Engine Specific Info and Questions > mTDI Mechanical TDI Conversions
MTDI in a boat
LabradorSteak:
First, I am so glad I found this site. Thanks.
I have been reading a lot about mTDI set ups and still have a few questions that may be obvious but the answers have escaped me.
Background...I have a lot of experience with jet boats and gas engines. I understand EFI and have rebuilt engines. I have had an ALH in a 99 bug that I worked on so I know the basic architecture and the basics of eTDI. Some basic assumptions I have may be totally off base so feel free to get simple with me.
1. do the injectors work like a gas injector where there is a gate that opens and closes or are they just a nozzle? If they are just a nozzle why are they so expensive? and if they are gated like a gas injector why does the injector pump meter and time injections? and what tells them to open and close?
2. Why not use a waste gate and BOV to control boost when using a VVT and discarding the computer? then just leave the turbo at what ever level you want to or even a lever that allows you to adjust it for optimal performance at the current driving conditions.
3. Am I missing something or are there more parts to the mTDI set up. Right now all i can see as parts are the:
a. engine...consisting of block, head, pistons, valves, cam, manifolds, oil pump, etc...mechanical stuff to move the air in and exhaust out.
b. Turbo...either VVT or WG BOV controlled
c. Injector pump and plumbing to supply fuel
d. Mechanical water pump and cooling system.
e. Front of engine stuff turned by belts off the crank...waterpump, alternator and injector pump
All of these things are individual systems that don't talk to each other and the only connection is the timing belt and moving air. No sensors tell one system to do something different because of another systems status. Basically no sensors or wires of any kind any where other than the alternator, starter motor, and shutoff valve.
Is this correct? I seriously feel like I am missing something. The injector pump is a complicated mechanism but other than that...???
Thanks, Matt.
libbydiesel:
--- Quote from: LabradorSteak on August 16, 2016, 02:29:29 pm ---1. do the injectors work like a gas injector where there is a gate that opens and closes or are they just a nozzle? If they are just a nozzle why are they so expensive? and if they are gated like a gas injector why does the injector pump meter and time injections? and what tells them to open and close?
--- End quote ---
Later PD and CR injectors are different, but the injectors fitted to TDI engines with the electronic VE injection pump are purely mechanical in operation. The injector nozzle is very precisely machined. It is basically an outer part that has a 'seat' and an inner needle/pintle. The pintle lifts when fuel pressure pressing acting on it overcomes the spring tension that keeps it seated. At that point, fuel sprays out.
--- Quote ---2. Why not use a waste gate and BOV to control boost when using a VVT and discarding the computer? then just leave the turbo at what ever level you want to or even a lever that allows you to adjust it for optimal performance at the current driving conditions.
--- End quote ---
A BOV is not a turbo control mechanism. It releases intake pressure which simply hurts engine efficiency. BOVs are sometimes employed as an engine safety device, but never as a turbo control and never should be.
In contrast, a wastegate operates on the exhaust side. It opens a valve in the exhaust that allows exhaust gases to bypass the turbine. Variable vane turbos (VVT) adjust vane position to control boost. None of the exhaust gases ever bypass the turbine. When the vanes close (direct the exhaust gases more perpendicular to the blades of the turbine), the speed of the turbine increases but they also restrict the exhaust flow and cause higher exhaust manifold pressures. When the vanes are more closed, you get more boost, but you simultaneously hurt engine efficiency by increasing the restriction of exhaust flow.
There are basically two ways to use a wastegate to control a VVT and both are far from ideal. One way is to make the vanes stationary at moderate position. An external wastegate can then be used to bypass the turbine. In that version, the VVT has been functionally turned into a wastegated turbo with the slight advantage of being able to adjust the fixed vane position to make the turbo 'larger' or 'smaller'. The second way would be to affix the 'wastegate' actuator directly to the vane lever. The vane position would be adjusted based on boost pressure and max boost would be regulated. The downside to that control is that it will always default to closed vane position. This hurts engine efficiency by causing excessive exhaust restriction at all times other than max boost.
--- Quote ---3. Am I missing something or are there more parts to the mTDI set up. Right now all i can see as parts are the:
a. engine...consisting of block, head, pistons, valves, cam, manifolds, oil pump, etc...mechanical stuff to move the air in and exhaust out.
b. Turbo...either VVT or WG BOV controlled
c. Injector pump and plumbing to supply fuel
d. Mechanical water pump and cooling system.
e. Front of engine stuff turned by belts off the crank...waterpump, alternator and injector pump
All of these things are individual systems that don't talk to each other and the only connection is the timing belt and moving air. No sensors tell one system to do something different because of another systems status. Basically no sensors or wires of any kind any where other than the alternator, starter motor, and shutoff valve.
Is this correct? I seriously feel like I am missing something. The injector pump is a complicated mechanism but other than that...???
--- End quote ---
That is correct. The injection pump accomplishes all of the tasks of fuel injection and ignition timing.
LabradorSteak:
Thanks for the reply.
I plan on using an ALH and a 300tdi rover IP to make 200-250hp reliably. Drivability is not an issue since driving a jet boat is like driving on a flat road in one gear. It takes a set amount of hp to turn the jet pump at a certain speed regardless of the boats speed. I am sure that there will be a reasonable learning curve but thats half the fun.
I know I have a lot more reading to do and will ask many more simple questions in the future.
Are there recipes for building these motors? My experience is mostly with small block gen1 Chevys where if you put in cam A with Carb B and exhaust C you should make about X HP.
Thanks, Matt
libbydiesel:
If you are going to operate the engine at a steady rpm/power then there is no advantage to a VVT. I would recommend using an appropriately sized wastegated turbo. TDI club will have more info pertinent to higher power output builds. Just a heads up... there's a fairly significant bias on that site against mTDI's.
vanbcguy:
Alcaid on here can set you up with a good turbo. There's a good thread on TDIclub from about a year ago with a TDI boat power plant - I think it was a Mercury but I can't recall.
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