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I've read on a few forums now that the carbed 900SS runs out of steam above 7000rpm because the inlet tracts are too long. I have just bough a 900SSie engine and injection gubbins to retrofit. While looking over the injection motor I noticed that the inlet tracts are at least as long as my carbed motor. The injector bodies are a good deal bigger in diameter than the carbs and the injection motor has longer cams so I would suggest THIS is the reason that the injection motor revs better than the carbed engine and that the tract length is about right for the engine. This conclusions is strengthed by the fact that I fitted injection heads and cylinders to my carbed bike over winter and it revs noticably better but is still a little breathless.
 

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Hordpower :: Ducati :: manifolds

more on the engine spec here - Hordpower :: Ducati :: KroneM944

i think it's probably a combination of things. the ssie inlet is longer from air filter to throttle, but it's larger and tapers. fitting larger carbs (ie, 41fcr) doesn't fix the carbed bike. shortening the manifolds does. but the ssie still makes more power than a short manifold carb bike ime as a direct comparison, so i'm sure the cams would help once the manifold length is reduced. and the ie cams are longer on the closing side of the centreline so should favour higher rpm by design.

as you say, yours with the ie heads and long manifolds is still a bit breathless. and, as ever, you'll find porting the heads can make a difference too. if you look at an st2 which has even shorter trumpets into the airbox you'll see that doesn't translate into top end. both std and my 94hp one peak pretty early. i did a high comp ported 900ssie a while ago that had 1mm oversize valves and vee two 212 cams (like my st2). these have about 14 degrees more duration than the specs gave - about 279 degrees, but it still peaked under 8,000 rpm.

it's a 2v motor, and the carb motor is good at what it is, but has designed in features that work under 7,000 and hurt it above and that take a lot to overcome. advancing the cam timing on a ie makes it feel a bit more like a carby motor as you change the shape of the toqrue curve too, so they're not really that different. i'm sure retarding the cams will make it feel better at the top end, but it'll be slower overall.

there's a guy in germany named mathias who sends me lots of stuff on a 90 900ss he has that has ported heads and quite a lot of power. it'll pull 15/37 gearing to the red line on the autobahn. he runs 41fcr on short manifolds with 90mm long tapered trumpets on them (see photo). so maybe it's the carb position, not the overall length.
 

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Discussion Starter #3
The picture of those carbs says a lot. A straight shot at the inlet tract. The standard carb set up is very convoluted to say the least where as the injection model is a bit staighter. That's probably the reason the bike rev's a bit better. It would be nice to make a proper downdraught head for the injection system - one day may'be.

All three sets of heads I have (1 carb, 2 injection) have a 'trough' in the bottom of the inlet port that I plan on filling with epoxy on my injection motor. I wonder if the trough is is delibrately made like that.
 

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All three sets of heads I have (1 carb, 2 injection) have a 'trough' in the bottom of the inlet port that I plan on filling with epoxy on my injection motor. I wonder if the trough is is delibrately made like that.
A friend of mine who is the chief mechanic on his sons N.Z. SuperBike team (4th in this years championship) used to race 900's years ago. His hot tip to me was to fill the bottom of the inlet port with epoxy (and screw it in place for safety) and D shape the port. He was convinced the inlet port is the key limiting factor.

This suggestion was also echoed by the very competant race shop who did the machining work on my heads.

I didn't do this to my bike as I was nervous about the epoxy coming loose on a street motor that I don't intend to pull the heads off very often
 
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