Topic: Project: Reverse Polarity Twin Turbo (NH750tt)

[KunipshunFit]

Hey everyone.  I know my bike is a DOHC, but there is a wealth of knowledge here I'd hope to have access to.

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 for now run with converted CV carbs, but possibly EFI at some point in the future.  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.

[KunipshunFit]

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?!! 

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

[Nicklopic]

Following because I like boostie noises and this looks interesting

[Dolomite]

Won't those under belly shocks cause some severe clearance issues?

[KunipshunFit]

Won't those under belly shocks cause some severe clearance issues?

They are not that much lower than some aftermarket exhausts.  I'm investigating ways to tuck them in tighter, but so far non are giving me the angles I want on the shocks for proper function.

Following because I like boostie noises and this looks interesting

Glad to have you on board! 

[KunipshunFit]

I have not updated this thread in over a year.  However PROGRESS HAS BEEN MADE.  It literally took me this long to find the required Harley parts.

Lots of progress on Reverse Polarity today.  The Harley shocks are mounted, but more bracing is definitely required.  They are also quite stiff so custom progressive springs will be in order.  Tossed the carbs in a box to a new owner, and chopped off that nasty rear frame that I wont need.  Next up:  Lengthen the swingarm 6" (twin turbos pull hard), then finish the bracing below the swingarm.

Follow the build at. https://www.facebook.com/RPcustombikes but Im still gonna update here too!

[KunipshunFit]

Today started with a leaky air compressor, gotta sort that out.  I managed to get the lower triangulation bars made and tacked for the swingarm.  You can really start to see the shape of this piece.  I had to remove the factory shock mounts so I could flip the axle bolt holder upside down to make room for the new bars.

The other swingarm will be here soon then I will extend this one and add yet more braces to make it all strong.  Clearance on the chain side is close.  I might have to modify the bar to stop interference, or might just install an aftermarket slider. Not sure yet.  Overall Im really happy with the way the swingarm is progressing.  Im even considering boxing it in, but not sold on that yet.

[754]

Interesting   softail shocks looks like, I think they pull, not push..
 What part of the sordid are you in ?

[KunipshunFit]

Softtail shocks indeed.  Yep they pull not push, interesting design for sure, and perfect for my application. 

Im down in Louisiana, US!

[754]

 I think I have same swingarm, Suzuki.. was going to cut 2 .5 inches out if it and change pivot , and run regular shocks.. for a CB 750 sohc.
 It was grey , set up for monoshock..... looks almost like aluminum  from 15 feet. ,