Mac Racing TRX500R Review:
Dan Wade, Contributing Editor
The TRX500R Testing is
Complete. The Results are Phenomenal.
Findings: What a Brute.
Source has completed the testing and review of the Mac Racing
from Salem Oregon, has created the latest in the escalation of
drag racing engines. With their hybrid combination of a Honda
TRX250R and a Honda CR500 engine - Mac Racing has set a new
standard to gage from. The Mac Racing TRX500R is a 500cc hybrid engine using the standard 250R bottom
end assembly that is transformed to accept the enormous
cylinder. The benefits of such a hybrid are
many, but first the details of how this engine came about.
Initially, Mac Racing Inc owners, Brent McMillan and Tim
Pettit, wished to create the ultimate in drag racing prowess.
Mac Racing has been crafting high output engines for many
years, but had not yet created a hybrid such as the 500R. The
500R was created with the intention of being the ultimate
for drag racing, however along the way it was
discovered that the 500R’s available power was suitable for
other applications as well.
To create such a hybrid as the 500R it requires extensive
welding and machining. The 250R engine cases are disassembled
and inspected. The welding process begins as the existing
cylinder studs are removed and the holes welded up. The
cylinder base and gasket-mating surface is built-up through
successive welding passes. After the welding build-up is
complete, the cases undergo machining by Mac Racing’s partner
Northwest Precision Machine (NWPM). Mike, the machinist at NWPM,
takes the rough looking cases, and machines them to precision
dimensions to ensure the critical surfaces are within
tolerance, as well as providing for a quality finish on the
exterior. In applications where the crank’s stroke will be
extended more than 4 millimeters, the cases must be “trenched”
to provide sufficient clearance for the connecting rod, this
operation is performed in conjunction with all other machining
done to the cases. In inspecting the exterior of the cases,
the craftsmanship and quality are very apparent.
Once the cases
have been welded and machined for the larger cylinder, the
work begins on completing the cases. New case stud inserts
are installed along with new studs. The water pump outlet must
be modified to allow for the larger cylinder. Additionally the
clutch cable mounting location is moved onto the stator cover
to provide clearance for the larger cylinder.
The remaining modifications are traditional processes to
crafting high output engines. To begin with, a Hinson clutch
basket is required for its stronger design, and then is
modified to accept 8 friction plates, providing for sufficient
clutch friction area to transfer the power. The flywheel is
lightened and re-timed for ignition advance as well. Further,
the crank is stroked, in the case of the test engine, the
crank was stroked 7mm's to a total 79mm's stroke. A new custom rod is polished to
increase its strength, then installed, followed by truing and
welding of the crank assembly. No work is required to the cylinder to allow it to fit to the bottom end assembly.
Mac Racing then, relying upon years of experience, begins to
methodically perform the porting alterations to net the
desired power characteristics. The cylinder head is modified,
then cut for o-rings to eliminate any head gasket and to
increase the thermal transfer from the cylinder to the head.
The cylinder and the cases are matched to provide a seamless
transition between the two components. A new Wiseco piston is
fitted, the cylinder is bored, honed, and the ports chamfered.
The engine is assembled, a leak down test performed, and then
installed into the chassis.
The intake side is handled from a Moto Tassarini V-Force reed
cage, as designed for the CR500. A custom CNC billet intake
and boot are used to mate up the carburetor. The exhaust side
is handled currently by a Mac Racing modified FTZ fat in-frame
drag pipe. Mac Racing has modified the pipe with a larger
diameter stinger to account for the increased exhaust gas
volume generated from this massive engine, also to accommodate
the different outlet angle on the exhaust spigot the head pipe
must be modified as well. Mac Racing has also created a custom
silencer, due to Oregon Dunes National Recreation Area
requirements; all ATV’s must meet a sound check of fewer than 93
decibels. While Team Source did not actually perform a sound
check on the silencer, the sound levels were greatly reduced
given that this was a big bore high output engine.
In using the
250R cases several chief benefits are presented. First, the chassis
need not be modified to accept a different configuration. The
engine bolts right up. Further, with the 250R having been
originally designed with a counter-balancer system, the
vibrations created by this massive engine is greatly reduced.
Team Source compares the vibration to that similar of the
larger Pro-X and Polonda engines (350-400cc). Mac Racing is in
work developing and incorporating innovative crank
modifications to further reduce
vibrations, and in doing so will also free up some available
power in reduction of rotating mass. Finally of the chief
benefits is a 6-speed transmission to provide for a wide range
of gear selection.
As tested the cooling system was that of a stock unmodified
250R system. During all of our test rides, never did we
experience any over-heating conditions. With plans to go to
methanol, the engine will run even cooler, making cooling
firmly a non-issue.
Team Source met up with Mac Racing in Florence Oregon for some
initial testing. Thankfully the weather was nice for the
Oregon Coast. As later and most recent testing sessions shows,
the weather can get down right nasty. Mac Racing had worked
diligently to get ready and had received continued help from
Bill Stewart at
with getting parts and accessories. Mac Racing would like to
thank Bill for all his help with this project and everything
Starting the 500R can be difficult when cold. Even with
spot-on tuning and good technique, the fact remains that you
are kicking over a +7mm stroke big bore monster. Mac Racing is
working on different ignition systems with initial ignition
retard to aid starting. Additionally this engine had moderate
head modifications resulting in higher cranking compression
leading to more difficulty in getting an effective kick in to
start the engine. Mac Racing knows this and is working on
improving it near-term.
We headed out to the dunes, after getting out to the sand
flats and having performed a good warm-up of the engine, some
test passes were in order. We made a couple of passes up and
down the strip to begin to get a feel for the shift points. Initially we noted how wide the power
spread was. Literally the power comes on at idle and runs well
up to and over peak RPM. This engine behaved expectantly as a
big bore would, but was able to rev surprisingly well.
We lined up to make some solo drag race passes. BRUTAL. The
ability of the 500R to launch out of the hole was simply
impressive. Keep in mind this engine has what would be
considered “recreational” mild porting alterations: we were
able to easily pull very hard and fast launches in 2nd gear,
with a 275 pound rider, 22X11-8 10 paddle Ultra-lite Haulers,
and 15-38 gearing (that’s TWO teeth UP from the stock 13-38)
in WET sand (Launch
Video). A 10 over swing-arm was barely
enough to keep the front end from pointing skyward. The power
of the 500R is mind-bending. It truly is not only a brute, but
at the same time it is very rider friendly. Literally lug it
in any gear, wick the throttle and it was able to torque its
way out and rev up and out. 4th and 5th gear wheelies with a
10 over swing-arm only require a blip of the throttle to get
it pointed skyward. While making hard fast wide open passes,
you can feel the quad torque-steer, and requires differential
air pressure to keep it going straight, this is a testament to
the massive power this engine is creating!
After getting a good feel of the engines personality, we lined
it up against several other very respectable drag race bikes.
The results were equally impressive, we were able to out pull,
out launch, out run them all. The 500R
truly owned the drag strip that day. This all from an engine
that had “recreational” porting and an experimental drag pipe.
We wrapped up testing for the day and headed home. We had made
plans with Mac Racing to meet up again for continued testing,
as they wanted to have the engine tested with the modified
fat in-frame drag pipe. Some coordination finally
resulted in us meeting up again with Mac Racing at Sand Lake
Dunes, near Tillamook Oregon.
This time the weather was NOT as cooperative. Heavy rains and
gusts to 40-50 mph made for quite an interesting and WET day.
During the time since our last test ride, Mac Racing had their
good friend and customer Marc Hernandez, from Salem Oregon; do
up a very nice
custom paint job on the 500R. Quite a change from the
plain white Fullbore fenders from the previous test ride. Marc can be reached at
503.365.7828, and provides full service custom painting.
Please note that in several of the pictures shown there are
raindrops on the camera lens making blotchy spots on them.
The weather relented slightly, and we had Brent make a couple
passes for us before taking over the controls. Again the 500R really demonstrated how hard this engine
pulls. From the previous test ride with the experimental (and
not very well suited) drag pipe, to this test ride with the
modified FTZ fat in-frame drag pipe, was a noted difference.
The power spread became even wider and amazingly more potent.
Again it launched
super hard and fast, and the speeds it ran
at were no less than impressive.
In summary, Mac Racing Inc, has truly created a very potent,
yet very ride-able brute of an engine. The engine does have
its drawbacks, however Mac Racing is diligently working on
resolving the issues involved with starting and vibration, and
do have several promising solutions to them. Price wise this
engine is within the current line of bigger bore 250R based
engines, though on the upper end of that
range. However the performance potential is much greater than
that of the available set-ups on the market making the
additional cost acceptable. The fact that the engine that we
test rode was in a very mild state of tune with only minimal
porting and head alterations only show that this engine is and
will become even faster and more potent. That is truly
mind-blowing as to how fast and how hard this engine pulls
already. With the addition of more aggressive porting and head
alterations and perhaps the addition of methanol fuel the 500R
will truly become a monster. To date this is the most potent
and fastest engine that Team Source has ridden, a testament to
Mac Racing’s innovation and skills in crafting high output
5137 Salem-Dallas Highway
Salem, OR 97304