twist

sooner or later I'll get to the point where I won't ask so many 'cruit questions. But that's not happened yet!

I've been reading a lot of posts about modifications for performance and so on. One that caught my attention is the velocity stacks inside the filter box. This is new to me, maybe I misunderstood. I understand the use of velocity stacks but are they being used inside the air filter box? If so, then they must be shorter than what would be used without a filter box. Inside the filter box would yield a benefit? There can't be much room inside that air filter box for a stack and VS are usually too long to fit inside a filter box. Have I missed something?

I don't plan on doing the velocity stacks but I am curious. For me, achieving 110 hp from the VTR is as far as I need to go. There simply isn't any use for horse power in the 120 to 150 range on the street. Best mods for me are suspension and handling. Then comfort. But I still like to know as much as I can get into my dried out brain.

twist

sooner or later I'll get to the point where I won't ask so many 'cruit questions. But that's not happened yet!

I've been reading a lot of posts about modifications for performance and so on. One that caught my attention is the velocity stacks inside the filter box. This is new to me, maybe I misunderstood. I understand the use of velocity stacks but are they being used inside the air filter box? If so, then they must be shorter than what would be used without a filter box. It's my understanding that velocity stacks are used on a track bike for better flow and increased power. Not using a filter isn't really the best thing for a street bikes life span. Inside the filter box would yield a benefit? There can't be much room inside that air filter box. Have I missed something?

I don't plan on doing the velocity stacks but I am curious. For me, achieving 110 hp from the VTR is as far as I need to go. There simply isn't any use for horse power in the 120 to 150 range on the street. Best mods for me are suspension and handling. Then comfort. But I still like to know as much as I can get into my dried out brain.

7moore7

It's more about controlled airflow rather than just height. The shape of a milled aluminum stack has finer tolerance than the molded plastic ones from the factory. This combined with a different profile and your large CV carbs are able to do more with the air coming in the airbox. Actually, I think the Dr. Honda stacks may be slightly shorter than the taller of the two OEM in the airbox, but don't quote me on that.

comedo

In the case of the VTR, the velocity stacks are within the air filter box. Aftermarket velocity stacks, such as those by Dr. Honda and Moriwaki, are used in conjunction with the air filter box. The Moriwaki (or HRC?) stacks which are the originals from which the Dr. Honda stacks were "inspired" are the product of considerable development. Longer stacks are unlikely to lead to a performance improvement. There are people on the forum who are far more capable than I am of giving a sound explanation . There's more than an evening of reading available if you search "velocity stacks".

twist

thanks! I really should get used to searching BEFORE asking questions. I don't need to modify the bike too much or tune it to the limit. This along with a flow master could be a nice improvement. I've seen how one change can lead to other changes so I want to take it easy and be prudent but at the same time make the bike my own and have it run great.

Sawzall86

From what I've come across/asked/read... 2 Long OEM stacks for more bottom with sacrifice on top end; 2 OEM Short stacks for more top end with sacrificing bottom end; Dr. Honda/Moriwaki/HRC/AL stacks are about mid-range height between the 2 OEM plastic stacks and show the best all around performance.

7moore7

I think this is slightly oversimplified... Remember, our carbs are jetted different front to rear (mainly because the rear cylinder runs hotter)... different mains, different emulsion tubes, and even different needles. So this requires a slightly different airflow into each of the carbs. I don't know the details on how all of this works, but I do know that you're not getting "more top end" from your rear cylinder and "more low end" from your front to get best of both worlds with the OEM setup. That would be a lumpy and inefficient power delivery. The power from each cylinder would be best if it were even. To get similar airflow/vacuum/fuel ratio, temp, etc... Honda made one of the stacks longer...

The billet stacks have much more controlled airflow, and this is where I'm not super clear on HOW it works, but are better in all respects than either of the OEM ones ( and not just an average of the two). The profile of the curvature is what's important, not the height. I'd even venture to guess that if HRC/Dr. Honda had enough time the front and rear stacks would be slightly different, but this is all speculation on my part. At that point they had FI with the RC-51...

Sawzall86

I won't argue that one bit. I didn't add the slight modifications to the slides needed for running the various stack lengths.

twist

so what you're saying, if I replace the stock plastic stacks with billet stacks of the same dimensions I will have better flow? If I don't mess with the length of the stacks I won't have to change the carboration. Increased flow doesn't necessarily equal more power, just better flow? I'm not looking to squeeze as much as I can out of the motor but I want it to run as well as it is designed to. Factory parts aren't always the best out there, plastic stacks for example, or the crappy CCT!

Sawzall86

You should probably start with the carb setup thread if you haven't done so. If you get the AL stacks they'll optimize the flow better than the stock stacks, but you'll need to plug a lift hole on each carb slide for them to work the best, iirc.

7moore7

Not entirely. The metal stacks DO have a finer tolerance than the injection molded mass produced ones (less likely to be oval, fewer rough edges), but the bigger benefit is that they also are much wider and their curvature rounds over in a smoother and less abrupt way than the stock ones. This is easier to do with billet aluminum where thickness of the material has no bearing on how easily the part is manufactured, where the stock part has to have even wall thickness and pop out of a machine thousands of cycles. So the material and the method of making the part allow for more flexibility in tuning

In another way of looking at it, if you made aluminum stacks with identical proportions to the stock plastic ones, the difference would be so minimal that it would probably be insignificant. But no one would do this cause it would be pointless...

twist

If you were going to "help" your VTR to run the best the design can, would you begin with aftermarket slip ons, add aluminum stacks, adjust the carburetors for the change in flow. Not modifying but merely adjusting for optimum performance and efficiency.

Just looking for simple, reasonable and affordable means to make the bike my own and run the best it can more or less stock.

HRCA#1

I would begin by doing what Sawzall86 suggested and read 8541Hawks carb guide and set up the carbs as he suggests to get the best and close to optimum setting. After that you can change anything you want and have a great baseline to compare it to.

7moore7

What HRCA#1 said. If I were to start from scratch doing power mods, I would do 8541Hawk's carb setup and then lighten the flywheel.

The stacks aren't really a good bang for your buck mod in my experience compared to other things (but they do look cool!)

Switching cans is more of a weight performance than a power one. If we're looking at the bike as a whole, suspension is even higher on the list for me

twist

it is true that weight is the easiest way to make a bike faster. I was under the assumption that the stock cans didn't flow all that well AND they are heavy. Weight is one reason I'm interested in the battery modification by Daugherty and shoria. I read the thread, great information, great pix too. I think the shock set up bu Daugherty is a great deal and an affordable way to help the suspension. There are more than enough projects to keep my busy for a while so I'll just read and learn for a while. I don't want to be a squid any longer than necessary.

Jack Flash

Nothing wrong with being a Squid. We all serve a purpose in life, and if squid it is, then so be it

I did the slip-ons first, and rebalanced my carbs for the new pipes. I did notice better throttle response, and better go on the bike. And before anyone attributes this to the carbs, I do them on a regular basis.

twist

first things on the list are CCT's and Reg/Rect upgrades. Saving my dimes for the cans I want but I can get the carburetors sewt up for optimum performance in the mean time. Most likely I won't get to that until I get the new mufflers. I have my short list tho. Mostly things that can't be seen like CCT, R/R,rear shock,brake lines, etc.....

8541Hawk

So I guess I should say something.....

I'll try to hit most of the points....

I'll will also try to keep the explaination simple as to what is going on.

Yes the stacks are inside the airbox. As for how long they are, that is related to where they make peak air flow.

As for what they do, CV carbs like nice smooth air flow, so the stacks feed them a nice smooth column of air.

With the stock set up, the longer stack flows better at lower RPMs and the short one flows better at a higher RPM.

They did this to get a broader torque curve.

Some people have tired and\or do run either 2 short or 2 long stacks.

The 2 long stacks give more bottom end with less top end

The 2 short stacks give more top end power with less bottom end.

Yes the carbs need to be tuned differently for each set up.

Now the billet stacks. These are in between the stock stacks in lenght but flow better than the stock units at all RPMs.

Yes this also requires a differnt carb set up.

So where did the billet stacks come from and why are they the same lenght?

Back in the day, as the kids would say, Honda gave Moriwaki the development program for the VTR (Yes there were others also like Roger D @ Revolution and Honda USA or Erion Racing) which was R&D work for the SP1 (RVT, RC51 whatever you like)

Among the many things they came up with, the billet stacks are one of the most useful for a bike that is ridden on the street.

The reason for bing the same lenght, From what I was told (which means I just have my notes, no "solid" proof, so believe at your own risk....) is that for below 130HP and the RPM range,Power\Torque Peak RPM of the engine and the airbox volume it really doesn't matter.

Now if you look in the airbox of a SP1 you will see stacks that look like the billet units but back to the staggered lenght.

00-06 Honda RC51 Velocity Stacks Intakes | eBay

You can see where they got the shape and they are just tuned to work in a differnt RPM range so the lenghts are dictated by the aixbox volume, injector size and all that stuff.

The stock cans also work pretty good, they are just really heavy....
So unless you have a Stg1 engine or better, which ever can you run will change the weight of the bike more than the power output, IMHO.

7moore7

Oops, I was wrong about this part from what I said earlier... I misunderstood what was going on with the staggered stock lengths.

twist

Well, I think that since I will ride this bike on the street with an occasional track day, I won't really change much. Weight, suspension and the standard upgrade of manual CCT's and R/R are the best first steps for me. Tuning the carburetors is something I will get around to eventually. I do like the idea of billet stacks and enhanced flow.

8541Hawk

Suspension and Brakes are the tops in my book..... You can tell by looking at my bike..... Though I am starting to collect parts for an engine build.

Plus a few new and new to me bits should be showing up in the next couple of weeks.... It is nice to be back in CA

Sawzall86

I'd start with the basics first, which I've done and suggested, and I feel the bike is a completely different animal from what I bought some 4 months ago. I don't think I can stress enough how much of a difference there is when the carbs are set up the way they should have been set up from the factory, which 8541Hawk had personally taken the time to write up and explain in full detail. Don't "get around to it", just do it, trust me and the others on here.

twist

you're saying you would do the carbs as a matter of routine along with CCT and R/R? Are you advising the addition of billet stacks at the same time? It is my intention to get this bike to run the best it can, stock. I'm building my short list of things needing to be done. Another question: can I assume that the carburetors will need adjustment to accommodate new mufflers with better flow?

twist

I want to thank all of you who have tolerated my squid questions. The search feature takes a little persistence but the information is there. So much to read and consider. Thanks again everyone. The only thing I have to contribute so far is a link to clip ons that may be useful for for those wanting to raise the handlebars. Check it out:
Results for Clip-ons

other good stuff there too.

Sawzall86

It depends on how often you feel you need to pull your carbs. I can probably have mine off within 20 minutes now, so it's not that big of a deal to me. If you want to add the stacks while you're in there, you can, since you'll need to pull the carbs to plug a lift hole on each throttle slide (as explained in the carb setup thread) You won't have to go bigger in your mains no matter what mods you have planned for your street setup, you should up your stock pilots to 48's though. The only time you should need bigger mains is when you start diving into the motor. I have slip-ons and I have yet to touch the jetting after setting my bike up per the carb thread and then dialing it in. Supposedly our carbs will need to be resync'd approx every 6 months as basic routine maintenance on them.