318 std piston quench with aluminum heads?

[340inabbody]

Guys, would I get any decent quench or any at all running std 1970 318 pistons with a newer aluminum head? I know the 318’s are a lower compression and the plug sits below deck like 20 thou or so. Or is that a bad combination?

The old heads I believe are open chamber?? and one question I have is are all the aluminum performance heads closed chamber?


Just kicking around some ideas.

 

[GTX JOHN]

The 318 pistons are generally 50 or 60 down
in the hole or more (Blueprint Spec is 41). Some 318 heads are closed
and some are open chamber. That low of compression would not be optimal
although it would operate OK. I would try to choose a head that was lower in CCs
if available or plan to take a .050 cut off of it.

I have race this engine in NHRA stock for many years and I am pretty familiar with it.

 

[junkyardhero]

not really, no.

better, yes. but not "optimal".

 

[340inabbody]

Eddy’s. 63cc
Trickflow 60cc
Speedmaster 65cc

Is there a calculation for quench or is it strictly the volume of the quench area?

Assuming original compression ratio of 8.6 stock heads is there a way to compare the above heads for quench volume or how ever it’s quantified? Same for compression?

 

[Professor Fate]

I wouldn't even worry about it.
Generally accepted clearances generally put effective quench at something approaching .035- if your stock pistons are .050-.060 down like GTX John says, I don't think there's any chance for you to get anywhere near that number; let alone when you throw a .028-.042 ish head gasket on it.
I think you're chasing your tail with a stock piston and deck height.

 

[340inabbody]

Thanks was just kicking some ideas around. I have a nice stock 318 short block that I was thinking of using either temporarily or a little longer than that.

 

[66Valiant528]

Put some zero deck pistons in it and get your quench.

 

[340inabbody]

Put some zero deck pistons in it and get your quench.

That's a definite possibility but then can I just hone to get the right surface for the new rings? I am trying to do as much as I can myself.

 

[496 polara]

Have the block checked and square decked as needed.Every little bit adds up.Head milling as well. Depending on what you are going for if you can muster 9.5-1 you have done better than the average teener.

 

[junkyardhero]

That's a definite possibility but then can I just hone to get the right surface for the new rings? I am trying to do as much as I can myself.

the long answer ends with "it depends"; but the short answer is: sure why not?

would i? probably not because if i'm doing new pistons & rings i'm probably doing bearings which means i want it all apart and a trip to the machine shop for a hot tank and cam bearings along with a basic check on the bore taper and just splash the cash for a light cleanup hone.

but... a low stakes build on a unit that's super clean with low miles? ehhh.... *shrugs*

 

[340inabbody]

Welp to do it right sounds more and more like a rebuild. I might as well use my 340 and build that. It’s the same cost machining wise but better/bigger block in the end.

 

[toolmanmike]

Put some zero deck pistons in it and get your quench.

I was thinking about doing that. Zero deck pistons, Speedmaster heads, on a roller 318 block.

 

[junkyardhero]

Welp to do it right sounds more and more like a rebuild. I might as well use my 340 and build that. It’s the same cost machining wise but better/bigger block in the end.

i mean, to do it "right" would basically be a rebuild.

but it really depends on what you're after and what your plans are in the long/short term of things and what you're comfortable with in the arena of suspect engine work and kinds of monies spent.

if you're just looking to get something rolling on the pronto while you build out the 340, why not just knock together a 318? reasonable cam, dual plane, reasonable carb. keep the supporting cast for the 340 and you'd be in it for not a ton of dough and have something that's peppy to cruise around in.

 

[340inabbody]

i mean, to do it "right" would basically be a rebuild.

but it really depends on what you're after and what your plans are in the long/short term of things and what you're comfortable with in the arena of suspect engine work and kinds of monies spent.

if you're just looking to get something rolling on the pronto while you build out the 340, why not just knock together a 318? reasonable cam, dual plane, reasonable carb. keep the supporting cast for the 340 and you'd be in it for not a ton of dough and have something that's peppy to cruise around in.

I blew way past my budget on my restoration. Looks like just the machine work and new pistons would be almost $3500K! If I could find a decent shop these days. They all left AZ or retired.

 

[33IMP]

I would be cautious that in trying to get quench, you might end up with more compression than you want
But I could be wrong.

 

[340inabbody]

I would be cautious that in trying to get quench, you might end up with more compression than you want
But I could be wrong.

The way I understand it is that quench can help manage detonation improve performance and yes increase compression. But it has to be done correctly in order to not excede the total compression ratio ( I don’t understand this part in calculating cr with some quench).

I believe I thought wrong that since I had 20-40 in the hole I might get some quench and some cr increase. Thereby being able to use the rotating assembly as is and have something decent.

 

[340inabbody]

Like going from 8.6:1 ~ to 9.5:1 This is exactly the cr I wanted to be able to on the gas at the pump here in AZ

 

[GTX JOHN]

MY 318 is about 65cc (Spec is 64.5) and as I recall
it took about 040/050 cut to get them down to NHRA
specs.