OK... so I'm now fascinated with these old Turbo Seca's. At the moment, I've got an 82 750 Maxim that runs like none-other. Its fully tuned, running an unrestricted intake and an open-pipe Vance & Hines 4-1... its the fastest thing I've ever driven... but not fast enough.

So here's my question.... Does the Turbo 650 Seca use the same carbs (basicaly) as the existing carbs on my 750? From what I can tell, they are the same.... except that the bowls are pressurized with the intake charge to compensate for the boost. I'm sure they use different jetting, as well. They also use a small fuel pump and regulator with about 20psi output. So, in theory, with the right jetting, some home made fuel system components, and the rest of the associated turbo hardware (I own and operate a machining and fabrication shop... can make just about anything), could I use the existing carbs on my 750 for a turbo swap? If not, any chance I might be able to "directly" swap on some carbs from a donor turbo seca? Give me your input on the best course of action for carburetion. I plan on running a custom turbo, custom header, custom intake plumbing, and a suitable waste gate, boost controller, and blow-off valve.... with an overall system boost pressure of 8-10 psi.... significantly lower than the 14psi on a turbo seca.... but with the larger displacement and higher compression of the 750. It would be wicked if it could be tuned correctly.

Next issue... Ignition timing. As you know, the 750 has a fairly high compression ratio... 10.2:1 I think... the seca is more in the range of 8.5:1... with careful ignition timing control, high octane gas, and relatively low boost pressure, the engine should run beautifully. I plan on using an MSD boost-timing master controller to automatically remove ignition timing as boost pressure increases. This essentially allows me to tune the ignition timing without ever touching the factory ignition module. This is the same thing I've done with my supercharged Nissan Pathfinder (www.LPPerformance.com). The turbo seca uses a knock sensor and probably has its own specialized ignition brain.... maybe I could swap on the ignition from a donor seca (vs. the MSD ignition). What do you think on this concept?

Other than the fuel and the timing (as above), nothing in the world is stopping me from doing this. It'd be one truly unique bike... and would probably push 150-180 hp if tuned correctly. Why do this to a Maxim and not just buy a turbo seca to begin with?... I love my Maxim… and the 750 makes tremendous power. Please give me any information you might have on the turbo seca... parts diagrams, carb info, ignition/computer info... anything can help.

Lee

The Turbo carbs are unique, in that they are properly sealed to prevent air loss under boost. There is also an aluminum surge tank with reed valves in it, which allows the motor to short circuit the turbo under low rpm conditions and carburete like an ordinary motorcycle. There is a unique computer controller with ignition retarding and a knock sensor which is located on the front camchain tunnel (your motor may have a blanking plug on the front tunnel). The Turbo cylinder head is different, in that it has more and deeper cooling fins. The Turbo rods also have oil passages drilled in them to spray the undersides of the pistons to remove heat. The pistons are heaver, forged units, the main bearings are cross drilled to allow more oil to reach the crankshaft, and the cases are much more heavily webbed. There is also a special oil feed line taken off of the front, left of the case to feed the turbo, and a scavenge pump to take away the hot oil from the turbo. If I were you, I think I'd source a wrecked turbo, and use the bottom end and electricals. I would think that there is a good possibility that the headers would bolt right up, This is usefull, since the inner walls of the Turbo headers are stainless steel to prevent rust entering the turbo. At least one other guy has built a 650 up with a 900 block and head and gotten over 130hp at the wheel. The 900 crank will drop right into the 650 bottom end with no modifications. The barrels require some relieving of the case with a die grinder. As turbocharged motorcycles go, the Seca is a pretty simple affair. With enough time, I think your project is realistic and quite interesting.

I really have no idea what you guys are talking about, but these posts are fun to read and one day (maybe) I'll be able to add something technical. Until then good luck and keep us up to date on that cool project.

OK... so I need to stick with the turbo seca carbs... unless we can find a suitable aftermarket carb. I know there are lots of bike carbs out there... know of any that are immediately compatable with blow-through boost?? Remember I am a master fabricator and machinist by trade.... I can fab just about any adapters you can immagine for probably most any carb that is of a reasonable size. Help me find some good carb. candidates if you feel inclinded. Aproximately how much airflow/hp can the turbo seca carbs handle with proper tuning?

Doesn't the turbo seca use the same basic type of crank-angle sensor as my 750? If so, wouldn't it be a breeze to swap on the ignition system from the turbo seca?... it might even plug right in!

The cylinder head I can deal with on the 750... material can be removed from the combustion chamber very easily to reduce compression ratio. I have many years of headwork under my belt.

Overall, I think the 750 will handle the output I expect from it... I will not be pushing severe amounts of boost.

The oil feeds I can deal with as well... I can tap into the block using standard fittings to take pressurized oil directly from the engine. A simple return line tapped into the oil pan will return the used oil from the turbo.

The header will be custom bent and welded by me. I plan on using heavy-wall mild steel tubing... this cheap material is still considered to be the best turbo header material available because it copes very well with the heat and constant expansion/contraction from heat fluctuations. The rest of the exhaust will likely be 304 stainless. The intake system will be made entirely of T6 aluminum. The turbo will likely be front-mounted directly in front of the engine block instead of mounted underneath the bike. This should take care of a lot of the problems associated with the turbo seca.

I'll see what I can dig up on the above stuff. Thanks for all of your help guys!

Lee

You will probably need a fuel pump with a few psi to spare over maximum boost to get fuel to the carbs, otherwise boost will prevent proper fuel flow. You will also need a fuel pressure regulator. Best, I think, to just pull such components off of a donor Seca Turbo. Since the motors are so similar, I'd be tempted to just use the Turbo motor and graft on the 750 block, pistons, rods and heads, then deal with the compression issues. After all, if you are going to go to the trouble of turboing your bike, why not start with a turbo engine that will drop right in, then customize it to your specs. I know that there was an 836 Wiseco kit for the XN85 that brought power up to the 130hp range with some mods, maybe there is something similar for the Seca?

I hear you... I agree. I'm trying to do this without a donor seca... they are just too hard to find. Unless anyone knows where I can get one...?

Is there ANY way that I can use my existing carbs? I can buy whatever jets/springs are necessary... and install check valves and a fuel pump and all of that stuff. If my 750 carbs cant be made to work, I am going to have to either find turbo seca carbs, or a set of aftermarket carbs that could be custom installed and tuned. Do you know if my hitachi carbs will handle the boost?? If anyone has a spare set of turbo carbs, I would pay good money for them... let me know if you do. I would also be looking for the ignition timing brain and its associated parts if anyone so happens to have a parts bike... again... I would pay good $$$.

In response to the block grafting... I actually have a better idea to deal with the compression. I need to get in there and freshen up the timing chain and tensioner, as well as re-shim the valves. While I'm there, I might as well swap on a copper head gasket and port and polish the entire head... at which point, I will remove material from the combustion chambers and "cc" the chambers for an equal compression ratio across all cyls. This is better for me since I don't have to deal with finding a donor seca. I really think this can be made to work with the 750 bottom end... again, I'm not looking to make MASSIVE power levels just yet.

Thanks for your continued input on this... I'm sure we'll figure this out. Please help me with the carbs most of all... I'm not very knowledgable with these bike carbs yet.

Lee

This guy has everything you need, if you don't mind buying across the border.

Turbo and Spares

Alot of large superchargers on cars that are blown place the carbs in a box and the whole box is pressurized by the supercharger(on this side of the circuit is no different that a turbo) With both side of the carb equalized in pressure there would be little problems with leaks/blowouts past seals or gaskets. I do think that you would need to give a 1-2 psi input pressure on the fuel using a small pump and a high quality reg. To much pressure and the floats would not be able to close the needles completly. It is doable. That being said I think you are nuts! Sounds like a project that will set uncompleted in the shop forever.

Jay Moyer :blink:

WOW - what an auction - that is going to be one hell of a deal for someone.