Adding to my early 80s fleet, I picked up another bike yesterday- a 1983 Honda CX650 Turbo w/ 10k miles. Somehow my current tastes have all my fun vehicles in a very distinct time period. Mondial, CX turbo, CBX.... I was born in 1986 and I don't know why I crave a collection that a middle manager of IBM would have owned in 1983 but here we are.
The mission:
Once everything is sorted, the goal is to turn this one up and see if I can beat the 95 whp my CBX just put down on the dyno. The performance plan is a ROM tune, upping the boost, injectors, throwing on an extra HKS bov I've had, and running 100 + octane. They both make 100 hp at the engine new but wildly different ways so I'm keen to see what I can do.
I had a $600 Yamaha Seca turbo that I put together a few years ago and eventually turned up and that was a rocket ship when modified. It ran great but they have a face only a mother could love. I think the Hondas and Suzukis are the prettiest of the factory turbos so I was on the hunt for a decent one for a while to replace the turbo void I was missing. Given that all my motorcycles are Hondas, I like having this combo.
This one runs but a little rough and has sat forever with old gas. I'm starting off with a baseline of getting it running well stock then I’ll be going through it replacing some cosmetics and doing some maintenance. Somebody painted it lime green then factory theme (missing some decals) back over that and also painted black over the gold front forks. The decal kit says 500 turbo yet the title, frame, engine, handlebars and forks are all 650. I think somebody just went wild on the plastics over the last 40 years.
I’m on the eBay hunt for parts- some side covers, rear turn signal lens, and exhaust baffles that were removed…. It goes on and on. Speaking of, the right side of the bike looks like it got hot and warped the side cover, rear turn signal and taillight lens. Too far from the exhaust so I’m wondering if it was overcharged at some point. These have stator issues around 20k so it's early for that but that’s #1 to check.
The CX:
missing baffles
and the goofy lime green popping through.
The inspiration:
Two different ways to skin a cat. May the battle begin:
ShawnG
MegaDork
12/3/23 2:11 p.m.
You suck. 
Those are two bikes I've lusted after for a long time.
Everyone playing silly buggers with turbo motorcycles in the 80s, then Honda steps up with the most pedestrian model and says "hold my beer and watch this".
I owned a CX650ED and would love to have had the Turbo.
Comments from friends who had one of each CX Turbo, the 650 is much more refined than the 500
That's a cool bike and a cool project. Looking forward to more posts!
Nice pair of bikes! I worked at the Honda dealer service department in the 80s when I was in high school and community college.
Well hooooo boy! Hello, friend!
I've not owned the 650, but you might say I'm somewhat acquainted with the CX500T. I owned two of them concurrently, in fact. I've also done the double bypass (stator and water pump surgery), which is a monumental pain in the ass. I don't know how susceptible the 650 was to stator failure, but I can tell you that pulling off that monolithic fairing and pulling out the engine to replace it is not a fun project.
All that being said, they were silly fun to ride. The turbo lag was absolutely a giggle -- nothing, nothing, nothing, WHOOOA!
While I enjoyed my time with them, I found that I rarely rode them and keeping them in tip-top shape was more and more difficult as time went on. I also hoarded parts: at one point I even had a full engine and transmission sitting atop my shop fridge. Ultimately I sold them to fund my first Corvette. (Fun note: For a while I actually owned two C7 Corvettes, too, both of the same color.)
Regarding the CBX: Those are proper neat motorcycles. I loved the brief flirtation with 6 cylinders in a naked bike. In fact, I have a KZ1300 and a ZN1300 myself. The ZN, however, is a donor for the KZ. I promise, PROMISE that one day I'll get around to finishing that project! These days, however, I tend to stick to my non-project bikes (a Honda Africa Twin and a Ducati Streetfighter V4).
I really look forward to how this thread evolves!
Also: Obligatory photos.
Following for customer work coming up.
Quite a bit more attractive than the original plastic maggot named original CX500 models. My brother had one and it was stupid reliable
Mini update:
Walbro GCL616 replacement fuel pump fitted (not through sorting the line routing). Early EFI 2.0 Prelude pump should give me enough headroom for a little extra boost.
Replacement side cover that was warped:
Spare relay from the CBX got the flashers going:
Charging, fueling, boosting:
Coming soon:
More actual maintenance coming that will sit and idle then paint and turning it up.
Maintenance supplies:
New iridium plugs. The previous ones were so black with soot it makes me wonder if the bigger pump that was on it was overrunning the fuel pressure regulator since the rest of the bike is other wise stock.
Shaft drive fluid was nasty and maybe original.
Uni foam cut up and piled on a gutted factory air filter frame since new ones are NLA:
New taillight to replace the melted one. Luckily melted from the outside in. Parked close to something hot? It's not over charging and melting anything at least.
First rip:
Confirmed all gears are intact and pulls pretty good under boost. Is not CBX fast but it also has lag then straightens your arms out for you. No real turbo noises from the intake or exhaust which is kind of disappointing considering the Seca turbo's exhaust sounded so good.
After the first ride I started pulling it apart to assess the charge pipe/ surge tank for the blow off valve install and I guess I just didn't realize how far that was buried.
Seems silly to tear into it to do that now so I might hold off on it until I need to get in there. We'll see if I can resist. 
Valve adjustment next and more cosmetics on order.
Valve adjustments on these are stupid easy, at least. They're the mechanical adjusters. I used to joke that I could do valve adjustments while straddling the bike at a long stoplight.
Did you rebuild the forks? Those are usually in pretty sad shape!
I've always wondered if you could get some or even a lot of lag out of these with an exhaust and a tune. Or gearing down.
Whelp, can't not watch this. I was an impressionable pup of ten when these were new and far too captivated by my dad's new V45 Magna (now in my garage awaiting the mythical Right Time) and all its many and varied V4 stablemates. The CBX was too exotic to exist as saleable merchandise in my podunk little town, and any manner of CX was a weird, lumpen oddity, sort of like a two-wheeled Saab 900 - who on earth would buy one when you could have a Nighthawk, or a Shadow, or an Interceptor, or just anything that wasn't so deliberately weird? What was the point?
Alright, well, that was 1983. I was a dumb kid. While arguably still dumb, I've grown out of the kid phase, and now CXs seem downright interesting. And weirdo 80s techie stuff is interesting. And a weirdo 80s techie CX warrants my full attention. Do carry on.
GCrites said:
I've always wondered if you could get some or even a lot of lag out of these with an exhaust and a tune. Or gearing down.
Can't change the gearing very easily - shaft drive!
I'm not sure if the 650T has the same gearing as the 650E or 650C, but the NA versions do have a taller primary drive (crank to clutch basket) than the 500 models do if I remember right. But the CX is really geared short - my 500 is ~7000 rpm at 70-75 mph in top gear.
This is a great thread by the way, I'm a big fan of these bikes.
Yours sounds like it's running really well in that video clip, I'm really surprised that you can't hear any turbo noises at all.
My final drive oil looked a lot like yours and I got scared, but it's been fine for thousands of miles after flushing as much metal out as I could. I think it just doesn't hold much oil, so even a small amount of metal makes it look like the world is ending.
GCrites said:
I've always wondered if you could get some or even a lot of lag out of these with an exhaust and a tune. Or gearing down.
Nah I think with these old bearing styles there isn't much you can do without swapping it with a modern style tiny car turbo. It's not terrible but it's a real feature. These have a delay whether you go WOT at 2.5k or 5k rpms and to me that is actual turbo lag. A few years ago I saw something about a 1.0 Fiesta turbo being adapted but I don't know if it ever came to fruition.
brandonsmash said:
Did you rebuild the forks? Those are usually in pretty sad shape!
LOL no I just did what I posted in the hour I've spent working on it. I just wanted to do enough to ride it down the road and confirm it has all the gears and shifts well.
gearheadE30 said:
Yours sounds like it's running really well in that video clip, I'm really surprised that you can't hear any turbo noises at all.
Yeah the intake is a mile long on these with a reed valve and surge tank so that sucks up a lot of it. On the exhaust side the opening on the baffles is super tiny and some folks take a hole saw to it to open it up more then cover them back up with the end caps (which I'm missing and on the hunt for). I haven't decided what I'm going to do on the exhaust side yet. Maybe get a spare set of silencers and completely gut them? Turbos make great mufflers.
Side note, the brakes on this thing are terrible. Smaller than the CBX with it being about the same weight. It's definitely getting upgraded pads minimum when I go through the calipers.
New turn signal lens, dash parts, and an old school HKS boost gauge are on the way. I like knowing real numbers when things are turned up (instead of five blocks lit up on the factory dash).
Broken trim pieces replaced, removed the wiring for the extra on/off switch, old school HKS boost gauge installed.
Waiting on a few more cosmetic pieces from overseas. I may get a couple more miles on it to diagnose anymore maintenance issues it needs.
6 months has gone by in a hurry but I'm getting back to this thing this weekend. First things first, I finally bought a place in the city that has a garage. It’s tight but all the stuff is fitting at least before the tools and shelves move in. Almost a decade since I've had all the fleet in the same zip code:
I had to remember where I was at in the process but basic maintenance was done. All fluids changed and valves checked and were in spec. Bigger Prelude fuel pump and boost gauge installed so I added the manual boost controller to ease the boost up.
Boost is 17 psi stock but it’s only 7.2 to 1 compression. 25 psi-ish is about the limit of the factory boost programming and 27 psi is the end of the stock injectors.
PIM205 on the turbo CX board has figured out how to remove the stock boost limits and has gotten deep into the EPROM chip. If I hit a wall and need it removed at least there’s an option. It’s wild that people have turned these up and found out Honda had extra headroom on these back in the day.
Bought the nerd book:
Stock boost:
Max injectors around 27 psi:
I’ll be running VP HP101 unleaded in it for some a little extra help with detonation protection. No room for intercooling and I might not need it according to others with experience with these so we will see. The easy button would be bigger injectors and e85 for more fuel and cooling but from what I understand, the stock Ecu isn’t easy to reprogram only remove some limiters. If you notice the mufflers with the rear endcaps removed, the internal restriction on these pipes is down to about an inch. I am thinking these may need a 2 inch hole saw run through them to get rid of some back pressure the increased boost is going to make.
I ran the bike up the road and yikes it’s hard to make subtle boost changes. I installed a Greddy Profec A in my Galant VR4 20 years ago and I remember why that felt like such an upgrade now. I cranked the dial-a-bomb controller down and went from 17 to 23 psi. Felt super strong. Touched it again. 28(?) psi, front end lift got light and hit boost cut hard. Whew. Backed it down to 20 psi and it liked it and felt less irresponsible. If I can open the exhaust up and up the boost to right before the factory boost cut I'll be happy and I’m hoping I’ll hit my power numbers around 24-25 psi.
Impressions are the motor doesn’t seem to protest the extra pressure. Brakes are still incredibly inadequate and front forks need love so these will get addressed first. Riding position is so uncomfortable with these pegs so high and I’m not a tall dude. This thing isn’t going to be a cruiser but just quick rips around town I think. Regardless of it not being a great all around unit, It's a riot to have a boosted bike again.
I wonder if there are more modern turbo designs you could swap on with less lag?
MadScientistMatt said:
I wonder if there are more modern turbo designs you could swap on with less lag?
Yeah I mentioned the Fiesta 1.0 turbo that somebody adapted but I don't know what became of it. Something the same size but ball bearing would be great. It spools around 5k now which isn't terrible.
63* degrees this morning so I went out on the turbo bike to see how it pulls with cooler temps. Well 23 psi hit fast and I found boost cut. It's kinda violent but jeez nothing else changed but that air.
Note the fuel system light that came on:
After coffee and a restart the light is off and running fine.
Backed down to 20 psi and I can hit that with no fuel system lights. At first I thought the CX didn't have it to hang with the CBX but now in these temps it might be close. There's a dyno day next month but I'm out of town. Once I get it consistent I'll take it.
Love seeing the updates on this! The footpeg placement on all CXs is way too high, my non-turbo bike is the same way. I'm not sure if there's a practical way to do it on the Turbo and those seats are probably pretty rare, but mine felt dramatically better adding a few inches to the seat foam to un-crunch my legs.
I had a buddy in high school who had a CX 500 Turbo. To my young senses, it was beyond a land bound rocketship. The LED boost gauge that told you EXACTLY how much fun you were having only solidified this perception. My buddy really knew how to handle the bike, too (unlike yours truly who is a squid). I was so disappointed to learn that the then current CBR 600 could eat it for lunch.
Thanks for the trip down memory lane. Upping the boost is the whole reason to have a turbo anything. Love the build.
Have I mentioned the Seca 650 Turbo with the shimmed wastegate (?!?!!) another buddy had? Also ballistic to my squidliness.
wheelsmithy (Joe-with-an-L) said:
Thanks for the trip down memory lane. Upping the boost is the whole reason to have a turbo anything. Love the build.
Have I mentioned the Seca 650 Turbo with the shimmed wastegate (?!?!!) another buddy had? Also ballistic to my squidliness.
I also had one of those with a boost controller, r6 fuel pump and some other silly things a few years ago when I lived in Alaska. Currently the old blow through carbed Seca still felt faster than this one currently.
