Why don't boat engines use more turbochargers ?
 

I was up snowmobiling with some friends this weekend and we were talking about boats and engines. Well a couple of the guys race a 5.0 Mustang in the Super Street Outlaw class. Those that don't know what that is it is a class were the cars have know more than a 10" slick and a pretty much stock looking appearance.(theres more rules) well most of the cars are around 400ci and they use either nitrous or turbos. The record in the class is 7:90@173 if I remembered right.
Well one of the class winners just dynoed his 410ci with a turbo and it made something like 2000hp.
Well why don't people use 500ci and a turbo in a boat, it seems like 700 or 800 hp would be easy and it's free power from the exhaust , it seems more efficient than a power robbing supercharger.

I run a twin turbo 486" Ford. @ 7lbs of boost I've got 700 hp. The problem with turbos is getting them proped right. I use a 27" Mirage prop cupped out to a 29" Much more prop and I could barly get on plane. Boost starts to come on an 3200rpm. I set my wastegate at 6.5 lbs. I can spin the engine way past peak hp, so I set the rev limiter at 5500rpm. I know I could be fast ( I run low 80's) or have a better cruise (3500=40mph, I think). But I'd have to do a lot of tricks to get up on plane.

I think with the new turbos , you can get boost building a little sooner. that would help. Even 200rpm sooner would help.

I love the sound of the turbos whinning, they also keep the exhaust quieter at low rpms.

The late Tom Gentry tryied for years to get his twin turbo set up to run right. He was getting very close to getting them to live for a whole race when he rolled it. With him went the engine program.

I believe that turbo lag is the problem in boating. Supercharging gives instant power. This may not be an issue on calm water but in when wave hopping you need the power the second you hit the gas, not a second later.

Just my opinion, I never played with either one.

maybe because you can never track down the guy that has your driveshafts to get your boat in the water

Yup Payton's right.........superchargers make good lowend power at the cost of top-end......But those little turbo's have a real hard time getting goin in a boat.....

Props choice can be real hard......too much and and it couldn't fight it's way out of a wet paper bag.....too little and she won't go anywhere up top......

Plus the biggest culprit of all......HEAT......them turbo's make a oven out of a otherwise nice engine compartment....:rolleyes:

Take a look at some turbo boats and look at what they go through to keep the heat under control......;)

Good question though...

Payton, I knew a guy that had twin turbos on his TransAm and a bottle of NOS to get off the line. It was all computer controlled so as the turbo boost increased the NOS would shut down slowly to maintain the power level. Supposed to be the fastest street legal car around. Ran in the low 7s at about 200.

This car was owned by the owner of Kendall motor oil.

PS. His daughters name is Kendall.

Try to guess his name. He raced open class in the 70s.

Scott,
I know where there at ! I've got one and Curt has the other one.
The hard part is when and how are we going to get them to you.
I'm easy to get ahold of ,I'm at work right now 313-792-1001.

Shor, my turbos run in a watercooled housing. I can shut the engine down and lay my hand on them. They are only as warm the exhuast manifolds.

The newer turbos have the waste gate on the ehaust side instead of the pressure side and are set to build boost sooner and with less lag. But that all costs more $$.

I think the biggest reason there are not more turbo boat motors is the lack of understanding as to how to do them the right way. I have been running a twin turbo efi 572 for several years now. Just made a bunch of changes to the configuration cause the motor is now going in a different boat. We just got done with the dyno work and there is NO lag. The motor made 450ft lbs at 1250 rpms, 536 at 1500, 772 at 2000, 922 at 2500 and 1002 at 2750. From that point on the ecm controls the boost so the motor stays between 1000 and 1070 through 6000rpms. All that on 93 octane. The boat falls over on plane at about 2400 so as you can see there is no lag. The genius who designed this is Tom Earhart who has been doing turbo motors for years and once held the land speed record on a snowmobile. He still runs a turbo on his sled as well as a twin turbo 572 in a 24 Eliminator cat. Oh yes, the ecm allows driver adjustable boost to take advantage of race fuel.

Turbos are great, but there is no such thing as free horsepower. Even a turbo, which is one of the most efficient way's to make power have downfalls. First, todays turbos are very efficient, but they are not 100% efficient.

The proper way to measure supercharger efficiency is total adiabatic efficiency. This takes into account the amount of power it takes to operate/drive vs. the temp that it creates moving the air and how much it leaks back through the system. Heat is created by more than one way, first when you move something, you create heat by friction, then you have transfering temps from whatever heated sources such as exhaust, bearings, oil, etc. You then have what is moved more than once or in one "cycle." If air leaks back through the system, it gets moved again and again. You then have turbulence, pressure, etc. So every supercharger creates heat in some way. Also, in order to understand efficiency, you have to know everything has a curve, think of it as a motor on a dyno. If it made 1000 hp at 6000rpm, then 500 @ 7500, then 500 @ 2500, you would then see it's curve. A SC is the same, one that might be 80% efficient at one spot may only be 50% at another, therefore, peak is not always the largest concern unless peak HP was your only goal, the efficiency curve would be more critical since your typically looking for a broad power curve and not a peaky one. CART teams and old F1 cars had very small rpm ranges because the turbo was maximizied for very small windows which make them tough or were tough to drive, especially on road courses where you are in multiple gears.

A good turbo would have a peak AE of 76-80% on most applications. They create tremendous back pressure in the exhaust because the resistance of the air against the turbines and the orifice in which it has to pass through, which is the boost. The more boost, the more back pressure, the more back pressure, the more heat in the cylinder, the more heat, the higher chances of detonation. Also, because there driven by 1200-1700 degrees air, the inlet temp to the motor is incredibly high therefore they certainly need to be intercooled. These are only a few problems, the biggest is turbo lag, in the marine, you need torque, not hp to turn the propshaft, especially at low speeds where a turbo does nothing. And, because the turbo is most efficient at higher boost levels, the motors must be low compression, but when you have low boost at low speeds with low compression, you have very little cylinder pressure to make power and therefore have even less torque than most NA motors.

So to answer your question, anything is possible, but turbos have trouble making power down low which the larger boats need to get on plane or react fast in the ocean (nobody wants lag when getting ready for a swell coming). There are ways around it, you can oversize the turbo which you lose efficiency, then run a pop-off valve to control peak boost, but typically you still won't make the low end grunt.

The one thing people always think is that turbo is 100% free horsepower, well when compared to a roots, the numbers are incredibly different, but when compared to screw-type superchargers and centrifugal, there not that big of a difference, especially at lower power levels. If were talking 2000hp, well then it's huge, 10% would be 200hp, while at 600hp, it would be 60. 10% is not a true number, just an example. Typically speaking, a screw-type will offer the same peak total AE that a turbo will, but with the benefit of having more flow down low for the peak torque. There have been a few SAE studies that show there is no better method at creating low speed or very flat torque curves than a screw-type. So I agree, the roots is no comparison to a turbo, 600-800hp is a walk in the park, but it is with screws and centrifugals. The other thing you have to look at as for OE is concerned, peak hp is not what always sale, "drive-ability" is very important. Take Mercury's new 1050 motor with our screw compressors on there, if you put a turbo or turbos on there, it would probably make approx. 1-4% more peak hp, but torque would be down an easy 200lbs in the mid range rpm. If you put a centrifugal, peak hp would be -/+ 2% but torque would be down probably 150-200lbs in your driving rpm range. If you put a roots, well you'll have a Merc 900 then :D, torque will be down 100-150ft lbs.

I hope this answers your questions.
Thanks,
Dustin