GJG's Turbo EFE update #1
It’s been almost a year since the Turbo from the states arrived and work started on the turbo kit. The first update on tuboing an EFE… the oldskool way.
The reason why Mr. Turbo charges around $4000 for kit like this all becomes clear when you start to build your own. Especially when you build it in a 6x3m shed, relying on other peoples enthusiasm and commitment to help you out doing things for you.
Then again, it won’t include a ball bearing T3/T4 Hybrid, or a stainless exhaust, or an Evolution wastegate, or Goodridge plumbing, or a prepped HSR…
This a Mikuni HSR 45 originally made for a Harley. Except this one has few tricks up his sleeve. Its internals have been specially tweaked for turbo use making the old S&S look a bit obsolete these days. It can only be purchased from one place, where they know what they’re doing when it comes to draw through turbo bikes: Big CC racing in the UK.
What’s precisely done to it remains a bit cloaked: Different needle and jets but, mainly, a beefed up fuel supply since it seems to be a bit of a problem keeping its belly filled up at boost. I don’t really expect it to be fully on tune when the bike is fired up first time, but it’s a good point to start from and therefore probably money well spent.

Like the turbo, the wastegate was purchased from Turbonetics in California. Although smaller than the so called “Deltagate” it’s derived from, this “Evolution” is still a bit bulky to be fitted to a bike although I don’t doubt it to be bullet proof. More or less aimed at the so called “import racers” (hot-rod Japanese cars) it’s a relatively cheap unit produced in large numbers. Rated appropriate too approx 400hp, it features a cast fully stainless steel body and valve and a polished membrane lid. It comes with several springs and chims to adjust boost level, not to mention a secondary pilot port for an external progressive boost controller…

It will come to no one’s surprise that most of the work went into designing and fabricating the intake manifold and exhaust system. Both had to be engineered more or less from scratch since they couldn’t be copied from a Mr Turbo kit.

The oil boiler engine in the EFE frame would have faulted the header pipes and frame, especially since the engine had to be tilted forward to make enough space for the turbine housing clearing the frame. And the T4 compressor housing is larger than a Rajay, putting the discharge point much further up. Both were designed using 3D-CAD. But that doesn’t mean it was easy.

First up was the plenum. The generator puts the turbo fairly high up, and the compressor housing was initially almost hitting the valve cover. Oh dear. I made a wooden mock up to get some basic dimensions. A traditionally hose between plenum and housing was out of the question. There just wasn’t enough space to sit a decent hose and clamp on.
Even cutting about 10mm from the compressor discharge was not enough. A 48mm Mikuni rubber flange adapter gained some precious millimeters. Also ditching the intake rubbers saved space. That meant bolting the plenum to the head directly, old Kawa ATP style.

This also has the advantage it can’t be blown of, and as it is heated by the head directly preventing fuel condensing and, possibly, improving low speed running manners.
To point out the struggle for space: The small recess in the middle of the front of the plenum is to clear the upper cam guide bolt head… There’s plenty of discussion about how a plenum should look like. Many have been tried over the years but few bikes seem to be flawed by its actual shape. Some are just a square box section with tubes and the Mr Turbo item also doesn’t seem really flow engineered. One feature was added though: a centre divider plate preventing the whirling fuel spray from the turbo entering, leaning out one side of the engine.
The parts were machined from billet and the plates cut out with a laser. All fitted perfectly.
After welding though on a fixing support, it had shrunk by about 2mm. It’s the odd thing of welding aluminum.
Once the plenum and turbo were in place, work on the exhaust started. All was fabricated using stainless AISI-304 tube and bends originally for the food industry. The bends have a nice constant diameter and come in a polished finish. I used 34mm primaries and 41mm for the link pipe, all 1,5mm wall thickness. The flanges were, again, laser cut. After the link pipe was made, design on the header started. To make a 3D CAD model, some accurate measurements were taken from the bike.
Once the dimensions like port spacing and collector centre point were fed into the computer, the tubes could be constructed. The limitations being pipe diameter, bend radius and frame tubes. Also, the flow of the pipes had to look good and natural. The pipes could then be broken down in tubes and bend sections.
For fabricating the bend sections, a special jig was made to measure them out. Sections were then cut out with a hacksaw.
The pieces were tack welded into pipes and proved to be amazingly accurate first time. Very few dimensions were adjusted. It all comes down to making accurate measuring and fabrication of the parts to approach the 3D model in real life.
After the pipes were made, I took it to a professional welder. We contemplated welding with backing gas as I didn’t wanted crusted rims inside the, already rather small, pipes possibly flaking of at high temperature sending debris into the turbine (eeks!). But the skill of a colleague welder pulled it of anyway leaving small and elegant welds from only about 25 amps from the TIG device.
You can take a job like this to any Joe public but sometimes it’s who instead of what you know that finishes a job just right.