350 or 400?

[prg machine]

stay away from the 400................they have a design problem with the siamesed cylinders and will not last as long as the 350. The cylinder bores go out of round due to uneven cooling and they turn into oil burners.
You can not just bolt any 400 flywheel on there either. The whole ASSEMBLY will need balanced.
stay with your 350

[bad421]

come on now if a siamesed block was bad do you think gm would use that design for their bow tie racing blocks? 400 sbc is great jus dont overheat it, cylinder walls are siamesed to be stronger and for bigger bore.

[muscletrucks]

Have you considered turning the 350 into a 383? Sounds like the perfect compromise to me. Thats what I am doing as we type.

[prg machine]

Originally Posted by bad421

come on now if a siamesed block was bad do you think gm would use that design for their bow tie racing blocks? 400 sbc is great jus dont overheat it, cylinder walls are siamesed to be stronger and for bigger bore.

This is the classic argument 400 vs 350 block

The reason they are siamesed is because the bore is too big for a reasonable wll thickness at the water jacket area. they cool unevenly and the cylinders go out of round.
The racing blocks you mention aren't even the same animal
The 400 was a short lived GM experiment that didn't last for a good reason.

Those are the facts!

[landjhallmark]

go with the 400 and put a 350 crank in i really liked mine

[prg machine]

383!!!

[prg machine]

here we go again!!! 350/383 vs 400!!!!

[muscletrucks]

Cock A Dodol DO

[67_C-30]

Originally Posted by prg machine

This is the classic argument 400 vs 350 block

The reason they are siamesed is because the bore is too big for a reasonable wll thickness at the water jacket area. they cool unevenly and the cylinders go out of round.
The racing blocks you mention aren't even the same animal
The 400 was a short lived GM experiment that didn't last for a good reason.

Those are the facts!

This man speaketh the truth! I have literally seen more cracked 400 blocks than I have seen good blocks in my 12+ years of engine building. There have been several guys all excited about finding a 400 SB out of the junkyard and as soon as we tear it down and check it, its cracked.

[BurnoutNova]

Originally Posted by prg machine

383!!!

you mean 377? a 400 with a 350 crank is a 377

[BurnoutNova]

Originally Posted by prg machine

here we go again!!! 350/383 vs 400!!!!

yep... im still sticking to my story, GM wouldnt have made it for 10 years if they had cooling probleoms, im sure they could identify the probleom sooner than that

im not saying they dont overheat, and they dont crack, but ive worked off and on at an automotive machine/ engine shop for 8 years. ive seen everything from original 1955 corvette 265's that have had cracked blocks to 90's caddillacs having porus block causing water leaks. it happens to all of 'em... and i have been around plenty of GREAT running 400 small blocks. TORQUE MONSTERS...

[prg machine]

Originally Posted by 67_C-30

This man speaketh the truth! I have literally seen more cracked 400 blocks than I have seen good blocks in my 12+ years of engine building. There have been several guys all excited about finding a 400 SB out of the junkyard and as soon as we tear it down and check it, its cracked.

Thank you my friend....................it takes a fellow machinist to understand this.
67 C-30 is telling you all exactly what i was told by an engine builder that replaced a whole fleet of trucks with the 400 SB with 350s simply because of what we are preaching here.
Sure the "concept" of a 4oo sb is exciting. The reality of the whole thing is that they CRACK!!!!

I personaly have no problem at all making my mind up...............to each his own................

and the famed argument continues..............as it always will.......................................................400vs350vs400vs350vs400vs350 on and on we go!!!!!!!!!!!!!!!!!!!!!!!!!!

[prg machine]

Originally Posted by BurnoutNova

you mean 377? a 400 with a 350 crank is a 377

nope I mean 383!!!!

and we all know that starts with a 350 block!!!!

[BurnoutNova]

Originally Posted by prg machine

The reality of the whole thing is that some of them have been known to CRACK!!!!

i fixed if for you

HAHAHA

[BurnoutNova]

Originally Posted by prg machine

nope I mean 383!!!!

and we all know that starts with a 350 block!!!!

you posted that right after the 400 w/ 350 crank post so i wasnt sure what you meant

and i'll agree 350's are great. i have about a dozen of them out in the garage aka "my inventory" but, as mant belive there is no replacement for displacement!!

[prg machine]

Okay to be fair to all reading these posts.....................let's look at it like this:

If you had a choice of the odds.......................and the 400 is very highly likely to crack and a 350 is way less likely to crack........................................what is the logical decision?

[67_C-30]

Originally Posted by prg machine

Thank you my friend....................it takes a fellow machinist to understand this.
67 C-30 is telling you all exactly what i was told by an engine builder that replaced a whole fleet of trucks with the 400 SB with 350s simply because of what we are preaching here.
Sure the "concept" of a 4oo sb is exciting. The reality of the whole thing is that they CRACK!!!!

I personaly have no problem at all making my mind up...............to each his own................

and the famed argument continues..............as it always will.......................................................400vs350vs400vs350vs400vs350 on and on we go!!!!!!!!!!!!!!!!!!!!!!!!!!

Just speaking my personal experience man! Now to be fair, I have seen and have even owned 1 400 myself that had almost no core shift and it was a running son-of-a-gun, but unfortunately they were produced at about the worst time they could have been produced in terms of quality control. The mid 70's - early 80's GM (all domestic manufacturers actually) lack of quality is why they are so many ricers on the road today. I have seen a small handful of 400's that even sonic checked good and were bored .060" over that lived. You don't usually get a second chance if you sling a belt and overheat one though. My point about a 400 is that they are truly a crapshoot. If you get a good one you're lucky, but the chance (probability) of getting a thin one steers me away from them.

[BurnoutNova]

Originally Posted by 67_C-30

unfortunately they were produced at about the worst time they could have been produced in terms of quality control. The mid 70's - early 80's GM (all domestic manufacturers actually) lack of quality .

that makes me steer away from any mid 70's motors, save for 454's ive had pretty good luck with those so far.

ive seen and had several sets of 70's lightweight casting 350 heads that i knew would be cracked before i even mag'd 'em

[BurnoutNova]

Originally Posted by prg machine

what is the logical decision?

you could also say racecars and old cars in general clash with what most people would consider a logical decision.

8 mpg, and dump in twice the money you'll ever get out of it, or save it and drive a kia?

you only live once might as well make the best of it a go all out

[ChevyC102007]

Heres a dumb idea.....if your pulling the 70 off to put on a '71 frame....why not spend the extra time and money and BUILD an engine? The list is varied 355, 358, 377, 383,406,408 and the list goes on and on. Or for that matter throw in a mild 402, 427 or a 454BB. After all is said and done, its your truck do what you feel works for you. Just my odd ball opinion

BTW stick with the 350!

[prg machine]

Originally Posted by BurnoutNova

you could also say racecars and old cars in general clash with what most people would consider a logical decision.

8 mpg, and dump in twice the money you'll ever get out of it, or save it and drive a kia?

you only live once might as well make the best of it a go all out

Just go the "right" direction if you are going "all out"...............................................build a "good" engine!


A 400 is not a good foundation for an engine build. Sure....get lucky and have a torque monstyer with little to no build work.yes I agree with the "concept"..

The facts are that the reality says "stay away from the 400SB."

[slammed1]

The 400 I took .040 was a 2 bolt 1970 model and ran real strong and checked out great. The reason for the .040 over bore and not smaller is that one cylinder wall was scored and t cleaned up at .035 so all the others were bored and then all honed to match. My 2 engines now are a 1976 350 that will stay standard bore with a polished crank,and another 400 1970 model thats been rebuilt once so condition is really un known right now but was running when I pulled it.

Yes these debates will run forever and will always do so. To tell that every 400 is bad and will not be as good as a 350 is not true,but opinion. There are way too many 406,427 and 434 engines built that prove otherwise.

It is to my understanding the reason so many 400 blocks were trashed was because the shorter connecting rods placed wear on the sides of the bore (pistons trying to push outward on the side of the block)which tapered the bores wearing the blocks out before the rest of the engine was ready to be trashed. Thats one reason 383 became a popular build as there were way too many 3.75 cranks sitting around with bad blocks and they were cleverly mated to 350 blocks for stroker engines that ran strong.

Personally,I will always entertain building a 400 if the choice is there and the building block is a solid one,but will always fully check for cracks and bore taper/wear to determine if its clean enough to work. I will also never pass up a good buildable 350 as those tend to outwear the 400 and are easily picked up for great prices. I am for building any stout reliable engine for its purpose,and if that 400 fits the bill,Im sold,and if that 350 also fits the bill I will run it.

At the time of my first 400 build I was building a 327 also for my race/drag car 68 Nova and the 408 was for my street 67 Impala.
I built the 327 on a budget with most money in the heads,great shape used forged .100 dome pistons and such with the 400 getting all new parts for the street car. IF I were to do it all over again I would have put the 400 in that Nova because my street car would have stomped my drag car.

I say to each his own and fully weigh your options for your build.

[Hittman]

Wow guys, I was looking for opinions and boy am I getting them. I didn't realize there was such a debate between these two - glad I asked.

So unfortunately I am still torn - though I am getting increasingly leery of the 400 with all the comments on their longevity and reliability issues. At this point I am not in a position to rebuild either one due to the all so common lack of finances at this time. Thus my question as to whether to drop the original 58K mile 350 back in or the 60+K mile "tuned-up" 400 this guy never had any problems with. I get the idea the 350 Chevy was around so long due to its inherant ability to hold up just about anything. I had a '78 shortbox with the original 350 that was at 215K miles without a rebuild when I sold it and it was still running strong (wish I would have kept that one btw!). Just another reason to stick with the 350 in my mind.

With the long weekend coming up I am planning on putting in one or the other. Sure wish I could just buy the 400, try it out for a while then decide which to part with. Again don't have the cash laying around for that option. You guys keep throughing your opinions out there and just maybe I will make up my mind on this end!

Thanks again for all the input!

[drivethechevy]

if it were me i would stick with the 350, i have a 400 sbc in my old plow truck and its a good strong motor but no matter what i do to the thing it just eats oil it dont eat alot but enough to frustrate me althought ive never had any problems with my 350 and i have beat the snot out of both engines and the 350 perfored just as good if not better so it really depends on how reliable u want ur engine to be the parts or different for 400s and there built a little different so not as many parts can be changed from bore to bore when running a 400 were as a 350 is alot more versitile parts and cost wise, not to mention u can still go to any junk or scrap yard and pull a 350 for a couple hundred bucks good luck with ur truck

[BurnoutNova]

Originally Posted by slammed1

It is to my understanding the reason so many 400 blocks were trashed was because the shorter connecting rods placed wear on the sides of the bore (pistons trying to push outward on the side of the block)which tapered the bores wearing the blocks out before the rest of the engine was ready to be trashed. Thats one reason 383 became a popular build as there were way too many 3.75 cranks sitting around with bad blocks and they were cleverly mated to 350 blocks for stroker engines that ran strong.

excellent point!