Any noticeable benefit of VHB velocity stack? -- CONCLUSION REACHED

[moto]

Does anyone have personal experience of a switching from the K&N (not FRAM, oops) filter that attaches directly to a VHB carb to a combination of the VHB velocity stack and the different K&N filter that attaches to it?

The bike is a T3 in stock tune, running well I think. But a chance to swap rides with another T3 made me think it could be better.  I'm looking for more low end and mid range performance that is clearly noticeable (and worth $200).

I'd like reports based upon personal experience with this particular modification. I know there are other choices I could make, but that is not what I'm asking about. 

[huub]

without the velocity stacks the fueling is a bit of a hit and miss in the midrange .
if you want pod filters , just slide the pod over the velocity stack

[Antietam Classic Cycle]

Never used the FRAM filter, but Loops with their K&Ns clamped directly to the carburetors without velocity stacks always seem to have "weird" fueling, particularly at higher speeds. Look at the inlet of a VHB - what do you think that squared-off step is going to do to air flow?

If you'd like to try them, I have a set of V7 Sport "velocity stacks" I'll send you, might even have some Uni-Filters to fit them as well. 

[czakky82]

Bub headers and sump spacer help too

I’ll add that I have some Ducati velo stacks you can try too.

[moto]

I meant the K&N filters not FRAM, of course. Fixed the original post.

I have the velocity stacks from MG Cycle in hand, but had forgotten that I need to change filters to fit them. So it's a question of another $130 for the filters or sending back the $85 velocity stacks. Thanks for the offers of loner loaner stacks!

I'll wait to see if anyone else chips in with their experience with this change, and then probably go ahead and order this afternoon. It's only money, honey, as some bard once said.

[Antietam Classic Cycle]

If you have the straight, original style "velocity stacks" then you can use the one piece K&N.
https://www.amazon.com/gp/product/B000E2CTN0
https://www.vividracing.com/-p-152401916.html

It's a bit of a pain to install, helps if you grease and warms the stubs that slip over the 'stacks. But, it works well and is about 1/2 the cost.

[Fontain25]

Recently installed velocity stacks you mention and KN one piece filter. Better low-end and mid-range.

[chuck peterson]

The velocity stack has a change in inside diameter that effects the….velocity…(ahem) of the air entering the carb. The opening narrows towards the carb..speeding up and condensing the air

Absolutely makes a big difference with subtle on/off throttle response

I had a machinist turn down the outside of yhe stacks to make a closer fit to the k&n’s

Smoother response, less of a sudden step up in engine response

The stacks use to be rare, but I think suppliers are making new ones…i.e. Mgcycle

To the OP, you have both, just turn down the outside of your stacks to make a fit to the pods

Helps to clean and oil the kn’s regularly so they have that nice pink shade

Lots more honking going on underneath you w the stacks

[Don G]

All I have to add is be careful of how far the air cleaner element goes on the stub, if the K&N is on too far it will restrict airflow, kind of a piss poor set up as the filters have to be pushed on quite a bit to clear each other, the single element likely works better than 2 singles.  DonG

[Road Rocket]

 My race Triumphs are not Guzzis but they are hemi head pushrod engines. in the range of 57 rwhp @7200 rpm and 48 ft lbs torque @5100 rpm.I have done hours of dyno testing and some with velocity stacks, air fliters and no filters.The engines have dual  34mm Mikuni flat slides on a 650cc engine.In all cases ,a velocity stack reduced high rpm power. 3x5 inch Uni or K&N filters reduced top end power a few percent and ..Highest HP and best torque band was obtained with the carbs mounted as close to the head has possible... Street engine has different varables of course.

[czakky82]

Great input!

[Antietam Classic Cycle]

My race Triumphs are not Guzzis but they are hemi head pushrod engines. in the range of 57 rwhp @7200 rpm and 48 ft lbs torque @5100 rpm.I have done hours of dyno testing and some with velocity stacks, air fliters and no filters.The engines have dual  34mm Mikuni flat slides on a 650cc engine.In all cases ,a velocity stack reduced high rpm power. 3x5 inch Uni or K&N filters reduced top end power a few percent and ..Highest HP and best torque band was obtained with the carbs mounted as close to the head has possible... Street engine has different varables of course.

But, Mikuni flat slides have a nicely rounded inlet, not a sharp edged threaded inlet like a Dellorto VHB. Apples to oranges.

[moto]

Thanks for a set of uniformly good and on-topic responses.

To update, I ordered the individual K&N pods RU-2450 from MG Cycle (and they were shipped right away!). So now I can test for the benefits of the stacks by swapping from my existing set-up:

Existing set-up: no velocity stacks, individual R-0642 filters (inside flange diameter 38mm)

New set-up: MG Cycle velocity stacks, individual RU-2450 filters (inside flange diameter 44mm)

I did consider the single shared filter, MG-2640, but rejected it because the inside flange diameter is 38mm and because of critical comments on the Amazon page about its symmetry not fitting well on the Guzzi's asymmetrically-positioned carbs. I'm sure it works, but I would rather spend the money and save the bother.

By the way,  that last one, the MG-2640, appears to be the same as my R-0642 filters, except that it has inlets on both ends. K&N is ginning up filters from a stock of standard parts, I believe.

Once I get the new parts I'll be able to make my own comparison, and will post here again.

Also by the way, Greg Bender has an interesting set of comments on various possibilities, here: https://www.thisoldtractor.com/moto_guzzi_loopframe_air_filters.html

The R-0642 and MG-2640 are hard to find in stock, and may be out of production, I suppose.

Photos (mostly to aid my own memory):

R-0642 (38mm flange):



MG-2640 (38mm flange):



RU-2450 (44mm flange):



Moto

[kidsmoke]

I did consider the single shared filter, MG-2640, but rejected it because the inside flange diameter is 38mm and because of critical comments on the Amazon page about its symmetry not fitting well on the Guzzi's asymmetrically-positioned carbs. I'm sure it works, but I would rather spend the money and save the bother.

That's the thought I had, having recently changing out pods and taking a closer look. Here's a photo (G5 w/ VHB30's) with new pods installed clearly showing the assymetry between the carbs.

Otherwise I really like that idea.

[Antietam Classic Cycle]

The straight 'stacks are long enough that the asymmetry/symmetry of the MG-2640 isn't a big deal - you just don't slide it onto one stack quite as far. It was made for the application after all. The 38 mm i.d. stretches out just fine. 

[Ratso88]

hey, all good information.

My question, regarding a '74 Police bike I'm bringing back after a 20 year nap. What I have are now very clean 20 year old PHF32 carbs that previously had UNI Filter pods on them, no stacks. I'm interested in finding a set stacks that will thread on as per the PHM's.

Will the original Guzzi/MGCycle velocity stack work or do I need to keep looking?

Same idea, looking for low and mid range rideability. I can figure out air cleaners along the way.

[Antietam Classic Cycle]

hey, all good information.

My question, regarding a '74 Police bike I'm bringing back after a 20 year nap. What I have are now very clean 20 year old PHF32 carbs that previously had UNI Filter pods on them, no stacks. I'm interested in finding a set stacks that will thread on as per the PHM's.

Will the original Guzzi/MGCycle velocity stack work or do I need to keep looking?

Same idea, looking for low and mid range rideability. I can figure out air cleaners along the way.

PHF/PHM have a rounded inlet, so 'stacks aren't as critical IMO. I normally just clamp filters directly to them.

[Ratso88]

Charlie, thanks for the quick reply.

Clamp on filters it is! 

[czakky82]

I had some time today to play around with my V7 sport.

I had some non standard v-stacks on mainly because I thought they looked cool and were cheaper than reproduction original style. These are 8mm longer and open to a 48mm taper. I carefully jetted and ended up with 135 mains, the rest pretty standard.

Antietam CC sent me a pair of originals (Big thanks BTW! ) and I went back through the jetting and found I went up to 145s! Same air filters, etc. 5th gear does roll on a bit better too I think.

Side note: At this point I’m pretty sure I can swap VHB main jets as fast as anyone.

[moto]

Wow.

How do you select your jets, by doing plug chops and looking at the color? Or by seat of the pants feel? Or with a dynamometer?

Very, very impressed.

Is your stock V7 Sport stack the same as or similar to the stock T3 reproduction from MG Cycle?

Thanks for doing and reporting this.

Moto

[czakky82]

Seat of the pants. I do plug chops on 2 strokes but on 4ts if I can’t notice a difference I just go on the rich side.

My process:

The non-stock v-stacks: I started at 145s it bogged at WOT, 140s slightly better, 135s pulled clean, 130s were slower and you can feel when they get lean.

The stock v-stacks: I tried 145s and the difference was apparent right away, stock w/airbox is 142s I tried those and it was slower. This was all with the needle at richest, once settled on mains I tried needle in the middle, was worse.
Robert’s your mothers brother!

I’ve got jets if you wanna play a bit.

[Antietam Classic Cycle]

Comparison of Guzzi "velocity stacks":

Left to right: V700/early Ambo with SS1 carbs, Ambo and Eldo with VHB29s, V7 Sport and 850-T with VHB 30s, (modified - o.d. turned down) Convert, T3, etc. with VHB30.



V700 w/SS1


Ambo & Eldo w/VHB29


V7 Sport & 850-T w/VHB30


Convert, T3, etc. w/VHB30

[larrys]

The small stock stacks/rings are missing on my Cal (36mm carbs). No clue why the PO took them off. Are they available and where?
TIA,
Larry

[Antietam Classic Cycle]

The small stock stacks/rings are missing on my Cal (36mm carbs). No clue why the PO took them off. Are they available and where?
TIA,
Larry

Are you sure it's supposed to have some? Not seeing any on the 1000S or Cal parts diagrams, looks like the elbows from the airbox attach directly to the carb, same as they do on other models.

My Ducati Pantah uses this type, but a large i.d. rubber boot slips up over it.
https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/carburettor-parts/phbephb-parts/trumpet-18mm-long/

[moto]

Comparison of Guzzi "velocity stacks":...

Charlie, great photos!

One thing that seems evident to me now that I have installed my new stack is that the stack is essentially a part of the carburetor. The carburetor was never designed to be used without a stack of some kind. With the stack installed, there is just a smooth tapering bore right down to the needle jet opening.





There are different opinions on where the stacks make the most difference, it seems. But one thing is clear, they must make some difference or Dellorto and Guzzi wouldn't have bothered with them. After all, they are invisible inside the filter. So I guess my original question has been answered in a way: there must be some noticeable difference with them installed.

My intuition agrees with the idea that a reduction of turbulence helps to smooth out slow speed running, including during quick throttle movements.

I should have a chance to try both setups tomorrow and report my own impressions. With luck I may be able to produce some empirical evidence on whether power is changed at some throttle opening, but I doubt I can get reliable data.

[larrys]

Are you sure it's supposed to have some? Not seeing any on the 1000S or Cal parts diagrams, looks like the elbows from the airbox attach directly to the carb, same as they do on other models.

My Ducati Pantah uses this type, but a large i.d. rubber boot slips up over it.
https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/carburettor-parts/phbephb-parts/trumpet-18mm-long/

No, I am not sure. Only asked because the neoprene? ring with the clamp that connects the plastic elbow to the carb doesn't seem to grab the mouth of the carb very securely, and slips off of the carb after a while. Getting annoyed with having to fool with it. Maybe I need a new rubber ring? It is is 27 years old...
Larry

[wirespokes]

My T3 came with K&Ns clamped to the carbs without the stacks. They wouldn't grip to the threads very well and over time had deformed to a much smaller inlet diameter.

Heated the rubber until they stretched enough to fit over the stacks, then installed on the carbs. Ran much better.

I've also installed K&Ns on two LeMans that connected both carbs. The filter doesn't sit squarely in the frame, but who cares? You only see the non symmetry looking from above. i prefer the filters combined that way. Due to valve overlap some fuel is sent out of the carb rather than into the engine and connecting both carb intakes with one filter helps with fuel economy and power. The LM3 gets consistently over 50mpg and that's not riding it easy either. I believe joining the two intakes is a factor.

[moto]

Thanks again to all for the valuable input that led me to buy the rest of the new setup.

Here are my own impressions after comparing the old R-0642 filters without stacks to the new RU-2450 filters with stacks.

Details: My T3 is in good shape, w/ 170 psi compression in both cylinders, a newish timing chain and tensioner, Dyna ignition, valves set not too long ago, and jetting that I went through last year, winding up very close to stock. The mains are new 120's (stock), the needles are new V5's (extremely close in profile to the stock V9's). Everything else is stock, I recall, except that I have a 33 cutaway throttle slide instead of the stock 40. I created the 33 following a tip from Pete Roper long ago, hoping to improve response at 1/8 to 1/4 throttle. (This worked up to a point.)

The stock T3 headers and crossover are fitted, and the Feked mufflers seem close to the original T3 ones, though I never owned those. Before making my comparison runs I washed and re-oiled my old K&N filters,  re-synched the carbs, and set the idle speed to 1100 rpm.

I did the same test loop on both the old filters and the new filters with the velocity stacks. This involved some neighborhood and city riding plus some slightly sporty riding in nearby hills and curves.

I first rode the bike with the old filters to make a note of carburetor weaknesses. I did notice poor carburetion while going 15 mph through a school zone, and also when accelerating through the range of 1/8 to 1/4 throttle. Rolling on at higher throttle settings in the hills also seemed like it could be better.

Today I repeated the route with the new filters and velocity stacks. I had not changed any carb settings, and observed the idle speed was still 1100. The 15-mph poor running is gone, and the roll on between 1/8 and 1/4 is much stronger. In the hills I had the impression that I was getting better response too. I couldn't be sure of any change in power at higher speeds.

The throttle response was more similar to the other T3 I rode last fall. (I also have a deep sump, with a Roper plate, by the way.  )

So I found what I expected. This is always suspect, but the results in the lower throttle openings seem very obvious. The change was worth the $200 to me.

I will try to physically measure changes in power at different throttle openings, using a tool that requires another piece of equipment ($15). I'll report what I find.

Moto

P.S. I took another neighborhood/city loop after lunch today to see whether the differences disappeared when the outside temperatures were more equal. They did not.

[John A]

All I have to add is be careful of how far the air cleaner element goes on the stub, if the K&N is on too far it will restrict airflow, kind of a piss poor set up as the filters have to be pushed on quite a bit to clear each other, the single element likely works better than 2 singles.  DonG

This ^^^^ .  according to  ‘The scientific and design and tuning of intake and exhaust systems “ the distance between the opening of the carb and the closed end of the filter should be at least 2.5 times the diameter of the opening . I proved this to myself by putting thin foam over the ends of open stacks. It would run better at less than WOT than at wide open throttle

[mtiberio]

For a set of VHBs with velocity stacks (either the Loop style of Tonti style) benefit from UNI filters. I used to get a single 8" long sock filter (U08?) and cut open the closed end. With a tube of UNI filter material, you simply slip it over both v-stacks simultaneously. A zip tie or hose clamp can seal it.