Turbo XJ650 Maxim (Maybe)

I've recently decided to rebuild my maxim ground up and had a crazy thought when I started to think about the intake...

Lots of people hate the look of the stock air box (including me) and pod filters are well... undesirable. So why don't I just throw a turbo on it?

My rationale for this is I recently put school on hold because the quality of online education is poor (covid-19) and in the coming year or 2 I have a capstone project to complete for my final year in mechanical engineering. Why not use this as an excuse to make a sweet ride?

I have full access to the schools machine shop and help from a machinist who works there full time including a 5-axis CNC mill and CNC lathe.

Just trying to get my bearings on what I might need to do to get the engine ready. I'm trying to figure out the differences in engines between the turbo Seca and maxim. Forged pistons, titanium valves, beryllium copper seats? What am I looking at here? Is there a thread that discusses the different materials used in the engine. What are the sleeves made from? What about the head?
etc..
Any guidance would be appreciated!

 

Pistons are forged, there is a different oil pump (with a scavenge section iirc), the clutch and gears are from the 900, aaand that's about it I think. Carbs are different.
I don't know what you are thinking of machining though, most of what you need is bolt on stuff, I've thought about doing this, and even though I have my own machine shop, machining stuff up for it never came into my thoughts.
Check out @Simmy s turbo seca build...

 

Thanks Minimutly.

I am a little concerned about the carbs as I would do a blow through setup. Looking to get 10-12 psi of boost, don't know if the seals would pop or the float would get ruined. I need to look at how the turbo carbs operate. Might be better off doing an EFI conversion.

As far as machining goes maybe brackets to hold the intercooler or the runners for the plenum (any excuse to use the 5-axis, its collecting dust!).

Drives me crazy not being able to have the info available used in the engineering of these bikes. e.g what the f#$@ is a yellow bearing?

 

The carbs on the turbo are entirely different, as is the fuel delivery to the carbs. The compression of the engine is lower too.

Start with this thread:
turbocharged-maxim-650-build.21112

Then peruse the rest of them:
turbo maxim site:xjbikes.com

 

Juat a propratairy measuring system that probably made it easier to build the engines on the production line. One that hasn't entirely been decoded yet so far as I know. Start a conversation with @chacal.

 

So compression ratio will need to be lowered for that amount of boost, but the forged pistons I need will solve that problem. Starting a list of to do's.

Thanks for the links!

 

Building it is one thing, tuning it to a rideable state is another thing.
Yamaha has already done the hard part and developed the final product. It is reliable, easy to operate and a complete blast to ride.
The further you stray from the Seca Turbo will likely result in complete frustration.
This was my concern when I built mine. Keep it stock as much as possible and get a good baseline bike running.

You need to research and decide what turbocharger is suitable if it's not the Yamaha OEM.
If it's another turbo, you're on your own as far as suitability, see my point above about straying far from the Yamaha concept.
If you're planning to mount it somewhere else you better have TIG or good MIG welding skills and pipe bending capabilities.
Paying someone with these skills to build just the exhaust will be $$$.
If you mount it same place as the Yamaha you will find the Maxim frame is too narrow between the centre stand pedestals to fit.

Turbocharging causes early detonation so you need to retard the ignition in relation to boost pressure.
To do this you will need the Turbo's TCI, boost pressure sensor and knock sensor.
You've already discussed the carbs, you will need them to.
Surge tank, turbo, air pipes from turbo, pressure regulator.
Turbo petcock.
Fuel pumps are available from the aftermarket.

The oil pan from the turbo will be needed to accommodate the turbo's oil scavenge pump.
May as well include the Turbo Seca oil lines and check valve.
The Turbo has o-ring sealed inlet manifolds, a threaded boss on the cylinder block for the knock sensor.
The Turbo pick up coils are needed to match the TCI.
Cam profiles are different for turbo charging.
Essentially you will need a Seca Turbo donor bike.

Building a turbo bike from scratch and having a rideable result is a monumental task.
The best way is to pick a performance bike (with brakes!) and an available turbo kit from several reputable vendors.
This is big bucks but you have some certainty of success at the end.

 

this is what I'm drooling about



https://www.extremecreations.com.au/yamaha-mt-07-fz-07-turbo-kit

 

To add philosophically to what Simmy said above, there are basically two distinct ways to turbo an XJ depending on two very distinct types of people:
1. The "I'm a decent mechanic, how hard can it be?" type. These should ALWAYS follow Simmy's advice if you want to be successful, and drop an entire turbo seca into a maxim frame. The only mods will be to the weld tabs or cut tabs on the frame.
2. The "I'm an automotive engineer and I don't need your help, I'm just showing off" type. Look up "Turbo Maximus" for inspiration as well, or just go here. In this case, fuel injection will probably be your best bet, and like Simmy says, nothing will "bolt on" you'll need to make specific design decisions along the way.

There's really no in-between with Turbo-ing an XJ. If you try the swap only a few components on and engineer around what you don't add, you'll end up doing as much work as #2. Your second paragraph screams #1, but mech E capstone project is a "maybe" on #2. You may want some guidance from experts on that as well. Not to dissuade you from trying, but a lot of people have started down this path and it's always great to see another finish.

(My only experience is restoring a Turbo Seca, but I appreciate those that can be #2).

 

IMO, for a UJM of this era it's far easier to supercharge it (though no less expensive).
No changes to the internals are required (though that will limit how much boost you can apply).
A belt drive pully can be machined to replace the reluctor (pully incorporates the reluctor, though extending the crankshaft would be better). And there is room to fit the appropriate sized compressor in the frame (perhaps with some frame modification), or plumb it and hang it off the front of the cradle.

It's still a lot of work though.

 

I like how @ManBot13 has categorized builds # 1 or 2.
As I tried to explain #1’s result in a proven rideable bike.
The #2’s we see a build process, sometimes with stunningly impressive results, visually anyway. Without at least dyno printouts there is no proof it actually works well enough to ride it.
I’ll bet even Yamaha didn’t deliver the Seca Turbo on their first go.

 

Yeah I was wondering about this. Trying to figure out the profiles without any success. Do you know if the turbo cams will drop into the maxim? How about the oil pan?

Most definitely sounds like I will be needing a donor. I see you're from Waterloo. Ever been to Zdeno Cycle? I paid a visit to grab a 650 Seca tank few weeks ago. Hogfiddles tank interchange thread was awesome, fits on my Maxim. I took a tour around the whole place and they had stockpiles of XJ parts it was incredible. I'll see if I can upload some pictures later.

This is partly the reason I want to do it, need something to look forward to.

Thanks for the feedback!

 

I certainly didn't mean to come off like that nor am I a number 2. I was just trying to communicate that I'm in the position to possibly pull it off. Just trying to capitalize off the fact that I might not be able to do this again. Having access to a machine shop at zero cost doesn't fall into your lap everyday. That coupled with the experience of the guys from this forum I thought maybe it could happen. I know I could never pull it off without a tremendous amount of help.

Fear not, I have seen what happens when you don't finish a game of Jumanji .

 

I meant no offense by that, just trying to be blunt. There are folks on this site who have done a “from scratch” turbo-ing of an XJ, but it’s a lot of skill, time, and money. If you’re going that direction, you’ll need to build up that much skill by the end, and better have the time/money. I’m sure TurboMaximus wasn’t cheap, and the thread took 6 years to develop.

Someone like me or Simmy can tell you the amount of engineering that Yamaha did on the Seca Turbo, and all the reasons it’s difficult to beat as a mechanic. Most folks on this site with “Turbo” experience fall into this category. But other than rebuilding every component, the only mods realistically that are done are increasing boost because the XJ650LJ TURBO engines had a good bit of design margin.

If you really want #2 to need to contact the folks that did it and get them to take you under their wing. Unless one of them answers this thread, you’re more likely to get steered towards finding a donor Turbo Seca...mostly for your own good. But if you’re determined, get the right support and have realistic expectations, then maybe you can pull it off.

 

You and Simmy do make a good point. With that much money tied up its a better (and cheaper) idea to start with the Turbo platform. Perhaps some middle ground would be swapping the turbo motor and carbs into my frame and fabricating a custom intake and exhaust for that custom look. Possibly adding an intercooler for higher boost?? Also another consideration that slipped my mind is the fuel return. I'll have to fab a new mount on my Seca tank for the turbo petcock. IIRC they do not interchange.

Out off curiosity how much boost have you reliably gotten out of this platform on pump gas? How much boost was factory tune?

 

Zdeno were probably the biggest bike breaker in Ontario at one time.
Its really nice to have a well stocked parts broker right in town when working on these old bikes.
They long ago pushed all their XJ stuff outside so the bone yard has decayed most things by now.
I'm jealous you found a good 650 Seca tank there. I didn't think to look.

There is a guy currently on Kijiji, Alberta who has stockpiled 4 turbos, 2 are complete bikes as I understand. Too bad so far away.
Having several is really the way to build an old bike like this as the Turbo stuff is getting rare.

There's another in Montreal right now I'm trying to buy his motor and carbs.
I'd like to build a monster turbo that I can bolt in.
I'll keep my numbers matching motor/carbs all original and ready to go back in, it currently runs too good to mess with.
If an experimental motor doesn't work out I can go back.
I have a 900 motor that actually looks pretty good. I have no idea why it was parted out.
Also a spare turbo motor but its just a bench mock-up.

If you look through my Turbo thread I have pictures of a skilled friend transferring the mount from the Turbo's tank to the 650 Seca tank so I could use the Turbo's petcock.
Alternatively you could also just drill a hole and slip a hose nipple through the bottom of your tank for the return line.
This fillet weld would be easier than the welding I had done. It could be brazed in too I suppose.
Just replace your vac tap with a simple on/off.

Like Danny from counting cars would say - I can dig it!

 

I can personally attest to 14 psi. It accelerates so strong at that pressure I swear it feels like something is about to break.
Some guys have cranked them up to 18 psi.
I've seen that number mentioned most often, I suspect that might be the limit the OEM turbo can pressurize but, truthfully I do not know.
18 psi has got to be insane anyway.

The original bike in 1982 was only 7 psi and probably felt too tame for all the hype and expense.
I bought one new in 1984 and it came with the Yamaha power up kit which took them to 11 psi.

 

Increased boost will bring about higher engine temps, air cooled motor is bad news. Added to that you might run into the limit of fuelling and run weak, leading to overheating, detonation and thermal runaway - this melts a piston in about 10 seconds - ask me kow I know?
So increasing boost past 10psi is a risky game, without some clever electronics monitoring egts, mixture, knock? You are risking it.
@Simmy has made noises about going to 900 ccs, which would allow equal performance for less boost - sounds like a good idea to me...

 

@Minimulty Yamaha specifically added the power up kit to increase boost to 12 psi. Fuel pump outputs 14 psi. I ran mine at 11 psi with a manual boost controller with no issue.

@JeffK ran 18psi by changing the fuel pump for an R6 one and shimming the blow off valve, and again, no issues.

Yamaha put a lot of margin in the Turbo engine, especially with the 8.0:1 compression ratio. That plus 91 octane (US) and even the boost sensor (MAP) and knock sensor and turbo TCI box, and I’d say it’s pretty safe. And it’s not like you are on full boost all the time.

There are specific issues you can have with the oil, I always changed it every 2000 miles. Never run at full boost and just stop the engine or you’ll cook the oil in the turbo. And of course, the turbo, carbs, and pressure regulator all need to work properly.

As for the intake, the hardest part is packaging it in the frame. Yamaha used a set of reed valves to bypass the compressor before it produced boost to lower the impact of turbo lag. You may want to consider this when fabricating an intake as well.

 

I've found the 1 page article describing the power up kit from 1984.
If anyone is interested just PM me an email and I will send it.