1-2 + 3-4 intake crossover

Here is one for you guys who have put the V-Boost on the Venture Royale xvz1300.

So if you have not figured me out by now I can't resist tinkering with stuff. Sometimes its a curse and I end up messing up more than I make things better. But this time I may have stumbled onto something worth looking into.

The head to carb boots on my engine were looking a bit rough, dry and cracking. So when @ the bone yard I picked up what looked like a set in better condition than what I had. I forget who but someone here mentioned to me that the V-Boost does not actually give more A/F. So I did some reading and found that to be scientifically and verifiable true. Seams what the issue is on the V-max engine is that @ higher flow the carbs or heads (I forget what one) just can't keep up with the flow efficiently enough. The V-boost isn't giving more fuel as much as it is allowing for better flow dynamics.

So that got me to thinking about Jasons MOD (connecting 1-2 + 3-4 with a vacuum hose) and my earlier hypothesis that the size of the tube didn't offer a big enough passage to make a major difference. Well being as I have some better boots I thought I would head to the hardware store and do a little experimentation. I just went ghetto and got me some 3/4in copper pipe and some JB weld. After getting home I removed the carbs and got out the trusty old rotary tool. I used a piece of copper tube and cut and shaved it to fit between the boots then marked them. Removed the boots from the engine as to not get anything in the intake and carved out the holes to fit. I then cut 2 new pipes a little longer so they would slide into the boots and reinstalled everything. Sliding the tube in one boot and then back into the other they had an already nice and tight fit without obstructing airflow. I sealed it up with some JB just for good measure.

WOW is all I can say. I do have my mufflers off with just a dump pipe after the collector chamber and I am Jetted up on the main with 2x #6 washers shimming the needle. I suffered some low end lag upto the 2000-2500 rpm range and tried to correct by turning out the pilot more and it got a little better. but then there was a little low rpm fit the carbs get when you have the air box off. So I put in a bigger pilot jet and upped the size of the #1 air jet some and it cleaned right up. I had also considered opening up the air hole in the slide some as I think that will help with finally shedding the stock air box but I opted not to until I had a backup set.

Now my opinion that it has a LOT more pull, faster throttle response, and it seams to pull threw the RPMs in each gear faster now is purely seat of the pants calibration. and I don't suggest you head out and start punching holes in you boots and try this without something to fall back to. I spend a lot of time the last 2 days changing jets and shims to get it to feel right but I think this could be a promising avenue to pull a little more kick out of the motor without the cost of a full V-Boost add on. in all I spent less than $40 on some pipe, jb weld, and a few jets not counting the backup boots. As $$ permits I will be getting a wideband A/F meter and get in some dyno runs to verify it makes a difference without unacceptable loss in other areas.

Interesting.

The purpose of the vboost is that over approx 6000-6500 rpm, the single 35mm carb throat becomes "restrictive" Ie: the heads can flow more than the carb can provide. By opening the the vboost, the single 35mm carb becomes essentially 70-ish mm and the heads continue to build power, limited only by valve and port size/design.

Below 6000-ish rpm there is no real advantage as the single 35mm carb has plenty of flow capacity for the head demands, so the Yammy engineers keep the vboost closed until 6000-ish to maintain intake velocities for lower end torque (imp on a street ridden bike). Intake velocity is king when trying to make torque.

I personally have never liked the "Jason mod". All its doing is leveraging the YICS architecture in a way it was never designed for. I personally think it just buggers up carb balancing. Same reasoning that carb balancing on a vmax is done with the vboost closed. But people see what they want to see so no sense telling them different...

Yours sounds more like it's simulating a smaller vboost setup that is always open. Might yeild some results at the magical 6000 rpm and still be small enough not to bugger up low rpm running.

Dunno, you're off in the outfield somewhere with this one. Although some of the vboost theory would seem to apply.

Interesting.

 

The purpose of the vboost is that over approx 6000-6500 rpm, the single 35mm carb throat becomes "restrictive" Ie: the heads can flow more than the carb can provide. By opening the the vboost, the single 35mm carb becomes essentially 70-ish mm and the heads continue to build power, limited only by valve and port size/design.

^^^ thats what I was reading^^^

You havn't steered me wrong in my tinkering yet so far your knowledge has been a great help in my tinkering. I think I can side with you on your comment. ""simulating a smaller vboost setup that is always open......not to bugger up low rpm running"" But I don't know that it is I made it small enough as not to bugger up the carb as much as I made it small enough that it is correctable with jets, but still give a %value of the added flow in upper RPM. If the carbs are 35mm and 3/4in = ~19mm thats ~50-55% more flow potential I have created. Add that to the position of the crossover and I am sure there are some losses as it makes the bend.

Also I noted that I am running a dump pipe Vs exhaust and I have opened up my airbox some. This gives my bike more flow than a stock VR and may also be why I am not getting a terrible drawback in low RPM. add that to the fact I am never under 3,000 RPM unless forced to by traffic, parking lot, stops. etc.

Maybe some 1200 Vmax heads will make it even better. I have ordered some from E-bay and should be getting them soon. They will spend some time getting cleaned up P&P and copper plated on the outside. So they may not make it on the bike this riding season.

Once my v-boost manifold shows up I'll measure it and you can compare that to the ID of your 3/4 copper.

Should give you an idea of where you sit.

The only big unknown with your system that I see is synchronizing the carbs and how it will act with those "always open" 3/4 interconnects. Even the Mighty 'Max synch's it's carbs with the vboost closed.

I'm no VMax or Venture expert by the way. Just a solid mechanical background and a willingness to learn. I'm working my way through this stuff too, but I'm a quick study.

The way it is there is no way to "turn it off" to sync. My carbs were already well synced prior to doing this so they should be still darn close. I had considered putting in a ball valve but there was not enough room to get a 3/4in one in easily. The general idea was just a what if I. I do agree it would be a good idea to find a shade tree way to shut it down to sync or maybe when you are forced into slow traffic. it wold be possible to install several 1/4in lines with a small shutoff then one could open is many as they wanted. But then you are to the point you may as well get a V-Boost valve for the $50-$75 and run a manual cable lol.

I believe its is a general conciseness with the V-Max guys that leaving the boost open ona STOCK bike does hamper the low end and even cost you 10-15HP. But a lot of them same guys say that with an open exhaust, intake, and rejetting it helps.

@ the end of the day I am leaving this MOD on for now to see how it works out on my every day ride.