|
The Response - Yes!
I enjoyed reading your letter about
the GP760 project and your adventures at the lake that day.
It sound as if you and your daughter had a great time. Since
I emailed you last, I have put the motor back in the trued
Raider 1100 hull. That took quite a bit of time with a 4" by
4" block of wood and some sheet rock paper. I now have about
6 hours of riding time on new motor. I did much like you
when it comes breaking it in. I did not baby it nor did I
hold it WOT. I also mixed the oil (Klotz synthetic) to about
20:1.
- My first ride was with some
friends who own 98 SeaDoo XP's which have factory pipes
and K&N flame arrestors. We decided to ride to the
sandbar (a popular place for boats and jet skis) which is
about 20 miles or the opposite end of the lake. The water
was extremely rough as you might expect for a weekend.
Anyway, on the return trip we decided to pick up the pace
a little - which to these guys means full throttle. I was
able to run side by side with just a little over 1/3
throttle and pull away at 1/2 throttle.
-
- The next weekend and several
tanks of gas later, I rode with another friend who has a
98 GP1200. We did exactly the same ride as the weekend
before only this time the weather was terrible and cold.
The wind was blowing about 20 MPH and had the lake
transformed into an ocean, but not a boat in site. I was
getting soaked and a little cold, therefor I decided to
make the ride time a little shorter. I let the engine run
at it's natural cruise speed or just when the main jets
open (about 1/4 throttle). When we got to the main
channel there were 3 foot tall long rolling swells. Much
different form the usual boat chop. I had the timing down
perfect, hit the gas in the bottom of the swell and let
of when the boat goes air born. By the time I reached the
sandbar I was exhausted. My friend was about a mile back.
He later told me that he was trying to keep his ski at
about 45 mph. I figure the natural cruise speed is about
51 to 54 mph.
-
- Later that day we went back in
a long cove and did some drag racing. This is the first
time I have tried this with the Group K modified Solas J
impeller. As soon as we both open up the throttle, I can
jump about 2 boat lengths in the first 75 feet or so.
From that point on it is a steady pull away. I have also
noticed, now there is enough power to cavitate the
impeller for about 1/2 sec. as soon as you hit the gas.
It never did that before. I figure the top speed is
around 63.5 to 64 mph.
-
- The next weekend I was feeling
pretty good about all my work which I had done over the
winter. I decided to mount the tiny tach and go get some
peak rpm numbers. Last year I was getting a peak rpm of
about 6730 with an air temp of about 70 deg F. The air
temp on this day was about 92 deg F with high humidity. I
did numerous runs on glassy smooth water. I am using
Ocean Pro flame arrestors with about 2" tall elements.
They have been taper bored while bolted on to the carbs
therefor they match up very well. With the flame
arrestors on I was only able to reach 6680 to 6690. It
did not seem to make any difference where I adjusted the
high speed screw, I began thinking that there was enough
signal to get the high speed screws to respond. I then
taped off about half of the flame arrestor with duct tape
in order to increase the vacuum in the inlet tract. The
RPM then dropped to 6650 with still no effect from the
high speed screws. Completely frustrated, I decided to
take the elements completely off. The RPM then jumped to
6710 although adjusting the high speed screws still made
little difference. Last year I was running 135 mains 2.0
needles with 16 lb. of pop-off and 90 pilots. This year I
have been using 145 mains 2.0 needles with 16 lb. of
pop-off and 90 pilots. There seems to be no hesitation or
sputtering when the throttle is cracked open from a long
1/2 throttle run. I think I am in the ball park when it
come to the jetting though maybe a little rich on the
mains.
-
- I feel much like you did with
the GP760 project. I know that I have increased the
bottom end and midrange but I am not so sure about the
top. My goal was to get the engine to turn 6850 to 6900.
I am not sure what to do from here. I would like to try
some 44's (carburetors) with K&N filters. Maybe
that's the trick but I would hate to spend the cash only
to see a 30 or 40 rpm difference. Group K says that their
Big Bore 1100 with Type 2 Porting turned several hundred
more with the 44's but used lots of gas.
-
- HUUUMMMM for whatever that's
worth lots of contradictions in their articles. Rick, let
me know what you think.
-
- Craig
-
-
-
-
- It sounds like you're close to where you want to be
but I agree you, the engine could be turning a bit
higher. Do you know the point where the rev limiter shuts
things down on that engine? I don't suppose Group K use
some ignition mods to achieve those revs do they? It may
be you were losing the revs due to the air quality only
and that testing another day with better air/water would
get them back. Air temperature, water temperature,
altitude, RAD (relative air density) and the condition of
the water affect your final outcome. Testing on a perfect
day will be tougher to achieve, but I'll bet your numbers
will improve. What were your final numbers for the
compression, compression ratio and port timing
anyway?
-
- I'd consider the 44 mm carburetors a waste of money
to get the extra revs you're looking for - and I doubt
the addition of them alone will get you the almost 2000
rpm's you're looking for. It could be that you're just a
bit over propped. Since you are experiencing a cavitation
problem from take off (not a good thing) you may want to
look into that as a major source of your peak water speed
problems as well.
-
- One of the nice things things about the 1100 triple
is that it can achieve high on water speeds with what
seems like little effort. I am amazed by the power
produced by that engine - especially the midrange hit.
It's all midrange - even when revving out it does so with
a sort of lazy attitude. And that big engine in the
light, flat Raider hull makes it even more noticeable.
The Raider may be the best high speed hull ever made for
a runabout watercraft. On glassy water there are few, if
any boats that can match the high speed of the modified
big engined Raider.
-
- I have also had the opportunity to try out the higher
displacement version (1200) of that engine, the power
delivery is nothing less than extraordinary - even when
pushing the additional weight associated with the XL1200.
I am also impressed by the on water manners of the big
XL. In rough water it inspires confidence when the Raider
would have its driver begging for smoother water - and
maybe some Pepto-Bismol. I have wondered if I'm the only
person who has literally blown lunch while riding a
Raider in heavy chop too soon after eating. Try to
remember that the day the engineers had the first test
Raider hull on the water there was no chop - so it made
its way into production...<jk>.
-
- Rick
-
-
- Thanks for your suggestions. I
just got back from the lake and may have arrived upon a
few conclusions. First I think you are probably right
about the 44 mm carburetors.
-
- I have a good friend who owns a
high performance jet ski shop close to my house. He has
an 1100 Raider that was ported by Riva Yamaha. At the
time the porting was done Riva did not offer any type of
recreational porting, only full blown race porting. This
ski has 44 mm Boswell carbs. In case your not familiar
with Boswell, they were very popular a couple of years
ago and were very expensive. It also has a Riva head with
the compression set at 180 (static). I had a chance to
measure the Riva ported cylinders before this engine was
put back together. The results are listed
below.
-
|
Spec
|
Riva
|
My Motor
|
|
Exhaust port (from cylinder deck - mm)
|
35.5 mm
|
35.5 mm
|
|
Exhaust duration (degrees)
|
191 degrees
|
191 degrees
|
|
Transfers (from cylinder deck - mm)
|
52 mm
|
53.5 mm
|
|
Transfer port duration (degrees)
|
?
|
124
|
|
Static compression
|
180
|
150
|
|
Carburetors
|
Boswell 44 mm venturi
|
Stock taper bore 38 mm's
|
-
- After warming both skis up, we
ran side by side across 4" chop. My boat was about 1 mph
faster on the top end. Next we went into a cove and
started from a dead stop. After about 4 seconds I was
about 75 feet in front. Oh well, so much for the bigger
carbs. We played around for about 20 minutes when a guy
with one of those brand new Kawasaki Ultra 150's came up
and started talking. Did not get a chance to run the guy
from a dead stop however we did run wide open across some
smooth water. This is the part that made all of my work
over the winter seem worth it all. My Raider was about 1
to 2 mph faster.
-
- As far as getting the rpm's I'm
looking for, Group K said they could repitch my Solas J
one more time. All I have to pay is the cost for
shipping. They said that "every boat is a little
different as far as getting the right pitch".
-
- I also agree with you about the
weather thing. I have noticed 40 to 100 rpm's more on a
cool day with low humidity. By the way the stock rev
limiter is set at 7050 and Group K does not modify the
stock CDI unit. If I use the stock impeller, I am bumping
the limiter on smooth water. I have a feeling that I am
very close to reaching the limit of this motor especially
without the help of a different pipe.
-
- Also you're right about the
1200 motor - it has an unbelievable amount of mid range
pull. Sure would like to try that motor in one of those
320 lb. Purple Hull Raiders. Wow talk about a screaming
machine.
-
- Craig
-
-
-
-
- When I wrote that last letter I was thinking you were
2000 rpm's, not 200 rpm's away from your target. Once I
reread the part about the rpm's I realized you were much
closer to where you want to be than I was thinking. I
think the bigger carbs may well get you the extra revs
(200) your looking for but the cost associated with
buying them is enormous and probably not worth it.
-
- I'm very surprised that your friends Riva Raider
isn't faster. With the higher compression and bigger
carbs it makes me think it should be. Is there a
difference in the way the two boats are propped? The
compression that boat is running is on the high side for
a 1100 cc triple. He may be losing some upper revs do to
too much compression - I wonder what rpm his motor pulls
at its peak.
-
- Thanks for including the specs of his engine - I'll
add it to my database of specs for ported motors. Having
the prop repitched again will probably allow you to hit
your target. Now that Klemm knows where your revs are,
what you did to your engine and what the result was he
should be able to set the blades just right.
-
- I used to like to race Bill's Raider against other
boats which were supposed to be faster than it. It's 700
cc Riva mill is a rocket! I like the revs it turned and
the sound that came from the engine compartment. He and I
raced (I was on my stock GP) at lake Havasu last summer
and the smaller engined Raider easily pulled away from me
- did I say EASILY with enough emphasis ?!? Unfortunately
since he bought a XL1200 last fall and a new (dare I say
it) Sea-Doo GSX Limited (I think that's the model)
[nope - wrong model, see below
- Rick] this spring both of his Raiders either
have been or are about to be sold. The best thing about
the big Yamaha triples is their ability to cruise at high
speeds with little effort from the engine. The gas tank
seems to need refueling more often though - for some
reason ;)
-
- Rick
-
-
-
-
- Since the last time emailed
you, I have gotten about 50 or 60 extra RPM out of the
motor. I am now at the same rpm as I was last summer when
the air temp and water temp were much cooler. That's good
because when the temp does start to drop I will be about
50 to 80 rpm's more or some where around
6800.
-
- I gained the extra RPM by doing
a couple different things. First I have two water bypass
fitting coming out of the side of the boat. Each hole was
supposed to be 6 mm according to Protec's dual cooling
line specs. One of the holes was only 4 mm so I drilled
it out to 6 mm. This should have dried the pipe out some
at peak RPM. Next I raised the front of the ride plate 5
mm. My hopes were to raise the bow up some, thus reducing
the wetted contact area at top speed. I knew that 5 mm
would probably be excessive, but I wanted to see what
kind of effect, if any, it would have. The boat seemed
very fast on top end but was very hard to stop from
bouncing. I then took 2 mm away from the front which made
it 3 mm. That seemed to be the happy medium. A little
bounce, but still a noticeable difference difference in
bow height.
-
- I have also modified the stock
ride plate - it is cut off flush with the back of the
hull, and the six large mounting holes have been filled
with epoxy and sanded smooth. I then drilled out the
mounting holes only large enough to accommodate a
stainless Allen screw.(about 7 mm dia.) I am not sure if
this actually helped or not but I figured it couldn't
hurt. I did not mention, but the ride plated was modified
earlier in the winter, so it was not responsible for the
extra revs.
Craig
- It has been sometime since I
wrote last. I think at that point I was getting ready to
Radar my 1100 and give you the results. We did this about
2 months ago when the outside temperature was around 95 F
deg. It radared at 64.8 to 65.2 with a couple of peaks at
around 66. The max rpm at that time was 6690 with the
Solas J prop. Now that the weather has turned much cooler
it is turning somewhere around 6750 to 6790. I am not
sure how fast that is but I would say, it should be a
solid 65.5 mph.
-
- My friend is working on a GP
1200 and has put a set of Buckshot 44's carbs on a motor
that he has just finished porting. I'll let you know how
that turns out. Anyway we are getting ready to remove my
modified 38 mm carbs and put on a 44 mm intake manifold
using his stock 44 mm GP 1200 carbs. The only thing that
has been done to them is removal of the choke plates. We
are not exactly sure what to expect, but we are hoping it
will turn about 150 to 200 more RPM on top end. If it
does it should make this boat run about 67 or 68 at about
6950 rpm. I will probably jet the 44 mm carbs a little
richer than a stock GP 1200, since it is very cool
outside and the fact that my motor has been ported.
-
- Craig
-
- P.S. - I'll let you know what
happens.
-
-
- I've got so much to write and no time to write it! I
buried in work because I started taking in more outside
engine builds. In addition to that we're heavily involved
in youth soccer. One of these days I'll write about my
trip to New Melones Lake with my GP760 - there were a few
surprises.
-
- It sounds like you're right on target with what you
wanted to accomplish. That's fast - and it seems even
faster on a Raider hull! I think you'll notice the carbs
will "hit hard" in the midrange and offer some revs on
top. The decrease in fuel mileage will be noticed.
-
- Rick
-
-
-
-
-
- This summer, like the past few I've been fortunate
enough to be able to spend a week aboard a house boat on
some of California's greatest watercraft hot spots. This
year we spent the time aboard the big floating home on
the water of New
Melones (ma-lone-eez) lake - it has about 100 miles
of shoreline and is a wonderful place to spend a
watercraft vacation. One of the nice things about the
house boat we were on this year was that it was equipped
with a refueling station at the rear of the boat. Gassing
up was a piece of cake because we wouldn't have to drive
a long distance (and burn considerable fuel) just to
replenish the thirsty fuel tanks. This boat was also
equipped with an electric watercraft ramp. At the end of
the day when riding was done or when performing service
we could drive our machines onto the ramp then use the
winch to raise the machines completely out of the water -
classy.
-
- Bill's new XL1200 was going with him as would his
even newer Sea-Doo XP Limited. Both of these machines
have been fully "run in" at our local lake (San Antonio)
so there would be no babying any of them during this
trip. I was bringing my freshened up GP760.
-
- Before going on this trip I searched around a little
bit to discover some information about the boats that
would be with us - I wanted to know the power to weight
ratio of each model so I could compare them. I found out
that my GP760 had a ratio of 5.22 lb. per 1 hp in stock
form (470 lb. and 90 hp). In its newly modified form the
ratio changed to 4.60 lb. per 1 hp (470 lb. and 102 hp -
calculated using two stroke design software) - a decent
improvement. The XL1200 has a ratio of 4.51 lb. per hp
(609 lb. and 135 hp) and the XP Limited has a ratio of
4.32 lb. per hp (550 lb. and 130 hp). The numbers
indicate the XP Limited has an advantage over the other
two machines in this category. I knew what to expect from
my GP since I had already established its power delivery
has been improved after the modifications I performed to
it earlier in the year. I wished Bill still had his Riva
Yamaha Wave Raider 700 so I could use it to make a
benchmark comparison against. It was gone and its
replacement (the XL 1200) was no slouch in the speed or
handling department. I knew very little about the XP
Limited - but after looking at the numbers it wouldn't be
slow.
-
- During one of our "site seeing" tours of the lake the
three of us (Jason aboard the XL1200, Bill on the XP
Limited and me on my GP) found a large inlet where the
water was relatively smooth. Smooth enough to do some
preliminary (ahem) testing. There was about 4 to 5 inches
of chop in this large cove (more like a branch of the
lake). It was there that the personality of these three
machines was discovered and directly compared for the
first time.To start things off Jason and I ran against
each other. You can imagine my surprise when I raced
against that 1200 and faired very well - beating it in
fact by a bit. During repeated attempts I could
consistently pull the large triple by 3 to 4 boat lengths
out of the hole. Remember, the power to weight of these
two machines was now very close (4.60:1 for my modified
GP and 4.51:1 for his XL). Through the middle of the
power range and even on the top end the XL1200 was not
able to recover from its starting line deficit. After a
short time Bill joined in on the post-adolescent fun (for
he and I anyway). Armed with a new XP Limited he had
plenty of machine between him and the liquid surface. The
three of us lined up to race. Though most of my attention
was being spent on my driving experience (I didn't want
to screw up) I gave a small peripheral glance and noticed
both of the other machines were playing catch up against
my torquey little GP. When my 760 was topped out and
running just below the rev limiter (it could go no
faster) Bill went by the two of us and began steadily
pulling away. The race between the 1200 and 760 was too
close to call, but it was clear that Bill's ride was
faster on top - by at least a few mph. After several more
runs which turned in the same results we found ourselves
at the end of our smooth/clear water and onto the more
mainstream and much choppier (about 8 to 10 inches of
chop) water.
-
- On that kind of water the outcome was definitely
different. Even though I could still pull ahead of both
of the other boats from a standing start, the XL1200 was
able to pull ahead of my GP760 through the middle of the
speed range and keep it up through the top speed and
slowly keep pulling away. The Sea-Doo also showed a
better personality in the cut up chop by pulling away
with even more ease and enthusiasm - it could easily walk
away from either of us on top. There was no way my GP
could make up the ground (water) it lost through the
rough stuff because the choppy top had it sucking air
instead of throwing water. It became clear that the other
boats with their larger engines and bigger pumps could
recover from cavitation much more quickly. They could
regain acceleration sooner if the pumps lost their prime
in that kind of rough water condition.
-
- During our week long stay the time came when we found
a cove with water that was very, very smooth. We had to
do some more testing (ahem). Once again we found
ourselves acting like little kids with new toys. The area
was smaller for that test (ahem) but the water was very
smooth and flat. Jason and I started the racing. Time
after time I could get a great holeshot on him and keep
the gained distance through the entire speed range - he
could not catch up. In fact I was very slowly pulling
away from him. The 1200 just could not win against the
760 on that kind of water. Even when racing for the
longest distance the area would allow the outcome was the
same. When Bill entered his XP into the mix it become
even more fun and interesting. Once again the 760 easily
pulled the other boats from a standing start - by about 3
to 4 boat lengths. It would lose all the advantage to the
Sea-Doo once its smaller engine was out of RPM's, power
and/or impeller. The 951 cc twin of the XP could put its
power to the water very well - especially up on top. It
let that boat show its style by outdistancing the
competition in (almost) humiliating fashion. It must have
a 4 to 6 mph advantage on top.
-
- Late one afternoon after towing the kids around on
their tubes and wake boards I looked across the water in
the cove where we were parked and noticed an unfamiliar
sight. Glass. The water was as flat as water can get.
Barely a ripple in sight. It's shiny surface showed a
near perfect reflection of the surrounding land. I
climbed aboard my GP and headed out to make some speed
runs. Within a couple of minutes the on board speedometer
registered the highest reading it has ever showed me. I
briefly saw 64 MPH before it settled back to a solid and
unwavering 63 mph. I was able to duplicate that speed
reading on several attempts. I do not have a radar gun so
comparisons come in handy. In an issue of PWI magazine I
noticed a test of the 1997 GP760 with and without a Riva
Yamaha RPM Engine kit (September 1999 issue). Their
baseline testing showed the GP760 to peak at an average
of 50.57 MPH @ 6800 rpm (stock - without the RPM kit).
After installation of the kit its peak speed increased to
an average of 53.98 MPH @ 7100 rpm (an increase of 300
rpm ). I checked the Riva web site and noted the price of
$1222 for that engine kit. PWI magazine also lists the
stock 1998 XL1200 as being able to achieve a speed of
54.47 mph at its peak according to their radar gun and
the top speed of the stock Sea-Doo XP Limited (1998 test)
averaged 62.63 mph.
I did the math. It seems possible (if not certain) that
the modifications I performed may have produced more
favorable results than the $1200+ Riva bolt ons. Judging by
the numbers, I may have gained about 1 MPH over the Riva
equipped GP Wave Runner. The Riva Yamaha RPM Engine kit
consists of a new tuned exhaust pipe, a Pro Series billet
head, carburetor adapters, flame arrestors and a jetting
kit. I find it interesting that the fuel octane requirement
for their engine kit is 93 and the static compression was
175 psi. I'm running virtually the same compression (175 up
front and 170 in back) and 89 octane is the minimum octane
requirement according to my engine building software
resources. I suppose the pricey tuned pipe could account for
the increased octane requirement.
The results were in and I could live with them. It became
clear that the overall power was increased (and perhaps the
top speed as well as evidenced by going as fast as the
XL1200) after performing the engine modifications to my
GP760. In stock form I doubt its 5.22:1 power to weight
(weight to power) ratio would have been able to stay ahead
of or even with the 1131 cc mill of the XL1200. After riding
my GP760 this summer it is clear that the octane I am using
is fine and the modifications I chose to perform were very
inexpensive and extremely productive. I'm glad I had the
opportunity to race against such premium competition while
vacationing. It felt good to know that under certain
circumstances the little GP could definitely strut its
stuff.
Rick
|
