[Nathan123455663]

I have a 350 block with Vortec heads bored to a 355 I would like to get a list of stuff I need to turn it into a 383 as cheap as possible.
1.) do I need to replace pistons if I put a (383) 400 crank in it if I use 5.7in rods
2.) would it be considered a 383 with different crank and .30 over pistons
3.) what is better internal balanced or external
4.) do I need to swap the cams
5.) do I need to change anything else
6.) how would I know how tall the (stack) would be if I were to order 383 crank 5.7 rods and pistons that are currently in it

 

[cerial]

Are you building this to build it or because you believe that will be the cheapest route?

If you want one built the cheapest consider a (local) longblock crate or longblock built from a local engine builder.

Proven numbers, often all new parts, and a warrenty for close to what you can build one for. Maybe less depending on machining and tool cost in your area.

 

[SoulSurfSD]

1.) Yes
2.) 383 crank (different than a 400 crank) and 383 pistons (different than 350 pistons)
3.)Internal, depending on what you want to do with it.
4.)Yes
5.)Yes
6.)You can't use the current pistons, and people typically use clearanced rods and/or small base circle cam.

In my opinion, you're better off dialing in your 355 to ~400HP (cam, intake, and a little head work... and proper fuel delivery).
Using any of your current stuff on a 383, you'd just end up with a lame 383.
So unless you're prepared to spend mucho dinero and build a 383 from the ground up (or buy one as cerial suggested), a hot 355 would be a better choice... just my opinion, having just gone through a ground-up 383 build ($$$!) .

I'm not the expert, but I'd bet most of them would agree with the above... mostly.

 

[Camaromeo]

I think the same.. New valvetrain and maybe an apropriate new Intake. Thats the best Bang for buck. Otherwise i would probably sell the old engine and buy a new 400 based Crate SB. Blueprint has one with over 500hp for 5.7k. Deduct the old engine from that and that deal is also good i think..

 

['49 Ford Coupe]

I feel compelled to throw something in here... I just did a quick check of the cost 383 crate engines, and it looks like they sell for around $4,500 to $5,500 ... I built my 383 from the ground up, and it cost me around $2,500. There is a huge level of pride and "bragging rights" if you want to call it ... in knowing you've done everything yourself to build your ride (except for the interior)...Of course, building or rebuilding a 350 is a LOT less expensive.. so the OP just needs to decide if the extra expense and work is worth the extra torque and satisfaction. If I were as poor then as I am now, I'd probably have just built a 350... Sometimes this kind of stuff will keep ya up at night... hard to get to sleep...ahahahha

 

[BogiesAnnex1]

You can’t use your current pistons as the stroke of a 383 crank will push them proud of the head deck at TDC and will pull their skirts into the counterweights at BDC. So the pistons are reconfigured to provide the necessary clearances at both ends of the stroke. Further the piston configuration in these regards are unique to the rods used the short 400 rod, the standard 5.7 inch rod and the favorable for getting to internal balance 6 inch rod each demand a matching unique piston.

Rods are a PIA in these things as they need to clear the cam, the pan rail, and the lower extension of the cylinder bore wall where it extends into the crankcase. To the end of fit that doesn’t require extensive grinding of the top of the rod bolts for cam clearance, the pan rail for rod bolt nut clearance, or the bottom of the cylinder wall extension for top of the rod bolt clearance in the old 5.56 inch 400 rod that offers the least cost but the worst force transfer and poorest balance characteristics. These do allow the use of the 400 damper and flywheel or flex plate pretty much without going to the balance emporium.

From there you get into the 5.7 inch rod which in the nut and bolt form requires a lot of modification of grinding the top of the bolt head on several of the rods to clear the cam and substantial grinding on the pan rail as well as the cylinder wall extension pad. The latter sometimes gets you wet as this area is pretty thin and easy to penetrate or set up a future in-service failure due to excess thinning of the casting without necessarily penetrating it. The 5.7 rod and it’s unique piston will use external balance as does the 5.56 inch rod and their respective pistons but unlike the shorter rod the 400 balancer and the flywheel or flex-plate isn’t quite correct so a balance emporium trip is highly recommended. Also, to be considered is the use of cap screw rods. These greatly reduce and often eliminate the need to grind for clearances on the rod or block.

The 6 inch rod and piston assembly is lighter than the 5.7 and can be internally balanced without the use of heavy metal inserts into the counterweights which is expensive. The weight savings comes off the piston and is significant. This uses a standard internal balance damper and flywheel/flex-plate. A trip to the balance emporium is needed because nothing hanging on the rod journals is similar to a 400 or 350.

I caution against buying a prebalanced assembly as it you have to hack on it for clearance on your block (mostly cam) the balancing that came with the assembly is tossed out the window. If you build enough of these you learn that there are differences in casting dimensions across blocks even with the same casting number so you don’t know how much material you may need to whack off the rotating assembly before you mock the assembly up in the block. Certainly with cap bolt rods the possibility of success with a pre balanced crank assembly is a quantum higher than with bolt and nut rods. Another way around this is with a small core cam but these increase the SBC’s already bad habit of digesting cam lobes and litfers.

The L31 block is a good starting place as it doesn’t extend the cylinder wall so deeply into the crankcase so this clearance grinding is pretty much eliminated, that holds pretty well for all one piece rear seal blocks using hypereutectic pistons.

So this is the real world of building a 383 based on my experience and not just selling parts for these things to make a buck.

Bogie

 

[ericnova72]

Only way to use your current pistons with a 3.75" stroke "383" crank is to use them with the short factory 5.565" 400 SBc rod....but none of the aftermarket "383" cranks will allow the use of those rods, they all have bigger counterweights than a stock 400 SBC 3.75" crank and are configured for a 5.7" or longer rod only
The only way to keep your pistons is with the short 400 rods and a reground old stock 400 crank with the mains ground to 350 size. This was the old school 1980's way of building 383's, before 5.7" or longer rod ready-to-run pistons were available.

You can do this fairly inexpensive with a 5.7" rod , cast crank, external balance rotating assembly, but whether it will be worth much as far as power is concerned will depend on the cam you are using now, and the intake manifold. Header primary size may make a difference too, depending on what you have. if you plan to keep RPM's below 6500 rpm, don't get to hung up on internal vs external balance, it doesn't help that much unless you are going to turn more rpm than that on a regular basis.

List some more of the parts you intend to keep using and we can see if this idea is worth the effort.

Parts stack is 1/2 of stroke + rod length + piston compression height + "xxxx" stack height.
Stock SBC block is nominally 9.025" tall, crank centerline to deck, so stack needs to add up to something close to that, with small allowances can be made using gasket thickness and block deck milling to accept a stack from roughly 8.990" thru 9.040".
Compression height is distance from centerline of wrist pin to top of flat deck area of piston, not dome or dish. Compression heights ("CH") are typically listed for most pistons.....stock 350 CH is 1.560".
Stock 350" stack is 1.74"(half stroke) + 5.700" rod + 1.560" piston = 9.000", and when used with the original designed .015" head gasket and 9.025" block height = a .040" quench clearance(piston to head distas nce as assembled with gasket),
Ideal quench is .035-.045"

 

[55_327]

Have to say that even using the same cam and heads from a well running 350 will make a noticeable difference in power (torque) with the extra .27" stroke.

And if it's already an over-cammed 350 with decent heads, you will also pick up some horsepower by using those parts in a 383. And you should be able to re-use the cam in the same block with each lifter in its same bore.

 

[SoulSurfSD]

The big question that hasn't been answered is "What's it going in, and what are your expectations?".

My remarks were based on my own perspective of wanting much more than a factory motor with a longer stroke.
But if that's all the OP wants, then of course he could achieve that much cheaper than what I inferred.

Assuming that his Vortec heads are in stock form, they'd require work just to accomodate a 383 cam, and I've been told by the experts commenting here that Vortec heads are a bottleneck on a 383.

I got the impression that the OP was trying to improve on what he has "on the cheap".
If that's the case, what's the best route to do a 383 on the cheap, and what are you going to end up with?

 

[55_327]

The big question that hasn't been answered is "What's it going in, and what are your expectations?".

Definitely. But Nathan the OP seems to have left the building.

On another note, this looks like a budget-friendly place to start: 383

With the 3.80 stroke, I assume it's from GMPP. What do you guys think?