Improved the velocity stacks

[PowerDubs_imp]

I was tooling around on Ebay looking at parts and came across a set of velocity stacks off a parted out bike.

What caught my eye is that I could see a lip midway down the throat. This is confirmed in the picture of the reverse side where you can see the notch cutaway gets thicker towards the middle.



So I bought them...and confirmed- yes, they do neck down in the center. ><



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Soooo...I did a little work on them. Hard to see from the pictures, but it is much better now. Here is comparison to a stocker.

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[PowerDubs_imp]

Finished them up this afternoon-


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[Ben70_imp]

I generally am in favor of allowing more air in, but I wonder if this particular "restriction" is for increasing the velocity of incoming air rather than the volume? Interesting though, please let us know what you think. Good old "butt dyno".
There is review on Motorcycle.com of the 2016 Triumph Street Twin where the reviewer says the bike runs a single 39 millimeter throttle body for "increased velocity at lower rpm". Possibly contributing to torque output? Let us know how it feels!

Ben

 

[jimgl353_imp]

that restriction would increase velocity, but having a sharp edge on it like it does would most likely cause turbulence. so some give and take going on here possibly.

 

[Ben70_imp]

You are correct, sir. The I.D. at the inner end would stay the same, and turbulence should be reduced. I imagine mpg improvement might be a way to gauge the success of this mod. Good luck with it PD. Also how much of a PITA to get those off?

Ben

 

[Gumby 1100_imp]

You are correct, sir. The I.D. at the inner end would stay the same, and turbulence should be reduced. I imagine mpg improvement might be a way to gauge the success of this mod. Good luck with it PD. Also how much of a PITA to get those off?

Ben

Devil's advocate here:

I don't think that you would ever be able to gauge your mileage accurately enough, even under controlled conditions, to tell the difference. The only real test would be a before and after dyno run...otherwise this may just have been an "off-season-make-work-project".

What if the sharp inner transition was intentional in order to create turbulence for better combustion? Honda could just as easily have molded-in a smooth transition just like the rolled edge at the opening...'cuz I doubt that leaving the sharp transition saves Honda any money.

On the other hand, it would be nice if this provides some noticeable improvement, but Ben's comment about the effort to swap these out is valid too.

 

[PowerDubs_imp]

Hi guys,

I haven't looked into how difficult it is to swap these out yet- but I can't imagine it is a deal breaker.

Yes, I am sure the stock shape is intentional. We all know the bike is made to put around at 2k, and have a very flat tame power curve. Heck, the ecu is limited in the lower gears.

These only cost me $16 shipped and a little work on a sunny day in the garage with tunes and beer.

Only way to really know what is what is to get the bike on a dyno and do a before and after.

Unlike the TSR units these will swap right on and completely reversible.

 

[jimgl353_imp]

if it had any more power in first gear you would need to be strapped on! it weighs 500+ and like I posted in another thread, with the last baffle drilled and the "plug" out of the air intake, it power wheelies. that's a lot of freaking power.

 

[PowerDubs_imp]

Really? I grew up on 2-stroke dirt bikes, so I guess perception is perspective.


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[Randy B]

if it had any more power in first gear you would need to be strapped on! it weighs 500+ and like I posted in another thread, with the last baffle drilled and the "plug" out of the air intake, it power wheelies. that's a lot of freaking power.

It wouldn't power wheelie with my fat butt on it...lol.

 

[jimgl353_imp]

I don't recall 2 strokes having torque. you must be thinking power to weight ratio... put a 2 stroke in a 500 lb bike and see what it does. ....or rather doesn't do...

 

[LongRanger_imp]

Gee, my RD350 had "Torque Induction," which was a fancy name for the reed valve. But you're right -- there was no torque.

 

[PowerDubs_imp]

I don't recall 2 strokes having torque. you must be thinking power to weight ratio... put a 2 stroke in a 500 lb bike and see what it does. ....or rather doesn't do...

Nobody mentioned TQ. What was discussed was power. Which 2-strokes had plenty of.


Refresher-

"if it had any more power in first gear you would need to be strapped on! it weighs 500+ and like I posted in another thread, with the last baffle drilled and the "plug" out of the air intake, it power wheelies. that's a lot of freaking power."

And yes- the RD350, predecessor to the RZ350 which begat the Banshee quad- which would easily lift the front wheels while pulling your arms out of their sockets and scaring the cuss out of you at the same time.

 

[Bheezy27403_imp]

I just bought two RD's...CAN'T WAIT!

 

[jimgl353_imp]

hmm... my first street bike, the bike I learned on, was an RZ350 and as I recall, it was rather tame. It was used when I bought it, so maybe it was worn out...

 

[the Ferret]

If it was tame you weren't revving it high enough lol. My RD 350 front wheel pointed to the heavens with no effort at all in probably the first 4 gears

 

[PowerDubs_imp]

 

[jimgl3_imp]

ok i retract my original statement. the CB1100 has no power. just torque. only torque ok. i never should have said power. but i stick by my stance on hp vs torque a 2 stroke has hp not torque. yes you can rev the heck out of a 2 stroke and pop a wheelie.

 

[Nortoon_imp]

My 1971 350 R5 (5 speed gearbox) was an very enjoyable motorcycle. It only produced 36 horsepower and 28 foot pounds of torque at 6500 RPM. But because it only weighed 322 pounds dry, it was quick and nimble. Yamaha had improved the 350 RD to point that there was useable power from 3,000 RPM on up. Mine had a top end of 103 MPH. It helped that I only weighed 163 pounds at the time, and had clubman handle bars mounted upside-down café racer style.

 

[PowerDubs_imp]

Hi guys,

I haven't looked into how difficult it is to swap these out yet- but I can't imagine it is a deal breaker.

Yes, I am sure the stock shape is intentional. We all know the bike is made to put around at 2k, and have a very flat tame power curve. Heck, the ecu is limited in the lower gears.

These only cost me $16 shipped and a little work on a sunny day in the garage with tunes and beer.

Only way to really know what is what is to get the bike on a dyno and do a before and after.

Unlike the TSR units these will swap right on and completely reversible.

Update- I’d call these a success.

The difference between these runs was the velocity stacks, an arrow header, and a power commander.

Although a portion of the gain is certainly fuel adjustment and loosing the cat- I don’t think anyone has put down over 98whp before, and there are no losses in the curve.

Install wasn’t hard- can be done in a few hours with basic hand tools.

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