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54mm vs 50mm

2399 Views 5 Replies 5 Participants Last post by  ADV_Addicts
For the full Termi systems on an 03 749s, is there a big difference between the 50mm and 54mm? I read on Section 8's site that the 50mm is good for the stock bore. I was just wondering a couple of things:

1) Is there a power difference between the two on a stock bore 749?
2) If you put a 54mm on a stock bore bike would it negatively affect the powerband, idle, etc?

Thanks all!
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· Bobaganoosh
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1,990 Posts
With a 54mm on a stock 749 you may notice a little loss on the bottom end, say up to 5000 rpms. This can be helped with a custom mapped FIM chip or power commander. Take it to a dyno for a tune. The 50mm will work well all through the powerband. Something to consider, do you forsee engine work down the road, Hotter cams, bigger valves or even a big bore kit? If you may plan for this later, buy the 54mm now. That way down the road you wont have to replace a pricey exhaust system just to upgrade 4mm's to accomidate new engine mods.

My 2 cents...
 

· Registered
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3,131 Posts
+1 on that. Got with the 50mm or even a 1/2 system for the street. I have the 54 and it had some "dull" spots to deal with. Plus, there may not have been a loss down low, but there sure wasn't any seat of the pants gains either. The PC did do wonders though after the fact. Still dissapointed I had to shell out the money for a PCIII & custom map to get it running the way it should, but in the end, it runs friggin great now. Over all, I'm very happy but if I had to do over again I would have done the 1/2 sytem or at a minimum the 50mm system but I don't think there is or was a full 50mm system for my new swing arm bike when I was shopping...or I just didn't look hard enough. I had also heard reports that the 54mm system even works better on a base 749 down low because of the cams. The S is overcammed for the street anyways and I think the big exhaust system only highlighted that fact. If you haven't done it yet, change your sproket. That will help tons, espicially on the S. +3 in the rear should be considered a minimum. I know a guy that went +6!!!!!!!!
 

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677 Posts
When I contacted section8 about the same thing, Jason stated that
as Termi no longer made the 50mm full system it was a a pretty clear indicator that it was not a great upgrade. Also the price on the full 50mm is
more than the new 05 54mm. I just put the new pipe on my 04 749s and it runs great. See my thread on the old board and recent thread on this board. Only issue was a lack of clearance between the swing arm and the pipe. Riding it created the clearance I needed, however it did rub away a small part of the cast seam on the arm. Not a big deal for me. Idle is affected but as Galaxy and Jason told me, you need to get the throttle position sensor reset on the Mathesis. I fortunatley didn't notice a drop in bottom end or any flat spots just a bit more power overall and a lot more noise, but my motor is different.
 
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