Hammer Down
Member
What is the difference between shaving the heads and cylinder lift? Why not just shave the heads?
Cylinder Lift
- Thread starter Hammer Down
- Start date
YAMMIEGOD3:16
Active member
TWO DIFFERENT THINGS. THEY SHOULD WORK TOGETHER. WHEN YOU '' CYLINDER LIFT '' YOUR CHANGING PORT TIMING. SHAVING HEADS IS TO RAISE COMPRESSION AND SHOULD WORK HAND AND HAND HERE NOT ONE BETTER THAN THE OTHER. 3;16 (yammie tony)
Lifting the cylinder and cuttings heads give completely different results:
Lifting cylinders:
- usually done by stacking base gaskets or adding a metal shim that is just a real thick base gasket.
-lifting the cylinder raises the exhaust and transfer ports that is not unlike what you would get when cylinders are ported for higher RPM
-the piston would now sit lower in the cylinder at top dead centre so this would increase the squish clearance between piston and outer band of cylinder head
-the raised cylinder would also effectively increase the volume of the cylinder at top dead centre reducing compression ratio
The reduced compression ratio and increased squish clearance would effectively reduce horsepower...although shims can be used to get a desired lower compression ratio if needed for a reason.
Shaving heads:
-reduces cylinder head volume at top dead centre raising compression ratio
-reduces cylinder head squish clearance.
As you can see you can do a poor mans porting job by doing both...raising the cylinder to increase port timing for higher RPM HP then cutting the head to get the compression ratio and squish clearance to where you want it.
This works on some engines to increase performance but will never compare to a properly ported engine specific to your needs.
Lifting cylinders:
- usually done by stacking base gaskets or adding a metal shim that is just a real thick base gasket.
-lifting the cylinder raises the exhaust and transfer ports that is not unlike what you would get when cylinders are ported for higher RPM
-the piston would now sit lower in the cylinder at top dead centre so this would increase the squish clearance between piston and outer band of cylinder head
-the raised cylinder would also effectively increase the volume of the cylinder at top dead centre reducing compression ratio
The reduced compression ratio and increased squish clearance would effectively reduce horsepower...although shims can be used to get a desired lower compression ratio if needed for a reason.
Shaving heads:
-reduces cylinder head volume at top dead centre raising compression ratio
-reduces cylinder head squish clearance.
As you can see you can do a poor mans porting job by doing both...raising the cylinder to increase port timing for higher RPM HP then cutting the head to get the compression ratio and squish clearance to where you want it.
This works on some engines to increase performance but will never compare to a properly ported engine specific to your needs.
Hammer Down
Member
Does this increase high rpm power? Specificly on a vmax4 what would this mod do to HP and power band?
Depending whether you are talking 750 or 800 Vmax4s, this was a common mod on the VMAX4s, they called it a "tune up kit". The Vmax4s were so conservatively tuned from the factory that a thicker base gasket and some material off the heads, and/or thinner head gaskets, added a few hp in the normal RPM band with stock pipes.
If you go over to VMAX4.com you should be able to get a lot of info on this.
If you go over to VMAX4.com you should be able to get a lot of info on this.
YAMMIEGOD3:16
Active member
it works very good on the vmax 4 and keeps ya at 8350 or slightly higher power band. example. the vmax 4 base gasket is 0.19. changeing to a .039 will approximately raise your exhaust port .1 mm. than part of the tune-up kit is to take material off head, you have a pretty good power adder useing stock pipes and rpm. like bob posted, this works, but its not a '' port '' job. 3:16 (yammie tony)
Last edited:
Hammer Down
Member
Thanks, great info. How about on 93 750 w/ psi pipes? It has stock clutching. Basically a lake and trail sled.
How much do u shave off the heads after installing the thicker gasket?
How much do u shave off the heads after installing the thicker gasket?
Yamahakid01
New member
I think if I'm correct it depends on the difference in thickness of your base gasket +\- a few thousandths depending on the compression you want.
If your sled is already piped, you may want to see if the cylinders have the thicker base gasket and head cut already as it was a common update/mod.
Normally the heads were cut at least .010" more then the cylinders were lifted ...but...with todays fuels and the fact the sled is a trail sled I would only cut the heads the same amount the cylinders were lifted.
JM.02c
Normally the heads were cut at least .010" more then the cylinders were lifted ...but...with todays fuels and the fact the sled is a trail sled I would only cut the heads the same amount the cylinders were lifted.
JM.02c
the problem in doing this is you gain whatever you raise the cylinders in added deck clearance, no matter how much you cut the heads this amount stays.
So if you raise them .030" you add .030" to the deck clearance, most engines have around .010-.012" deck clearance so now youll have .040-.042" deck clearance with the piston at TDC.
This all doesnt seem to matter to people until you check the piston timing to the exh port and the transfer port floors, youll see how the piston may now shroud the port opening, hindering the flow and losing performance or go below the exh port opening at BDC.
your way better off to port the cylinders and have the heads set up for the fuel your using then going this shim method.
So if you raise them .030" you add .030" to the deck clearance, most engines have around .010-.012" deck clearance so now youll have .040-.042" deck clearance with the piston at TDC.
This all doesnt seem to matter to people until you check the piston timing to the exh port and the transfer port floors, youll see how the piston may now shroud the port opening, hindering the flow and losing performance or go below the exh port opening at BDC.
your way better off to port the cylinders and have the heads set up for the fuel your using then going this shim method.
mrviper700 said:
I could not agree more...I never did the shim and cut on my 800s...I just ported them to match my application.