Thread: Questions on 383 SBC build

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Mr. Dobbs, the following is written more with newbies in mind than it is for you and your son. Not knowing the details of your build precludes me from addressing your build specifically, but I wanted to bang hard on the block deck height/squish, because it is applicable to anyone building any motor. As in all builds, the fuel determines the details. If the car will be limited to using pump gas, then the generally-recommended limits are currently 9.5:1 static compression ratio, with 10.5:1 being the current limit with pump gas and aluminum heads. If the motor will be operated on racing gas, ethanol, methanol or E85, then there would be no limit to the SCR and the cam you can use. Your post reads like the motor will have to use pump gas at least part of the time, so that will limit your build to the aforementioned 10.5:1 SCR. As far as revs, you said you will wind the motor to ~7000. This would call for either a flat tappet solid lifter or a roller tappet solid lifter design, determined by the SCR and operating characteristics. Hydraulic rollers, due to their weight, tend to loft up off the cam lobes at revs over about 6200, as advised by the cam manufacturers.

Any build should begin with measuring the block deck height on all 4 corners. This operation can be done at home with a 12" caliper, either dial or digital. I'm pretty sure the 350 main bearing bore, less bearings, is 2.6410", but snug the front and rear caps up and measure the bores to make sure. After you have the main bearing bore, divide it in half and write it down. Should be 1.3205". Now, measure from the lip of the bore to the block deck where the heads bolt on, as shown on the photo here, then add the radius of the bore, less bearings.
http://www.jamisonequipment.com/picPage/BHM-24-1.gif
Design blueprint measurement of the block deck height of a small block is 9.025", so your measurement from the lip of the bore to the deck should be on the order of 7.7045". 1.3205" plus 7.7045" would make a 9.025" block deck height. Your actual measurement could be less than that due to the block decks having been machined in the past or a little more due to manufacturing tolerances.

The reason you need to address the block deck height is that you will need to choose a "stack" of components to fill the cylinders that when added together, will reach a desired piston deck height (measurement from the crown of the piston to the block deck, including head gasket thickness, with the piston at top dead center). The reason you need to know the piston deck height is so that you can choose the proper head gasket compressed thickness to set the squish at somewhere between 0.035" and 0.045" to help prevent detonation and make the most power from your combination. David Vizard, noted engine builder and writer, has said that the tighter he builds the squish, the more power the motor makes with no other changes. With a small block motor, I would urge you to set the squish at ~0.035", on the tight side of the range.

The other thing that needs to be addressed with aluminum heads, is that they will want composition gaskets. Steel shim gaskets will not allow the expansion and contraction that are needed to allow the heads to move a little without fretting the aluminum surfaces of the heads. The movement created is due to the different expansion and contraction rates between the cast iron block and the cast aluminum heads. Airflow Research recommends a Fel-Pro 1003 and Pro-Filer recommends a Fel-Pro 1010. Both these gaskets have pre-flattened fire rings to prevent brinelling of the aluminum.

Let's say, for instance, that your block deck height measures 9.025" on all four corners (not likely) and that you are shooting for a squish of 0.035", using a composition gasket with a compressed thickness of 0.039" (1010 gasket) to 0.041" (1003 gasket). You might choose a piston with a 1.250" compression height, rods that measure 6.000" center to center and add in the crank stroke radius of 1.875" (3.750" stroke crank divided by 2). These values add up to 9.000" stack height. If you put this stack together with a 1003 gasket, into a block with a block deck height of 9.025", the squish would be 0.066", far too wide to contribute anything to the combination in the way of squish. Again, let's say that you were shooting for a squish of 0.035". With this combination of parts stack (9.000"), you would want to cut the block decks for a new block deck height of 8.994". This would pop the piston crown up out of the block by 0.006" with the piston at top dead center and when combined with a 0.041" head gasket thickness (Fel-Pro 1003), would result in a 0.035" squish. If a fellow wanted to use a little wider squish, like maybe 0.041", he would cut the block decks to 9.000" so that when used with a stack of 9.000", he would have a zero deck. Then using a 1003 gasket, the squish would be 0.041", still in range for anti-detonation and power production qualities.

You would want to have your machine shop cut the angles on the intake manifold to fit between the heads and seal up. This is a critical part of any build, as the angle being off between the manifold and the heads can allow a gap between them on the lower side of the port that will allow the pistons to pull oily crankcase vapors into the cylinders on each intake stroke. No amount of checking for vacuum leaks from the outside of the motor will find this gap. It must be sealed by proper measuring and machining when the build is being designed.

buy no parts until you have all of this worked out on paper and have run it past the fellows on this board. I see it all the time where fellows will jump out there and purchase something ahead of time, usually a cam, and then paint themselves into a corner when the cam doesn't work out with their final combination. BUILD THE MOTOR ON PAPER FIRST.

The other thing you need to be aware of is the matching of the cam to the static compression ratio of the motor. You don't choose the cam by reaching out into thin air and choosing one by the specifications that look good to you. You choose a cam to do what you want it to do based on the static compression ratio of your build. Here's an article I wrote that explains it.....
http://www.crankshaftcoalition.com/w..._compatibility

Different builders will like different intake manifolds, but the one that produces the most power on the dyno between 1500 and 6000 is a dual-plane, high-rise manifold such as the Edelbrock Performer RPM 7101 or the Weiand 8150. You should make yourself aware of the term "power under curve". It means simply that a single plane intake, for instance, might make more power past 6000 rpm's, but less power on the way up as compared to a dual-plane intake such as the RPM. If you're going to build your motor to make power from 5000 to 8500 rpm's, then by all means use a 4500 stall converter and a single plane intake manifold, but if your goal is strong street power stoplight to stoplight with a little drag strip action, use a dual-plane, high-rise manifold together with a converter that allows the motor to "get up on the cam" from a standing start. Other manufacturers have produced this dual-plane, high-rise type of manifold in the past and it may be found used on craigslist or other sources as Weiand 8016 or Holley 300-36. For max power, use a 750 or 850 carb, vacuum secondaries if auto with less than 3000 stall converter or double pumper design if using a manual trans or auto trans with 3000+ converter stall. Use as much air filter as you can fit. I like a minimum of 14" diameter x 3" or 4" height so the motor can breathe.

The torque converter should be the final purchase, right after the camshaft. A good quality converter that will do what you want it to do will cost you right around 600 bucks. Of course there are cheaper converters out there, but be aware that they will not do the job as well as one that has quality parts and engineering built in. In my opinion, the optimal converter, if the vehicle is to be used on the street most of the time, is 3000 stall. Coupled with a cam that makes power beginning at 2500, this will make a very strong combo that is fully streetable. If the car will be drag race only, then of course the sky is the limit based on cam and gears.

Be aware that a 383 build will have connecting rod to cam lobe interference that must be addressed. There are 2 ways to get around it, either by using a camshaft with a reduced base circle (that I will not recommend) or by using an alternate connecting rod that has been clearanced in manufacture. Some fellows are OK with grinding on stock rods to gain the clearance, but that is not an avenue that I would recommend. Scat makes quality components, including rods that are clearanced for a stroker motor. My best recommendation would be here.....
http://www.summitracing.com/parts/sca-26000p/overview/
Minor clearancing may be necessary at the oil pan rail on the block. 0.050" clearance is good enough. As we used to say, "a miss is as good as a mile".

As far as heads, if you're bucks-up, there is no better choice than Airflow Research 195cc Eliminator 23 degree Street heads, available in 65 or 75cc chambers. Next choice would be Pro-Filer 195cc heads, available with 64, 70 or 72cc chambers.


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