posted 10-26-2007 10:36 PM ET (US)     

http://www.mercurymarine.com/look_deeper/head_to_head.php?ID=57& Filter=3,4

Let's forget the really excellent perfromance on the Verado (we know those numbers are rigged!), but what is of interest to me are Merc's test results on the Yamaha F150 vs the Etec 150, supposedly where they have no preference to push. After all, as a 4-stroke, Merc would consider the hugely popular Yamaha F-150 as Verado competition, not the Evinrude 2-stroke.

If you remember, Evinrude did a video on the E-tecs pulling the Yamaha under water by the Evinrude, and also of the Yamaha 150 not being able to plane off the twin powered boat.

Mercury's testing, at least, disproves all of that baloney.
The F150 performs VERY well or better against the E-tec. Check out the acceleration (pullingpower) times. They are a dead heat. Here a non-supercharged 4-stroke matches the hole shot of a DFI 2-stroke. This is not the assumed condition. A Verado faster than a 2-stroke on acceleration I can believe, since I have hit the DTS throttle on one, and you can go out the back of the boat really easily. They are a rocket.

Honda and Suzuki owners may also be interested in the comparative results.

posted 10-27-2007 12:19 AM ET (US)            

There is a natural suspicion about the validity of the data since it was gathered and reported by Mercury itself. And it is not surprising that the Verado does well in the tests, otherwise they would not have been published.

With regard to the E-TEC fuel consumption, previous tests have shown that the E-TEC does tend to burn more fuel than the naturally aspirated four-strokes at mid-range and high-speed operation. However, the E-TEC has been extremely efficient at idle speeds, due to the use of a stratified charge combustion. The report from Mercury seems to omit this data point, and that is probably because it would have shown an advantage to the E-TEC.

posted 10-27-2007 01:47 AM ET (US)         

http://www.mercurymarine.com/look_deeper/head_to_head.php?ID=56&Filter=6

By using the E-tec data from both tests as the common ground, the Optimax and Verado can be compared, something Mercury NEVER does.

posted 10-27-2007 10:02 AM ET (US)            

I do find amusing the handicap disclaimer in the Mercury home grown head-to-head twin 300 test:

"* Suzuki engines were mounted lower to ensure they maintained water traction at higher speeds".

I think they used the wrong word in the disclaimer. I think they meant "friction", not "traction".

These latest low budget "look deeper" comparative tests bring back to mind that Mercury published a comparative test between the Verado 275 and the Yamaha 300 HPDI. In that test, Mercury handicapped the Yamaha 300 HPDI by overpropping it so that it would only turn 4500 RPM at WOT. In their eyes, that was OK because at WOT it was turning within the specified operating range of 4500 to 5500 RPM. Of course by doing that, the Verado would surely win the top speed and acceleration tests. It would also win a fuel consumption test if measured at 4500 RPM. But nobody would ever prop the Yamaha 300 HPDI that way in real usage.

So Larry, since you are so delighted with the low budget "Look Deeper" performance comparison that has absolutely no backup data whatsoever (what propellers, what pitch, what WOT RPM was achieved, how much fuel in each boat, how many people in each boat, dry weight of each boat, etc....), please tell us how to understand the gallons per hour graphic in the 150 comparison. I am particularly interested in the segment where they have a legend that says "4501+ RPM WOT". What does that mean? Does this legend give Mercury even greater latitude to take liberties with the competition like they have done in the past such as by overpropping the E-TEC so it will only run at 4500 RPM at WOT and then measuring fuel flow of all motors at 4500 RPM?

Of course, it really doesn't matter that much because comparing one motor's fuel consumption to another on an RPM to RPM basis is absolutely meaningless but I guess no one in the Mercury R&D department bothered to tell the Mercury marketing department. To illustrate using Mercury's own products, we can do an RPM to RPM comparison of the Optimax to the Verado and cast the Optimax in a negative light even though it is widely known that the Optimax is more fuel efficient than the Verado. For example, at 5000 RPM, the Optimax consumes 12.6 GPH but the Verado only 9.5 GPH. That comparison looks really great for the Verado, doesn't it, until you see that the Verado powered boat is running 8 MPH slower at 5000 RPM because it has a WOT max of 6400 (versus 5750 for the Optimax) and is propped and geared to reach that.

With respect to the graphic regarding the statement that the 150 E-TEC can cost $2,500 more to operate over a 5 year period than Verado, if you do the math, the difference in the hourly fuel consumption is 1.57GPH (1.57 GPH x 500 hours x $3.18 gallon = $2500). Again meaningless without any backup data. Is the 1.57 GPH difference across the entire operating range for both motors running at the same average boat speed or is this another meaningless RPM to RPM comparison of one motor with an operating range maximum of 5800 RPM versus one that runs up to 6400 RPM and would be propped differently?

What I do find interesting in all of this latest low budget comparative Mercury marketing material in a thematic way is how focused they are on bashing the E-TEC, just like Larry is. Contrary to what Larry wants everyone to believe, Evinrude must be doing something right for Mercury to devote so much of the comparative advertising's focus torward casting the E-TEC in a negative light on both the 4-stroke and 2-stroke fronts. It's impressive to me that a single product can apparently be taken as a serious challenge to both the 2 and 4-stroke formats. So Larry, if the E-TEC only has a very small dwindling marketshare and will never amount to much, as you say, why do they spend so much effort to bash it in the comparisons?

Lastly, comparative advertisements are dangerous for the advertiser if they are done in a sloppy manner like these home grown "Look Deeper" tests are. The leave the comparison open to many, many questions about the testing which is not a good thing.

Note to marketeers: If your product comparison requires handicapping the competition's product for your product to win, don't do a comparative advertisement like this one. All the handicapping or other misleading moves do is create doubts about the product that you want to paint as superior and creates doubts about the credibility of the folks behind the product. If you are going to do a comparative test, do it carefully. Get an independent tester to conduct the tests or evaluate the testing methods and results and don't handicap the competition, otherwise your published test results aren't worth the paper or pixels they are printed on in the consumers eyes. Consumers are far more sophisticated than these marketeers seem to understand.

posted 10-27-2007 06:04 PM ET (US)            

I found it interesting that the Honda 150 was excluded from the fuel economy comparison. Why do you think that was? If they had a Honda powered boat for the exceleration and top speed, why not the fuel economy test.

posted 10-28-2007 10:45 AM ET (US)            

One, four-stroke outboards do not make near as much low-end torque as two-strokes. Low-end torque determines performance in such areas as "hole-shot", and time-to-plane numbers. I thought this was pretty much understood. However I've seen some recent posts that are acutally trying to say that some 4-strokes are as strong, or even stronger in this area. That is just simply not true.

Two, even the mighty Verado, with it's screw-style supercharger, DOES NOT MAKE AS MUCH LOW-END TORQUE AS A TWO-STROKE OF THE SAME HORSEPOWER. This is even acknowledged by Mercury. Mercury touts the Verado as "the most powerful 4-stroke available". They do not say "the most powerful outboard, period", because even they know that even with a supercharger, DFI 2-strokes like their Optis, still make more low-end torque.

That said, I really like the Verados. They are without a doubt, the most powerful, 4-stroke platforms available.

posted 10-28-2007 02:08 PM ET (US)            

I may not be giving the Verado the low-end, torque "credit" it deserves.

posted 10-29-2007 11:38 PM ET (US)            

A DF 150 is almost 2.9L for a 4 cylinder.
It can swing a 16 inch prop.

The verado gets its power form the the super charger but from a smaller displacement engine.

When you stress a smaller block it probley won't last as long.

I own a Honda BF150 but its 2.4L struggles to twist a 15.5" prop , and rattles like crazy with such. I can run a 14.5 " and it runs pretty smooth but thats about the most i can get away with.

posted 10-30-2007 08:49 PM ET (US)            

I went on a long trip past San Clemente Island, which is about 57 miles off shore from mission Bay here in San Diego. I had about 730 lbs in passenger weight with a full load of gear and extra cooler with ice and managed 4.6-MPG.

The key is the lean burn system with an air-fuel ratio sensor . Under cruise conditions it pulls back the fuel up to 20%. It does work well.

The main draw backs with my Honda is the weight, and maybe lacking a bit of low end. It runs strong at the top end with that VTEC system . But I do my best to stay under 4,200-RPM as it sucks the fuel down quickly. Kind of reminds me of the two-stroke motor I got rid of.

posted 10-30-2007 11:51 PM ET (US)            

About the Honda BF225 you write:

Fuel consumption is an astounding 7.2 gals/hr at the operating speed of 21 knots laden.

About the twin Mercury 150 EFIs on the same boat you write:

...Merc 150 EFI's that sucked an eye popping 22 gallons per hour @ 21 knots.

posted 10-31-2007 09:25 AM ET (US)            

We don't need an indian chief or his medicine man to do some simple math.

I mistakenly attributed centerline's claim of good fuel economy to a Honda BF 225 when in fact he write that it is his twin Honda BF150s that get an astounding 7.2 gallons per hour at 21 knots. Astounding indeed.

7.2 gallons per hour at 21 knots equates to 3.35 statute miles per gallon. This on a 27 foot boat with a gross weight of 9200 pounds. Does this strike anybody else as absurd?

That is about the size of a Whaler 27 Full Cabin Whaler Drive with twin V-6 four stokes, full fuel, gear and ten passengers on board. 3.35 MPG at 24 MPH? I don't think so.

posted 10-31-2007 01:10 PM ET (US)            

There is no way that any, naturally aspirated, four-stroke, is going to run side-by-side to any DFI two-stroke, on hole shots.

Any test that says otherwise, is seriously flawed.

And another thing, the E-TEC 150, the Optimax 150, and the former HPDI 150, are all VERY CLOSE in performance. Not surprisingly, there all DFI 2-strokes!

I had to add that, because once again, by stating that the Yamaha F-150 "runs with the 2-stroke E-TEC", and NOT saying "runs with the 2-stroke E-TEC, and Opitmax", he's implying that somehow the Optimax performs MUCH better than the E-TEC. I know this is a penetrating glimpse into the obvious, but that is just pro-Merc BS.

posted 11-02-2007 08:51 PM ET (US)            

Internal combustion engines are rated for fuel efficiency by their brake specific fuel consumption (BSFC). The range of values for gasoline internal combustion engines only varies from 0.4 to 0.6 lbs/HP/hour, or in a ratio of 1:1.5. This is considerably less than the reported ratio of 1:3 observed. If the reported data is accurate, there must be other factors besides the engine change which contributed to enhanced fuel efficiency. A change in propellers could affect the resullts.

See:

posted 11-05-2007 07:30 PM ET (US)            

LOL.

posted 11-06-2007 05:24 PM ET (US)            

My first boat 31ft has twin 200 Optimax and weighs 10,000lbs
boat 2 is 23ft has a single 200 ETEC and weighs 5200 lbs.

I'm a Merc man but the ETEC is starting to impress me , you can't compare my fuel figures as the boats are too different but the one thing that no-one has mentioned is "oil consumption" and if you use your boats allot like I do you need to add this to your fuel consumption figures. The ETEC hardly uses oil compared to the Optimax it absolutely leaves them for dead in this department.

I still wear a black cap as there are days when I want to burn my ETEC but I'll leave that to another thread but overall the Etec performs well against the Opitimax with miserly oil consumption being its stand out feature.

Rob

posted 11-07-2007 02:53 AM ET (US)            

1. Equal horsepower engines will propel the same boat at equal top speed if propped correctly, assuming only the weight, air resistance (negligible probably) and hydrodynamic lower unit drag are comparable. Power is power is power. Equal horsepower engines will consume close to the same amount of fuel per unit time if putting out equal horsepower; any differences are due to varying internal friction and parasitic losses, plus possibly differences in fuel mixture.

2. Equal horsepower engines may have very different curves of (full throttle) torque vs RPM. This affects acceleration but has little affect on steady state performance. Stated another way, an engine that can produce greater midrange torque than another, does not "produce" that torque unless the boat is accelerating. A boat requires a certain amount of torque, converted to thrust by the prop, to go a certain speed. If more torque is applied, the boat accelerates. If not, nobody knows you have the "extra" torque available.

3. The RPM at which max power occurs is meaningless because lower unit gearing can trade RPM for torque or vice versa.

posted 11-07-2007 11:32 AM ET (US)            

quote:

---

4. The idea that 2 stroke engines produce "more torque" because of twice the power strokes is unscientific. Full throttle torque at any RPM is largely a function of how much fuel/air can be pumped, which is equal to the displacement times the volumetric efficiency. (Peak torque usually occurs at max volumetric efficienty by the way). For four strokes you multiply the displacement by .5, for two strokes by 1. But two strokes usually have pretty terrible volumetric efficienty. So you have to consider displacement, volumetric efficiency, and intake strokes per revolution all at the same time.

---

Do you have any scientific data to support this?

posted 11-07-2007 12:46 PM ET (US)            

"In a four-stroke naturally aspirated engine, the theoretical maximum amount of air that each cylinder can ingest during the intake cycle is equal to the swept volume of that cylinder (0.7854 x bore x bore x stroke).

"Since each cylinder has one intake stroke every two revolutions of the crankshaft, then the theoretical maximum volume of air it can ingest during each rotation of the crankshaft is equal to one-half its displacement. The actual amount of air the engine ingests compared to the theoretical maximum is called volumetric efficiency (VE). An engine operating at 100% VE is ingesting its' total displacement every two crankshaft revolutions.

There are many factors which determine the torque an engine can produce and the RPM at which the maximum torque occurs, but the fundamental determinant is the mass of air the engine can ingest into the cylinders, and there is a nearly-linear relationship between VE and maximum torque."

For two strokes, of course, there is an intake stroke ever revolution. However VE is significantly less. See, e.g.

A Textbook of Power Plant Engineering By R.K. Rajput

posted 11-07-2007 03:35 PM ET (US)            

Is it me or have all those nasty responses taken a vacation?
It's refreshing to see debate without the insults and bashing.

posted 11-07-2007 04:39 PM ET (US)            

Higher full throttle torque can certainly accelerate a boat through a high drag region and allow it to plane. But planing speed is a function of the hull (meaning the hull design, the weight and weight distribution, the angle of thrust being applied, and maybe other things). The hull does not know how much additonal thrust might be applied if the throttle were opened more.

For unaccelerated motion, thrust equals drag. Excess thrust (torque) accelerates. If the drag exceeds the thrust available at that throttle setting and RPM, the boat goes no faster. If the throttle is open, and the thrust equals the drag, that is called top speed. If the boat is heavily loaded, that top speed might be 12 mph. An engine able to produce more thrust at low RPM might allow the boat to accelerate and reduce displacement and wetted surface through hydrodynamic lift, which we call planing. All that assumes the factors of propeller design, trim, thrust angle, and the like are unchanged.

Why could one engine produce more torque than another at the same boatspeed? If all gearing issues are equivalent, better VE. If they are not, more gear reduction. Note that gear reduction (by gear or prop) is no free lunch because a large reduction gear means the engine might reach redline RPM while the boat is still able to accelerate.

posted 11-07-2007 05:34 PM ET (US)            

I do understand what you are stating about VE being easier to optimise with the valvetrain of a 4-stroke especially if variable valve timing is being used.

However, it has to be considerable more efficient to provide more power at low RPM when compared to a 2-stroke. Overall 2-stokes are more efficent per volume of displacement. Typically all the normially asperated 4-stokes are of larger displacement than the equilvant HP 2-stroke.

posted 11-07-2007 08:16 PM ET (US)            

Please see the link...
http://i65.photobucket.com/albums/h211/BigJayR/boating/E-TEC200specs.jpg

That's 83 pounds difference (if you were comparing the Verado 200 HP 25" shaft) and the E-TEC is a V6 not a V4 like the Verado.

posted 11-07-2007 08:49 PM ET (US)            

This where I got from plus I also own a 200HO hp ETEC and in the broucher I originally got it has the engine as weighing 516 pounds? It is sitting in front of me as I type this??????? The only thing I can think of is we are getting old stock here in Australia.

I'm not a plugging the ETEC and flogging the Verado infact it's the reverse I am about to replace my 15 month old Etec with the Verado.

posted 11-07-2007 09:27 PM ET (US)            

http://continuouswave.com/ubb/Forum4/HTML/005738.html

It's dragged on too long I over it.

posted 11-08-2007 12:52 AM ET (US)            

Well, not exactly. There is some energy loss to bearing and ring friction, of course, so the fact you have to run a 4 stroke twice as fast (equal displacement and VE) to pump the same air means more frictional loss, but the main losses inherent in the piston engines are "pumping" losses, heating and air friction incidental to pumping air. (Eliminating pumping losses is the theory behind the "variable cylinder" engines now being produced for automobiles). Two strokes have about the same pumping losses as 4 strokes if they are pumping the same amount of air. And any friction difference would be greater at high speed, not low speed.

"However, it has to be considerable more efficient to provide more power at low RPM when compared to a 2-stroke. Overall 2-stokes are more efficent per volume of displacement. Typically all the normially asperated 4-stokes are of larger displacement than the equilvant HP 2-stroke."

It is not more "efficient" per unit volume of displacement, but 2 strokes have an advantage per unit volume per revolution because they pump twice as fast. However, low RPM torque for 2 strokes is terrible, reflecting the inherently poor VE due to the problems of getting mixing intake and exhaust, scavanging exhaust, exhausting intake charge, etc. The value of 2 strokes was that historically they could run sustained at higher RPM because they had no valve train to worry about and because they had needle bearings (poor for low RPM high load, good for high RPM low load).

"Another factor to consider is that with a DI 2-stroke the VE is greater than with conventional 2-stroke. Consider that the fuel charge no longer has to pass through the intake port, the port can now be sized and tuned for just the combustion air as the fuel charge (and all of its mass) enters after the port is closed by the piston."

Thats an interesting idea, one I have never heard before. The mass of the fuel is small in relation to that of the air (about 1/14th), but it does take up 1/14 of the volume, so I guess you are right in a way. You get a free 1/14 of extra air I guess, all other things being equal. However, the energy required to do the direct injection has to come from somewhere, and it comes from running the high pressure pumps off the engine. But on the subject of VE, yes, maybe DI gives you 1/14 extra displacement. Never thought of it.

posted 11-08-2007 12:00 PM ET (US)            

quote:

---

reflecting the inherently poor VE due to the problems of getting mixing intake and exhaust, scavanging exhaust, exhausting intake charge, etc.

---

And as far as the hole shot, it isn't just the extra frictional losses of the 4-stroke, but, like you said yourself:

quote:

---

of course, so the fact you have to run a 4 stroke twice as fast (equal displacement and VE) to pump the same air

---

If 4-stroke doesn't spin up twice as fast as the 2-stroke it won't put the power out to get things moving as fast. Having double the power strokes at low RPM is a huge advantage when you are trying to move a stationary object.

Now I do agree in practical applications the form 0 rpm, 2-strokes need a little help which is why most well built outboard props have tunable ports in them (Merc calls theird PVS) to allow some slipage until you get in to the meat of the torque curve, but once you are there which doesn't take long, watch out.

Have you ever seen a 4-stroke in outboard drag racing

http://www.odbaonline.com/

posted 11-08-2007 12:44 PM ET (US)            

It's not really "double the power strokes" because the power strokes are not the same. While it is true that for 2 and 4 stroke motors of the same number of cylinders the 2-stroke will have twice the frequency of power strokes, but each 2-stroke power stroke will have a lower "amplitude" (force) than each 4-stroke power stroke. In a 6 cylinder 250 HP outboard, for example, the 2-stroke will have 6 smaller bangs versus 3 larger bangs for the 4-stroke for each crankshaft turn. In essence the power deliver of the 2-stroke is smoother because there is less of a gap between power pulses driving the crankshaft.

posted 11-08-2007 01:03 PM ET (US)            

I understand that the 4-stroke may be more efficent per power stroke (plus as stated above most 4-strokes of similar HP have greater displacement) but for this theory to work out each your 3 big bangs would have to produce greater power (force, work, or however you want to chose to calcualte it for this argument) than 2 of the smaller 6 bangs, and then still make up for the losses of the dead stroke and make up for the extra weight of the motor.

Like I said above, you don't see to may (if any) 4-strokes in outboard drag racing.

Heck, lets take this to a smaller scale. I will bet anyone that I can beat you in a dingy dragrace. Two identical dingys, I will put on my 15hp merc 2-stroke on one, you put on any 15hp 4-stoke of your liking on the other one and drag for pinks, LOL

posted 11-08-2007 01:21 PM ET (US)            

What I was trying to convey in a simplistic sense is that the 3 big bangs of the 4-stroke are the rough equivalent of the 6 small bangs of the 2-stroke. For example, if a 250 HP 4-stroke and a 250 2-stroke require 25 GPH to make 250 HP, then the fuel converted into useful work is spread out over 6 pulses per crankshaft revolution verus 3 pulses. The combustion product in each of the 6 pulses of the 2-stroke must be approximately 1/2 as forceful as the product of the 3 pulses in the 4-stroke.

The above assumes all pumping, frictional and other parasitic losses are the same, which they are not. We know this because the 4-strokes need more displacement to match the power curve of a 2-stroke.

posted 11-08-2007 01:31 PM ET (US)            

http://www.megoutboard.com/

Regards,

posted 11-08-2007 02:26 PM ET (US)            

What I am trying to say is the 2-stroke will build power faster in the RPM band, in other words greater acceleration. I agree top speed with be the same if you make adjustemts in weight to equalize them on the same hull.

Back to my dingy example, the top speed will be the same if they both put out 15hp (and you handicap my dingy with the extra weight), but I will get there first :)

posted 11-08-2007 05:50 PM ET (US)            

Remember, also, that it is thrust that is important, which is converted by the propeller from torque input. So it is not engine torque but propeller torque (allowing for the reduction gearing) and secondly propeller pitch, which must be considered in the equation.

A high revving engine can be geared lower, and thus produce more propeller torque, possibly, than a low revving engine. If all other things are equal.

What I said earlier was the design of the 2 stroke makes it problematic to achieve high VE at very low engine speeds. This is because the exhaust is not entirely removed, and the intake air is partially removed, unless there is a good powerful flow,i.e. higher mass velocities. This is true whether the engine is a carb or DI design. Extremely effective design (akin to variable valve timing in 4 strokes) may alleviate this to some degree.

posted 11-09-2007 02:14 AM ET (US)            

A decrease in VE does not however have anything to do with fuel economy. Less VE just means less air is pumped. If you meter the fuel accordingly, fuel mixture is unaffected.

Superior fuel economy in DI 2 strokes, over some 4 strokes, is due to: 1. less internal friction (needle bearings, more pumping per RPM); 2. possibly the ability to handle leaner fuel mixtures due to having no exhaust valve to burn; 3. lighter weight.

posted 11-09-2007 11:12 PM ET (US)            

Two strokes pump more per revolution, having twice the intake strokes, but not per intake stroke, so it depends on how you define VE. The way it is usually defined, a 2 stroke would pump twice the air as a 4 stroke, assuming equal displacement and VE and RPM. As it is, at equal RPM and equal displacement, the 2 stroke pumps something like 1.5 times the air. The difference is due to lower VE, due primarily to intake/exhaust mixing.

Here's a quote from a patent claim:
"As methods of scavenging in two-stroke cycle engines are conventionally known cross scavenging, loop scavenging, and uniflow scavenging. In this connection, if the amount of scavenging mixture is increased so as to improve scavenging efficiency, uniflow scavenging is considered to be most desirable, in order to obtain the highest scavenging efficiency without causing direct escape of the scavenging mixture to the exhaust manifold. In view of this, and in view of the aforementioned drawbacks, the actual application of two-stroke cycle gasoline engines has been conventionally limited to the field of small-size engines in which simplicity of structure and low manufacturing cost are essential conditions. Therefore, conventional two-stroke cycle gasoline engines presently used generally employ crankcase compression for scavenging. However, scavenging by crankcase compression cannot deliver a sufficient amount of scavenging mixture, thereby causing incomplete scavenging, which leads to a relatively low volumetric efficiency."
http://www.freepatentsonline.com/4254745.html

posted 11-10-2007 01:46 AM ET (US)            

.... I just have never seen anyone measure a big outboard or DI outboard's EGT.

The following link is an article on outboard EGT gauges and a list of manufactures.

posted 11-10-2007 10:26 AM ET (US)            

OK that is interesting. Peak EGT for 4 stroke engines at high power is typically upwards of 1700 degrees; metallurgical limits are imposed around 1650. Lean-misfire/detonation limits may be imposed before that. In a multicylinder engine, the EGT and mixture are a separate ballgame for each cylinder, although few have the intelligience to adjust fuel flow for independent cylinders. Usually the leanest cyl controls.

Without seeing a fuel mixture vs EGT plot for a 2 stroke outboard, I can't say what the resultant mixture is at 1300 degrees. Is that peak or far richer? I am inclined to think it is substantially richer, but can't say for sure.

The instruments sold in the website are interesting, but you have no control (other than throttle) of EGT in your outboard, unless you rejet (carbs) or reprogram (DI).

The art and science of leaning airplane piston engines fills volumes, and there is substantial disagreement among practitioners. It is a big deal, though, because running full rich doubles the fuel consumption and running too lean destroys the engine.

posted 11-10-2007 11:25 AM ET (US)            

"A remote control unit ...allows for leaning or enriching the fuel mixture on the fly.... We used the Digatron exhaust temperature gauge to help us zero in on the right fuel-air mixture at each rpm level."

The retro-fit of this electronic system was quite expensive, about $3,700 for kit and quite a bit of work to install it, and it is probably targeted only at high-performance enthusiasts who have a particular love of older motors.

See:

posted 11-10-2007 03:50 PM ET (US)            

True 4 strokes can direct oil right on the underside of the piston. Hard to do with 2S.

My earlier question was, is peak EGT in a 2S near stoichiometric, and is it over 1600? If so, 1200 is pretty overrich. I would say 2 gph richer than peak for a 150 hp engine. A lot of gas to waste.

posted 11-10-2007 10:40 PM ET (US)            

Back in my boat racing days a local mechanic developed an adaptor plate that bolted to the face of an Merc Mod VP race engine which enabeled you bolt 2 carbies per cylinder it was called a 12 pack and it worked achieving the world speed record for a mono hull (Bullet One) the only problem with was keeping the engine together , quite often boats running this system were towed to shore with a hole through the side of the cowling were the engined had lunched itself and sent a piston out through the side of the engine.

posted 11-11-2007 09:21 AM ET (US)            

http://i27.photobucket.com/albums/c191/floridaboy2053/boats2/100_0003. jpg