolts are splayed on a 20 degree angle. The more meat you can keep in a high stress area the better off you are. The 377 ci motors are a rev to the moon engine. We are using them at the dirt tracks because they give up torque when you are coming out of the turns ( less likelyhood of blowing the tires off), but they have a great rush down the straights. Awesome.:rockon: :rockon: :rockon:

Hopes this helps.

 

9.025" = stock deck height

So take a 350; the stroke is 3.48". ½ of the stroke which works out to 1.74", plus the rod length of 5.7", plus the "compression height" of the piston (the distance from the center of the pin bore to the top surface of the piston) which is 1.56", equals 9.000". This leaves the stock nomnal deck clearance of .025"

Now look at a 400. Same deck height of 9.025", and the same 1-9/16" (1.56" approx) compression height. The stroke is 3.75", ½ of that is 1.875". So, 9.025", minus .025" deck clearance, minus 1.56" compression height, minus 1.875" journal offset, leaves 5.565"...... which just happens to be the length of a 400 rod.

Note that the sum of the journal offset plus the rod length, is always a constant number, if the compression height is the same. Since a stock 400 piston and a stock 350 piston have the same compression height, then all you have to do to make a 372 is to put a stock 350 crank into a stock standard bore 400 block using bearing spacers, with stock 5.7" 350 rods, and stock 4.125" diameter 400 pistons with stock 1.56" compression height. A 377 is the same thing except bored .030" over. That combination worked fine the last time I built one.

Less time reading magazines, and more time actually doing the things you're talking about, would teach you what works and what doesn't.

I don't know why everyone has this thing about how a 377 will "rev to the moon" just by virtue of being a 377. True, it has a large bore-to-stroke ratio, so there is less reciprocating loss compared to power output; but the laws of physics still require that the induction system flow the required amount of air in order to produce useful power at high RPMs, just the same as any other motor. The RPM range it will run best in is still determined by the cam, heads, intake, and exhaust, far more than it is by the short block dimensions. If you take an otherwise equal 400, 383, and 377, the torque curve only shifts a few hundred RPMs from one to another.

I know of no possible way to splay existing main caps in the field. However, you can buy splayed main caps from Milodon, Callies, and others, and a competent racing machine shop can install them into a factory 2-bolt block. These are available for both the 400 main journal diameter and bolt spacing, and for the main diameter and bolt spacing of all the other small block motors.

 

well, RB83L69, The reason that a 377 will," rev to the moon," is because of the large bore and short stroke and the favorible rod to stroke ratio. Much the same way a 302 will rev very freely and make upper rpm horsepower. I was trying to demonstrate that the person starting this thread might want to consider putting a different motor in that truck, of his friends. A 400ci or a 383 might be better suited. More torque = getting that truck moving alot faster. Not trying to flame anyone. Also I misspoke about splaying your main caps. You cannot splay a cap. You can just drill the block to the 20 degree angle that I mentioned earlier. They have machines that will do this or some have a fixture that will mount on the block and a normall drill will do the work. My $.04:rockon: