I have a question. Is it possible to have a 1.54 piston at 10:1 compression with a 64cc head. I ask because this is what my builder is using. I want to change piston if this is not correct. The reference books for these pistons seem to be all over the place. I just called summit and they agreed.. Said i'd have to call KB in the morning. I just did not think it was possible with a de-stroked piston.
Carlos9
I assume you have a +0.030" 350. I further assume the block is virgin at 9.025". And even further assume that the piston is a flat top with nominal 6cc's of valve relief and that the builder will use a standard 0.040" gasket.Carlos9 said:
727cc's in the cylinder
64cc's in the head
9.4cc's in the piston deck
6cc's in the piston
8.65cc's in the gasket
Total ingested 815.05cc's. Total compressed 88.05cc's. Divide and find 9.25:1 static compression ratio and 0.085" squish.
It'll rattle like a can of marbles on pump gas.
A standard first-class 350 piston is 1.560" compression height. He's using a cheapo rebuilder piston with 1.540" compression height.
Swap to 1.560" piston and 0.015" shim gaskets for 10.26:1 static compression ratio and 0.040" squish. Use a cam with 230-240 degrees duration @ 0.050.
Further technical specifications from you will elicit further calculations from me. :thumbup:
I am sort of straying from my original build plans and letting another outfit put my engine together. This company uses silvolite pistons. I have had this discussion on this board numerous times.. and thought I was up to speed until I was thrown a curve ball today by the engine assembler. The block was virgin with 8 thousands shaved off the decks. I was under the impression the 1.540 pin height pistons was not what I wanted. When I asked the pin height on the new piston (silvolite), he mentioned it was 1.540. This shop is really not into performance type stuff and will only rattle off to you what the books say, but they do build a good solid motor. I know plenty of folks that have had motors built there.. That's why I opted to take my stuff there.
I was originally going with the sealed power cast piston (ZH345NP40), which is the 1.560 pin height piston and has a compression ratio of 9.35:1. This shop doesn't do anything but KB or silvolites. I need to ask them tomm if they deal with other piston manuf. Anyway, the cam I am running is an Isky 262/270 HL on a 110 lobe, vortec heads. I picked this cam (along with an isky rep in person) with this piston in mind. Now the problem I have is I'm not sure what I'm getting piston wise.
I just did not know they had a 10:1 compression piston with a 1.54 pin height. I think I need more clarification myself on exactly what piston he's using. I should have stayed with my original plans. Almost forgot the duration on the cam is much smaller 208-216 @ .50 if I remember correctly. I am building for torque in a heavy vehicle.
I was originally going with the sealed power cast piston (ZH345NP40), which is the 1.560 pin height piston and has a compression ratio of 9.35:1. This shop doesn't do anything but KB or silvolites. I need to ask them tomm if they deal with other piston manuf. Anyway, the cam I am running is an Isky 262/270 HL on a 110 lobe, vortec heads. I picked this cam (along with an isky rep in person) with this piston in mind. Now the problem I have is I'm not sure what I'm getting piston wise.
I just did not know they had a 10:1 compression piston with a 1.54 pin height. I think I need more clarification myself on exactly what piston he's using. I should have stayed with my original plans. Almost forgot the duration on the cam is much smaller 208-216 @ .50 if I remember correctly. I am building for torque in a heavy vehicle.
Or you could go with these pistons with the correct gasket thickness to get the quench correct and land on your feet compression ratio wise.
http://store.summitracing.com/partdetail.asp?part=STL-H670CP30&autoview=sku
http://store.summitracing.com/partdetail.asp?part=STL-H670CP30&autoview=sku
That's fine. You can get the 1.560" comp. height pistons. Just won't be Sealed Power.Carlos9 said:
This was simply a matter of calling back, drilling the guys, finding out I was right (they have no clue on the compression ratio) then ordering the correct piston. I am not an expert nor do I proclaim to be.. but it just surprises me when you know a little more than your engine builder. I really can't blame them though. They are a volume shop that do mostly stock rebuild stuff of all kinds.. foriegn and domestic...so they are not up on this at all. They can care less about compression ratio etc. I think we are on track now.
Thanks guys.
Thanks guys.
Probably most people putting engines together don't even know this dimension.Carlos9 said:
The factory lists the deck height above the piston crown as .025 inch with a piston having a crown height of 1.560 inches (sometimes up to 1.566 inches) between the top edge of the piston on the quench side to the middle of the pin bore.
This is really variable depending on the height of the block from the centerline of the crank to the block's head deck as well as the length of the components inbetween.
While SBC blocks are listed as being 9.025 inches, production tolerance and rework/repair of mistakes made on the production line will often change this. Plus all dimensions are subject to normal production tolerances that result from tooling setups and usage wear. This applies to all manufactured parts. Nominally 3.48 inch stroke/2 plus a 5.7 inch rod plus 1.56 inch piston pin to crown yields 9 inches against a block height from the crank centerline to the head deck of 9.025 inches leaving a clearance of .025 inch.
The latter leads into dimensional variation of individual pistons and rods as well as where the stroke on any given journal ended up against the specs. For rods this is a nominal 5.7 inches on centers and a 305/350 crank as being 3.480 inches in stroke. This all leads to taking the measure of crown to deck height when you pull the heads off the engine so you know where you're starting from. Checking this dimension upon assembly will only tell you that if you used a 1.54 piston on a standard height block, you're low on compression and squish/quench. A little late in the game to go fix the problem. You can at this point mill the head to recover compression, but this doesn't improve squish/ quench; which in fact, makes the detonation problem worse because now you have too much compression for the squish/quench that can be generated from the excessive clearance. Don't ya just love chasing your tail.
It is typical for the big rebuilders to just whack .020 inch off the decks to true them, whether they need it or not. To keep compression from going to the moon, the piston builders who mostly supply the production rebuilders take .020 inch off the piston pin to crown height. This makes the pin center to crown 1.54 inch. If your block wasn't decked by .020, you end up with less compression and a less effective squish/quench function.
The solution is to shop for a brand piston that has the full height between the pin and crown, or deck the block.
Bogie
Bog, you are right about chasing tails.. I've been doing just that all day. I had to call silvolite tech dept. and speak to them (because details on their pistons are not published anywhere for public to see) about what was going on. They did the math (based on what I told them, basically .008" off the deck, 64 cc head, and the piston 6cc relief) and came up with 37thou down in the hole/quench of .077/compression ratio of 9.45:1 with the 1.54 piston and a 40thou head gasket.
The calculation on the standard piston (1.560) put me 17thou in the hole/.057 quench. Again, this is based on what I know. My block had not been decked before. Does this sound about right.
He also mentioned I could use that piston (1.540), but I'd have to take another 20 thou off my deck.. and I think that pretty much answers my question about which piston I need to be running. I do not want to deck anymore.
The calculation on the standard piston (1.560) put me 17thou in the hole/.057 quench. Again, this is based on what I know. My block had not been decked before. Does this sound about right.
He also mentioned I could use that piston (1.540), but I'd have to take another 20 thou off my deck.. and I think that pretty much answers my question about which piston I need to be running. I do not want to deck anymore.
This sounds right. I'm with you on decking, which also applies to head milling and boring; with thin wall castings I don't want to take more than what it takes to correct normal wear and warpage. These engines made since the mid 1970's are just on the edge of having enough meat in them, and I try not to temp fate by seeing how much iron I can remove.Carlos9 said:
Quote}They did the math (based on what I told them, basically .008" off the deck, 64 cc head, and the piston 6cc relief) and came up with 37thou down in the hole/quench of .077/compression ratio of 9.45:1 with the 1.54 piston and a 40thou head gasket.{Quote
Yeah, the piston is too far down the hole for good quench, but a thinner head gasket might prove to be a less expensive solution. Though the compression is getting up there for 92 octane and cast iron with your current configuration.
Bogie
What is the safe range for 87 octane. A friend of mine swore I could run 87 with 10.1 compresion. Now I see the importance of piston selection. The piston I was originally going with netted me 9.35:1 with correct pin height 1.56. This place does not have anything in between. Now do we do the same going this route.. meaning using a thicker gasket to lower. Can someone please jot the different gasket sizes (part no's included) so I can tell the amigos what to use either way. I'm a little ticked for straying from the plans.. but I think we can remedy it.
It's funny, the guy told me I'd be at 10:1 with his 1.54 piston.. and I am closer to 10.1 with the correct piston. I think to fix it i just use a thicker gasket.. is this correct. The cam I have calls for a min. of 9.5:1. Will a little more hurt things. This is what you get when you go for good deals. I should have stayed patient and continued building to spec. The good deals turn out to be bot so good in the end.
It's funny, the guy told me I'd be at 10:1 with his 1.54 piston.. and I am closer to 10.1 with the correct piston. I think to fix it i just use a thicker gasket.. is this correct. The cam I have calls for a min. of 9.5:1. Will a little more hurt things. This is what you get when you go for good deals. I should have stayed patient and continued building to spec. The good deals turn out to be bot so good in the end.
Why don't you just run a dished piston with the 1.56 pin height and the .015 shim head gasket?
The 0.015" head gaskets are
Fel-Pro 1094 (w/4.100 bore) or
Specialty Component Engineering (SCE) 511101
FWIW, Fel-Pro 1142 is 0.040" and has a 4.100" bore instead of 4.166" like the 1003 and the 1010.
EDIT- For some reason the FP 0.015 p/n wasn't showing up at first in the post above, so I added it.
This is the second time that the entire post of someone hasn't shown up until later. Odd...
Fel-Pro 1094 (w/4.100 bore) or
Specialty Component Engineering (SCE) 511101
FWIW, Fel-Pro 1142 is 0.040" and has a 4.100" bore instead of 4.166" like the 1003 and the 1010.
EDIT- For some reason the FP 0.015 p/n wasn't showing up at first in the post above, so I added it.
This is the second time that the entire post of someone hasn't shown up until later. Odd...
Probably talking about Mr. Gasket 1130 0.018"-0.020". http://www.amazon.com/Mr-Gasket-1130-Embossed-Steel/dp/B000BWAOYY
6426yy said:
This is what I am wishing someone would tell me. I am not sure if I'm way off here, overreacting.. or in a serios bind. My original piston as ZH345NP40. Which is just a plain cast piston with 1.560 pin height which would have given me compression of 9.35:1. My cam was selected with this piston in mind. I personally sat down with an isky rep and picked this thing. I don't know my best route out here. I am thinking about telling him tomorrow I will bring him the piston to use. It is cheaper and IMO better than the heavy silvolite he's selling me.
On the other hand, If I opt to work with him (as you don't want to piss the guy off that's building your motor) what are my options. Is .057 quench too much. we figured it would have been .077 with the 1.54 piston. This is where is gets technical and out of my realm of good judgement. I just want good torque on junk 87 gas. I can run the higher octan gas.. but I sure do not want it to be a requirement.
I don't find the numbers you were given by Silvolite to be that off. So you can take this apart and run your own numbers the formula you need is diameter squared times .7854 for surface area. To get volume, the surface is multiplied by depth. To convert inches to cubic centimeters (which is also milli-liters) multiply English measure by 16.4. To convert linear English measure from inches to milli-meters multiply by 25.4.Carlos9 said:
If your engine is a 350 at .030 over, I get 727.74 ccs of swept cylinder volume. Swept volume is that of piston displacement. It does not include crown to deck clearance or the gasket.
Your nominal deck is .025 minus .008 or .017, this is 3.55ccs. This of course assumes the engine had the nominal clearance to start with, All we know is it has .008 inch less of what ever that number was. But for argument's sake we'll assume the factory .025 is where it started.
Head gaskets are usually larger than the bore, I took 4.100 X .025 inch thick gives 5.41ccs. There are larger diameter gaskets so this can go to heck easily if you don't watch the part numbers.
The piston you have is .020 further in the cylinder which is another 4.1ccs. There is some benefit to this because the upper .037 inch of the cylinder is going to have a pretty direct path to the cooling system, instead of having to get top end cooling just thru the head gasket as happens with a zero deck block and full dimension (1.56) pistons.
The piston has about 6ccs of valve reliefs
The combustion chamber is 64ccs
This makes a total cylinder volume of: 727.75ccs + 3.55ccs + 5.41ccs + 4.1ccs + 6ccs +64ccs which equals ccs.
The volume above the piston is the total volume of 810.7 minus the swept volume of 727.65 which nets 83.1ccs
810.7 divided by 83.1 gets a static compression of 9.76 to 1. This should be manageable on 91/92 octane with cast iron heads. The squish/quench with a .025 thick gasket and your current pistons is .062 inch. This isn't too bad, it's leaning toward the high side of maximum effectiveness, but is much better than the effective quench you get with a factory circular dished piston.
If you keep your head gasket thin, your compression and squish/quench numbers will be fine with the pistons you have. But the next stop over a .025 gasket will show a marked reduction in compression ratio and detonation resistance; which isn't a direction to move in. I think you're Ok with the basic configuration. Thankfully you didn't use a 76cc head as this would have killed getting any power or efficiency from this engine.
Lots of factors go into the octane an engine will tolerate against compression ratio, so it's hard to tell how your friend gets away with high compression on 87 octane. Lower operating temps, cold air intake, rich mixtures, aluminum heads, heads with fastburn chambers, reduced ignition timing, long duration cams, manual transmission instead of automatic, automatic with a high stall converter, stiffer rear gearing, lighter vehicle weight are examples of things that will let an engine operate with higher compression without detonation. Of course modern fuel injected engines adjust to the detonation limit automatically, the computer just takes out timing lead till the detonation stops and the driver remains clueless. I have a pretty high strung 350 Franken-mouse which is an LT1 top end with the LT4 HOT cam pushing Miller 1.6 roller rockers. Intake is OBD1 continuous flow MAP managed port injection getting air thru a four barrel throttle body built on a Holley 4150 throttle plate. All modified to work on a 880 Vortec short block and stuffed into a 89 S-15. Anybody could do the same thing with Fast Burn aluminum heads and save a pile of effort welding, drilling and milling to get them to flow water in the conventional way. This is my daily driver and parts truck. It'll run on 87 but it ain't as much fun as with 92. On 87 you can hear the headers ring and power is definitely down from 92 octane. That's the effect of the computer pulling the timing back when it gets a detonation signal. Oh yeah, it smogs; but what doesn't come out the exhaust, you can burn off the tires.
Bogie
There is only one catch about running a thinner gasket. That is the blocks deck and the cylinder head deck must be perfectly flat. This is why the stock replacement fel pro gasket is .041 thick, it can contour to decks that aren`t as square as they should be. Most times if the decks are out of square by more than .002 the gasket can`t compensate enough for it which results in a blown gasket. .057 Quench isn`t real good, however, it`s not a total loss. There is no Quench past .060 and .057 is border line. Lets say the gasket that gives a .057 Quench is .041, so we decide to use a gasket thats .028, that will put us at .044 Quench which is ideal. Use a gasket that will get you somewhere in the .040`s zone and you`ll be fine.
I forgot to mention my block was .040 overbore. How much does this change things if I stuck with my original piston. I am thinking about calling him and telling him i'll bring pistons. I REALLY see how important piston selection is now. I think I would have a good combo if I left things as I originally intended because it looks like I am on the border either way. I didn't think .057 was good. Why pay $75 more for a piston that will still not give the best performance. Is it as simple as using a thinner gasket with his piston. Both the decks and heads are flat.
Would a dish piston settle this. I'd like to be between my original 9.3-9.5 compression wise. Here, I think i'd still be safe running 87 octane. Do I run a thinner gasket with the 1.54 pistons. I don't know guys help me out here. This is united engine I'm dfealign with so they only know KB or silvolite pistons. :smash: :smash: :smash: I don't know why I let my friend talk me into this....
Would a dish piston settle this. I'd like to be between my original 9.3-9.5 compression wise. Here, I think i'd still be safe running 87 octane. Do I run a thinner gasket with the 1.54 pistons. I don't know guys help me out here. This is united engine I'm dfealign with so they only know KB or silvolite pistons. :smash: :smash: :smash: I don't know why I let my friend talk me into this....
As I said in my first post, these pistons should fill the bill, unless there is something about them you don`t like. They are also avalible in .040 oversize. With the correct quench distance and careful spark timing they will work fine.
http://store.summitracing.com/partdetail.asp?part=STL-H670CP30&autoview=sku
http://store.summitracing.com/partdetail.asp?part=STL-H670CP30&autoview=sku
Parts stack = 9.000"
Piston deck height = 0.017" (assuming 9.017" block deck height)
731.02 in the cylinder
64.00 in the chamber
3.57 in the piston deck height
11.00 in the piston crown
5.40 in the gasket (Victor Reinz 5746 4.100" x 0.025")
Total ingested 814.99
Total squeezed 83.97
Static compression ratio 9.70:1
Squish 0.042"
Piston deck height = 0.017" (assuming 9.017" block deck height)
731.02 in the cylinder
64.00 in the chamber
3.57 in the piston deck height
11.00 in the piston crown
5.40 in the gasket (Victor Reinz 5746 4.100" x 0.025")
Total ingested 814.99
Total squeezed 83.97
Static compression ratio 9.70:1
Squish 0.042"
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