Thread: 350 sbc build need advise

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Originally Posted by techinspector1

Hold on there Hoss. The block will likely have to be bored and honed to the next oversize , +0.060", which could make the cylinder walls too thin, depending on core shift when the block was cast.

There are thin wall blocks and there are thick wall blocks in the same engine family. All production blocks are cast. Casting is a mature, but not particularly exact process. There will be core shifting and such going on that will make one block come down the production line with pretty much equally thick cylinder walls all around, then the one right behind it could have thin walls on one side of the cylinder and thick walls on the other side.

The thrust side of the cylinder on a small block Chevy is on the inboard side of the cylinder on the driver's side of the block and the outboard side of the cylinder on the passenger's side of the block. Most engine builders will prefer to have 0.200"+ on the thrust sides of the cylinder after boring and honing. Other areas around the bore can be slightly thinner. Famed engine guru Smokey Yunick said he likes to see a minimum of 0.135" anywhere in the cylinder after boring and honing. He said further that there must be enough mass in the walls to quell vibrations set up by the piston rings skidding up and down the walls (yep, he said they SKID, rather than moving smoothly up and down). Smokey used to cut windows into the cylinder blocks and install glass panels so he could witness what was actually happening with the motor running. If these vibrations are not kept under control by the mass of thicker cylinder walls, they can transfer to the water jacket side of the cylinder wall and separate out little air bubbles from the cooling water, which then cling to the wall and prevent cooling water from getting to the wall to cool the cylinder.

Now you know why an over-bored block with thin walls will have a tendency to over-heat.

Ultrasonic equipment is used in most shops to determine the cylinder wall thickness of a block. This equipment has come down in cost over the last 20 years, but is still in the $1000 range. Affordable for a shop or even an engine builder who builds a few high-buck engines a year, but still a little pricey for the home-builder. Check with automotive machine shops in your area to find out if any of them have the equipment to sonic-check your cylinder walls before you buy yourself into some trouble with money invested into a freshly bored and honed block that is useless except for a door stop.

The other thing is, you must build your motor to the fuel that is available to you. If that fuel is pump gas that is available down on the corner, then you will need to pull back a little on your expectations. It is generally accepted in the hot rod community that current fuel quality will support as high as 9.5:1 static compression ratio if the motor is using iron heads, which are slow to shed heat. If you want to invest in a set of aluminum heads, then you can safely build the motor to 10.5:1 static compression ratio. Anything over 10.5:1 will require E85 at the pump or racing gasoline or racing ethanol or racing methanol.

Using aluminum heads has aspects that must be paid attention to as well. In order to prevent fretting the soft aluminum material, thicker composition head gaskets must be used. For instance, several aluminum cylinder head manufacturers recommend the builder using Fel-Pro 1003 composition gaskets with their heads. These are 0.041" thick, so to end up with a squish/quench somewhere between 0.035" and 0.045", the builder must zero deck the block so that the pistons come up even with the block deck at top dead center. Since one of the goals in building the motor is to retain as much metal in the block as is possible, it becomes attractive to use a piston that has a very tall compression height so that a minimum of material must be removed from the block decks to arrive at ZERO DECK. Skip White Engines sells the Wiseco line of forged pistons that feature a +0.015" compression height over the stock 350 Chevy dimension of 1.560", so that with these 1.575" pistons, you need to cut the block only 0.010" to achieve zero deck. This is one of the best kept secrets in the hot rod community. I used Wiseco pistons in a racing go-kart in the early '60's, so I can bear witness to the quality of the brand.

https://www.skipwhiteperformance.com...orged-pistons/

https://www.skipwhiteperformance.com...-pistons_7452/

Pretty good prices in my opinion, for a piston and ring package of this quality.
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Ok so, after much pondering and considering the great information you have provided I think I'm going to have simons machine here in charelston hopefully give me a thumbs up on the bore as is at .040 as it was built only 3000 miles ago.I'm now considering a 383 kit with wiseco Pistons as suggested and having the block decked as suggested.
I will then possibly go with skip whites aluminum heads, maybe still use the air gap intake? and possibly a 750 Holley? Still not sure about the cam but feel a roller would be a nice touch? By the way what's the difference between a regular 383 crank and a scat crank?
So, what do you think? Please keep in mind this has been a learning curve for me.