V-boost is glorified solution for bad carburetors. Funny!!!

VMAX  Forum

Help Support VMAX Forum:

DreamV4

Well-Known Member
Joined
Jun 30, 2021
Messages
1,041
Reaction score
278
Carburetor engereers couldn't design a carburetor, providing enough air/fuel over 6000RPM.
So V-max engineers had to find a solution, glorified as bike science discovery.
AFAIK this problem was solved by car carb engineers gazillion years ago: carbs have some kind of "power valve", providing extra fuel at higher power modes.
BTW, my 92 ZX11 had similar power (146HP), but Kawasaki guys didn't need V-boost to get there!
Maybe V-boost had only one goal, to attract buyers.
Let us see if we can use car carburetor instead of Vmax carbs + V-boost (theoretically)
We just need to find a car with at least 145 HP (same air and fuel amount), no big deal!
 
Last edited:

02GF74

Well-Known Member
Joined
Mar 26, 2020
Messages
1,501
Reaction score
706
Location
UK
Hmmmm now there's a question.
Twin weber/dellorto 40s are capable of supply a 1600 engine with fuel to give 150 bhp.

I need a moment to sit down for a moment and do some sums, I think it may come down to rpm, vmax enginr revs 1.5-2x the car engine.
 

DreamV4

Well-Known Member
Joined
Jun 30, 2021
Messages
1,041
Reaction score
278
Engine size doesn't matter, only HP. Power depends on amount of air, engine can suck in, and carbs have to provide fuel according to air.
 

VMAXXIMUM

Well-Known Member
Joined
Apr 23, 2014
Messages
551
Reaction score
339
Location
North Kingstown, RI
…a trick that works. I mean “a trick” suggest slight of hand. But we’re not imagining the effect. So I don’t think a trick. How about innovative engineering to solve a problem.
 

MaxMidnight

Well-Known Member
Joined
Dec 1, 2007
Messages
2,692
Reaction score
673
Location
Cumbria, England.
Carburetor engereers couldn't design a carburetor, providing enough air/fuel over 6000RPM.
So V-max engineers had to find a solution, glorified as bike science discovery.
AFAIK this problem was solved by car carb engineers gazillion years ago: carbs have some kind of "power valve", providing extra fuel at higher power modes.
BTW, my 92 ZX11 had similar power (146HP), but Kawasaki guys didn't need V-boost to get there!
Maybe V-boost had only one goal, to attract buyers.
Let us see if we can use car carburetor instead of Vmax carbs + V-boost (theoretically)
We just need to find a car with at least 145 HP (same air and fuel amount), no big deal!

That is just wrong and shows a lack of knowledge about the purpose of V Boost.
It is very feasible to use a carburetor to provide sufficient air/ fuel over 6K but this will reduce the available torque at lower r.p.m's.
The bigger the venturi you choose the bigger the effect on torque at lower revs.
That solution would be OK if all you were interested in was maximum power as in a sports motorcycle but this is not suitable for a cruiser wher a big fat torque curve is what the doctor ordered.

Utilising a power valve would correct any leaning off of the mixture during acceleration but has no effect on a constant throttle.
The issue is not how much fuel you can pump in but how much air can go through a venturi of a given size and pressure drop.

This explains the principles of the venturi. Note what is says in 'Carburettor Venturi and vaporisation' The aim is to get the fuel droplets as small as possible which will allow the mixture to burn quicker and this give a higher brake mean effective pressure (BMEP) i.e how much pressure is exerted on the top of the piston during combustion.
Whilst I may be wrong here it may also contribute to lower emissions?

Back to V Boost - small(er) venturi will give higher venturi air speed = better fuel atomisation = smaller fuel droplets = better BMEP = higher torque a low engine revs.
As the small venturi size limits how much air can be flowed at higher revs V Boost sidesteps that problem by drawing mixture from another carb.

Or to put it another way - you get high torque spread over a much wider rev band than would normally be possible.

Whist your ZX11 may have produced the same power I would like to see how the torque curve compares with the Max.

I seem to recall that Holly carbs have been tried but as they do not feature regularly I suspect this is because at best it isn't worth the effort or it is less effective than what is OE.
The skeptic in me thinks that given the time the Max has been around if there was a better solution someone would have come up with it by now

V Boost was one solution to the problem engineers faced and there have been others e.g. Variable venturi's, additional ports that open at higher revs and so on.
They may also have been sent down this route due to patents on other solutions?

I'll always applaud those who want to try something different and look forward to hearing the progress you make.
 

Parminio

Well-Known Member
Joined
Apr 22, 2016
Messages
1,418
Reaction score
954
Location
Suwanee, Georgia
Carburetor engereers couldn't design a carburetor, providing enough air/fuel over 6000RPM.
So V-max engineers had to find a solution, glorified as bike science discovery.
One of the dumbest comments I have personally ever seen.

AFAIK this problem was solved by car carb engineers gazillion years ago: carbs have some kind of "power valve", providing extra fuel at higher power modes.
That's not why the power valve was created. Carbs were already easily capable of doing that. The power valve was created to make carburetors more efficient. It allowed you to use smaller primary main jets to make the engine more efficient at crusing / low rpm speeds but still allow for larger fuel amounts at higher rpm.

In short, the power valve was created to save gas. Nothing more.

BTW, my 92 ZX11 had similar power (146HP), but Kawasaki guys didn't need V-boost to get there!
I had a ZX11 in '92. My Vmax would leave that thing off the line like it was a herd of grazing cattle. Of course once we hit about 40 mph the ZX comes into it's power band and would start coming by the Vmax and there's nothing you can do about it.

But that's because they're completely different engines. It's like comparing a golden age Formula 1 3 liter V10 to a NASCAR 5.87 liter V8. They're two completely different engines. One develops its power off of high revs the other off of large size.

A 3 liter F1 V10 could pound out 850 HP with relative ease at around 17,000 RMP.
A 5.87 liter NASCAR V8 produces roughly the same horsepower at only 9,200 RMP.

Roughly the same horsepower at different RPM with one engine roughly twice the size of the other. Guess which one uses more gas.

The NASCAR V8 of course. It gets about 4.5 MPG at racing speeds. The F1 V10 could get nearly 7 MPG.

It's where you're making your horsepower that counts. And contrary to your misguided beliefs, size does matter. A lot.

I don't think you have the first clue what you're talking about.
 

schudaddie

Well-Known Member
Supporting Member
Joined
Jul 27, 2010
Messages
177
Reaction score
34
Location
sw michigan
I saw what DreamV4 wrote and was going to write exactly what MaxMidnight wrote but he did it for me, quicker than me and better than me. Vboost is simple, clever, works well and sold thousands of bikes.
AMEN...... I think the boost was to strengthen your grip, straighten your arms and put a smile on your face.:D
that's why I bought my '85, in 85 (1st one in town & after the test ride all I had to say was "where do I sign?".
And I'm still smiling!
later, bill
 

Fire-medic

Well-Known Member
Staff member
Moderator
Joined
Mar 25, 2011
Messages
13,298
Reaction score
2,894
Location
Miami Florida
The V-four engine readily-adapts to the installation of a VBoost system, it's compact, ingenious, functional, fairly-simple, and effective. Something to understand is the value to the owner/consumer. They get good operation at smaller throttle openings, decent torque at that same time/RPM, and a great cam-like surge at higher RPM, better HP than without it, and a cool idle sound, for wow'ing all your gearhead friends.

An inline-four or -six doesn't have the proper geometry to allow such a system. More-modern systems to achieve a similar result are on other engines: VVT-variable valve timing; VIR-variable length intake runners; EXUP-exhaust length variable valving are used. It's more-than a gimmick. It works, and has proven to be relatively trouble-free.
 
Last edited:

DreamV4

Well-Known Member
Joined
Jun 30, 2021
Messages
1,041
Reaction score
278
Calculating replacement carb diameter to eliminate v-boost and keep 145 HP.
Based on 85 Magna V65 (116 HP, 36mm carb)
116/36 square =145/D square (D is substitute carb diameter)
D=sq. root((36 sq x 145)/116)=40
Kaw ZX11 (147HP) carbs are 40mm
 

DreamV4

Well-Known Member
Joined
Jun 30, 2021
Messages
1,041
Reaction score
278
The easiest conversion would be 2 injectors from 84 Corvette (205 HP).
1 injector for cylinders 1 ane 2 and 1 injector for 3 and 4
 

Parminio

Well-Known Member
Joined
Apr 22, 2016
Messages
1,418
Reaction score
954
Location
Suwanee, Georgia
Calculating replacement carb diameter to eliminate v-boost and keep 145 HP.
Based on 85 Magna V65 (116 HP, 36mm carb)
116/36 square =145/D square (D is substitute carb diameter)
D=sq. root((36 sq x 145)/116)=40
Kaw ZX11 (147HP) carbs are 40mm
What on earth kind of craptastic math is that?

The square root of 36 is 6. 36 squared is 1,296.

So your equation 116/36sq is actually equal to 116/1,296 which = .089506

116/6 = 19.33

So 1296 x 145 / 116 = 1,620
Or 6 x 145 / 116 = 7.5

So either way your math is COMPLETELY wrong.
 

Tom Determan

Well-Known Member
Supporting Member
Joined
Oct 11, 2019
Messages
155
Reaction score
114
Location
Minneapolis
There are lots of guys out here that know this better than I do but my understanding of V boost is that at higher RPM the "momentum" of the incoming air flows to the "other cylinder" when 1 intake valve closes and the other intake on that side opens, when the V boost is open. This allows the use of a smaller bore carb for low end torque but effectively provides more air / fuel at higher RPM where more CFM is needed. It's possible in a V engine configuration where the manifold layout and the intake valve timing of the cylinders will allow and take advantage of the incoming air / fuel to flow to one intake valve or the other, based on the V boost butterfly. The system provides better low end atomization and high end air flow with ideally sized carbs that can effectively become "larger" at higher RPM.

I haven't thought about the system much but looking at it one night this is what I came up with. Help me out with corrections or blow my whole theory up, LOL.
 

Parminio

Well-Known Member
Joined
Apr 22, 2016
Messages
1,418
Reaction score
954
Location
Suwanee, Georgia
In the end it's really this simple:

VBoost effectively turns the individual intake runners into a tunnel ram.

In layman's relation to a car, you're going from one of these:

1626622415664.png

To one of these:

1626622304249.png
 

DreamV4

Well-Known Member
Joined
Jun 30, 2021
Messages
1,041
Reaction score
278
What on earth kind of craptastic math is that?
"square" doesn't mean "square root"
I did my best. I don't want to explain something which I learned in school at age of about 10.
I don't know how to type sign square. Do you?
Based on 85 Magna V65 (116 HP, 36mm carb)
116/36 ² =145/D ² (D is substitute carb diameter)
D=sq. root((36 sq x 145)/116)=40
 
Last edited:

Tom Determan

Well-Known Member
Supporting Member
Joined
Oct 11, 2019
Messages
155
Reaction score
114
Location
Minneapolis
What on earth kind of craptastic math is that?

The square root of 36 is 6. 36 squared is 1,296.

So your equation 116/36sq is actually equal to 116/1,296 which = .089506

116/6 = 19.33

So 1296 x 145 / 116 = 1,620
Or 6 x 145 / 116 = 7.5

So either way your math is COMPLETELY wrong.
Lots of guys have tried to come up with a better carb system than Yamaha did in 1983-84 during the development and testing of the V Max. If you toss out any of the constraints put on the engineers to meet CA emissions - Yamaha corporate (profit / no recalls), Yamaha sales, (price point) mfg, (packaging and assembly) materials, (available vendors and reliable on time production volume) and every other design objective, with probably only 20 or 30 pretty smart people, and only $ 5 to $ 10 million of the development budget allowed for the intake system you might have a shot at doing 1/10th of what Yamaha did. They didn't do a very good job because it was only used for 22 years without changing it AND, they failed to use their crystal ball and address the stupid ethanol gas issue that our wonderful guvmint d---heads pushed on us to solve the MTBE oxygenate problem that was fixable for a much lower cost to the nation. Man, those Yamaha engineers sure could have done a better job !
 

Parminio

Well-Known Member
Joined
Apr 22, 2016
Messages
1,418
Reaction score
954
Location
Suwanee, Georgia
"square" doesn't mean "square root"
I did my best. I don't want to explain something which I learned in school at age of about 10.
I don't know how to type sign square. Do you?
I did it both ways pal because I wasn't sure what you were getting at.

BOTH WAYS you are wrong.

And by the way, to type ² you just type alt 0178

So as I stated, your 36² = 1,296
 

DreamV4

Well-Known Member
Joined
Jun 30, 2021
Messages
1,041
Reaction score
278
Thanks! I am getting smarter every day! 😁
Calculating replacement carb diameter to eliminate v-boost and keep 145 HP.
Based on 85 Magna V65 (116 HP, 36mm carb)
116/36 ² =145/D ² (D is substitute carb diameter)
D=sq. root((36 ² x 145)/116)=40
Kaw ZX11 (147HP) carbs are 40mm
 
Last edited:

Latest posts

Top