I’m sorry I’ve been slow to get back to this thread. I’ve been pretty busy these last few weeks. I though I'd start a new thread rather than add on to the other 348 build thread. I will add a link to that thread because a lot of the info there also applies here... http://www.348-409.com/forum/showthread.php?t=12872
I don’t have ANY experience with 348 strokers but thanks to the helpfulness of some of the other members I think I can come up with a reasonable estimate of what will be required. As always I’d appreciate any input or suggestions and let me know if I get something wrong I can always come back and edit this post.
There are three basic stroker configurations we’ll look at. The easiest and most popular setup is to put a 409 crank in your 348. The next step up is to use a crank from a 396 or 427 Big Block Chevy. And finally there’s the 454 Big Block crank.
If you bored a stock 348 .030 you’d have 353ci.
With the 3.5” 409 crank and a .030 overbore you’d get 380ci.
With the 3.76” stroke 396/427 crank and .030 over you’d have 408ci.
And with the 4” stroke 454 crank and .030 over you’d have 434ci.
We’ll cover the 380ci (409 crank) build first and I think we’ll do a few different horsepower targets like we did with the stock stroke builds.
A 409 crank will pretty much drop right in. The only clearance issues you should have are with the oil pan. A 409 pan will solve the problem but you should also be able to get adequate clearance by massaging the 348 pan with a hammer. Show Cars does have aftermarket 409 oil pans available.
Aubrey recommends using standard, 6.135” big block Chevy rods. The big block rods are stronger than the rods that came with either the 348 or 409 so this is a good upgrade. You can get pistons from Aubrey or Show Cars. You just have to tell them which crank and rods you’re using. I think we’ll use big block rods and forged pistons in all of the stroker recipes.
I should add that you CAN use a combination of 409 rods and regular 348 cast pistons but this would only be appropriate for low horsepower builds. The 409 rods are shorter than the 348 rods so they pretty much compensate for the extra ¼” of stroke. A stock 348 piston coupled with a 409 crank and 409 rods will be .010 higher in the bore at top dead center. That shouldn’t be a problem as long your block hasn’t been decked too much. But the compression ratio for a stock 348 piston is based on a 3.25” stroke. You’ll be trapping more air with a 3.5” stroke so a 9.5 to 1 piston for a 348 will actually give you 10.5 to 1 with the 409 crank and rods.
By the way, it’s rumored that there are some 348 blocks that can be bored out far enough to take 409 pistons but blocks like that are very rare. Curt Harvey has built hundreds of W motors Here’s what he had to say in a magazine article…
“Although some 348 blocks have thick cylinder walls, most cannot be bored out to the larger 409 diameter.” “Cylinder wall thickness varies widely because casting techniques back then weren’t up to current standards. Usually .030 over is no problem, but .060 requires sonic testing the block.”
I’ll get started on this thread in the next few days.
I don’t have ANY experience with 348 strokers but thanks to the helpfulness of some of the other members I think I can come up with a reasonable estimate of what will be required. As always I’d appreciate any input or suggestions and let me know if I get something wrong I can always come back and edit this post.
There are three basic stroker configurations we’ll look at. The easiest and most popular setup is to put a 409 crank in your 348. The next step up is to use a crank from a 396 or 427 Big Block Chevy. And finally there’s the 454 Big Block crank.
If you bored a stock 348 .030 you’d have 353ci.
With the 3.5” 409 crank and a .030 overbore you’d get 380ci.
With the 3.76” stroke 396/427 crank and .030 over you’d have 408ci.
And with the 4” stroke 454 crank and .030 over you’d have 434ci.
We’ll cover the 380ci (409 crank) build first and I think we’ll do a few different horsepower targets like we did with the stock stroke builds.
A 409 crank will pretty much drop right in. The only clearance issues you should have are with the oil pan. A 409 pan will solve the problem but you should also be able to get adequate clearance by massaging the 348 pan with a hammer. Show Cars does have aftermarket 409 oil pans available.
Aubrey recommends using standard, 6.135” big block Chevy rods. The big block rods are stronger than the rods that came with either the 348 or 409 so this is a good upgrade. You can get pistons from Aubrey or Show Cars. You just have to tell them which crank and rods you’re using. I think we’ll use big block rods and forged pistons in all of the stroker recipes.
I should add that you CAN use a combination of 409 rods and regular 348 cast pistons but this would only be appropriate for low horsepower builds. The 409 rods are shorter than the 348 rods so they pretty much compensate for the extra ¼” of stroke. A stock 348 piston coupled with a 409 crank and 409 rods will be .010 higher in the bore at top dead center. That shouldn’t be a problem as long your block hasn’t been decked too much. But the compression ratio for a stock 348 piston is based on a 3.25” stroke. You’ll be trapping more air with a 3.5” stroke so a 9.5 to 1 piston for a 348 will actually give you 10.5 to 1 with the 409 crank and rods.
By the way, it’s rumored that there are some 348 blocks that can be bored out far enough to take 409 pistons but blocks like that are very rare. Curt Harvey has built hundreds of W motors Here’s what he had to say in a magazine article…
“Although some 348 blocks have thick cylinder walls, most cannot be bored out to the larger 409 diameter.” “Cylinder wall thickness varies widely because casting techniques back then weren’t up to current standards. Usually .030 over is no problem, but .060 requires sonic testing the block.”
I’ll get started on this thread in the next few days.
