I want to make a bb 361 have a little more punch while it’s being rebuilt. Can I put in a crank from a 440 with a 3.75” stroke to raise the displacement to 400 cubic inches?

What pistons/rods are you going to use?

I haven't done the math on your proposed conversion for the exact cubic inch, have you?
I have usee a bunch of 440 cranks in low deck and also offset stroking them to 3.91 stroke using BB Chevy H beam rods in both 6.800 and 6.700 long with the Chevy .990 wrist pin size and custom made pistons
I have a 400 block that I used the customers 440 crank and his 440 LY rods, I had the mains and counterweights turn down and the rod journals ground down to .010 under per his request, that motor (451 C.I.) made 490 HP on CA pump swill with a set of big valve ported 906 440 heads and a Eddy RPM intake and a Holley 950 HP carb.
On your deal with the 361, 413 bore size pistons and rings will be your hardest and biggest expense
I recently built a 1972 413 truck motor for myself, I used a Mopar brand 4.150 stroke 440 crankshaft and sonic tested the block, it tested safe to be bored to 4.25 so that is what piston size and rings I used
If I was you I would have your block magnafluxed and then sonic tested to see if it is a good block or not

use the 3.75" crank and make a 413 low deck. custom pistons needed but shouldn't be a big deal. use an alum quench head and have fun.

A 4.125" bore and 3.75" stroke is a 400, exactly the same dimensions as a chevy 400 smallblock.

First things first, the B and RB have different main bearing diameters. So the crank has to have 2.625" main journals rather than 2.75" 440 journals.

Second, the counterweights need to be trimmed or else the block relieved for the counterweights of the crank. I'd suggest using a cast 440 crank and moving material out of the block.

Third, pistons are going to be expensive if you can't find something close off-brand.

Fourth, I do have a concern about the connecting rod shank running into the lower edge of the bore.

Fifth, everyone and their sister is going to chime in that you should scrap the 361 and build a 383 or 400 stroker.

R.

I just ran some numbers and one possibility is the 3.75 crank, a 6.535" rod, and a Chevy 400 piston. The chevy piston has a 0.927" crankpin. I have a broken set of 6.535" rods with smallblock Shevy big and small ends, so they can be had. Key to this is using off-the-shelf stock pistons.
Break out the calculators!

You can do anything you want as long as you have the money and the time. I'm in the process of putting a 4.250 stroke crank in a 426W block for my '65 Dodge Coronet.

You must have a real good reason for using the 361 block. Otherwise you would be better off with a 383, and better yet a 400.

You are asking the heads to breathe through a more shrouded set of valves by using the small 361 bore, then you are making things worse by adding stroke.

Yes you can,just have .125 cut off the mains to make them fit your block,have the counterweights cut down and custom pistons and your good to go.

Google 451 manifesto and it will give you the basics.

Why do some people climb mountains, because they are there.

Why do some people climb small hills, same reason.

As the saying goes, “you take the high road and i’ll take the low road”.

I decided a little while back to take the maxwedge out of my 62 before giving the car to the wife.

I decided to build a low deck 383 2 x 4 inline clone.
I could use a very common 383 block but decided the 400 block was a better choice.

Why spend the same money machining a 383 versus a 400, when I can immediately gain .090” more bore size with the 400.

Like I said earlier, must have a real good reason for using the 361 block.

You are correct. If a person wanted the most bang for the buck then the block to start with is a 400. For some reason (unknown to us) the OP wants to use a 361 block.

Can he? Yes. Should he? I don't know. Would I use a 361 block? Nope.

My concern would be valve to bore clearance with the aftermarket heads, which all come with oversized valves.

Plan on doing some relieving.

Well, let’s think about it a second. The head issue really isn’t as bad as some of you think. Why?

Small block strokers w/4.00 arms are turning good numbers with ported stock heads and 2.02/1.60 valves. The 361 comes with what head? Valve sizes? And ports out how well?

the only problem I can see is the specific pistons for the build, I think not available from the shelf

the rest is a piece of cake and has being done many times in diff displacements but same B block. So you won't have ANY problem building it with heads, valves or whatever, aside just the pistons. Will need to decide if use B or RB rods, that's all, to decide on the pistons.

Why use a 361 and not a 383/400... is your problem, go for it

( many times ppl locally told me why stroke my 400 instead use a full 440... simply JUST BECAUSE I WANT... aside being the matching block with my car )

there are some difference between the 400 and 440 decision that are not applicable to picking the 361 over the 400.

400 is a smaller package than the 440, making it easier to fit.
400 has the largest bore diameter of the B/RB's making breathing easier.
Then there is the difference between rod lengths to take into account.

http://victorylibrary.com/mopar/rod-tech-c.htm

The only reasons to use the 361 is because you have no other choice or you just really want to.

I hope the OP lets us all know when done and he has "the cat eat the canary smile", so we can then next discuss the merits of stroking the real mopar red headed motor, the low block 350.

Why would anyone(normal?) want to try and find one of those oddball motors to work on
Is this statement meant to create a discussion on another tangent?
If so why not discuss the building of the one or two year only(1959/1960) high deck 383 motors

build it,it will come...

The problem with this logic is valve placement, a BB has the valves too close to the bore even when using the bigger bore blocks. Look at a BB head chamber through the bottom of a cylinder bore, the valves are offset to one side of the bore then spaced even more to the front and back, a BB head like a 906 or 515 is going to flow less on a 4.125 bore than a magnum 308 or X head will on a 4 inch bore.

I always find it funny when people say an engine is a "TQ engine", what they mean is it wont make any HP. A 361 with a 3.75 crank is going to be one of those "TQ engines".

Agreed on everything you told point by point, and thats why I made the 400 on mine, being at the same time my matching engine

and specially on bolded LOL ( too ) for the OP