carb conversions

[cowpuc]

Really? NO! 5252 is just an overlap of graph. It is just the scale math.

 

Good enough... Like using Ohm's Law when working thru a problem in Electricity/Electronics, I choose to use this stuff when planning a build to know what I am building to so for me,, it is very important. I definitely can see where folks like yourself or @Flyinfool can resist/second guess the math behind all this stuff though as my regard for such is more based on results I have achieved by following such theory's.. I guess, if you end up where you want to go without regard for such it's all good...

[Patch]

Good enough... Like using Ohm's Law when working thru a problem in Electricity/Electronics, I choose to use this stuff when planning a build to know what I am building to so for me,, it is very important. I definitely can see where folks like yourself or Flyinfool can resist/second guess the math behind all this stuff though as my regard for such is more based on results I have achieved by following such theory's.. I guess, if you end up where you want to go without regard for such it's all good...

 

This was my self imposed caution Puc throughout this thread. I know that torque is found by manipulating volume metric efficiency, ratios and duration so I shoot thru these, then you can prove via dyno. Now if I am moding a touring bike then I will state what I am dynoing for at what angle are of interest to me, then go for broke and print off the results; then I can finalize my tune based on the important stuff not just the higher HP output!

 

I see no entry you posted that is wrong rather you wanted to based on 5252 take a stand.

 

SO, I live in the prairies, I can stand on the rails with another and ask "do you agree that the tracks join right under that 2nd electric pole?" as you know if we walk to and stand at that point....

 

You mention measuring in ohms what if we get a solid swing and we then assume the wire, contact or coil is good would that be definitive or, would that suggest we load test knowing there is a problem and can now assume that it will be proved only under load and temp conditions?????????????

 

really a good thread Puc & Jeff and you made it so cause ya made me dig deep

[cowpuc]

You mention measuring in ohms what if we get a solid swing and we then assume the wire, contact or coil is good would that be definitive or, would that suggest we load test knowing there is a problem and can now assume that it will be proved only under load and temp conditions?????????????

 

really a good thread Puc & Jeff and you made it so cause ya made me dig deep

 

Actually, IMHO, that would just be in kin to a simple continuity test and not necessarily applying OHM's law to layout a pathway/road map to the outcome I would planning.

 

YEP,, having all kinds of fun here = GREAT THREAD IMHO!!

[Patch]

I found this, half is two stroke then the four stroke.

These tests done for mods of cams and exhausts.

Note the comment about loading the dyno up @ these higher rpms.

You could think of it as cruising on the flat then climbing a hill.

 

[cowpuc]

OK Puc same dilemma new approach. I wanted to take some time between to think of how I might express this differently, yup I sometimes think slow.

 

Would you agree that in the mentioned graph, torque is still present past 5000 rpm?

Yes or No

 

Would you also agree that in a naturally aspirated engine, low pressure is the fuel delivery system used to transfer the charge or fill the jug?

Yes or No

 

Would you agree that low pressures alter in direct relation to the throttle angle?

Yes or No

 

Would you agree then, that torque peaks seems to correlate to peak velocity?

Yes or No

 

All should be yes even tho I predicked you would say no to it. We can not agree with 3 and disagree at 4 so I fingered I would expose the splinter and just wordsmith the reasons.

Jeff made the mistake of "freeze frame" not that he doesn't know, but that his training reflex kicked in, meaning the piston was not traveling down.

.

 

Quick question just to make sure we are still on a level playing field Patch,,, ""All should be yes even tho I predicked you would say no to it."" is just a matter of your opinion, correct?

 

I found this, half is two stroke then the four stroke.

These tests done for mods of cams and exhausts.

Note the comment about loading the dyno up @ these higher rpms.

You could think of it as cruising on the flat then climbing a hill.

 

 

Not sure of your point in this one Patch? All of info contained in the video you reference is obtained well above the R's you operate your bike at, most of the charts do not even begin until 7200 RPM, wayyy beyond your target R's. Perhaps a relook at the video that both Jeff and I posted would be to your advantage in determining the blueprint for your build and decision making thereof.

[Patch]

It's not about my build Puc. It is showing torque above 5252.

 

The comment about 6500 rpm was me stating that I don't usually need to push my touring rides above that!

 

I've tried to leave that build out of this thread. But because here we are I can say that, as one of my targets is range (fuel tank) needing to run high revs to make use of torque would cause me to miss all my targets for the touring bike, the Kat is a different story.

 

Now if as in the barb conversions we were to only take a small piece of why intake runner lengths can improve bottom end torque, then it is not enough to justify converting to one single carb when and where it will shut of torque too early over canceling the potential range of any given touring bike I know of!

 

In the 4 stroke dyno results they clearly demonstrate the filling challenge via scavenging diminishes at higher the rpms and is what we would expect to see in these posted carb conversions with restricted flows?

Remember these conversions make no suggestions relating to cams. Cams are the timing limits so in these conversions one would need to change duration of the lobes or starve the engine!

[Flyinfool]

Wow Puc how about an easy one?

I am assuming that we are talking modified street averages, naturally aspirated and pump gas.

I get why you limit @ 5000ish but to just agree or disagree stunts growth.

If the question is solely based on should the torque curve be above the HP curve? Then yes, but, I am uncomfortable with the limit!

I am not going to comment on catastrophic failures of components because, this usually has more to do with the bottom line more so then possibilities. Then or as described in the vid..

 

So regarding curves, where can we find a 25% equalizer? That’s not gain but equalizer of such curves?

 

Where we divide again: I am going to study my flows; I have to start with air flows and velocities.

 

Now change how we measure these 2 curves and don’t point at the crank output efforts for what the wheels are or aren’t producing and, maybe

So is there an rpm range when admiring the sexy curves of a cam? Hmmm Are there impacts to torque?

​

 

OK Puc same dilemma new approach. I wanted to take some time between to think of how I might express this differently, yup I sometimes think slow.

 

Would you agree that in the mentioned graph, torque is still present past 5000 rpm?

Yes or No

 

Would you also agree that in a naturally aspirated engine, low pressure is the fuel delivery system used to transfer the charge or fill the jug?

Yes or No

 

Would you agree that low pressures alter in direct relation to the throttle angle?

Yes or No

 

Would you agree then, that torque peaks seems to correlate to peak velocity?

Yes or No

 

All should be yes even tho I predicked you would say no to it. We can not agree with 3 and disagree at 4 so I fingered I would expose the splinter and just wordsmith the reasons.

Jeff made the mistake of "freeze frame" not that he doesn't know, but that his training reflex kicked in, meaning the piston was not traveling down.

 

 

I will tell you all the dark side but not the ratio targets. The true evaluation of torque is based on displacement. The challenge will remain volume metrics, duration and angles.

 

These are just my opinions, not judgments, they are as mentioned based on wins and losses as well as, the good fortune of having shared experience with much smarter guys willing to share than myself, that does not mean they figured it out for me, but rather they set me straight, more than once.

 

You said that if I agree with 3 I must agree with 4. But I agree with neither so I am still consistent.

 

When the piston is traveling down on the intake stroke to generate air velocity in the system the torque is actually negative as the piston requires a source of torque to turn the crank to pull the piston down. Your question was a bit ambiguous which is why I included an explanation of my interpretation of the question, Since there is no torque being generated at max intake air velocity I made the assumption that you were referring to the average airflow over the complete 4 cycles. Now you could have also been referring to piston velocity which would bring in a whole nutter set of answers. Peak airflow velocity does not happen at peak piston velocity. There are many velocities happening, I am not sure which velocity you were asking about.

 

Of course it is very possible that we are not even talking about the same thing here.

[cowpuc]

 

Of course it is very possible that we are not even talking about the same thing here.

 

:rotf::rotf::rotf::rotf::rotf::rotf::rotf::rotf:

 

Ohhhh Magoo,, ya did er again = I am DEFINITELY gonna add that to my "All Time Favorite VR Quotes" list!!!

[Patch]

You said that if I agree with 3 I must agree with 4. But I agree with neither so I am still consistent.

 

When the piston is traveling down on the intake stroke to generate air velocity in the system the torque is actually negative as the piston requires a source of torque to turn the crank to pull the piston down. Your question was a bit ambiguous which is why I included an explanation of my interpretation of the question, Since there is no torque being generated at max intake air velocity I made the assumption that you were referring to the average airflow over the complete 4 cycles. Now you could have also been referring to piston velocity which would bring in a whole nutter set of answers. Peak airflow velocity does not happen at peak piston velocity. There are many velocities happening, I am not sure which velocity you were asking about.

 

Of course it is very possible that we are not even talking about the same thing here.

 

When reading your answers I was reminded of the old saying that goes like this: If you want 100% fillage then put the head on a hinge!

 

As you know Jeff there is a minimum speed at which the engine must turn or spin to generate enough vacuum, fill and then compress in order to run; that is what the starter does at around 500+ rpm.

 

When the piston is on her intake stroke it produces vacuum because of the difference in size of valve diameter in relation to piston and bore, this also creates velocity of flow.

There is a very important angle here that works in relation to the lobe. This angle is that of the throttle plate restricting flow and thus increasing velocity reducing potential volume therefore controlling output. Bernoullie's and Venturi's laws apply meaning that flows restricted increase velocity regardless of fluids and volume in question.

 

Given equal chambers and fixed duration's the filling of jugs is where the trophy is to be won or lost. This also includes every cycle of exhaust and again where both flow volume and velocity are critical sequences.

 

Flow Velocity is key to torque just as flow volume is key to HP.

 

The questions are based on dyno testing and is why I chose the explanations given. The dyno shows and tells where and what is to be found at which rpms and angles of throttle, these are tied together after the build, the results may be used for tweaking or for the driver who is expected to ring out the given performance targets if on a track.

If you are running street you would likely want to find your power down low where torque rules (4 stroke) so you will need volume at velocity, one without the other leaves you too low in volume metrics, or wastes displacement!

 

Again this thread was for carb conversions on touring bikes and, is why I think that the runners and plenum plus throttle angles are problematic, given what we have seen.

Edited February 25, 2019 by Patch

[Patch]

I thought I share these thoughts and add a question.

 

Here is something to think about with the exhaust and intake ports interactions and when for a brief moment they are both exposed to one another during overlap.

 

For this example I ignore throttle angle.

@ TDC top/end of exhaust stroke, both the intake and exhaust valves are slightly open.

The exhaust fluid has been pushed up and out thru past the ex valve by piston @ velocity; if the port and pipe diameter are correctly sized velocity should continue to be maintained say for the first foot or so of travel.

Because both valves are open and according to Venturi, a slight vacuum must exist caused by the moving fluid being pushed out. In other words something below atmosphere exist @ TDC both valves open, 2 flows in progress piston stopped before reversing direction.

This overlap is expected to one allow the exhaust fluid to continue out while the slight low pressure caused by the velocity of exhaust will cause the new charge to fill this void, in a sense freeing the exhaust tail, (Kind of best of both cycles/worlds) It is hoped that this rule will help expel the combustion chamber volume of unusable mix replacing it with fresh charge.

Keep in mind that for a brief moment the piston has stopped travel and will then reverse moving down. In more than 1 cylinder engines this new intake cycle is an energy blead off the crank as Jeff alluded to.

If we change designed exhaust then this has an effect on flow and velocity and therefore has effect on filling. Sometimes you win and sometimes not.

Again as Jeff alluded to earlier when atmosphere is removed pressures are unequal, then another rule applies that says pressure wants to equalize. This equalizing generates velocity as the two pressures seek to balance/equalize, this is how we fill the jugs.

As the piston now travels down in naturally aspirated engines, these pressure differentials continue and the race to equalize/fill is on.

 

So what’s the problem and why don’t we achieve 100% volume metrics on each stroke?

[cowpuc]

I thought I share these thoughts and add a question.

 

Here is something to think about with the exhaust and intake ports interactions and when for a brief moment they are both exposed to one another during overlap.

 

For this example I ignore throttle angle.

@ TDC top/end of exhaust stroke, both the intake and exhaust valves are slightly open.

The exhaust fluid has been pushed up and out thru past the ex valve by piston @ velocity; if the port and pipe diameter are correctly sized velocity should continue to be maintained say for the first foot or so of travel.

Because both valves are open and according to Venturi, a slight vacuum must exist caused by the moving fluid being pushed out. In other words something below atmosphere exist @ TDC both valves open, 2 flows in progress piston stopped before reversing direction.

This overlap is expected to one allow the exhaust fluid to continue out while the slight low pressure caused by the velocity of exhaust will cause the new charge to fill this void, in a sense freeing the exhaust tail, (Kind of best of both cycles/worlds) It is hoped that this rule will help expel the combustion chamber volume of unusable mix replacing it with fresh charge.

Keep in mind that for a brief moment the piston has stopped travel and will then reverse moving down. In more than 1 cylinder engines this new intake cycle is an energy blead off the crank as Jeff alluded to.

If we change designed exhaust then this has an effect on flow and velocity and therefore has effect on filling. Sometimes you win and sometimes not.

Again as Jeff alluded to earlier when atmosphere is removed pressures are unequal, then another rule applies that says pressure wants to equalize. This equalizing generates velocity as the two pressures seek to balance/equalize, this is how we fill the jugs.

As the piston now travels down in naturally aspirated engines, these pressure differentials continue and the race to equalize/fill is on.

 

So what’s the problem and why don’t we achieve 100% volume metrics on each stroke?

 

I am not sure that our Yamaha V-4's have a cam grind that is ground for valve overlap. Noticing the amazing low end torque that the 74 inch/1200cc engine produces and while thinking about building up a "V-Maxed" Venture (I actually had all the parts in my possession to do this but health got in the way and ended up selling everything) and still wanting to keep some of that torque (plenty for the amount of weight those ft/pds had to get moving so hp could take over once the R's crossed above 5252) , if memory serves, I think I did check and find these scoots are "0" valve overlap. I might suggest that you do some research and find out one way or the other..

One of the things to remember about valve overlap, while it does promote HP gains in the upper R's do to exhaust scavanging inviting higher velocities and cleaner fills,, it also is not a friend to emissions as your actually pulling unburned fuel into the exhaust (why those old muscle cars had such a sweet exhaust smell - I AM IN LOVE!!!) and for this cause, it is not uncommon for bike/cars being built since the 80's to not include valve over lap in their stock design.. Something to think about I reckon.