Quench Vs Piston To Head Clearance

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Here' pics of piston. Forged TRW 2332P 030 (.030 over and 8cc valve reliefs)
Unmilled block and unmilled X heads(70 cc comb chamber)
My understanding (limited) is that a bone stock unmilled open chamber head(like mine) will have negligible effect on quench.
Theoretically here' #'s
0.080" Quench area "depth" + hg thickness (let's say felpro) 0.038"
Gives us 0.118"
Now cuz piston is proud of the deck(0.034"), you subtract that dimension from 0.118"
So 0.118- 0.034" = 0.084".
From what I've read, depending on a LOT of other factors, the "ideal" quench I'm looking for is 0.035-0.050" My 0.084 is a TON away from 0.050. My understanding is in my situation to attain 0.035-0.050 I could....
1. Mill head to block mounting surface (either block or head??)
2. Thinner head gasket
3. Increased piston compression height (new pistons)
I thought I was getting a grasp on it lol then when my math gave me 0.084 I'm starting to question my sanity.
Thanks all.
rumblefish360 said:
How could it be a non factor unless there is none?

Take some clay and soften it up in your hands to place on the piston top. Install the head gasket and cylinder head and tighten and torque to spec. Remove, measure the clay. Take this measurement against minimum piston to head distance spec.

Do you have pictures of the piston and it installed at top dead center? Is the head chamber stock? Has the head been milled?
Click to expand...

20180118_211641.jpg


20180118_211637.jpg
 
The chambers on all factory LA heads is smaller than the bore diameter meaning there is some quench ....but not in a beneficial way.

We are trying to squish all the a/f over toward the spark plug for a more complete burn from a more compacted mix and therefore faster burn, and not just a more compacted mixture that helps ... but the squeeze is compressing/atomizing the mix further helping it light off and burn faster near the ignition point aka plug. Without squishing it over to the plug side, situatuons like edgy high cylinder preasure coupled with marginal octane would allow the mix to possibly light off in more than one area of the bore/chamber causing 2 flame fronts to collide and that breaks pistons and pushes head gaskets.
I just woke up and maybe be confusing some, but good thread.
 
4spdragtop said:
Here' pics of piston. Forged TRW 2332P 030 (.030 over and 8cc valve reliefs)
Unmilled block and unmilled X heads(70 cc comb chamber)
My understanding (limited) is that a bone stock unmilled open chamber head(like mine) will have negligible effect on quench.
Theoretically here' #'s
0.080" Quench area "depth" + hg thickness (let's say felpro) 0.038"
Gives us 0.118"
Now cuz piston is proud of the deck(0.034"), you subtract that dimension from 0.118"
So 0.118- 0.034" = 0.084".
From what I've read, depending on a LOT of other factors, the "ideal" quench I'm looking for is 0.035-0.050" My 0.084 is a TON away from 0.050. My understanding is in my situation to attain 0.035-0.050 I could....
1. Mill head to block mounting surface (either block or head??)
2. Thinner head gasket
3. Increased piston compression height (new pistons)
I thought I was getting a grasp on it lol then when my math gave me 0.084 I'm starting to question my sanity.
Thanks all.


View attachment 1715156855

View attachment 1715156856
Click to expand...
Take heads and mic the chambers like a clock @12,6,1,10,2,8,4 o'clock.... now how big is the cylinder again...

340s....ever see the pistons clean around the outer edge on a stock style piston rebuild where they "mill" an unknown amount for compression?
 
A "Quench" piston would do the trick, with that open 340 chamber. Aka a dome piston......but then you would have to run racing gas.
 
Agree with what you are saying, but do my math/numbers seem "high"? Is my math correct?
Thanks!
MOPAROFFICIAL said:
The chambers on all factory LA heads is smaller than the bore diameter meaning there is some quench ....but not in a beneficial way.

We are trying to squish all the a/f over toward the spark plug for a more complete burn from a more compacted mix and therefore faster burn, and not just a more compacted mixture that helps ... but the squeeze is compressing/atomizing the mix further helping it light off and burn faster near the ignition point aka plug. Without squishing it over to the plug side, situatuons like edgy high cylinder preasure coupled with marginal octane would allow the mix to possibly light off in more than one area of the bore/chamber causing 2 flame fronts to collide and that breaks pistons and pushes head gaskets.
I just woke up and maybe be confusing some, but good thread.
Click to expand...
 
.
4spdragtop said:
Here' pics of piston. Forged TRW 2332P 030 (.030 over and 8cc valve reliefs)
Unmilled block and unmilled X heads(70 cc comb chamber)
My understanding (limited) is that a bone stock unmilled open chamber head(like mine) will have negligible effect on quench.
Theoretically here' #'s
0.080" Quench area "depth" + hg thickness (let's say felpro) 0.038"
Gives us 0.118"
Now cuz piston is proud of the deck(0.034"), you subtract that dimension from 0.118"
So 0.118- 0.034" = 0.084".
From what I've read, depending on a LOT of other factors, the "ideal" quench I'm looking for is 0.035-0.050" My 0.084 is a TON away from 0.050. My understanding is in my situation to attain 0.035-0.050 I could....
1. Mill head to block mounting surface (either block or head??)
2. Thinner head gasket
3. Increased piston compression height (new pistons)
I thought I was getting a grasp on it lol then when my math gave me 0.084 I'm starting to question my sanity.
Thanks all.


View attachment 1715156855

View attachment 1715156856
Click to expand...
.084 isn't doing anything for you.
Wanna be creative?
Take those pistons and mill .040 off of the top 'the plug side/open chamber side' of the piston, then mill the heads .040 , leave the smaller side near valve reliefs as is so that you have a quench pad.

.040 from piston, .040 from head, .039 gasket.... .045 quench.
 
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yup thats what sucks, a 10.5: piston that is actually 9.4:1 or step up to the 11.5:1 piston (dome piston) that of course IS a true 11.5:1.
That was my biggest frustration with my first 340 build. Daily driver, can't afford to mix racing gas all the time.
A dish/dome piston......YEAH THAT WOULD HAVE BEEN NICE!!!!
 
Last edited:
4spdragtop said:
Agree with what you are saying, but do my math/numbers seem "high"? Is my math correct?
Thanks!
Click to expand...
The way it is now, its probably near 9.7
If you don't keep the cylinder psi on that particular setup under 165 , 91 octane won't be enough and you may have to give up a lil power in the tune to keep from rattling under hard throttle in any gear after 1st.

I didn't see which cam you're running
 
Thanks for the pictures. I was having trouble seeing the piston in my head and not really knowing how high the some side is or is t is a big part of the mystery to don’t want to leave out.
 
No more machining done this year. Just not in the budget.
So the only variable I can alter is the hg thickness correct? I haven't decided on it thickness yet, but it looks like I should/can run a thin one? Say 0.026 (if I can find Felpro that thin)
Cam is a comp cams 270S solid flat tappet. Factory adjustable (273) rockers.
After your machining advice, how did you arrive at 0.040 quench? I don't see the math working there?
My ballpark compression at this point is approx 10:1.
Pistons are flat tops with 2 (8cc) valve reliefs.
Thanks all!
MOPAROFFICIAL said:
.
.084 isn't doing anything for you.
Wanna be creative?
Take those pistons and mill .040 off of the top 'the plug side/open chamber side' of the piston, then mill the heads .040 , leave the smaller side near valve reliefs as is so that you have a quench pad.

.040 from piston, .040 from head, .038 gasket.... .044 quench.
Click to expand...
Cudafever said:
yup thats what sucks, a 10.5: piston that is actually 9.4:1 or step up to the 11.5:1 piston (dome piston) that of course IS a true 11.5:1.
That was my biggest frustration with my first 340 build. Daily driver, can't afford to mix racing gas all the time.
A dish/dome piston......YEAH THAT WOULD HAVE BEEN NICE!!!!
Click to expand...

rumblefish360 said:
Thanks for the pictures. I was having trouble seeing the piston in my head and not really knowing how high the some side is or is t is a big part of the mystery to don’t want to leave out.
Click to expand...
 
Find out which head stick up the most in the block(these blocks, head surfaces, are not square from the factory!)
us a dial indicator to find the one that pop up the most. get some clay, throw on a old/used head gasket, tighten down and turn in over. measure the clay and the thickness of the head gasket and you know your clearance.

Now i said all of that....it just don't matter! choose a gasket and install it.

What you need to pay attention to, How Ever, is your valve to piston clearance. My .474/280 Purple hyd cam did NOT have enough clearance.

I had that same piston design and the valve pocket is plenty deep.HOW EVER!!!!!
Take a look at the valve pocket on you piston. Do you see were the valve pocket makes a SHARP turn up to the flat top of the piston?????
If you have a old valve, just lay it in that valve pocket, you will see it.
by rounding that ledge off, you will have plenty of clearance.
I don't know why they did it that way, but they did!
 
4spdragtop said:
Here' pics of piston. Forged TRW 2332P 030 (.030 over and 8cc valve reliefs)
Unmilled block and unmilled X heads(70 cc comb chamber)
My understanding (limited) is that a bone stock unmilled open chamber head(like mine) will have negligible effect on quench.
Theoretically here' #'s
0.080" Quench area "depth" + hg thickness (let's say felpro) 0.038"
Gives us 0.118"
Now cuz piston is proud of the deck(0.034"), you subtract that dimension from 0.118"
So 0.118- 0.034" = 0.084".
From what I've read, depending on a LOT of other factors, the "ideal" quench I'm looking for is 0.035-0.050" My 0.084 is a TON away from 0.050. My understanding is in my situation to attain 0.035-0.050 I could....
1. Mill head to block mounting surface (either block or head??)
2. Thinner head gasket
3. Increased piston compression height (new pistons)
I thought I was getting a grasp on it lol then when my math gave me 0.084 I'm starting to question my sanity.
Thanks all.


View attachment 1715156855

View attachment 1715156856
Click to expand...
If the piston is proud .034, gasket is .039, ...thats .005 in the gasket or shy of the gasket.....now the head is .080 deep but you mill .040 and it's . 040.... =.045

If you machined the open chamber side of the piston down say .040, it would bring you into a livable compression ratio on 91. Because just milling the heads down .040 without addressing the piston would screw you .
 
OP
what you may not be getting is that you are only gonna machine the part of the piston under the valves, leaving a step dome on the squish side of the chamber. This makes room for the heads to come down a similar amount, to maintain the Scr.
Read post 39 as many times as you need to, for it to make sense. It's a very elegant solution to an age old problem........
although custom pistons or longer rods would also work.

I'm a really big fan of a tight squish. I have run as tight as .028, but currently run .034 (+/- .0015).
I know this doesn't compare properly, but with aluminum heads, I have run an Scr of 11.3 with the Mopar 292/292/108 cam, in at 100.........on 87E10.......with full timing. The pressure was over 190 on my gauge. Mr. Wallace calculates it to 183psi.
What this proves to me is that A) squish really works,or B) aluminum sucks a lot of heat out of the chambers, or C) some combination of the two.
In any case 180psi makes a killer street 367, now with a 276/286/110
I know you said money is tight, but I highly recommend you continue down the path of tight Q, in the zone of .034 to .045, as others have mentioned, in conjunction with raising the Scr to obtain 160ish psi with your chosen cam. But try and chose the right cam the first time, or at least the smallest you dare, cuz every smaller cam you install is likely to increase the pressure.......perhaps right into detonation, as 160 doesn't leave much room for adjustment, without messing the combo up. Bigger will be Ok; the pressure just drops.
 
Last edited:
AJ, well said!
I would try and run a slightly less ratio but try to maintain as much quench as possible. It’s a catch 22 and hard. Your cam is a slight small for a high ratio.

Ether build for quench or just forget about it and run it as is and let it rip.
 
I understand now how the quench values are arrived at guys thanks.
This is the 1st time for me calculating quench in a build. It's surprising how pi$$ poor the quench value is on a stock 340.
Why didnt they engineer/design withquench values in mind??
The dilemma I face now is that do I run the 270S cam from my 273. Or choose another one.
A thinner head gasket is going to raise my compression(already at approx 10:1)but have no effect on quench due to combustion chamber volume.(and other factors)
Frig...
Thanks for the input guys.
MOPAROFFICIAL said:
If the piston is proud .034, gasket is .039, ...thats .005 in the gasket or shy of the gasket.....now the head is .080 deep but you mill .040 and it's . 040.... =.045

If you machined the open chamber side of the piston down say .040, it would bring you into a livable compression ratio on 91. Because just milling the heads down .040 without addressing the piston would screw you .
Click to expand...

AJ/FormS said:
OP
what you may not be getting is that you are only gonna machine the part of the piston under the valves, leaving a step dome on the squish side of the chamber. This makes room for the heads to come down a similar amount, to maintain the Scr.
Read post 39 as many times as you need to, for it to make sense. It's a very elegant solution to an age old problem........
although custom pistons or longer rods would also work.

I'm a really big fan of a tight squish. I have run as tight as .028, but currently run .034 (+/- .0015).
I know this doesn't compare properly, but with aluminum heads, I have run an Scr of 11.3 with the Mopar 292/292/108 cam, in at 100.........on 87E10.......with full timing. The pressure was over 190 on my gauge. Mr. Wallace calculates it to 183psi.
What this proves to me is that A) squish really works,or B) aluminum sucks a lot of heat out of the chambers, or C) some combination of the two.
In any case 180psi makes a killer street 367, now with a 276/286/110
I know you said money is tight, but I highly recommend you continue down the path of tight Q, in the zone of .034 to .045, as others have mentioned, in conjunction with raising the Scr to obtain 160ish psi with your chosen cam. But try and chose the right cam the first time, or at least the smallest you dare, cuz every smaller cam you install is likely to increase the pressure.......perhaps right into detonation, as 160 doesn't leave much room for adjustment, without messing the combo up. Bigger will be Ok; the pressure just drops.
Click to expand...

rumblefish360 said:
AJ, well said!
I would try and run a slightly less ratio but try to maintain as much quench as possible. It’s a catch 22 and hard. Your cam is a slight small for a high ratio.

Ether build for quench or just forget about it and run it as is and let it rip.
Click to expand...
 
4spdragtop said:
I understand now how the quench values are arrived at guys thanks.
This is the 1st time for me calculating quench in a build. It's surprising how pi$$ poor the quench value is on a stock 340.
Why didnt they engineer/design withquench values in mind??
The dilemma I face now is that do I run the 270S cam from my 273. Or choose another one.
A thinner head gasket is going to raise my compression(already at approx 10:1)but have no effect on quench due to combustion chamber volume.(and other factors)
Frig...
Thanks for the input guys.
Click to expand...

Advancements in engine tech are derived by necessity, be it the racing department or federal mandated requirements, they had better gas and there was no 'need" for it then.
 
Oh aggreeed! Also the factory as to warranty everything so pushing limits is not in there best interest. Quality control was, LOL, IMO, not yet invented then. Today’s everyday people mover engines are closer to yesteryears race engines.
 
Shaving .040" off of the head is basically shrinking your combustion chamber down to a "closed chamber head"

My 340 had 71cc heads and a steel shim head gasket...it was 9.4 I don't thing you will be 10.0 compression in stock form.
How ever i built 2 of these in this configuration and they ran Good!

I really, really like Moparofficial Recipe! Just make sure your machinist in on board to make it all come out good in the end
 
Cudafever said:
Shaving .040" off of the head is basically shrinking your combustion chamber down to a "closed chamber head"

My 340 had 71cc heads and a steel shim head gasket...it was 9.4 I don't thing you will be 10.0 compression in stock form.
How ever i built 2 of these in this configuration and they ran Good!

I really, really like Moparofficial Recipe! Just make sure your machinist in on board to make it all come out good in the end
Click to expand...
Oh agreed! And your right. It’ll run good.
 
4spdragtop said:
No more machining done this year. Just not in the budget.
So the only variable I can alter is the hg thickness correct? I haven't decided on it thickness yet, but it looks like I should/can run a thin one? Say 0.026 (if I can find Felpro that thin)
Cam is a comp cams 270S solid flat tappet. Factory adjustable (273) rockers.
After your machining advice, how did you arrive at 0.040 quench? I don't see the math working there?
My ballpark compression at this point is approx 10:1.
Pistons are flat tops with 2 (8cc) valve reliefs.
Thanks all!
Click to expand...

4spdragtop said:
I understand now how the quench values are arrived at guys thanks.
This is the 1st time for me calculating quench in a build. It's surprising how pi$$ poor the quench value is on a stock 340.
Why didnt they engineer/design withquench values in mind??
The dilemma I face now is that do I run the 270S cam from my 273. Or choose another one.
A thinner head gasket is going to raise my compression(already at approx 10:1)but have no effect on quench due to combustion chamber volume.(and other factors)
Frig...
Thanks for the input guys.
Click to expand...

If good quench isn't in the cards and running pump gas then I would try to keep compression lower and cylinder pressure / dynamic compression lower to keep away the rattles.
 
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