Variable runner intake

[Craigster]

It's those boring winter months when folks are dreaming of what they would like to do to their bikes someday. Some are performing maintenance on their bikes. Me? I'm performing maintenance on the dyno. A lightning strike has me doing more work than I'd like.

That said, while sorting through some stuff, I came across some old files of a bike I once dynoed for a guy with variable runner intake. If any one is actually interested, I can post the story and some data.

It was a very interesting build. 1992 V-Max converted to EFI using a variable intake system. The goal was more top end power without hurting the bottom end. In the end he had a nice set up that was pretty fun to ride.

 

[one2dmax]

That is what the OEM vboost provides lol. Still, post up the pics!

 

[Craigster]

V-boost does provide for breathing through an additional carb. And, since the intake is out of phase, the wave created from the opposing cylinder's intake valve closing event surges into the receiving cylinder's open intake. This still did not provide enough for this particular customer. You see, with V-boost open or closed the length from the valve to the top of the carb belmouth never changes.

But what if you could change it? He decided to test a series of velocity stack diameters and lengths to see the effect they had on the engine's performance. In the end he found a diameter and length that worked to produce great top end power. He also found that it worked far worse below 7500 rpm than the smaller diameter longer stacks that gave great low end power. Much of that is to be expected, except that very few people actually dream of a task and then actually set out to complete it. He found what worked and then built a contraption that allowed the bike to run both sets of stacks and switch between the two.

The rig was basically a set of intakes with the correct diameter (and very short) stacks for best top end power. A set of smaller diameter and much longer stacks fit down in side the top end stacks and are lifted up and out of the way when the bike crosses through 7000 -7500 rpm. It was a clever design.

 

[Craigster]

Here is a chart showing the power the bike made with the low rpm long stacks fixed in place. The tuning was not fully sorted at this point, but it showed how the intakes performed.

 

[one2dmax]

The effective length is essentially changed with the OEM design but of course new ideas are always exciting to see. Wonder what year he did that?

The gen 2 vmax uses a design that sounds exactly like what you are talking about. This of course came out in 2009 so it's been a few years since that concept was invented. If his design predates that then great, if after then it may be a retro application to the gen 1.

Sean

 

[one2dmax]

What was the starting power? So far that number isn't terribly impressive?

 

[Craigster]

With the short stacks in place the bike, again with out being fully sorted produced a curve like the one below. Notice how saggy the bottom end is. Yes there is also a huge lean spot, but he did not want to alter the fueling curve he was developing for the bottom end. Still this shows the tremendous high rpm power available when the intake is modified appropriately.

 

[Craigster]

For comparison here is the two overlayed.

 

[Craigster]

This is the system fully active. Mind you he started developing this around 2003. His own dynamometer was far less cooperative so he came to see me in 2005. He continued to work on the system until around 2008. The real goal was to have an EFI turbo motor, but sometimes inventive people get side tracked. He did. For a while.

 

[Craigster]

This is all the curves overlaying each other. The blue is the system fully active. Notice how the blue curve runs along withe the green curve up to 7500 rpm. then as the long stacks are lifted out of the way, the blue curve departs the green and continues up along the the red curve.

 

[Craigster]

In the end, he made a peak of about 133 to 134 hp on a motor with this intake and a modified stock exhaust (gutted cans with Supertrapp end caps adapted to the ends of the cans for tuning).

 

[Craigster]

Here's a comparison to a guys '88 with just exhaust.

 

[Itgoes]

Interesting! The charts look a lot what it looks like when people remove the YCCI (variable intakes) on the Gen 2 to install a big air kit (individual filters).

One of my least favorite mods.......in fact I took my big air off and returned to the stock system.

I came up with another mod, that doubles the filter area while retaining the variable stacks. That gives me the best of both worlds, and gains everywhere.

 

[Itgoes]

YCCI & YCCT in action

https://www.youtube.com/watch?v=pSonecPgtuQ

 

[Craigster]

I asked if the owner was sharing any of this online. He said no. I guess there was some discusion about it back in the day, but a lot of naysayers. As there is always is with forums. Lots of experts who already know it won't work, so he just developed it himself and kept it to himself. The EFI itself was a little crude. It was an early Hahn Racecraft system which is just a rebadged Accel system. Great for a dragbike app., but lacked things like voltage compensation which is essential for the daily driving fueling perfection we expect from out current cars and bikes.

Still, he made it work real well and was going to continue the fueling development on his own dyno. I have not heard back from him in years, so I have no idea where the turbo project sits at this time. I figured the real technical folks would enjoy seeing the measurable differences regarding intake runner length and the effect it can have.

 

[Craigster]

The video you show is effectively what this system is. Only several years earlier - on a Gen I! Although i will say, that I saw the same type of system on an MV Agusta about the same time.

 

[Itgoes]

The video you show is effectively what this system is. Only several years earlier - on a Gen I! Although i will say, that I saw the same type of system on an MV Agusta about the same time.

Very cool!

 

[Craigster]

And I agree. I would not remove the variable runner. I would come up with another way to breathe better without removing the variable runner intake. Good for you for developing a real work around.

 

[CaptainKyle]

Great power for a mainly stock exhaust system I would like to see what he done & do a little work with a full header

 

[one2dmax]

Exactly, a full header would have hurt torque a bit but brought up power even more. Wish you had pics of the setup. Of course it wouldn't exactly fit the Vmax unless he used the stock carbs as the throttle bodies (which there is an EFI kit out there to do that).

You can't compare another guys 88 to his. Even two identically setup bikes will make different power. Still, I like the overall effect and improvements you were able to get.

If you posted up his name perhaps someone on here would remember him? I've been around these since 88 with other guys on here even longer.