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Old 01-21-2012, 09:06 PM
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383 rotating assembly

hey guys, new to this. got couples of question. Plan to built a 383 stroker with a 350 block (2 or 4 mains)...Already got alum heads (190 cc runner, 64cc chambers, 2.02/1.60 valve size), camshaft (.465/.488 LIFT .225/.235 DURATION @0.050" (hyd. flat)), edelbrock airgap intake, roller rockers, pushrods, Headers and many other parts...The machine shop guy offers a 383 rotating assembly with this specs:FORGED FLAT TOP PISTONS (1.425 compression height, 4.000 BASE BORE and 0.350 deck thikness), 5.7" RODS. What do you think about this combination? I have no idea about deck height or P/V clearance stuff...I appreciate any advise or idea.

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Old 01-21-2012, 10:18 PM
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let the machine shop do the assembly for you and you'll have a nice 383, don't forget they need balancing, a damper and flywheel from a 400.
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Old 01-22-2012, 12:00 AM
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Thank you for your respond Augusto. Kit comes fully balanced with balancer and flex plate. Unfortunately, seller's location is far from me and I'll only be able to purchase the kit from there and I have to send the block to somewhere close to me for machine job...As I said, my concerns are "deck height" and " valve to piston clearance" which I'm not sure about them. I appreciate if you or anyone else check this item description and clarify me if this will work with my other parts or not...

http://www.ebay.com/itm/SBC-CHEVY-SC...item5645ad52e9
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Old 01-22-2012, 11:03 AM
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I would say that unless your gona use the engine for all out racing, you wouldn't have to worry much about deck height and stuff, just install those nice parts in a sound block and enjoy.

I would though, make a valve to piston check just in case, your cam is not that radical but is better being a little safe, use an old compressed head gasket and assemble one head, put some modeling clay on top of a piston and slowly make it rotate a full 4 cycle ( 2 turns) then remove the head and see how much the valves compressed the clay (forgot to say that you should smear some grease on the valves to avoid the clay from sticking to the valves) some will not agree but for me 0.040 or more clearance is fine.
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Old 01-22-2012, 12:58 PM
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Quote:
Originally Posted by crossbolted
Thank you for your respond Augusto. Kit comes fully balanced with balancer and flex plate. Unfortunately, seller's location is far from me and I'll only be able to purchase the kit from there and I have to send the block to somewhere close to me for machine job...As I said, my concerns are "deck height" and " valve to piston clearance" which I'm not sure about them. I appreciate if you or anyone else check this item description and clarify me if this will work with my other parts or not...

http://www.ebay.com/itm/SBC-CHEVY-SC...item5645ad52e9
First, figure up the sum of the crank radius, rod length and piston compression height.
If the radius (half the stroke) is 1.875", the rod is 5.700" and the piston compression height is 1.425", then the sum of these parts is 9.000". The block deck height (measurement from the centerline of the main bearing bore at the bottom of the block to the flat deck of the block where the heads bolt on) on a SBC is ~9.025", so that will leave the piston down in the bore by 0.025" with the piston at top dead center. Using a conventional 0.040" compressed gasket will leave a squish (measurement from the piston crown to the underside of the head with the gasket in place) of 0.065".

Now, since David Vizard has dyno'd a slew of small block Chevys and found that the tighter the squish, the more hp a motor makes and the more detonation-resistant the motor is. He reduced the squish down to aroustand 0.026" before the piston kissed the underside of the head. A squish of 0.035" to 0.045" is considered by many to be the optimum squish for detonation-resistance and horsepower. At speed, the crank flexes a little and the rod stretches a little and the piston grows a little taller from the heat of combustion, so the piston will end up just slight of kissing the head with the squish at 0.035" to 0.045" on the engine stand.

So, if you had a stack of 9.000" and a block deck height of 9.025", you may want to cut the block decks some, so that you could use a conventional composition gasket and still have a good squish. Personally, in this case, I'd cut the block to 9.005" and set the squish at 0.045" with a 0.040" gasket.

I'm getting a little ahead of myself. First thing to do to the block is to have it magnafluxed for cracks. If it's valid, then check the main bearing bores for being round and parallel with each other. You may need to align-hone or align-bore the main bearing saddle to get the bearing bores in line, round and parallel. This is the basis of the build, getting the block square. Once the main bearing bores are round and parallel, have the machine shop register the block on the main bearing bores and cut the block decks to 9.005". This will not only set the proper groundwork for the correct squish, it will also square the block so that all four corners are the same distance from the main bearing bore. This will allow the same static c.r. on all cylinders (assuming that you equalize the chambers in the heads) and the tight squish will allow the use of a lesser grade of fuel without detonation. It will also allow the heads to sit squarely on the block so that the intake manifold will line up and seal up. Pay attention to the china walls on the block, they may need trimming to allow the intake manifold to sit down on the heads properly. I don't think anyone uses the black rubber seals there anymore, opting for a line of RTV between the ends of the intake manifold and the china walls to keep the oil in the motor.

This checking and possible cutting of the main bearing bores is essential in any build where the builder cares about the end product. And the cutting of the block decks makes a square block, allows the intake to sit properly on the heads, equalizes the static compression ratio between cylinders and therefore equalizes the squish between cylinders. Doing the mains and the decks should be considered the minimum of work that all you fellows should be doing to the block to get ready. If you don't have the money to have it done now, then wait a little while longer until you have collected the money to do them properly.

For piston to valve clearance, please read thoroughly this tutorial written by Ed Iskenderian, the "Camfather".
http://www.iskycams.com/camshaft.php
Skimming over it will not help you. Sit down and read through this thing thoroughly several times, then ask questions about it on this thread.

Oh yeah, one last thing, the pistons in the kit combined with 64cc heads will produce a squeeze in the area of 11.1:1 static compression ratio. If you have fuel to support this SCR, great. If not, either change the heads or the pistons to arrive at a lower SCR. A piston with an 18cc dish combined with 64cc heads will produce a static compression ratio of around 9.7:1, so that's what I'd do. Pay close attention to the compression height. This piston that I'm linking is 1.433" compression height, so it's 0.008" taller than the Probe piston in the kit. This would make your stack 9.008", so you would need to cut less off the block decks to arrive at your target piston deck height (distance from the piston crown to the block decks where the heads bolt on).
http://www.kb-silvolite.com/kb_car/p...etails&P_id=93

Last edited by techinspector1; 01-22-2012 at 01:11 PM.
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Old 01-22-2012, 08:45 PM
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You prevented me from mistakes. I really appreciate that.
OK, I'll use "FEL PRO Z1003" head gasket (4.166" bore, 0.041" compressed thickness). Using the C/R calculator you linked, with -4 cc flat top pistons, 3.750 stroke, 5.700 rods, 4.040 bore and 1.425 compression height (assume deck clearance is 0.025") gives 10.563:1 and using -12 cc pistons, it is 9.716:1. Do you think 10.563 is too high, I'll be in risk of detonation and it needs high octan gas (not pump gas)? Or, it would be better (safer) with 9.716:1 C/R? My buddy says with higher than 10.00:1 CR, engine continues running after turning of the Ignition with Carb (like Diesel!!) sounds funny to me. Is this true??
One more thing, What's gonna happen to valve geometry stuffs and intake, if I mill the deck to 9.005"? Any problem when instaling intake??Thanks again.

Last edited by crossbolted; 01-22-2012 at 09:01 PM.
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Old 01-26-2012, 07:38 PM
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The guy who does the block will know how much to remove from the intake manifold/head surfaces. On your final trial assembly, sacrifice a couple of manifold gaskets to make sure the intake ports are sealing all the way around the port (gasket pinched all the way around the port). Snug the heads down with an old head gasket, then torque the manifold down with the exact gaskets you plan to use on final assembly.
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Old 01-26-2012, 08:20 PM
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Quote:
Originally Posted by crossbolted
hey guys, new to this. got couples of question. Plan to built a 383 stroker with a 350 block (2 or 4 mains)...Already got alum heads (190 cc runner, 64cc chambers, 2.02/1.60 valve size), camshaft (.465/.488 LIFT .225/.235 DURATION @0.050" (hyd. flat)), edelbrock airgap intake, roller rockers, pushrods, Headers and many other parts...The machine shop guy offers a 383 rotating assembly with this specs:FORGED FLAT TOP PISTONS (1.425 compression height, 4.000 BASE BORE and 0.350 deck thikness), 5.7" RODS. What do you think about this combination? I have no idea about deck height or P/V clearance stuff...I appreciate any advise or idea.
This makes a 9 inch stack of 3.75 stroke/2+5.7 rod+1.425 compression height. Depending on decking which the stock SBC is 9.025 from crank center to deck this would leave stock clearance if the block isn't decked.

But you're suggest .035 total which I' guessing is a zero deck block and .035 gasket. My calculator gives this an 11.3 DCR. The compression is high, although I haven't run a DCR as to do that needs the actual timing events on the cam lobe with respect to the crank degrees, and the squish/quench on the tight side while good for squish/quench it's dimensionally tight for piston rock about the pin. With flat tops this is a place where you need to be pretty close with the math or you'll be in compression trouble for unleaded premium very easily.

The .035 squish/quench clearance to the head makes you pay more attention to keeping the piston to wall clearance on the minimum, which can be difficult with a forged piston. but you need to avoid a situation where the wall clearance lets the piston rock to where it takes up the squish/quench and hits the head don't loose sight of carbon accumulation on chamber and piston and piston to wall wear down the road.

Aluminum heads will be more tolerant but 11ish is asking a lot. The combination of high compression and wide squish/quench can walk you into a detonation situation so you've got run numbers till your eye's bleed as once built the choices are torpedo the power by backing off the timing, adding water injection, or ripping it apart to change pistons and or heads. Don't know about the car or gears light car and stiff gears especially with a stick gives you more situational management, if not tolerance, of high compression. depends a lot on stuff we don't know at this end.

All-in-all it sounds pretty nice but do the math, send us the cam number or timing card data so we can run the Dynamic Compression Ratio, the cam might save you, but gotta have the data to crunch the numbers. Right now knowing what little I do I'd say your compression is iffy high.

Bogie
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Old 01-26-2012, 10:14 PM
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Thank you with your helpful information...
So, it seems I need to lower compression. I focus on the kit with "dish top" pistons. Here are the specs:

Piston Material:4032 Forged Aluminum
Engine Family: SBC 383 cid
Base Bore:4.000"
Stroke:3.750"
Compression Height:1.425" - Dish top
Net head volume:-12cc
Deck thickness:0.350''

And for Camshaft (Hyd. flat tappet):
•VALVE LIFT WITH 1.5 ROCKERS : INT .465 / EXT .488
•DURATION IN DEGREES : ADVERTISED - INT .279 / EXT .289
•DURATION @0.050" : INT .225 / EXT .235
•LOBE SEPERATION ANGLE : 110º

Heads: Aluminum 190cc runner/ 64 cc chamber / 2.02 in.,1.60 ex

Do you people think I'll be in trouble with this combination (assume deck height remains stock 9.025) and C/R (or P/V or other things) are still to high???

I appreciate that.
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Old 01-27-2012, 12:14 PM
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Quote:
Originally Posted by crossbolted
Thank you with your helpful information...
So, it seems I need to lower compression. I focus on the kit with "dish top" pistons. Here are the specs:

Piston Material:4032 Forged Aluminum
Engine Family: SBC 383 cid
Base Bore:4.000"
Stroke:3.750"
Compression Height:1.425" - Dish top
Net head volume:-12cc
Deck thickness:0.350''

And for Camshaft (Hyd. flat tappet):
?VALVE LIFT WITH 1.5 ROCKERS : INT .465 / EXT .488
?DURATION IN DEGREES : ADVERTISED - INT .279 / EXT .289
?DURATION @0.050" : INT .225 / EXT .235
?LOBE SEPERATION ANGLE : 110?

Heads: Aluminum 190cc runner/ 64 cc chamber / 2.02 in.,1.60 ex

Do you people think I'll be in trouble with this combination (assume deck height remains stock 9.025) and C/R (or P/V or other things) are still to high???

I appreciate that.
Crossbolt, what I (we) need out of the cam is the actual events of intake open and close and exhaust open and close or the manufacturer and part number so these specs can be looked up. Actually to do DCR the really important event is when the intake closes referenced in crankshaft degrees. The reason for this is that at RPMs under the torque peak, the piston will actually reverse pump an amount of mixture back into the intake. You can think of this as one cause of "reversion" which usually results in a cloud of mixture standing above the carb inlet. So the Dynamic Compression Ratio is a trigonometric calculation of how high the piston is in the bore when the inlet valve closes. The DCR model treats this as lost stroke which makes the displacement side of the Static Compression Ratio model look smaller which then reduces the SCR. For best performance we're trying to get into a range from about 8 to 9 to one for the DCR. This calculation is also variable with the rod length which you already gave.

This is a circular calculation where you build the SCR then do the equations to get the DCR. Then if the DCR falls outside the general ranges for best performance with the octane fuel you want to spend money on, you go back and adjust the volumes above the piston at TDC including any volumes in or on the piston's crown and recompute the SCR to rerun the DCR till you get it dialed in. My rule of thumb for DCR is iron heads and regular fuel of 8:1 to premium at 8.5:1. For aluminum heads with regular fuel at 8.5:1 to premium at 9:1. There's other considerations that affect this but this gets you into the ball-park. Squish/Quench is one of the biggest of the other concerns getting a separation of .040 inch between the opposing head step and piston is close to ideal. The effect lessons as the gap becomes wider or the surfaces that close toward each other become smaller as happens with a circular dish piston. The effect becomes greater as the clearance becomes less than .040 but there are mechanical limits to avoid the possibilities of collisions between the piston and head. If you're racing the trade will be tighter for better power and efficiency against the risk. For a street motor one usually favors less risk for less than optimum power and efficiency. When adjusting the compression using a dish in the piston you want to use a piston with a D shaped dish in the crown as this presents the same flat surface to the head on the squish/quench step side as a flat top so the function remains much the same between these two designs.

To do's would be:

What do you mean by deck thickness of .35 inch?

So get the timing card events or the cam part number so we can get them.

Get the piston manufacturer and part number.

Be sure of the rod length.

Bogie
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Old 01-27-2012, 02:32 PM
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Quote:
Originally Posted by oldbogie
What do you mean by deck thickness of .35 inch?
I figured he was talking about the piston crown thickness, 0.350", a number thrown out there by the supplier to try to lend credence to the package he's trying to sell. A tempest in a teapot.
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