750 Seca Turbo?

I have an 82' 650 Turbo that I am rebuilding this summer. I bought it in pieces with a PILE of new and spare parts. Among these parts were the heads, pistons, rings etc. of a 750 XJ that fit perfectly onto the 650 engine. I know this because I have it all assembled on the bench.

Talking to a mechanic friend of mine, he questioned whether or not the bike would even run because of the high compression ratio? I am not exactly sure what he was going on about.

Question is, anybody out there put 750 heads on a 650 Turbo? Did/will it work? Any help is appreciated.

Rob

 

Just about everything is interchangeable between the 650, 750 and 900 engines. The 750 head will fit, but it probably isn't much different from the 650 (except not as strong). The 900 heads will flow considerably more air, and some people have gotten over 130 rear wheel horsepower from the setup. If you go to turbomotorcycles.org there is a guy there who is currently messing about with interchanging parts from a 900 into the 650 turbo, and another guy who has had a 900 head on his. I'd love to find a good 900 or Maxim X engine to put into mine, as it is getting rather clattery now. The starter clutch is also going bad, although a mechanic I trust says it might be related to the Amsoil I'm using not allowing the starter clutch to grip adequately. Long story shot, head, rods, cranks, pistons, blocks, all interchangeable. BUT you must keep the compression ratio in line or you will damage the motor from detonation. Use the 650 cams, as they have the proper timing for turbo work, and double up on gaskets to keep the ratio sensible. The 900 block and pistons on a 650 bottom end gives about 740cc btw, so going with the 750 block and pistons may not net you much of an increase in displacement. The 900 crank drops right in, so I wouldn't be surprised if the 750 did as well. You must remember that the 650 components were bullt to handle the stress of turbocharging, so use as many of them as possible. You will also need to reject for any increase in engine size, which, on this bike, might be a problem, consdiering the work required to get them in and out.

 

Yes it will work.

Yes it will run.

You will need to drill and tap the 750 head to accept the 650 knock sensor. Without the knock control you will smoke the pistons.

The higher compression will require premium fuel.

The 750 top end on the 650 will net about 45 more cc's.

And Mac's guidelines on the cams are spot on.

I recommend that you do not disable the waste gate on the turnocharger.

If you can find an adjustable BOV to add to the intake plenum you can dial it down and start with low pressure. Work your way up to a good running tune.

I myself and working on a 650/900 hybrid and it will probably be an LPT until I can install H20 injection.

 

Perfect! Thanks for the info. I'm a bit new to turbos though so I don't understand the ackronymes you used.

What is a BOV? LPT?

Thanks.
Rob

 

Blow Off Valve

(guessing) Low Pressure Turbo???