Quench Query

[FElony]

So we know the 360 has dismal quench and compression from the factory. We also know it takes the same pistons as the 390. So what happens when you load a 360 with L2292 domes instead of the flats?

[My427stang]

.110 in the hole, plus gasket at .040,  72cc chamber, .030 over = 8.91 compression with .150 quench, add .010 more with a standard blie Felpro.

At that point, it could be a mile of quench, no worse at .150 than .100, likely would be a healthy-ish 360, but man, a L2291 390 would run circles around it on cheaper fuel

[FElony]

.110 in the hole, plus gasket at .040,  72cc chamber, .030 over = 8.91 compression with .150 quench, add .010 more with a standard blie Felpro.

At that point, it could be a mile of quench, no worse at .150 than .100, likely would be a healthy-ish 360, but man, a L2291 390 would run circles around it on cheaper fuel

What are you using for a dome value? I guess the question can be rephrased: Will the dome induce more swirl than the flat top and thus help offset the lack of quench?

[My427stang]

10.8 cc for the dome, and yes it could churn a little but nothing like flat quench pads tight against each other

[FElony]

My thoughts about this have reverted to old ideas in light of Brent's failure in the junky junk build. Tossing around combos with junky I have AND the Futura.

[Joey120373]

on the topic of quench, I know "everyone" says that ~.040 is a good number, but i also have heard that in certain racing circles, builders try to get as close to zero as they can. They look for ghosting or very light marks on the piston tops to indicate they are where they want to be; the tightest possible quench without causing any damage.

So, the question is, if .040 is a safe bet for any old build, how tight could you go ? Assuming good rods, pistons, crank and all clearances checked and trued up, deck true and level etc.

one thing ive always wanted to try, but no money or other means to make it happen, would be to build an engine with ~.040 CH, and the pistons at 0.000, set the quench with the head gasket. Then try progressively thinner gaskets and pull it apart and inspect after every swap to see where the limit is.

[My427stang]

.040 is a safe number, and I am not sure any tighter makes that much difference in terms of movement from the quench surfaces, if fact, .040 is probably more than you have to go.  Regardless, I'd be interested in more or less too, but a lot of work to swap gaskets, set lash, potentially retune and make a pull. 

I also think it is very much chamber and piston-dependent, a small chamber with a nice shallow dish will behave different than something with surfaces in the way.

Would be cool to play with if someone wanted to pay the labor   I have heard guys going to .032 or so.  I tend to shoot for .041-.045

[Gaugster]

So when folks list the gap 0.040" is that the clearance with a cold engine? I guess I am more accustom to this type of study considering how the engine components change dimensions ever so slightly when at operating temperature. It's a stack up of several items. Block iron/Aluminum, Piston/Deck clearance at TDC, Head gasket type and crushed thickness etc.... So like a Harley street engine (air cooled) gets the clearance set at a minimum cold since the aluminum cylinders expand more than the iron/steel rotating assembly.

[64PI]

I run .040" cometics on my stroker with the pistons @ .001"- .002" out of the hole. I turn it to 7000-7200 rpm and have never had an issue. Any time I've pulled the heads the quench pads are clean and there are no "kiss" marks of the piston to head. I'm not sure what is to be gained with going any tighter or looser. I'm going to be putting a 406 together for my summer daily driver in the following weeks with true flat tops and C4ae-g heads(75CC chambers). I'm not sure where the pistons will land in the hole but at 0 it puts me at 10.8:1 compression. I'm going to be trying to run 93 octane so I'm curious to see if running tighter quench will help with detonation or run a thicker gasket to knock the compression down but have a larger quench. This will be with an edelbrock pro flo EFI and a comp 270s cam.

[CaptCobrajet]

How tight you can go depends on bore size, and piston rock, as well as the other things.......steel crank and really good rods, as well.  At 4.190, with about .008 piston to wall, and all good parts, the pistons will kiss the head with no damage or rod bearing issues at .035 quench. This is an 8400 rpm example.  I have seen looser stuff touch harder.  I am sure that a really tight clearance on the piston, and a 6000 rpm situation would probably make it closer to .030, but that engine will wear eventually, and might lead you to problems before it should be "time".   I stop at .037-.038 on stuff that isn't coming back apart frequently, and clearance is generally tighter on streetable stuff to start with.

[Barry_R]

Similar to Blair on data.  I have had a couple engines at .036-.037 that put a visible witness mark from the surface of the head in the carbon on top of the piston, but seemed to run well.  I could see signs of stress on rod bearings but cant really be sure that the contact was the cause or a contributor - booth were pretty far out on the fringe in terms of tuning.  Both were +/-7000 RPM packages.

[blykins]

I've ran .020" total quench without issue.

Just kidding.

Like the others, I will go about .038-.039, but usually about .040". 

[Gaugster]

So the Killer B's (Blair, Barry & Brent) have it.... If that isn't a consensus than I don't know what is.

[Joey120373]

No kidding. Thanks guys.

[gt350hr]

   Blair's reply (#9) is as good as it gets. Minimum quench is affected by piston weight , stroke , rod length , rod material, RPM , compression ratio, wrist pin (wall thickness specifically), operating temperature, piston to wall clearance and piston rock. I recommend .035 absolute minimum with a steel rod. To generalize a number "standard" to which all engines should be built to avoid detonation is debatable. Certainly iron heads are more subject to detonation than aluminum as well as "open chamber" or large chamber volume head designs. .040 is the number "repeated" most often and is safe. That alone doesn't guarantee an engine to be detonation free. Tapping or "ghosting" the head should be reserved for drag race only engines where carbon build up is minimal and maximum compression is critical.
   Randy