Velocity Stack on the 35 gasser ??

Velocity Stack on the 35 gasser ??
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Velocity Stack on the 35 gasser ?? - 2/18/2008 9:02:46 PM

the Wasp

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From: Rutland, VT, USA
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so I was wondering if any of you MVVS tech guys have tested a Velocity Stack on the MVVS 35cc gasser (or even the 35cc glow)

I was wondering what the results were, more power, more RPM maybe ??, it would be nice to pick-up another 200 RPMs cheaply

Jim

Post #: 1

RE: Velocity Stack on the 35 gasser ?? - 2/18/2008 9:31:06 PM

DarZeelon

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From: Rosh-Ha'Ayin, ISRAEL
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Jim,

What most people think is a 'velocity stack', isn't...

To actually increase the performance of a two-stroke engine, at its second harmonic in its operating RPM range (7,500-9,000), it would typically have to be ~7.9" inches long...

The nice 'skirt' intake may smoothen the flow a bit, but adding power requires the length for optimum flow, for a pulse strength of ~10%.

Can you imagine an 'intake chimney' nearly 6" long (2" are in the carburettor and the crankshaft), on your MVVS 35 cc engine's carburettor?...

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Post #: 2

RE: Velocity Stack on the 35 gasser ?? - 2/19/2008 6:10:01 AM

the Wasp

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From: Rutland, VT, USA
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OK, LOL Carburetor Trumpets as RC Showcase calls them (see links),, Velocity Stack is what the Auto Parts Industry call (ed) them for years,,

anyway, I was thinking it might help with that big tapered mouth right behind that big prop..

http://www.rcshowcase.com/html/accessories/filterstrumpets.html

Jim

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Post #: 3

RE: Velocity Stack on the 35 gasser ?? - 2/19/2008 8:37:20 AM

Hans Meij

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Tried this first on the 35 gasser

Result, only a very small (100) increase rpm, but unstable running. Removed it.

With the MVVS stack

Same rpm but a more stable running, so it is a keeper.

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Post #: 4

RE: Velocity Stack on the 35 gasser ?? - 2/19/2008 3:03:36 PM

pe reivers

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From: Arcen, , NETHERLANDS
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@hans:
That more stable running probably was due to the more recessed location of the choke valve.

@dar/wasp
in my 50cc racer, we found a best total intake duct length (by cut 'n try) of 40cm, with the carb located 1/3rd that distance from the piston skirt.
Torque started above 9000 rpm. Anything below that rpm caused the engine to flood instantly if the throttle was more than just slightly open, due to the multiple blowback gas passage past the jets.

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Pe, Dealer for MVVS, MTW and Mejzlik; www.mvvs.nl
There is sanctuary in analisys.

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Post #: 5

RE: Velocity Stack on the 35 gasser ?? - 2/19/2008 3:44:32 PM

DarZeelon

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quote:

ORIGINAL: pe reivers

...Anything below that rpm caused the engine to flood instantly if the throttle was more than just slightly open, due to the multiple blowback gas passage past the jets.

Pé,

Tuned length runners work great with port fuel injection, like in many cars.

This is because those multiple reverberations don't affect the mixture strength, with the fixed amount of fuel injected at the port.

Any power boost will only happen at the various harmonic RPM values, but the mixture will not be affected.

The software for the calculation of the intake runner length assumes the runners precede the point of injection. It is also designed for four-stroke engines, so the RPM numbers must be halved...

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Post #: 6

RE: Velocity Stack on the 35 gasser ?? - 2/19/2008 10:06:31 PM

pe reivers

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Dar, the link is for 4- strokes, and lacks valve cam timing input possibilities..
With two strokes, timing is more complicated, and must take into account whether you hace rotary, piston, or reed induction.
Also, the Bowling & Grippo guys have their facts wrong (in the text). The result is OK though.
A suction wave is reflected as a pressure wave when it meets an open ended tube. So in very short tracks, the wave is bounced back to and fro, until it eddies out. This is the least critical, but causes blowback at low rpm if the piston or disk closes late.
Full length, or 3/4 length tubes work better, but are critical at rpm below resonance.
Injectors (active fuel injection) should sit as close to the crankcase volume as possible, carbs (passive injection) should be as far away as possible.

_____________________________

Pe, Dealer for MVVS, MTW and Mejzlik; www.mvvs.nl
There is sanctuary in analisys.

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Post #: 7

RE: Velocity Stack on the 35 gasser ?? - 2/20/2008 1:46:43 AM

octanehuffer

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I think MVVS should look to the future and start with fuel injection. Have an EEPROM fuel management unit(FMU) with a couple of basic tunes and a USB cable for tuneability. Make a simple program for changine fuel and injector timing, RPM, etc. A small piezo electric injector(already developed) and a throttle position sensor. Map sensor installed in the FMU. Just your basic speed density EFI. Just like new age hot rods. I can tune my cars all day long with my laptop in the front seat. Would be fun to have the ability to do it to an airplane. Rid ourselves of carbs and tuning issues!

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Post #: 8

RE: Velocity Stack on the 35 gasser ?? - 2/20/2008 2:00:58 PM

pe reivers

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you want me to tell them?
Could be fun if prices soar due to small production quantities.

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Pe, Dealer for MVVS, MTW and Mejzlik; www.mvvs.nl
There is sanctuary in analisys.

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Post #: 9

RE: Velocity Stack on the 35 gasser ?? - 2/20/2008 10:53:38 PM

the Wasp

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From: Rutland, VT, USA
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thanks for the info guys !!

but you know what we really need ? an in-cowl muffler that will increase power a bit over the today's available mufflers, something like the Youngblood MP2/MP5 heli mufflers,,

http://www.heli-world.com/detail.aspx?ID=5679

a 300 or 400 RPM increase would be quite noticeable on my GBY !!

personally I wouldn't mind a long tuned pipe mounted to the side on my GBY, I think it would look cool, but the guys at the field would really give me a lot of grief about it !!

Jim

(in reply to pe reivers)

Post #: 10

RE: Velocity Stack on the 35 gasser ?? - 2/21/2008 3:00:39 AM

octanehuffer

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I am not one to be a price shopper. Infact I spend more money to have the best product for the best power. I spend tens of thousands on cars and hp, yearly. Just for fun. I do see your point though.
I laid money down once to have a supercharger custom built for an engine but once the builder stated that he was going to charge me more money to make it than it would cost to produce the system for other people, I pulled my 10k+ money back. I dont want to pay to be the guinea pig when others will benefit. Thats the companies job.
Just tell MVVS to make great and powerfull engines please. Thank you Pe.

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QQ 120" Yak, QQ 86" Evolution, QQ 69" Saito 1.25, QQ 49" 32SX, QQ E-Yak, H9 T-Craft G-26, etc

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Post #: 11

RE: Velocity Stack on the 35 gasser ?? - 2/21/2008 6:27:51 PM

pe reivers

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I think they are doing just that. If there is a market for fuel injection, and a sustaining profit can be made, I am convinced they will do it.
But just look at OS. Some aerobatic crowd people use the engine, and pay through the nose for it, to be beaten by the humble MVVS glow engine in matters like reliability and userfriendliness. OS is a huge company that can afford to have up front devellopment, even if they loose bigtime on it. The spinoff is advertising value.
Judging by the teething problems, fuel injection has to come a long way before it is ready for our engines.

_____________________________

Pe, Dealer for MVVS, MTW and Mejzlik; www.mvvs.nl
There is sanctuary in analisys.

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Post #: 12

RE: Velocity Stack on the 35 gasser ?? - 2/23/2008 7:45:59 AM

fiery

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Which MVVS Engine are you referring to Pe?

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RE: Velocity Stack on the 35 gasser ?? - 2/23/2008 8:56:19 PM

pe reivers

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None in particular.
With RC aerobatics, the 1.60 glow competes alongside with OS glow engine types, and holds its own. The gas engine was at a very slight disadvanage because of it's lower specific output. Not much, just slight. For champs that is enough to notice.

_____________________________

Pe, Dealer for MVVS, MTW and Mejzlik; www.mvvs.nl
There is sanctuary in analisys.

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Post #: 14

RE: Velocity Stack on the 35 gasser ?? - 2/28/2008 8:36:24 PM

John Serjeant

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From: HARWICH, UNITED KINGDOM
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Hello from the U.K.
Velocity stack or trumpets?.
Anyway, I,ve two MVVS 1.60 engines and both run well.
However, I do notice a certain amount of unused fuel, or more precisely, the oil part of the gas, seems to "get out" of the carbie and sprays the engine and interior of cowling.
Not to a large degree, but enough to ask, why does this happen?.

Would a "stack" minimise this fuel being blown out, thrown out of the carbie?.

I do like the look of the MVVS stack fitted, as in the picture in a previous post to this thread. Where do you get one!!.
Comments welcome please.

John Serjeant.

(in reply to pe reivers)

Post #: 15

RE: Velocity Stack on the 35 gasser ?? - 2/28/2008 9:16:24 PM