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Discussion Starter #1
spent several hours trying to find out what compression ratio these pistons ... http://store.summitracing.com/egnse...dSearch&DDS=1&N=700+4294925232+4294839001+115
will make with a 400 small block bored .030 over with stock crank and rods. anyone have a clue. i'm ready to pull my hair out and can't find much info on these pistons other than the tiny bit summit gives. oh almost forgot vortec heads 64cc. oem size head gasket.
 

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SEALED POWER Part # 400AP30 {0.030" oversize Cast Piston}
Chevrolet engine; 2-5/64, 1-3/16 Ring Grooves; 1.540 CD; 0.9275 Pin Dia. Recessed Head .160" deep x 3.445" dia. - 8.5:1 C.R.; 8 Req'd

For a stock rebuild I hope?
I get a 24.4cc dish volume for those pistons. The compression height is also reduced by .020 from stock and lowers the compression more...

Assuming the following with the above pistons:
9.025 deck height block
4.165 x .040 head gaskets
Compression = about 8:76
 

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Discussion Starter #3
they are basically stock pistons. the stock motor with 76cc heads made 8.5:1 compression (i think. can anyone verify what a stock 1975 400 smallblocks compression was?) but the new heads are 64cc vortecs. so trying to figure out how much compression you will gain from going from 76cc to 64cc head.
 

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If you were using stock pistons with a stock bore, about a full point, to 9.5:1. To land in the 9.5 area with vortec heads, assuming your using a standard fel pro gasket with a .041 thickness and a standard deck height of .025, your going to need around a 18cc dish. I looked on summit and KB offers a 18cc dish for a 5.7 rod, but not a 5.565 rod. It`s always been a mystery to me why piston companies don`t make pistons that will land in the ratio we need when dealing with street machines that are compression limited. Instead they always make it hard to find a piston and when you do find it, you will pay for it, it`s either forged or something else you don`t need, they seem to have never heard of "stock replacement piston" that`s identical to the factory piston, sure, they make these, but always with a .020 reduction in compression height which kills the whole effort, you just can`t win.
 

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DoubleVision said:
they seem to have never heard of "stock replacement piston" that`s identical to the factory piston, sure, they make these, but always with a .020 reduction in compression height which kills the whole effort, you just can`t win.

Rebuilt engines usually have had the heads milled .010 for trueness...... and the block deck milled .010 for trueness....... there's the .020 lower piston compression distance that they build the pistons to fit. They are also cast pistons. "Cast rebuilder pistons"..... not forged or hypers. Cheapo made pistons for grandma's grocery getter.

So in essence, they are STOCK pistons in that they maintain the stock clearance and compression for a stock engine rebuild.

Piston manufacturers build higher comp pistons with shorter compression heights to fit longer 5.7 rods because 96% of the people will stick stock 350 rods in a 400 with those pistons.
 

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I`ve seen many a remanned block, and many rebuilt ones, and I`ve got a pile of SBC`s laying around that are scrap, some are remanned bought from parts houses and the like, none have been decked. I`ve seen blocks get used multiple times and take many overbores and have sleeves installed for those that needed them, none were decked. While I do see what your point is, I don`t see the reason to have a block decked if it doesn`t need it. Aftermarket replacement gaskets are thicker for this reason, to compensate for warpage on the decks on the block and heads. Like you I`ve had many tell me the piston company`s reduce the deck height for the same reason, they don`t know what the deck height will be, but they also "forget" to tell the buyer the compression height has been reduced .020, They don`t put this information on the box or give it to you on a piece of paper in the box.
On the flip side of things, I don`t think it matters if there`s no quench with a dish piston and small chamber heads, if I was looking for a street performer or a daily driver, I wouldn`t worry about quench if the compression ratio was in check, it`s not going to give a engine in close to stock form more than maybe 3 horses more? It`ll have more power with smaller chamber heads with the compression ratio increase.
 

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DoubleVision said:
and have sleeves installed ..........., none were decked.

I don`t think it matters if there`s no quench with a dish piston and small chamber heads,

, I wouldn`t worry about quench if the compression ratio was in check, it`s not going to give a engine in close to stock form more than maybe 3 horses more? It`ll have more power with smaller chamber heads with the compression ratio increase.

So....You have never seen a block surfaced when installing a sleeve?..... that is interesting... How do you get the sleeve surface perfectly flat so it seals compression? Guess at it with the boring machine?

Since you believe in leaving the decks wavy at a rebuild... :rolleyes: . god help you.
Every customer got decks surfaced... unless he absolutely refused it. And what are you going to do if he can't keep head gaskets in it and he tells everybody that YOU did the block work????? :rolleyes:

Compensating for the possible is what the piston mfg does. Everybody knows about it, so what difference does it make.

Lack of quench= detonation..... Build a 70s smog turde that knocks on 91 octane if you want to.

I said that with the same compression, quench is substantially better for power, detonation resistence= octane tolerance...open chambers sux....

with which every big name person in the industry agrees.
 

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I`m not a machinist, I`m a CNC machinist, there`s a difference there.
I`m not in the automotive field of machine work, Never have been never cared to. Sure I agree what they all agree to. if you got 9.5:1 compression with a closed chamber and dished pistons there`s not much chance of detonation, those combo`s are done all the time on smog engines, the vortecs came from the factory this way, no one said in this post if this was a performance engine or a basic street engine, since he wants to run a dish piston I would assume he wanted to keep the compression low enough for a basic street engine.
My former machinist before his death set many a sleeve without decking it, I and many people I know ran those blocks without issue. we weren`t building race engines, we were building common street engines. If the deck is slightly wavy but still seals up what difference does it make? it won`t effect power any as how many decks from the factory are tipped? Lastly when a company reman`s a engine to sell I could care less if they decked it, that`s not up to me, I don`t buy there engines, never have. my blocks I have decked, the 4.3 I just got back was decked .010 so I could get a good quench out of it.
 

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DoubleVision said:
I`m not a machinist, I`m a CNC machinist, there`s a difference there.
I`m not in the automotive field of machine work, Never have been never cared to. Sure I agree what they all agree to. if you got 9.5:1 compression with a closed chamber and dished pistons there`s not much chance of detonation, those combo`s are done all the time on smog engines, the vortecs came from the factory this way, no one said in this post if this was a performance engine or a basic street engine, since he wants to run a dish piston I would assume he wanted to keep the compression low enough for a basic street engine.
My former machinist before his death set many a sleeve without decking it, I and many people I know ran those blocks without issue. we weren`t building race engines, we were building common street engines. If the deck is slightly wavy but still seals up what difference does it make? it won`t effect power any as how many decks from the factory are tipped? Lastly when a company reman`s a engine to sell I could care less if they decked it, that`s not up to me, I don`t buy there engines, never have. my blocks I have decked, the 4.3 I just got back was decked .010 so I could get a good quench out of it.
I think there is a confusion between making a block flat for the gasket and "decking" for height and squareness to the crankshaft/bore line.

Any machine shop that bores a block and does not flatten the surface is stupid. It will come back to haunt them sooner or later. Sure some of the "rebuilders" throw a straight edge on it so they can save 30 minutes. There are lots of people in this world who just want to scape by with the minimum effort and expense possible to maximize profits. They are not craftsmen. Lack of ethics is their problem, IMO.

Dish pistons remove quench. Pistons with more than .025 dish have ruin the quench except for the ring around the edge of the pistons. If a person choses to install the old technology and they get away with it. good for them.

Personally I think that we should think on a level above just-getting-by with "what works most of the time".

I try to tell people what is right. They can do what they want. :thumbup:

Don't confuse me with someone who really cares.
 

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Discussion Starter #11
ok xntrik answer me this. you seam to have a fountain of knowlegde on this subject. what is a good set of pistons for a 400 skinny bored .030 over with 64cc vortec heads that will get me to 9.5:1 compression with stock 5.565 rods standard head gasket where block or heads have not been decked. every aftermarket set i find is shooting me up to 10.5:1 or so way too high for what i am wanting. the motor will never see over 6,000 rpm so no need for forged set just some good cheapies. thanks. oh and anyone verify what the stock compression ratio was on a 1975 chevy 400 smallblock truck motor?
 

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I don't think those pistons have a big enough dish to get 9.5:1 with 64cc heads. Even through they don't list the cc on the dish, they fall into the 12-14cc dish group using the sorting feature on summit's website.

You will have much more choices in pistons if you use a 5.7 inch rod.

You will need to use a 20cc dish to get 9.5:1 cr with a 4.155 inch bore, 3.75 inch stroke, 64cc heads, stock gasket, and a piston 0.020" under the deck.

Cylinder volume= 832cc
head volume= 64cc
head gasket volume= 9cc
piston under the deck 0.020 = 4.5cc
dish volume = 20cc

(832 + 64 + 9 + 4.5 + 20) / (64 + 9 + 4.5 + 20) = (832 + 97.5)/ 97.5 = 9.53

I would use a 5.7 inch rod with either one of these pistons:
SRP-139625, forged, 21cc D-shaped dish, 515.00 (9.45:1 cr)
UEB-KB147030-8, hyper-cast, 18cc D-shaped dish, 252.00 (9.7:1 cr)


The nice thing about these pistons is they have D-shaped dishes so there will be some quenching with the vortec heads and will not require as much ignition timing. And a set of 5.7 rods can be had for cheap. 190.00 a set, SCA-35700P
 

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Posted by 454C10:
"The nice thing about these pistons is they have D-shaped dishes so there will be some quenching with the vortec heads and will not require as much ignition timing."

Exactly :) That's what I like about KB's. The flat part of the piston crown on their dished pistons matches up with the flat underside of the head to form a perfect squish area. Set the squish at 0.035" to 0.040" by juggling deck height and gasket thickness and you're good to go.
 

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XNTrik... hello,
I've been reading your threads and I agree that you know whats best!!
Please, Can you help me with my piston problem too? I'm building a mild
1982 350, I went with vortec 64cc heads ,upgraded springs 130 seat pressure,a comp cam HR258HR 206/212- 480/487 lift (retro-fit),hyl,roller lifters, and comp roller rollers manly to get more torque.. I'm going to
have block bored .030" and decked. how much should I take off deck,
should I go 0 decked to 9 inches or what, and what would be a good
piston to get max compression on street driven gas?? (cast iron heads)
Please reply,Thanks
 

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DBourg said:
XNTrik... hello,
I've been reading your threads and I agree that you know whats best!!
Please, Can you help me with my piston problem too? I'm building a mild
1982 350, I went with vortec 64cc heads ,upgraded springs 130 seat pressure,a comp cam HR258HR 206/212- 480/487 lift (retro-fit),hyl,roller lifters, and comp roller rollers manly to get more torque.. I'm going to
have block bored .030" and decked. how much should I take off deck,
should I go 0 decked to 9 inches or what, and what would be a good
piston to get max compression on street driven gas?? (cast iron heads)
Please reply,Thanks
Your doing things backwards you should choose a cam depending on you compression ratio. If it were me i'd try to keep as much deck height as possible. Have the decks cut to 9.015" and use a clevite head gasket #5746 .026"x4.1" to give you a quench of .040". Then use http://store.summitracing.com/partdetail.asp?part=UEM-KB193030-8&autoview=sku
piston with a 12cc dish which would give 9.6:1 which would work on pump gas with your cam. Just my 2 cents! Oh I forgot to mention install that cam on a 110 intake centerline as apposed to 106 which it comes with.
 

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DBourg said:
XNTrik... hello,
I've been reading your threads and I agree that you know whats best!!
Please, Can you help me with my piston problem too? I'm building a mild
1982 350, I went with vortec 64cc heads ,upgraded springs 130 seat pressure,a comp cam HR258HR 206/212- 480/487 lift (retro-fit),hyl,roller lifters, and comp roller rollers manly to get more torque.. I'm going to
have block bored .030" and decked. how much should I take off deck,
should I go 0 decked to 9 inches or what, and what would be a good
piston to get max compression on street driven gas?? (cast iron heads)
Please reply,Thanks
Use a "D" dish piston. This improves squish and quench which has the effect of building mechanical octane into the engine. The reasons are that a "D" dish places the compression adjusting cavity under the valve pocket while maintaining a close closure space on the stepped side of the combustion chamber. This close closure needs to be less than .080 inch to be effective, less like .040 to .060 is ideal. This distance has to be the sum of the piston crown to cylinder deck clearance (Chevy SBC uses .025 inch) plus the head gasket thickness, plus the distance from the head's step to the bottom of a circular dish if that's what the piston presents under the step. So a .025 piston to cylinder deck plus a .050 head gasket, plus a .1 inch deep dish quickly gets to .175 inch which is way too much.

The two events that add mechanical octane and improve burn speed is squish and quench.

1) Squish, as the piston closes on TDC the close closure of the piston's flat crown and the combustion chamber step forces the mixture violently toward the valve pocket and spark plug. This breaks up fuel droplets and throughly mixes them with the air, this results in a homogeneous mixture that burns rapidly and completely.

2) Quench, as the burn proceeds across the combustion chamber temperatures and pressure rise to a level that spontaneous combustion can occur ahead of the flame front, this is detonation. With the flat surface of the piston and combustion chamber close to each other, there is a lot of surface area compared to gas volume. This takes heat out of the end burn reducing the tendency for spontaneous combustion to occur.

Compression ratio calculators are all over the web, but being able to to it manually is helpful in understanding what's going on and to explore changes.
Basically is just total cylinder volume divided by combustion space volume.
Total cylinder volume is the swept cylinder volume (bore area times stroke) plus the combustion space volume. Combustion space volume is all volumes above the piston measured from TDC. This includes and dish or dome volume the former being additive and the latter subtractive; plus cylinder deck to piston crown volume (cylinder bore area times clearance; plus the gasket volume (gasket bore area times thickness); plus the head's combustion chamber volume.

Some conversion is needed since combustion chambers are given in cubic centimeters and cylinder volume in cubic inches. There are 16.4 cubic centimeter/milli-meters in a cubic inch and there are 25.4 centimeters to a linear inch.

Have fun!

Bogie
 

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Which pistons to Use

Hi. I looked at the KB193 dish pistons 12cc. I originally was goning to
use these, but I'm not to sure now.. These pistons look short and the
face between rings is make strange... I'm looking for the D shape dish
piston, ,, but I was wondering about the trough. with a 480/487 lift
Roller cam,will I need a trough with the D shape piston? Just want to
know, What is the compression for a bone stock 1996 350 vortec 64cc engine? AND the HP?, Compared to a 1982 stock 350? Stock 350 piston
for the vortec, I believe they are just D shape dish pistons. Can these pistons work with the cam??? If I bore .030 and 0 deck and put a .39
head gasket would that give me about 9 compression?
 

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DBourg said:
Hi. I looked at the KB193 dish pistons 12cc. I originally was goning to
use these, but I'm not to sure now.. These pistons look short and the
face between rings is make strange... I'm looking for the D shape dish
piston, ,, but I was wondering about the trough. with a 480/487 lift
Roller cam,will I need a trough with the D shape piston? Just want to
know, What is the compression for a bone stock 1996 350 vortec 64cc engine? AND the HP?, Compared to a 1982 stock 350? Stock 350 piston
for the vortec, I believe they are just D shape dish pistons. Can these pistons work with the cam??? If I bore .030 and 0 deck and put a .39
head gasket would that give me about 9 compression?
The "D" dish incorporates the area of the valve relief. It looks different because with a "D" dish, the pistons are specific for the left and right sides of the engine. Circular dish and 4 valve relief type pistons are made interchangeable left to right side. This doubles the production that can be made on a set of tools. So the tooling and machining set up costs are amortized over twice as many pistons than with the "D" dish style for a production run to support some given number of engines. So circular dish and 4 valve relief pistons are less expensive to manufacture, one could say cheap. The factory uses circular dished pistons strictly for economy of manufacture reasons not for design engineering purposes of efficiency and effectiveness.

Much of you car is like that, the finance people driving toward the least cost design greatly affect/effect the engineering solutions for purposes other than good or even proper design. The Vortec/Fastburn chamber inclusive of names given to the heart shaped chamber by manufacturers other than GM is a case in point. The automotive industry would have you believe this is the latest technology from their (so called) research centers. I fact it's an old design developed by Sir Harry Ricardo and friends back in the 1920s. Ford successfully applied it to the flat head V8 to improve its lack of power and fuel efficiency. Later Ford incorporated the design into the Lincoln and later Ford/Mercury "Y" blocks. They discontinued it in 1955 as a cost reduction measure, saving them a few pennies per head in simpler tooling and less material. I guess the thought was that OHV engines were such a basic improvement over the flathead in all areas of measurable performance that giving the customer more efficiency and power through excellent design wasn't necessary. Besides fuel octane was raising significantly and doping the fuel with lead could be used to hide a great number of engine design sins and transfer the cost to the consumer at every fill up.

The original SBC head also had a pretty decent chamber, albeit different with quench on both the spark plug side and the more conventional side opposite. All this design was abandoned in the emissions era when reduction in NOx became a requirement. Without a catalytic converter, NOx reduction can only be achieved by reducing combustion temperatures and pressures. You can always go after unburnt HCs and CO with air injected into the exhaust stream, this has a minimal effect on performance. But the solution to NOx strikes at the heart of what makes power and provides fuel efficiency these being compression ratio, burn speed, cam timing, and fuel ratio. So compression went down as did burn speed with low compression open chambers, EGR, and retarded or at least reduced spark advance, hardly any cam timing featuring the elimination of overlap while the carb became tightly controlled delivering mostly a lean mixture.

This changed with oxidation/reduction converters and fuel injection. These two technologies along with computer controlled spark management when combined with the Ricardo combustion chamber allowed a return to higher compressions within what today's unleaded fuels octane ratios will allow*. But the factory continuing to stay with circular dish pistons for cost reduction reasons always keeps a compromise in there. Again these engines that began to appear in the mid 1980s were such a great improvement over the 1970s that the factories felt you were getting enough and didn't bother with completing the loop till into the late 1990s early 2000 designs.

So in short, though that's long past, the "D" dish piston will do much to provide the best power output with the best fuel economy and lowest emissions with the Vortec type head while keeping the compression ratio where modern fuels will tolerate.

*A side note, before heavy TEL lead doping of auto fuels in the mid 1950s, high compression was considered to 6 or 7 to 1. Use of lots of TEL allowed much higher ratios and 10-12 from the factory became common place. Though these fuels were pretty hard on spark plugs, valves (contrary to current popular myth) and the oil. Engines of the era seldom say more than a few thousand miles on a set of plugs, valve jobs were required around 30 to 50 thousand miles, and it was a feat to go 100,000 miles without a complete rebuild; oil was changed every 2000-3000 miles because of lead contamination. When opened up, these engines had many and massive pockets of silvery lead sludge in every nook and cranny of the block, heads and pan.

Bogie
 

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Trying to get compression ratio before I buy pistons

Hi,I want to thank or all this Knowledge,,,, But that wasn't my
???.. Will stock D shape pistons work with a 480/487 lift roller cam??
If I bore .030 and deck to 0" and use a .39" gasket will I have about
9.1 compression????? If not do you know what it would be?????
If not can I be planly explaned what to do????????
 
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