Albuquerquefx

I'm quite familiar with the theory, the problem I have is determining how much he gained from reduced quench clearance (bringing the piston face closer to the head) versus how much he gained from the grooves cut in the quench pads. The obvious theory is that the "funny shape" helps to atomize fuel; here's the problem:

By bringing the quench clearance to near-zero (ie decking the block + shaving the head + using a tiny head gasket), you increase atomization by almost an order of magnitude by forcibly shoving the air/fuel mixture into the center of the combustion chamber as the piston crown approaches TDC. The turbulence involved here is obvious and significant.

Now cut a groove into that quench pad. All the sudden, the air/fuel can collect in the groove. You've effectively created a very small hotspot outside of the primary combustion chamber point. This groove now becomes a tightly compressed 'pocket' of air and fuel that is NOT in the direct line of fire for the spark plug. This means inconsistent burn characteristics (flame front propagation) in your combustion chamber, and worse, you've at least partially focused it at the edge of the piston crown.

The entire concept of quench area is for atomization - closing the gap between the piston face and the cylinder head so that you focus the air/fuel ignition right over the piston face center, so that maximum force is applied to a minimum of surface area, giving you a more effective (read: efficient) conversion of the chemical reaction (gas expansion forces from the burning of fuel) into mechanical (pushing the rod down) energy.

By opening up these groves, you've lost that focus. Further, you're now allowing heat and fuel droplets to more easily atomize at the crown edges, meaning higher heat loads to the compression rings on the load-bearing portion of the cylinder walls.

If absolutely nothing else, I might be able to buy these groove ideas if you weren't already optimizing quench space. But in this scenario, I simply cannot recommend anyone do it.



Not necessarily. The stock pistons have a bit of "pop top" to them. If you deck the block to zero, the stock head gasket might have enough clearance to allow that "pop top" portion to avoid the head. But at high RPM and under high heat, the combination of normal piston expansion and rod stretch could conspire against you and result in massive and epic failure. I'm not saying it's guaranteed, but this is the entire reason you measure such things.

With advice from Ross, my forged pistons are expected to grow somewhere around 0.005" at full temperature (450-550HP boosted). Which means I need some piston-to-wall clearance to soak up that movement, which means I should expect a bit of piston "rock" when it rolls past top-dead center. Thus, at full heat, full RPM's and full load, I should expect piston expansion in all three axis' -- my head clearance needed to be at least 0.010" by my estimate to ensure I didn't smack a quench pad. I went for 0.015" just as a precaution.

Stock pistons will not experience enough "rock" to matter, and their heat expansion is very little (by design.) Nevertheless, rod stretch is quite real, and assuming that a zero deck + milled head + head gasket will be 'sufficient' is still pretty dangerous.

iheartmyrd

WHOA WHOA WHOA
so i don't have exact measurements to what the clearance is i am sorry, but the reason i cant run 87 all the time is because i use n2o.
And stocker yea you can use those pictures you want.
and for any abnormal ware on singh grooves when i had the head off that was the first thing i looked at.
no build up of carbon or soot or black shit if you will.

idk i am not an expert but it bothers me that you tell people not to do this. i will keep it updated and post as time passes.
But to automatically write it off and say its bad. Unless you can show some example or some scenario where what your saying happens
"pre-detonation" or hot spots dont write it off just yet. I have asked so many people about singh grooves no one seems to know anything
(that lives around me). My clearances are not 0 and that is for sure, i had all decking and machine done at a machine shop.

If my motors fails you will hear about it, but it obviously works and runs on 87 where others have said it idled rough and idles smooth.

Albuquerquefx

You don't have to answer any of my questions or concerns; everyone is perfectly allowed to do whatever they like to their own car smile.gif

As for higher octane as a necessity of nitrous? Sure, but if the quench pads and/or Singh groves are doing their job, you actually have mechanical octane to combat predetonation -- which would invalidate (or at least, significantly lessen) your need for chemical octane.

iheartmyrd

i have not shot nitrous yet due to the fact that my msd went out i can not. and motor break in period.
if you are suggesting i shoot nitrous ill properley to try and prove singh groove theory, then im sorry i will not.

Albuquerquefx

I wouldn't trust singh and his groves enough to test it that way either. As for your MSD DIS2? A 75 shot? Pfft. Not needed smile.gif

Here's something I've not ever seen: a back-to-back, empirically-driven scientific test of a motor with and without these groves. Dyno numbers, crank acceleration sensors, detonation sensors, fuel efficiency tests, the works.

I've seen big piles of people go "OOoooh I cut grooves into my head and suddenly idle is awesome and pinging doesn't happen and blah blah blah." Unfortunately, we also see this with a full head "cleanup" at the same time, so how much of their results were from a nice fresh head, and how much was because of funky sharp grooves cut into the quench pads?

Again, I'm quite far from convinced.

Stocker

iheartmyRD, don't get sideways, Red is a Good Guys and if he's commenting in your thread, it's almost certain to be for your own benefit. Don't let his low post count or recent membership date fool you 'neither.

I've heard enough anecdotes to make the grooves worth a try for me (low power N/A build), as obviously iheartmyRD has. I've also been all over the 'net looking into it and along the way I saw a BUNCH of pictures that show the burn under the quench pads, even right at the edge of the cylinders is *better* than without the grooves.

Red, I was referring to the piston-to-head clearance, not just the edge-of-piston's height above the deck. A 2mm dome doesn't sound like much, until that's how much your piston wants to shove (of itself) into the aluminum bits that comprise your head's combustion chamber. wink1.gif To restate the question:

If I have zero clearance with no gasket, from whatever part of the piston to whatever part of the head it would be touching, then add a head gasket, is THAT ok?

likeyoumeanit

iheartmyRD- the head and the mani look real nice man, you did a real clean job cutting the grooves too fing02.gif

Slightly off topic:

RED- THanks for the quality post man, its awesome to see people who are capable of forming coherent opinions based on fact and reason, not just "its fake carbon fiber and has an LED, must be a good idea"

Also thank you for the first contextual, non classroom use of the word eutectic

iheartmyrd

thank you likeyoumeanit. i was very careful while doing it.


The reason msd is needed is because it is recommended to retard ignition timing for anything after 55 shot of nitrous.

iheartmyrd

If you don't believe it works then don't do it. i dont understand why you wanna bash on my thread so baddley red.

dddude55

o_O

I can't tell if this has just turned into a heated argument, or if this is all educational and should continue lol. It all sounds interesting to me.