Thread: Lako Stealth Stacks
01-24-2008, 11:31 AM #1
Lako Stealth Stacks
Stealth Stacks installed in the test SL1050 Time to hit the water for the next phase of testing of the LAKO Stealth Stacks in the real world as recorded by our Stalker ATS system using a controlled loop testing scenario. We averaged four runs each with and without the Stealth stacks. The testing backed up what we saw on the bench; most of the gains were in the bottom and mid-range of the speed/time curves, i.e., 0-50 times dropped by almost a second! Mid-range pull was much sharper than before and the top-end speed stayed the same (just got there quicker). This is even more amazing when we reveal that stock jetting was in place! The only change to fuel was to keep the low speed screws at 3/4 turn. At the 3/4 turn setting and the stacks removed, the SL1050 had a bad lean bog off idle, the stacks helped this problem to the point of eliminating it. This is due to the laminar flow achieved over the low speed circuits instead of turbulence. We have been successfully using these kits on any Polaris 700, 800, 1050 and 1200 engines installed in Virages, SLs, SLXs, etc. If it has a Keihin carbs with a 3mm step from the airhorn to the carb throat, these Stealth stacks will help. Since we made a short production run, quantities are limited.
01-24-2008, 01:01 PM #2
- Join Date
- Jul 2007
- near Toronto, Canada
Carburetor efficiency rant
So the whole purpose of these Lako stacks is to create a smooth, non-stepped transition between the base of the stock Polaris flame arrestor and the Keihin carbs. The OEM stepped intake transition causes flow turbulence, which affects the carbs ability to manage the fuel mixture.
I have never been a carb guy, just fixing them when they gave me grief on whatever piece of equipment they were mounted (car, lawnmower, snow blower, etc). Mostly other people's gear - I try to take care of my own stuff. Actually, I don't own anything with a carb...
Now, the more I read about PWC carburetors, the more I am amazed how sloppy and wasteful they are. The operating fuel air mixtures seem to be all over the map, even on a well tuned set up. The ideal stoichiometric fuel:air ratio seems to be very roughly delivered, especially over a range of throttle openings and engine RPM.
Mikunis seems to be worse than Keihin for fuel waste, but that may not be saying much.
Piston wash seems to be a term for unburned fuel exiting the cylinder. Elsewhere I have read that a well running 2-stroke with carbs is still discharging something around 40% to 50% of the total fuel input right out the exhaust, unburned. That percentage number may be on the high side, but there is plenty of fuel going out the exhaust.
Between the jets, adjustment screws and various circuits and venturis, it seems that the actual fuel:air mixture varies wildly with RPM and throttle position. Pop-off valves that leak fuel into the intake with engine vibration, and so on.
PWC are not a particularly fuel efficient form of entertainment, of course, but to think that a season of riding a carb'ed boat is the equivalent of pouring 1/2 of the entire fuel budget onto the ground, vs running a fuel injected model, gives me pause.
It seems that a really well running carb set up provides almost as good throttle response as a decent direct fuel injection motor, while burning substantially more fuel.
Many seem to be turned away by the apparent complexity of modifying and working with fuel injection systems, and the apparent learning curve. Carbs seem inexpensive to buy and install, but I think that when one adds the cost of extra fuel over multiple seasons, carbs are not so cheap.
The Polaris Ficht system may seem to be hard to modify, but I think that is mostly due to limited familiarity and availability of the needed tools and information, rather than the system itself, which seems functionally straightforward.
Not sure why I got onto this tangent... I just keep encountering examples of how inherently fuel sloppy carbs are, at least for PWC applications.
I have been toying with the idea of buying an SLX next winter, and swapping in a 1200 Ficht motor, just because using carbs seem so sad.
If I ran the boat for a few years, the savings in fuel usage might even pay for the Ficht swap. Even if it doesn't, I wouldn't feel so bad about whats going out the exhaust... And it would be a different project from the norm!
Last edited by K447; 05-09-2010 at 12:37 AM.
01-24-2008, 01:43 PM #3
01-24-2008, 09:25 PM #4
01-25-2008, 07:57 AM #5
Any Body Notice The 1 Second Acceleration Drop???and No Gain In Rpm,mph Or Top End Performance,yes The Stock F/a Is That Good
01-25-2008, 11:08 AM #6
They are awesome but I'll take the aftermarket as most still flow better than the stock units, even with the lako's. You can install the water socks (not so with the stock Flame Arrestors), the ease of tuning makes them worth the money alone, then there's the bling factor and ease of removal during single cylinder repair.
For me I think the single most important thing is keeping the water out of the engine. I can't tell you how many times a simple water sock would have saved an engine.
Seats aren't mounted correctly, a seal goes bad, speedometer hose comes off, water rail gasket leaks etc.
Don't get me wrong, the Lako's DO work, I just think there's a better option in terms of flow and safety during the modification process.
01-25-2008, 12:26 PM #7
Can you post the graph from the Stalker ATS gun for us?
01-25-2008, 04:00 PM #8
I'll Agree On All But One Point,the Stock F/a Flows More Than Enough Air For Any Stock 40mm ,sleeper Modded 40mm ,and 42mm Racing Keihin Carb,my Personal Flow Bench #'s Back It Up As Well As Group K's,any F/a Adapter Listed To Fit Polaris Keihin Carbs Is Usually For The Bigger Throat Of The 38mm's And Not The Smaller Throat Of The 40's,ask Absentx He Had Exactly That Happen To Him,so To Get The Correct Adapters For The 40's You Get Them For The Kawasaki 40's Which Has Two Equal Length Bolts Which Won't Work For Polaris Intakes.so If Somebody Knows Who Sells The Exact Adapters For Polaris 40MM Carbs And Not The 38'SDo So Here....so If I'm On A Budget I'd Rather Spend 63.00 On The Inserts & 150.00 On Carbon Tech Petals For A Total Of 213.00 And Get Very Noticable Gains In Throttle Response Then 200.00 For F/a's And Adapters And Get Something I Might Notice.although Matching F/a's,head Cover,and Pipe In Another Color Are Pretty Cool Looking In A Hull
01-25-2008, 09:43 PM #9
Prok makes matching adapters for both the 38's and 40's that go with either their Quick fit or Standard F/A's. They come with bolts and use the stock intake manifold. I have a set of each and each set cost me a grand total of $95...of course I scored these brand new items on ebay!
01-25-2008, 10:34 PM #10
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- Jan 2008
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