Hi all

My thoughts were picking up a block and doing a 383 over the next year and I was talking with a buddy of mine about it. He has 2 400 motors he has been sitting on for 10 years. One is complete motor and trans he is keeping the other is a fully assembled lets call it a long block 2 bolt mains.

He has offered me the long block for free but it was seized and he pulled the heads and such and oiled it up and the buttoned it back up.

I also seem to have a rotating assembly I can get a hold of. I do not know a lot about it yet but here is what I do know.

lightweight 3.750 stroke Crankshaft, Lightened ,Gun drilled
8 eagle h beam forged con rods 6in. centre
arp bolts full floating pins
8 srp 4.165 forged flat top pistons and pins
set up for 1/16 x1/16x 3/16 rings
Assembly internal balance

Rotating assembly would cost me say 1k.

So I guess my question is take my time and stay on the 383 path over the next year or pick up these parts and have the 400 checked out?

Is it even worth beaking down the 400 block and having the machining done to find out if it can go .040 over?
As well I would want to go roller cam if I can on such an old block?


Well hopefully I can learn something from the replies.

Thanks

 

Is the rotator assy 350 mains or 400 mains? The cranks are different sizes.

 

Good question, I will have to ask.

Can a 350 even be punched to 4.165?

 

It might be wiser to just buy a Dart block. As to $1000 for a rotating assembly. I would like to see the purchase price.

 

if this is for mild HP, up to 5500 rpm
it is worth sonic checking the 400.

 

No, a 350 can't be bored that much. 400 blocks have simeise cylinders (they're connected instead of separate for cooling jackets). So you have two chooses, get a 400 block if its a large main crank or do what I would do, go to PAW or Summit and order a 383 balanced rotating assemble for a 350 block

 

No.

 

I have an email into the guy about the rotating assembly.

The type of crank will give me a good idea of the purchase price of the assembly. Since it has 4.165 bore pistons I assumed it was a 400 crank kit as I thought you could not bore a 350 that much.

That being said the SHP block has 350 sized mains?

My thought was to stick to a 350 and go 383 but my buddy and I were throwing around the idea to build both 400's as he has a street rod and wanted to use the 400 in it.

As for the build I was going for 6K max RPM and in the upper 400 torque range.

 

okay, I'm confused

You want to destroke a 400 block? (it is a nice combination of large bore, short stroke).

I guess, were it me (and it might be after I get a couple other projects done) I'd stroke the 400 block to 427 or 434 (bore plus stroke) and use an external balance crank.

The biggest issue with the 400 is the siamese bore - that point between the center two cylinders gets hot in performance builds and can cause all sorts of head gasket problems (personal experience on this issue).

That said, 400s are a great motor - but whether it's a great motor for your car will depend on what you're looking for

 

No, he wants to build a 408.

 

That's correct the 400 stock stroke is 3.75 I believe. This build really is a bore .040 over mind you this kit has 6'' rods which are longer than original as I understand it.

As stated which is around 408ci.

Really all I want is a reliable build to the above numbers if that requires not using a 400 then so be it, it was just an option I thought I would let you guys tell me if it was reasonable.

 

CarCraze, I'm not a 400 block fan. stock blocks kind of have a
500 some HP main web limitation. 4 bolt main caps, angle bolt main caps, and billet main caps like what I have on my 383 are bandaids.

The 400 is weaker than a 350 block and then you are talking about an additional .040 over bore. By the time you pay for all the machining the aftermarket blocks become more attractive in price. They are thicker and can do the bigger over bores.

 

if you can get away with it, don't bore a 400 except to clean up the bore.

the 400 is a (very) good truck motor; they can be made to perform, but the detriments (cooling issues), that most Corvettes that perform well trade hp for torque, and IMO you'd be far happier with a 383 based on a 350 block.

not sure why someone says weaker block; if anything they'd be stronger because the center two cylinders are tied together and tied to the block - but I don't know much so it's probably something new to me

 

.030 over bore is the normal limit for a 400 block .the 2 bolt blocks are good for converting to 4 bolt.use head studs ,less likely to crack the cylinder walls .

 

I do boosted things - so heat is a really big issue. The block can be bored .060 over (they do make pistons), but the wall gets so thin next to where it's siamesed that the motor will come apart in a variety of entertaining ways (as long as you're not the owner of the block - then it's not so entertaining).... but the A number one way of problems with the 400 comes from the gasket between the center two cylinders, it'll melt first.... but unlike a fuse, the car can keep running long enough to cause this:



I really need to snap a picture of the block, it's quite entertaining (to everyone but me - actually, I find it entertaining now, it reminds me what "too much boost" and "not enough gasket" looks like)

 

The OP said that the rotating kit was a .040 over bore 4.165.

The 400 crank mains are a bigger diameter taking strength out of the core of the block. years ago when people tried adding stroker cranks like 3.875 to make 415-421 ci the crank shafts broke because of block and main cap flexing. GM even saw the problems and made the original Bowtie blocks as did others back in the day like Rodeck, Donavan, and several other aftermarket manufactures...... Keith black.

Just like big block chevy has a power limitation and when it was reached with the back in the day drag racing blown/nitro cars. The stronger block Chrysler Hemi and Fords were what was used for racing

 

Well with most of this discussion I will have to leave the 400 block.

Now I have to convince my bud if he wants to do 2 engines he should leave his other 400 where it sits. Probably make a good motor for his boat though.

Any thoughts on a Shafiroff 434, I know there is a short block up for sale but it has 9 passes on the rebuild, which concerns me lots can happen in a pass?

It uses a world products block O ringed, Lunati rods, 4" stroke eagle crank.

I have read due to the rod angles they are not that reliable?

I have never really dealt with a 434 SB before, thought it looked interesting.

 

They can be plenty reliable they just wear a little faster
Price you pay to go fast.

 

You need to do some math before you make blank statements.

What is the the rod angle of a 400 SBC with a 5.565 rod?
a 350 with a 5.7, not to forget 351 Fords.

I ran 9 back to back 1/4 mile runs on my 434 this summer and I decided to drive home because I could smell a little clutch and the wheel hop made it not worth continueing. My 420# new mono spring was not stiff enoungh compared to my over 500# steel

 

I was just quoting some of the material I have read, that the angle is fairly steep.
Also that due to the deck height the wrist pin is into the oil ring because of the 4in stroke not sure if that factors into reliability or even if that is the case.
I was unable to do the math as I am not sure what that unit is running for rod length as I had not gotten that deep into yet.
These type of engines are new to me back in the day all we ever played with were 355.

That being said I want to do this once and having a reliable engine at the mid to upper 400 area is what matters most. I figured a race preped 434 tuned down to be steetable may be fairly bullet proof.

Not sure even what a short block like that is even worth at this point I assume new would be in the 5k area.

There are quite a few 350 blocks closer to home, most seem to be of the older style though.

Just checking options with the people who know the most.
Once I start the plan I hate changing.