Why are 4Valve Hemi Heads better than 2 Valve heads for my V-Twin?
Quite simply, our 4 Valve Heads flow 1.5 times more air than conventional 2 Valve heads. More air in+More air out=More Power.

Why is a 4 Valve Hemi Head Kit a good deal?
In fact, we feel it is the best bang for the buck-add on for your V-Twin! If you compare a Hot Set Up Kit (2500. to 4K+ labor), Big Bore Kit (1300.+ labor) or Performance 2 Valve head kit (1200. to 2500.), you still will not increase the air flow in/out of the engine, not have as good of a power gain and linier torque curve as with our 4 Valve Hemi Head Sets!

Test Bikes to ride.
We have an 80" Dyna, with a Stock Bottom End, a Mikuni Carb and our 4 Valve Hemi Head Set and 17k miles, ready to ride anytime! This bike has pulled away from a 100" Custom! You must ride it to believe the Torque Curve!
We also have a Carolina Style Custom with our Custom Built 97" 4 Valve Hemi Motor. Come by and ride it!

What engines will our 4 Valve Hemi Heads fit?
Any Evo or Twin Cam V-Twin style engine up to 128 cubic inches, from 3.50 to 4.25 bore. The 128” is a special order item.

How much power can I gain?
Dependant on your engine and with our AR exhaust modification installed near the heads, you can expect an approximate 20% Gain in HP & Torque.
Approximately 85% of your available torque will come in at approximately 1500 RPM!

What is the advantage of a 4 Valve vs. a 2-valve?
Our 4-Valve Hemi Heads move 1.5 times more air and can run higher compression due to the central position of the spark plug, allowing for a 25 degree ignition curve vs H-D's 35 degree curve.

What modifications do I need to make?
Pistons: The 4 Valve relief pockets must be cut into the piston tops (this costs about $100 at a shop, we will provide the drawing you need). Or use a dished piston set.
Exhaust: Must be modified (instructions provided) our exhaust ports are located fore and aft on the heads. We utilize our Anti Reversion exhaust system design for added torque. The exhaust flanges and upper tubing is supplied. We are designing complete exhaust systems now.
Ignition: For EVO (not required for Twin Cam), we recommend a Crane HI-4 Dyna Single Fire set at 25 degrees.
Our Large Bore Motors will require your bike to have Chain Drive and Heavy Duty Drive Line Components!

Which pistons are recommended?
Stock H-D, JE, KB, Wiseco, S&S or Ross. Dished pistons do not require the valve reliefs.

What is the size of the combustion chamber of the 4Valve heads?
62 cubic centimeters.

What is the compression ratio?
Stock H-D’s have a 9:1 ratio, with our conversion it climbs to10.5:1.
Add our 4-Valve 62 cc heads on larger than stock engines and the ratios change to:
80 to 96 cubic inches: 11:1
97 to 125 cubic inches: 11.5:1
Our Hemi design develops a finer atomization of fuel in the combustion chamber, generating a clean burn.

What is the maximum cam lift for these heads?
.561 inches

Is the total engine height on a 4-valve more than stock?
No, it is actually shorter by ¼ inch.

How do the heads handle the crankcase breathing?
They hook up and breathe through the air cleaner, similar to stock.

How different is the valve adjustment than the norm?
Our 4 Valve requires no lash.

Do you build complete engines?
Yes! RPMHemi builds:
97 cubic inch motors
107 cubic inch motors
114 cubic inch motors
120 & 128 cubic inch motors (special order only)
All are available with our 4 Valve Hemi Heads or with 2Valve Heads

What bottom end do you use?
Delkron, their bullet proof.

Do you have any performance results?
Yes, please see our 96 ci comparison chart on our Technical Info Page located on the Products Link.

How will the 4 Valve Hemi Heads change the torque on my V-Twin?
It will add 15 to 20% more torque and horsepower and a broader power band. It will also, change the exhaust note.

Do I need to change my cam?
No, your stock cam will work fine.
If you want to experiment with a new cam; any long duration low lift: 239-260 duration and .490-.561 inch lift will work. We recommend Crane H310-2 cam.

What is the highest lift cam I can use?
.490-.561, .561 inch is the maximum.

How can you run higher compression without knocking or pinging?
With the spark plugs on the side, H-D’s timing is 35 degrees. With the spark plug in the Hemi center, our 4 Valve Heads run a 25 degree ignition curve. The change in ignition allows higher compression without pinging and knocking. Our Hemi design develops a finer atomization of fuel in the combustion chamber, generating a clean burn.

What carburetors should I use?
We recommend the following:
Main carburetor: Mikuni 42-45 mm.
Secondary carburetor for street riding: HD Keihin CV (constant velocity) carburetor.

Do I have to use dual carburetors?
No, but be sure to specify when ordering, our Ram Chamber for dual carbs requires additional parts.

What is the advantage of using dual carburetors?
Fixed carburetors run out of cfm, based on their individual size, whereas dual carburetors have a constant velocity (CV) secondary carburetor supplying more cfm when the engine vacuum demands it.

Can I stay with 2-valve heads and go dual carburetors? What’s the advantage?
Yes, with our Patented Dual Carb Ram Chamber, that way you do not run out of air and fuel at the top end.

Will your 4 Valve Hemi Heads fit my S&S Super Motor?
The S&S Super has a unique Bolt Pattern that was designed to make the owner buy only the S&S head kits. We can match this bolt pattern and you may utilize our 4 Valve Hemi Head Kits.

Hemi Head, Pent Roof...
The Old School Engineering terminology states a Hemi Combustion Chamber has the Spark Plug at 90 degrees, to the roof of the piston, from between the valves. A true Hemispherical combustion chamber, in this application, will yield inefficient air pockets and cause problems, so a Pent Roof Design is used.

Made in USA   RPMHemi.com