This was something that came from a graph I pulled up out of curiosity’s sake. I looked and saw something that I realised I had seen before, then the correlation struck me. This is not so much a right/wrong report, just some observations.

The graph below shows two 748 and two 996 torque curves. I’m sure you can tell which is which ( hint : 996 makes more ). All are running the same cam timing specs ( not std, but my usual ), both 996 have the FIM UM222 single injector chip, both 748 have the FIM UM211 chip. The difference between the two of each set is that one bike has 45mm Termi slip on mufflers, the other has Arrow 50mm cross over and muffler kit. Many refer to this as a 1/2 50mm exhaust kit.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Which is not to say that the brand is the problem. I seriously doubt there would be any real difference between Arrow and Termi muffler power output of comparable size mufflers. Both companies know a bit about making pipes.

The thing is, both the _ 50mm kit bikes have a big hole in the bottom of the range. The fact it is numerically the same – 7 ft.lbs – is a bit too odd, but the shape and RPM range are consistant. In fact, the curves are almost identical shape all through, with the 4 peaks in the same places. The 996, which places higher demands on its ports, has a sharper rise and fall off at either end, but that is to be expected. The 996 also emphasises peaks 2 & 3, whereas the 748 emphasises peaks 3&4. Some of you are probably thinking "so", but this kind of thing really interests me. Of course, the fact they all have the same inlet and exhaust design and lengths does go a long way to explaining it. But I would normally have expected the smaller engine to have all its peaks offset much more to the right.

The green 748 has some under tank filters, which may take the top end torque away a little, but the bottom end is pretty flash. The red curve is actually the after curve from the 748 report, which was already pretty damn cool. The green bike is almost like a 2V 750, in that it has no noticeable torque peak when riding. It just accelerates, without a real top end rush like you expect on a 748. Odd. Hopefully, the guy who owns it won’t come back and tell me it’s slower now just because of the way it feels.

The only thing, however, is that many people say the 1/2 50mm kits really help the top end. Maybe not on a dyno, but out on the track. Maybe they do. Or maybe the loss of bottom end makes them feel better at the top. Like they really come on, man. Back to the immeasurable "feel" thing again.

It reminds me of an article I read in a recent Sport Rider magazine. A tester had ridden a hotted R1, and commented on the killer midrange it now had, at the expense he felt of the top end. On a dyno it had 14 hp over a std bike at the top end, with even more through the middle. So much for feel. Even confuses me sometimes, when I’m trying to decide if something is better or not.

For a better comparison, the graph below shows four 748 torque curves. Red is std & 45mm Termis, green is std & 45mm Arrows, blue is cams dialed & 45mm Termis ( from above ), purple is cams dialed & _ 50mm Arrow ( again, from above ). That blue line is up around 20% at 5,000 RPM. And that, campers, will make a hell of a difference on the street. The top end advantage of the 1/2 50mm Arrow bike is better shown here too, although in percentage terms it’s not that great.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

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