Tunnel drive performance issue

[Guest625101138]

Originally Posted by CDK

S....
When I received the engines all hoses and cables were sheared off with a bolt cutter, so there were no VW fuel filters. They connect to both in- and output hoses and have a small plastic valve mounted on top. The manual says that below a 19 C. fuel is returned to the filter and above 30 C it is returned to the tank. I made new plumbing and connected the return to the tank only. Did I make a mistake there?

CDK
I have been reading through some of the variations on the TD configuration. I gather your version is the ECO model using the turbo for emission control rather than power boost. Without the LDA you will only get the power of a naturally aspirated engine.

I will have a look around for the appropriate torque curve for this engine. It may be the engines are delivering all they are capable of without the fuel enrichment.

I have attached some discussion on the LDA and various engine configurations. It seems that fitting a fuel pump with the LDA is one way to get extra power.

Rick W

[CDK]

This VW forum discussion about the LDA is meaningless. One guy buys an engine with an empty LDA, the others have no inkling about why and how, but still ventilate their opinions. A catalytic converter on a lean burning diesel engine does not make sense because there is nothing to convert. A filter might make some sense, but the pre 2000 models didn't have any.

The 1.9 TD, labeled ABL does not have an LDA nor are there any provision on the injection pump to install one. It was used only in the Transporter (Vanagon). The same engine, with a different fuel injection pump, with LDA was labeled AAZ and used in VW and Audi passenger cars. Torque was about the same, but it produced more hp at slightly higher rpm. In the Audi it did 85 hp, in the VW Passat 78 hp. I have not been able to find out why or how.

[Guest625101138]

CDK
This does explain the lack of black smoke though. These engines are aimed at clean burning. The turbo is an ecological benefit not there for power boost. Just cools the exhaust.

I would be interested in a torque curve for the abl engine if you have one.

The most common suggestion for increasing the power is to fit a pump with LDA and an aggressive enrinchment pin taper. There are warnings about overheating oil though. Some just turn up the fuel but then you will lose economy in the lower speed range.

Rick

[pistnbroke]

Well we are back to the power valve .....irrespective of the lack of power valve if you put 10 psi boost on it by adjusting the link rod to the gate then you can turn up the fuel and get more power

[Guest625101138]

CDK
I have done the drag calculation based on the 6 degree angle and accounting for the lift. The attached curve shows the torque demand at various engine RPM and the boat speed.

It shows present peak torque is 80Nm and you will need to get to 110Nm at 15kts to get over the hump. Once over the hump the torque demand drops back to 90Nm before steadily rising with planing speed.

The idea of getting a tow is not bad. At 3500RPM the power demand should be only 32kW (42HP), which may be within the engine rating.

Barring the tow you need to tweak the fuel or get a new fuel pump with the aggressive fuel/boost pin taper.

You might also do it with a smaller pitch prop. At 15" pitch the peak torque at the hump drops to 84Nm at 1800rpm. So you may be able to push through the hump.

HOWEVER the easiest way has to be to tweak the fuel to see if you can get the torque up.

The way to reduce the hump is to reduce weight, and shift as much forward as you can. This would be worth the effort to confirm how close you are.

Moving the CofG forward by 400mm effectively eliminates the hump. What have you got in the stern that can be taken forward. Where are the fuel and water tanks. How much have they got in them?

Rick W

[Ad Hoc]

"..Moving the CofG forward by 400mm effectively eliminates the hump..."

Spoken like a true designer of high speed craft

You really must tell everyone how you eliminate the hydrodyinamc laws of high speed craft!...is that why all those books have been in need of an update for years...or is that just in Rick's world?

[pistnbroke]

Keep telling you to take the KISS route ...up the turbo pressure to 10-12 psi and then turn the fuel up until it smokes a bit ...thats all you are going to get out of these diesels ...take it for a run and if it goes over the hump good ..if it dont you need to look elsewhere

[baeckmo]

Originally Posted by Rick Willoughby

CDK

Moving the CofG forward by 400mm effectively eliminates the hump. What have you got in the stern that can be taken forward. Where are the fuel and water tanks. How much have they got in them?

Rick W

With his weight of 3600 kg, that is a trim moment of 1440 kgm; equals a redistribution of 288 kg aft to be moved forward 5.o m. Imagine what that would do to static trim, course-keeping, propeller submergence et c.! Smart, didn't think of that, huh????!

[Ad Hoc]

baeckmo

The breath taking ignorance of the basics of design is outstanding with each posting. Simple checks like this are the very things one does in the early stages of design, well it is for any professional engineer/naval architect. Not to mention lacking in comprehension regrading Froude and what the prismatic hump is..!!