retarding the cam from 4 degrees to straight up

[Elroy]

I always shoot for having that tight but sometimes it just doesnt work out that way. There is no doubt that the O.E's don't see it as something worthwhile to chase. It would take a crazy amount of testing to qualify or disqualify it if you think about it.

You would need to test piston to head clearance ad different distances while maintaining the same compression ratio. Think about what that would involve, and the variables that would be introduced in doing so...and how small the measured differences would likely be. And would they even be within the margin of error on the average dyno.

So, I try to keep that distance snug, while also considering the effect on the actual compression ratio. But no doubt, Ive seen shit run real hard with "tight" quench, and shit run real hard with "loose" or no quench "full round dish" like was previously mentioned with the factory vortec piston... I've made some good power on those at 10.5:1 on pump gas and no detonation.

Ill keep it as a consideration and most of my stuff will likely end up tight because im trying to put compression in things usually , but I'll stay mostly focused on the big stuff, like getting flow through the engine in the right direction and trapping it.

[panic]

It's not a debate.
It's a patent (Sir Harry Ricardo), successfully defended in court thousands of times beginning over 100 years ago. Sidevalve engines only exist because of quench. The first production OHV V8 engines were closed chamber wedges with quench (1949 Oldsmobile and Cadillac).
Small negative effect: the clearance volume in the quench space burns too late to add cylinder pressure, but still contributes to emissions (quoting Chrysler w/r/t the 915 head vs. 906 head).

[Tom68]

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.

I'm undecided, I like tapered quench like you do on 2 strokes. No trapped mix.
But it's way beyond me, you can fool yourself visualising it. Dyno dyno dyno.

[rfoll]

In regards to the dished piston discussion, there is a world of difference in the types. The Vortec piston has a nice 1/2" flat at the perimeter. I'ts predecessor had a big chamfer to reduce crevice volume for emissions. The Vortec piston will tolerate much more timing without issue, and the chamfered dish piston will rattle like a can of marbles at 8.5:1 compression with the same head. I've made the swap. Considering the 70s smog 350s, it's no wonder the Vortec engines were such a big deal when they showed up.Not much more than a piston and head swap. Some Chrysler 360 engines have the piston a mile in the hole, and I think I remember some Ford engines did it as well. I think I remember reading that after about .060" quench is negligible. I've measured the deck on many sbc engines just because I can. From .025" in the hole at #1 piston to .045" on one of the back corners. Before CAFE, the engine was only required to run and pass emissions.

[skinny z]

In regards to the dished piston discussion, there is a world of difference in the types. The Vortec piston has a nice 1/2" flat at the perimeter. I'ts predecessor had a big chamfer to reduce crevice volume for emissions. The Vortec piston will tolerate much more timing without issue, and the chamfered dish piston will rattle like a can of marbles at 8.5:1 compression with the same head. I've made the swap.

Sounds like a compelling argument for the value of quench.
It's not the same for all engine types as that's been discussed earlier.
For the subject at hand, I'd say it has credibility.

[rfoll]

For the discussion at hand it's a matter of how much is enough. The original question was about retarding the cam 4 degrees. It took 3 days and 2 pages to get an answer.

[skinny z]

For the discussion at hand it's a matter of how much is enough. The original question was about retarding the cam 4 degrees. It took 3 days and 2 pages to get an answer.

Such is the nature of internet forums.
You did sign off a few pages back but as is often the case, these things take on a life of their own.

[rfoll]

The engine won't get built while is play at the computer. It has been a good discussion.

[digger]

For the discussion at hand it's a matter of how much is enough. The original question was about retarding the cam 4 degrees. It took 3 days and 2 pages to get an answer.

What was the answer?

[travis]

viewtopic.php?f=1&t=62282&p=878942&hilit=Vortec#p878942

I wish I could find my notebooks. I had the cams open and close points written down, plus cranking compression numbers. Seems like it was around 195 psi iirc, but I've slept since then.

[rfoll]

With IVC @ 63° the DCR is 8.3:1, about 192 CCP gauge psi, volume/pressure index is 457 (input is CCP × reduced stroke length, etc.). Guessing ratio of heats @ 1.25...
Retarding it to 67° gives DCR is 8.05:1, about 185 CCP gauge psi, volume/pressure index is 420. Combustion pressure is down about 8%.
Another retard to 71° gives DCR is 7.79:1, about 177 CCP gauge psi, volume/pressure index is 383. Combustion pressure is down about 16% from original.

Basically this tells me that if it rattles too bad, retarding the cam might help.

[rgalajda]

For the discussion at hand it's a matter of how much is enough. The original question was about retarding the cam 4 degrees. It took 3 days and 2 pages to get an answer.

I thought the answer was on the first page.

[Bigchief632]

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?

Essentially, yes, that's what I am saying. I've done this scenario numerous times over the year. Build engine, max compression pump gas for example. Engine gets run for years. Comes back for freshen up. Hone, re ring, bearings, etc. Say for example, a 406. 11.5:1 with flat tops, and 64cc. Mill heads .010. I had a .041 thick gasket on it originally, to maintain same compression, I switch to .051. These are usually re dynoed too. I see the difference. Same dyno, that repeats very well. Usually, they make a touch more power, certainly not less.

[Bigchief632]

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, hat a tighter quench provides for a greater resistance to tdetonation? 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.

No,it hasn't. It's more likely to detonate, and more sensetive to total timing. Less forgiving. Think nitrous engine, but less sensitive.

[Stan Weiss]

Essentially, yes, that's what I am saying. I've done this scenario numerous times over the year. Build engine, max compression pump gas for example. Engine gets run for years. Comes back for freshen up. Hone, re ring, bearings, etc. Say for example, a 406. 11.5:1 with flat tops, and 64cc. Mill heads .010. I had a .041 thick gasket on it originally, to maintain same compression, I switch to .051. These are usually re dynoed too. I see the difference. Same dyno, that repeats very well. Usually, they make a touch more power, certainly not less.

Did you cc's the heads after cutting them? I don't see any way cutting the heads 0.010" and then adding 0.010" to the head gasket doesn't reduce the CR.

Stan