81 400xs turbo build

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Thedoityourselfguy

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So I picked up this bike a while ago and decided to try a turbo project. Aside from this bike looking great from a distance.....it needs many....many.....odds and ends to be tied up. The previous owner just lost interest I think.

Anyways.....after research I have decided a blow through turbo setup will be the best route.

Fuel injection would be great but....positioning all the sensors and cost really are not a appealing. There are some universal small engine kits but after more research I found that some ppl complained about dialing their bikes in.

Draw through setup would be fine but tuning is potentially a nightmare in that it is difficult to accomplish a good air/fuel ratio through the range of throttle from idle to full boost. Also....finding a Carbon sealed turbo is extremely difficult.

Now this is my first turbo build so please point me in the right direction if I'm going the wrong way at anytime.

I am waiting on.....
A gt15 turbo with a .35 ar
A 115 lph electric fuel pump
A boost referenced fuel pressure regulator
And a new cdi to make sure that this bike even runs......if not I have another 400 xs parts bike with a very low miles engine.
 

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Ok I received the turbo and the fuel pressure regulator today so getting closer. You guys know these things way better then I do......where would be the best place to tap into a pressurized oil circuit? It would save me all the clutter and expense of installing a separate oil pump and reservoir. Thanks
 
Easiest access might be at the oil filter. In the other turbo thread lcgtr mentioned using a sandwich plate but I didn't see any further details about which plate might fit.

Curious to see how this goes. It'd be really cool to see some more blown XSs.
A supercharged 400 with tuned intake and exhaust would be awesome....
 
Should be. You could remove the sensor to tap into the system. It'd mean plumbing a separate return line but it's doable.
 
That is probably what I will do.....it should simplify the process and tapping a return line in the oil pan is no big deal. Thanks. I can't wait to get started on this build!
 
Be very careful if you go that route. The oil pump puts out just enough for proper oiling in the top end. If you split off somewhere, and then just dump it back to the case, you will get a drop in pressure. I'd be worried about my top end. Use a remote pump or tap inline and return in a series fashion.
 
Also, what carb are you going to use? I think in your original post you may be off a bit. You say draw through is hard to tune.... It's actually the opposite. Blow through is an absolute nightmare to get right. 115lph fuel pump is insane for an air cooled 400 BTW. You will never get anywhere near needing that much fuel.
 
Typically you would restrict the inlet line on your turbo since it does not need a large amount of pressure to be safely operated. And it doesn't matter what fuel pump you use as long as you have something that is reliable and consistent in operation. That is the job of the boost sensing rising rate fuel regulator......to regulate the pressure to a usable 10 or so psi under full boost for this application. Using stock carbs because they should be super easy to modify......pretty sure all I have to do is pressurize the float bowl using a pilot tube.
 
You need to do a bit more research.... The stock carbs will never work unless you cage them and seal them. Even then, CV carbs won't work
 
Attached is a crappy translation of the XJ550 oil cooler on an XS400 writeup.
Credit goes to FrankWw for the original work.
 

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It's certainly possible to do blow-through CV carbs. Suck-through will supposedly result in a better fuel/air mixture and better combustion.

I'm not as familar with turbos but it shouldn't be toooooo much trouble to seal all the atmospheric ports on the carbs and then plumb some lines into the bowls from after the turbo to equalize pressure.
An inline fuel pump will be required to keep the boost pressure from blowing the fuel back into the tank. There are even ways around this but the pump is the simplest.

No idea about tuning, probably quite tricky in either configuration.
 
Don't recall where I read it but one recommendation if leakage there became a problem was to flip the seals around.
Makes sense since the pressure difference is reversed under boost and the seals are directional.
 
Well I give him credit for trying, just trying to save him troubles before they happen. Fuel injection with a single TB would be the way to go.

Carry on!
 
I've got an FZ600 and the oil cooler looks the same as the XJ550. so maybe the xj600 will fit too.
come to think it, i have a spare setup off an '91 xj600 (FJ600 in USA)
 

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