I bought a perectly-running 1973 Chevy 350 with TH350 for $400. The engine was purchased new less than 1000 miles ago, but the original intake and quadrajet were put back on with no rebuild. The carb has seen better days but runs. It also has stock heads that were new 1000 miles ago. It's going in my Jeep eventually and was purchased with the intent of being a super-budget friendly swap. Eventually I plan on putting projection on there and so forth. I've always dreamt of building it into a 383, though. I can install any new pistons, rods, bearings that I need myself. The only thing I have to contract out is the machine work. But I've heard that you either need new rods or pistons to do the conversion, which I'm not really willing to invest in at this point. Is it true that I need them? Is the conversion just something that I should wait on seeing as how I have very little money right now and still need wheels and a t-case adapter? Or if I choose to do the conversion, is it pointless without a more effiecient/performance fuel delivery system?

J. J.

ok, heres how i see it. the block gets bored 30 over for a 383, you will need 30 over pistons and rings to match. rods can be reused, but while there out, Why not upgrade? A 400sb crank must be obtained, or you need to buy a new one. also entailed is the switch to external balanced dampener, and a new flexplate i think. The breathing part all depends on the quad you have now. i think they came in 600 650 and 700cfm varieties but im not too sure on the exact #. the bigger ones will be better (obviously) but they will all "work"

So, IMHO, id swap in the running 350 you have now, and get your wheels and tcase adapter. then you can wheel the rig. while you are running with the 350, find a good 350 block and start the 383 buildup, keep it on the stand and build it RIGHT as your fundage becomes available. when its done, just drop it in place of the 350, and then sell the 350 to some poor sap who needs one.

At least, thats what id do.:cool:

I do not remember all the specs but the 350 stroke is 3.48 while the 400 has a 3.75 stroke. So you have .27 inch more stroke which you have to take away from the piston/rod combo. The 400 rods are 5.56 inches long while the 350 rods are 5.7 inches long which makes up for .14 inches leaving .13 inches to make up from the piston. You can also use the 5.7 rods but with a supershort piston but this allows the piston to rock more than the 5.56 rod does.

Oh, I forgot to say that the block is already bored .030.

J. J.

Don't use the 400 rods (5.56" long). Use either the 350 rod or get some 6" rods, either new or from an Olds diesel 350. Your rod/stroke ratio is atrocious with the short rod, so it won't perform as well as it could. Big reason for me is that a short rod causes you to wear the rings and cylinders much faster - that's why there were so many 400 cranks needing a new home a few years ago. In the custom pistons for a longer-rod 383 the pin holes are shifted up toward the oil control rings, but they have essentially the same bearing surface in the cylinder bore. These days most original 400sb cranks have been through a couple of blocks and are nearing the end of their service life. Also the rod jounals on the 400 cranks must be ground down for the smaller diameter rods of the 350 (also to clear inside the block) and this should be done with a large fillet radius - hard to get because most shops hate to change or shape their wheels. By getting a new small-journal crank (try Scat - hiqh quality and reasonable prices) the only machine work you'll need will be to take a die grinder and remove tiny amounts of metal from the bottoms of the cylinder walls to clear the rods. By getting Scat's rods with that crank it should all clear with little or no grinding. 400's (and therefore 383's) are externally balanced, so you will need a harmonic balancer and flexplate. Your induction system should be just fine unless you want high rpm, which all depends on whether you want to crawl or sling mud. Ditto for the heads. I agree with shaggy - it runs, don't fix it or you won't be wheeling. Get your wheels and adapter, save up for a new Scat crank, and maybe rods (6" I'd say). Keith Black hypereutectic pistons are an excellent choice for something like this and a lot cheaper than forged.
It's a lot cheaper to do it right than it is to do it twice.

Speed-O-Motive Budget 383 kit 465.00$ I have one. Works great

Speedomotive Website (www.speedomotive.com)

If ya wanna spend the $$$$$$

lloyd, I agree with your points. Let me add that you will have to grind all the rod bolt and side of the rods a bit for cam clearance (this must be checked). I say all the rods because they will need to be balanced. It is probably easier to go with a small base circle cam, which leaves plenty of clearance (depending on how cam figures). To do yourself can be a chore, the rods should have eqaul amounts removed to ease balance. From what I understand even though it is external balanced the rotating assembly needs to be balanced. A balancer (dampner) is not a true balancer in that sense, it is a harmonic dampner, to dampen harmonics within the engine. I think the easiest is to use 383 stroker pistons (they have the pin hole moved up and a shorter skirt to clear the crank and keep the piston top from going above the deck), stroker rods or (close to stroker) Eagle SIR I beam 5.7" rods (they have 12 point ARP rod bolts which have a smaller head to help clear the oilpan rail, cam, and cyl. bottoms), clearance the block for .080" clearance at the oilpan rail (not always needed) and bottom of the cyl, careful not to take off too much here or you will find water (water jacket), and finally a small base circle cam will almost gaurantee you will not have rodbolt to cam clearance issues. It hard to get in there to measure that clearance anyway. Goodluck. John

Wow, thanks for all that info, you guys! I think I'll wait for now like you said. Or I may leave in the 6-cylinder for now and build the 350 while I wheel. Either way your advice is greatly, GREATLY apreciated.

J. J.

Im not sure, you probably know more than i do, but i thought you have the BLOCK clearanced to make room for the rotating assembly, not grind the rods/bolts to clear the block? In my logic the rods and bolts need all the strength they can get, since theoretically they are directly taking all the force the engine generates? i dunno....:confused:

Shaggy - you've got to grind the rods/bolts to clear the CAM. Then you grind from the bottoms of the cylinders to clearance the rotating assembly in the block. CJ8 is absolutely right, balance the rods and bottom end carefully. CompCams has an inexpensive rod balancing fixture that is well worth using. It has a round section that the big ends of the rods clamp onto, with the small ends 180 degrees out. This round piece has two small diameter protrusions that sit on parallel rails, and allow you to find balance at the small end of the rod (where it matters most at rpm). To get the most out of this, first clearance the rods for the cam, then get the block taken care of. Now you can static-balance the rods with a good balance, just get them all the same weight, by removing tiny amounts of metal from the big ends. Next use the CompCams fixture to balance the small-ends. This way you get paractically the same effect as an expensive dynamic-balance job at a fraction of the cost. Eagle rods are excellent; so are Crower. I've built a lot of engines, and read a lot of books on the subject, but one book that really stands out to me on this subject is by David Vizard, something like "How to build High-Performance Smallblock Chevy's on a Budget." I recommend that one highly for what you want to do. It's not necessary to use a small base-circle cam but it will reduce the time spent balancing. Mine has an Isky 292 duration 505 lift, and it's REALLY TOO DAMN BIG. Except for running mud. For more of a general-purpose thing you shouldn't go much over 270 duration, and if crawling is your deal get one of the really slow grunt cams. You get a lot of low-end potential out of that extra stroke, unless you choke it off with extra overlap. For one of these you'll want about a 108 lobe center. Get a copy of Desktop Dyno and play in there first; you can try different cams, heads, intakes, etc. much cheaper and easier that way; see what works best for what you want it to do.

Gotcha. I see what you mean now. thanks.:D

OR...you can use that 350 as a core for a crate 383. That's what I did. I love my 383!

I just completed a 383 buildup. I used 5.7 rods with Keith Black 72cc pistons. My compression ration is about 9.3 to 1 and a custom Comp Cam. It's a full roller setup. Both the Rods and Crank are Scat. I use a 400 fluid dampner which worked fine. My HP is about 520 with 450+ in torque. If done right the block will need extensive grinding and clearancing. Not so much for the pistons but to improve oil flow.

Stroker383, let us know if you have any problems with that FluidDampner harm. bal. I had read on their website (I believe) that they do not suggest using the Fluiddampner on the scat cranks (I am using a SCAT crank also). I believe their concern is more with drag usage, but they say you have a sudden shift with the viscous fluid upon sudden acceleration or decceleration, and you take a chance on breaking the snout off the crank. I have heard of this happening, it is due to the viscous fluid suddenly shifting and "slamming" forces are transmitted to the crank. I will and find a lead to that info on their site and post it here. Thanks. John

John,

Thanks for the tip. The machine shop that assembled the engine didn't have any concerns. The rotating assembly was balanced at a race shop in Dallas TX and they didn't mention that. I'll be sure to watch out for it and let you know if I have any problems.

Shane "Stroker383"