DK Custom Products

Phone: 662.252.8828
Text: 662.420.4891
Email: [email protected]

Cooling down Your Harley-Davidson

Twin-Cam Engine



Part II


Here are methods that are proven effective at cooling down the Twin Cam Engine.  They are organized by cost & effectiveness.

Inexpensive (under $100):

1.  Remove the left side thigh protector.  This will help the air flow very fast past the rear cylinder and out the left side...this is good for the engine, and will reduce the amount of felt hot air on the right side.  

With the right side shield still in place, it acts like an air scoop pulling air into the space behind the cylinder...but with the left side removed, that air can now exit easily. With both installed, they are essentially two scoops that push air from both sides to collide and swirl, with no real good place for the air to exit.

It is not symmetrical looking, BUT, you can only see one side at a time, so it is unlikely most will notice you have a thigh protector on one side and not the other.

Doing this will cool the engine overall, so while riding & when coming to a stop you have a cooler engine than you would otherwise.  However, if you are at a stop long, or in continuous stop & go, you will feel more heat on the left than the right.



2.  NO fork wings or umbrella baffles when ambient temps are 70* or more.  These block a substantial amount of air that should be flowing past the engine.  With them installed they typically raise engine and oil temperatures by 20-25* F.



3.  This next one can be No Cost or High Cost.  Remove the Catalytic Converter.  This will not decrease engine heat very much, but it will reduce Felt heat tremendously.  You can remove it from your stock headers, this takes a bit of work.  You can purchase aftermarket headers, like the V&H Power Duals, that do not have a catalytic converter in them.



 4.  Install a Tank Lift with a Deluxe Option.  Not only will you benefit from a 10-15* drop in engine temperature, more of your chrome will be visible, it will be easier to clean, and many experience less buffeting.

Without a tank lift the tank is covering the top of the engine, trapping in the tank channel.  It is also preventing air from flowing over the engine.  With a tank lift, air that previously was hitting the front of the tank and flowing over the top of the tank to hit the rider in the chest….that air is now flowing Under the tank, and across the engine, cooling it down.



5.  Install Cooling Wings.  These take air that previously went around the tank and over the tank and redirects that air to shoot directly onto the engine.  These can be used with or without a tank lift.  They provide an additional 8-10* drop in engine temperature.

They also make for less rider and passenger buffeting.


6.  For Dyna & most Softail Models, relocating the Coil so that is it not blocking air flow around the rear cylinder will cool down the rear jug by 10-15 degrees at cruising speeds. 


7.  No matter what air cleaner you are running, make sure that it has an External Breather System (EBS).  All DK Outlaw Air Cleaner Systems come with an EBS as part of them.  But if you already have an air cleaner that you are happy with, make sure to modify it with an EBS.

An EBS will prevent hot, oily, oxygen depleted air from flowing through your throttle body and into the combustion chambers.  Having only cool, clean, oxygen rich air going into your engine makes for a stronger & cooler running engine, plus one that does not get carbon build up on the pistons which causes more heat and pinging down the road.  



8.  XiED's will help the engine run more efficiently, resulting in a cooler running engine.  This is better than a Dealership download, but not as good as a flash tuner like the FP3 or Power Vision.  We have many Customers running the XiED product on their Rides that are completely happy with it.  The engine will definitely run cooler, stronger & last longer with them installed...I am not sure it will last any longer with an FP3 or Power Vision, but you can get extra performance out of the FP3 or Power Vision.  The XiED product typically lowers engine temperature by 5-10*.



9.  Free flowing exhaust slip-ons are a very important factor in cooling the engine down.  The stock exhaust mufflers (slip-ons) are restrictive, resulting in the engine fighting against itself.  In doing that it generates heat with no resultant forward movement.

By removing this restriction, you are allowing a free flow of exhaust exiting the engine, which plays an important role in keeping the engine cool.

The stock headers on Harley’s are very respectable, and are not restrictive.  Replacing them will not have a significant benefit in lowering engine temperature.  If your Catalytic Converter is in your headers (all Touring & Trike models) you can remove it, or replace the headers for a reduction in Felt heat from the exhaust.

There are many choices in Slip-on’s.  Some of them can get quite expensive.  If you are not sure what you want (sound wise), it may be best to modify your stock Slip-ons by removing the baffle and installing some Thunder Torque Inserts.  Our experience has shown that this creates the most power and the coolest running Slip-on you can get, besides being the least expensive!

However, they will not be quiet.  Check out some Youtube videos.  If you want something more quiet, check out bike nights, figure out what sound you like.  Once you have your slip-on’s, add some Thunder Torque Inserts to them.  You will get more power for less gas burnt.  This will result in a cooler running engine (besides being stronger).

The above can be Low, Moderate, or High Cost

Moderate Cost (under $200)


10.  A Free Flowing Air Cleaner System (with an EBS) is a very important factor in cooling the engine down.  The stock air cleaner is restrictive, resulting in the engine fighting against itself.  In doing that it generates heat with no resultant forward movement.

By removing this restriction, you are allowing a free flow of cool air thru the engine, which plays an important role in keeping the engine cool.  With a good free flowing air cleaner you will typically see a 8-15* drop in temperature.



11.  Re-locate the oil filter.  Not only will this put the oil filter out in the wind, it will let more air hit the engine, and it will make for mess-free oil changes.

This will result in an 8-10* drop in oil (and engine) temperature.



12.  A Permanent High Performance Oil Filter. These give superior oil filtration, reduced drag on the oil pump (engine does not have to work as hard=less heat), and the finned billet case provides a small amount of extra cooling.  (Will be cost neutral after 10 oil changes)

Higher Cost (over $200)


13.  Flash Tuner.  Twin Cams run too lean from the factory.  Again, this is to meet EPA guidelines.  Whether you add free flow intake and exhaust, or keep the restrictive intake and exhaust, the engine will run cooler, longer, stronger, & more efficiently with a better tune.  Above, in point #7, the XiED will add more fuel, which is a big step in helping the engine run stronger and cooler, and is an excellent budget solution.

However, a full tune, which includes adjustments to timing and a host of other tables, can be achieved with a Power Vision, FP4 or a host of other tuners.  You can see a complete overview of popular tuners at this LINK.

Whichever device you use, it will pay dividends in a cooler running, stronger engine.  Typically you will see a 10-15* drop in engine temperature.

14.  Oil Coolers.  These are powerful tools to achieve a drop in oil & engine temperatures.  Below are three distinctly different situations that Twin Cams Fall into-


FIRST- Air Cooled Twin Cams that already have a factory Oil Cooler


There are two routes to go with a Twin Cam that already has a Factory Oil Cooler-


A.  Add a second oil cooler.  If you have lowers, use the Dual-Cool Oil Cooler, if you don’t have lowers, add a 10 Row Oil Cooler off the downtube.  This is a proven method that we see typically adds a solid 25* drop in temperature.


B.  Replace the factory Oil Cooler with a Fan-assisted Oil Cooler.  It is not just the fan that helps, but the actual oil cooler is much better at shedding heat than the, less than quality, OEM cooler.  Every time we have done this we’ve seen a solid 20* drop in temperature.

SECOND- Air Cooled Twin Cams that have no factory Oil Cooler


You can add a low mount or side mount oil cooler to any Twin Cam.  The side mount (down tube) are not as discrete as the low mount, but they are more out in the wind, resulting in a minimum of 25% better cooling than a low mount of the same size.  These typically give anywhere from a 20-40* drop in temperature (depending on size and low or side mount).

THIRD- Twin-Cooled (Wetheads) Twin Cams


Use the Dual-Cool Oil Cooler, specifically designed for the Twin-Cooled Engine.  Combined with the CnC Oil Filter Relocation you should see a 30-35* drop in temperature.

15.  Cooling Fans.  For decades there have been “parade” fans.  A fan that mounts on the left side of the engine and blows air between the cylinders.  This is better than nothing, But they are very poor at cooling compared to the newer style fans that blow air directly across the heads and cylinders.

Wards Parts Werks & Love Juggs both center at the spark plug on each head.  Not only does this blow air across the fins on the heads and cylinders, it pushes air thru the channels that are in the heads.  This results in an amazing amount of heat dissipation, both when sitting still and while moving.  

These fans are easily good for a 50* drop in engine temperature in stop n go traffic on a hot day.  Even at highway speeds they are good for a 10-15* drop in temperature.



On Air Cooled Twin Cams, if all, or most, of the above are used, the ideal balance of having the same oil and cylinder head temperature of no more than 230* after 45 minutes of riding on a warm day at highway speed is achievable.


On Twin-Cooled Twin Cams it is a bit different.  The heads will always be cooler, the oil and rest of the engine will always be warmer.  By using all, or most of the above, the heads should easily stay Below 230*, closer to 210-220 on a warm day.  The oil temperature, and the rest of the engine is likely to be between 230-240* on a hot day after 45 minutes of highway speed travel.  This is ok.  It still allows for a spike in extreme conditions, while keeping the temperature below the 270* mark, which is where sluggishness in power starts being noticed, and where engine longevity is being sacrificed.


***One option for Lowering Felt Heat for the Passenger is to close the Right Side fairing lower vent.  While this is counter-intuitive, it does reduce the amount of heat that the passenger feels.  This strategy should NOT be used unless you have done many/or all of the things above to lower the actual engine temperatures.  The reason is that in closing the right side fairing vent you are reducing the amount of air that goes past the engine to cool it.  If you have your engine temps down where they should be, then it will not spike up too high when you close this vent.


While there are other things that can be done (swapping cams, headwork, etc.), what is listed above is relatively inexpensive, easy to do, and we’ve never seen any of it void a warranty.


These modifications are the result of years of looking for the best way to cool these down. Thousands of hours of thought, fabrication, testing, riding, & measuring, seeing what works and what doesn’t.  


We are not necessarily done.  We may discover other solutions, but for now, the urgency of our quest for reduced temperatures is abated.  We have found what works for engine performance, engine longevity and rider/passenger comfort.


Live Free - Ride Free!