Hi everyone, a few people suggested I post here to try to figure out a strange dip in the power curve at 2900 RPM on my 98" big bore. The build has the following:

Just got my bike back from Suburban Motors in Thiensville, WI. Bike had 53k on it, and a nice running stock/stage 1 88". The original plan was to go with a cam swap to eliminate the chain drive cams and install a 2 into 1 pipe. Then one thing led to another. Ended up doing the 98" big bore high compression "Street Stomper" kit they offer. It consists of the following:

Bore stock jugs
Custom forged Mahle pistons
S&S 585G cams
45mm Mikuni carb
SE HD clutch spring
Adjustable pushrods
Daytona Twin Tec ignition controller
Ported & flow benched heads
Compression releases
1.9 Intake valves
10.5:1 C/R
Rinehart 2-into-1 full exhaust.

I'm wondering if it has anything to do with the cams or the exhaust?

 

It's the exhaust. There is no air/ fuel graph probably because it would show a severe rich spot where you have the dip. Jetting won't cure it--only a different pipe. Having said that, do you feel the dip when riding or does it just bother you to see it on the graph?

 

+1 The Rinehart 2:1 isn't much better than slip ons, but it looks good. You might want to look at a Thunderheader or a Fat Cat if you want performance. That is a pretty high compression ratio for a 98" with 585 cams, but I wouldn't think that would give you issues.

 

Yes without the afr graph it's tough to say... lots of times we have a little too much fuel on the accelerator pump and that combined with a 2-1 will cause that. Less back pressure in the pipe also contributes..

 

Thanks for the quick replies, you guys rock! I haven't had a chance to ride it due to cold and salt so we'll see how it is going down the road. I did notice when revving it hard it does blow a little black smoke but no hesitation or stumbles. The builder was pushing a FatCat but it was too loud for my likes.

 

IMO a Fatcat would be much better--Thunderheader much worse. I'd ride it and see if it's a problem for you or not.

 

They have different baffles in varying degrees of decibels for the Fat Cat.

 

Yeah and they're all bloody loud-as even the so called quiet baffle

 

What is the ccp of that engine?
Scott

 

The cam and the pipe, coupled with too much exhaust flow for motor size, don't like each other. Bike is over exhausting..