Hi H.A.M.B.er's, I have read many, many threads here and elsewhere regarding 400 sbc builds and now I am both overwhelmed with information and slightly confused. So I am now asking for help from all you guys & girls with all the knowledge. I am wanting to build a 400sbc, hopefully using mostly parts that I already have which have been collected over the years (cheap at swap meets, not used on previous projects, etc.). All of the parts I have are new, never fitted, most still in their original boxes. I have a 49 Merc build I would like to put the motor in, daily drive / street project, would like to make 500+hp. This is what I have as the basis for the build: Dart 31131211 Little M Block, Bore=4.125", Deck=9.025", 350 Mains, 2pc rear main seal. Arias Pistons (new old stock) flat top, for 400sbc, for standard rod length, compression height 1.56". Eagle 5565B3D Forged H-beam 5.565" Rods. Edelbrock 77619 Victor Jnr aluminium heads, 70cc combustion chamber. Crankshaft - don't have one yet. Various intakes / carbs / cams to choose from, but don't think these form any part of my current problem. My initial problem is the Crankshaft. I really want to use the pistons & rods I have, but does anyone know if there is an aftermarket Crank made to suit 5.565 rods, with 350 mains, and 3.750" stroke? Or would I have to do something like getting an aftermarket (? Eagle 104003750) crank that is 400 mains, 3.750" stroke, and suits 5.565 rods, and get the main journals machined down to 350 main size? I understand that the general consensus is that everyone ditches the 5.565" and goes for a 5.700" rod and piston to suit, but the rods and pistons I have are brand new and pretty good gear so I would really like to use them. Any help would be greatly appreciated. Kaos
Aftermarket 3.750" stroke 350 main crank's are avaliable from just about everywhere. Your short rod's will work just fine on them. It might take a little more work to balance, is all.
What he said . As long as the piston clears the counterweight at the bottom of the stroke,,,you should be good . Balancing will be the only problem really,,,,,and you can still internal balance with heavy metal . With an aftermarket crank,,,,,,you could get lucky and internal balance even without added metal . Tommy
Problem is, all your aftermarket forged cranks specifically state cannot be used with 5.565" rods, must use 5.7" minimum....and most are 6.0" rod minimum. Nobody makes a forged crank for 5,565" rod use because there is no market for it (beyond you and maybe 4 other guys, LOL). The Eagle #104003750 is a cast crank, and it also says 5.7" rod minimum on Eagle's website listing. No go with a short rod. The 350 size mains version, #103503750 is the same way, 5.7" rod minimum. You could end up trying to use your short rods and run yourself into a situation where the crank must have the counterweights cut smaller to clear and now you've got a huge balance problem that requires $500-700+ worth of mallory slugs to get the weight back....on top of the normal balance charge and the crank counterweight cutting charge. You could end up with $3k just in getting the rotating assembly fitted, if not more. With the parts you have, this is my suggestion...build it as a 372(standard bore) or 377 (.030" overbore using a 3.48" stroke crank, which allows keeping the Arias pistons .....but sell off the 5.565" rods and buy a new set of 5.7". Then everything fits, with the minimal amount of replaced parts from what you have on hand. If it has to be 400" or bigger, your rods and pistons are just not usable on any sort of budget build.
Since this doesn't appear to be a race application, why not run a stock crank? I ran one which I had internally balanced in my sprint car for a season and it did fine. The only reason I went back to a 350 is that we were doing some USAC shows and they had a 355 cu in limit. However, I did find that the Clevite 77 bearings did wear the rod journals. Sold the short block to a drag racer and he had the crank turned and ran it quite a while before he blew it up. A really high rpm launch got it.
I'd say that while you want to use what you have, you already know its not the best choice. Much better to buy the longer rods as you are going to create a bunch of other costly issues. Using Mallory metal to balance any set up is expensive. A lot of people make the mistake of buying an inexpensive crank and rod set up and then find that rod and piston weight are going to require mallory metal ($$).......so it costs them more in the long run. Resell the components that aren't the best choice and buy the right stuff. Not the answer you were hoping for, but its the best way. Pay attention to the weights of the parts, as you may not need mallory if you get the right stuff. Note: This info is 10 years old so prices have changed and there may be newer stuff available.
Engine building legend Joe Sherman made a living building stout 400 small blocks when everyone was scared to death of building one. Joe would sometimes even use the factory 5.56 rods and spin 'em to 6500!
It’s hard to believe one of the replacement cast or forged cranks even the ones that for internal balanced use would not work but all the ones I look up said 5.7 or 6” rods. Your purchased pistons have become the problem and finding a stock crank is a must in your situation. Today an internal balance is the way to go…
I'm in the 5.7 rod camp............You have a high dollar block, might as well use it accordingly.........
350 and 400 pistons have the same compression height [just the bore is different] You could use either a 3.75 crank with 5.565" rods or a 3.48 crank with 5.700" rods and still keep the same pistons, a 3.48" [350] crank in a 400 block = 372 cubes with a standard bore [this was a common circle track configuration] If you want a lazy street engine keep the longer 3.75 crank and 5.565" rods
Hi Kerrynnzl & all other HAMBer's, Thanks for all the info you have provided. Looks like I have to decide between a 372/377 or a 406 combination. I know there are pro's & con's to both, and everyone has an opinion or experience as to which they would prefer, but I need to do some more investigation on parts pricing to complete either option. (I'm in Australia so parts pricing and availability can be somewhat different and variable). Once I've made half a decision on which way I think I'm going to go, I may need to call on you all again for some more invaluable advice. Much appreciated. Kaos.
There is no replacement for displacement...........on a street engine. You can lower the compression so that you can run on regular gasoline and still have as much or more usable power as a smaller engine. Gasoline prices are often a factor that should be considered if you will drive the vehicle regularly. The thing I find is that when I try to make the wrong thing work, it usually bites me later on.
If you figure out the parts you want to use; a 372 is a killer. Our first Dart block, 4.155” bore because it was used, and a 3.48” could run with the 406-422” at our dirt track. When we did go to a longer stroke it was 3.875” I always thought the 383” SBC’s got it backwards.
Stock rod length 400 SBC has a 1.56" compression height piston GM did the Ford trick of lengthening the stroke and shortening the rods Most aftermarket pistons are for long rod combos 400 SBC = 1.875" crank throw + 5.565" rods + 1.560" compression height = 9" 350 SBC = 1.740" crank throw + 5.700" rods + 1.560" compression height = 9" Both are 25 thou down the hole with a 9.025" deck height block I know of a 400 stroke [scat 383"] crank being dropped into a 305 using 400 short rods, and stock pistons [off-the-shelf stroker pistons aren't available for the unloved 305] The end result was a "square" engine of 330"
The cheap way out is use a stock 400 crank and have the mains turned down. For what you are doing it will be fine. It doesn't fit with the image of the other parts you have, but the dumb crankshaft doesn't know who made it. I built a 415" using an offset ground 400 crank. (Final Stroke was 3.83") Killer combination. Pistons had a 1.435" compression height.
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