4 Valve Hemi Heads for Harley Big Twin Engines

RPMHemi 4 valve hemi heads for Harley Davidson engines

RPMHemi 4 valve conversion kit for Evo Big Twin engineRevolution Performance Motors has introduced the RPMHemi 4 valve heads for the Evo V-twin and early Twin Cam engines, Twin Cam EFI kits are currently being tested and will be available soon. If someone asks, "That thing got a hemi?" just install these heads and you can say yes. Sweet! The heads bolt directly on to the stock engine, the only changes required are valve clearance pockets must be cut into the pistons and the exhaust must be modified.

RPM has both conversion kits or complete engines in several displacements. There's also an intake plenum that mounts 2 carburetors, the second CV carb serves as a vacuum secondary for high RPM runs. The heads fit any bore size from 3.5 to 4.25 inches. The hemi combustion chamber and center location of the spark plug as well as less spark advance allow compression to increase from the stock 9:1 to over 11:1. Evo kits start at $2995, Twin Cam kits from $3099.

4 valve heads can dramatically increase engine breathing and with no other modifications, engine horsepower and torque increase by 15 to 20 percent, with gains everywhere in the RPM range but it's especially dramatic above 4000 RPM. Modified engines will see even bigger gains. Engine height is 1/4 inch lower with the 4 valve heads than with the stock configuration.

These 4 valve hemi heads seem like a pretty nice setup, either alone or as the first step before further modifications, and they would seem to be just right for a big twin powered sport bike or cafe racer. It will be really interesting to see some back to back performance comparisons.

Press release follows:

Ever hear of a V-twin Evo or Twin Cam motor with approximately 85% of available torque coming in at approximately 1500 RPM? We have! At RPMHemi.com we do it all day long with our patented 4 Valve Hemi Bolt on Head Conversion Kits. “This is simply the best performance bolt on for the buck in the V-Twin market!” states Phillip Holmes, VP of Marketing & Sales for RPMHemi.com. You can estimate an approximate 20% power gain. This is a proven technology with both street and racing applications.

How it works: Utilizing our patented 4Valve system in a hemispherical combustion chamber we can increase airflow 1.5 times, increasing the compression ratio while maintaining a 25° spark advance, which gives an equal full burn in the chamber, while preventing pre detonation. All this in a package that is ¼” lower than stock heads. Our headsets and engines are also low in emissions.

RPMHemi.com manufactures their patented 4 Valve Hemi Head Kits and sells complete 97”, 107” and 114” motors with or without our 4Valve Hemi Heads and we have our patented Ram Chamber for single and dual carburetor V-Twin applications.

Currently, we have several OEM motorcycle manufacturers testing our products and all looks good.

Link: Revolution Performance Motors

Comments

  1. willie schmitz says

    Inpressive performance figures for sure. A bit expensive but a nice set up.
    A question here is added stress on cam bearings. The Evo with one set would be most suspect to failure. From personal experience the Twin Cams are subject to the same failures. Harley makes a kit for the TC for cam bearing replacement that includes everything in the camcase. If the total valve spring pressure from 2 valves to 4 valves along with wieght of the valve gear is the same then failures shouldn’t be any worse then with a stock set up.

  2. John J Redmond says

    Harley in the 21st century-heresy I tell you heresy.
    Glad to see it happen. With FI it sold be complete rock and rolling package thumping many rice burners.
    I’m a gear head from the 60′s and it gals me to see 4 bangers beat a 426 hemi; or any V-8. Even the marque – Moto Guzzi I ride is going back into 4 valves. Harley and Moto Guzzi are the oldest continues production motorcycles and v twin no less. My next bike-yep a Harley with this conversion. Autobahn Cruiser
    Great job RPM
    John

  3. todd says

    You can tell by the dyno charts these heads and cams are designed to flow at RPMs that aren’t typical of the average Harley. I bet if they decreased the size of the carbs and valves they could get even more impressive torque figures. As it is now, you can see the affect of valve float due to the push rods coming into affect around 5500 RPM, right when it’s starting to flow really good.

    How high can you rev a big twin?

    -todd

  4. says

    THIS IS IT. I LOVE IT, BUT DIDN”T BOB METZ AND ARLEN NESS MAKE SOMTHING LIKE THIS. I ALSO BELEVE IT HAD A OVERHEAD CAM KIT INCLUED WITH. GOOD LUCK RPM.

  5. kneeslider says

    I’ve heard reference to the Arlen Ness heads before, not familiar with them but I do remember the Rivera/Feuling 4V heads back around ’88 or ’90 or thereabouts.

  6. dIRT says

    quatoum motorcycle is Melbourne Fl. had those “Hemi” on thier production bikes for years. Problem is that the air box is a joke. LEAK CITY!!! not a bad start to a great design. Riveria had a hand at this too.
    Recently sold a setup on Ebay for a few hundred. Like I said…great start to a great idea. FUEL INJECTION is really the way to go with it.

  7. nicolas says

    Guys, I need some explanations, because I’m both not knowledgeable in harleys and not American either … I thought the Hemi name described either a big ass large displacement V8 that made the good ol days on the muscle cars, or the latest version in use on Chrysler/Dodge cars/trucks that uses 4 cylinders in rotation instead of 8 when cruising at stabilized speed … ? What is left on this Harley heads, it’s not a bigger bore stuff or a VTEC technology that commands 2 or 4 valves based on the engine load … ? Have I missed something ?

    Now if I had not missed something, Ducati or Honda or Aprila make twins who have a much better power output than this Harley powerplant ?

    Thanks for your enlightened comments.

  8. B*A*M*F says

    In response to Nicolas:

    Hemi refers to the shape of a cylinder head. If it’s hemispherical, it can be referred to as a “hemi”. There have been plenty of hemi headed engines. Chrysler has historically used the term in their advertising and promotion.

    The theory behind multi valve engines is that while the valves are smaller, there are more of them which offers more flow, particularly at higher rpms.

  9. guitargeek says

    Not to split hairs, but it denotes a hemispherical combustion chamber (as opposed to a pent roof or other combustion chamber shape), not the whole head.

    For the record, my 28 year old, fifty dollar KZ750 is also a hemi. ;-)

  10. Enginegeek2 says

    Given we may be headed for $4.00 per gallon, I ask why?

    Why not go to a Direct-Injection Cylinder Head, even one that may burn Gaseous (cheaper) Fuels?

    With DI you can go higher compression ratios as well.

    Go here: http://www.flexdi.com/

  11. Walt says

    I’m not seeing any photo of how they set up the rockers. Wonder how they adjust the individual valves. If they’ve got two valves driven by each rocker, how do they allow for individual valve adjustment? Harley’s stock hydraulic lifters won’t account for differing rates of valve recession.

    Also I’m pondering the claim of 85 percent of peak torque available at 1500 rpm. If these guys are after diesel-like torque delivery, why do they need four valve heads that typically perform best at high rpm? Sorry, my money goes elsewhere.

  12. todd says

    Four valves can flow better at all RPMs. The key is in the smaller valves. A small valve and tract will flow much better at low RPMs as velocity is much higher. This helps fill the cylinder faster and keep the fuel in suspension. Efficiency goes up which increases torque. You can tailor the sizes of all the components to flow best at whatever RPM you want. More torque you add higher in the RPM range will give you more HP numbers than adding the same amount of torque at lower RPMs. Most aftermarket companies shoot for adding torque up high because the HP increase makes it look more dramatic. Like I said earlier, they should have reduced the sizes of the valves and carbs to give it more power at the kind of low RPMs that the typical Harley rider runs at.

    -todd

  13. Jurneyman says

    Maybe I can help answer a few of the questions and concerns. First of all the Evo head has a quench shelf on half of a bathtub shaped combustion chamber. The description of the 4valve head being a Hemi, is from a centrally located spark plug.So it
    is actually a pentroof Hemi 4valve head design. The
    rocker arm is designed with one pushrod arm and two actuating arms with adjustable swivel foot adjusters one for each valve at their ends.As far as torque goes, so goes horsepower, one of the major benefits of the 4valve head design is the ability with the proper application of cam timing,
    and compression, to have a wider torque band,
    because of the inherent design of the shallow combustion chamber, and flattop piston, that can keep the compression high enough at low RPM, even
    with a lessor amount of A/F mixture, this also allows a longer closing duration, because the higher velocity slows down the reversion of left over gases after blowdown.

  14. greer says

    As far as I know a cylinder head is designated a hemi when the valve faces are arranged in an arc over the piston forming a rough hemisphere, regardless of spark plug location. So yes, the evo head is a hemi.

  15. todd says

    It needs to be an arc in more than one plane to truly be called a Hemi otherwise it is actually a pent-roof head (or “semi-hemi”). The valves all need to be pointing to a common imaginary center that would be the center of the “sphere”. If you look closely at the photos you can see that both intake and both exhaust valves are parallel to each other. Take a look at one of Honda’s old RFVC singles; it utilizes sub-rockers to accomodate the non planar valve movement.

    “Hemi” is more of a marketing term which brings about images of purple, monster horsepower, Chrysler family cars. Even Chrysler (Dodge, Desoto, not Plymouth) used hemi heads on motors before and after WW2 long before it was ever a marketing term for them. They certainly weren’t the first but they’ve made the most success out of the term.

    RPM should be more proud that they have a satisfactorily performing 4-valve head and not resort to marketing hype and misleading half-truths.

    -todd

  16. jurneyman says

    Todd, Thank you, your post backed up almost word for word an E-Mail I sent to RPM. including trying
    to capitalize on the Hemi. The description that I posted above was their response to that E-Mail.
    It was my response to the Evo not being a Hemi,the original heads from the factory came with the D shaped chamber, that was designed for a flat top piston, and the valves were at a 58 degree included angle. I would agree that the Shovelhead model that was produced before the Evo was more of a Hemi design because it needed a domed piston to
    generate any compression, and the valves were at a
    45 degree included angle. BTW the 4 valve pentroof design above has a 46 degree included angle.J-Man

  17. jurneyman says

    I should have read over what I typed before I posted the Shovelhead has a 90 degree included angle.

  18. John Santos says

    I have a used 2000 sport sportster 1200 with dual disk brakes and 4 spark plugs??? Is that normally stock??

  19. Darren Kicker says

    I have the original 4 valve hemi heads that were designed by Jim Feuling. They are the pattern that your heads were made from. It was a venture between Jim Feuling and Rivera engineering. What I have is a 1987 Heritage softail. I did the machine work to the pistons myself. I purchased mine as a complete stage 2 top end. It came with the heads,matched cam, dual carburetor intake, anti reversion exhaust head pipies with a 3 bolt flange at the heads, and everything needed to assemble the top end. I am running dual HSR 42 Mikuni carbs. This bike is fast. No matter where I am at in the RPM range, if I grab the throttle my bike is gone. Just bolting it on and performing the final adjustments my bike produced 125 horsepower !
    The lower end is a stock evolution motor that has been balanced and blueprinted. No modifications at all other than the cam that came with the kit. Anybody with doubts should read my comments because WOW does my bike go.

  20. 1QIK1 says

    I too have the original 4 valve hemi heads that were designed by Jim Feuling. For over 10 years I have been running a combination that I was told would not work, a set of Sputhe cases and cylinders, with a set of ported and polished Feuling 4 Valve Heads, Andrews EV-9 Cam, two S&S E Carburetors and many other items, all top of the line of course. I was told by many that the motor would not run correctly, but with a dyno of 133 HP and 134.3 pounds of torque at the rear wheel, I would say that the combination worked. I can tell you that not only does the bike run well, but my friends all know when I am near because of the sound that the motor makes, it sounds like no other. It is always a fun ride!

  21. Aaron Smith says

    I race a 750 ducati monster as a speedway sidecar. it is fast but needs more horsepower to really do the trick. Hence the question. Do you make heads small enough for a 750 v twin, and would they mount up? I am not very mechanical minded but wondered if this is something i could look at getting done. any replies would be appreciated.

  22. reply says

    John Santos 01.25.09 at 3:40 pm

    I have a used 2000 sport sportster 1200 with dual disk brakes and 4 spark plugs??? Is that normally stock??

    way of subject. but yes

  23. says

    nicolas 02.26.08 at 10:11 pm
    Guys, I need some explanations, because I’m both not knowledgeable in harleys and not American either … I thought the Hemi name described either a big ass large displacement V8 that made the good ol days on the muscle cars, or the latest version in use on Chrysler/Dodge cars/trucks that uses 4 cylinders in rotation instead of 8 when cruising at stabilized speed … ? What is left on this Harley heads, it’s not a bigger bore stuff or a VTEC technology that commands 2 or 4 valves based on the engine load … ? Have I missed something ?

    Now if I had not missed something, Ducati or Honda or Aprila make twins who have a much better power output than this Harley powerplant ?

    Thanks for your enlightened comments.

    B*A*M*F 02.26.08 at 11:37 pm
    In response to Nicolas:

    Hemi refers to the shape of a cylinder head. If it’s hemispherical, it can be referred to as a “hemi”. There have been plenty of hemi headed engines. Chrysler has historically used the term in their advertising and promotion.

    The theory behind multi valve engines is that while the valves are smaller, there are more of them which offers more flow, particularly at higher rpms.

    _____________________________________________________________

    For the record,

    B*A*M*F is correct, the “Hemi” is simply a chrysler marketing ploy. The first Hemispherical head was designed in the early 1900′s. The Ford Flat head was technically a ‘Hemi” as is nearly every four cylinder made since 1984 lol. they are all ‘Hemi’s”. So the next time you are driving your Ford Focus, and some Redneck yells “that thing got a Hemi!?” you can reply with a simple yes.

  24. larry crow says

    so you say motor height will be .250 shorter than stock?if so thats good no more removing front motor mount. and would my thunderheader be a good exhaust to use i sure do like them thanks

  25. baldoldfxr says

    Thanks , looks an interesting project , there is also a thread on HTT evo section about them.

  26. jurneyman says

    Jurneyman here, I had over 200 E-Mails to read and answer, so if it is O.K with Kneeslider maybe this will reach those who have been trying to reach me. I have been laid up with some health problems, then a couple months ago I got hit hard with high wind driven rain followed by a major flash flood wiping out roads and dragging cars and small trucks along with it, but didn’t see any motorcycles. The house got hit tearing up the roof and flooding the basement, but I was very thankful that the shop was spared, it also took out both my computers and until a couple weeks ago. I have been off line since July 12th. I am trying to get back in the shop and get caught back up with previous orders, but as I had mentioned on a previous thread it is hard to find good help. I hope that anyone interested in these heads contact me and I will be happy to help you out with any info or parts your might need even if you didn’t buy them from me. For me it is all about the heads and has been for the last 20 years. If you are having a problem we will find it and fix it. With the new spam filter below, and
    again if it is O.K with Kneeslider this is my E-Mail precmc@localnet.com, if it isn’t please delete it, thank you jm

  27. says

    With all due respect, Chryslers use of the word “Hemi” is not a marketing ploy but a literal use of an engineering design in which the combustion chamber utilizes a hemispherical shape (hemi means half, spherical means round, thus one-half of a round shape). Chrysler did a tremendous amount of R&D work on this design in WWII and found it to be highly efficient (it utilized this design when re-engineering the engines used on the B-29 Superfortress which initially had high failure rates). Chrysler first introduced its Hemi V8 in the early 50’s as a 331 c.i.; it grew to 354 (which was the first production V8 to produce more than 1 hp per cubic inch) than to finish as a 392 in the late 50’s. It broke practically every major record in competed in be it land, air or sea. It was reintroduced in 1964 as the 426 hemi and (to this day) holds more speed records than any other internal combustion engine in recorded history. In drag racing, ALL top fuel drag racers and well as funny cars (irregardless of the body which lies upon the frame) use a variation of the spendid Chrysler 426 Hemi, as no other compares.

  28. todd says

    The point is that RPM’s use of the term “HEMI” is misleading marketing. These are pent -roof heads. The valves are parallel. Plain and simple. In order to achieve a true hemishperical combustion chamber with four valves is to arrange the valves hemispherically. The Honda RFVC single is the only true 4-valve hemi I’ve ever heard of (got one in my GB500 and XR650L). Honda was able to accomplish this with 8 rocker arms.

    The point of Chrysler using it as a marketing hype is the fact that, as you state, they (and Desoto) had “hemis” long before they ever marketed the “HEMI”. Now that nearly every 2-valve motor has a hemi head they are using it primarily as a marketing ploy. After all, they deserve it.

    -todd

  29. Bill says

    It is correct to state that “RPM”’s use of the word “Hemi” in its advertising is indeed erroneous (a ploy). RPM’s heads are the exact items that Jim Fuelling engineered back in the late 80’s ~ early 90’s and are in fact a pentroof design and not a “Hemi” ( I considered buying the stage I kit for my FXRSSE in the early 90’s but found them too expensive). I simply disagree with the use of the word “ploy” when referencing the Chrysler Corporation (R.I.P.) as this insinuates a dishonest act (the Cambridge dictionary defines a ploy as “something that is done or said in order to get an advantage, often dishonestly”). While one is correct in stating that Chryslers new Hemi is not truly a “hemi” (its combustion chamber is a shallow hemispherical chamber with the addition of two squish bands perpendicular to the intake and exhaust valves), it still employs the basic elements of a hemispherical combustion chamber (a semi-hemi) and ties in with Chryslers well earned reputation and history (DNA) with this engineering design. Hence, it is deserving of the use of the word “Hemi” in its advertising as it is well desreved (“Hemi” is a registered trademark of the Chrysler Corporation).

  30. Kazoom says

    Warning… for those interested in these heads, in the posts above… (jurneyman/john mansell)…. this guy has had my money since July 2008 and I still dont have my heads or my 2 pistons I sent him over a year ago for a one hour job to cut valve reliefs. It is now january 2010. I have had nothing but problems and bs with this guy as soon as he got my money ($3187cnd). For anyone that needs more info… vascarperf@hotmail.com