[Zmagnette] Stub stacks

Fri Nov 15 14:50:04 MST 2013

There are so many misconceptions that have been brought up in this discusion it would be impossible to address them all. 
Air, water and our cars do not like to make tight 90 turns. When you go around a corner in your MG you make a nice radius, not an L. If you did bad thing would happen. Experiance teaches us we can not trun on a dime or we will hear the crashing of metal as your car rolles over. The same is true of air flowing into our carburators. The air crashes togeather causing swirling and blockage. 
Velocity stacks work by increasing the inlet track length, eliminating turbulance and improving air flow. I almost all cases they will help low end power, as most intakes are way too short. They are designed to fit under the hood, be inexpensive and allow an air filter to protect the engine. VS also provide better mixing of fuel and air.
More air flowing through the same size carb usually requires leaning the mixture, not making it richer. Higher vacuum is created with more air flow enriching the mixture. Bigger carbs reqiire larger jets because there is less vacuum to suck the fuel up and out.
Most veloicty stacks on the market are very poorly designed. They have too large an inside diameter and/or to short and do not have a proper radius. The radius should wrap all the way around.
A proper VS can have other benifits as well. I was lucky to work for one of the top motor flow experts when I was younger. He showed me a lot of tricks on his custom built flow bench. Since then I have done cylinder heads for many AMA national champions like Kenny Roberts. I have been able to almost double the air flow on a head without increasing valve size. More then double with larger valves. 
Most performance mods come at a cost. Ie you lose bottom end to gain top end. But with good air flow that is not usually the case. Proving better air flow will usually help throughout the power range. 
-- 
Sent from my Android phone with mail.com Mail. Please excuse my brevity.

Allen Bachelder <bachldrs at comcast.net> wrote:

Are we comparing apples with oranges here?  Take an air cleaner off any carb and you'll hear more noise. Why? Air cleaners themselves absorb/insulate some sound.  And different kinds vary.  The K&Ns are slightly noisier than stock MGB air cleaners. I don't think that's because they're less efficient.  My guess is that they provide less acoustic insulation. 

Kelvin - your point is well-taken. Are you saying that even if everything else is spot-on, it's still not worthwhile to mess with velocity stacks for those of us who spend most of our lives below 3500 rpm?

*********************************************

Allen & Florrie Bachelder
North Street, MI

bachldrs at comcast.net
*********************************************

On Nov 15, 2013, at 1:18 PM, charles durning wrote:

Just my 2 cents.  The extra noise from a fan or an engine is just the noise made from  air movement.  Though our engines do make more power at the higher rpms (thus more noise) it's actually not as efficent at processing the air movement as it is at a slower speed.  I believe that the most efficent engine in the world has an 8 foot stroke and maxes out at102 rpm.  It's most efficent speed is 100rpms.  That gives plenty of time to extract all of the engergy from the fuel/air misture.  When the heater fan is turning at 3 times the low speed it is not moving 3 times the air, just moving more air.  Noise is just unused energy. 

In my case I really don't care one way or another.  I have pancake air filters with no air flow enhancements.  A nice throaty sound from a MG exhaust is a plesant sound no matter how it gets there.

Charlie Durning

If you are using Google or Gmail, Big Brother is watching.

On Fri, Nov 15, 2013 at 11:08 AM, Wayne & Isabel Hardy <gwhardy at suddenlink.net> wrote:

Yea that sounds nice all that about efficiency, but fact of the matter is that the big old factory cleaner was much quieter than the small cleaners or just velocity stacks...more air seems to make more noise, just turn your garage fan from low to high speed and tell me which setting is loudest or sit in the car and turn the heater / ac fan up to high and compare it to the low setting and see which one you like best.

The intake roar doesn’t bother me in the least nor does a nice hum from the exhausting gases but some folks do not like gaseous noises from either end.

From: Gene deRuelle 

Sent: Friday, November 15, 2013 

To: Michael Anderson ; List for the Z Magnette Group - North America 

Subject: Re: [Zmagnette] Stub stacks

If you run the little stacks, aren't you subjecting the fuel/air mixture to whatever is IN the air?  In other words, you can't run the stacks and an air cleaner, can you?

Gene D

----- Original Message ----- 

From: Michael Anderson 

To: List for the Z Magnette Group - North America 

Sent: Friday, November 15, 2013 6:58 AM

Subject: Re: [Zmagnette] Stub stacks

I respectfully disagree that more air = more noise by default. "Noise" to a mechanical engineer (or most any engineer) is an undesireable by-product of inefficiency, i.e. whatever is causing the noise is sapping energy from whatever the machine is supposed to do (unless it's job is to make noise). Having said that, stub stacks should reduce noise -all else being the same - because the efficiency of the system is increased.

To that end, Allen opens up the issue of Bernoulli. In our carbs Bernoulli is working hard for us at the piston/bridge, not the inlet throat. Without some kind of "stack" Bernoulli is screwing with us at the carb inlet as the "apparent" inlet diameter gets smaller due to the air having to make a hard 90-degreee turn... turbulence is also introduced before the piston/bridge which is not a happy thing for nice even fuel induction.

Those two reasons are what makes the mixture "change" when you put a stack on. Not more air, per se, but quality of air flow. 

Mike!

Michael Anderson
One of a Kind Stuff/AEU
775 772-2056

_____________________________________________
From: Wayne & Isabel Hardy <gwhardy at suddenlink.net>
To: List for the Z Magnette Group - North America <zmagnette at autox.team.net> 
Sent: Friday, November 15, 2013 1:19 AM
Subject: Re: [Zmagnette] Stub stacks

If the carbs are tuned again to compensate for more air to the inlet, then more power should always be the result. If more power is “Better”, then the answer is yes. But you must adjust for more airflow to get a more better running motor..ie more air will need more fuel too if a result is to be more power. Maybe a new, slightly richer needle is the ticket to heaven. I know the K&N filter people caution that their filters flow so much more air than the usual paper ones, that a richer needle, or jet, or slight enrichment adjustment may be desirable for best running.

Of course all this extra air flow is also likely to create more inlet roar under acceleration. Is that “Better” or not???

I personally run the MGA cleaner assemblies rather than the Magnette one for better access to the carb adjustment screws for keeping up with summer 100 degree days now swinging to winter 50 - 60 degree days and the resultant changes in idle speeds due to cooler, denser air, and the need to richen the mix by about 1/8th of a turn.

MG put on the big old ugly oil bath filter for better engine life in a variety of dirty dusty operating situations around the world, and for more civilized operation in a quieter manner. Their true race motors ran with velocity stacks and no filters usually.

Wombat

From: Allen Bachelder 

Sent: Thursday, November 14, 2013 10:21 PM

To: List for the Z Magnette Group - North America 

Subject: Re: [Zmagnette] Stub stacks

I'm cautiously venturing beyond my paygrade here, but are we not talking about the Bernoulli Principle: stating that as air enters a conical tube the air pressure is maximized, but as the tube diameter conically diminishes, air pressure decreases as air speed increases inside the carb.  Without a conical stub stack, there is no acceleration in the air entering the carb inlet.  How much lift would we get from a cross-sectionally flat airplane wing-top with a squared-off leading edge? 

That being said, how can the original Magnette intake plenum perform any of this function? Same question for the intake plenums on T-series cars. I would think they would be Bernoullian disasters.  Would a Magnette engine always run better with stub stacks rather than the original plenum?

Curious in Michigan.

(Allen)

**************************************************************** 

Allen & Florrie Bachelder       =iii=<
Spring Creek Home for Wayward MGs

'57 ZB, '65 B, '69 C/GT, '73 B/GT

North Street, MI 48049, USA

http://www.mgexperience.net/member/bachldrs 

****************************************************************

On Nov 13, 2013, at 7:33 PM, John Park wrote:

Depending on length it can produce a much smoother flow, some say a bit of a ram effect which increases power and torque . Longer stacks as in longer runners means more torque while shorter ones mean more power.  Not lots, but it all contributes to a freer flowing intake which helps your freer flowing exhaust to make a bit more power/torque and slightly better fuel economy.  You note vintage racers usually have anywhere from2.5 to 6 inch stacks. Some with a stocking for a coarse filter, most just hoping nothing of consequence enters the throat… I have a set of 2.25 inch stacks in my 3.25 inch K&N’s on my MGB and they seem to help. Just the ho hum stock setup on my Magnette.

From: zmagnette-bounces at autox.team.net [mailto:zmagnette-bounces at autox.team.net] On Behalf Of Richard Greenberg
Sent: Wednesday, November 13, 2013 12:34 PM
To: List for the Z Magnette Group - North America
Subject: Re: [Zmagnette] Stub stacks

What is a stub stack? Would it allow for a filter that lies closer to the engine than a regular pancake filter?

On Nov 13, 2013, at 9:53 AM, Allen Bachelder wrote:

I've always just used the item #54 from the Moss catalog: http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28996#top  Are these from APT or Rimmer better?

Always anxious to learn...

Allen

****************************************************************

Allen & Florrie Bachelder       =iii=<
Spring Creek Home for Wayward MGs

'57 ZB, '65 B, '69 C/GT, '73 B/GT

North Street, MI 48049, USA

http://www.mgexperience.net/member/bachldrs

****************************************************************

On Nov 13, 2013, at 4:10 AM, monster at caverock.net.nz wrote:

Hi everyone,

I'd like to get a pair of 1.5" H4 stub stacks and I've tried emailing Steve Ash several times to see if he would make some more, but I haven't got an answer from him.

So... from a light scour of the internet there appears to be two types available at a reasonable cost:
$32.50 ea -http://www.aptfast.com/ShowItem/101221%20Billet%20Alloy%20Stub%20Stack%20SU%20HS4.aspx
$57 pair - http://www.rimmerbros.co.uk/Item--i-RL1396ALT

I've excluded the K&N ones as they are very rough, by all accounts.
Are there any others that people would recommend?

They're going to fit inside K&N filters that are 2 1/8" thick.

regards,
-- 
Robert (in NZ)
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