Uprating turbo-diesel engine power 7

[Paulista]

I DIY marinised a pair of 4-cylinder, 4.2 litre MWM Series 10 turbo-diesel truck engines, rated each at 145 HP/2600 rpm and installed them in my boat. These engines are manufactured in Brazil and MWM (Deutz group)is probably the oldest name in the manufacture of diesel engines.

I was wondering if there would be a sure-fire method to uprate their power to say 200HP/3000 rpm. It is known that opening-up the fuel delivery on the fuel-injection pump can increase power, as it can also spend fuel, make for exhaust smoke and not generate useful work output.

As usual, the manufacturer is unhelpful, which is understandable, as he does not wish to entertain warranty claims of any kind. A great deal of after-market shops will uprate the power of your petrol engine, but very few or none for diesel.

You may wish to look up the site

http://www.mwm.com.br

- they even have a page in English.

 

[CESSNA1]

PAULULISTA: You are looking at sizeable boost in power, about 37%. The classic way of doing it is by turbo/supercharging and/or larger injectors. That means going from .57 hp/in^3 to .78 hp/in^3. That is quite a jump. There will also probably be a decrease in reliability/life of the engine. The real question is why? You may have to change your propellers to match the new power, how about shafting design also. Since power is equal to the cube of speed, your theoretical speed increase is only about 10%. It will probably be closer to 1% or 2% when the propeller and other things are factored in. You probably would be better just putting in different engines. A good rule of thumb is that you can only get so much power out of an engine before you have to go to a bigger engine.

Good Luck
Regards
Dave

 

[Paulista]

Thanks for your comments Dave.The original engines were 170 HP/3600 rpm petrol coupled to 1.5:1 gear boxes.

My curent BW gear boxes are 2:1, which does not help much for making speed.

I saw a HINO 3,9 litre marine turbo-diesel today on the Internet that churns out 210HP (pleasure) and 180 HP (light-duty) at 3000 rpm.

Also there is a 3.9 litre CUMMINS 4BTA... 250HP/3000 rpm, but this one has pistons, turbo and fuel-injection pump totally different from the 135HP/2600 rpm truck 4BTA.

Perhaps would be best to replace with 6-cylinder MWM 240 HP/2600 rpm turbo-diesels at a later date.

Thanks Cedric

 

[unclesyd]

Have you got everything out of your props?
You could also look at the gear box ratio.
As post by CESSNA1 I had rather go with an engine swap instead of boosting an engine.
That said, you still could look at a 1 or 2 jump in injector sizes.

We just went down on our Detroit injectors from 90's to 60's and as stated the loss/gain in engine power is hard to translate. Our measured speed dropped less than .5 knots and probably wouldn't be that much in weather.

Have you ever tried to anchor a boat in 1600 fathoms of ocean with nary a soul in site.

 

[MikeHalloran]

You're able to turn 2600 rpm now, right? Actually using any more power than you've got now therefore means you'll have to spin the engines faster, and that won't do them any good.

I, personally, would try going up a couple of propeller pitches before doing anything else. If you can get enough prop on there so you can't make rated rpm, then you can actually use more torque.

Can you get 1.5:1 gearsets for your boxes? That would also be worth a try. Off the top of my head, I'd have expected to 145/2600 motors to outperform the 170/3600 motors, using the same gears.

Or, I'd just put in bigger motors with appropriate gears. A boat is no place to be doing engine development work.

If you can prop or gear the motors so they're torque- limited and not speed- limited, check your exhaust backpressure. Upsizing the exhaust pipes might then make a noticeable difference. You'll probably need bigger pipes if you uprate the motors anyway.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Paulista]

unclesyd, judging from your recent experience with the DDs, the expected increase in current speed (15mph)will probably not be worth the effort with the proposed power uprating target.

Mike Halloran, that torque-limiting idea is interesting. If I understood correctly:

1.Upping the prop-pitch a bit will increase the load on the engines and see the motors making say 2400 rpm max., instead of rated 2600 rpm ;

2.The propulsion plant consequently would be torque-limited, working at its max.power at the engine speed of 2400 rpm;

3.The boat would (or may ?) make more speed with a higher-pitched prop (as above) at 2400 rpm than it would at 2600 rpm ?

 

[optimum]

It sounds like you have way to much gear for a turbo engine. I know the cat turbo's run a very steep gear to keep the engine loaded. I would not be afaid to crank up the fuel and boost in a marine engine, they are steady load applications unlike a truck which is not. Marine engines live in a marine application better than a truck at the same power levels because of this. I would load the engine harder at a lower rpm with gear/ prop changes. If you are going for speed keep in mind your hull design. Semi or full displacements eat fuel when pushing beyond designed hull speed. I would measure egt's and boost in your current set-up to see where you are at. If the engine is just revving, you wasting fuel. Load that thing and keep rpms down.
Tim
Disclaimer: People with different opinions may disagree

 

[Paulista]

Optimum, This is a 1962 woodie that I restored to brand-new condition.

The boat´s original specs say 20 knots cruising and 25 knots top speed. That is with the original power plant, namely, 170HP/3400 rpm engines and 1.5:1 gear boxes. I would say it is a semi-displacement hull.

Any idea where I could find parts for the Borg Warner 5000 gear boxes to step them down to 1.5:1 ?

Some of the official BW dealers I contacted suggested that I BUY NEW GEAR BOXES as the cost for alteration would be prohibitive. I suppose they would like to see you swallow that and buy two new boxes at 2-3K each !

I have no qualms about opening up the fuel-injection pump. It should provide more output power and correspondingly boost too.The engines are equipped with raw-water-cooled aftercoolers, BTW.

The exhaust manifold is fresh-water-cooled, which robs about 10% of the normal exhaust gas power that drives the turbo, so these engines may actually be making less power than they would in a truck.

 

[MikeHalloran]

I think you understand what I said. Props are probably the cheapest thing to try, especially if you can borrow them.

Changing props is really just a way to estimate your torque margin, with better resolution and for less money than changing gearboxes.

I assume you're using something close to the original prop for the boat. Within limits, you may be able to increase the prop diameter, in addition to increasing the pitch. There has to be a point where the prop stalls, but if you're not near that, you've got maneuvering room, so to speak.

You could do some more prep work before getting our your wrenches. Try to get the torque curve for the original engines and the torque curve for the replacement engines, and put 'em in Excel. Multiply both by the respective gearbox ratios, and scale both by percent of rated rpm, and you can compare them directly. You'll probably find the MWMs could pull a way different gear, maybe down to 1:1.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Paulista]

Mike Halloran,
The prep work you have suggested seems expedient as some quantitative feel is necessary prior to cut-and-try hands-on assessment.

The previous petrol engines were early 60´s raw-water-cooled, blue-coloured GM Chris Craft V-8´s, 170HP/3600 rpm. Any idea of where I could obtain a Torque curve for these ?

I agree that multipying torque curves by respective gear-box ratios will result in final torque available at prop hub. The original torque curves will simply be multiplied by a number, 1.5 for the original installation and 2 for the current one.(torque= force X distance = lbf.ft, say)

Note that for the original installation the propshaft will be at 3600/1.5= 2400 rpm at max. engine speed and, similarly, just 1300 rpm for the curent MWM/BW 5000.

However, I somehow do not follow the argument that scaling these curves as percent of rated rpm will allow for direct comparison between the resultant curves, for quantitative evaluation of the said engine/gear-box alternatives.

Can you explain please ?

Thanks

 

[CCycle]

My experience has been with ag and heavy equipment
but what fuel injection pump is being used?
Is there a governor involved?
Most pumps are adjustable as far as the amount of fuel injected. Before you start playing with that you should be able to see the exhaust to determine when it starts to smoke. If you are at full governed speed raising the amount of fuel injected will not help. It is not usually advisable to raise governed rpm on diesels particularly if reliability is a concern.

As others have suggested you probably need more prop pitch. A good marina could help but unless you are established or they see $$ they probably will not jump at the opportunity. Since you are a DIY type look the props over carefully. Look for consistency between blades. If you have a lathe or mill you can set them in it helps. If they are old beaters you can probably bend another two to four inches pitch on them. Another trick is to cup them. Hammer a bead or bur on the trailing back edge. This makes the prop act like it has a couple more inches of pitch and usually helps hole shot.

Another comment; discount manufacturers stated speed. Particularly in that age 40 years ago. Manufacturers made irresponsible claims.

 

[Paulista]

CCycle,
Thank you for your comments.

I am interested in the "bead" or "burr" method for upping the pitch of the props. Did you say rear-side of the trailing edge of the prop blades. What tool would you use for putting the "bead" or "beads" ? A punch-type of tool ? Close to the hub or away from it ? And "burr" with a Dremel-type tool ? "Burr" the whole rear-side of the trailing edge or just some part of it ?

The fuel-injection pumps are derived from a rotary-Bosch that was first introduced in VW diesel passenger-car engines (Rabbits etc.) in the late 70´s/early 80´s. Some early Dodge Ram´s with Cummins 6BTA engines are also so equipped. I usually hire a competent diesel service nearby that knows these pumps inside out. They alter them for 3000 rpm for whole fleets of VW-brand/MWM-engined 8-ton delivery trucks that do flat-out intercity 24X7. No harm done to the MWM engines.

What might interest you is the design of these MWM Series 10 engines. All engine parts, including for the individual heads, are IDENTICAL, irrespectively if the engine is NA, Turbo or Turbo with aftercooler. Obviously pump settings, turbo and injector sizes vary. This is not the case with MB 4/6-cylinder truck diesel engines. Some clever and unusual design on these MWM Series 10 engines.

Will appreciate more info on upping prop pitch.

Thanks

 

[patprimmer]

I think they are talking about what I call cupping the prop, which increases the pitch dramatically for the last 1/4 to 1/2 inch of the props trailing edge. It literally throws the water back of the trailing edge, thereby developing more thrust, but absorbing more power.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MikeHalloran]

Maybe I got mixed up in there somewhere. I normally avoid doing math in my head, because my brain is very good at some things, but it's not a reliable calculator.

Where I'm trying to go is to normalize the torque curves to see what the MWM engines could do, with the perfect gearbox ratio for them, whatever ratio that is, in order to figure out what that perfect ratio might be.

So, let me restate that. Normalize the gas engine torque curve to the prop shaft speed. Then normalize the MWM torque curve to get the same shaft speed. If you've got surplus torque then, normalize them to a little higher prop shaft speed.

Off the top of my head (there I go again) a first approximation looks like a 1:1 gearbox might let them pull 2600 rpm on the prop.

I.e., the gearbox you have may be the wrong one, maybe by a factor of two. Cupping the props is not going to make that kind of difference.

Maybe you could splice a driveshaft in place of one of the gearboxes for test purposes. But do the math first. ;-)

Chances are that the gas engines were really small block Chevrolets. Got a photo of the rocker covers? I'd bet some of the old- time cam grinders would have torque curves. If you can't find specific info for boat engines, look at truck engines.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[patprimmer]

My experience with cupping props is about a 10% drop in rpm is typical.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[hydrae]

Paulista
"The boat´s original specs say 20 knots cruising and 25 knots top speed."

I had a 57 owens (wood) that had the straight 6 replaced with 289 v8, nearly double the horsepower. Hull was also semi dispacement.
I bought it cheap, yes it went faster but the hull started to break apart where the new highspeed waterline was. The boat was not designed for the higher speed, are you sure yours can handle the higher speed?
I sold the boat for the value in the engine and velvet drive transmission after is started to leak too much.
Hydrae

 

[MikeHalloran]

I'm getting the impression that the boat speed is way down from the original with the new engines, thanks to a somewhat less than perfectly optimal gearbox ratio.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[CCycle]

Interesting engine Paulista. I would like to see the installation.

There are different ways to cup a prop. Most of them now are a bead on the last eighth inch trailing surface. The bead will usually be some what less than an eighth inch high measuring from the blade surface. You can quite conveniently hammer it on the blade. Aluminum or brass makes it easy. If your props are stainless or steel you will have to work harder. Smooth them out with a hand grinder. A mig welder that will push Al is handy, assuming the props are Al. Its hard to get the mind set to tackle rebending and repairing a prop but once you get into it, it isn't bad. We run in lakes and rivers and you must consider the prop expendable.

The faster you turn a prop the more effect the cup has. A common application is for light sport boats that are used for water skiing. For example, if the boat needs eighteen inches pitch for optimum top speed, you can fit a cupped sixteen inch which will give you the top speed but have better out of the hole performance.

Here in the states the last few years there have been low cost aftermarket props available. These can be less than $100 in your hp range. You can get cupped or regular. These would be Aluminum.

 

[Paulista]

Thank you all for your help.


HYDRAE: At around 2200rpm, the boat makes 15 mph (GPS-wise). How many knots will that be ?

I hardly ever operate at full throttle (2600rpm). It isn´t good for your pocket, both in the short and long term.

I have just finished refastening the bottomsides, and replanked the stern-to-midships region. This boat has a double hull, longitudinal outside planking (1.5 cm) and diagonal inside planking (0.7mm) The whole underbody now feels as solid as a rock. So even if I had to jack up the power output of the engines to 250 HP, I would not be too worried !

Mike Halloran : you are probably right. The gear boxes on all most all fibre boats of this size and class are 1.5:1,but their engines vary from 170-250 HP

Ccycle : Thanks for the input concerning cupping the props. does this Forum handle posting photos from Sony Image Station ? If so, I could provide some phots for you to see. But the installation is not exactly special. Coolant Expansion tanks in SS installed by the side of the helm, at roughly the same height above engines as in the truck. Had I incorporated the same with the engines in the bilge, would make the latter longer and taller ! Single-pass heat exchangers installed on hull sides in bilge, using frames for structural support. Pulley-driven raw-water pumps imstalled on engine stringers All this has a bit of plumbing associated with it !

 

[rdd48856]

Hi Paulista, here we are to portuguese native speakers writting in english. I don't have any experience on marine engines but I have on Car Diesel Engines. Here on Europe 50% of new cars are turbo-diesel powered. I succesfully increased by aprox.25% the power of two Diesel engines just by installing intercoolers, raising boost presure from 0,7 to 0,9 bars and increaing fuel flow, by changing both injection advance and fuel pressure. On a marine engine you have what we only dream on cars: water at 30ºC. If you install a good charge-cooler, raise boost pressure by 0,2 bar and increase fuel delivery by 20 to 30% you will have all the power you need without longterm side-effects.
Good-luck