Vboost or no Vboost

[blaxmax]

So here's a question: has anyone actually dynod the difference between vboost and no vboost?

I mean on the same NA spec bike, not comparing the NA model to the neutered "rest of the world" bikes.

It doesn't seem to follow to me that simply linking two carbs together above 6000 rpm would make the difference between 98/100 hp and 145 hp.

If that were the case, all the head and cam work done on the vmax doesn't make any sense (financially for Yamaha) because the stock Venture engine makes (rated) 98hp.

I'm a bit suspicious that the neutered bikes had Venture spec cams and/or heads.

I'm interested because my 1200 Venture is going to get NA spec vmax heads, cams and 1300 carbs this winter but no vboost. I'm hoping for a 20-30 hp jump from the stock 98 hp. It's also getting a 33/9 final drive and a 2002 royal star Venture transmission (lower overall gearing than the Venture 1-3, 4the the same and deeper 5th over) to make better use of that extra hp.

It has been on the dyno and the vboost will actually lower by 10 hp in the lower rpm range. From 0 to 3800 it is acually better with it off. On the street i do not pull it untill 4000 rpm- on the track i use a manifold with the venturi's taken out.
The final drive will help.- the only difference being the '85 manifolds venturi's were 1mm smaller.
The venture's 1300 carbs are 32mm mikunis and not 35mm as the vmax's are.

 

[great white]

It has been on the dyno and the vboost will actually lower by 10 hp in the lower rpm range. From 0 to 3800 it is acually better with it off. On the street i do not pull it untill 4000 rpm- on the track i use a manifold with the venturi's taken out.
The final drive will help.- the only difference being the '85 manifolds venturi's were 1mm smaller.
The venture's 1300 carbs are 32mm mikunis and not 35mm as the vmax's are.

83-85 Venture 1200 carbs are 34 mm, 86-93 1300's are 35 mm.

32 mm was the 99+ models.

There was even a dark time when it had 28mm carbs, but that was only a 96-98 model.

I'll be using a rack of carbs from the 86-93 years, so 35mm, same as Mr Max (with some jet work) except that I get to keep my cable operated choke....

 

[blaxmax]

I thought you meant 2002 venture-
The larger mm carbs will help also the heads and cams but you still have a lower compression piston.

 

[great white]

I thought you meant 2002 venture-
The larger mm carbs will help also the heads and cams but you still have a lower compression piston.

Now that's something that has always confused me a bit. Everything I've ever seen lists the VMax (1985) as 10.5:1 but my service manual for my 83 lists the 1200 venture engine as 10.5:1 also:

They do list a difference in combustion pressure though: 1176 KPa for the venture and 1422 KPa for the VMax. Odd that the static compression ratio is the same and the dynamic is different.

There does look to be a diff between the Venture and Vmax pistons though.

Venture:

VMax:

Sure does look like the Venture piston is a flat top and the Vmax piston is domed, which typically means a bump up in static compression ratio all other things being equal.

Perhaps the higher cylinder pressures have something to do with the VBoost cramming more air and fuel into the cylinder about 6000 rpm.

Or it could be the larger valves and longer cam profile.

Or it could be recurved ign timing, that's a very easy way to change peak cylinder pressures.

Or all of it together.

Dunno, just guessing now. Someone like Sean Morely could probably shed a bit more light on the issue I'm thinking.

Regardless, I'm not tearing apart a tight 19,000 mile engine at this point just to swap in used Std pistons and new rings. The engine is tight and well sealed, not messing with that.

I'll save that money for when I go down that route in the future once I find a 1300 engine to rebuild....

I'm figuring with the heads and cams (but no VBoost) on my XVZ12 I'll be up on the stocker around 20-25 hp but down on the Max by about 10-15 hp. But that's a pure guess.

So, hoping to come out around the 120-125 BHP mark, maybe 110-115 RWHP.

 

[desert_max]

With two non-functional Vboost controllers in the shop, I was poking in the archives here. This is one of the more comprehensive discussions on the matter.

I just powered my boost full on and the first thing I noticed… And not something that I saw mentioned in this thread...was that it was a very difficult cold start. I am certain this machine is running the stock jetting, but I wasn’t smart enough to verify that when I had them apart last weekend. But, I do know that it’s 100% original. Of that there’s no doubt. I’m thinking that the pilot jets need to go up a couple of steps to get this thing to start with the boost full on. On the other hand, I believe I’m going to follow the very simple and inexpensive method of employing a DPDT switch to power it open and closed recommended by one of our own.