Does quench affect power?

[skinny z]

882heads.jpgRHS.JPG

The SAR for the wedge head is 31.4%. The SAR for the heart shape is 26.4%.

For given clearance, the wedge will produce higher squish velocity.

However, the shape and direction of the squish jets will not be the same and will result in
a difference in turbulence, even if the velocities are the same. Which they will be at some
engine rpm.

And I believe you've stated that higher velocity is not necessarily a good thing. The 50% SAR is too much correct?

[David Redszus]

882heads.jpgRHS.JPG

The SAR for the wedge head is 31.4%. The SAR for the heart shape is 26.4%.

For a given clearance and rpm, the wedge head will produce higher squish velocity.

However, the shape and direction of the squish jets will not be the same and will result in
a difference in the turbulence pattern, even if the velocities are the same. Which they will
be at some engine rpm.

And I believe you've stated that higher velocity is not necessarily a good thing. The 50% SAR is too much correct?

A head/piston with a SAR of 50% cannot tolerate a tight clearance, especially if the rpms are high.
A tight clearance can be used if the engine speed is kept low.

Remember that even if SAR and clearance are identical, engine speed will have a large effect on SqV.

Clearly, we end up with a three dimensional map for squish velocity. And if we add squish pad shape,
we have a four dimensional map to visualize. Which is why engine simultion programs re very useful.

[brentry]

The 882 is deceiving looking in 1st pic in this thread, i never figured it's sar.
But that's why you should always figure it out.

[skinny z]

The 882 is deceiving looking in 1st pic in this thread, i never figured it's sar.
But that's why you should always figure it out.

Is the 882 being described as having a SAR of 31% ?

[englertracing]

IMHO cutting the quench pad at a angle is roughly equal to cutting in SInGH grooves for effect.
So does any of this add horsepower ?
On a typical SBC? How much quench is enough quench?
.033" .040" .060"?
I once consulted a noted superstock engine builder on his .. answer .055" on his.

Nearly all 2 strokes run the quench at an angle.
A light spherical dome and the squish cut to Match.

Sometimes the squish is cut divergent.
These things do have an effect on power delivery on 2ts

An angled, or tapered squish zone is often used to prevent mixture being trapped and forced into the
upper ring land volume. where it cannot burn.

The actual squish clearance is neither the largest or smallest clearance distance; it is the mean distance
of the entire pad.

So with a tapered squish zone the mean is what counts.

But what are your thoughts on an angled squish as in both surfaces at say 5*

[NewbVetteGuy]

It's the task of calculating the area of the quench pad "crescent" and well as the remaining less than circular chamber.
I could in there with a ruler and calipers but it seems to me there's software out there that could "scan" the areas in question and crank out the requisite numbers.

100% a pretty easy thing for software to do with an image as input.

In microbiology there's software that will take a microscope image containing hundreds to thousands of yeast cells and rapidly identify just the yeast cells and count them. By comparison identifying and measuring the squish pad area from a photo of a cylinder head's chamber area should be pretty simple.


Adam

[NewbVetteGuy]

Sketch area calculator
Which is what that is.
I didn't put the results.
I know very well what needs to be measured.

My reply wasn't meant to imply that you didn't know. It was more of stating the obvious.
And the sketch area calculator was the software I was referring to.
If you're so inclined, you can post the results for that chamber...

I downloaded a trial copy of an area calculator.

Looks to be roughly about a 25% squish area ratio.


IMG_6720.JPG

At 7000rpm
SAR = 25%
Clearance....SqV (m/s)
.025..........33.0
.028..........30.7
.030..........29.4
.034..........27.1
.039..........24.5
.047..........21.6

Now I suppose the question is, what would be the difference in combustion activity between a SqV of 27.1 m/s vs 21.6 m/s ? And to what benefit?

Can you post a link to said area calculator? -Does it take an image of the chamber as input or??...


Adam

[skinny z]

Can you post a link to said area calculator? -Does it take an image of the chamber as input or??...


Adam

I didn't explore the free download to any great depth and it may have more functionality than I'm aware of.
In my case, I plotted points on the image and the program generated the area. One plot of the crescent and another of the area that represents the bore.
It's a scaled plot so that actual values don't translate directly to the cylinder head but the ratio between the two plots is the same regardless of the scaling.

https://www.sketchandcalc.com/

[David Redszus]

So with a tapered squish zone the mean is what counts.

But what are your thoughts on an angled squish as in both surfaces at say 5*

A directed squish jet could be very effective to create desired combustion flame front motion.

CFD analysis of the combustion process is important especially with the advent of direct injection.

[David Redszus]

I didn't explore the free download to any great depth and it may have more functionality than I'm aware of.
In my case, I plotted points on the image and the program generated the area. One plot of the crescent and another of the area that represents the bore.

Before we had CAD programs to make accurate scale drawings...we did this.

Take a pix of the chamber with a cell phone. Load it to your laptop.
Print it on a sheet of graph paper.

Count the squares.

[brentry]

I was with in 0.5% of David's numbers with my crude method. I do have software but don't have the heads here

[skinny z]

I was with in 0.5% of David's numbers with my crude method. I do have software but don't have the heads here

Which picture of which heads are we talking about here?

[skinny z]

The reason I ask is because the 882 "bathtub" heads don't look to have more quench pad than the Vortecs or the RHS Vortecs I posted.
I calculated my RHS to be about 25%.

[F-BIRD'88]

You can place a sheet of graphing paper on the deck of the head and trace the chamber and bolt holes and bore circle. Then add up the # of squares and # ½ squares on the graph paper to calc the quench pad area VS chamber area.. A close approx is good enough.

You guys are getting all lost in the math. tech, theory
KISS .
Does quench matter? How much.?
How much quench clearance is enough.?
Does low rpm (eg stock engines) require tighter quench clearance than high rpm. to be effective?

I recomend not falling down the deep rabbit hole of technical theory and exoric engines far removed from a SBC and other relevent 2valve push rod engines.
keep it practical.
Does .033" clearance work and better than .060"?
Is .080" clearance enough for effective quench clearance on a racy SBC that runs from 5000 rpm UP?
Lots of piston speed there. = Lots of quench squish speed and energy at rpm. How much quench energy is enough?
Keep it real and relevent .
All the theory doesn't matter until you test this stuff,
on real relevent running engines.

[skinny z]

Keep it real? KISS?
I don't need to test it. It's been tested. Ad nauseum.
Look. Yes. Quench matters. In an SBC that's indisputable. Yes. It's from the internet. Yes, we're discussing this via the internet.
General consensus from the thousands of test done (look it up) quench improves combustion efficiency, reduces the propensity for detonation, increases power and reduces emissions.
There is too much evidence to say otherwise. To keep asking how much is enough or too little, or by how much, etc, etc, is a waste of time.
It's up to you to find that out for your own particular ride.
For my particular ride, it'll be a choice between .034" and .047".
Done.