Full Throttle Marine
496 Mag Dyno Testing & Myth
Busting
Written by Bob
Lloyd
We at Full
Throttle Marine are one of the few facilities that have a prop shaft dyno
capable of up to 800 HP and an engine dyno room plumbed to run marine engines in
a complete wet environment. Thanks to one of our customers, Mark LeBlanc, an
opportunity arose to do some comprehensive testing on a Mercruiser, 496 Mag. HO.
The engine is installed in a 2006 Nordic Heat. He brought us the boat to upgrade
the engine with a
Raylar 525 kit. Our
first order of business was to get some baseline numbers on the boat. We headed
to our local lake, GPS in hand. Weather conditions were 65 degrees, flat water
and approximately 900 ft. elevation. We made 5 different runs, with 2 different
drivers. The slowest speed was 62.6, fastest 63.5. Average RPM was 4920 on the
smartcraft digital tach. Let me interject at this point the Heat really does not
like glass smooth water. I’ve personally driven this boat a couple of MPH faster
in more chop. Nevertheless, those were the conditions presented to us, now we
have our baseline. Back to the shop for a dyno pull. We hook up our Land & Sea
13” Siamese-rotor prop shaft dyno with automatic load valve and DynoMax 2000
data acquisition software on the lap top. We made a total of 4 pulls all within
a couple of HP of each other. Final prop shaft HP was
387.8
at 5000 RPM, using SAE Standard correction method.
The Nordic is
equipped with dual gas tanks. This made it handy to test one myth that is
commonly questioned. Will I gain any power by running premium fuel? We filled
one tank with 87 octane the other with 93. Peak HP came in at
387.3.
That is ½ of a HP less than with
93 octane. Studying the dyno sheets shows the 87 test to be within 1-2 HP of the
93 octane across the board, which falls within the acceptable tolerance of
repeatability. I think we can safely say there was no difference between the 2
type fuels on this engine.
OK, let’s
make some horsepower! Off come the cast iron Mercruiser exhaust
manifolds(earlier years have aluminum manifolds). We have a brand new set of
polished Dana Marine exhaust manifolds with the Vortex IV risers. Talk about a
nice kit! Everything was neatly labeled and went on without a hitch. Total
install time was less than 2 hours. We had ordered these with the optional 02
sensor blocks so we could run our dyno’s oxygen sensor. From testing done by
Dana Marine and Ray Broady of Raylar, I was expecting the engine to run a bit
lean requiring a fuel pressure adjustment, but decided not to touch it to begin
with. Again we made several pulls. The best of which netted a peak HP reading of
408.7
at 5000 RPM. The A/F ratio was right around 13.6:1 which is where Ray said the
496 made best power, so we didn’t touch it. We’ll fine tune it after the Raylar
kit. That is a 21 HP increase at peak RPM. I was expecting more based on
advertised claims ***. Well, let’s go to the lake and see what we gained. My
first observation was the engine sounded better and had more throttle response.
We idled out of the no wake zone and nail it. Seat of the pants told me it was
much stronger out of the hole. I didn’t measure time
to plane, but it was
noticeably better. Cool, so far so good. Weather conditions were very similar to
the baseline testing, except
there was more wind. I could not find a
glassy
smooth stretch of water like we had the first day. With the added chop the boat
aired out better.
Again we made numerous passes, same lake, same GPS, same
driver. Our slowest speed was 64.6 and fastest was 65.5. RPM increased by 80.
I’ve set up and run many Nordic Heats. I know that it takes approximately 17 HP
increase to gain 1 mph in this boat. Interestingly we gained 2 with 21 HP. A
quick calculation tells us that the prop slip is less on this test (same prop as
before). Why would that be? A couple of thoughts come to mind. First, we saved
about 50 lbs with the aluminum exhaust over the cast iron. Secondly, there was
more chop on the lake. Remember my comment about this boat liking chop? There
you have it. We hoped for a little more increase based on Dana’s 48 hp increase
claim ***, but based on all of my experiences with exhaust this is about what I
expected. Did I mention they look really cool?
***Dyno
tests performed by Dana Marine were with wet exhaust manifolds, but the water
was collected and not mixed into the exhaust gasses as they are in a marine
application. This may well account for the higher hp increases they were able to
achieve during dyno testing as opposed to “in the boat” data.
Now it’s off
to the shop to pull the engine and bust some more myths.
Well, the engine’s out and on
the dyno stand with the Dana exhaust in place. One question that comes to mind.
On the Nordic installation the exhaust uses an S pipe, so the exhaust makes 2
almost 90 degree turns before exiting the boat. Could this be costing us some
horsepower? Easy enough to prove. We pulled the complete exhaust system out of
the boat and set it up on the dyno.
We made a
couple of pulls with a resultant
454
HP. Next we removed the boat exhaust and routed it straight. No change. Shoots
that theory down. Back on with the stock exhaust manifolds. Now we get
431
HP. That is a 23 HP improvement at the crankshaft with the Dana exhaust, 21 HP
at the prop. Well what do you know, we have an opportunity to verify another
myth. Let’s remove the turbulators and see what we get. How about
438.8
HP. That’s 8 HP, or about ½ mph on this boat. Every little bit counts though. We
have one last opportunity. I have a set of custom Lightning headers hanging on
the wall that came off my 28 Heat with 900+ HP. We bolted them up and fire it
up. Sure sounds sweet. Even more responsive than the Dana’s. One quick dyno pull
and there’s no more speculation. 451 horsepower. That’s 3 less than the Dana’s.
Interesting! They did make 10-15 ft.lbs. more torque at all lower RPM, with the
Dana’s finally passing them at 5000 RPM.
One last Myth
to bust. How much horsepower does a Bravo drive absorb? For those of you that
are observant, you’re probably ahead of me. It’s certainly not 25 or 30 HP like
many have come to believe. It is a percentage. In this case with a Bravo X
drive, right at 10%. I’ve done testing on 600 HP engines and lost 60+ HP to the
drive.
Stay tuned
for our next installment:
Raylar
kit install……..
We’re back.
Several months have passed and we’ve completed the Raylar install and testing.
Sorry it’s taken so long. Just too much work and not enough time. As this
article is directed at results, I’ll save the details of the install for another
time. The instructions were thorough and it went together without a hitch. Now
it’s back to the dyno to see what we accomplished. The one caveat to the project
is that we sent the PCM to Whipple for their stage 2 programming. They tweak the
fuel mixture, raise the rev limiter and adjust the spark timing to be much more
aggressive. This requires a 120 degree thermostat and 91 octane fuel. We
installed the stock exhaust manifolds, with turbulators removed for our initial
tests. We made several pulls, tweaking the fuel pressure up and down to get a
feel for what air fuel ratio worked best. It made best power at 13:1 air fuel
ratio. More than a few points either direction and the power started falling
off. Off course this is what Ray had already told us, but being hard headed we
had to see for ourselves. The numbers? 530 HP at 5400 RPM. We’ve already
established that the turbulators cost us 8 HP, so I didn’t see a need to revisit
that. Keep in mind that Raylar’s testing was done without water mixing with the
exhaust, whereas these tests had complete wet exhaust. This would certainly
account for some HP loss as compared to his testing. Next we bolt on the Dana
exhaust manifolds. Again we make several pulls to adjust the A/F ratio and
arrive back at the 13:1 number. This time we get 553 HP at 5400 RPM. Very nice
numbers and right in line with the manufactures claims. Let’s see what it does
in the boat. This time the test conditions were the same altitude as before,
about 10 degrees warmer air temperature and smooth water. We were able to
consistently get 72 mph with a best of 72.8. Cruise A/F ratio is a bit lean so
we were forced to raise the fuel pressure a couple of pounds to bring that in
line for now. We’ll send the PCM back to Whipple for some fine tuning in the
fall. In summary, with the Raylar kit, Stage 2 programming and Dana exhaust we
picked up 9 mph. As a comparison, these numbers are slightly better than what
that boat will run with a Merc 525 EFI under the same conditions.
