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Topic Review (Newest First)
10-11-2012 06:57 PM
57Chevy3100 These are the exact pistons I have but in .060 over instead of std. bore.
Sealed Power H345ACP Speed-Pro Digital Diamond Profile Hypereutectic Pistons
10-11-2012 03:49 PM
techinspector1
Quote:
Originally Posted by 57Chevy3100 View Post
So will the motor run better on higher octane with the lower squish or dose that not have anything to do with it?
Yes, Vizard has stated that power goes up the tighter the squish is, up to the point of piston/head interference of course. It makes sense, because like I stated above, the squishing (or "jetting") of the fuel/air mixture across the chamber homogenizes the mixture and eliminates rich and lean pockets just as the spark plug fires. The thing that you want to do when maximizing this effect is to provide the largest flat area on the piston crown that is possible. Stock-type Chevy pistons and other pistons that I have seen in the aftermarket have only a very thin band of material around the perimeter of the crown that comes up close to the head and are cut into a shallow dish from there toward the center of the crown, so you have very little area to generate squish. Take a look at the Keith Black hypereutectic pistons. Even with a large dish, they have a generous flat area on the crown to mate up with the underside of the head and generate squish. Here's a 22cc dish design from KB. On the left side of the photo, you'll see a very large flat area on the crown.
KB Pistons for Automotive Applications
This design will provide maximum squish from a dished piston. Of course, a genuine flat top will work best, one where the crown of the piston is absolutely flat with no cut for a shallow dish.
KB Pistons for Automotive Applications
This type piston will work very well also....
Sealed Power L2256F40 Speed-Pro Powerforged SB-Chevy Pistons
This is the type of piston that I will not use....there is no squish pad on the crown....
Sealed Power L2323F30 Speed-Pro Powerforged Oldsmobile Pistons
10-11-2012 07:38 AM
57Chevy3100 So will the motor run better on higher octane with the lower squish or dose that not have anything to do with it?
10-10-2012 11:55 PM
techinspector1
Quote:
Originally Posted by 57Chevy3100 View Post
Sorry for my lack of knowledge but what is squish?
Squish is the clearance between the piston crown and the underside of the cylinder head with the head gasket in place and the piston at top dead center.
The tighter you can run the squish, the more fuel tolerant (knock resistant) the motor becomes. What happens is that as the piston comes to top dead center, the space between the piston and the head diminishes to a certain point and that clearance is called squish. The piston "squishes" the fuel/air mixture out from between the piston crown and the underside of the head and "jets" it across the chamber just as the plug fires. This "squishing" homogenizes the fuel/air mixture and eliminates lean and rich pockets of air and fuel and results in a cleaner burn which in turn makes more power, plus makes the engine less detonation sensitive for the fuel you're using.

I'm just gonna throw some figures out here, so don't take them to the bank. Let's visualize that the motor has a squish of 0.080" and detonates on 87 octane fuel. If we cut the block decks to reduce the piston deck height or use a taller piston compression height and reduce the squish down to 0.040", the motor may run on 87 without any detonation. This is just a "what-if" set of figures, so don't hold me to them.

David Vizard, famous engine builder, has said that the motor will pick up power and run on lesser fuels the tighter he builds the squish. I think he got all the way down to 0.027" before the piston crown began kissing the underside of the head on a small block Chevy. The parts don't keep their same dimensions as they had sitting on the shelf when the engine is under operating conditions and getting hot. The crank bends a little, the rods stretch a little, the piston gets taller from expanding as a result of heat, etc., etc. So, if you build the motor with a (for instance) 0.027" squish while it's sitting there on the engine stand, then the heat and stretching as a result of running will close up the gap to zero. Most small block Chevy builders will shoot for a squish dimension of between 0.035" to 0.045".
10-10-2012 11:28 PM
57Chevy3100 Sorry for my lack of knowledge but what is squish?
10-10-2012 11:13 PM
techinspector1
Quote:
Originally Posted by 57Chevy3100 View Post
Thanks for the info tech. What I meant by casting number was heads with the casting number 3927186 they have the 2.02 in and 1.60 ex valves. The heads I have now are 354434 casting number which have 1.74 in and 1.50 ex valves.
3927186 is a double hump head that was probably the best head you could bolt onto a 350 block back in 1972. They can be fitted with 2.02"/1.60" valves pretty easily if you find a casting with slightly smaller valves. But that was 40 years ago and there have been quite a few improvements in cylinder head technology since then. Still, if you find a set of 186 heads for reasonable money, they will do a fine job on a warmed-over 360 motor.

354434 is, I believe, a 305 head with small valves and a ~60 cc chambers.

Let's check this out a couple of ways....
738.28 cc's in the cylinder
~60 cc's in the chamber (using the 305 heads) (a SWAG)
~8.5 cc's in the piston deck height (a SWAG)
~9 cc's in the head gasket (0.039"/0.040" thickness) (a SWAG)
~7 cc's in the piston crown (a SWAG)
822.78 cc's total
drop out the cylinder volume for a total of 84.5 cc's
Divide 822.78 by 84.5 and find a static compression ratio of 9.73:1
270 Magnum CompCam closes the intake valve at 38 degrees ABDC @0.050" tappet lift.
KB calculator says the DCR will be 8.423:1

If we knew that the motor would have a good tight squish, this would be an ideal DCR. Since we have no idea what the squish will be, I would use the 64cc heads instead of the 60cc heads to drop the SCR down to 9.34:1, which would bring the DCR down to 8.092:1 to make sure and prevent detonation on pump gas.

SWAG=scientific wild assed guess
10-10-2012 10:03 PM
57Chevy3100 Thanks for the info tech. What I meant by casting number was heads with the casting number 3927186 they have the 2.02 in and 1.60 ex valves. The heads I have now are 354434 casting number which have 1.74 in and 1.50 ex valves.
10-10-2012 09:53 PM
techinspector1
Quote:
Originally Posted by 57Chevy3100 View Post
Im building a sbc 350 bored .060 over to put in my 57 chevy truck (5500lbs). Im using a Magnum Flat tappet comp cam (.499 lift, 270 duration), Sealed Power hypertonic flat top pistons, stock chevy heads with 1.74 in, 1.50 ex valves with comp cam recommended valve train components, performer eps intake, Holley 650cfm electric choke vacuum secondary carb, and its in a 010 4 bolt main block. And behind it is gonna be a 2000 stall 2 speed powerglide. What I'm wanting to know is if these parts will go good together and is there any changes yall would recommend I change keeping in mind this will be kind of a budget build? Oh yea I intend on using as weekend driver street truck and where I live emissions are not a concern as far as being checked.
I'm thinkin' that the curb weight (sittin' at the curb with a half tank of gas and ready to drive) is about 3360.

What is the casting number on the heads? It's under the valve cover, in between the valve guides and should be a 6, 7 or 8 digit number. Chances are pretty good that they are 3998993 heads, but I'd like to know for sure before I post my opinion. Also, if you measure the intake valves again, I'm pretty sure you'll find that they're 1.72", not 1.74".

To help you further your education, let me explain the piston type for you. The correct word is hypereutectic (high-per-you-tech-tick). It means that the material the pistons are made from has a very high silicon content mixed in with the aluminum alloy.
Hypereutectic piston - Wikipedia, the free encyclopedia
Piston diameter growth from heat is minimal, so that the piston can be fitted to the cylinder wall with very little clearance, usually around 0.001" to 0.0015". These pistons are cast, not forged and fall into the middle of the range for taking abuse. Cast pistons are the cheapest and most brittle, then hypereutectic pistons, then the top of the line is forged pistons, which will take the most abuse. Forged pistons will also grow the most from heat and are normally fitted very loosely to the cylinder walls (piston to wall clearances of 0.007" to 0.008" are not uncommon.
10-10-2012 09:48 PM
57Chevy3100 This all i could find in the computer will post some more later. And i was thinking vortec heads down the road but would 186 casting heads work better or bowtie heads?
10-10-2012 09:37 PM
vinniekq2 put that cam in 2 or 3 degrees early. The 3 or 4 speed automatic should take priority over the heads
10-10-2012 09:14 PM
RWENUTS If you're going for better heads down the road that cam will work for now. I've done the same trying to save some work and money. It might not run super duper with that combo but it's workable.
Nothin' wrong with a glide. Strong tranny. You gotta use what you got.
Got any pics of your ride.
10-10-2012 09:00 PM
57Chevy3100 I already bought cam and I intend on getting larger heads there all i got right now. The rearend has 4.10 gears may go to 3.73 which would be better? Powerglide because I have it and cant afford anything else right now. And your probably right on the weight but it has a subframe swap from a 74 camaro and has been lowered.

And thanks for the reply.
10-10-2012 08:47 PM
RWENUTS 5500 lbs?? Weigh it again!! Likely less than 4000 lbs!!
Too much cam! Less duration and lift considering your heads. Closer to stock would be better.
Why the glide?
What rear gears?
10-10-2012 08:14 PM
57Chevy3100
SBC 360 Build

Im building a sbc 350 bored .060 over to put in my 57 chevy truck (5500lbs). Im using a Magnum Flat tappet comp cam (.499 lift, 270 duration), Sealed Power hypertonic flat top pistons, stock chevy heads with 1.74 in, 1.50 ex valves with comp cam recommended valve train components, performer eps intake, Holley 650cfm electric choke vacuum secondary carb, and its in a 010 4 bolt main block. And behind it is gonna be a 2000 stall 2 speed powerglide. What I'm wanting to know is if these parts will go good together and is there any changes yall would recommend I change keeping in mind this will be kind of a budget build? Oh yea I intend on using as weekend driver street truck and where I live emissions are not a concern as far as being checked.

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