Pods on a CV Carb

[Patch]

Hey guys. So as mentioned I’ve decided on two more last projects.

I’ve been polishing up on flows which was a topic I was involved in many years ago over the GV.. While reading through some old papers I had flagged I came across this quote a little further down in this post.

 

What is it about this study that remains relevant today? Well for me it circles around the internet mechanic, not to say the internet isn’t a solid learning library rather, to suggest that we too often place too partial an input above fact and above known or proven theories!?

 

As our bikes age many of us want to bring improvements or cheats to design that go against study; and while this is the sport, and completely get it within the context:: But, theory and physics still have their place and, should offer up some mapping as to limits or potentials for enthusiast.

 

Often we read on the gen 2s – pods, I for one can’t see its benefits, am I wrong or just stubborn?

No neither. What I always read is an explanation as to what makes it walk the talk.

 

So not unlike a like a cane may help you walk after……….. Well in performance that means benching the pilot/driver, that is absolutely true if he is also the mechanic.

 

So a CV carb is just what the name entails, a Constant Velocity Carburetor! Thinking that you can cheat Constant does not buy you a seat at the bar, period. The complications and effect t of Velocity negate pods, period! And,,,,,,,,,, they cannot,,,, in and of themselves promote flow, that is a fact. Period!

 

And so we read about the “done this and that’s” to compensate??? HMMMMMM

 

Stacks stream flow before the venturi. The Venturi accelerates so , increases Velocity. Resulting Velocity creates low-pressure somewhere and more. Angles play a very big role after Velocity, this cannot be ignored or overruled, now I’m leaving out much cause and effect.

Read this quote:

“mass driven flow initial conditions are computed from the inlet. In the mass flow driven case there is no problem setting a initial velocity to zero at the inlet.(this has to be range predictable) In the simulations conducted with pressure driven flow initial velocities at the inlet has been set a bit arbitrary. Velocities around 30-50 m/s at the inlet has showed to give good results. The main problem is if the initial velocity is set to high this will lead to a divergent solution caused by pressure build up in front of the throttle plate or sudden decrease in temperature near the throat caused by super sonic flow conditions. 4.3 Solver There are two numerical methods available in Fluent to solve the governing equations (mass, momentum and energy) and in this case also turbulence.”

 

The very last word “turbulence” generated by the pods verses Velocity stacking is the cane. So in my experience there is no substitute for performance if we have choosen between disruption of flow @ atmosphere verses velocity @ atmosphere,,,, being all else equal such as density and temperature! (yes density is…)

Does this help make sense for the reasoning behind not podding? Or ,,bike to bike with pods verses stock without, which truly has the upper hand given the CV Carbs?

 

[cowpuc]

A Puc opinion:

Though they are still a carb with similar design as their mechanical counterparts (low speed and main jets, metering rods, floats ect), CV's have a completely different operational method. Their dependence on vacuum and precision controlled environmental properties for proper function and the R&D put into all those operational parameters (everything from airboxes to exhaust systems) can never be overlooked. I hot rodded an 03 Anniversary 88 inch Twin Cam HD one time with a really neat 5 pounds of boost gear driven blower that I ended up using a CV carb on as a finished product. I specifically chose a cam profile for the build that showed no valve overlap in its design. The CV did pretty dog gone good with an 18 horse increase on the dyno and the bike looked and sounded great because I purposely stayed away from valve over lap which would have led to a need for scavanging on the pipes which would have increased the viable option for a Velocity stack to assist the Super Charger in its effort to stuff the fill on the chambers that were being scavenged upon. Sure, the build could have easily included a cam profile with some overlap in that would have required a mechanical carb and a stack with a set of drag pipes to allow for proper scavaging and in the end I could have squeezed another 20 horse out of her BUT to what detriment? It would have sounded good if ya like lumpy but would have not been much of an everyday rider IMHO. The sweetness of a CV is found in its delivery of linear, smooth power from the bottom of the R's to tapped out with all of the natural twitches of the riders wrist - much more forgiving for sure, the vacuum operated slides see to that. Probably not explaining myself here to well.. Let me try another example..

I have read lots of thoughts on altering the airboxes on our scoots by more than one person. Usually, not always but usually some very experienced and knowledgable V-4 tinkerer like zagger will join in and mention the need for placing restrictors in the top of the venturi's of each carb (washers?) to return the needed restriction that the airbox once provided to get the bike to run right. I have ALWAYS nodded in understanding whenever someone like our own Zag mentions such a thing because the CV carb, as tryed to describe above, needs to have those original design parameters maintained one way or the other in order to function properly.

It may sound right or be right but thats my story and I am sticking to it,, unless someone much smarter than can learn me something:essen_018:

[luvmy40]

There is one valid reason to get rid of the original air box on any factory motorcycle; Cosmetic, a custom look. It seems to me to be obvious. Evidently it's not obvious to everybody as I see so many vintage bikes with aftermarket pods. I also hear many riders of these bikes complaining about the performance of their modified bikes.

 

I'm sure there are ways to make pods work fairly well in one area or another, i.e. smooth at mid throttle or strong at WOT. It's hard for me to see any way to make them work well across the full range of throttle.

 

I did see a beautifully fabricated WWII style bobber made from a Yamaha XJ frame and engine that used a custom intake manifold and a single pod. The owner claimed he gets similar performance to the original system and it looks great.

[CaseyJ955]

If ditching the factory airbox for a less restrictive design, like stage 7 PODs or a Morleys Jet Kit, you will want to use the restrictors to fool the carbs. I got mine from Morley included in the kit but he sells them separately, and they are pretty cheap. I used these on my VMax when I went to the free flowing airbox modification and full Kerker exhaust.

 

Not only does it work but it's brilliant, it's sort of a given for tuning a Vmax as the engine with full exhaust flows enough for that to make sense. I'm not sure the same is true for a Venture, at least with factory exhaust. I would really vote for keeping the factory airbox unless it's a project and the airbox wold be an aesthetic issue. We've seen some bobbed Ventures with pods, pretty sweet looking.

 

I'm sort of a fan of the CV design, at least when they work.

[Flyinfool]

Makes perfect sense. It is very well documented that any changes to the "system" will require other changes to compensate, because you just messed things up. As mentioned Cosmetic preferences can trump almost anything. There are a lot of people that will gladly give up performance for what looks good to them. Really the looks are ONLY important to the owner. It does not matter what anyone else thinks of it.

 

And then there are those like me that wanted to ditch the CV carbs altogether and go with EFI on my Venture. The opening up the airflow would make all the sense in the world. But alas I have sold the Venture so that project has come to a screeching halt. But then as I was making it it would also look cool to ME.

[Freebird]

Back in 2009, I bought an '89 here locally. Didn't known when I went to look at it that it had the full V-Max conversion done to it. V-Boost, V-Max Heads, V-Max rear, etc. I bought it because it was a great deal but sold it pretty quickly. So, I didn't get to ride it as much as I wanted to but the little I did ride it, it ran like a scalded ape. It truly felt like it was on steroids. Since I didn't do the work, I don't have details on the air filter setup but did find a couple of old pictures that I told at the time. I will also say this. The guy that bought out didn't keep it very long. I asked him when I saw him the next time why he sold it so quickly and his response was that it drank gas like crazy. So, I guess with the good came some bad.

 

[Patch]

Hey guys, there's some good posted content.

 

Wow Puc on the boost! I have thought more than once about adding boost in a project as well but, usually get pinched by available cams..

Wouldn't mind knowing how you set your targets or say what measurements and how you achieved them. would be interesting read.

I am surprised you used the CV carbs, that would have been one of my first assumptions to leave on the bench..hmm

 

A different conversation with a fellow some 8 years back, also I guy that had deep theory, both of us bombarded by marketing bolt on HP tried to thread the basics of torque and HP, gains and losses and,, so the story usually goes and so it went. Find in many cases the first page is what gets read, if contradicted then they usually have a friend that proved it, somewhere;)

 

Some of what I just read say intake as an example changes how we view the induction and so changes potentials down stream. Another that likely suggests success in HP gains with the VMax upgrades (for sure hard on gas or the project would have had a meltdown) yet may disappoint others. Still if the guy hit his targets then in my view he wins, one wouldn't expand muscle without expending energy.

 

In my last 2 upcoming projects both are about flow and volume, but both are very different the kat I have the head, cam and carbs, the GV I have everything but this project will require math, flow bench, machining; fuel and ignition management, I am hoping lager throttle bodies, (I have an additional experiment for this). Because the GV will be injected I am going to have some room for corrections in case I mess up my volumes. I also want to focus on a dual plenum, I will be disappointed if I can't make that happen.

 

All that said we come full circle in that we are all looking for greater flows. What we don't all accept is that that is the most complex task of HP.

Turbulence is a real drag and not in a hippy way, it is a true loss valve up; and can completely spoil your efforts. Flow stall/choking is another kick in the pants.. Lift and duration those centuries literally known to be unbribable, no amount of flow will sneak past there parameter! Still there's the valves lets not forget the all important throttle angle.

 

So how can adding a pod create more power or response when the first thing they do is create turbulence above the venturi and jets?

Another thing. when we have gained flow, then we benefit from larger exhaust ports and pipes, assuming EPA isn't in the mix.

 

You mentioned Zag, I get Zag's need for pods, his is more of a sculptured iron.

Velocity stacks stream and I have seen some aftermarket @1" L but the ones designed for which ever bike, are tuned for L so shorter would suggest less efficiency.

 

Anyways that's how I see it

[CaseyJ955]

I've spoken to a small handful of folks who have done the VMX head/cam/intake conversion onto an XVZ. One of those fellows is/was a member here with lots of credibility. It makes sense, add another 55+hp and 3000rpm and it will be fun, but the efficiency thing is something that should plan in. I have heard if they are dialed in correctly the MPG is not much worse than a stock XVZ.

 

I know from owning/tuning my VMX (Vmax) that tuning is absolutely critical for mpg as well as power. Even a stock VMX can be sluggish and thirsty as they tend to be so rich, then the DJ jetting kits exacerbate that problem (if the directional inlay is followed). For the VMX the bottleneck is the factory downpipe diameter. The Venture exhaust is even more restrictive with the weenee downpipes. Marks makes/made some exhaust components for Venture. Making this conversion worthwhile will require a free flowing ($$$) exhaust. I kept parts of a stock Vmax exhaust but I'm probably going to butcher up a Kerker and have some exhaust work done $$$ cough cough $$$$$.

 

When I got my stock XVZ and it was besting under 30mpg, I tried several things. What worked to get up to around 40 mpg was Skydocs shim kit. That tells me that the problem could be worn emulsion tubes. For a Venture I would not drill slides/use stage 1/7 springs (common VMX tuning practice) as it lifts the needles closer to 3400rpm rather than the factory 4000rpm. I cant see that as a positive for a touring bike. Besides when I did the slides on my Vmax it really didn't make much difference but did cost some mpg, especially at highway speeds. Also if the Vmax block is used the gearing is lower than with the XVZ, at least 5th gear. Venture and Vmax final drives are compatible but different ratios. That can make quite a difference too, especially on a bike that weighs an Oprah more than a Vmax. A few things come to mind that would effect the mpg like that. It's a challenge I would have loved to dig into.

 

Where is that bike now Don? Long gone is it?

[Patch]

There's a lot there Casey that may be best solved in increments.

Addressing a mode like you mention is a challenge and is best in my experience to set an objective first. Then start implementing the steps in small batches. That we we can determine quickly what is working as expected or, will the next step punch more life into the plan or, should we rethink the last mod.

Some time back Bongo and I talking about ratios, I mentioned I don't usually say which or where I've landed but the fact is there are only to general options, rich or lean!

Both have consequences throughout the rpm range even though we can alter the ratios at chosen rpm's.

 

Pipes: confusing subject and the answers are found through flow dynamics. A basic understanding gets us pretty far add a bit of seat of your pants magic dust and you can big.

But it starts at the port not the pipe!

Naturally aspirated engines will usually benefit from some overlap------That has to be kept in mind and I get that this one brief cycle is not easy to comprehend but we can think of it this way (forgive my english as I try this)

Bear this in mind as well the closing of a valve rings and creates a pulse, its a pressure pulse.

When the piston moves up to clear combustion up through the open valve velocity is equal to the rate of travel of the piston below the combustion chamber- that changes through the porting and again at the pipe header.

Now if you were to drop a basket ball as it moves through atmosphere it displaces volume, it also generates a current that atmosphere must rush to fill in. Basically this is what we count on for filling the jug or the sudden reversal of the piston will cause a back draft and carbon will displace the fresh fill. o a port is also a venturi so piping size will alter it predicted characteristics!

 

This is the same challenge as it relates to and with pods, just that its at the other end!

 

Unfortunately I have to get goin now but if you'd like to hash this more I'm around later.

 

Also and quickly Puc chose no overlap in the project mentioned, he could because he replace it with a pressure fill...

[Freebird]

 

Where is that bike now Don? Long gone is it?

 

Have no idea. It was sold to a member here and he sold it not long after buying it. AdVenturer was his username and he lived somewhere around the Buffalo, NY area. His membership here has expired.

[CaseyJ955]

Have no idea. It was sold to a member here and he sold it not long after buying it. AdVenturer was his username and he lived somewhere around the Buffalo, NY area. His membership here has expired.

 

That would put it out of my reach, but too bad. I hope it found a good home! Maybe I'll get lucky and find one like that before mine goes under the knife.

[CaseyJ955]

There's a lot there Casey that may be best solved in increments.

Addressing a mode like you mention is a challenge and is best in my experience to set an objective first. Then start implementing the steps in small batches. That we we can determine quickly what is working as expected or, will the next step punch more life into the plan or, should we rethink the last mod.

Some time back Bongo and I talking about ratios, I mentioned I don't usually say which or where I've landed but the fact is there are only to general options, rich or lean!

Both have consequences throughout the rpm range even though we can alter the ratios at chosen rpm's.

 

Pipes: confusing subject and the answers are found through flow dynamics. A basic understanding gets us pretty far add a bit of seat of your pants magic dust and you can big.

But it starts at the port not the pipe!

Naturally aspirated engines will usually benefit from some overlap------That has to be kept in mind and I get that this one brief cycle is not easy to comprehend but we can think of it this way (forgive my english as I try this)

Bear this in mind as well the closing of a valve rings and creates a pulse, its a pressure pulse.

When the piston moves up to clear combustion up through the open valve velocity is equal to the rate of travel of the piston below the combustion chamber- that changes through the porting and again at the pipe header.

Now if you were to drop a basket ball as it moves through atmosphere it displaces volume, it also generates a current that atmosphere must rush to fill in. Basically this is what we count on for filling the jug or the sudden reversal of the piston will cause a back draft and carbon will displace the fresh fill. o a port is also a venturi so piping size will alter it predicted characteristics!

 

This is the same challenge as it relates to and with pods, just that its at the other end!

 

Unfortunately I have to get goin now but if you'd like to hash this more I'm around later.

 

Also and quickly Puc chose no overlap in the project mentioned, he could because he replace it with a pressure fill...

 

All excellent points, I was more throwing things out there that might kill the MPG/performance of a hybrid VMX/XVZ bike based on doing my own research and tuning on a Vmax (my own, with plenty of help from guys on the Vmax forum) but since I'm planning on building a hybrid like this I'm definitely interested in learning more. I've gathered great info from others here who have gone before me, and others on the Vmax forum with hybrids.

 

Getting deeper into exhaust theory is healthy. With the Vmax we have availability of premade systems. Some are known to lack backpressure, kill power and just be obnoxious while others are known to perform quite well. There is no such thing for the Venture. I recall learning a bit about this with the Veedubs. I played with different intakes/rockers/carbs/ spark curves and of course, exhausts and stingers, while I got the basics there was more to learn then, just as now. I think I learned about back pressure and scavenging the same way every 14 year old kid with a Sawzall does though.

 

Since this project will essentially be a Vmax +100cc and 300lbs, designing an exhaust system should be less dark art and more reflection on what works with Vboost equipped Yammers, or so I hope.

[Patch]

I found with all the time that has gone by I tend to forget bits and pieces. So as Puc says "learn me" its really more like, remind of what I once knew so well.

 

Forums are often short cuts that most often leave out the reasons why things work. Instead guys often just point you (generally speaking) in a direction, and some times the pointing is right on.

 

What often gets my attention in a forum is when someone asks a question because he/she is missing a piece or 2 of the why (s) Those questions are usually found in the guys willing to share there experience and mistakes leading up to what works.

 

A for example don't mod around back pressure. Its not the back pressure that matters as much as it is the result of it being there! Work the other end first, clean staged flow and ratios, then test and decide on the dirty end

 

And stick to the game plan. In my posting not sure where??? I state the general objective for my GV, if you lay it out like cards there can only be one conclusion as to what my mods hopefully will produce. The Kat isn't for my riding and outside of testing... well just say a young mans bike.

[Patch]

Hey Casey, I found this yesterday. The fellow although a bit jumpy explains theory from the ex valve down.

Somewhere here I mentioned the pulse created by valve action, he touches on this as well.

The other point he mentions as have many of us is at which range of rpm. A street setup has different requirements the a track setup so some trick can't transfer.

In exhausting at high rpm we loose rhythm so we tune for length and other necessities.

In a touring our consistent/cruising ranges are much lower so rhythm of flow provides higher efficiency with some valve overlap for filling the jugs.

This is where we decide which of the 2 base potentials we are after, HP or torque.

The overlap is meant to create a brief input from the intake side,,,,,this will help flow the spent charge remaining at the top of the deck,,, this is where pipe sizing or to much back pressure can screw it up by reversing flow. Easy to visualize if we think of water flowing thru a hose, a constant flow creates a low pressure above, same for siphoning a tank. The perpetual nature of rpm is used to keep the pipe full and flowing. We add to this flow/draw by using collectors or crossovers. In theory.

The theory is the same for cars or bikes.