VBoost all the time
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kwarnke
Active Member
Now I’m confused. Why would having them open all time make it slower. I get the gas part and the gas tank is small enough already but slower?
You need to understand how carburetors work and what V Boost does.
The venturi causes a pressure to drop as the air flows through it which in turn pulls the fuel through the main jet.
As the air speed increases the droplets become smaller and the smaller droplet = more complete and quicker burn = higher cylinder pressure = more torque (or power if you factor in revs).
When the engine is running at low speeds a smaller venturi is needed to maximise the air speed. There is a limit to the volume it can pass and this is reached before maximum revs is achieved and therefore you will loose power.
To flow enough air at higher revs a larger diameter venturi is required but this will mean that at lower revs the airspeed through the carb(s) will drop and result in a poorer burn and a resultant reduction in the potential power at lower revs.
V Boost overcomes this issue by allowing a smaller venturi that will maximise torque at lower revs and as the V Boost butterflies open effectively increasing the venturi diameter by taking the intake mixture from the second carb .
You can have your cake and eat it!
The effect of having permanently open V Boost is that the airflow will be reduced at lower revs, atomisation will suffer and you produce less power at lower revs...you also loose the addictive shove at 6K.
Put in a Morely jet kit, air box mod and one of the custom header sets available and you will have a bunch of low end grunt and still have v boost hit when it should.
Pighuntingpuppy
Well-Known Member
Overfueling will toast ANY engine. Thats why you rarely saw carburated engine automobiles going beyond 100K. 2 carbs feeding 1 cylinder all the time is not gonna be good long term.
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Zeus36
Well-Known Member
MaxMidnight gave the best explanation I've seen on V-Boost. I have a T-Boost from the prior owner, but I don't use it.
Just ride in a higher RPM range (stay in lower gears longer) and you'll get to boost almost instantly.
**** O'Brien, working with noted tuner and intake/head specialist Jerry Branch, made the Harley-Davidson flathead engines competitive long-after other manufacturers had given-up on the flatheads. In an interesting comparison as-to why higher airflow can be beneficial to performance, due-to smaller ports, which increase airflow in the intake side because of higher port velocity, Branch discovered that making the H-D flathead intakes smaller increased the airflow, which produced more power. Motorcycle Airflow Specialist Jerry Branch Was Driven By Curiosity
Over-carbuerating an engine may allow it to-make more power at the top-end, close-to redline, but it destroys the low-speed capacity of the engine to operate with good throttle response, torque lower in the rev-band and including midrange, qualities pretty-much useless unless you're in the habit of running your engine at the last 20% of the rev-band. Unless you're a Bonneville racer, a dragracer, or a masochist trying to run a top-end tuned vehicle on the street, big carbueration is a curse, not a gift.
The VBoost switches which allow the VBoost open all the time give you a rumpety idle which makes you king of the root beer stand drive-in , while costing you actual performance. You can do the same thing by removing the left air scoop, and disconnecting the round plastic connector to the stepper motor for the VBoost butterfly operation, which cycles-open when you turn-on the key. Unplug the connector when the cable opens the VBoost manifold, and now you'll have everyone at the root-beer stand wondering, "how-much bigger are the pistons over-stock in that monster? Did'ja throw high-lft cams innit too? Who ported them-heads?"
Disconnecting the VBoost stepper motor power makes it easier to synch the carbs as you simply re-connect the VBoost round electrical connector, and now you can synch the carbs as it says in the factory service manual, a job which takes about 15 minutes, and is worth-it in idle characteristics, pick-up off closed throttle, and overall throttle response, and fuel economy.
More-on Jerry Branch, an innovator in cylinder heads:
https://www.odd-bike.com/2016/03/harley-davidson-vr1000-gods-own-voice.html
Over-carbuerating an engine may allow it to-make more power at the top-end, close-to redline, but it destroys the low-speed capacity of the engine to operate with good throttle response, torque lower in the rev-band and including midrange, qualities pretty-much useless unless you're in the habit of running your engine at the last 20% of the rev-band. Unless you're a Bonneville racer, a dragracer, or a masochist trying to run a top-end tuned vehicle on the street, big carbueration is a curse, not a gift.
The VBoost switches which allow the VBoost open all the time give you a rumpety idle which makes you king of the root beer stand drive-in , while costing you actual performance. You can do the same thing by removing the left air scoop, and disconnecting the round plastic connector to the stepper motor for the VBoost butterfly operation, which cycles-open when you turn-on the key. Unplug the connector when the cable opens the VBoost manifold, and now you'll have everyone at the root-beer stand wondering, "how-much bigger are the pistons over-stock in that monster? Did'ja throw high-lft cams innit too? Who ported them-heads?"
Disconnecting the VBoost stepper motor power makes it easier to synch the carbs as you simply re-connect the VBoost round electrical connector, and now you can synch the carbs as it says in the factory service manual, a job which takes about 15 minutes, and is worth-it in idle characteristics, pick-up off closed throttle, and overall throttle response, and fuel economy.
More-on Jerry Branch, an innovator in cylinder heads:
https://www.odd-bike.com/2016/03/harley-davidson-vr1000-gods-own-voice.html
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desert_max
Well-Known Member
Except that I am not sure I understand how the Vboost butterflies have any bearing or effect on the size of the venturi. They open up and allow air flow across two carbureto r venturis, but the the size doesn't change. It's essentially the same effect as the secondaries opening up on a 4 barrel carburetor. More fuel, more air. And yes, both are really only needed as either displacement or engine speed increase. Or both.
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one2dmax
Well-Known Member
The vboost increases CFM giving similar results to having a variable venturi (about the best you can do with these carbs).
+1 Fur shur!!
OK, think if it this way, we have lots of people in a room (they are the air about to go into the engine) and to get to the get to the cozy fire in the next room they have to go to through a sliding door (the throttle butterflies and venturi).
They start to move slowly towards the door (low engine revs) they are well spaced apart and pass through without any problem.
This is taking too long so they are asked to move more quickly (revs increase) the door is opened some more (burrterflies opeming) and they still pass through but are closer together.
If they then walk quicker they still get through but start to bump into each other because the door is now fully open.
As they start to run they start to back up (the venturi is too small) because the door isn't big enough for them to get through.
Someone has a great idea, lets start to slide back another door (V Boost opens) which allows those waiting to get through.
As more arrive the sliding door is progressively opened and everybody can get through.
So whilst the venturi size does not change the size of the hole that will allow the intake mixture does as the V Boost butterflies open.
Hope that helps.
kwarnke
Active Member
you know what... I aint touching them, leaving as is. its fast enough for me as it is. but man, some great stories. Did you guys see the post about a Vmax as a first bike? Almost all of the Vmax riders said that he should have no problem, take it easy, go slow, etc. I was the only one who disagreed. and I made it very simple, I asked for a show of hands on who would let this guy ride their Vmax first. Crickets. The Vmax is number one on one very important list, bikes only the most experienced riders should own.
MaxMidnight's 'people moving to exit a room' unfortunately reminds me of a tragedy which occurred in the Station nightclub fire in W. Warwick, Rhode Island.
The popular band Great White was playing there, and a fire broke-out. Because the nightclub had undergone renovations where the work wasn't permitted properly, including compliance for the NFPA (National Fire Protection Association) Life Safety Code, construction components and decorations used contributed to a rapid spread of a fire, causing panic among members of the audience and workers, as-well as the band & entourage.
The entryway was a labrynth design, it also happened to-be the main exit. As the rush of people trying to exit the nightclub overcame the design of the entryway to allow orderly movement of people seeking egress, people fell to the floor. Others trampled them, and soon the main entrance/exit became an impassible mountain of bodies.
The building wasn't equipped with fire sprinklers. The furnishings used for sound attenuation were easily-ignited, and the byproducts of combustion asphyxiated most of those found dead. One of those was a guitarist for Great White. In-all 100 people were killed. Hundreds more were injured.
Great White had a pyrotechnics display as part of their show. The use of the pyrotechnics ignited club components, and the deaths occurred.
Here is a study of the events leading up to the tragedy:
https://www.nist.gov/el/station-nightclub-fire-2003
The band had been on-tour in south Florida before the W. Warwick Rhode Island fire. They applied to use their pyrotechnics at one show, the fire marshal told them, "when are you going to demonstrate the system for us before the show?" Remember, this was again inside a closed building, not at some outdoor event.
"We're not going to spend the money to do that," was their response. "These pyrotechnic devices are expensive!" They also had to submit a plan of their devices, the listings for them as being approved for use (below), who was in-control of them, and what safety provisions for emergency extinguishment they were providing. There's more, but you get the idea.
"OK, you can have your show, but you aren't allowed to use pyrotechnic devices." The show was given, and the pyrotechnics weren't used. Then the band headed to Rhode Island, for the next leg of their tour.
There is a NFPA standard for this: NFPA 1126 Standard for the Use of Pyrotechnics Before a Proximate Audience
https://www.nfpa.org/codes-and-stan.../list-of-codes-and-standards/detail?code=1126
A comparison of fluid dynamics to a crowd of people can help the lay person to comprehend esoteric engineering principles without having a B.S.E. For a few, it might dredge up an unpleasant memory of a past tragedy, and one which didn't happen because of a vigilant fire service employee.
The popular band Great White was playing there, and a fire broke-out. Because the nightclub had undergone renovations where the work wasn't permitted properly, including compliance for the NFPA (National Fire Protection Association) Life Safety Code, construction components and decorations used contributed to a rapid spread of a fire, causing panic among members of the audience and workers, as-well as the band & entourage.
The entryway was a labrynth design, it also happened to-be the main exit. As the rush of people trying to exit the nightclub overcame the design of the entryway to allow orderly movement of people seeking egress, people fell to the floor. Others trampled them, and soon the main entrance/exit became an impassible mountain of bodies.
The building wasn't equipped with fire sprinklers. The furnishings used for sound attenuation were easily-ignited, and the byproducts of combustion asphyxiated most of those found dead. One of those was a guitarist for Great White. In-all 100 people were killed. Hundreds more were injured.
Great White had a pyrotechnics display as part of their show. The use of the pyrotechnics ignited club components, and the deaths occurred.
Here is a study of the events leading up to the tragedy:
https://www.nist.gov/el/station-nightclub-fire-2003
The band had been on-tour in south Florida before the W. Warwick Rhode Island fire. They applied to use their pyrotechnics at one show, the fire marshal told them, "when are you going to demonstrate the system for us before the show?" Remember, this was again inside a closed building, not at some outdoor event.
"We're not going to spend the money to do that," was their response. "These pyrotechnic devices are expensive!" They also had to submit a plan of their devices, the listings for them as being approved for use (below), who was in-control of them, and what safety provisions for emergency extinguishment they were providing. There's more, but you get the idea.
"OK, you can have your show, but you aren't allowed to use pyrotechnic devices." The show was given, and the pyrotechnics weren't used. Then the band headed to Rhode Island, for the next leg of their tour.
There is a NFPA standard for this: NFPA 1126 Standard for the Use of Pyrotechnics Before a Proximate Audience
https://www.nfpa.org/codes-and-stan.../list-of-codes-and-standards/detail?code=1126
A comparison of fluid dynamics to a crowd of people can help the lay person to comprehend esoteric engineering principles without having a B.S.E. For a few, it might dredge up an unpleasant memory of a past tragedy, and one which didn't happen because of a vigilant fire service employee.
