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  Topic Review (Newest First)
Mar 19th, 2017 8:46 am
Originally Posted by ducvet View Post
.....2v/ 853 motor used toyota rods.....
.....now you're just teasing us.....
Mar 15th, 2017 3:04 am
bradblack which toyota and how long?
Mar 13th, 2017 10:16 am
ducvet Brad
I am not sure what rods Bruce used in the 1000/883 build But can find out when he gets back from Daytona. Not sure on the Honda but my 2v/ 853 motor used toyota rods which were longer than stock.

I seldom see much Hp increase from exhaust systems, most of the gains come from improved fueling. There are some exceptions of course but most manufacturers do not plan to make their exhaust systems down on power but must make them quiet so a lot of R&D goes into keeping much of the power. Opening an airbox can be the biggest gains though you have to be careful of messing up drive ability so though open often = Hp it can make the bike run poorer more often due to inconsistent air flow or rain messing the jetting up.

Doug Cook used to make some of his full systems with necked down venturies as he was an aerospace tubing welder and saw them used at work he tried with some success. He also found that most of the time the smaller motors worked well with a 2-1 where the 900's on up preferred 2-2 arrangements. I can tell you one area he never spent R&D time was making muffler volume a prioity, His systems were often all core and no packing, the louder the better. Both systems I have by him have Db killers I had to fit so I did not go deaf and yes they cost me a little Hp, more so on one than the other.
Mar 11th, 2017 9:54 pm
bradblack interesting what eric says. i've got an aprilia racing akrapovic muffler at work from an early rsv mille, the ones that had the 2-1. it has a 60mm inlet and 48mm ish outlet, with a tapered core. also, a lot of the late 996 chassis termi systems had muffler outlets noticeably smaller than the inlet.

i recall one of the now gone local exhaust guys (mark from madaz) saying his zx6 (?) race bike made more power with a reducing taper collector between 4-1 merge and muffler.

eric - did those motors have a honda car rod in them? if so, any idea which one it was? 999 crank?

i think tom has sent me some stuff he has done with 1x98 where he has run baffles with 35mm ish holes in them that is the smallest you can go without hurting the power, even though there is quite a good reduction in noise. all my dyno work with baffled mufflers has been noise based, with baffles having probably 20 - 25mm id holes in them. i think the old staintune ones would be about 20mm id?

the 750ssie made about 2-3 hp more with open pipes and airbox lid compared to all std, but they did feel quite a bit better from memory. i have runs showing no improvement in peak power when the only change is mufflers. so quite possibly the expansion from the collector into the two mufflers is enough there.

BikeBoy.org - Ducati750 SS IE : MUFFLER, AIRBOX AND ECU MODS

conversley, my hot 750 engine in the monster chassis with std monster mufflers as quite noticeable. from memory a similar result to the gt1000 dp kit with baffles in, which were almost std muffler quiet. amazing that a outright flow volume restriction can hurt low flow power, but not higher flow power.


BikeBoy.org - Ducati GT1000 with Ducati Performance Termi kit (first graph)

so it does depend on the muffler. i think the monster ones were not too flash as a std muffler, like the 900ss mufflers they gave a real midrange hole. the ssie ones were comparatively better. but i do also have some m750 runs with a straight through aftermarket muffler that made no more anywhere compared to std.

sorry about the rambling.
Mar 11th, 2017 4:37 pm
swamp2 Well, my stock ebay cans came today... and they're perfect/virtually new... so rather than chop them up, I may just try the Harley cans for a while and see how that works out...

The centers of the HD mufflers have been suitably bored for sound enhancement.
Mar 9th, 2017 6:53 pm
duc96cr As long as you don't go too restrictive you won't hurt much, and if it's too restrictive you'll know right away from the loss of power. As you were saying, the mufflers are from a bigger bike. I would bore the centers out though,, for sound enhancement.😳
Mar 9th, 2017 3:44 pm
Originally Posted by bradblack View Post
the larger 900 headers will make more power (a couple), but the 750 engine is sort of restricted everywhere power wise - valve sizes, cams, low comp and exhaust.

open exhaust is an exhaust of the same or increasing internal diameter from port exit to muffler tip. anything you put in there will generally knock it back to some extent.
So... given the 2 into 1 into 2 nature of the headers, the diameter of the muffler is effectively doubled, right? So if that sum is greater than the exit port diameter, shouldn't be overly restrictive?

Just to be clear here, I realize it's a 750 and I'm not trying to pray to the HP gods with it or anything - just wanted to make sure I wasn't doing anything really stupid and strangling it. Also, since it has PC3 and has been effectively running with open pipes for the last several years, I didn't want to introduce a dramatic map incompatibility. I have no idea what's in it at the moment, but based on my limited time so far, it seems to run pretty well.

If I really feel the need to go fast, I have a Buell 1125CR with Barker exhaust and tuned ECM. It's plenty spunky enough for me...
Mar 9th, 2017 8:32 am
ducvet Years ago we were building a race bike for a series on the west coast of the usa. The rules were it had to be about 883 and air cooled so you can guess who it was aimed at. Bruce (BCM) came up with a combination to de-stroke a 1000ss to the displacement so it would be legal for the class.

The plan was to build the motor for maximum power and then Doug cook was going to restrict the end cap to lower the Hp because there was a 100hp maximum in the class checked on a dyno. All went to plan until Doug started to change out end caps with smaller and smaller outlet diameters and the Hp went up not down. Now this is no scientific test but It was a clear example that some times a motor will tell you things you did not expect, they are all different enough that all you can do is try and see what your results will be.
Mar 8th, 2017 5:39 pm
bradblack the larger 900 headers will make more power (a couple), but the 750 engine is sort of restricted everywhere power wise - valve sizes, cams, low comp and exhaust.

open exhaust is an exhaust of the same or increasing internal diameter from port exit to muffler tip. anything you put in there will generally knock it back to some extent.
Mar 8th, 2017 6:50 am
duc96cr I've bored out the center of those stock Harley cans several times. That mod is worth about 5 hp on a Harley and still be acceptably quiet but throaty. I think they should be fine on a 750.
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