Lightened Flywheel - will it help Holeshots?

[Oz Dude]

Hi All,

After a good weekend testing we are now looking for a bit more out of the hole than what we already have. Will a lightened flywheel allow the motor to spin up faster and thereby allow me either a faster holeshot OR go to a higher pitch with the same holeshot as now.

We are towing 2 skiers on race skis with a 17.5ft lightweight boat and using a 1999 injected 3L Merc with the 250 ignition ecu.

All opinions greatly accepted :)

Thanks,
Oz

[Simon]

Yes it helps the holeshot and acceleration.

[Oz Dude]

Hi Eric,

Thanks for the opinion. I thought it would but wasn't sure. I used to have a little BMW Z3 that had been supercharged and it had a lightened flywheel in it's list of mods and it used to spool up very quick off idle. I figured a 3L Merc wouldn't be much different in concept (without the s/c of course!).

Is there anything else that is simple and cost effective I could do to improve our holeshot??

Thanks,
Oz

[kostas74]

Are any disadvangages when lightening the flywheel?
Why dont factories make it lighter from the begining?

[Raceman]

Are any disadvangages when lightening the flywheel?
Why dont factories make it lighter from the begining?

There aren't any real disadvantages, as long as it's not lightened enough to make it weak. A lighter flywheel is easier on the top of the crank/crank bearing. On some heavier boats with a lot of pitch a light flywheel MIGHT make it have a tendency to make it stall when shifting from neutral into gear. I've never experienced that myself but have heard a couple of people claim they did.

As far as acceleration advantage, on a race boat, ESPECIALLY drag boats, where small differences are important a light flywheel is worth the effort/money. On a lake toy or ski boat it's doubtful you'll feel much of a difference.

As far as lightening from the factory, it would add to production costs and would have limited advantage on a large percentage of applications.

[Simon]

The factory 3.0l flywheels are 14lb's stock. I lighten them to 11 lb's. You will not have a problem with stalling or breaking. You will feel a big difference in the hole shot and the acceleration.

[MENNO]

higher compression heads will give you the most gain in holeshot

it was lower compression heads from factory in your year engine

or add a little prop ventilation for holeshot
what i experienced with my 3.0liter was that it needs the small pvs vent plugs in the prop if you give it too much ventilation holeshot will suffer from it





Hi Eric,

Thanks for the opinion. I thought it would but wasn't sure. I used to have a little BMW Z3 that had been supercharged and it had a lightened flywheel in it's list of mods and it used to spool up very quick off idle. I figured a 3L Merc wouldn't be much different in concept (without the s/c of course!).

Is there anything else that is simple and cost effective I could do to improve our holeshot??

Thanks,
Oz

[Oz Dude]

Raceman - you're thought is that any application outside of a drag race situation will provide negligible improvement (if any at all). Like all sports, when you are chasing every single last HP increase, this would make sense to do as a mod but for general racing where you aren't pushing for the last drop out of everything the motor has, it shouldn't make any improvement.

Eric - you on the other hand have said that it will make a big difference in the hole shot and acceleration of the motor. Are you referring to the same application as Raceman (drags) or are you speaking in general terms.

More specifically, as we are pulling a lot of weight behind the boat out of the hole (2 skiers @ 200lbs + drag from skis/suits), do you guys believe that a lightened flywheel would make a difference to our scenario. Other than a rebuilt powerhead (no performance bits though), there are no other race parts on the engine (well, yet anyway :)).

Menno - the fuel we have here in Oz is crap. Our best grade of unleaded is equal to your 91 octane so we can't push bigger compressions in the motors without switching to race gas and, as of next year, race gas will not be allowed in our sport so there's no point coverting to it now.

We are also playing with props at present. Rather than too much ventilation, our problem is the motor keeps bogging down (hence my original question if a lightened flywheel would help). What we have now found with a couple of props is that we can get a reasonable hole shot but I have to be ready to back off the throttle as we come up out of the hole. As the boat starts to plane (and as the skiers pop up), we get massive ventilation that can't be recovered from. I have found though that if I can modulate the throttle just as it starts to break loose, I can control it until we are properly on plane. Not the ideal situation but it's closer to a good result than what we had previously.

Thanks,
Oz

Thanks,
Oz

[Simon]

I am talking about 3.0 flywheels.


Raceman is talking about 2.5 flywheels.

[jay j]

Didn't The 3.0 Litre Have Alot Of Water In The Leg That Had To Be Released So The Exhaust Could Exit Which Caused Alot Of The Bogging? Dewitt Deweese Had A Fix To That Which If I Remember
Was Cutting The Tuner Above The Water Line And A Few Other Things. Eric Might Have More On This.

[MENNO]

what speeds do you get now and what props do you use ?
at what pitch

i don`t know if the flywheel will make big difference in the way you use the engine
but i think Simon is the expert on the 3.0ltr engine tuning
he may have tried it on a ski boat or aheavier boat

try an 4blade offshore vensura prop for faster take offs
if 23 pitch is enough for you (that is the biggest they make)
it is a smaller diameter as the rev 4 prop
and will rev up easy with heavy skiers

or an tempest plus prop for little more topendspeed and decent takeoff
play with the ventholes

with an rev4 prop you might loose a little on top end
but have good take off

how much compression do you have on this engine now ?
little differences can make huge gains


More specifically, as we are pulling a lot of weight behind the boat out of the hole (2 skiers @ 200lbs + drag from skis/suits), do you guys believe that a lightened flywheel would make a difference to our scenario. Other than a rebuilt powerhead (no performance bits though), there are no other race parts on the engine (well, yet anyway :)).

Menno - the fuel we have here in Oz is crap. Our best grade of unleaded is equal to your 91 octane so we can't push bigger compressions in the motors without switching to race gas and, as of next year, race gas will not be allowed in our sport so there's no point coverting to it now.

We are also playing with props at present. Rather than too much ventilation, our problem is the motor keeps bogging down (hence my original question if a lightened flywheel would help). What we have now found with a couple of props is that we can get a reasonable hole shot but I have to be ready to back off the throttle as we come up out of the hole. As the boat starts to plane (and as the skiers pop up), we get massive ventilation that can't be recovered from. I have found though that if I can modulate the throttle just as it starts to break loose, I can control it until we are properly on plane. Not the ideal situation but it's closer to a good result than what we had previously.

Thanks,
Oz

Thanks,
Oz[/QUOTE]

[Oz Dude]

Eric - now that explains a lot more. BIG difference between 2.5 & 3.0 as well as the application being used. Thanks for clarifying that for me. Can you also shed further light on the point jay j made about water in the leg? We are very back end heavy at rest so the motor is a long way down. For noise regs I can have the thing scream it's head off with open exhausts but I'd like to know what "fixes" are available.


menno - props are really hard to come by down here so we've been a little limited in what we can try. What has complicated matters further is that when the motor first went on the boat, it had a powerhead issue. That was fixed but then there was a fuel issue (unknown at the time) so we swapped motors to a spare which was a bit tired. We've now got the good motor back on, with a rebuilt powerhead, good compression, and from last week's run, it would appear that our revised fuel sytem (new from tank pickup to motor) has cured more ills. We are now going to go for a full course run early on Saturday morning (70 miles) with a 23P Laser II (old style - square vent holes) and that will tell us how solid the power train now is.

So far with the "refreshed" combo we've has success with the 23P Laser II and a 26P Tubed Cleaver. The Cleaver did pull them out but it was a bit slow so they had to drag for a while. It is also a home-made prop so not sure of the specs on it. We tried a drag-style solid hub prop in a 26P and it couldn't get enough forward motion to get past the initial venting.

I have a 28P Trophy Plus that previously worked on my old setup but that was also with a 1.87:1 gearbox. In the current configuration it bogs down too much and won't spin up. I have the large plugs in there at the moment and, for the sake of the exercise, I am going to take the pluds out all together and see if the new "refreshed" combo has the mumbo to get it up and out.

Ultimately we will need a 28P to race in the bigger classes and be competitive. It's now a case of trying to find something that will give us enough initial slip to spin the motor but then also give us the grip we need to get out of the hole.

Can anyone shed light on the Aerostar Props? I don't know anyone who has used one down here and so far I haven't seen anyone talking about them over there. The theory sounds right for the application we have but it's a lot of money to shell out for something that then might not work...

Oz

[Kings Marine nz]

Hey OZ
have you tried a lightning et ?? a lot of ski racing guys over here are using this prop which works really well, on a rig like yours you should be able to swing a 28" or 26"
also with the probs of the older 3.0 ltr bogging down try setting TPI as lean as poss. at idle but make sure you still get the WOT volts as per spec.

[THE HOGG]

eric is the man!!! he has forgotten more thatn i know. yes, i have a simon cut wheel. have you looked at the taylor mids? their 15" offshore is sweet!!! what gears now??? 1.62's? i changed from 1.87's to 1.62's and have so far i have been un-happy. i just got an absolutely beautiful wheel from leading edge that im dying to try though:D.

[Oz Dude]

Kings Marine nz - we tried a Lightning ET a couple of weeks ago. Just vented and went nowhere. This is the problem - we're caught in the middle - either get all ventilaltion and no forward movement or no ventilation and no forward movement.

We're running a borrowed 23P LaserII at the moment. It pulled out very well on the weekend and will run us for the Bridge Race but we need a more permanent solution. This particular prop vents once the boys pop out of the water and the boat comes on plane. If I don't catch it by backing off the throttle, it just continues to vent and we literally slow down and fall back into the hole. It's like the motor can suddenly get full gas and it overpowers the prop.

We also had a homemade 26P Tubed Cleaver. Fairly small diameter and the tube allowed gas to pass over the hub. It did the same thing as the LaserII. As soon as the boys pop up it would vent. As long as I can catch it we're ok. It did drag them for a while though - too long for my liking. I'm hoping to get me hands on a couple of more props after the Bridge to Bridge and we can do some more testing.

I also want to check the TPI voltage and play with that a little after the Bridge. We ran the full course as a practice on Saturday and it went well so we'll keep the setup as is until we run and then we can play again.


THE HOGG - we changed gears from 1.87:1 to 1.75:1 so not as drastic as yours but yeah, the difference in the torque is more than I thought it would be.

Oz

[MENNO]

the laser is not the right prop for what you are doing
you need big hub trophy or rev4 or offshore vensura
or mirage plus tempest plus
much more pulling power for 2 skiers

i have 21 feet boat with 225 3.0ltr merc carb on it
i have tempest plus prop now with small ventholes in it
23 pitch take off as a beast

i have tried laser props but they have a lack of take off especially with heavy loads

what speed are you running at what rpms ?

[olmo40]

Hi Oz,

Just a thought how heavy are your skiers? Do they start wrapped or unwrapped,
Having a skier who can get way forward over the ski can be a big help in engine class racing .
:)

[Oz Dude]

Menno - now that we have a fit motor and fuel system we are going to go back over all the props we previously tried to see if there is an improvement. The reason we ended up with the Laser II was because without the vent holes, a big hub prop just bogged and we couldn't pull out. I have a 21P Quicksilver (so full hub / no vent holes) and it wouldn't even pull us out of the water. That's why it was getting so frustrating!

As I said, we'l lgo back and do some more testing now but when I look back at my old setup and old motor, other than it being a 1.87 gear box ration, the only other big difference I can see is that we were running a whale tail. I'm just wondering if that's making a difference.

Of course, if the exhaust is being restricted more in the current motor than the old one, THAT's gonna be the giggest culprit.

Eric - if you're around, can you comment on whether or not a 1999 3.0L 225 Injected motor suffers form any exhaust restriction that a 1994 3.0L Carb motor wouldn't have had?

olmo40 - dude, you Aussie?? How else would you know about wrapped starts?? :) At the moment they are starting unwrapped cause they are both new to the sport. After the next race, we're gonna start getting them to practice with wrapped starts. As for weight, yeah, they're both big boys coming in at 220lbs a piece. The two of them together weigh as much as my boat when it's bare!!

Oz

[olmo40]

Skied a lot in oz in early 90s,I think your problem is partly with the weight of your skiers.I think a trophy 4 blade will be the go .As you know some skiers just pop up on the water and some impersonate submarines.

[Oz Dude]

Yeah and I got 2 subs!! I wonder how they'd feel if I said go on a diet :p

One of the guys only just figured out (with some hints from those observing on the bank) how not to go down "dive dive dive" style which is helping a lot :)

I have a 28P Trophy Plus 4 blade which used to work perfectly on my old setup. When we originally tried it on our new setup it wouldn't even pull the boat out of the water, however the motor now has a rebuilt powerhead and a rebuilt fuel system so we have to try it again. We've also gone from a 1.87:1 gearbox ratio to a 1.75:1 so that obviously has a big impact.

Now that the motor is more healthy than previous, if I can pull out with my 28P Trophy Plus then we'll be sweet. If not, it's back to the drawing board...

Oz

[ghind]

Do their skis have double boots? You are asking a lot to pull two big fellas out two feet in with a tall prop. Easiest solution is to get them to drag a leg.

91RON is standard fuel here in Australia. Premium is 95 and you can get 98. I'm sure you could increase compression for 95 or 98 RON.

[gmjim]

From what i can see, our 98 RON is the equivalent to the 93 AKI sold in the US. Just rated differntly to give different numbers.

[Oz Dude]

ghind - Yep 2 boots. If ya want to go fast ya gotta be strapped in. Makes it harder to get out but far safer for the skiers. They just gotta learn to tuck up a bit tighter :)

gmjim - our fuel rating uses the RON method where as the USA uses both the MON and RON method. MON is a far better measurement of Octane in fuel. It goes something like this:

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane rating, shown on the pump, is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, the octane shown in the United States is 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, is 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and some even deliver 98 (RON) or 100 (RON).

Typically the 91 avail in the USA is the same as our 98.

Oz

[gmjim]

Yeah thats the info i read, i figured AU98 to be US93 going of the "4 to 5 points lower" eqaution in the last paragraph?

[GTRMick]

There is something wrong there. I have a kevlar 1850 with a stock standard 2002 225 EFI merc. My social ski prop is a 23" trophy plus and with that on, it will pull 3 skiers and pulls me oout of the hole faster than any centremount I've skied behind.

With a 28" TE cleaver, I can pull a skier out easy enough.

[Oz Dude]

Hey GTRMick - I have another thread on here that goes into a lot more detail about the issues we've been having.

It's been a lot better over the past 3 weeks. We revamped the whole fuel system and the rebuilt powerhead now has several hours running on it.

After the Bridge race we're gonna go back to testing props again to see what gains we've really made.

I need to get my hands on a 28P TE Cleaver cause everyone reckons that's the go. Does it hook up fairly quickly with your set up or do you drag for a bit??


gmjim - typically the gasoline avail in the USA from the pump is 87, 89, and 91. From what I've read they're roughly equivalent to our 91, 95, and 98. Basically our fuel is crap :(

Oz

[Oz Dude]

Yeah thats the info i read, i figured AU98 to be US93 going of the "4 to 5 points lower" eqaution in the last paragraph?

gmjim - further to what we tere talking about last week re Octan Ratings, here's an excerpt from a Mercury Press Release:

Will Help Save on Fuel Costs,
X-haust Noise Reducer Kits Released

FOND DU LAC, Wis., Oct 8, 2008 – Mercury Racing (http://www.mercuryracing.com/) is pleased to announce the fuel requirements for the 600 SCi sterndrive engine package have changed from 91 posted octane (R + M)/2 (98 RON), to a new minimum posted octane requirement of 87 (R+M)/2, (91 RON). The change affects both current and late model 600 SCi sterndrive engine packages. Mercury Racing engineering made the fuel requirement change after reviewing over two years of engine run data which validates that the difference in fuel grade does not adversely affect engine life, power or performance. The only measurable change consumers will notice is a savings at the pump.

As you can see, 87(R+M)/2 is our 91 RON and 91(R+M)/2 is our 98 RON. Just thought you'd like the info.

Oz :thumbsup:

[gmjim]

Yeah, sweet, i was looking to get my heads cut soon to, might have avoided a costly mistake!
cheers!

[Roddles]

Hey Oz Dude how are ya?If you go with what the winning teams are using(generally speaking) then you should have a baseline to start with.You probably know this part that Im going to say:Make sure your engine height is (centreline of prop shaft)approx 40mm under the plank/pad.This should be your starting position and you can adjust up or down from there accordingly.Im assuming you are racing in SMOC?Other thing is sometimes the skiers have a technique that needs some work.Im not saying that they are at fault but you do need to address every aspect of ski-racing.What Boat are you running and what configuration is it at?How heavy are the skiers?Just a few of many variables to check.

[Wizard]

Couple of things. One the 98 EFI has a very rich ECU. Get a Brucato ACU and you will see a huge improvement in performance across the board plus a big gain in fuel milage.

Second is props. All of the exhaust is being vented through the gearcase on that motor. So venting is critical. A vented four blade prop like the Trophy or Bravo will give the best holeshot without sacrificing top end. A 26 Trophy would probably be best. Get a ring to close the gap between the prop and gearcase then get a set of solid plugs. Start drilling holes in the centers of the plugs with differnt size drill bits until you hit the perfect holeshot. Get two sets so if you go over you can reproduce the right combo.

Finally are you using a hydraulic jackplate? That may really help as you can find the best engine height to holeshot and move it up for top speed. :cheers:

[Oz Dude]

Roddles - I hear what you're saying re baseline starting point however there aren't many Bullet 1750's around anymore in ski racing so trying to do what others are becomes a little harder. We do have heavy skiers (210lbs each) and that's obviously a big part of the problem but I can't chop parts of the moff so we have to deal with it. They also need to learn how to pull out a bit easier. The boat has only a small planing surface and this is only multiplied by their starts.

We aren't racing in SMOC for the reason that one of the guys doesn't want to go that fast. Also we would only be eligble for MOC as the ECU and throttle case are off a 250.

We ran this season in 60mph but will upgrade next year to 70 (or 80 if they bring it in) but that's as fast as my guys want to go at present. One advantage we will have next year will be longer ropes. In 60mph you can only run 100ft lines but next year we will be unrestricted. An extra 100ft will help with a bit of spring in the ropes out of the hole.

Re engine height, we are running a hydraulic jack plate so we can vary height between 25mm below the pad (top) and 105mm (bottom).


Wizard - the Brucato ACU is on the list after we try a few more configurations with props, etc but thanks for suggesting it!

I have a 28P Trophy Plus that used to work perfectly with the old setup (3L Carby engine with a 1.87 gear ratio) but now it's a slug out of the hole. Boat only it will spin up and get going but it can't pull one slier out, much less 2. I've also found it wants to lift the bow a bit too much and makes the boat squirly.

We have had fairly good results with a 23P Laser II (square holes) so I'm now waiting on a 24P to show up to try out. It becomes a bit of a balancing issue with the prop as it wants to blow out as soon as the boys pop up out of the water but as long as I can catch it by backing off the throttle and then leaning back on it we seem to be ok.

I've also been told to try a TE Cleaver - seeing if I can get my hands on one at the moment. Not sure if it will just vent and go nowhere though. I can't pull a skier out with my 26P Mazco so not sure how different the Cleaver will be.

Re closing over the holes and drilling plugs, with the 28P Trophy plus I had removed the plugs altogether and we stil lcouldn't pull one skier out so I don't think we'd have much success with a 26P and 2 skiers. The boat just seems to bulldoze it's back end through the water too much.

I'm hoping to put a whale tail on it in January to see if that helps us with our hole shot problem. Perhaps the props will react differently if we can get the nose down faster.

I've identified another anomoly with the boat now as well. We'll be able to confirm more next time we get it in the water, but 2 weeks ago I ran a 21P Laser II for a practice run and, boat only, we got 75.5mph. When you use the prop slip calculator it gives negative slip numbers.

I started checking things. The gearbox is definitely 1.75 so now we're wondering if the ECU has been modified to give a 7,000rpm limit. I would expect 5% slip with a prop like that and using the 7K limit, the calculator delivers the correct results.

Once I can get it back on the water after Christmas with a 23P Laser II, I'll be able to see what that tops out at. That will at least prove if it was prop related.

If the ECU does have a higher rev limit, this will help with prop selection as I won't have to go as high in pitch to get the numbers I need for 70 or 80mph.

Thanks for the input guys - greatly appreciated!

Oz

[olmo40]

I assume you are using a quick release system off the ski hooks ??

[Jay Smith]

I have built MANY OS ski race engines from Europe and they all used light weight JSRE modified flywheels ( 2.5's ) I also sell allot of parts going to NZ used in the ski race circuit ... ( Flywheels, Wizard pistons, 1" spacer plates ,etc )

BTW: a JSRE engine rigged boat won the Diamond Series this year in their class. They are from Super Mare, England ( The Dowlings ) ...

The lighter flywheel WILL help acceleration and is easier on the upper bearings...That should be "common knowledge 101" about rotating mass weights and acceleration.

my .02

[Roddles]

Hey Jay do you make hi-po stuff for omc/brp engines?

[Jay Smith]

Sorry no, the "dark side" engines keep me very occupied..:)

Jay

[Oz Dude]

olmo - yeah - definitely using quick releases. You have too much of a "God moment" without them. You know, looking straight up at the sky and saying "Why am I here God?" :)

My guys also don't do wrapped starts yet. That's the next thing to learn but we'll see if that worsens the hole shot due to the changed posture...

Jay - thanks for the input. As I understand it, the resip[rocating mass of these 3 Liter engines is pretty heavy anyway so taking weight out of the flywheel should see an improvement IMO. I think at the start of this thread I compared it to a Z3 I used to own which had a lightened flywheel and that thing used to spin up like nothing else. 2.8L S6 Vs 3.0L V6 - similar weight so similar theory.

Do you find the 1" spacer plates make much difference or are these more od a 2.5L specific improvement?

Oz

[Jay Smith]

A 1" JSRE intake spacer and our angle cuts to the plates and rear of horn on the 2.5's will pick one up 250-350 rpms with no other mods....

Cheers,
Jay