big block mopar with zero deck, flat top pistons, & open chamber heads?

[the nitro man]

have any of you built a big block mopar with zero deck, flat top pistons, & open chamber heads? i know it wouldn't be a quench motor, but would it run on 93 octane pump gas? i'm putting a 451 together & i'm using 452 heads, i still need to buy pistons. i know i can get a step head piston, but the chambers on one head are around .100-.110 deep, & the other head is around .075-.085. how do you make them all the same? if i can use a flat top i won't have to do anything if i ever do decide to change to stealth or rpm heads.

would a step piston, open chamber head, & a .040 quench be to much compression for 93 octane pump gas?

any help would be grateful.

[firefighter3931]

Hi Nitro....welcome to the site. 

As for the build ; use the flattop slugs so you can install closed chamber aluminum castings in the future. The 452's have large chambers so you should be able to dial in your target static compression with a specific head gasket...there are several to choose from. I prefer to keep compression in the low 9:1 range with a "no quench" iron head build. 


Ron

[Nacho-RT74]

Ron... can you start an informative thread about what is "quench" and "no quench" and when to consider it or not ? Although I more less understand whet it is, I'm still some confused about the quech deal and compression etc....

[Chatt69chgr]

I did some research on the web concerning Quench and found that it is akin to hitting a tomato with a sledge hammer.  It squishes the fuel mixture and this action causes it to be mixed and thus reduces detonation or pinging.  You need a flattopped piston and a flat surface on the cylinder head for it to squish against which you get in a closed chamber head.  You only get quench when you have piston top to head distances of 35 thousands to about 55 thousands and by 60 thousands it is about gone.  The open chambered head doesn't provide for quench.  So if you build a zero deck short block and use a closed chamber head, then the quench distance is the thickness of the head gasket.  Using cometec head gaskets which they will make for many different thicknesses, you can set the quench distance.  I don't think it's recommended to go below 40 thousands quench distance due to piston rocking which could allow the piston to contact the head.  Forged pistons have wider gaps than hyperutectic pistons so a hyper could have a closer quench distance.  The generally accepted CR is said to be about 9:1 for iron heads and 10:1 for aluminum heads since the aluminum dissipates heat more and so can run a point higher static compression ration.  The actual compression ratio that the engine sees is the dynamic compression ratio which is determined by the cam's characteristics.  So with proper choice of cam, you can run a higher static CR.  The quench will just help keep the old problem of detonation at bay which will destroy an engine.  Detonation can be present but not be audible.  This is what I have picked up from surfing the net.  I hope the real experts on here will chime in with much better info and info gathered from real world experience.

[Nacho-RT74]

I started a thread on Moparts long time ago, but, dunno, in some cases I can find still some confusing

[Challenger340]

IMO  
The first problem with the subject "quench", is that invariably it gets bogged down on "what" exactly, is the optimum number to achieve it ?

The second biggest problem, is that the answer to the first question above, usually, centers with answers based upon smaller 4" bore based SB Engines

My point being, don't go chasing your tails on "perfect" quench being Under .060" on a BB Mopar.

Here's an Engine with "less than perfect" quench of .110", that PICKED UP H.P. & Trq. !!!
with much Lowered Compression,
and RAISING the Quench to the .110", from the prior .060".

Everything else was "same-same", Cam, EVERYTHING !

see here;http://www.youtube.com/watch?v=VzWhkC4dAI0  

[elacruze]

Rule of thumb with quench is stay away from 0.080". For some reason, that's a clearance that detonation likes-0.025 closer or wider is ok.

I don't know enough rocket science to figure out why. 

[elacruze]

IMO  

Here's an Engine with "less than perfect" quench of .110", that PICKED UP H.P. & Trq. !!!
with much Lowered Compression,
and RAISING the Quench to the .110", from the prior .060".

Everything else was "same-same", Cam, EVERYTHING !

see here;http://www.youtube.com/watch?v=VzWhkC4dAI0  

I wonder was there any difference in the piston domes? Maybe the increase was due more to flame front propagation improvement than quench change? (sorry if the video answers the question, I don't have bandwidth to watch it)

[the nitro man]

Rule of thumb with quench is stay away from 0.080". For some reason, that's a clearance that detonation likes-0.025 closer or wider is OK.

I don't know enough rocket science to figure out why. 

i must say, I've never heard that before.

I've asked this same question a several boards & i keep getting different answers. Lot's of people still use older open chamber heads on their mopars, & i would bet most of them don't use the step head pistons. I've heard it will detonate, & I've heard it won't. I've heard so much i don't know what to believe. whats real bad, two local engine builders that just happen to be brothers, one says it will be fine, the other says it will detonate. WTF?

[elacruze]

My 440 has 11.0:1 static compression, MP .509" cam, TRW domed pistons (not matched to chamber) and polished combustion chambers in Iron Stage IV heads. I have the old MP electronic conversion ignition, with ~14* initial timing and ~35* all in.

I have zero detonation *as far as I can tell*. I have never heard nor seen and evidence of detonation. I've only ever put in one new set of spark plugs since build, that was due to fouling after installing the single-plane M1 manifold.

The point is I have higher than recommended compression for street, simple ignition and zero squish. It still works without problems, so spending a bunch of worry over it is pointless. On my new engine build, I will set the squish to about .045" + or - .005" just because that's what I've had success with in the past, and many researchers I know find that to be a good number in the laboratory/dyno room.
Just to throw a wrench in the machine, I'll throw out the idea that the productive squish area has a limit with gasoline, and the ratio of squish/open area has significance.
Ultimately the goal of squish is to produce turbulence in the open area of the combustion chamber. If more squish does not produce more turbulence, it is not productive and may only produce hot spots at the far distant points. The balance of dome height/compression/squish affects flame propagation, detonation, and performance also. On our engines, this is pretty academic since the research work has been done to death by everyone from Chrysler to Edelbrock to the piston manufacturers, and the difference seen on something less than full race engines is not visible on the street anyway.