Today I finally finished my fuel pickup unit, or sender unit, as some people call them.
It was a major pain to make. It would have been way easier to modify the trunk floor and fit a safety cell fuel tank with a transfer pump
and a catch tank. Even a stock GTI arrangement would have been fine. But, I don't like adding electric devices to a mechanical fuel system.
Working as a car spares salesman has taught me not to trust cheap fuel pumps, and expensive ones are, well, expensive. One more part
to fail is an unnecessary worry, and I wanted to keep the OEM touch to everything as well.
The stock fuel system is designed for 80 hp max, so my goal of 200+ hp called for an upgrade.
Think what you may, we have seen benefits and some have even broken engines with the stock fuel system...
So this is what I wanted to replicate in my build:
And to make the new unit this is what I had to play with:
...there are two 1.6 TD sender units and one 1.8 carburetor one.
The carb one was chosen to serve as a donor unit so I started by cutting it in pieces:
...as you can see the standard unit not only has small diameter fuel lines, they are crimped as well!
Then it was time to pull out the original fuel pipes altogether, and fill the holes:
Next up was cutting a 1.6 TD sender unit to see how the internals were designed:
It's a real clever system, it has a swirl channel, baffles and a breathing system. All that is spring loaded onto the fuel tank too,
to work with different fuel loads and tank pressure.
Here's how the bottom part works: (
imu means
pickup,
paluu means
return )
So now I knew what I needed to accomplish. Then the real work began...
The top cap needed to be re-drilled, and an attachment system needed to be made for the new 'catch can' of sorts.
Aluminum was my material of choice, for its lightness and ease of working on. 10x8 mm pipes were chosen for
the entire fuel system. That gave me options for filters and connectors etc. Stock pickup line has a maximum of 6mm inner diameter.
The net benefit of this? Maximum flow capacity is now at least 1.6x the original. At least, because the OE system has
those bottle necks... OK, the capacity did not grow 2.5 times, but considering there is still extra potential in the OE system, this should do.
Making the lines bigger would have yielded many kinds of fitting problems.
I made caps for the catch can and a support for the fuel gauge sender:
The gauge sender had to be a specific type (Valeo origin) because the VDO one would not fit onto the catch can without serious modification.
Here it is, cut off of the old 1.6 TD sender unit:
And of course holes needed to be drilled, and room made for the connecting bolts:
At this point what I had was this:
Top cap and pipes were then welded onto the catch can:
Mocking up a baffle system:
The final design welded up, and pickup holes also drilled (to the same angle as the original design). Fuel pickup pipe is in the middle:
I made the chamber a little different than the original, mainly to allow the return line only flow to the whole fuel tank through the pickup area.
I believe this is a safer design since I did not include the original "outer curve" for the primary inlet.
After that, the bottom was sealed up with a round cap. There is only a 2mm gap between the end of the pickup pipe and the catch can floor.
Should make it difficult for air to get in there!
Supports were welded onto the catch tank/upper retainer. Then I epoxied the upper retainer to the top cap to keep all the fuel fumes inside the
fuel tank and the breathing system that was designed for them. That 2-component epoxy glue withstands all typical fuels, so it was a good find.
Here, finally, is the completed sender unit:
You WOULD NOT believe how difficult it was to get everything to fit, and sit at the correct angle. In all, building this unit took more than
ten working hours. And making it fit inside the fuel tank was even trickier. I had to modify every part of the gauge sender and grind
off material form the catch can too. It was a real big pain... But I made no short cuts, now everything is like I wanted.
It's a great help that I get to use the services of a good aluminum welder since that's something I can't do myself. Big thanks to
Raision Jäähdytin!!!
There she sits:
As of now, the fuel tank has been fitted to the car and next day at the garage I will make the fuel lines from the tank to the filter.
I'm even contemplating a twin filter system as on Merc diesels. You know, a "rough" filter up front and the fine filter after that.
Whatever they are called in English... What would your thoughts be on that?
