Volkswagen Jetta 1.6 - how many HP - prop calc

Discussion in 'DIY Marinizing' started by sailingmonica, Oct 20, 2009.

  1. liki
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    liki Senior Member

    Using the evidence at hand, VAG spare parts catalog tells that his pump has been used on ' 86 Jetta 1.6 D and TD, engine models JP an JR.

    So, all together I'd believe the engine to be 1.6D JP, as I wouldn't believe many to bother with stripping a broken turbo to sell the engine as naturally aspirated for a few hundred. 40kW@4800rpm and 100Nm@2300 rpm should be correct, or atleast very close to the correct values, with the engine in pristine condition.
     
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  2. Angélique
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    Angélique aka Angel (only by name)

    You don’t need many, only one. And you would be suprised by what people would do for a few hundred or less. The numbers are never filed off for no reason.

    @ Monica, Was there a exhaust manifold on the engine when you bought it? Or was it taken off already as you needed a marine one anyway?

    Regards,
    Angel
     
  3. sailingmonica
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    sailingmonica Junior Member

    Marshmat, the throttle linkage is moving at full range

    CDK,

    When not in gear max RPM reached is 3,800 - 3,900
    Under full load, if throttle is pushed quickly to max there is really black smoke, like from burning rubber, the kind that you can see on the water surface as it is eliminated with exhaust water. It is not oil, more like the stuff you get in your chimney. If throttle is increased gradually to max under load, there is no black smoke.
    There is no black smoke at highest RPM when not in gear.
    There is no grey smoke or diesel smell at idle.
    Can you clarify what do you mean by the last question related to the start assist lever?

    Liki,

    The 40 Kw converts to 53.6 Hp. If I input 53 Hp and 4,800 RPM in the boatdiesel program, it gives me a 3 blade 15.3 diameter with 7.5 pitch. Looks kinda small, especially given that I have a full keel and my prop is in aperture.

    I can't seem to wrap my mind around this. If maximum torque of 100 Nm is reached at 2,300 RPM, and the rest of the RPM range all the way to 4,800 is useless to me, should I then calculate based on 2,300 RPM? If yes, do I still enter 53 Hp at 2,300? Because if I do, I get diameter 23.8 and 15.6 pitch, which looks pretty big.

    If it is not 53 Hp at 2,300 RPM, how can I determine Hp?
     
  4. liki
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    liki Senior Member

    Power = Torque times revolutions in radians per seconds.

    100Nm at 2300 rpm is a little over 24kW in power, and the rest of the rpm range is not useless, although the torque decreases. The maximum power output is still at 4800 rpm, and gearing increases torque at shaft directly in proportion to the gearing.

    40kW at 4800rpm is a little under in 80Nm torque.
     
  5. CDK
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    CDK retired engineer

    To start with the last sentence:
    VW engines from that era had a device to facilitate cold starting. It was a lever mechanism on the back of the injection pump to simultaneously advance the injection timing and reduce the spring pressure against the governor assembly, resulting in more time for the mixture to burn and increase idle rpm from 900 to 1100.
    On some models the mechanism was operated manually with a bowden cable, while others had an aneroid thermostat.
    If there was a manual control, the lever should be secured in a position where the idle rpm just starts to increase. Leaving the lever free will cause it to drop and retard the ignition start, resulting in insufficient combustion time and consequently a reduction of power.

    Rpm without load:
    With a proper throttle link mechanism and correct injection timing, the rpm should be 400-500 above the rated rpm/hp. For your engine, regardless of the engine code, that would be almost 5000 rpm.
    When you look at the top of the Bosch VE-pump, you see a stop screw the throttle lever is pulled against. Turn it out a few turns and check max. rpm again. If it makes no difference, something is wrong with the governor and in that case the pump needs service.

    Black smoke under full load:
    That means the engine gives all it can but there is too much load. Since you don't see that, there is no such problem. Baeckmo told you in post #5 what the actual power delivered to the prop is; there will also be some loss in the gearbox but not more than a few hp., so the engine clearly doesn't generate what it should be capable of.
    Below the 4 nuts that attach the injection lines to the pump you can see a capped screw with a nut. If you loosen the nut and turn the screw clockwise for half a turn at a time, full output power is increased considerably, but it also shifts the idle rpm somewhat. If you see black smoke at full rpm under load, you've turned too far.

    Grey smoke and fuel smell at idle:
    There is insufficient internal pump pressure to keep the injection timing within range. That is caused by a fuel return line without the proper restrictor.
    The banjo bolts on top of the fuel pump look the same but the one from the return line has a very small hole compared to the other one.
     
  6. baeckmo
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    baeckmo Hydrodynamics

    Ha, everybody been busy here, while I've been in the woods over the weekend, training the dogs for moose tracking....! Good job folks!

    After this first round, we can conclude that there are uncertainties regarding the engine. Before we can dig into the propeller details, we must be safe on the engine side:

    1/ The engine tachometer should be checked for calibration, using a separate light-beam tacho or similar for comparison (borrow/hire from engine shop).

    2/ Engine room ventilation deep down in the boat should give an engine room temperature of 40 degr C at the absolute maximum, preferably lower. Engines are radiating heat at a rate of 10 to 20 percent of shaft power, depending on design. This has to be ventilated away. Vent openings should be minimum 7 cm2 per kW, in this case 2 openings 140 cm2 each, arranged so that a natural draft is created. This incudes area for combustion air.

    3/ The return fuel must circulate all the way back to the tank, in order to dissipate the vapour bubbles and heat generated in the injection pump. Some VW engines have a thermostatically controlled shunt in connection with the fuel filter, diverting cold fuel back into the pump suction line. This device includes a calibrated nozzle that gives the correct back pressure for the injection pump housing. Iiki would probably be able to see the original configuration of your engine. The shunt should not be used in a marine engine, but the nozzle is important.

    4/ Marine exhausts often differ from car types in terms of piping configuration. 4-cyl car engines today practically always have cyl's 1 plus 4 and 2 plus 3 connected in groups before they join together. This gives better and more equal gas exchange than the common inline arrangements we see on most watercooled marine manifolds. The result is a power loss from "car power" to "marine power" of about 10 percent, giving your engine 49 hp at max rpm's. The exhaust back pressure should not be more than ~1.2 m water column, preferably 0.6 m max. Excessive back pressure could result in lowered max rpm's (even in no-load high idle) due to the pumping power needed. Until this is checked, we don't know if the speed governor is ok! If you use a water-cooled system, the hose innerdia should not be less than 60 mm, preferably 75, since there probably is a pretty lengthy piping in your boat.

    5/ The reduction ratio 2.63 to 1 gives a relatively high rotational speed to your propeller, making it very highly loaded (I would have preferred something like 3.5 or 4 for this engine). You might say that the area swept by the propeller is too small to give it authority over the mass and area of the boat. This is why we have to be very careful, so that we use the power installed to its optimum. As a result, the selection of propeller may not follow normal standard routine; I will return to this when we know your engine limitations better.

    Hope I haven't flipped your nose with obvious statements in the list; just got to be methodic in search of engineering "truth".
     
    Last edited: Oct 25, 2009
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  7. Ad Hoc
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    Ad Hoc Naval Architect

    Just a minor addition to baeckmo's excellent summary in point 2, as a good rule of thumb:

    Whatever combustion air by volume intake is required by the engine, call that V, then the air into the ER is 2V, 1V for the engine and 1V for the venting. This is for a standard 10degree temp rise over ambient.
    If you wanted only say a 5 degree rise, then you would need 2V for the ER, ie a total of 3V.
     
  8. liki
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    liki Senior Member

    This sounds a little like the engine is already giving out the maximum torque it can provide in its present condition, especially as it is slow to pick up revolutions. Since the engine should be able to deliver more then enough power and torque with also the current gearing there likely exists some mechanical or adjustment problem.

    Some things to check, in no particular order:
    a) Compression test
    b) Cam shaft / toothed belt timing
    c) Worn cam shaft / valve mechanism
    d) Condition of injectors
    e) Injector pump condition and especially injection timing

    All these tests are fairly easily performed, perhaps save for injection timing adjustment. If you plan to check these matters yourself, you should find http://vagcat.com helpful.
     
  9. Jasonsansfleece
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    Jasonsansfleece Junior Member

    Given the engine is circa 1985, spent its previous life in an automobile and has already done many thousands of miles, unless its been rebuilt its probably worn out.
    A compression check on each cylinder will confirm this.

    The injectors are good for 60,000 miles or so, the "pop" pressure will be out of spec and the spray pattern might not look so good.

    The Injection pump timing should be checked as well as the pump internal pressure as this affects timing advance.

    I mention all of the above as they all adversely affect engine output.

    Even if the compression ratios are within specs ( or not far out) I would recommend looking into the injectors and pump.

    Although is primarily a car forum, these folks know alot about these particular engines
    http://www.vwdieselparts.com/forum/

    Guy
     
  10. sailingmonica
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    sailingmonica Junior Member

    Guys, I cannot thank you enough for taking the time to research in order to help me solve my problem. As for my nose, I don't mind it when it is flipped by smart people, and I love learning from you.

    A fellow boater used to own a Corbin 39 which had a Pathfinder engine and even though he sold the boat he kept a copy of the manual.

    These are the specs: Pathfinder 1.5, Max output 37 kW (50 BHP) @ 4,500 RPM, Max torque 82 Nm (71 ft/lb) @ 2,500 RPM, Continuous rating - pleasure craft 36 kW (42 BHP) @ 4,000 RPM. He had a 2.63:1 transmission as well. While he doesn't remember the displacement of the boat, I assumed it lighter than mine, say 25,000 lbs. Since 1 PS = 0.98632 SAE and from what I understand 1 PS is the same as 1 BHP (correct me if I am wrong), for the sake of simplification we can say that they are all equal.

    Now, this boat had a 19X13 propeller. And it worked well. How on Earth is this possible, because if I enter all the Corbin's data in the program I am way off in the result.

    Going now back to my boat:

    - I agree with the tachometer perhaps giving false readings. It is connected to the alternator via the W connector, so it is actually reading the RPM from the alternator.
    - The timing is OK
    - The injectors are new
    - The engine is an '86 but was rebuilt, good compression ratio
    - Exhaust hose is not that long, it comes out on the side, above waterline, not at the stern. Hose inner dia is more than 60 mm.
    - Return fuel circulates back to tank.
    - Engine room is spacious and is ventilated to the outside

    Let's assume for a moment that my engine is in perfect condition. Then, car engine on a boat equals 90% of HP? Can I then calculate my prop based on 49 HP at 4,800 RPM?

    The thing that bothers me about the calculation is that nowhere does it ask you whether the propeller is an aperture or does it have free water flow. I am no expert, but common sense dictates that there have to be some differences based on that.
     

    Attached Files:

  11. Angélique
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    Angélique aka Angel (only by name)

    Second round...

    I found this and this but I can't read it (you could try to increase it, I didn’t). Or you may find the Corbin’s displacement here or ask for it to compare it with your boat.

    That sounds a lot like the 1.5D engine#2 at post#13 only the rpm's are 500 lower and torque is +2 Nm. I saw a Corbin 39 1981 brochure (page say's ‘‘that might have been purchased in 1979’’). So that could match with the listed 1978+ engine#2. The Pathfinder marinized version of it could have modifications to lower the rpm's by 500 and + the torque by 2 Nm, and keep the same power!!...?? Maybe if you can figure out how that's done on the Pathfinder you can do it too.

    P.S. about the torque of engine#2 vs. the 1.5 Pathfinder. It could have been that Pathfinder has translated 8.2 kgm into 82 Nm which sould have been 80 Nm.
    P.P.S. torque data of the 1.5 Pathfinder ‘‘82 Nm (71 ft/lb)’’ is not correct: 82 Nm = 60.5 ft·lb and 71 ft·lb = 96 Nm.

    If you want to end up with the right prop size you can't say ‘‘they are all equal’’. There are to many differences between engine#1 and #2 at post#13 to say so. The 1.5 Pathfinder is most likely a marinized version of engine#2 and you most likely have something like engine#1.

    That sounds like a bit newer as the listed 1983+ 1.6D engine#1 at post#13, except from the fact that the listed engine#1 has non hydraulic lifters the rest of the spec's could be the same as your engine.

    Liki, about post#31, does the 1986 1.6D JP engine have hydraulic lifters? Or are the hydraulic lifters only on the 1986 1.6TD JR version of these two?

    Succes !!

    Regards,
    Angel.

    P.S. about 12 small additions and changes in the first 2 hours, so earlier readers there is some additional info.

    P.P.S. (10-29-2009)
    They are almost the same: It is Horsepower = HP/PS/PK/CV/etc. vs. brake horsepower = bhp

    Eg engine#1: Maximum power: 54.8 HP/PS/PK/CV/etc. = 54.0 bhp = 40.3 kW @ 4800 rpm
    Eg engine#2: Maximum power: 50.7 HP/PS/PK/CV/etc. = 50.0 bhp = 37.3 kW @ 5000 rpm

    See: HP Horsepower / PS Pferdestärke / PK Paardenkracht / CV Cheval-vapeur / etc. They all also mention bhp (brake horsepower).
     
  12. baeckmo
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    baeckmo Hydrodynamics

    You friend's figures fit perfectly well, Monica. But first your question on propeller working in an aperture (or any structure that obstructs flow). That is influencing the propeller as if the inflow velocity is lower than the actual speed of the vessel. So, when your vessel is making 7 knots through the water, the propeller only "feels" a mean advance speed of about 85 % of this, say 6 knots, or 3.06 m/s.

    Then to the engine characteristis. The maximum power is varying with rpm; at 2000 rpm you have ~29 hp at the shaft, at 3000 rpm there is 39 hp, at 4000 rpm 47 hp, topping 51 hp at 4800 rpm. A rough first indication on propeller diameter (in inches) is:

    D=630 * hp^0.2/(shaft rpm)^0.6;

    If we check the performance at 3100 engine rpm's, available power should be ~41 hp and, alas the prop dia for this point of operation will be 19". Now, your engine only pulls a 16" propeller at this rpm, which tells us that there is something wrong; either is the power restricted, or the gear ratio is ~2:1 instead of 2.63:1. CHECK THAT THE GEAR RATIO IS SAME IN BOTH DIRECTIONS! These things have to be settled first of all, hence my previous questions.

    Now, given that your engine and transmission is ok, we can make a (more) complete analysis of the options. The 19 x 13 prop would give you 3100 rpm on the engine and produce a force on the hull of 3978 N at 7 knots.

    If we want to use more of the available engine power, we have to let it spin faster, say 3800 rpm. To do that, a smaller propeller is used, here a 17 x 12 would be the choice, resulting in a thrust of 4191 N at the same hull speed. Here, the engine is producing ~46 hp. This is a 12 % increase in power for 5 % increase in thrust, demonstrating the importance of low propeller load. The "classical" prop load factor is the Taylor load factor; Bp=(shaft rpm)*sqrt(hp)/(knots)^2.5, where "knots" is the advance speed.

    If you put your data into the Taylor load factor, you get very high figures, in fact so high, that a Kort nozzle, as used on tugs would be appropriate. But that would conflict with sailing performance of course....

    So, back to the dirty checking, remember that propeller power is depending on rpm^3; any error in rpm readings give gross errors in power estimation.
     
  13. liki
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    liki Senior Member

    The only difference in cylinder head, cam shaft and valve assembly for 1986 JP / JR engines seems to be different exhaust valve, and neither engine seems to be equipped with hydraulic lifters. Also, a different model of cylinder head seems to be possible.
     
  14. sailingmonica
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    sailingmonica Junior Member

    Liki, I just wanted to say that it is my understanding that the engines that did not have hydraulic lifters didn't have that additional hole in the block with a corresponding hole in the head to allow more oil to circulate for the lifters. My engine and head have these holes. So, while the fuel pump part number indicated an '86, the hydraulic lifters seem to indicate maybe a newer model. In any respect, it's a Frankenstein but I like it.

    I wanted to buy a VW marine SDI - 40 but it is computerized and that is not a good thing on the boat, so I'll stick with what is simple to fix and parts are available anywhere (this being the reason why we chose to go VW in the first place).

    Baeckmo, the transmission is a ZF 12 brand new, 2.63:1 in forward and 1.95:1 in reverse and it is connected correctly. Couldn't find a higher reduction ratio transmission that would fit.
     

  15. liki
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    liki Senior Member

    Okay, do not give up just yet. :) After all I can tell you about the engine is:
    a) The pump part number matches a 1986 Jetta 1.6D
    b) Should the engine be from a 1986 Jetta, it is most likely 1.6D JP with the aforementioned specs.

    The head might well be replaced with a spare part that has the oil channels as the same head is used on a few different engines and especially the spares are made to fit even a larger variety.

    As the engine is rebuilt, I'd suspect that the lack of output is due to timing misalignment.
     
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