Great post Sam, thanks for the level of detail.

Rob Schmitt

-----Original Message-----
From: KRnet <> On Behalf Of Samuel Spanovich via
Sent: Monday, May 25, 2020 2:45 AM
Cc: Samuel Spanovich <>
Subject: KR> N6399U Flight Test Report with New Engine

Get ready for another long read, because after fighting one obstacle after
another, I finally managed to get the plane airborne today with the new
upgrades, and all I can can say, was I impressed with the engine.
See below for details.

I won't beat a dead horse on the events leading up to this, so for a
complete background on the aircraft/engine, please see my previous post.
That said, here is my complete setup.

Revmaster 2100D
94mm AA Pistons/Cylinders
MOFOCO 041 Heads
CB 2232 Camshaft
SDS CPI Electronic Ignition (Dual)
AutoLite 4164 Spark Plugs
Sterba 54" x 54"
Fixed Timing at 25 BTDC (to replicate the magneto) Compression Ratio: 9.5

RAF48 Airfoil
Stock KR2S (~650 lbs empty weight)

Clear Skies
Light Winds On deck and aloft
ALT: 3024
Temperature: ~58F

Ground Testing/Runup - My previous post discussed getting a very powerful
3300 static RPM with the engine barely broken in.  One thing I did not
mention (and didn't really notice until today) is just how different the
idle/low power throttle response is when compared to the stock VW cam.  I
set my idle at about 1000 rpm, and I will say, the CB 2232 has a pretty big
lope at idle, which is one change I DON'T like.  It makes the engine sound
sort of rough, but still retains the throaty-ness at the same time.  It
isn't as big of a deal with the propeller off the plane, but as soon as you
add the extra load on the engine, it is very noticeable.  Where the stock VW
cam had a pretty snappy throttle response throughout the entire RPM range,
the CB 2232 has a pretty sluggish throttle response from about
1000-1500 RPM.  Once above 1500 RPM, up to about 2000 the throttle response
gets better, and above 2000 RPM everything is fairly normal.  The Cam does
state that the power band is from "1500-4500 RPM" range, but I did not think
it would be this literal.  As soon as you hit 1500 RPM, everything smooths
out quite a bit, and by 2000 RPM it feels almost like the stock cam, with
quick throttle responses.  This is very important when coming in to land,
because in the event of a botched landing and/or go-around, you have to
really be prepared to add power, because it will take that extra second to
spool up.  It doesn't sound like much, but trust me, it is just enough to
potentially get you into trouble if you're late to add power.

If this lope or laggy throttle response is a potential annoyance to you,
then do not go with this cam.  In that case, the CB2280 may not be a bad
option, since it has a decent power increase throughout the entire RPM
range.  However if you don't mind the lope and want the extra throaty-ness
of the CB2232, this cam is a solid choice in my (limited) experience so far.

Regarding the SDS ignition, I set the timing to 25 BTDC since I knew the
engine would work in that configuration, since the magneto was fixed at this
setting throughout the entire RPM range.  The SDS does allow the user to
configure the timing however they want at a particular RPM (10 BTDC at
1000 RPM, 12 at 1100 RPM, 25 at 2500 RPM, etc.) however since the engine was
designed for 25 degrees BTDC at all RPM ranges, I just stuck with this for

In addition, the SDS dual ignition incorporates a "Run-Up" feature, in which
you can shut off one ignition coil for approximately 3 seconds, then shut
the second coil off for approximately 3 more seconds, listening for the drop
in RPM very similar to a magneto check.  Mine both checked out okay, and I
noticed no abnormalities between both ignition coils.  The only downside (at
least on the basic CPI version) is that when you're in "Run-Up" mode, you
cannot monitor the RPM on the CPI controller to see just how much RPM is
lost.  You just kind of have to listen, and gauge it appropriately. The CPI
controller does include a lead wire to hook up to an analog RPM gauge, which
you could use to note the drop in RPM, however the lead wire itself is
calibrated in thousands of RPM, not "hundreds" of RPM like my old gauge was
(with the magneto).  Basically my  analog RPM needle is always in the very
lower portion of the gauge since it thinks my engine is running 1/10th of
it's actual speed.  So for the time being, all I have is the digital readout
on the CPI controller, and to re-iterate, cannot be used in the "Run-Up"

That's ultimately a minor complaint, and I completely forgot about it when
this happened:

Takeoff - After running up the engine on the ground, and running it up
again, then again, to the point where I was confident the engine would not
fall apart on me upon takeoff, I taxi'd onto the active runway and gave her
full power.  I noticed the same 3300 static RPM that I was getting on my
previous ground run ups.  With my old setup (Stock 2100D with the magneto),
my takeoff roll was somewhere in the realm of 1500' on takeoff (I never
actually tested it exactly).  With this new setup however, I reached 80 mph
very easily almost dead smack on the 1000' marker.  I lifted off and noticed
that the plane EASILY accelerated to 100 mph (my desired climb out speed,
not my Vy).

At this point, after accelerating to 100 mph, I increased the pull on the
stick to where I typically would with the stock 2100D to maintain 100 mph,
however this time, the plane kept accelerating.  I gave it a little more
back-stick, and it STILL kept accelerating.  By the time it stopped speeding
up and was maintaining 100 mph, I was in a pretty nose high attitude, and
was seeing a 1000-1100 fpm rate of climb which felt like a dang rocket!
Typically with the stock setup, I would get somewhere in the realm of
700-800 fpm, sometimes 900 if I was very light on fuel, the weather was very
cool and/or the plane was freshly washed and waxed.  This time I was
maintaining 1000 fpm like it was absolutely nothing, with an absolutely
filthy airplane; covered in grease and oil on the cowling and underside of
the belly from all the work I have been doing to it.  Had the plane been
washed and waxed, I am confident I could have gotten 1200 fpm sustained.
Remember this is a stock KR2S, with virtually no aerodynamic upgrades at
all.  For those of you that are running the new AS50XX airfoil, I'm sure
your climbout will be even better.

Cruise/Tachometer Puzzle - I didn't expect my cruise speed to be that much
different, if at all, since I did not change my propeller and didn't plan on
changing my cruising RPM, however this actually became the most interesting
(and most fun) part of my entire test flight.

With my old setup, the tachometer was connected to the magneto itself, and
at 3100-3200 RPM, I cruised around 108-110 knots, sometimes 111-112 if the
plane was washed and waxed and/or very light.  These numbers come from me
flying a cardinal heading, taking the ground speed, making a 180 and flying
the opposite cardinal heading, taking the groundspeed, and averaging the two
together.  There are reports out there of magneto tachometers being terribly
inaccurate, however I had never thought about this before and had always
relied on mine giving me accurate information.  I just realized today that
it must have been off by an awful lot, possibly several hundred RPM, because
this time when I conducted my speed test, I set 3200 RPM (reading directly
off the SDS CPI ignition controller), and
indicated......119 knots?

You might say, "hold on Sam, how is this possible?  To gain nearly 10 knots
of airspeed in cruise without changing a thing to the propeller?"

While I don't have any proof to back this up, my theory is that the Magneto
Tachometer was off by roughly 250 RPM, so what was indicating 3250 RPM was
3000 RPM in reality.  The science behind this is listed below:

The airspeed generated by the propeller is directly related to it's pitch,
it's revolutions per minute, and the prop efficiency.  This is a very
simplified version (I'm not a physics major after all), but should get my
point across none the less.

Prop Airspeed = Pitch x RPM x Prop_efficiency .  In this case, we have a
Sterba propeller made of wood (approximately 75% efficiency), a 54" inch
pitch (every revolution moves the prop "forward" 54 inches).  Let's compare
the RPM values of 3000 and 3250 RPM for this given propeller.

Prop Airspeed at 3000 RPM = 54 inches/rev x 3000 (rev/min) x 60 (min/hour) x
(1 ft / 12 in) x (mile / 5280 feet) x 0.75 = 115 mph.  Even though this may
be a very rough estimate, let's use 115 mph as our propeller airspeed at
3000 RPM

Prop Airspeed at 3250 RPM = 54 inches/rev x 3250 (rev/min) x 60 (min/hour) x
(1 ft / 12 in) x (1 mile / 5280 feet) x 0.75 = 124.6 mph.

When compared to 3000 RPM, This is about a 9.6 mph difference, or an 8.5
knot increase between the two RPM ranges.  Almost the 9-11 knot increase I
was seeing today.

So does this mean exactly?  It means that when I was running my magneto, I
was setting about 3100-3200 RPM indicated on the tachometer, but in reality
the engine was truly only spinning about about 3000 RPM.  Now that I have
the SDS tachometer, which is an actual digital computer taking the
measurements, I realize that with the magneto, I was running the engine much
slower than I could have been.  There is nothing wrong with cruising at 3000
RPM, I'm sure the CHT's appreciate it, but when the recommended cruising
speed by the engine manufacturer is 3200 RPM, I'll be crazy not going to
take full advantage and get all the cruising speed out of it that I can.
Now when I set 3200 RPM with the SDS system, I know for a fact that I am
getting a true 3200 RPM.

Another thing to consider is that since the magneto tachometer was off by
200-250 RPM, that meant that my static RPM (with the magneto) was much lower
than I originally thought; When it was indicating 3100-3150 RPM during
takeoff, this was likely only 2900-2950 RPM in reality.  Now that I am
getting 3300 with the SDS ignition, that makes this setup that much more of
an improvement, since I really gained about 350-400 static RPM, as opposed
to the 100-200 like I originally thought.

Is it possible that the opposite could be true?  That perhaps the SDS is
indicating 200-250 LOWER than the engine is actually spinning, so when
indicating 3200 RPM, the engine is running 3400 or so (hence the reason for
the increase in cruising speed).  Maybe the magneto tachometer was right all
along?  I'll let you guys be the judge on that one, but personally I trust
the SDS system more; it is much newer than a 30-40+ year old magneto, and is
digital as opposed to analog.  In addition, I can recall times when running
that the magneto, that electrical interference would disrupt the tachometer,
and it would fluctuate ever so slightly, perhaps from 3000-3200 RPM without
touching the throttle in level flight.  This tells me that right off the
bat, the system is prone to errors, and is likely not the best source of
accuracy.  I have not heard of, nor witnessed such interference/inaccuracies
with the SDS system.

Whatever the case, while I may be drastically overthinking the setup, today
when I was cruising at 3200 RPM indicated on the CPI controller gauge, I was
averaging 119 knots of True Airspeed, at around 2500' MSL.

I did not get a chance to test the duration of the electronic ignition
without power from the alternator, because my time was limited, and I was
also having too much fun flying after nearly 2 months out of the KR2S.  But
one day, I will have that result.

The remainder of the flight was pretty uneventful; I cruised around Skagit
Airport (KBVS) and the beautiful surrounding area for about 30 minutes, then
returned to Anacortes (74S) for a full stop.  All the while, I noticed no
abnormal oil temperatures, and the Cylinder Heads held up fine as well.

Coming in to land, ironically, I did have to go around once due to traffic
landing the opposite direction of me (winds were favoring 36, but the
landing traffic was coming in on 18, and I caught his radio call just as I
was about to turn final).  What I mentioned earlier about the spool-up time
still holds true; It took just "that" much longer to achieve full power,
unlike the stock cam which was virtually instantaneous even at low power
settings.  However, once the engine is spooled up past 2000 RPM, the engine
feels remarkably similar to the stock cam.

To Summarize:

Ground Runup - 3300 static RPM compared to 2900-2950 with the magneto and my
old stock setup.  The CB2232 cam has quite a lope at idle, and spool up time
increases a fair amount at low power settings.  The worst region is
1000-1500 where throttle response is a hair sloppy.  From 1500-2000 the
response gets better, and above 2000 the engine performs basically like a
stock cam, with decent power response throughout.

Takeoff - 1000' takeoff roll vs. ~1500 with my stock engine.  In addition,
once airborne, the airplane accelerates a lot quicker to 100 mph for
climbout, and a lot more stick pressure was required to maintain 100 mph to
avoid accelerating during climbout.

Climb - Easily achieved 1000-1100 fpm with an absolutely FILTHY airplane.
I am confident that I can (and will) get more rate of climb once I clean the
airplane.  With my old setup, I usually averaged 700-800, 900 at the most.
A pretty significant increase to say the least.

Cruise - Saw 119 knots at 3200 RPM despite not changing the propeller or
cruising RPM speed (again, with a very filthy airplane).  Determined that my
old tachometer on my magneto was likely reading 200-250 RPM higher than the
actual engine speed, because when running the magneto, I would still cruise
at 3200 RPM, but this only achieved 108-110 knots TAS.  When I throttled
back to 3000 RPM with the SDS system, I was getting the same TAS as when the
magneto indicated 3200 RPM.  There is obviously a 200 RPM difference between
the two systems, but considering the SDS is newer and digital, I trust it
more than the magneto.

Go Around Power Performance - You have to anticipate the power up a little
more than with the stock cam since the throttle response at low RPM (when
coming into land) is a touch sloppy, but as long as you are smooth with the
throttle and can make it up to about 1500-2000 RPM, you can then apply full
power and the engine will give you all that it's got for the go around!

Thank you all VERY much for all your helpful posts regarding my alternator;
I did get it fixed, and it puts out 12-13 VDC now.  I hope this post isn't
too painful to read, and feel free to email me with any questions you have
regarding this setup, or the Revmaster engine in general.  I am very happy
to be a KR owner, and be a part of this community.


Sam Spanovich
74S, Anacortes WA
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