Licks Cycles: Suzuki GS400 Twin-Turbo Scrambler!

Twin-Turbo Scrambler: “Manic Melina” from Physician Bike…

Launched in 1977, the Suzuki GS400 might have appeared very similar to its middleweight twin rivals on the skin, however the engine boasted twin overhead cams, 180º firing order, and a counter-balancing system to dampen vibration. Cycle World known as it “the smoothest machine within the class,” and the GS400/450/500 collection would earn a repute as among the most underrated, most dependable bikes ever constructed.^[1^,2]

“It’s really superb how Suzuki might give you such an excellent first-time effort in a market they’d by no means actually entered earlier than. If one had been to argue that the GS400 was one of the best machine within the class, they’d have greater than only a leg to face on.” –Cycle World

After all, in the event you’re going to turbocharge a motorbike, significantly a classic one, it pays to start out with the hardest donor doable, and making use of pressured induction to bikes is the specialty of our new good friend James Kauder of Arizona’s Physician Bike.

Like many people, James obtained his begin on a boyhood grime bike…though it blew up proper after he obtained it. Luckily, James had a grandpa with a black thumb, who tore down the highest finish and despatched off the cylinder for re-plating.

“My grandpa re-installed it and had it operating the subsequent day. I simply thought that was the best factor ever, and that was the start of eager to learn to wrench.”

James spent his teenagers and early 20s shopping for non-running bikes, getting them roadworthy, and promoting them on. From 2015-2020, he labored on bikes as a sideline to his full-time job as a CNC machinist, and through the pandemic, he based Physician Bike and his extremely fashionable Youtube channel (180,000+ subscribers!), the place he focuses on turbocharging bikes — Sportsters, Buells, Viragos, and extra.

The ’77 Suzuki GS400 you see right here is considered one of his private bikes. Whereas his road setups often run 8-9 psi, James had been wanting to construct a fuel-injected, intercooled twin-turbo system to permit for increased enhance ranges.

“I’d all the time wished to transform a bike to EFI, and my GS400 appeared like the right candidate because it’s principally an off-road and dune bike, so it doesn’t should have good road manners.”

To organize the engine for enhance, James lowered the compression to eight.6:1, full with a ported head and widened ring hole. He particulars the complete turbo setup beneath, however highlights embody a MicroSquirt ECU, twin VZ21 turbos, intercooler, Ninja 650 throttle our bodies, ZX10R injectors, antilag launch management, on-the-fly enhance management, and even a quickshifter.

The entire system is rather more refined than many of the turbo setups we see, significantly for a classic bike:

“We additionally utilized a flex gasoline sensor, so you’ll be able to run something in between straight 91 pump fuel and 98% ethanol, and the tune will modify itself accordingly. On 91 pump fuel you’ll be able to run 12psi of enhance safely, and on E85 you might in all probability get away with 20psi, although I maintain it at 15-16psi in order that I can experience it onerous.”

James estimated 65 hp — practically double the manufacturing unit output — and a moist weight of lower than 350 lbs. As for the suspension, he’s operating Race Tech springs, heavier weight fork oil, and 14″ rear shocks, with 5.5″ (F) and 5.2″ (R) suspension journey.

“Individuals on the paths are genuinely shocked at how shortly this bike could be hustled round. Suzuki GS400’s and 450’s are a superb alternative for scramblers, as they’re already sub 400lbs from the manufacturing unit.”

The aesthetics had been extra of a secondary concern to the efficiency and driving expertise, however “Manic Melina” appears imply as hell with the turbos hanging off the edges…and she or he’s one hell of a hoot within the grime.

“It’s a smile machine! Everybody that rides it comes again with a tacky grin on their face.”

Under, we speak to James for the complete story on this GS400 turbo scrambler, and we extremely suggest you subscribe to the Physician Bike YouTube channel for extra force-inducted enjoyable.

Turbo GS400 Scrambler: Builder Interview

• Please inform us a bit about your self, your historical past with bikes, and your workshop.

I grew to become desirous about bikes after my first grime bike blew up proper after I used to be gifted it for my twelfth birthday. The earlier homeowners didn’t clear the air filter and it was simply slowly ingesting grime. The highest-end seized, and I assumed it might by no means run once more. My grandpa tore it down, despatched the cylinder out to be replated, and the day the cylinder confirmed up, my grandpa re-installed it and had it operating the subsequent day. I simply thought that was the best factor ever, and that was the start of eager to learn to wrench.

I spent my teenagers and early 20’s shopping for non-running bikes, getting them operating and roadworthy, and promoting them. All types of bikes, starting from SV650’s to grime bikes and quads. Because the years went on, and I’d gotten a couple of dozen bikes going, I had the urge to purchase an outdated Japanese bike for grime low-cost and make it my very own — a full customized construct. So in 2015, I purchased a 1982 Suzuki GS450 from a good friend of mine for a couple of hundred {dollars}, and over the course of a yr, turned it right into a Brat Type bike. At the moment, I used to be a CNC machinist. I didn’t have sufficient expertise or cash saved as much as begin a enterprise, so I spent the subsequent 5 years persevering with to work full time as a Lathe Setup Specialist and work on bikes on the facet.

The pandemic was the start of my enterprise, and the Honda CM185 Scrambler construct that’s on my YouTube channel was my first construct video. After 4 or 5 months, the video all of a sudden took off, and I went from 30 subscribers to some thousand, as was making a couple of hundred a month from YouTube. And that’s how Physician Bike got here to be.

• Why was this bike constructed?

The bike was constructed as a result of I’d all the time wished to transform a bike to EFI, and my GS400 appeared like the right candidate because it’s principally an off-road and dune bike, so it doesn’t should have good road manners.

There have been additionally another issues on my bucket record that I wished to cross off, a kind of being a purposeful, high-boost twin turbo setup (I often simply run 8-9psi) with an intercooler. The intercooler permits me to maintain increased enhance ranges and push back detonation. This bike can be on E85 in addition to having decrease compression, so I really feel fairly comfy operating 15psi as my base enhance degree.

• What was the design idea and what influenced the construct?

I am going into every construct with a efficiency really feel in thoughts, the best way the bike appears is sort of an afterthought. My essential objective with a scrambler is to make the bike truly experience and deal with nicely off-road, all the things else is secondary. It’s why my scramblers usually find yourself tremendous naked bones, stripped all the way down to nothing however the necessities.

• Inform us in regards to the construct and setup.

Turbo Setup – Twin VZ21’s (IHI RHB3), intercooled, Tial blow-off Valve, a guide enhance controller (to regulate the enhance on the fly), antilag launch management, quickshifter. Completed bike was on E85 and 15psi of enhance.

Engine Setup – Unique untouched backside finish, new piston rings with opened up ring-gap, the top is ported and the combustion chambers had been opened as much as get the compression all the way down to a calculated 8.6:1. Estimated energy on the crank is 65HP.

Suspension / Chassis – Race Tech fork springs, 20WT fork oil with raised oil top to stiffen it up. The shocks are 14″ lengthy, which necessitated the removing of the passenger pegs. Suspension journey is just below 5.5″ up entrance and 5.2″ out again. The chassis is de-tabbed as you’d count on and we welded in a body loop.

Electrical / EFI – We transformed the bike to EFI with a MicroSquirt ECU, Ninja 650 throttle our bodies, ZX10R gasoline Injectors, a 180lph gasoline pump, and an AEM wideband o2 sensor. The remainder of the sensors (consumption air temp, MAP sensor, and so on.) are GM sensors, and the ignition coils are GM LS2’s.

The crank set off for spark management was the toughest half, we ended up utilizing a VR sensor with an 18-1 set off wheel that we needed to modify to get to work, together with machining a spacer to maneuver the wheel out an inch (this was proven within the construct video). We additionally utilized a flex gasoline sensor, so you’ll be able to run something in between straight 91 pump fuel and 98% ethanol, and the tune will modify itself accordingly. On 91 pump fuel you’ll be able to run 12psi of enhance safely, and on E85 you might in all probability get away with 20psi, although I maintain it at 15-16psi in order that I can experience it onerous.

The bike stays kick-start solely.

The remainder of the wiring is bare-bones; that is primarily an off-road bike so it has a rear operating gentle and a headlight, and that’s it. Rather than a speedometer and tachometer is the wideband Gauge, which makes use of our 3D-printed mount, and a lift gauge. The truth is, this bike is principally a dune bike, and we initially deliberate to run a paddle tire on it and take it to Glamis for the ultimate construct video, however we’ve got another initiatives proper now that may’t wait, so it would occur early subsequent yr. So look ahead to some fairly epic driving footage of this bike within the dunes early subsequent yr!

• The place does the “Manic Melina” nickname come from?

The bike is manic to experience offroad; as quickly because the enhance gauge swings over to full enhance it simply lights the tire up — it seems like driving a 250 2-stroke MX bike. So I knew I wished to name it manic, and provides it a lady’s title. Melina was prime of thoughts for no matter cause.

• Are you able to inform us what it’s wish to experience the completed bike?

It’s finest on 12psi or so for off-road driving in grime and sand, any extra and it simply doesn’t hook up in any respect. The enhance is adjustable on the fly, so once I hit the grime I flip it down from 15psi. Even with full-on non-DOT grime bike tires, it doesn’t get traction at full enhance till 4th gear. The ability is definitely linear at half-throttle and fewer — simply placing round, it’s comparatively docile. Even at ¼ to ½ throttle, it’s solely making 5-7psi of enhance — it pulls much like how a 650cc or 750cc parallel twin would pull.

It’s not till you go broad open that the enhance gauge swings over and it takes off like a scalded cat. Ripping shifts with the quickshifter is a blast, and also you get the occasional pop and fireball out of the exhausts which is fairly cool. The rolling antilag feels like gunshots, so I don’t use that each one too usually. It’s a smile machine! Everybody that rides it comes again with a tacky grin on their face.

I’m operating Race Tech springs and thicker oil up entrance, and together with a 130/90/18 tire up entrance, it’s comparatively straightforward to experience within the sand, which is the place I supposed this construct to be ridden. I spent lots of time on the rear shock valving as nicely, and eventually settled on a shim stack that’s good and agency.

Individuals on the paths are genuinely shocked at how shortly this bike could be hustled round. Suzuki GS400’s and 450’s are a superb alternative for scramblers, as they’re already sub 400lbs from the manufacturing unit. Even with the 2 turbo’s and intercooler (intercooler solely weighs 3lbs), I’d wager with the 4.2 gallon tank full, it’s not even 350lbs.

• Was there something finished throughout this construct that you’re significantly pleased with?

I’m significantly pleased with the sticker bombed tank — the thought didn’t come to me till the day earlier than filming the ultimate photographs of the construct video. I’ve all the time thought sticker bombing was cool, however thought that it appeared like there was an excessive amount of happening when folks do the entire tank. So I had the thought of utilizing vinyl reducing tape to chop it right into a form; to my shock, it truly labored! It was a kind of uncommon moments the place it labored out how I assumed it might in my head.