Advanced Hemi 212cc Predator Build

[bob58o]

The Before...

 

[Denny]

Good idea Bob have the head milled to raise the compression ratio and then polish out all those gains and at the same time polishing out the texture to reduce the swirl in the combustion chamber for a poorer mix of air and fuel.

Denny

 

[bob58o]

Good idea Bob have the head milled to raise the compression ratio and then polish out all those gains and at the same time polishing out the texture to reduce the swirl in the combustion chamber for a poorer mix of air and fuel.

Denny

Well, you have at least convinced me to research and smooth out the details before I smooth out the chamber.

These are just some of my thoughts. And I know this is a debated topic and I never took a class in fluid dynamics.

I am aware that polishing will increase the cc's of the chamber and reduce the compression. I bought a Medicine Dropper and Spoon from Wallgreens. I'm assuming I can get better than +/- 0.5cc accuracy with this. Will do this anyway, just to see where I am.

I am aware that any theoretical gains may be negligible. And Carbon will build up anyway, even after polishing. (maybe removing those cc's I added?)

I am aware that less atomization of the fuel may happen once inside the chamber.

I was more concerned about being able to run pump gas with raised compression, 32 degree BTDC ignition timing, and a rough combustion chamber without detonation killing my engine.

The idea was/is to give a smoother surface that will...
A) Remove Potential Hot Spots (Possible Detonation)
B) Reflect Heat Better for Increased Efficiency (less heat absorbed into surface of chamber)
C) Slow Carbon Build Up
D) Allow Uniform Deposit of Carbon
E) Allow Easier Clean Up (If going to do maintence, i.e. Sea Foam, H20)

As for rough surfaces for atomization, I left the intake port at 80 grit IIRC (possibly 120, but I don't think so). I could maybe just take a carbide burr to it if it is too smooth?? But I think it is OK.

As far as laminar flow vs turbulent flow... I thought velocity is the determining factor. At a critical speed, doesn't laminar flow turn into turbulent flow? I thought all intake and exhaust flow speeds were high enough to make for turbulent flow. I read this on the internet so it has to be true!

Once passed the valves...
I'm not sure that a rough surface on top of the chamber will increase swirl or tumble. I could see how it would increase atomization, if it has not been sufficiently atomized already.

This is just what I came up with for a defense. Most people say it isn't worth it.... Most don't say it is a horrible idea. Not too much info on it for carbureted small engines...

Now I am undecided, but still leaning toward doing it.
I'm going to keep looking for answers. Need more Fortune Cookies!

 

[Poboy kartman]

You pretty much got it right Bob. I personally prefer mirror polish myself on combustion chamber and exhaust .

And it is debatable, but I waited for you to do some homework before chiming in because there is a lot of good information that comes up while research polishing combustion chambers that is more important than finish.

 

[Denny]

Well on a 440 I had dyno'd the difference between polished and unpolished chambers was on average exactly -1 horsepower. On a BBC that I did there was no change.

Denny

 

[bob58o]

Now it is too late to run the air compressor. So Game of Thrones Ketchup Marathon it is!

 

[Poboy kartman]

Well on a 440 I had dyno'd the difference between polished and unpolished chambers was on average exactly -1 horsepower. On a BBC that I did there was no change.

Denny

The $64,000 question: did you CC the heads before and after?

 

[bob58o]

Well on a 440 I had dyno'd the difference between polished and unpolished chambers was on average exactly -1 horsepower. On a BBC that I did there was no change.

Denny

Thats good info. Surprising to me. I will CC the head and see what the chamber is at now. If a add 1 cc to the chamber I will probably reduce compression by 4/10 of point and overall output by 1/4 -1/3 HP tops if I get no gains back, and only losses due to reduced compression. I'm hoping polishing gains will come close to losses due to reduced compression. Giving similar HP and increased longevity?

Not sure how noticeable 15HP vs 16HP is anyway. I only race my shadow! Most of this stuff is just to keep me educated, entertained, and busy.

I don't think I will need remove a whole CC, but I don't know what a CC looks like spread out over the surface of a half-sphere either. It has been milled so surface area is already reduced. Shouldn't need to remove much at all.

If I do it, please don't feel like this or . I had my heart set on it already and bought new toys to play with just for this.

 

[ezcome-ezgo]

The GAB is overwhelming me.

 

[bob58o]

OK, about to try my FIRST attempt at CC'ing a chamber. Because there was NOT a previous attempt involving gasoline, cardboard, duct tape. Even if there was a previous attempt, it did NOT cover the head with sticky glue after the gasoline wicked through the cardboard and and started dissolving the adhesive. It definitely DID NOT require an 3am emergency parts washing in the slop sink in the basement. And my house did not become a toxic enviroment after using carb cleaner in the basement.

OK, since that was all hypothetical stuff.... Moving on!

Green 50% Rubbing Alcohol
Plexi Glass with hole drilled
Antibiotic Ointment
Medicine dropper

 

[bob58o]

Who's down with CC CC

Looks like this.

 

[bob58o]

Best I could find

 

[bob58o]

18.5 +/- 0.75 cubic centimeters/milliliters.

 

[bob58o]

2nd Attempt with same method (I feel more confident with this 2nd test)

18cc +/- 0.5cc is best guess measurement with these tools and set up.

Now to the calculator.

 

[Poboy kartman]

Did you remember to thank Jim Jones for the cool-aid?

That's for sure good enough, buddy....now...slurp up the "Kool-aid" and get to grinding. Remember to save the shavings for Mrs. Chancer's Christmas fruit cake...so you have an "extra special " one for Denny....so he can. "Dyno" it on a Koehler toilet dyno! Sorry...Denny, you know I'm just messing with ya!

To let the rest of y'all in....polishing combustion chambers is a bit like choosing Democrats over Republicans...the debate will probably never be settled...

One area Denny is ABSOLUTELY wrong is.....is the swirl factor of the head surface...once the charge leaves the valve/seat area...it's pretty much headed down...and never gets much chance to settle before it gets EXPLODED. All that happens BEFORE it gets to the valves....soooo..."Swirl Chambers? " Strictly shape...not texture...(the direction in which the fuel charge enters...not the texture of the head surface.)

So....to go a bit deeper...you will find A LOT of racers who polish the combustion chambers. A lot of people who say it's a waste of time...very few who will say it hurts anything.

Here's my feelings on it...(shared by Chancer....and a lot of engine builder's....) first...those little sticky up bumbs can get hot...and act like a mini spark plug..and ignite the fuel charge before the ignition even fires. To explain it: try to light a piece of fire wood or a toothpick for the same amount of time...the toothpick will burn to ash while the log won't even get warm...That's the idea.

Now...this isn't as pronounced in aluminum heads as it is in cast iron...BUT...consider this: at 8000 rpms that fuel charge is coming in PDQ! : 8,000÷60=133.33333(repeating per SECOND!) Keep in mind; thats the COMPLETE cycle...not the interval between the time the fuel combusts...(and starts heating up the head) and the time the completely heated charge evacuates the chamber. In fact they overlap...soooo....IT'S QUICK! !! (Not to mention the temps are around 1800° f!

Hence Bob is totally correct when he says folks do this to combat "pre-ignition" .

Also..you want as complete a burn and evacuation as possible to gain maximum performance. Well...again...sorry Denny...but all that rough surface is doing is hindering evacuation of the combustion chamber, which brings me to a couple of last points.....

I don't look at polishing combustion chambers as an INTAKE thing....but an exhaust! First off...as previously mentioned : less heat retention and more efficient evacuation of exhaust gases. (Which in turn....equates to a cooler INTAKE chamber which allows the INTAKE charge to remain denser.

And finally...yes...Bob and I both agree...even a mirror finish surface will eventually carbon over...but....IN THE MEAN TIME....take a mirror out in the sun and a cast iron skillet and let them sit for an hour....then put your hand on each....

Class dismissed!

 

[bob58o]

70mm bore
55mm stroke
70mm gasket diameter
flat top piston
0.003" in the hole
18cc chamber

0.045" gasket > 10.33 : 1
0.036" gasket > 10.70 : 1
0.027" gasket > 11.11 : 1

With 18.5cc Polished head
0.045" > 10.13 : 1
0.036" > 10.48 : 1
0.027" > 10.88 : 1

With 19cc Polished head
0.045" > 9.93 : 1
0.036" > 10.28 : 1
0.027" > 10.65 : 1


No matter what I do, I'm looking at a static CR between 9.9 : 1 and 11.1 : 1.
Any would be an significant increase over 8.5 : 1.

I think I will polish in the morning, then lap the valves, then Check P2V and proceed from there. <This normally means lots of gabbing, not much GABing.

---------- Post added at 06:56 PM ---------- Previous post was at 06:52 PM ----------

Did you remember to thank Jim Jones for the cool-aid?

The kool-aid was delicious.
Thank you Poboy, also for advice on cc'ing my kool-aid cup (or combustion chamber, which ever the case)!



EDIT: I should probably check P2V while I still have the 10.8lb springs in IF I am going to use the dial indicator method. This involves a degree wheel and taking 20ish measurements per valve. More complicated, but more accurate than clay. I will probably try both tomorrow, see what gasket I can use, and then decide on polishing, then lap the valves

NO AND THEN!!!

 

[Denny]

Oh Doug, you poor ignorant child. Some years back I believe it was Trick Flow Heads or some engine builder using TF heads on a small block Ford actually proved you CAN GET BETTER mixing and atomization by dimpling the combustion chambers with a center punch. It was worth 5-7 horsepower on average on pump gas. In the early 1990's I worked on a set of heads for a nostalgia racer that also had dimpled heads. No one had a problem with pre ignition. Now who needs to go back to school?
Man all this engine talk has me wanting to go back to racing again, if I only had the money. I'd skip the circle track stuff though this time.

Denny

 

[Poboy kartman]

Oh Doug, you poor ignorant child. Some years back I believe it was Trick Flow Heads or some engine builder using TF heads on a small block Ford actually proved you CAN GET BETTER mixing and atomization by dimpling the combustion chambers with a center punch. It was worth 5-7 horsepower on average on pump gas. In the early 1990's I worked on a set of heads for a nostalgia racer that also had dimpled heads. No one had a problem with pre ignition. Now who needs to go back to school?
Man all this engine talk has me wanting to go back to racing again, if I only had the money. I'd skip the circle track stuff though this time.

Denny

Yeah but this is a OHV valve engine...back when you were racing Fords they were all flatheads
..(snicker...snicker)

 

[chancer]

Hmmm dimples.
Like Golf balls!
No really Mythbusters Dimpled a Ford Taurus to match a golf ball.
They actually fot better fuel mileage.
I know different but.... Still it is just messing with Airflow. and the dimples help reduce drag.
So in a combustion chamber better flow?? eh...eh! you know I'm right

 

[Denny]

Yeah but this is a OHV valve engine...back when you were racing Fords they were all flatheads
..(snicker...snicker)

Funny you should mention Ford flatheads last week I just got one given to me I finally picked it up. I don't know what kind of shape it is in yet and I have never worked on one either. I do know it is seized from rusting outside though. Where's that darn face palm smiley when you need it?

Denny