Project: Reverse Polarity Twin Turbo (NH750tt)

Kunphushun

Big Dreams. Small Funds!
I guess its time I finally introduce my project here. I've been lurking around for over a year.

Bike: 1993 Honda Nighthawk 750 with a 1998 engine(no clue why)

The Plan: A radically customized homologation of a retro modern cafe racer/brat/thing... IDK what to call it. Hence the name. I intend to borrow the rear suspension from a Harley Davidson (dont oust me yet) softail and locate the shocks under the belly of the bike. Doing so will free up the room I need to do an underseat install of two tiny turbos (I've done the calculations). It will be intercooled, and will run with GSXR throttle bodies and microsquirt EFI. It will not be a fast build, but the end goal is a production quality bike. 100hp at the wheel. And, completion of my most ambitious mechanical project to date (not my first).

I picked up the bike for $500 from my wifes boss, it had been sitting for 3 years. Hooked up some power to the battery, turned it over for a few second, and she fired to life. Only on 2 cylinders though, and then 3 but never 4. It had pod filters that I could pull off by hand, all the plastics were broken, cracked, and barely hanging on with zip ties. The grips didnt fit, the handle bars were too small for the clutch and brake bracket so they were loose, the headlight was falling off, wires were cut, it was a basket case.

So I removed everything that was damaged, broken, or useless and was left with what you see below. It took me a year to come up with a solid plan and do 99% of the research to get started, but now we are there!

The turbos chosen, after hours of calculations, are the Ecotrons VZ21's. They're knock off IHI RHB31s. I'd prefer to use the IHI turbos, but I cant find even one much less two! At some point in the future they may get swapped out with some high quality Garrett GT12's, but that's way off.

The sketches below show the plan a bit, everything circled in yellow is gonna go away to make room for the rest of the plan. The blue will be added to the swing arm, and the green is the shocks.

The final plan has been slightly sketched out in the last pic. Also, I know this isn't everyone's cup o tea.

Details:
Brat style seat for 2 up with removable fake "hump" for solo
Frame, engine, center of wheels, calipers, and other bits powder coated anthracite grey
Tins painted Ford Ruby Red
Clip on bars with all wires hidden with bar end blinkers
Headlight/gauge cluster with two projector LED headlights
3" extended swing arm with fender added to swing arm
 

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Kunphushun

Big Dreams. Small Funds!
Re: Project: Reverse Polarity Twin Turbo

JustinLonghorn said:
Yep, I'm on board.
canyoncarver said:
Wild. Twin turbos eh? I'm in.
Peaked your interest did I? lol Until this morning I had never seen a twin setup on these bikes, but I accidently found one this morning. However, it used older tech, and didnt really appeal to the eye like I hope mine will. Tuck in, cause its gonna be a long ride. (Im also renovating a house at the same time. lol) :eek: 8)

Oh did I mention a stretched swing arm. Dont think I did... Im doing that too.
 

sav0r

Member
Re: Project: Reverse Polarity Twin Turbo

Here's what you do. Sell the house, start building the bike.

Man I made this easy for you.
 

Kunphushun

Big Dreams. Small Funds!
Re: Project: Reverse Polarity Twin Turbo

Sav0r said:
Here's what you do. Sell the house, start building the bike.

Man I made this easy for you.
Already did! Thats how I ended up in this predicament!!! hahaha :p

jordandogtown said:
I'm absolutely in on this one.
Happy to have ya taggin along!
 

Kunphushun

Big Dreams. Small Funds!
Re: Project: Reverse Polarity Twin Turbo

Had a bit of time to do some work today. I'll keep the words short and let the pics talk, We all like pics right?!! :eek:

I needed to remove the center stand mount, but wanted to keep the frame rigidity intact, so I welded in a brace in front and tucked close to the engine to give plenty of access to the swingarm. The brace is 1" x 1" x 0.125" tubing so its plenty strong. Glad I didnt try it with 0.65, weak sauce. Then I stood there for an hour staring at the shocks and building the swingarm in my head, and making choo choo turbo noises. lol
 

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Bevelheadmhr

Member
DTT BOTM WINNER
Good luck with the project. What was the logic for using a Harley Softail rear suspension setup, to give room for the Turbos? Softail rear suspension isnt exactly known for performance, having limited movement. On a Harley the two shocks are tucked up inside the frame beneath the gearbox, but in your case the shocks will have to be positioned pretty low, will you have an problem with ground clearance?

Here's an alloy swing arm I made for my own Softail, its half the weight of the original..
 

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turbodog

New Member
Nice! Subscribed. Ive been following a similar path, but with an XV920R and a Buell-based rear suspension...
 

Kunphushun

Big Dreams. Small Funds!
spotty said:
this looks both very silly and very exciting, keep it up
Thanks for being part of the madness!

Bevelheadmhr said:
Good luck with the project. What was the logic for using a Harley Softail rear suspension setup, to give room for the Turbos? Softail rear suspension isnt exactly known for performance, having limited movement. On a Harley the two shocks are tucked up inside the frame beneath the gearbox, but in your case the shocks will have to be positioned pretty low, will you have an problem with ground clearance?

Here's an alloy swing arm I made for my own Softail, its half the weight of the original..
I’ve had a vision of the bike in my head that I wanted to accomplish. I want the rear of the bike to be very sparsely populated with crap. Lol Also, I wanted a challenge, and a unique build that no one else has done. I intend later to upgrade the shocks to progressive 422’s with remote adjustment, but for now I can mock up with these. Ground clearance should be ok as they don’t hang any lower than some of the aftermarket exhausts out there. Im not lowering the bike at all, if anything the ass end will be raised slightly. We shall see. Im also considering ways to tuck them in tighter, but so far non of them give me the angles of functionality that I want. I dont want the shocks to bind at all.

That swingarm is a thing of beauty! Don’t have an old softail swingarm laying around do ya? Lol

turbodog said:
Nice! Subscribed. Ive been following a similar path, but with an XV920R and a Buell-based rear suspension...
I love the look of that. What turbo did you choose? What intercooler is that? Do you have a build thread anywhere?

TranceMachineVienna said:
Very interesting!keep it coming!
Thanks for joining the ride! Its gonna be frought with newbness and crazy ideas.
 

Bevelheadmhr

Member
DTT BOTM WINNER
I haven't got around to fitting that alloy arm to the bike yet, so still need the original. That said its not from a standard Harley frame, but from an aftermarket frame from Germany, so it wouldn't work with a standard Harley. Though you've not got a standard Harley lol. Besides I'm in the UK, I suspect the postage would cost more than its worth.

Looking forward to seeing how you progress with your project.. being different is good, though not always easy. My mate is currently making four of these.. homemade billet superchargers, one is for his Honda CB72, but I could have one of the others.... very tempting :)
 

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turbodog

New Member
I added an update to my (very) old thread:
http://www.dotheton.com/forum/index.php?topic=39633.msg922200#msg922200

The turbo is from a Yamaha Seca Turbo 650. I ciphered that a 650 turning 9000 RPMs would have sorta maybe the same flow requirements as a 920 turning 7000 RPM, given the lower volumetric efficiency of the 920 twin vs the four cylinder 650.

The intercoolers is from these guys:
https://bellintercoolers.com/
The main proprietors are Corky Bell (wrote what was once considered the bible of turbocharging) and Gerhard Schruf (Scuderia Ferrari turbo boss from the 1980 -88 turbo era, including 2 World Constructor's Championships). I spoke with Gerhard about sizing the intercooler to my requirements (~ 100HP). Nice guy.

I can only dream about having the facilities and skills to do machine work like I see in those superchargers. Very cool.
 

Bevelheadmhr

Member
DTT BOTM WINNER
turbodog said:
I added an update to my (very) old thread:
http://www.dotheton.com/forum/index.php?topic=39633.msg922200#msg922200

The turbo is from a Yamaha Seca Turbo 650. I ciphered that a 650 turning 9000 RPMs would have sorta maybe the same flow requirements as a 920 turning 7000 RPM, given the lower volumetric efficiency of the 920 twin vs the four cylinder 650.

The intercoolers is from these guys:
https://bellintercoolers.com/
The main proprietors are Corky Bell (wrote what was once considered the bible of turbocharging) and Gerhard Schruf (Scuderia Ferrari turbo boss from the 1980 -88 turbo era, including 2 World Constructor's Championships). I spoke with Gerhard about sizing the intercooler to my requirements (~ 100HP). Nice guy.

I can only dream about having the facilities and skills to do machine work like I see in those superchargers. Very cool.
Its always more difficult to turbo a twin than an inline four, good luck with your Yamaha project. The superchargers in the pic use rotors from an Eaton supercharger, the cases and drives are made on an ancient miller in my mates shed.. no CNC here. The reason for making them is to have the inlet and outlets in a better location to use on the CB72 and to make them look better and match the billet barrel he made for the CB72.. allows the engine to be taken out to 500cc. Anyway don't want to hijack this build.
 

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Kunphushun

Big Dreams. Small Funds!
Well a slight update I guess. Ive been working a lot lately 36hrs on and 36hrs off for two weeks ish, so Ive been doing a lot of research.

I have measurements now to start mocking up shock placement. Still trying to source the Harley parts I need without buying a swing arm, but that may be my only hope. I have also decided to go EFI first go round using a self tuning version of Micro squirt with a digital dash. Attempting to source throttle bodies now that are close enough to use with only silicon boots for adjustment.

I've decided on the length of the swing arm extension at 4" also trying to source box tubing in the correct sizes to both match the swing arm outside as well as make a plug for inside. The search continues.

Next up on the list is to start fabrication on the shock mounts. I may actually have to flip the bike back over to mock it up at ride height.
 

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