How bad is your torque curve?

[oroepke]

At 7000 it feels like the good old 2-stroke Kawasaki widow maker! Literally, I have to be pointing it straight when hitting 7k!

[EMS]

If you ever decide to replace the exhaust and don't have the original one, try to find a Prolink system with a crossover. This will give you a much better mid-range and makes the bike more rideable.

[bobcat]

Cam timing.

[Rick Pope]

I'm not an engineer, nor have I slept in a Holiday Inn recently, but I believe the head pipe diameter has as much to do with the torque as whether it's a 6-1 v, 6-2 system. Typically, aftermarket pipes have bigger head pipes, causing the flow to slow too much at lower rpms.

My old CB750 wears a Hooker 4-1, breathed on engine (RC836), and is a relative torque monster compared to other 750's of that era.

[Larry Zimmer]

Indeed, Rick. I think a number of folks don't realize that many stock headers are smaller than they appear because they are double layer to prevent bluing. So, smaller functional pipe. Aftermarket tends to be single layer of same diameter as stock outer Consequently, the exact thing you are describing.

[EMS]

It has to do with "scavenging". The exhaust gas is being put under pressure pulses from the pistons and it starts to oscillate. The diameter of the pipe and length of the header contribute to the resulting frequency with which the exhaust gas column "swings" and helps "sucking" burned gas from the cylinder, thus helping fresh load coming in when the oscillating frequency is right. This concept was basically behind Peter Schüle's header design.
I don't think playing with cam timing is an easy way for the amateur engine designer and mechanic to address performance low spots.

[Syscrush]

I don't think playing with cam timing is an easy way for the amateur engine designer and mechanic to address performance low spots.

That may be. This is purely anecdotal, but when Scott Miller built my engine, he degreed the cams. He's a former crew chief for Honda Canada, which puts him at least a bit outside of "amateur engine designer and mechanic" IMO. The midrange with those cams was not great, but the engine had other issues. The midrange after being rebuilt with all OEM valvetrain was worse, but the engine still had other issues.

If I can flatten that dip a bit with modern EFI and dialing in cam timing, I'll be a happy man.

[bobcat]

Amateur engine designer and mechanic ?

[Jeff Bennetts]

Back to the D&G header and collector, I also believe the collector of this system has as much to do with the flat spot as does its header pipe design, most six into one systems seem to have a midrange flat spot, a six into two into one is a better overall performing system.

[bobcat]

Back to the D&G header and collector, I also believe the collector of this system has as much to do with the flat spot as does its header pipe design, most six into one systems seem to have a midrange flat spot, a six into two into one is a better overall performing system.

BINGO !

EMS, how many championship bikes have you built ?

[bobcat]

I don't think playing with cam timing is an easy way for the amateur engine designer and mechanic to address performance low spots.

That may be. This is purely anecdotal, but when Scott Miller built my engine, he degreed the cams. He's a former crew chief for Honda Canada, which puts him at least a bit outside of "amateur engine designer and mechanic" IMO. The midrange with those cams was not great, but the engine had other issues. The midrange after being rebuilt with all OEM valvetrain was worse, but the engine still had other issues.

If I can flatten that dip a bit with modern EFI and dialing in cam timing, I'll be a happy man.

Scavenging is what ideal valve overlap (cam timing) is all about. A good exh. sys. makes it
work even better. Velocity, mostly ignored, is what it's all about.

[daves79x]

Rick, and in the past, I am/are referring to the average or even above average, handy hobbyist that is capable of doing most maintenance items on a CBX, but for which degreeing cams is far beyond our understanding or capabilities. I doubt that degreeing cams will eliminate the DG flat spot anyway, unless you degree just specifically for that system.

Dave

[bobcat]

Trying anything to tune for that DG pipe is a waste of time. There's several
reasons why that pipe doesn't work, not just the collector.

Dave, degreeing cams is not that hard. It's easier than rebuilding carbs.

[EMS]

Rick, and in the past, I am/are referring to the average or even above average, handy hobbyist that is capable of doing most maintenance items on a CBX, but for which degreeing cams is far beyond our understanding or capabilities. I doubt that degreeing cams will eliminate the DG flat spot anyway, unless you degree just specifically for that system.

Dave

That's what I was trying to say! The average person on this forum who does his own wrenching is in over his head with degreeing cams. When I said

Amateur engine designer and mechanic

of course I was not referring to you, bobcat. I wish you wouldn't take everything personal.

[Syscrush]

Amateur engine designer and mechanic

of course I was not referring to you, bobcat. I wish you wouldn't take everything personal.

For what it's worth EMS, I read it as you intended.

I also wanna say I love you both. The depth and breadth of experience and knowledge on this site is what makes it possible to own and enjoy one of these bikes.