Excuse my ignorance regarding GM block design....

but,
whats the difference in the 350 and 400 block castings?

and, how far can you go with the 350 2blt block as far as safe boring/stroke with crank kits ?

I ask because I wanted to build a 406 BUT I am having a hard time locating an appropriate 400 sbc short block...a roller/hyd ready to go is almost unheard of around here. I have found a couple, but 1 is a 30 yr old mystery that has been laying in the dirt/weather for 29 yrs...and the other is somewhat a mystery but the guy wants wayyyyyy too much for an unknown.

Also whats here has to be retrofit lifter etc..

Piles of 350 sbc blocks laying around. Whats the practical limit to this block?

I am willing to do the machine work to a 350 as long as its going to remain solid...I don't want to end up with something that will crack like glass the first time it gets stressed or overheats.

My current 350 is oversized (45 or 60, I forget on this one) and that alone created heat issues. I wanted to avoid anymore of that if possible.

Are 400 sbc cast with larger water passages? different?


TIA

 

GM 400s have weak webbing in the mains weak decks etc. Not made for high rpm useage

Do some guys do it and have good luck and seem to last a long time
sure
Others can crack from merely torquing down head bolts after a fresh build.

Crapshoot imo really others will have different opinions.

A 4 bolt 350 can take a pounding even with the stock caps. 3-5/8 crank gets you a 396, 3.75 stroke gets you a 383

4" bore on the 350 4.125 on the 400

 

If you can swing it, a Dart or World Products block will come fully machined with thicker bores that can take enlarging. They have priority oiling. You'll spend more for the block but save on machining and have a stout motor that can take a few overbores. If you want to spend even more, there is the GM Bowtie block...

 

I do not really agree with the above comments. A 400 SBC is a fine performance engine (in my opinion), and is no stronger or weaker than a stock 350 block. A 350 block is a 4" bore and can be bored safetly to 4.03" but some people go higher. If you sonic check the block you may be able to bore it more. A 400 block is a 4.125" bore and can be safetly bored to 4.155" may be able to go higher if it is sonic checked.

Where I live they are fairly easy to find, use craigslist and you can probably find a few. I have five of them and use two of them for performance applications. The other three I have just collected over the years as good deals.

 

The 400 uses siamesed cyl walls. This can trap steam in these areas. GM drills a relief hole in the deck and head to allow trapped gases to escape preventing hot spots. AFR has good instructions for the procedure. I always drill the holes, most of the ones I have built (probly about 10) are for short oval. A lot guys feel it is not not necessary. GM felt it was necessary. I see it as kina like lookin down the barrel of a gun, you dont have to unload it, lotsa guys didnt n they are fine. But its still a good idea to unload it.

 

this guys at Tri star Engine use Dart block for their crate.you can order a 406 cid with Dart aluminum heads, forged internals,10.2 compression and a mild street cam for $ 5.500.It came with valve cover ,harmanic balancer,fully assembled and dyno tested ready for an intake and you have 500 hp and 500 lb/ft...
http://www.tristarengines.com/catalo...der-heads.html

 

The 400 was produced with a 4 bolt main for a short time in the early 70's. The remainder are 2 bolts, and non were produced with factory roller cams. The main journals are slightly bigger at 2.65 from the others at 2.45 after 1967.

I agree with going aftermarket here. Just the roller portion saves $400 from aftermarket lifters. And, as already mentioned additional machining costs for clearances.

 

Thanks, but nobody really answered the question directly...

someone DID state that the 400 block can be bored further..............WHY?

the question stands......

What is the difference in the 350 block casting and the 400 block that makes the 400 take a bigger bore? water passages? because the cranks are the same fit, whats different about the block?

I guess to simplify... why can't a 350 block be bored to 4.125 ?
Another way of putting it...
If I bore a 350 to 4.125 what is different compared to a 400 block that comes at 4.125 ?

What makes the 400 sbc block accept the big bore? are the decks different? liners? what?

That's what I am trying to learn here. That will help me make a decision to take a 350 to the limit OR keep searching for a 400 and spend the cash to upgrade it to roller hyd.

BTW, the intent is a winter build project. If I just wanted to have a 'built' bad-*** motor ready to drop in I WOULD go buy a DART short block..I was staring at them all friggin morning. I found a doz or more 500+hp that were drop-in's...not interested. I want the "Build" part..the HP will be the result of THAT, not a shop.

This is to be a build. Not a race ready install. There is no fun in buying someone elses engineering and then claiming that you "built" it. Some guys do that...I won't.

TIA

 

Thanks, but nobody really answered the question directly...

someone DID state that the 400 block can be bored further..............WHY?

the question stands......

What is the difference in the 350 block casting and the 400 block that makes the 400 take a bigger bore? water passages? because the cranks are the same fit, whats different about the block?

I guess to simplify... why can't a 350 block be bored to 4.125 ?
Another way of putting it...
If I bore a 350 to 4.125 what is different compared to a 400 block that comes at 4.125 ?

What makes the 400 sbc block accept the big bore? are the decks different? liners? what?

That's what I am trying to learn here. That will help me make a decision to take a 350 to the limit OR keep searching for a 400 and spend the cash to upgrade it to roller hyd.

BTW, the intent is a winter build project. If I just wanted to have a 'built' bad-*** motor ready to drop in I WOULD go buy a DART short block..I was staring at them all friggin morning. I found a doz or more 500+hp that were drop-in's...not interested. I want the "Build" part..the HP will be the result of THAT, not a shop.

This is to be a build. Not a race ready install. There is no fun in buying someone elses engineering and then claiming that you "built" it. Some guys do that...I won't.

TIA

 

buy a Dart block for your build
NEW Dart™ SHP Block
Featuring upgrades including...

•True Priority Main Oiling System:
In a priority main oiling system, the oil from the engines primary oil galley is supplied first to the main bearings and then to the cam, lifters and top end. This ensures that the critical crankshaft main bearings receive adequate lubrication for highly stressed racing applications.

All Dart blocks employ priority main oiling systems.

Factory OE blocks, in contrast, typically feed oil to the top end first as it is easier to machine them in this fashion and factory blocks are not designed for the demands of racing.
•Siamese cylinder bores with extra-thick walls that resist cracking and improve ring seal for more power:

Traditional GM blocks have a water passage between the cylinders. All new Dart™ blocks have Siamese bores, meaning they are solid metal between the cylinder bores. Siamese bores are much more stable and greatly improve ring and head gasket sealing for increased power and durability.
•Extra thick decks ensure reliable head gasket seal
•Blind head bolts don't go through to water jacket
•Splayed outer bolts on middle main bearing caps:

All engines in the Pro Star series feature splayed main caps. The outer bolts secure the main cap against the block register which prevents "cap walk." Cap walk causes premature bearing wear.

Splayed main caps are far superior to OE style main caps which have straight outer bolts.
•All OE bolt holes for starter, clutch ball, etc...
•MADE IN THE USA

 

A GM 350 can be bored 4.060 over at the most. This would make the cylinder wall marginally thin. For racing, less than ideal because ring seal will be compromised (cylinder walls flex, the thinner they are, the less they seal). Also, thinner cylinder walls will result in the motor running hotter. If you tried to bore a 350 to a 4.125 bore, you would hit water. A 400 block starts out with a bore of 4.125. This can further be bored up to .060. These iron blocks have no liners, the cylinders are cast in. Hope this answers your question.

 

As stated above the 400 block is cast different then a 350 it has cylinder bores that are cast larger then a 350 block. The bores are siamesed together and this allows you to bore it to 4.155. A 350 block bored to 4.125 would hit water between the cylinders or be so thin it would fail.

 

bjankuski & 383....

THATS what I was looking for. Not having the 2 blocks sitting here side by side to compare, I did not know exactly what the difference was in the bare block. I knew cyl line bore was the same since cranks swap around, so I assumed that the cyl was cast in with a larger diameter to start with and water jackets were spaced around the cyl in a different way to allow the larger diameter bore.
Thank you for confirming that.

Again, this is a build project for the winter. BUYing a Dart motor and dropping it in does not work as a winter project.. That's no fun for me. The entertainment value (and pride in accomplishment) comes from assembling the machine, doing the work and seeing it do what was/is expected. There is more to this than I am willing to go into, so please trust me when I say that a "build" is important to me. Buying the heads, selecting intakes, calling Jon for the right size injectors.

Yes, there ARE a LOT of these ready to run....
Not for me. I like to build. THAT is what this is about..learning things and stepping up to the challenge. I may not be getting the opportunity again.

bjankuski.....I searched local CL and that's where I found a couple...there were a few built but that's NOT what I'm interested in. I AM tempted to make an offer on a couple different motors that are built long blocks, ONLY if they will remove most of their bolt on stuff and sell me just the short block...but I kind of doubt that any of these builders will do that.

The hard part is finding a block that's in decent shape and been running lately. I do not feel like going thru the hassles of buying, cleaning up in a tank to find that its cracked or damaged beyond repair. One I found looks like it sat on the bottom of Galveston bay for a few yrs....No thank you.

Guess I'll call some bone yards and see if they have any clue whats sitting in the inventory.

Thanks to ALL that responded, it is all useful information.

 

Hey Lee, why not start with a Dart or World Products bare block, select a rotating assembly of your choice and spend the winter assembling the thing? You can pick and choose your components and have the self satisfaction of knowing that you assembled the beast. You'll have at top line motor without having to magnaflux and machine an old block which might be compromised. I've been beating on my World Products block for the past 6 years. Started at .020 over and now am .030. Because of the thickness of the cylinder walls, I could go .040 or up to .060 with no problems. This should keep me going for a few more decades.

 

that's why i've reported the tech specs of a Dart SHP block before,just buy the block,not the entire crate,you can choice the better foundation for your build.Why searching for an unknow style of casting with different styles during decades? spend a little more (but you save in the machine shop part of job,not to talk about how skilled is the machine shop).Why choosing the best crank,conneting rods,pistons,lifters,bearings,camshaft,t iming,and then start from an old,unknown block bored out to the tech limit and then race it until it broke a connecting rod out of the block itself!

 

..... My first engine in the vette was a 400 + .040 = 409ci ... the current is a 400 + .030 = 406 ..... finding a good block is the challenge ..... Visually , its almost impossible to see the differences between a 350 and 400 ... its mostly internal to the casting ... GM internally expanded the cylinder walls to accommodate the larger bore ... the outer walls of the block were "bulged out " a little to expand the water jackets ... very little ... most 400 blocks have three freeze plugs on each side , or at least three bosses for them ( sometimes the center one was not drilled out ) ... the main bearing caps are much larger than a 350 , more like a big block ... most were two bolts ... the critical areas to look at are the cylinders and block deck ... look for cracks , especially around the steam holes ... the uppers are very close to a head bolt hole and they crack easily between but if there are ANY cracks into the cylinder walls PASS on the block ... the deck surface between cylinders is very narrow and has to carry the compression seal for two cylinders ... these blocks NEED to be surfaced anyway to square them up ... have your machine shop test the cyl walls for thickness before any work starts ..... Good Luck ! ... remember , there is NO substitute for cubic inches .........

 

From the outside, most but not all 400 blocks have 3 core plugs on each side of the block. 350s have 2 plugs, each side. I did once own a 400 with only 2 plugs. A circle track racer wanted it because he could pass it off as a 350.

 

Try and find a running known good 400 if youre going that route. So many have cracks in them its not funny. 4 bolt or 2 doesnt matter at all if its good go for it if thats what youre stuck on

 

yep, TP85 it may come to that...The more junk I see the more it makes me want to go ahead and start with a GOOD platform to build on, such as the Dart bare block. Expensive but not as costly as a bad purchase. I don't need a boat anchor.....

409 & Jack,
That's what I figured, just common sense really. If the rotating assy is in the same configuration then it has to be a relocation of the water to accept the bigger bore....and a pooching out of the block in some areas to keep a min wall thickness yet still keep it in the SBC category.

Heck, I've been drooling over Scat kits all month...and all the other critical internals. All I need is a good block to start bolting thing on to....
having a 400+ in my C4 is my dream...and its GONNA happen ! somehow/someday

thanks again for all the help and advice!

 

First off, if it were me I wouldn't bother with an aftermarket block unless your final goal was a full on racing platform in excess of 600bhp. Like others have said, find a running 400 and roll with it.

Also, all this "junk" you are seeing....how do you know it's junk? You are in fact the person who is on an internet forum asking essentially if you can bore a 350 block into a 400 block...which is a widely known no. You are also stating that "because the cranks are the same fit"...which they most certainly are not. The main journal diameter is different between the 2 sizes. This isn't meant to be mean, but if that's your level of knowledge on this subject perhaps you should have someone else do the leg work on finding a block. You may be surprised to find out how many good blocks that machine shops know of through their customer base (even some used Bowtie variants that racers are no longer using). Best of luck on you build. Just my .02