in doing so unshrouded the valve
ProComp/Speedmaster aluminum heads
- Thread starter j par
- Start date
-
j par
Well-hung Member
Just on the one chamber?!..
No he just took a picture of one chamber so you could see a side by side comparison. Come on now. Lol
j par
Well-hung Member
Oic..
yellow rose
Overnight Sensation
Here is my AJ length answer to quench. It's long on words and short on math.
Ok, let's clear up some myths.
The small block Chrysler is one of the most detonation resistant engines I can think of. And that was with open chambers.
Compare that to its competitor, the 23 degree junk block Chevy. Comparing heads from the same generation, those chambers or horrible. Spark plug location looks like it was either a low priority or an after though. That's why anyone who tells me they have that type of chamber and run 34-36 total timing is either lying or doing it wrong. That chamber needs 40-42 total, and depending on things like dome size and shape and density altitude and you can run as high as 46 or so and I've done it many times. And when you tell the low timing idiots where you set the timing, they say it will be dead on the first lap or pass.
So, let's discuss this (remember me saying to correct an error takes 100 times more work/writing than it does to repeat the error) chamber verses timing conundrum.
How can it be that the lowly, mostly disrespected and often HATED open chamber Chrysler head take that much LESS timing than the beloved and adored closed chamber max quench head? Why is that?
It's because plug location is almost as important and chamber shape. Certainly, timing is much more influenced by plug location than and open verses closed chamber. And why quench is essentially useless when it comes to reducing the timing requirements of an engine. Spark plug location is the most critical factor in timing requirements and not quench.
Want another example? Look at the Hemi. An open chamber with the volume of an Olympic sized swimming pool and it needs only 31-32 degrees of advance to get it done. Which should obviously tell you how good the plug location is on the SBM as it needs only 3 degrees more total timing than the Hemi.
Quench. That's the area of the chamber that is flat and perpendicular to the bore axis. I hear there is R&D going on using tapered quench (which can then become squish if the piston matches the shape of chamber) not unlike what is done with 2 stokes.
In reality, you either need quench, or you don't. You don't want to be inbetween or you can make your tune up window very narrow.
When the deck of the piston approaches the flat pad of the cylinder head at TDC is how you get "quench". Quench means exactly what you think it means...it quenches like quenching your thirst.
As the piston approaches TDC, it meets up with flat pad on the head and literally "quenches" any possibility of combustion happening at that part of the chamber. And with a crappy chamber and plug location, if you don't "quench" combustion away from the plug you will have a tune up window the width of a pubic hair, and power on either side of whatever timing number you need (let's say max power is at 38 total and if that junk chamber and plug location has middling quench...say .050-.060) the power at 39-40 degrees will drop like a rock. And if you time it at 36-37 you see the same power loss. So effectively you have a timing setting of 38 degrees plus or minus 1 degree. That's tight.
Now let's consider a quality chamber with best case scenario plug location...the lowly small block Mopar. And we will ASSume that this engine came off the assembly line exactly as the blueprints called for...that is a .100 recess in the head, an .028 gasket and a positive deck height of .017. Doing the math says you have piston to head clearance of a paultry .111!!!!!
WOW!!! Yet this chamber will take a max timing of 35-36 degrees and is highly detonation resistant! How do you explain that. It's easy. Because chamber SHAPE and SPARK PLUG LOCATION are just as important as quench. And if you compromise chamber shape and plug location then quench becomes a serious priority.
The deck of the piston and the deck of the head coming together in close proximity creates quench, which does exactly what is says it does. It reduces the propensity for detonation and reduces total ignition timing. In the old days, where Pistons had clearances of a minimum of .008 and .012 wasn't considered junk, you could run the piston up to the head about .045-.050 from smacking. Then, as technology moved forward and .008 was clearance was considered a used up piston, you could get the deck clearance (quench) down to .040. Today, you can get down to .030 if your clearances are tight and spot on and your machine work is good.
The question may be asked what would you rather have, a chamber and plug location that needed quench or a chamber and plug location that didn't need quench??? The answer is easy. Why not both??? You can have both and not indulge in those compromises. How you say?? It's easy.
Take you sorry old junky X or J or O or whatever run of the mill production head and get them flat. Surprisingly, if you get brand new castings (for example I have brand new never used W2 casting in the shop and with a deck bridge and the recesses are all within .010) the recesses will be close. When heads are used they move and warp and turn and when they are surfaced that's where you see the most deviation in the recesses.
You take those castings and you equalize the recesses. It's not hard. You can do it by hand. I've done it in the mill with a ball end mill, but I can do it just fast by hand and get it plenty close. So get your recesses the same and cut the heads to equalize the chamber volumes of both heads. You don't need to mill the guts out of the head. Measure the recess. I like the recess at .070. So you'll know how much to mill the head now because let's say you are at .100 recess and you want .070 so the easy math is mill .030 and you've got that done. That leaves you some more to mill off if you need to touch up the decks for whatever reason. People ask why not just mill the recess out? Because it makes the deck so thin it's hard to get a gasket to seal if you get the CR up where it should be, and it significantly alters the flow and not in a good way. You are wrecking what is a very good, in fact great chamber. So I don't do that. You are doing counterproductive work. We want a very good chamber AND quench because I we all know brother YR hates leaving anything on the table, and this isn't just about max HP race engine junk. I'm talking about daily driver, street/strip stuff.
Ok, the recesses are equal and at .070 and we have to do the dreaded math. We want (for this type of head and because after this distance you gain almost nothing) .040 quench at the recess. That's all you need. Again, anything else is just mental and machining masturbation.
I add up the distance I have to account for first. Soooo we have a .070 recess plus let's say an .040 gasket. My math says that's a distance of .110 and we want .040 so we need to stick the piston out of the .070 and yes, that sound like a bunch. But wait...if the piston is made correctly, the deck of the piston should have been designed to be .020 out of the hole, even if it's the flat top. So that means the piston needs to be .050 positive from the deck and that's really nice. You reduce the crevice volume, got your quench and a very good chamber.
What if the piston morons made just a true flat top piston, or a domed piston that wasn't made with the deck .020 positive? Simple. Move the piston positive by .070 because it doesn't matter. Think about it.
Most ring packs today are usually .180-.200 down from the deck. If the piston is positive by .050 the rings are still .130-180 down from the deck, so plenty of room.
Now you have quench and a good chamber. It will be even less sensitive to detonation (just another reason I think I can run 12:1 on pump gas...a good chamber AND quench) and you can adjust the CR by adding a small dome (my stock stroke needed a .180 come to get 11.08:1).
One issue that will crop up is finding a machinist who doesn't have chevythink. If it's not good to have a positive deck height on a Chevy, then it's wrong for everything else too. It's stupid, but many think that way. There is nothing wrong with positive deck height with this type of Mopar head. So you have to overcome that flat earth thinking.
The next issue is the piston people. Some of them (most really) are just stone headed dullards. Convincing these guys to make a piston with a dish and a raised deck so you can get quench with these heads is nearly impossible. BTDT many times. With the longer strokes being used today, trying to get quench with these heads without going way past 12:1 CR is not easy. The best piston would be a reverse dome with a raised deck. And by raised deck I mean only .020 if you want the Chrysler number. I'd rather they raise the quench .050-.060 and then you wouldn't have to deck the block as much, but I'd rather deck the block .060-.080 than the heads.
So that's my musings on quench and how to get it on OC Mopar heads.
The TL
R version is quench is really important with junk chambers and plug location. As the chamber and plug location gets better, quench becomes less important.
The best of both worlds is correct chamber, correct plug location and quench. Easily said, not so much done, but easily doable.
Ok, let's clear up some myths.
The small block Chrysler is one of the most detonation resistant engines I can think of. And that was with open chambers.
Compare that to its competitor, the 23 degree junk block Chevy. Comparing heads from the same generation, those chambers or horrible. Spark plug location looks like it was either a low priority or an after though. That's why anyone who tells me they have that type of chamber and run 34-36 total timing is either lying or doing it wrong. That chamber needs 40-42 total, and depending on things like dome size and shape and density altitude and you can run as high as 46 or so and I've done it many times. And when you tell the low timing idiots where you set the timing, they say it will be dead on the first lap or pass.
So, let's discuss this (remember me saying to correct an error takes 100 times more work/writing than it does to repeat the error) chamber verses timing conundrum.
How can it be that the lowly, mostly disrespected and often HATED open chamber Chrysler head take that much LESS timing than the beloved and adored closed chamber max quench head? Why is that?
It's because plug location is almost as important and chamber shape. Certainly, timing is much more influenced by plug location than and open verses closed chamber. And why quench is essentially useless when it comes to reducing the timing requirements of an engine. Spark plug location is the most critical factor in timing requirements and not quench.
Want another example? Look at the Hemi. An open chamber with the volume of an Olympic sized swimming pool and it needs only 31-32 degrees of advance to get it done. Which should obviously tell you how good the plug location is on the SBM as it needs only 3 degrees more total timing than the Hemi.
Quench. That's the area of the chamber that is flat and perpendicular to the bore axis. I hear there is R&D going on using tapered quench (which can then become squish if the piston matches the shape of chamber) not unlike what is done with 2 stokes.
In reality, you either need quench, or you don't. You don't want to be inbetween or you can make your tune up window very narrow.
When the deck of the piston approaches the flat pad of the cylinder head at TDC is how you get "quench". Quench means exactly what you think it means...it quenches like quenching your thirst.
As the piston approaches TDC, it meets up with flat pad on the head and literally "quenches" any possibility of combustion happening at that part of the chamber. And with a crappy chamber and plug location, if you don't "quench" combustion away from the plug you will have a tune up window the width of a pubic hair, and power on either side of whatever timing number you need (let's say max power is at 38 total and if that junk chamber and plug location has middling quench...say .050-.060) the power at 39-40 degrees will drop like a rock. And if you time it at 36-37 you see the same power loss. So effectively you have a timing setting of 38 degrees plus or minus 1 degree. That's tight.
Now let's consider a quality chamber with best case scenario plug location...the lowly small block Mopar. And we will ASSume that this engine came off the assembly line exactly as the blueprints called for...that is a .100 recess in the head, an .028 gasket and a positive deck height of .017. Doing the math says you have piston to head clearance of a paultry .111!!!!!
WOW!!! Yet this chamber will take a max timing of 35-36 degrees and is highly detonation resistant! How do you explain that. It's easy. Because chamber SHAPE and SPARK PLUG LOCATION are just as important as quench. And if you compromise chamber shape and plug location then quench becomes a serious priority.
The deck of the piston and the deck of the head coming together in close proximity creates quench, which does exactly what is says it does. It reduces the propensity for detonation and reduces total ignition timing. In the old days, where Pistons had clearances of a minimum of .008 and .012 wasn't considered junk, you could run the piston up to the head about .045-.050 from smacking. Then, as technology moved forward and .008 was clearance was considered a used up piston, you could get the deck clearance (quench) down to .040. Today, you can get down to .030 if your clearances are tight and spot on and your machine work is good.
The question may be asked what would you rather have, a chamber and plug location that needed quench or a chamber and plug location that didn't need quench??? The answer is easy. Why not both??? You can have both and not indulge in those compromises. How you say?? It's easy.
Take you sorry old junky X or J or O or whatever run of the mill production head and get them flat. Surprisingly, if you get brand new castings (for example I have brand new never used W2 casting in the shop and with a deck bridge and the recesses are all within .010) the recesses will be close. When heads are used they move and warp and turn and when they are surfaced that's where you see the most deviation in the recesses.
You take those castings and you equalize the recesses. It's not hard. You can do it by hand. I've done it in the mill with a ball end mill, but I can do it just fast by hand and get it plenty close. So get your recesses the same and cut the heads to equalize the chamber volumes of both heads. You don't need to mill the guts out of the head. Measure the recess. I like the recess at .070. So you'll know how much to mill the head now because let's say you are at .100 recess and you want .070 so the easy math is mill .030 and you've got that done. That leaves you some more to mill off if you need to touch up the decks for whatever reason. People ask why not just mill the recess out? Because it makes the deck so thin it's hard to get a gasket to seal if you get the CR up where it should be, and it significantly alters the flow and not in a good way. You are wrecking what is a very good, in fact great chamber. So I don't do that. You are doing counterproductive work. We want a very good chamber AND quench because I we all know brother YR hates leaving anything on the table, and this isn't just about max HP race engine junk. I'm talking about daily driver, street/strip stuff.
Ok, the recesses are equal and at .070 and we have to do the dreaded math. We want (for this type of head and because after this distance you gain almost nothing) .040 quench at the recess. That's all you need. Again, anything else is just mental and machining masturbation.
I add up the distance I have to account for first. Soooo we have a .070 recess plus let's say an .040 gasket. My math says that's a distance of .110 and we want .040 so we need to stick the piston out of the .070 and yes, that sound like a bunch. But wait...if the piston is made correctly, the deck of the piston should have been designed to be .020 out of the hole, even if it's the flat top. So that means the piston needs to be .050 positive from the deck and that's really nice. You reduce the crevice volume, got your quench and a very good chamber.
What if the piston morons made just a true flat top piston, or a domed piston that wasn't made with the deck .020 positive? Simple. Move the piston positive by .070 because it doesn't matter. Think about it.
Most ring packs today are usually .180-.200 down from the deck. If the piston is positive by .050 the rings are still .130-180 down from the deck, so plenty of room.
Now you have quench and a good chamber. It will be even less sensitive to detonation (just another reason I think I can run 12:1 on pump gas...a good chamber AND quench) and you can adjust the CR by adding a small dome (my stock stroke needed a .180 come to get 11.08:1).
One issue that will crop up is finding a machinist who doesn't have chevythink. If it's not good to have a positive deck height on a Chevy, then it's wrong for everything else too. It's stupid, but many think that way. There is nothing wrong with positive deck height with this type of Mopar head. So you have to overcome that flat earth thinking.
The next issue is the piston people. Some of them (most really) are just stone headed dullards. Convincing these guys to make a piston with a dish and a raised deck so you can get quench with these heads is nearly impossible. BTDT many times. With the longer strokes being used today, trying to get quench with these heads without going way past 12:1 CR is not easy. The best piston would be a reverse dome with a raised deck. And by raised deck I mean only .020 if you want the Chrysler number. I'd rather they raise the quench .050-.060 and then you wouldn't have to deck the block as much, but I'd rather deck the block .060-.080 than the heads.
So that's my musings on quench and how to get it on OC Mopar heads.
The TL
R version is quench is really important with junk chambers and plug location. As the chamber and plug location gets better, quench becomes less important.The best of both worlds is correct chamber, correct plug location and quench. Easily said, not so much done, but easily doable.
Wholly crap. I gotta read that tomorrow morning
yellow rose
Overnight Sensation
If you think it's bad reading it, you should have typed it.
But I had to answer jpars question so his thread got back on the rails.
Thanks for taking the time post that .
Good explanation, but you left out the part on the effect of quench on air/fuel mixture.
yellow rose
Overnight Sensation
Sure did. My fingers started popping and cracking and my wife said stop before it gets worse. They are hurting right now but not too bad.
Want to fill that in for me???
TIA
Air/fuel is swirled into a finer mist creating a faster burn, which in turn minimizes the ability of hot spots to form in the chamber.
With the fuel particles being condensed more finely , the mixture is easier to light.
lowering the octane requirement.
yellow rose
Overnight Sensation
j par
Well-hung Member
Holy crap I don't mean any disrespect by this but I got halfway through and and fell asleep in my chair in front of the fireplace! LOL I'm with Pittsburgh I'm going to have to read this again in the morning so my brain can get around it more.. you need voice command! That way you just go back and proofread and fix the bad spots... I just woke up and went to bed, good night.. thank you for all that and I'll read it again the morning when it will make more sense to me...Here is my AJ length answer to quench. It's long on words and short on math.
Ok, let's clear up some myths.
The small block Chrysler is one of the most detonation resistant engines I can think of. And that was with open chambers.
Compare that to its competitor, the 23 degree junk block Chevy. Comparing heads from the same generation, those chambers or horrible. Spark plug location looks like it was either a low priority or an after though. That's why anyone who tells me they have that type of chamber and run 34-36 total timing is either lying or doing it wrong. That chamber needs 40-42 total, and depending on things like dome size and shape and density altitude and you can run as high as 46 or so and I've done it many times. And when you tell the low timing idiots where you set the timing, they say it will be dead on the first lap or pass.
So, let's discuss this (remember me saying to correct an error takes 100 times more work/writing than it does to repeat the error) chamber verses timing conundrum.
How can it be that the lowly, mostly disrespected and often HATED open chamber Chrysler head take that much LESS timing than the beloved and adored closed chamber max quench head? Why is that?
It's because plug location is almost as important and chamber shape. Certainly, timing is much more influenced by plug location than and open verses closed chamber. And why quench is essentially useless when it comes to reducing the timing requirements of an engine. Spark plug location is the most critical factor in timing requirements and not quench.
Want another example? Look at the Hemi. An open chamber with the volume of an Olympic sized swimming pool and it needs only 31-32 degrees of advance to get it done. Which should obviously tell you how good the plug location is on the SBM as it needs only 3 degrees more total timing than the Hemi.
Quench. That's the area of the chamber that is flat and perpendicular to the bore axis. I hear there is R&D going on using tapered quench (which can then become squish if the piston matches the shape of chamber) not unlike what is done with 2 stokes.
In reality, you either need quench, or you don't. You don't want to be inbetween or you can make your tune up window very narrow.
When the deck of the piston approaches the flat pad of the cylinder head at TDC is how you get "quench". Quench means exactly what you think it means...it quenches like quenching your thirst.
As the piston approaches TDC, it meets up with flat pad on the head and literally "quenches" any possibility of combustion happening at that part of the chamber. And with a crappy chamber and plug location, if you don't "quench" combustion away from the plug you will have a tune up window the width of a pubic hair, and power on either side of whatever timing number you need (let's say max power is at 38 total and if that junk chamber and plug location has middling quench...say .050-.060) the power at 39-40 degrees will drop like a rock. And if you time it at 36-37 you see the same power loss. So effectively you have a timing setting of 38 degrees plus or minus 1 degree. That's tight.
Now let's consider a quality chamber with best case scenario plug location...the lowly small block Mopar. And we will ASSume that this engine came off the assembly line exactly as the blueprints called for...that is a .100 recess in the head, an .028 gasket and a positive deck height of .017. Doing the math says you have piston to head clearance of a paultry .111!!!!!
WOW!!! Yet this chamber will take a max timing of 35-36 degrees and is highly detonation resistant! How do you explain that. It's easy. Because chamber SHAPE and SPARK PLUG LOCATION are just as important as quench. And if you compromise chamber shape and plug location then quench becomes a serious priority.
The deck of the piston and the deck of the head coming together in close proximity creates quench, which does exactly what is says it does. It reduces the propensity for detonation and reduces total ignition timing. In the old days, where Pistons had clearances of a minimum of .008 and .012 wasn't considered junk, you could run the piston up to the head about .045-.050 from smacking. Then, as technology moved forward and .008 was clearance was considered a used up piston, you could get the deck clearance (quench) down to .040. Today, you can get down to .030 if your clearances are tight and spot on and your machine work is good.
The question may be asked what would you rather have, a chamber and plug location that needed quench or a chamber and plug location that didn't need quench??? The answer is easy. Why not both??? You can have both and not indulge in those compromises. How you say?? It's easy.
Take you sorry old junky X or J or O or whatever run of the mill production head and get them flat. Surprisingly, if you get brand new castings (for example I have brand new never used W2 casting in the shop and with a deck bridge and the recesses are all within .010) the recesses will be close. When heads are used they move and warp and turn and when they are surfaced that's where you see the most deviation in the recesses.
You take those castings and you equalize the recesses. It's not hard. You can do it by hand. I've done it in the mill with a ball end mill, but I can do it just fast by hand and get it plenty close. So get your recesses the same and cut the heads to equalize the chamber volumes of both heads. You don't need to mill the guts out of the head. Measure the recess. I like the recess at .070. So you'll know how much to mill the head now because let's say you are at .100 recess and you want .070 so the easy math is mill .030 and you've got that done. That leaves you some more to mill off if you need to touch up the decks for whatever reason. People ask why not just mill the recess out? Because it makes the deck so thin it's hard to get a gasket to seal if you get the CR up where it should be, and it significantly alters the flow and not in a good way. You are wrecking what is a very good, in fact great chamber. So I don't do that. You are doing counterproductive work. We want a very good chamber AND quench because I we all know brother YR hates leaving anything on the table, and this isn't just about max HP race engine junk. I'm talking about daily driver, street/strip stuff.
Ok, the recesses are equal and at .070 and we have to do the dreaded math. We want (for this type of head and because after this distance you gain almost nothing) .040 quench at the recess. That's all you need. Again, anything else is just mental and machining masturbation.
I add up the distance I have to account for first. Soooo we have a .070 recess plus let's say an .040 gasket. My math says that's a distance of .110 and we want .040 so we need to stick the piston out of the .070 and yes, that sound like a bunch. But wait...if the piston is made correctly, the deck of the piston should have been designed to be .020 out of the hole, even if it's the flat top. So that means the piston needs to be .050 positive from the deck and that's really nice. You reduce the crevice volume, got your quench and a very good chamber.
What if the piston morons made just a true flat top piston, or a domed piston that wasn't made with the deck .020 positive? Simple. Move the piston positive by .070 because it doesn't matter. Think about it.
Most ring packs today are usually .180-.200 down from the deck. If the piston is positive by .050 the rings are still .130-180 down from the deck, so plenty of room.
Now you have quench and a good chamber. It will be even less sensitive to detonation (just another reason I think I can run 12:1 on pump gas...a good chamber AND quench) and you can adjust the CR by adding a small dome (my stock stroke needed a .180 come to get 11.08:1).
One issue that will crop up is finding a machinist who doesn't have chevythink. If it's not good to have a positive deck height on a Chevy, then it's wrong for everything else too. It's stupid, but many think that way. There is nothing wrong with positive deck height with this type of Mopar head. So you have to overcome that flat earth thinking.
The next issue is the piston people. Some of them (most really) are just stone headed dullards. Convincing these guys to make a piston with a dish and a raised deck so you can get quench with these heads is nearly impossible. BTDT many times. With the longer strokes being used today, trying to get quench with these heads without going way past 12:1 CR is not easy. The best piston would be a reverse dome with a raised deck. And by raised deck I mean only .020 if you want the Chrysler number. I'd rather they raise the quench .050-.060 and then you wouldn't have to deck the block as much, but I'd rather deck the block .060-.080 than the heads.
So that's my musings on quench and how to get it on OC Mopar heads.
The TL
The best of both worlds is correct chamber, correct plug location and quench. Easily said, not so much done, but easily doable.
And also I appreciate the rerailment!...
73smallblock
Well-Known Member
Their 40% off sale is live again!
j par
Well-hung Member
Stop the freaking phone! 40% off! I haven't even put the heads on yet and I could have got yet another $100 off!
I was going to wait for the sale and I caught the one in September and couldn't think it could get any cheaper!
ALERT! ALERT! ALERT.....
I was going to wait for the sale and I caught the one in September and couldn't think it could get any cheaper!
ALERT! ALERT! ALERT.....
- Joined
- Mar 17, 2018
- Messages
- 13,275
- Reaction score
- 30,084
On plus side YR explanation rivals any of AJs long winded disortations.
I still haven’t read that. My attention spell isn’t that long unless a young, beautiful, naked girl was reading it to me.
- Joined
- Mar 17, 2018
- Messages
- 13,275
- Reaction score
- 30,084
yellow rose
Overnight Sensation
1. You are WAY TOO OLD for anything young, beautiful and naked. The resulting heart attack would be Biblical!!
2. I can't help all you ADD/ADHD types. They have drugs to help you with that.
3. I'm trying to dethrone AJ for the longest posts on FABO. I'm working my way into as that's hard to do.
4. HAPPY THANKSGIVING
j par
Well-hung Member
If I don't get my cheeseburger next week you are not human!..
Happy Thanksgiving...
Here is my AJ length answer to quench. It's long on words and short on math.
Ok, let's clear up some myths.
The small block Chrysler is one of the most detonation resistant engines I can think of. And that was with open chambers.
Compare that to its competitor, the 23 degree junk block Chevy. Comparing heads from the same generation, those chambers or horrible. Spark plug location looks like it was either a low priority or an after though. That's why anyone who tells me they have that type of chamber and run 34-36 total timing is either lying or doing it wrong. That chamber needs 40-42 total, and depending on things like dome size and shape and density altitude and you can run as high as 46 or so and I've done it many times. And when you tell the low timing idiots where you set the timing, they say it will be dead on the first lap or pass.
So, let's discuss this (remember me saying to correct an error takes 100 times more work/writing than it does to repeat the error) chamber verses timing conundrum.
How can it be that the lowly, mostly disrespected and often HATED open chamber Chrysler head take that much LESS timing than the beloved and adored closed chamber max quench head? Why is that?
It's because plug location is almost as important and chamber shape. Certainly, timing is much more influenced by plug location than and open verses closed chamber. And why quench is essentially useless when it comes to reducing the timing requirements of an engine. Spark plug location is the most critical factor in timing requirements and not quench.
Want another example? Look at the Hemi. An open chamber with the volume of an Olympic sized swimming pool and it needs only 31-32 degrees of advance to get it done. Which should obviously tell you how good the plug location is on the SBM as it needs only 3 degrees more total timing than the Hemi.
Quench. That's the area of the chamber that is flat and perpendicular to the bore axis. I hear there is R&D going on using tapered quench (which can then become squish if the piston matches the shape of chamber) not unlike what is done with 2 stokes.
In reality, you either need quench, or you don't. You don't want to be inbetween or you can make your tune up window very narrow.
When the deck of the piston approaches the flat pad of the cylinder head at TDC is how you get "quench". Quench means exactly what you think it means...it quenches like quenching your thirst.
As the piston approaches TDC, it meets up with flat pad on the head and literally "quenches" any possibility of combustion happening at that part of the chamber. And with a crappy chamber and plug location, if you don't "quench" combustion away from the plug you will have a tune up window the width of a pubic hair, and power on either side of whatever timing number you need (let's say max power is at 38 total and if that junk chamber and plug location has middling quench...say .050-.060) the power at 39-40 degrees will drop like a rock. And if you time it at 36-37 you see the same power loss. So effectively you have a timing setting of 38 degrees plus or minus 1 degree. That's tight.
Now let's consider a quality chamber with best case scenario plug location...the lowly small block Mopar. And we will ASSume that this engine came off the assembly line exactly as the blueprints called for...that is a .100 recess in the head, an .028 gasket and a positive deck height of .017. Doing the math says you have piston to head clearance of a paultry .111!!!!!
WOW!!! Yet this chamber will take a max timing of 35-36 degrees and is highly detonation resistant! How do you explain that. It's easy. Because chamber SHAPE and SPARK PLUG LOCATION are just as important as quench. And if you compromise chamber shape and plug location then quench becomes a serious priority.
The deck of the piston and the deck of the head coming together in close proximity creates quench, which does exactly what is says it does. It reduces the propensity for detonation and reduces total ignition timing. In the old days, where Pistons had clearances of a minimum of .008 and .012 wasn't considered junk, you could run the piston up to the head about .045-.050 from smacking. Then, as technology moved forward and .008 was clearance was considered a used up piston, you could get the deck clearance (quench) down to .040. Today, you can get down to .030 if your clearances are tight and spot on and your machine work is good.
The question may be asked what would you rather have, a chamber and plug location that needed quench or a chamber and plug location that didn't need quench??? The answer is easy. Why not both??? You can have both and not indulge in those compromises. How you say?? It's easy.
Take you sorry old junky X or J or O or whatever run of the mill production head and get them flat. Surprisingly, if you get brand new castings (for example I have brand new never used W2 casting in the shop and with a deck bridge and the recesses are all within .010) the recesses will be close. When heads are used they move and warp and turn and when they are surfaced that's where you see the most deviation in the recesses.
You take those castings and you equalize the recesses. It's not hard. You can do it by hand. I've done it in the mill with a ball end mill, but I can do it just fast by hand and get it plenty close. So get your recesses the same and cut the heads to equalize the chamber volumes of both heads. You don't need to mill the guts out of the head. Measure the recess. I like the recess at .070. So you'll know how much to mill the head now because let's say you are at .100 recess and you want .070 so the easy math is mill .030 and you've got that done. That leaves you some more to mill off if you need to touch up the decks for whatever reason. People ask why not just mill the recess out? Because it makes the deck so thin it's hard to get a gasket to seal if you get the CR up where it should be, and it significantly alters the flow and not in a good way. You are wrecking what is a very good, in fact great chamber. So I don't do that. You are doing counterproductive work. We want a very good chamber AND quench because I we all know brother YR hates leaving anything on the table, and this isn't just about max HP race engine junk. I'm talking about daily driver, street/strip stuff.
Ok, the recesses are equal and at .070 and we have to do the dreaded math. We want (for this type of head and because after this distance you gain almost nothing) .040 quench at the recess. That's all you need. Again, anything else is just mental and machining masturbation.
I add up the distance I have to account for first. Soooo we have a .070 recess plus let's say an .040 gasket. My math says that's a distance of .110 and we want .040 so we need to stick the piston out of the .070 and yes, that sound like a bunch. But wait...if the piston is made correctly, the deck of the piston should have been designed to be .020 out of the hole, even if it's the flat top. So that means the piston needs to be .050 positive from the deck and that's really nice. You reduce the crevice volume, got your quench and a very good chamber.
What if the piston morons made just a true flat top piston, or a domed piston that wasn't made with the deck .020 positive? Simple. Move the piston positive by .070 because it doesn't matter. Think about it.
Most ring packs today are usually .180-.200 down from the deck. If the piston is positive by .050 the rings are still .130-180 down from the deck, so plenty of room.
Now you have quench and a good chamber. It will be even less sensitive to detonation (just another reason I think I can run 12:1 on pump gas...a good chamber AND quench) and you can adjust the CR by adding a small dome (my stock stroke needed a .180 come to get 11.08:1).
One issue that will crop up is finding a machinist who doesn't have chevythink. If it's not good to have a positive deck height on a Chevy, then it's wrong for everything else too. It's stupid, but many think that way. There is nothing wrong with positive deck height with this type of Mopar head. So you have to overcome that flat earth thinking.
The next issue is the piston people. Some of them (most really) are just stone headed dullards. Convincing these guys to make a piston with a dish and a raised deck so you can get quench with these heads is nearly impossible. BTDT many times. With the longer strokes being used today, trying to get quench with these heads without going way past 12:1 CR is not easy. The best piston would be a reverse dome with a raised deck. And by raised deck I mean only .020 if you want the Chrysler number. I'd rather they raise the quench .050-.060 and then you wouldn't have to deck the block as much, but I'd rather deck the block .060-.080 than the heads.
So that's my musings on quench and how to get it on OC Mopar heads.
The TL
The best of both worlds is correct chamber, correct plug location and quench. Easily said, not so much done, but easily doable.
Printed it, because i know how much you hate to repeat yourself
I think AJ would be proud.
As I always say to AJ, nut shell it and drop the math.
Get to the fuckin point! Skip the math lessons!
Thank you @yellow rose for condensing what I have type out over the long term/multiple posts to multiple posters.
This has been written about in many publications over the years. But sometimes you just have to re hash it again and again.
The best part is the “major limitation“ on math!
Hemioutlaw
Make America Great Again!
Been in the market for some small block aluminum heads for a 408' single turbo build and been following all of the threads on the SPEEDMASTERS, I don't have the luxury of owning my own flow bench and honestly wouldn't know WTF I was doing anyway. Since everybody and their brother claims to own a bench why it seems like it'd be easier to split atoms in the garage then obtain flow numbers for the SM ported heads is beyond me. I'm not a bare budget guy but ain't afraid to save a buck either if I can and i've (rightfully or wrong) come to the conclusion that the castings seem to be fine. Though I've been talking to someone that has been running their ootb springs,valves and retainers for going on five years now the valvetrain hardware is where i'm tentative and will end up buying name brand stuff and It will assuredly end up costing me more but will allow me to feel a little more secure when I stand on it.
The tariff stuff has definitely impacted overseas goods but we can't have it both ways and sacrifices need to be made so i'm cool with that because we finally got more than an empty suit in the oval office. Talked to Speedmaster just fkn Wednesday and even mentioning Black Friday got offered $1400 Bucks, today via their site pair of ported heads to the door $965 bucks so their on the way. Not real thrilled with the salesmen I spoke with since it's a HUGE price difference but it is what it is and that's a good chunk of Dinero to save.
The tariff stuff has definitely impacted overseas goods but we can't have it both ways and sacrifices need to be made so i'm cool with that because we finally got more than an empty suit in the oval office. Talked to Speedmaster just fkn Wednesday and even mentioning Black Friday got offered $1400 Bucks, today via their site pair of ported heads to the door $965 bucks so their on the way. Not real thrilled with the salesmen I spoke with since it's a HUGE price difference but it is what it is and that's a good chunk of Dinero to save.
-
