How bad is your torque curve?

[Syscrush]

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

I think it's worth noting that "easy" or "hard" are not one thing. What we can do easily or what we struggle with depends on our experience and aptitude.

At least, that's what I tell myself about my inability to do good wheelies.

[bobcat]

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.
[/quote]


Sorry EMS, I can see how it appears that way.

I was an amateur mechanic who didn't know how to degree cams until I read a magazine tech
article describing how to do it. Once I tried it I found that it's not that difficult. It does require
a few special tools. I wish it wasn't so quickly dismissed as some kind of "too technical" procedure
that is beyond the ability of the average mechanic to attempt.

[daves79x]

Bob - I know I can easily learn to do it, but I'm speaking from the perspective of most here that just want their CBX to run close to how Honda intended and have everything else work right too. I'm good at that and too old to start fiddling with something that does not need fiddled with, in most cases and for most guys. Expertly rebuilt and tuned carbs means far more to most than exact cam degreeing.

Dave

[EMS]

I think we have to differentiate between being able to mechanically degreeing cams and knowing what happens when you do what and how much.

[bobcat]

Bob - I know I can easily learn to do it, but I'm speaking from the perspective of most here that just want their CBX to run close to how Honda intended and have everything else work right too. I'm good at that and too old to start fiddling with something that does not need fiddled with, in most cases and for most guys. Expertly rebuilt and tuned carbs means far more to most than exact cam degreeing.

Dave

Dave, how can you make that claim if you haven't tried it. I know there's a whole thread here
about adjusting the ignition timing, partly to account for primary chain stretch. It requires
setting up a degree wheel and it's not much more complicated to adjust cam timing. Pro Link
models all you would need to do is advance the intake cam about 4 degrees, 79 model advance
the IN. cam about 6 degrees. The EX. cams are right about where you want them with around
2 degrees of cam chain stretch. All that's needed is removing the right side cam half to slot the
bolt hole. Notice I used "about" and "around" because it doesn't have to be absolutely precise.
Hell, just slot the bolt holes "about 1/16" inch and it will be better than it was. If you don't
like the way it runs, loosen the bolts and put it back where i was. You only slot the holes in
one direction to advance it. The other side of the hole is the original position.

I'm not trying to be obtuse but I hear so many complaints about low end flat spots, power lag
and no low end torque that I can't resist promoting cam timing because it will take care of the problem but I guess if the subject is going to continue to be poo pooed I will give it up. I think
I laid out my case in my R&D thread so I'll leave it at that. PEACE.

[bobcat]

I think we have to differentiate between being able to mechanically degreeing cams and knowing what happens when you do what and how much.

Please see R&D Platform thread. I think I explained what happens and what numbers there.
I guess I need to put together a simplified pictoral explanation of how to do it.

[bobcat]

IMO the lag/dip in the torque curve isn't a fuel/air problem but a cylinder
filling issue. At the low/midrange where the dip occurs there's not enough
port velocity to fully fill the cyl. It is only as the rpm picks up enough that
the velocity is sufficient to more fully fill the cyl. and that's where the torque
curve picks up. That is where more valve overlap at lower rpms come into play
as it initiates and increases the port velocity at lower rpms thus filling the cyl
more completely and picking up the torque curve where the lag/dip occurs.

Hmmm, kinda repetitive huh ?

[Syscrush]

IMO the lag/dip in the torque curve isn't a fuel/air problem but a cylinder filling issue.

I agree 100% with this, which is a source of considerable stress for me.

At the low/midrange where the dip occurs there's not enough port velocity to fully fill the cyl.

But I don't think this is the whole story, because at 4250 RPM, the engine is making 53 ft-lbs, which then drops to 46 at 5000, and back to 52 at 5500. I think that this means there has to be some kind of resonance issue like reversion happening.

I'm not a fluid dynamicist, but looking at my graph, I see that there's a local maximum in the torque at a bit over 4000 RPM, and the global max is at a bit under 8000. Similarly, there's a local minimum at 5000, and the curve has dropped off entirely by 10,000.

The curve from 4000-5000 is not exactly the same shape as from 8000-10,000, but it is similar.

Again, to me this suggests some kind of resonance going on.

I think that there's a positive resonant effect at 4000 that helps despite the low port velocity, then a negative resonant effect at 5000 that exacerbates the low port velocity. Then by 8000, we have the positive resonance and the high port velocity working together, and at above 8000, the steadily increasing port velocity mitigates the negative resonant effect.

Maybe I'm just reading tea leaves and telling myself stories here - I don't know.

[bobcat]

At the low/midrange where the dip occurs there's not enough port velocity to fully fill the cyl.

But I don't think this is the whole story, because at 4250 RPM, the engine is making 53 ft-lbs, which then drops to 46 at 5000, and back to 52 at 5500. I think that this means there has to be some kind of resonance issue like reversion
[/quote]


At about 4000 is where the slides open and the port velocity isn't established well enough
to fill the cyls. to meet the demand of the rpms. The velocity continues to fall behind (lag)
the rpm demand until enough velocity is created by rpm* to more completely fill the cyls.
Advancing the IN cam* would accelerate the port velocity enough to better fill the cyls. and
the torque numbers would improve if not continue to rise producing a more linear curve.
a lot of tea leaves ?

*the scavenging effect created by the exiting EX gasses when opening the IN valves earlier
and timed at the ideal EX valve closing. When enough rpm is reached it takes over from
the scavenging effect continuing to fill the already filling cyls.

It is at this point the further attempted explanation by this tool results in the graph line
going off the chart in many directions and the mind is lost!

[Syscrush]

Very good point about the slides. I'm looking forward to being rid of them - as a reduction of obstruction, and pumping losses, AND a source of resonance.

You're giving me some hope here, Bob.

[bobcat]

Phil, loose the individual throttle butterflies too ! Then there will be
no obstructions.

Keep the stock look ? Maybe this would work; when you get rid of the slides, use
slides cyls.(carb tops, domes etc.) to connect/conceal a main throttle body channel
with a central butterfly (like automotive systems). Once the slide is gone you have a
properly sized passage/throat to the IN port. !?
...and if you use the recessed injectors you have no, 0 obstruction at all.

[bobcat]

...but even with all the obstruction gone you still want to
"pre accelerate" the port velocity by advancing the IN cam
as described to most completely fill/pack the cyls. or you
might still have the velocity lag/demand issue.

come to think of it, with the single CV carb setup eliminated you would
have the issue that a direct lift carb presents; too much throttle
before the rpm demand is there to handle it and the bike falls on
it's face until the revs pick up so you wind up having to apply throttle
gradually to get it to run. Use a single CV slide*to open the throttle
as the demand is there !?
*instead of the single throttle body butterfly/direct lift effect.