ok, have my 350 torn down completely. Block has already been bored 30 over by prev. owner. Heads are 461s (194s)from a 1965 whatever. Thinking about going with a 400 crank,but dont have one. I know it has to have machine work,ect to fit my (medium) block. Now, is it better and cheaper to get a 400 crank local and have it machined or is it best to get one from the vendors? Cast is ok with me,aint no big time racer,but will buzz up to 5 or 6 sometimes. Do they make a dampner that will take care of the balanceing issues? My old rods should be ok,right?

 

If you can get a good 400 crank, have it checked, then machined, you would be good to go. Depends on how cheap you could get the crank and how reasonable the machine shop rate is. I just got mine from a vendor. If you go this route, you will likely end up with an externally balanced 383 meaning that you would run a dampener and flywheel from or for a 400 sb. If your old rods are GM originals, have them checked, sized, etc. They should be strong enough for what you need.

 

Just buy a balanced rotating assembly and save yourself a ton of time and might even save $ in the long run. This site sells them starting at $700, many other sites to choose from.

http://ohiocrank.com/chevy_rotating.html

 

Even if you can get an orginal GM 400 crank the cost of having the mains turned down is going to come very close to the cost of just buying a brand new Eagle or Scat cast steel crank. Due to rock wear on a machine shops crank grinder I would be amazed to see it done for less than $120. Also the Eagle or Scat peice is going to be far superior to the GM part.

Buying an entirely new rotating assy from one of them is a very good option but it is going to cost you a bit more more and if your stock 350 rods are in good shape that saves you some money. However 6000 rpm is getting pretty hard on a 5.7 rod 3.75 stroke motor, normally a good set of stock rods are plenty strong for most street cars not exceeding 400hp but IMO your going to be pushing it at 6Krpm due to the 1.52 stroke to rod ratio. If you had ARP bolts and polished beams, stock rods would be OK but using them as is in used condition COULD be a bad idea IMO. Your choice of course, they could fail.

Be aware with a 3.75 stroke crank you will have rod bolt interference using stock or any stock style rods (like the Eagle SIR nad lower priced Scat rods) with the camshaft depending on your cams base circle. You will have to grind a few of them for clearance, not a big deal but just making you aware.

As for the balancer it all depends on what crankshaft you buy. Scat and Eagle both make 2 types of crankshafts. Either external balance (which use a counterweighted 400 type balancer) or internal balance (which would use a regular neutral 350 type balancer). The factory GM 400 shaft is external balanced only.
Will

 

I am i building a 383 too. I prefer to use the stroker kit that comes with everything including the rods. Usually a chevy guy does not have to spend a bundle for a kit. A cast crank is good for 5-6 rpm, if you do not spend too much time there. I would get the entire kit including the rods which are usually a step above a stock rod. Remember the connecting rod is the most streesed compontent in the engine.

 

If you go the 383 route, I would get an aftermarket cast crank. It will probably be cheaper than getting a 400 crank and having it cut.

 

Definitely buy the kit. Make sure it includes the crank, pistons in the compression you want, cap rods(as opposed to rods where the bolts are pressed in), and the right balancer and flexplate. Reason for the cap rods are for cam clearance. The shoulder of the rod may have to be ground to clear the cam, and this can weaken a pressed bolt. Then after you've clearanced eveything, take the rotating assembly to a shop you trust and have it balanced.
Keep us posted on your progress

 

The block clearance needs checked too, on the pan rail areas as well as the bottom of the cylinders. The Cam lobe clearance can be checked with some soft aluminum rod after installation, but definitely the stock I beam rods will need to be ground on each top rod bolt to clear the cam (at an angle). None of this is hard, but it is tedious. Also, if your going to have it balanced, have the machine shop grind your rods, they should know how much approximately, even without assembling the whole motor if they do many 383's (which is very likely).

 

lots of good advice offered here, thank you,one and all. Ok,now will go amuse myself in different crank vendor sites

 

I will be keeping an eye on this thread. I'm thinking about dropping in a newly rebuilt 383 into the pacecar, all info provided is appreciated.