retarding the cam from 4 degrees to straight up

[rfoll]

Would you do it? We have a 2 piece timing cover and can retard it later if necessary.

[Monza355]

What octane is a premium fuel in your area ?

[skinny z]

I'd run a .051thick gasket. That will work better, I promise. It actually works the opposite of what most believe. What elevation are you at in Oregon?

Would you care to explain?

I'd like that explanation myself.
Are you talking about pumping losses as referred to in another thread?

I remember a line in Bill Jenkins Book where he suggested not to run the piston to head clearance too tight as he thought there may be some pumping loss when the operating piston to head clearance approaches zero. The suggestion was there may be gains up to .030" min operating, compression permitting, at least in that time and application.

Bill’s theory is analogous to lifting a sheet of glass off a flat surface and they stick together. They’re called Van Der Waals forces.

In my opinion, combustion measurement and technology has moved to point where I don’t think that is a consideration and because the gains there far outweigh any losses from that. It would be very hard to quantify as well.

[skinny z]

Would you do it? We have a 2 piece timing cover and can retard it later if necessary.

Although the larger bore might add to the end gas ignition/detonation by how much is probably difficult to quantify. This is as compared to the 4.030" build I posted earlier.
But, since we're talking about typical Gen 1 SBC architecture and a compact chamber as the Darts look to have, DCR is relevant to our similar builds and chassis. 8.4:1 was about the limit in my street/strip experiences. That still allowed for a proper timing curve although there were times when it would rattle. Teardowns though show no signs of damage from detonation.
Considering that I'm the position of having to make this decision again, I'd opt for a little less DCR via a little more seat timing while still maintaining the 10.2:1 SCR that comes about from a .008" piston below deck, an .026" gasket and 65.4cc chambers.
Seeing as you have the cam installed, retarding the installed ICL would have somewhat a similar effect on DCR although all of the valve events are obviously changed as a result. How will that play into it?
That said, with the two-piece cover (I've got the Cloyes two-piece myself), I'd go with the earlier IVC and go from there. I'd rather start aggressively and dial it back than start on the weak side, then see if more is better only to have to dial it back again (from a labour perspective).

Anyway, that's two cents worth. Please be sure to post your progress. This is a hot topic for me at the moment.

[Bigchief632]

Is that enough to make it less sensitive to pinging?

I'd run a .051thick gasket. That will work better, I promise. It actually works the opposite of what most believe. What elevation are you at in Oregon?

We already have the 1014 .039" gasket. Purchased a long time ago. I gave some thought to the 1044/.050" gasket, but I debated the extra .010" of quench. It would drop the static from 10.2 to 10.0. The CR might change when I get my hands on the heads. Publishes volumes can be different from reality. I plan on polishing the chambers some to reflect some heat. We are under 100' in most of the surrounding area. The drag strip is about 30'. "It actually works the opposite of what most believe". Would you care to explain?

Debate all you want, I told you what to do. It'll work. I've done it 50 times since the mid 90's. But listen to guys with "opinions ". Good luck, hope it works out for you. . Quench works the opposite of what everyone on here thinks. Making it "tighter" isn't better or more "efficient" because it wants less total timing, it wants less total timing because it will detonate otherwise. You add compression, that's it. These engines we are talking about do not become more "efficient" with tighter "quench", they gain compression, and become MORE sensitive to timing. They want less total timing because they have more compression, and are more likely to detonate on the same amount of octane, as in pump gas.

[rfoll]

We will likely spring for the gaskets, The valve timing can be tried if needed. Thanks for all of the replies, Rick.

[rfoll]

We will likely spring for the gaskets, The 2 piece timing cover allows for changing valve timing if needed. Thanks for all of the replies, Rick.

[skinny z]

Debate all you want, I told you what to do. It'll work. I've done it 50 times since the mid 90's. But listen to guys with "opinions ". Good luck, hope it works out for you. . Quench works the opposite of what everyone on here thinks. Making it "tighter" isn't better or more "efficient" because it wants less total timing, it wants less total timing because it will detonate otherwise. You add compression, that's it. These engines we are talking about do not become more "efficient" with tighter "quench", they gain compression, and become MORE sensitive to timing. They want less total timing because they have more compression, and are more likely to detonate on the same amount of octane, as in pump gas.

Hasn't it been clearly demonstrated, and this is with respect to the engine at hand, that a tighter quench provides for a greater resistance to detonation? And this is with equal compression ratios?
I'm not sure where "efficiency" came into the conversation but if you reduce the elements that contribute to detonation in the first place, that is the amount of end gases not exposed to the flame front or the lack of mixture motion in the compressing cylinder, you'll reduce the tendency to detonate. This will allow additional timing but only if the total timing had been previously compromised due to that tendency to ping.

[rfoll]

Debate all you want, I told you what to do. It'll work. I've done it 50 times since the mid 90's. But listen to guys with "opinions ". Good luck, hope it works out for you. . Quench works the opposite of what everyone on here thinks. Making it "tighter" isn't better or more "efficient" because it wants less total timing, it wants less total timing because it will detonate otherwise. You add compression, that's it. These engines we are talking about do not become more "efficient" with tighter "quench", they gain compression, and become MORE sensitive to timing. They want less total timing because they have more compression, and are more likely to detonate on the same amount of octane, as in pump gas.

Hasn't it been clearly demonstrated, and this is with respect to the engine at hand, that a tighter quench provides for a greater resistance to detonation? And this is with equal compression ratios?
I'm not sure where "efficiency" came into the conversation but if you reduce the elements that contribute to detonation in the first place, that is the amount of end gases not exposed to the flame front or the lack of mixture motion in the compressing cylinder, you'll reduce the tendency to detonate. This will allow additional timing but only if the total timing had been previously compromised due to that tendency to ping.

The quench debate could go on forever, but the reality is for a given engine to have enough quench. The Vortec motors have a .028" gasket with a piston .025" in the hole and a very small quench pad on a dished piston. They seem to run pretty good, the one in my 2 ton Impala gets 18-19 mpg. But I doubt those heads are any real comparison to the Dart SS with a 76 cc chamber.

[digger]

Debate all you want, I told you what to do. It'll work. I've done it 50 times since the mid 90's. But listen to guys with "opinions ". Good luck, hope it works out for you. . Quench works the opposite of what everyone on here thinks. Making it "tighter" isn't better or more "efficient" because it wants less total timing, it wants less total timing because it will detonate otherwise. You add compression, that's it. These engines we are talking about do not become more "efficient" with tighter "quench", they gain compression, and become MORE sensitive to timing. They want less total timing because they have more compression, and are more likely to detonate on the same amount of octane, as in pump gas.

Hasn't it been clearly demonstrated, and this is with respect to the engine at hand, that a tighter quench provides for a greater resistance to detonation? And this is with equal compression ratios?
I'm not sure where "efficiency" came into the conversation but if you reduce the elements that contribute to detonation in the first place, that is the amount of end gases not exposed to the flame front or the lack of mixture motion in the compressing cylinder, you'll reduce the tendency to detonate. This will allow additional timing but only if the total timing had been previously compromised due to that tendency to ping.

it has been stated that the increased CR from tightening up the squish clearance offsets the increase in CR from a knock resistance perspective. I am not sure it has been clearly demonstrated as i have never seen (don't recall at least) and not done any tests. There is probably a lot of application dependencies, noting that there are awful lot of different combustion chamber sand pistons shapes etc.

Maybe it is me but the OP is jumping at shadows?

[Chris_Hamilton]

I'd run a .051thick gasket. That will work better, I promise. It actually works the opposite of what most believe. What elevation are you at in Oregon?

We already have the 1014 .039" gasket. Purchased a long time ago. I gave some thought to the 1044/.050" gasket, but I debated the extra .010" of quench. It would drop the static from 10.2 to 10.0. The CR might change when I get my hands on the heads. Publishes volumes can be different from reality. I plan on polishing the chambers some to reflect some heat. We are under 100' in most of the surrounding area. The drag strip is about 30'. "It actually works the opposite of what most believe". Would you care to explain?

Debate all you want, I told you what to do. It'll work. I've done it 50 times since the mid 90's. But listen to guys with "opinions ". Good luck, hope it works out for you. . Quench works the opposite of what everyone on here thinks. Making it "tighter" isn't better or more "efficient" because it wants less total timing, it wants less total timing because it will detonate otherwise. You add compression, that's it. These engines we are talking about do not become more "efficient" with tighter "quench", they gain compression, and become MORE sensitive to timing. They want less total timing because they have more compression, and are more likely to detonate on the same amount of octane, as in pump gas.

If two engines that are nearly exactly the same, and have the exact same CR, only difference being one has a tight quench and one has a larger quench, which is preferable? Are you saying it doesn't really matter and that more is better?

[skinny z]

Some excellent information in the link below.

https://www.enginelabs.com/engine-tech/ ... -and-head/

[Tom68]

Debate all you want, I told you what to do. It'll work. I've done it 50 times since the mid 90's. But listen to guys with "opinions ". Good luck, hope it works out for you. . Quench works the opposite of what everyone on here thinks. Making it "tighter" isn't better or more "efficient" because it wants less total timing, it wants less total timing because it will detonate otherwise. You add compression, that's it. These engines we are talking about do not become more "efficient" with tighter "quench", they gain compression, and become MORE sensitive to timing. They want less total timing because they have more compression, and are more likely to detonate on the same amount of octane, as in pump gas.

Hasn't it been clearly demonstrated, and this is with respect to the engine at hand, that a tighter quench provides for a greater resistance to detonation? And this is with equal compression ratios?
I'm not sure where "efficiency" came into the conversation but if you reduce the elements that contribute to detonation in the first place, that is the amount of end gases not exposed to the flame front or the lack of mixture motion in the compressing cylinder, you'll reduce the tendency to detonate. This will allow additional timing but only if the total timing had been previously compromised due to that tendency to ping.

it has been stated that the increased CR from tightening up the squish clearance offsets the increase in CR from a knock resistance perspective. I am not sure it has been clearly demonstrated as i have never seen (don't recall at least) and not done any tests. There is probably a lot of application dependencies, noting that there are awful lot of different combustion chamber sand pistons shapes etc.

Maybe it is me but the OP is jumping at shadows?

I think all the OEM's know how important it is or isn't, how little effort most of them put into it speaks volumes.

The Rfolls Vortec example is a good case in point, that dished piston stops charge trapped by the quench getting burnt late and making a longer than necessary burn.

[Elroy]

I think all the OEM's know how important it is or isn't, how little effort most of them put into it speaks volumes.

Ain't that the truth.

[skinny z]

I think all the OEM's know how important it is or isn't, how little effort most of them put into it speaks volumes.

Ain't that the truth.

Sounds to me like neither of you two think quench is worth anything. In the context of this SBC build that is.