377 sbc

[badfast47]

May have ask this b4 but... Can u use a stock 400 2 bolt main sbc to make a 377 and it work without it coming apart ? Will have the mains and heads on studs. The heads will be aluminum with 2.100 and 1.60 valves... Pistons ? Flat top or dome don't care.

[Jim11h]

Yea it'll work. Had one long ago with 12.5:1 domes stock rod stock stock crank internal balance. I bought used from friend and they twisted it7k all time with 4 barrel on alky. I bought and ran till I screwed up reassembly and blew motor something about forgetting to torque the rod bolts the motor didn't like.

[badfast47]

I have been able to read in a couple of places the 377 isn't as hard on the bottom like a 406 for example. I would like to try one just for the hell of it.

[Ronnie9]

I have been able to read in a couple of places the 377 isn't as hard on the bottom like a 406 for example. I would like to try one just for the hell of it.
Good combo, just make sure its balanced correctly

[billetbirdcage]

It's still a stock 400 block so thin cylinder walls, weak mains to cam area are still there, as well as the steam holes in deck that will crack over to the head bolt.

Couple of things that might help it live:

1. Have block sonic checked on wall thickness before spending any money on machine work

2. Don't square the block, meaning if it's out of 90 degrees don't correct it as cutting deck differently then the head bolt holes where machined will pull sideways on the bolts/studs and increase the chances that the head bolt hole will crack over to the steam hole. You can deck it, but only cut parallel to original surface as not to change the angle of the deck to the bolt holes. Also advise the use of head studs.

3. I also like to plug the steam holes. Do this by tapping the steam holes but not all the way thru, then install a cheap grade 2 bolt and tighten until it twists off or stop once it jammed in there and cut off. Then deck the block.

4. When using spacer bearings to go down to the 350 main bearing size: Use .020 or .030 under bearings (thinking .010 is what is used when you buy them already made) and make your own. This way you can have the block align honed with the extra undersized bearings and remove all the soft material down to brass. This will make things repeatable and more consistent to reuse later.

5. Installing main caps: I prefer the stepped caps that you don't cut out the register over the flat caps. I've seen way to many of the flat caps with cut out register crack and split up to the cam right at the corner of the new register due to having no radius there.

6. Think about a short fill on the block, you can do this yourself but need to do weeks before hand to let it cure before you do any machine work. You can use concrete if you get the correct stuff, instead of buying block filler. (EMBECO #882, it's a special non expanding concrete)

Good luck but anything over 600 HP is starting to get to danger zone, some blocks will take that and more and others will fail shortly.

[fastford]

all that is good advice billet , one thing to add , i cant remember where we got them , my dad may have made them , but we used still spacers in the mains and aligned bored them to 350 size , we also half filled the block , just like i do the 302 ford blocks , with moroso hard block , i think this is probably the most important part , we also used a 2 bolt main block and built them both ways , meaning we put splayed center caps on some and we used just stock 2 bolt caps on some with good studs , which IMO is just as good when staying under 600 hp , and like you stated , none of them is good for much more than that no matter what you do........

[Kromulous]

I built a 380 years ago, 10 at least, and its still out there racing. 400 block, 3.5 Callies crank, 6.125" rods.

Step caps, to 4 bolt, plugged steam holes, block half filled. 350 main size, line honed etc.

It was intended to be an alky motor from the get go. Watch your cam size, you will need a small base circle. I think what Billet said is on point, this motor was right at 600 to 625, but it was one of my favorites.

[fastford]

only time i have had to use a smaller base circle cam was with a 4 inch stroke , that 3,5 stroke should easily clear a standard cam.......

[Kromulous]

Was it the bolts? that was in the way. I remember bolts being a problem, but that may of been on another Engine. Always good to check thou.

[over4T]

Billet has a lot of good ideas, including a few I hadn't thought of, but after seeing too many stock 400 blocks fail too early I just stay away from them. Pouring time and a lot of $ in them just never made sense to me and I pretty much just keep building 383s & 385s with stock 350 blocks. Had a lot of reliability and, generally, good luck with them.

My machinist usually has several, he says, good 400 blocks and is constantly trying to sell me on doing one but I just keep saying no thanks.

[fastford]

its like every thing else over4t , its according to what you are trying to do with it , i did some work for a guy that asphalt raced a limited type car that required a bone stock crank shaft , every one stuck with a 350 crank because of the junk 400 crank breaking , but my guy wanted to stay with the 400 crank because he was winning races , we finally figured out that after about 20 races , the 400 crank started to spider web(crack) so every 15 races we would swap the crank , he killed them for 2 years till they changed the rules to an aftermarket crank.......

[JustAddDirt]

If you Can find the high nickel 400 blocks they are extremely strong (for a stock 400)
I think they were in school buses, etc.
Someone told me they were a Mexican casting, but dunno if that is true information

[Lizardracing]

So where does one know if the casting is high nickle or not?

[fastford]

i have herd of this before but i dont know about the nickle part , the 509 block with only 2 freeze plugs per side instead of 3 was the best IMO , and had less core shift and most can be bored .060 over with no problem , this is the one we convert the 3 center mains to 4 bolt splayed caps, i have pulled a bunch of 350 four bolt main blocks out of school buses but have never saw a 400 in one.....

[JustAddDirt]

i have herd of this before but i dont know about the nickle part , the 509 block with only 2 freeze plugs per side instead of 3 was the best IMO , and had less core shift and most can be bored .060 over with no problem , this is the one we convert the 3 center mains to 4 bolt splayed caps, i have pulled a bunch of 350 four bolt main blocks out of school buses but have never saw a 400 in one.....

I could have gotten bad info on the school bus part.
that 509 seems to ring a bell on it being the better blocks.

[Lizardracing]

Since no one answered my question Ill just say that in my 40 years of hotrodding, not a single person ever has produced a document from GM on what 010-020 numbers mean except for a few guy's I know who worked in the foundries. They say they are casting numbers from the mold machines and that it. Even metal analysis has never produced something to verify the claim. At least in my experience, they all machine the same and tool life isn't any different.
The 509 does have the two bolts mains so there is enough material on those to add splayed caps and add some rigidity to the webs. I'm guessing that's where the rumor started and perpetuated over the years of bench racing.
400's come in large cars with 2v or 4v carbs and some of the larger trucks like the 3/4 ton K5 blazers. Special ordering the engine was possible in trucks and cars back when you could do that. Those would be very rare however. All that is verifiable with GM. GM didn't give a rats behind about giving these blocks any more attention than needed as they were only available in grocery getters and trucks. They were NEVER put into the performance oriented vehicle.
I wish I had a nickle for every time I heard some one say "My all original Corvette, etc....with the 400ci....."

[LRtireCHANGER]

Piston speed would be lower in the 377 than in the stock 400 stroke motor. With good heads, the 377 would produce less torque at lower engine speeds, which should be an advantage on a slick track. Put some gear in the 377 and let it eat.

[fastford]

lizard , from my experience , the early 350 casting with just 010 were the best , they had less core shift ( did your guy in the foundry explain this ) and could easily be bored .060 and have good cylinder wall all the way around , now the later block with 010 and 020 were junk IMO , most you see had bad to terrible core shift , which meant thin cylinder walls on one side were thinner and some could not be bored even .030 , i figured most of these were jiged up on monday by the factory machinist.......lol.....

[Krooser]

The guys making the cores in the foundry core room are responsible for good cores and castings.

If course a little QC would have helped, too. Not something the Auto industry was known for in the 70's/80's...

[fastford]

the easiest way to detect core shift on a SBC is to look at the machined surface around the front cam journal where the gear runs , if that surface is the same thickness all the way around its usually a good block , but but if its thinner on one side and thicker on the other , then there is core shift and the cylinders will be thinner on one side as well.....

[Krooser]

its like every thing else over4t , its according to what you are trying tomy buddies ran those do with it , i did some work for a guy that asphalt raced a limited type car that required a bone stock crank shaft , every one stuck with a 350 crank because of the junk 400 crank breaking , but my guy wanted to stay with the 400 crank because he was winning races , we finally figured out that after about 20 races , the 400 crank started to spider web(crack) so every 15 races we would swap the crank , he killed them for 2 years till they changed the rules to an aftermarket crank.......

My buddies ran those 400 cranks one season then went on the scrap heap....

[Lizardracing]

lizard , from my experience , the early 350 casting with just 010 were the best , they had less core shift ( did your guy in the foundry explain this ) and could easily be bored .060 and have good cylinder wall all the way around , now the later block with 010 and 020 were junk IMO , most you see had bad to terrible core shift , which meant thin cylinder walls on one side were thinner and some could not be bored even .030 , i figured most of these were jiged up on monday by the factory machinist.......lol.....

The best I can remember from the conversation right now is during ALL machining operations, the block was clamped down on its machining pallet as it passed through the 28-station line, located by two master gauge holes - one in the pan rail below the fuel pump boss, and another one in the middle of the starter pad. Regardless of core shift, the cam bearing bores and lifter bores will always have the same relationship to one another. There will be some variation between machined surfaces and cast surfaces as a result of core shift, but none between machined surfaces. Core shift is just that, the multi piece mold got shifted around a bit. Probably because humans were involved and some were done on Mondays and Fridays. The biggest thing to remember in all of this is that GM never did anything it didn't have too to get past the warranty period and build in some life on top of that. They build production cars that pick up groceries and pick up kids and need to be reliable enough for that. Anything else just isn't what they were after.

[fastford]

i was always curious why there was no evidence of core shift on the 307 blocks , an old man that helped me years ago loved the 307 block because of this , he bored them to a 350 and swore they were a lot better than a regular 350 block, i have 3 old 307 block stashed away and i looked at them a while back and the ring i was referring to earlier was even all the way around , i have 10 or so 010 350 blocks and only a few are like this....by the way , we have tested the ring thickness theory on the cylinders with a sonic tester and it holds true , if that surface is thinner on one side , the cylinders will be to. maybe those locating points you are talking about were not properly done and caused the core to be shifted on the milling machine,s......

[billetbirdcage]

i was always curious why there was no evidence of core shift on the 307 blocks , an old man that helped me years ago loved the 307 block because of this , he bored them to a 350 and swore they were a lot better than a regular 350 block, i have 3 old 307 block stashed away and i looked at them a while back and the ring i was referring to earlier was even all the way around , i have 10 or so 010 350 blocks and only a few are like this....by the way , we have tested the ring thickness theory on the cylinders with a sonic tester and it holds true , if that surface is thinner on one side , the cylinders will be to. maybe those locating points you are talking about were not properly done and caused the core to be shifted on the milling machine,s......

I used a lot of 307 blocks to make 311's and all of them are way thinner on wall thickness at a 4" bore then a 350 block was. May not had much core shift but they wasn't thicker or even as thick as a 350 when taken out to 4"

[fastford]

maybe the old man had figured out that a thin wall would dissipate heat way back then , because my understanding is thats what brought about the thinner 350 castings that came later IDK......

[badfast47]

I ran across a 509 block a guy want's to sell and says it's a standard bore. The numbers on the block are 3951509 and 2 freeze plugs. Sound like a good place to start for a 377 with the right machine work and assembly ?

[ZERO25]

I ran across a 509 block a guy want's to sell and says it's a standard bore. The numbers on the block are 3951509 and 2 freeze plugs. Sound like a good place to start for a 377 with the right machine work and assembly ?

And some decent parts! lol...…...Our shop built quite a few of those for mods many years ago. Had great success using Eagle bottom end, Mahle pistons, and Dart heads.

Our shop owner was a world champion drag racer, and he really liked the 377's. I don't remember the term he always used, but it related to the size of the bore and stroke being closer together. Maybe someone on here does!

[bullittwrench]

"I don't remember the term he always used, but it related to the size of the bore and stroke being closer together. Maybe someone on here does!"

I heard that theory a long time ago also. Worked for a LM owner who swore by 4" bore, 4" stroke engines. They did run good.

[JustAddDirt]

lighter crank
wind up quicker
easier on bottom end webbing
less stress on cylinder walls due to less stroke.
less torque to help with traction up off corner in slick


I believe most competitive wide bore motors are being de-stroked to help with drivability for same reason.

[Jking24]

"I don't remember the term he always used, but it related to the size of the bore and stroke being closer together. Maybe someone on here does!"I heard that theory a long time ago also. Worked for a LM owner who swore by 4" bore, 4" stroke engines. They did run good.Probably "over square"

[ZERO25]

Probably "over square"

That sounds correct!