Stepped piston hitting head, options and advice needed.

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With the 268* cam I think you would need to get the Scr down to under 10/1
A 408 has a swept of 835.7cc so a 10/1 Scr will need 835.7/9.0 =92.86 minimum total chamber volume.
Anyone else see a problem here?
92.86 less (62heads + 8.9 gasket) = 21.96 in the dome and deck clearance .
And you don't want to take much off the Q pad, so I think we're looking at a step-D cup, aren't we?
I think OP needs different pistons,(Probably the cheapest solution)
or iron open chamber heads with a lot more volume,
or aluminum open chamber heads.
And some custom fitment

I entered 64* for the ICA, of the 268*/110 cam in at 106. This for iron headsand pump gas.
Static compression ratio of 10:1.
Effective stroke is 3.15 inches.
Your dynamic compression ratio is 8.09:1 .
Your dynamic cranking pressure is 162.22 PSI.
V/P (Volume to Pressure Index) is 156

With aluminum heads you could probably run close to 9.0Dcr on 91gas.
So that gets us this,still the 64* ICA
Static compression ratio of 11:1.
Effective stroke is 3.15 inches.
Your dynamic compression ratio is 8.88:1 .
Your dynamic cranking pressure is 182.96 PSI.
V/P (Volume to Pressure Index) is 176

And to run 11/1 we need a new minimum chamber size of 835.7/10= 83.57cc
Assuming 63 for the heads and still 8.9 for the gasket, now we are down to 11.67 in the deck/dome.
But get a load of that 176VP. You could blow a lot of that off and get a bigger cam, more suited to the 408.
And the 340 Eddies might save a teardown, depending on the current pop-up.

So I worked this out with a 284 cam and an ICA of 68* and with the 65cc Eddies PN 60179 complete.
Static compression ratio of 10.5:1.
Effective stroke is 3.04 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.61 PSI.
V/P (Volume to Pressure Index) is 154
So this is about the lowest Dcr I'd run. This should burn 87E10.
Now back to the total chamber volume. 835.7/9.5= 88cc ,And we have 65+8.9=73.9 so that allows up to 14.1 in the dome/deck.
So is it doable yet?
I guess the next step is to measure the dome volume and the pop-up height.


If you have to machine the pistons no matter what, the following would be a better target with that 284 cam, and aluminumheads;
Static compression ratio of 11:1.
Effective stroke is 3.04 inches.
Your dynamic compression ratio is 8.60:1 .
Your dynamic cranking pressure is 175.57 PSI.
V/P (Volume to Pressure Index) is 163
The VP is climbing again, so you could probable get away with a low-stall TC and hiway gears. But the cruise rpm should really be a little higher for that 284 cam, like maybe minimum 2400 I'm guessing, to get the best fuel-mileage,lol. So that points to minimum 3.23s at 65mph.
 
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Thank you for the replies, seems like open heads or mill the pistons seems to be the best options? Some of your replies I am man enough to admit I don't really understand.

I understand that Edelbrock makes a head that "might" work designed for the 68-71 340 with pistons similar to mine?
 
popinsmoke said:
Thank you for the replies, seems like open heads or mill the pistons seems to be the best options? Some of your replies I am man enough to admit I don't really understand.

I understand that Edelbrock makes a head that "might" work designed for the 68-71 340 with pistons similar to mine?
Click to expand...


I think they used to make an open chamber head but I haven't seen a new one for years. Someone else will probably know if they still make it.
 
The kb's are intended to be milled from the manufacturer. So even if you switch to an open chamber, you will still be milling to get optimum quench height.
 
gregsdart said:
Better yet, fill the valve notches with clay, turn the motor over till the piston is exactly .500 down in the hole, use grease to seal the piston to bore, measure the volume with alcohol, and subtract it from the bore square area times .500. If you have a 4.030 bore, then 2.015x2.015x3.1416 x .500= 6.378 cubic inches, or 104.5 CCs. Divide the difference by 16.387 for the CCs You can divide the dome height into the CCs of the dome, and multiply times the cut for the amount of volume removed. There are formulas for the weight of aluminum if you search for them. Go to United Engine and Machine web site for a compression ratio calculator that allows quick changes for gasket thickness and piston dish volumes to get ypou the answers you want. That is how I did it.
Click to expand...
Don't use grease, it gets messy and into areas that in real time are filling with gasses, cyl volume.
 
AJ/FormS said:
what do you use to keep the alcohol from leaking away?
My math suggests there's less than .3 cc in that space.
Click to expand...
I do the math using the advertised 23.5 dish volume and figure .5 cc for ring land and above ring piston to bore area, and figure it based on a 0 deck height.
The dynamic matches in reality to the mathmatical formula coupled with ivc figured.
 
69_340_GTS said:
#60179 are 340 specific. https://www.summitracing.com/parts/edl-60179/overview/make/dodge
Click to expand...
looking at that picture, that is not a open chamber head. is is a closed chamber head that is cut for a flat top piston that pop up above the deck.(340) AKA, the only head that will accept your piston pop up is a stock chrys head.
In my opinion, you have to remove the pop up no matter what. Even if you keep the pop up on the piston, and us factory open chamber iron, your going to be over 11:1 right? and you plan to use pump gas right?(no racing fuel)

If that was mine, i would use racing gas (not worth it on a street car) or by a dish(stepped down flat top) that will work with your rhs heads and still be able to use pump gas.
You have plenty of option above, but, selling them pistons to recoup some of your money and buy the right piston is the way i would go.
 
Hold the phone on milling.... The 60179 head may be a very good way to solve this. The milled area in the 60179 head is .060" deep. The standard open chamber stock head is .090" to .110" deep in the same area. So it depends on how far the quench pad sticks up as to whether it will work. If this is the KB356 piston, then it will stick up about .073" above the stock, uncut LA block deck.

If that is the case, then a .050" thick head gasket would give a quench-pad-to-cylinder-head clearance of .043" with the 60179 heads, which should be a very reliable, never-will-hit quench gap. A .045" thick head gasket would nominally set this gap to .038" which is a bit better for detonation resistance. The Cometic head gaskets will allow you set this head gasket thickness in .005" increments, so the OP cane set this as he pleases.

Of course, all of this depends on the deck of the block. OP, at this point, you REALLY REALLY REALLY need to measure each piston and find out exactly how much the quench pad comes above the deck to work up some final numbers on this idea. To do it right, you REALLY REALLY REALLY need to get/borrow a dial indicator and measure the quench pad height above the deck on all 8 pistons when each one is at the top of its stroke. You need to measure them all because of possible end-to-end and top-to-bottom slopes on the decks and possible crank and rod length variations can sometimes cause significant variations in piston-to-deck heights. You need to find out which is the highest piston top and work with that to achieve a safe quench-pad-to-cylinder-head gap, plus know what variations you have. And, we don't know if the deck has been already cut....so that will come out of these measurements.

But the good news is that if you do this work, then the 60179 head idea looks pretty good for your case.

As for compression ratios.....OP, can you post some pix of the piston tops so we can make sure what you have? Or do you have the part number info? It is time to stop guessing and know this piston PN for certain.

If this IS the KB356 piston, then it IS a D-step piston top with a quench pad. If so, this will have a static CR of around 9.5 with a .045" thick head gaskets, 60179 heads, and uncut block. So it looks to be in a quite safe operating area for the 268 cam, where DCR will be about 7.9. If the info that the OP provides on piston type and actual deck heights works out this way, then he is in a good spot to move the cam specs around for better low RPM torque or high RPM HP, and the aluminum 60179 heads and the quench gap will keep things pretty darned safe from detonation problems.

IMHO, this looks like a very good plan, pending the OP making sure on piston PN and measuring piston-to-deck heights.
 
Cudafever said:
looking at that picture, that is not a open chamber head. is is a closed chamber head that is cut for a flat top piston that pop up above the deck.(340) AKA, the only head that will accept your piston pop up is a stock chrys head.
In my opinion, you have to remove the pop up no matter what. Even if you keep the pop up on the piston, and us factory open chamber iron, your going to be over 11:1 right? and you plan to use pump gas right?(no racing fuel)

If that was mine, i would use racing gas (not worth it on a street car) or by a dish(stepped down flat top) that will work with your rhs heads and still be able to use pump gas.
You have plenty of option above, but, selling them pistons to recoup some of your money and buy the right piston is the way i would go.
Click to expand...

You'd need a stock un cut head, but then you would be hurting from the 72 ish cc to get anywhere near 11.1

The quench side of a stock J head is about .085-.100 ish deep
Average head gasket I've measured..
1008=.039 crushed
8553=.046 crushed
521sd=.054 crushed
Kb356 Piston=.085 quench head aka .085 out of the hole.

This is the piston we're talking about, right?
I had to get a 60cc chamber, milled from 69cc castings, then mill the quench pad down to clear the head in order to get a 10.1 static.
 
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I used the 6017 head for a 340 project

003.JPG


004.JPG


007 (3).JPG
 
MOPAROFFICIAL said:
You'd need a stock un cut head, but then you would be hurting from the 72 ish cc to get anywhere near 11.1

The quench side of a stock J head is about .085-.100 ish deep
Average head gasket I've measured..
1008=.039 crushed
8553=.046 crushed
521sd=.054 crushed
Kb356 Piston=.085 quench head aka .085 out of the hole.

This is the piston we're talking about, right?
I had to get a 60cc chamber, milled from 69cc castings, then mill the quench pad down to clear the head in order to get a 10.1 static.
Click to expand...

Are we talking about a 408(stroker)?
All i know is that with a 408 with 0 deck(proud .0015) flat top piston, w 4cc valve reliefs, 62cc rhs heads i was over 12.5:1
how many cc is the pop up? 72cc combustion chamber...- dome or pop up.........I can't see it being below 11:1 Haven't done the math but can't imagine.
I imagine the pop up must be more then the step down dish piston or what would be the point of the dome/ pop up????????
 
Cudafever said:
Are we talking about a 408(stroker)?
All i know is that with a 408 with 0 deck(proud .0015) flat top piston, w 4cc valve reliefs, 62cc rhs heads i was over 12.5:1
how many cc is the pop up? 72cc combustion chamber...- dome or pop up.........I can't see it being below 11:1 Haven't done the math but can't imagine.
I imagine the pop up must be more then the step down dish piston or what would be the point of the dome/ pop up????????
Click to expand...

It's a dish cup quench head, if we're talking about the same piston.
Their specs are close, your deck height will determine wether or not the raised outside edge around the quench head ends up zero deck or not. Mine is, the quench pad was a hair more than .085 too

Screenshot_20170903-222428.png
 
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yellow rose said:
I can't think of exactly what the OP's pistons look like but IIRC they are a flat top with the quench pad raised. If that's the case that head will work.

With the Pistons I use, that head won't work. Unless you can open up the plug side of the chamber.
Click to expand...
After milling .060 and sometimes finding a chamber that is cast smaller or what have you, I usually do have to open them up to avoid piston interference and to dial in the chamber cc across the board. They're cups, the diameters start to close
 
yellow rose said:
I can't think of exactly what the OP's pistons look like but IIRC they are a flat top with the quench pad raised. If that's the case that head will work.

With the Pistons I use, that head won't work. Unless you can open up the plug side of the chamber.
Click to expand...
If the op could mount the heads on his bare block and scribe the bores to the heads....he could get a shop to cut the chambers.

This was a poorly thought out build, costing more now for op.
 
According to that, 62cc =9.9 But, some one need to explain "affective head volume"?
Because, that term, to me, says that i should subtract 23.5cc from the head volume. aks 72-23.5=48cc WOW now thats some compression for a open chamber head!
 
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Cudafever said:
According to that, 62cc =9.9 But, some one need to explain "affective head volume"?
Because, that term, to me, says that i should subtract 23.5cc from the head volume. aks 72-23.5=48cc WOW not thats some compression for a open chamber head!
Click to expand...


I have 11.08:1 on open chamber heads with a 3.31 stroke. A thinner gasket will get me 11.25:1
 
The point i'm making is that if the total volume at TDC(Effective head volume) is 48cc on a 408 then that is damm sure not 9.0:1 compression.
obviously Im misunderstanding of something.........

screenshot_20170903-222428-png.png
 
Cudafever said:
According to that, 62cc =9.9 But, some one need to explain "affective head volume"?
Because, that term, to me, says that i should subtract 23.5cc from the head volume. aks 72-23.5=48cc WOW now thats some compression for a open chamber head!
Click to expand...
It's the opposite, I don't use their calculators much. They say effective, but it's really affecting the ratio.
9.99 & I'm closing the intake mid 40's and crank 185 @500 ft elev. It would be a lot higher if it were 11.1
 
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So you're saying that that dome/step piston had less compression than a Standard Step/dished piston????? Im still missing something here
 
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