[markwemple]

Other than an p/c set, what else needs to be done to do a 944 conversion on a 95 900ss

 

[bradblack]

generally they have more compression than std and will require some sort of ignition mods to stop it pinging. std st2 pistons would be the only thing to not need that.

possibly some carb tuning if you are inclined, altho i'd normally consider that as part of the job to get the most from it.

 

[ducvet]

Any other work that is best done while the engine is out and apart.

valve guides while the heads are off.
crank plug inspection while the cylinders are off.
cylinder stud change if you have chrome studs.

As Brad said ignition timing change.
lap cylinder to head.
check carburetion.

 

[markwemple]

I keep seeing reference to the crank plug issue but do not know what to look for or where to look. The ST2 was the mod I was thinking of. Cheap, but will I see any real power increase. Valve guides and seals, or just guides? Would I have a machine shop do it or are these DIY possible?

 

[ducatimike]

I installed a 944 kit with high comp pistons on a 94 900 Monster years ago. Also switched out the carbs to Flat Slides. Added lightened wheels. Cut the lid off the air box. I have to say this bike rocked. Power wheelies effortlessly. The Flat Slide carbs really sharpen the throttle response. Make sure the timing is retarded a bit or you will get detonation which can damage the pistons.

 

[markwemple]

The ST2 has 40 more CCs but 1 less hp while running more compression. Should I just not do a ST2 mod?

 

[ducvet]

The ST2 has 40 more CCs but 1 less hp while running more compression. Should I just not do a ST2 mod?

Not sure where this data came from but I would be surprised if it were true.
St2
short intakes, more aggressive (and sought after ) camshafts, bigger pistons.

I do not have dyno numbers for you with the st2 pistons but I have installed them in a few bikes in days past and though not as much Hp as hi comp 944 pistons the benefits were there. If I were looking to run 87 octane = st2
max hp = higher compression
not change timing =st2
can get used st2 pistons for cheap= st2

 

[markwemple]

Yeah, st2 cams and intakes are crazy money. About the price of a good running engine. Where would you buy new rings?

 

[ducvet]

I would usually NOT buy new oem rings, we would simply use low mile st2 pistons and the rings would be fine. you used to be able to find a GOOD set of st2 pistons for $100 and then bore and hone cylinders was $400ish so outside of labor you had a very reliable low comp 944 for close to $500. Now you have to decide if the added work makes it worth spending another few hundred to get hi-comp 944 power.

I do not think the aftermarket makes a more durable piston than oem so for longevity st2 pistons are decent if you can find a good set for the right price. Also great for the elefants and grand canyons that see hot slow speed use.

 

[markwemple]

I think I'd use the jugs too and have them modified. There are threads on it. Seems an easier proposition.

 

[Combi245]

Ducati Spares have a conversion kit that comes with high comp JE pistons and a set of rebored/plated cylinders, no exchange required. Pistons are the same weight as the originals and you can have the swap done and the bike back on the road in a couple of hours all going well. Only other thing that I would look at would be to put a "total seal" top piston rings on them and put a factory pro kit on the carb which will be a change of jets, needles and needle slides. Have done this on a number of bikes now here in NZ and gives best bang for buck. I have gone down the road of lighterweight pistons which is goiung to require men to pull the engine apart and get it rebalanced but that is another story all together.

 

[ducvet]

I think I'd use the jugs too and have them modified. There are threads on it. Seems an easier proposition.

I have not used water cooled cylinders and converted them to oil cooled yet so I do not know of any pitfalls. I would be concerned with heat transfer as oil does not shed its heat as well as water. The early air cooled cylinders had/have a oil jacket around the cylinders and there were no issues but later (post 99) dropped these for straight air cooling. I must say I would be tempted to try it myself as the st2 cylinders have little to no value they should be cheaper than a bore/plate job.

In that case be sure to either buy a matched set of pistons /cylinders from the same bike or at least make sure you buy matching sized pistons and cylinders (A,B or C sized).

 

[bradblack]

a 4.4% capacity increase at the same comp would be a waste of time imo. comp really wakes them up.

 

[ducvet]

IIRC we used to see about 1/2 the gain of hi-comp 944 kits so right around 5ish Hp and torque gains. Often we tightened up squish at the same time so possibly some of the gain had more to do with us not using a base gasket.

 

[bradblack]

so it was a difference worth the spend?

 

[ducvet]

Depends on what you are looking for.

seat of the pants boost? yes
still running any fuel you want? yes.
runs cooler than high comps? yes
Cheap high quality pistons? Yes -Often longer lasing than a number of aftermarkets.

Would I do it on a customers bike where they are paying labor just to do this? No, I would go for the larger gain for an additional $300-500. If the st2 cylinders work well then the savings are greater. If the motor is apart for other reasons so the labor is already mostly covered it is a small up-charge and why not?

99% of people will chose to put in aftermarket pistons with higher compression because they simply view it as a one time build and want the most power gain they can get.
For a few the do it your selfer where there is NO labor costs so they are out relatively short money and done right it would be a good gain for little $$ and who does not like that?