|
HD recently started offering a new set of XL
performance cams, dubbed the "High Output" cams.
Like all the modern XL cams, they fit all the way
back to 1991 models when used with an appropriate
pinion gear.
We were curious how these cams would stack up to the
venerable favorite cam grind of the SE family, the
SE 536. We've used the SE 536 with excellent results
for many years and this new grind looks, on paper,
like it might work a little better. The intake lobe
is 2 degrees broader on each end, opening sooner and
closing later, than the 536. The exhaust lobe is
very similar, just advanced a couple degrees, which
helps lower the troublesome TDC lift figure of the
536. But most interesting of all is the additional
lift of this new grind. Head porting and larger
valves tends to help heads more at higher lifts, and
a relatively narrow, broad grind like this offers
the possibility of more power across the spectrum.
The test mule chosen was a typical 100hp XL motor
equipped with our Stage 2 head work and an
NRHS/Axtell 1250 kit. Like all standard Stage 2
heads, these were set up to accommodate up to .600
valve lift and have moderate seat pressure suitable
for typical street performance cams, along with Ti
retainers and 10 degree locks. The rest of the
valvetrain consists of stock pre-00 lifters,
Hurricane fixed length pushrods, and stock rockers.
We baselined the bike, swapped the cams, and dyno
tested again within about a 3 hour time frame, on
the same dyno with the same operator. No other
changes were made to the bike except for a one-size
jet change that the air/fuel monitor said we needed
when we went to the new cams (the timing was
optimized for each grind as well). Here's the
result:
As you can see, the 575's give up nothing to the
536's at any rpm (don't read too much into that low
rpm advantage, the throttle is being rolled on at
that point and the repeatability is poor). But the
575's had a clear advantage on top.
The lobe shape is not particularly aggressive on
these new cams. The chart above shows no signs of
seat bounce despite the moderate spring pressure.
Valvetrain noise is also very similar between the
two grinds.
So it looks like SE has come up with an attractive
new cam grind for XL's, one that's mild enough to
not require an expensive cast of supporting
components and yet offers a very real performance
advantage over the 536's.
Both of these cam sets and many others are available
from NRHS. See our
camshafts page.
Return to tech articles index |
