Head Milling and what it does to you...

[quam]

i think erb's right, but i don't really know exactly what it means. i think squish angle is the angle that the head shapes up toward the spark plug hole, right? and if you mill the head down, you have to change the shape of the cone somehow.......maybe.

 

[erbe01]

I hope this makes sense
Cylinder Head Modification

Cylinder-head shape also affects the powerband. Generally speaking, a cylinder head with a small-diameter, deep combustion chamber and a wide squish band combined with a high compression ratio is suited for low-end and midrange power. A cylinder head with a wide, shallow chamber and a narrow squish band and a lower compression ratio is suited for high-rpm power.

Cylinder heads with wide squish bands and high compression ratios will generate high turbulence in the combustion chamber. This turbulence is termed maximum squish velocity (MSV) and is rated in meters per second (m/s). A cylinder head designed for Supercross should have an MSV rating of 35m/s, whereas a head designed for motocross should have an MSV rating of 25m/s. The only way to accurately determine the MSV rating of a head is by measuring some basic engine dimensions and inputting the numbers into a TSR computer program called SQUISH,
Which I dont have yet.

 

[quam]

so does the shape of the head directly affect the compression? and bringing the head down increases compression too right?
also, how does a high compression piston work? is it shaped in a way to displace more of the combustion chamber?

 

[daniel3877]

im definitly not saying that erbe01 is wrong, he may know more than i do possibly....BUT...I gotta say that I have four different toys; an 02 mxz 800 snowmobile, an 04 kx 250 bike, my blasty, and i just picked my son up a yamaha 100 bike. three of my toys all have port,polish and head milling done from a very well know high performance race engine shop named Bristol Racing located in new york . and I can honestly say that i have never ever even heard of anything called a "squish angle" . and also never had any shop tell me that a "squish angle" would have to be alterd when having head milling done when i have had my engines built. ...lol..but im gonna have to call up bristol and get to the bottom of this asap, im sure that erbe01 may ne right and if so I would like to know more about all this, i'll post my findings after i contact my shop.

 

[misterww225]

Blaster Compression Ratio Calculations

Bore = 68mm
Stroke = 57mm
Displacement = 207cc
Formula CR=D+H/H :where D=Displacement, H=Head Volume(total)
Formula H=D/(CR-1)
Altitude = 4900 ft.
Positive Wave Pressure (approx.) = 7 Psi

Compression Ratio, Total Head Volume, Effective C/R @ 7Lbs. Boost
9.0, 25.9, 13.3
9.5, 24.4, 14.0
10.0, 23.0, 14.8
10.5, 21.8, 15.5
11.0, 20.7, 16.2
11.5, 19.7, 17.0
12.0, 18.8, 17.7
12.2, 18.5, 18.0
12.5, 18.0, 18.5
13.0, 17.3, 19.2
13.5, 16.6, 20.0
14.0, 15.9, 20.7
14.5, 15.3, 21.4
15.0, 14.8, 22.1
15.5, 14.3, 22.9

 

[misterww225]

PORT TIMING VALUES FOR RPM RANGE.
THE FIRST DURATION IN THE XXX-XXX FORMAT IS THE MIN FOR THAT RPM.
EXAMPLE: TO GET TO 9000 RPM YOU HAVE TO HAVE AT LEAST 184 EXHAUST
AND 125 INTAKE

EXHAUST TIMING
7500 RPM 176-178
8000 RPM 180-182
8500 RPM 183-185
9000 RPM 184-186
9500 RPM 186-188
10000 RPM 190-192
10500 RPM 193-196
11000 RPM 196-198

TRANSFER TIMING
7500 RPM 122-125
8000 RPM 123-127
8500 RPM 124-128
9000 RPM 125-129
9500 RPM 126-130
10000 RPM 128-132
10500 RPM 129-133
11000 RPM 130-134

Q: Does this information make any sense to you guys? Is it anywhere near right?

 

[erbe01]

Im going by my last few 2 strokes, the LT500 have bad head design to begin with, thats why most folks went to a cool dome but Pro design cuts the heads wrong they run best at a 14 deg angle they cut them at a 15cdeg yes 1 deg can make or break HP, went through this also on my sons 4 Trax his head was cut and the angle of the squish was also changed, even with higher compression he dosent ping as mush as the stock head now.
Im having the Blaster head done next week I have 2 heads I will take pics before and after of each

Remember every motor builder has there way of doing things when you purchase a ported motor your buying there recipe, meaning this porting this head this reed this carb this pipe that all works in that a builders design if you chage something you chang the recipe and may not work the way it was supposed to, I run into this all the time on 4 strokes and 2 strokes

 

[misterww225]

Seems the squish angle should be related to the piston dome angle at the outer edge where the squish is- however, as we all know, the piston top is spherical in shape (rounded), so just about any reasonable angle you choose is going to be closer to the piston in the middle of the squish band. I understood that the squish band should be approx. less than 0.040" and anything closer is ok except for paying attention to the piston/head interference at high RPM- which depends a great deal on the engine itself. Are we looking for a "wedge" shape for the squish band(?)

 

[hickskateboarder]

i wouldn't say you have to change the squish band when you mill the head, but i'm sure it can be improved upon. how big your squish band is and how steep the angle is makes a difference on where your powerband is. i'm thinkin about changin mine cause my p&p killed my low end, milling brought it back some, i just don't want to screw it all up. although you can get a new head off ebay pretty cheap lol.

i bet i'd get some mad power back with a rebuild... my piston/cylinder wall clearance is over 12 thou... don't know how the compressions doin but she still runs!

 

[erbe01]

DO you mean squish clearence??? is the Blaster at .040?? wow, I thinking it was .050 to .055, I am going to do the solder squish test

Seems the squish angle should be related to the piston dome angle at the outer edge where the squish is- however, as we all know, the piston top is spherical in shape (rounded), so just about any reasonable angle you choose is going to be closer to the piston in the middle of the squish band. I understood that the squish band should be approx. less than 0.040" and anything closer is ok except for paying attention to the piston/head interference at high RPM- which depends a great deal on the engine itself. Are we looking for a "wedge" shape for the squish band(?)

 

[quam]

hey hick, what's the piston to wall clearance supposed to be? do you know the spec on that?

 

[coreyownz]

does this increase hp by a lot? is it worth the cash to get it done?

 

[misterww225]

I would have to agree with others when they say porting (by someone who knows what they are doing) would be first, then a pipe that MATCHES the increased RPM setting of the porting, and then V-force reeds with a larger carb

 

[erbe01]

I looking forward to getting the Blaster Bored and Ported and the Head Work done this weekend, I just need my Slave Labor , My son to pull the top end off for me LOLOLOLOL Im stuck putting in a DS650 motor in this weekend, and adding my Plus 2 Arms on.

 

[erbe01]

OK popped the top off today, I have 2 pics the stock head an a head I had done by Denton Racing last year, it was cut by .025 and see the dome shapes stock vs Cut Head.

 

[coreyownz]

but will milling the head after other stuff noticable increase?

 

[erbe01]

Its part os the other stuff, if your getting port work done, Cutting the head for a stock motor only increases Bottom end great for wheelies and woods trails, most modified the head to add HP through out the powerband when they do a midrange Top End Port to retain some of that bottom end.

 

[coreyownz]

but if im porting for bottom end and cuting head id have awesome bottom end eh?

 

[erbe01]

Talk to the person doing your porting.

 

[coreyownz]

im between 2 ppl ones alot cheaper but i got a good feeling bout the more expensive one..