377 or 421???

Rebuilding a 400 block that was a 377, with stacked main bearings. If we decide to keep it a 377 (379 because had to take it to .040 over) it will get an Eagle forged crank with 400 mains so stacking isn't a worry. This will be in my sons mod and is his first year in an open mod, vs last 2 years in a crate. Brodix IMCA spec aluminum heads, 6 of the 8 rods were ok so 377 we only need to buy 2 rods. 421 we'll have to get all new rods and clearance the block. Mostly running 1/4 mile tracks and occasional a 3/8 track. Just looking for opinions on which way to go. Thanks!

What block?

I am sure from what he is describing is a stock 400 block. Since this is his first year running an open mod from crates, I would save your money and rebuild the 377. Work on making sure the car is setup and he is comfortable with the difference in driving an open versus a crate. Once he feels comfortable and you guys are having finishes that you are happy with, build the bigger engine. Just remember to have fun and enjoy racing with your son. That is worth way more than any engine.

Stock 400 blocks is pissing into the wind, especially at .040 over

It's a 511 stock 4 bolt main 400. And I'd rather he went for the 377 as well, especially being first year. And from what I've read the 421 will stress that block a lot more.

Go with the 377.

stay with the 377 , half fill the block with moroso hard block and go with the one piece bearings to run 350 journal in 400 block.....JMO

Honestly having run both, i hate my 377. ill take a 421 over it any day. i like the low end torque.

The 511 block isn't known for being the strongest so a longer stroke stressing it might not be good. With oem blocks though, you really won't know what it'll take until it can't. A shorter stroke should be easier on it..

Stick with 377 or just make it a 408 (40 over). Can't beat a good 400 for torque and HP all the way around even motor.

love my 377. don't need the extra low end torque on a 8 inch tire mod and lots of slick tracks to race on by feature time.
engine builder told me the 2 bolt factory blocks better than 4 bolt with 4 bolts more prone to cracking. always have run 2 bolt, 12 to 1 compression and never hurt a thing.

I agree on the 2 bolt being stronger and less crack prone. Mine is a 2 bolt, 14:1 and I turn it as high as 8500rpms. Haven't hurt it yet.

Been thinking about building one of these 377's. Found a rotating assembly with 6" rods. Whats the difference between that and using a 5.7 rod ?

6 inch rod will just take a lighter piston.

and help rod angularity

511 are junk

2 bolt allows you to have splayed caps which take the stress better then a "true" 4 bolt block. 6" rod reduces stress internally as well and these items cost but add to longevity

the longer rod extends piston dwell , it stays at the top longer , which helps with higher rpm power , this is more common with the shorter stroke 377 combo because you are normally turning it more with the destroked combination , the longer rod also decreases rod to stroke ratio which usually extends piston life , if you dont have good enough stuff to turn high rpm,s , then i prefer the shorter rod to help with torque off the corner. I have a 302 ford block with a 3.5 stroke and 5.4inch rods , its a beast off the corner but is rough on pistons.....also Jim is correct above , we just done a 4 bolt conversion on the three center mains , this is way better than the original 4bolt block , but expensive , your about as well off to find an aftermarket block , like i said above , a half fill with moroso hard block is inexpensive and really strengthens the block.......