what is needed to make a 383 ?

 

A "383" is a motor with a 3.75" stroke and and a 4.030" bore. So, to make your 350 (3.48" stroke, 4.000" bore) into a 383 the block needs to be bored and you need a new set of pistons along with a new crankshaft.

Rich

 

now im not totally sure but does it matter about the length of the rods?

my stock ones were 5.7" and i have 6.0" rods in now. I may be wrong.
anyways i love my 383!!

 

The combined length of the crank throw (1/2 the stroke), the rod length, and the compression height of the piston have to add up to the height of the block (the distance between the crank centerline and the deck surface) plus or minus the desired "deck". Compression height is the distance between the pin center line and the piston crown. The "deck" refers to the distance from the piston crown to the deck of the block. So, when any two are fixed, the third dimension needs to be changed to make up the total.

For example, a stock 350 has a 9.200" deck height. Stock crank is 3.48" stroke, rod is 5.70" long and the piston compression height is 1.55". 1.74+5.7+1.55 = 8.99". 9.20-8.99 = 0.01" Therefore, with stock dimension components the piston is ~0.010" down in the hole. They actually usually measure a little more, I think the stock pistons may be a little shorter. Stock engines typically leave the piston between 0.010-0.20" down in the hole to allow for manufacturing tolerances.

Performance engines are often "zero decked" - set up so that the piston crown is flush with the deck. There is no particular advantage to this. But it is a custom and gasket design often reflects this. That's why many performance gaskets are in the 0.039-0.041" range. With a zero deck this puts the quench close to the optimal range. Quench refers to the clearance between the flat part of the piston crown and the corresponding area of the head surface. A tight quench promotes turbulence in the combustion chamber which has a number of beneficial effects.

Rich

 

but if i wanted to could i use stock heads for a little bit till i get them ported and a bigger tb or is that a no go

 

If you are going to want any benefit to having a 383 your going to need the heads and cam to go with the combo. If you built a 383 and don't touch the top end you are better off just getting a heads and cam package for your 350 before you get a 383.

 

Theres hardly "no benefit" to going 383 with stock heads, if there was no benefit to going 383 with stock heads then there would be no benefit to a 383 with ported heads. A 383 will always make more torque and at a lower rpm than a 350, now you may not necessarily gain horsepower by getting your block redone to be a 383 but you will feel it in the seat of your pants, just like swapping out the gears.

 

Besides boring of the block for the 4.030" pistons, you'll also need to have the block clearanced for the 3.75" crank. The flywheel will also need to be changed as 383's are internally balanced and your stock 350 was externally balanced in the rear via the stock flywheel.

 

Just doing some research on building a 383 and came across something here that didnt make sense, just looking for some clarification. Rich I know you are pretty knowledgeable, maybe you typo'd or I missed something, 9.20 - 8.99 = .01" ? Looks to me like it should be .21" ?

Basically I was looking for how far in the hole a stock LT1 piston is. Why do some people use 6.0 rods .vs 5.7 rods when stroking? What would be better for a boost engine? Preferrably not decking unless necessary.

 

Sorry for the math error. Stock deck height is 9.025". Not sure what I was thinking.

Rich

 

Not necessarily. Eagle (and probably others) make LT1 specific cranks that are internal front/external rear so that it isn't necessary to change the flywheel. That is what mine has.They're a little more expensive (like maybe $50), but cheaper than a new flywheel.

 

The theoretical deck height is 9.025". I've measured a few and came with 9.010 to 9.030". Before decking a block it must be measured and no assumption be made that it should have the corrrect height.
The 5.7" rods are more suitable for boosted and nitrous application because the piston ring could be pit lower and further from chamber heat.