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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Fri Jun 03, 2016 11:45 pm Post subject: Velocity stacks and filter heights |
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So, currently my IDF's have 2.25" velocity stacks with 3.25" airfilters. Leaving only 1" between them and the lid. I know the underside of the lid is getting "washed" by fuel, because last year when I first got the car back on the road I had plasti-dipped the chrome bases and lids black cause they looked better. I had also coated the insides of them to cover all the chrome edges better. After driving some, when I removed the lids for some reason, the undersides were clean.
Today I went to local VW part shop to ask what was tallest filter I could fit under my deck lid w/o standoffs, nobody had an answer. I was pretty sure that 6" filters would be a no go. So, tonight I made a 1.75" cardboard spacer to see if that and my 3.5" filters would fit, the cardboard was a bit more than the 1.75" and it seems that a measured filter height of 5.25" will just fit on 1/2 side and the same will easily clear on 3/4 side to deck lid(and even clear my engine harness connection above carb on that side).
What kind (if any) benefits can I expect with the added room above the stacks? I know the air will have a better entry into the stack opening, and this will translate to what? Better cylinder filling, better throttle response?? Just looking for a better understanding of what makes a carb tick and how to optimize what I have.
One of the resources that the parts shop called and asked what a good minimum distance between top of stack and lid said that 2" was his min distance and 6" was even better(I think the latter was partially in jest). And based on what buggies and baja's can get away with.
Last edited by ps2375 on Mon Jun 06, 2016 9:58 pm; edited 2 times in total |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7214 Location: Videbaek Denmark
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Posted: Sat Jun 04, 2016 1:04 am Post subject: Re: Velocity stacks and filter heights |
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In a perfect world we like to have the venturi diameter as space between the stack and the filter top. In real life that is rarely happening, because when comes down to it the intake length has more influence on the power than the perfect free space over the stack. The reason is that most stacks are, at least to some extend, shaped for good air pick up around the outer perifer. That extra mouth width can make up for a good deal of free height.. Of course the more power the engine makes and thereby the more air it needs, the more important the free space gets. also, the higher rpm the more important the free space gets.
If you have say a 2275 with 44 IDF´s that has 36 mm venturies, 58 mm stacks and 27 mm free space over the stacks, it will still pull 170 - 175 hp with out problems. But you might notice that it may have a little more power over the curve if you remove the filter top.
If that same engine is on the edge, meaning 38 mm venturies, hot cam´n compression etc etc, you will definitely get an advantage by having the venturi diameter as free space over the stacks.
The 6" filters that you see around is not necessary as such. The advantage is that on baja´s etc you slow down the incoming air through the filter so that the filter has a higher chance of parting sand and air. also, some baja´s runs with some very long stacks to try improve torque. Then they of course need high filters too. If we look at it from a flow perspective, one 6" filter will flow enough for at least 210 hp and there is usually 2 filters on a dual carbed engine
Hope this makes sense to you.
T |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7214 Location: Videbaek Denmark
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Posted: Sat Jun 04, 2016 1:21 am Post subject: Re: Velocity stacks and filter heights |
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Woops! |
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Sat Jun 04, 2016 7:47 am Post subject: Re: Velocity stacks and filter heights |
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Mine is only a 2087, but does have 36 vents and I would love for it to make 170-175hp, but I'm guessing it is far below that. So, from what you have said, I most likely won't see any gains from adding free space over the stacks, but I think I will proceed with my plan as it won't hurt anything. |
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mark tucker Samba Member
Joined: April 08, 2009 Posts: 23937 Location: SHALIMAR ,FLORIDA
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Posted: Sat Jun 04, 2016 10:20 am Post subject: Re: Velocity stacks and filter heights |
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top shape can give good results too not just adding more space but using some direction of the incoming charge. |
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modok Samba Member
Joined: October 30, 2009 Posts: 26785 Location: Colorado Springs
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Posted: Sat Jun 04, 2016 1:08 pm Post subject: Re: Velocity stacks and filter heights |
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As far as airflow is concerned 1" is probably ok
As far as the carburetor signal is concerned, 1.5 min
For containing reversion fog, 2" is needed
So why do they make tall stacks at all?
The fog hits the lid and goes out the sides of the filter, getting it wet and wasting fuel too. This will give you some strange AFR results.
Gauze filters will stand this but if you want to have air filters that clean the dust out of the air They won't stand it, then you will need 2"+ clearance. |
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vince1 Samba Member
Joined: December 14, 2003 Posts: 823 Location: Burgundy, France
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Sat Jun 04, 2016 3:06 pm Post subject: Re: Velocity stacks and filter heights |
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Looks like there is nothing to lose and can only gain, if there will be changes. |
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theDrew Samba Member
Joined: May 17, 2011 Posts: 1155 Location: Camas, WA
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Mon Jun 06, 2016 4:22 pm Post subject: Re: Velocity stacks and filter heights |
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theDrew wrote: |
do the HA-0800 fit under the deck lid on a type 1? |
On my car with the manifolds I have, yes, they will fit as those are 4.65" tall and it looks like I can get a 5-5.25" filter to fit under my deck lid. At the 5.25" height, it will be VERY close on the pass side with plenty of room on the drivers side.
For $30 total and some minor fab work, I'll have 5.25" of filter, so, some additional room above the stacks will be had by adding the 1.75" filters to mine. |
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Sat Jun 18, 2016 4:27 pm Post subject: Re: Velocity stacks and filter heights |
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Here's where I'm starting from, about 1-1.25" from top of stack to the lid.
Here's how it'll happen.
I took some extra tops and bottoms I had, tacked them together and had a friend weld the seam.
Then I cut and ground on them till they looked like this:
So that my new 1.75" filters fit like so:
To allow my existing filter to sit as such:
After powder coating and install, I should have close to 3" from top of stack to the lid. |
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mark tucker Samba Member
Joined: April 08, 2009 Posts: 23937 Location: SHALIMAR ,FLORIDA
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Posted: Sun Jun 19, 2016 7:53 am Post subject: Re: Velocity stacks and filter heights |
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I wood add some small tangs so the filter's cant warp inward any in the center portions(slide in the housings inward) I do like your idea. I wood add a inverted conewith flair where it meets/connects to the tops.(welded to be one peice) to help the incoming charge be directed for better flow.... of corse if you had a flow bench you could test all kinda shapes to find what works best than....have them injection molded or cast & sell the crap out of them!!! |
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Sun Jun 19, 2016 9:59 am Post subject: Re: Velocity stacks and filter heights |
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mark tucker wrote: |
I wood add some small tangs so the filter's cant warp inward any in the center portions(slide in the housings inward) I do like your idea. I wood add a inverted conewith flair where it meets/connects to the tops.(welded to be one peice) to help the incoming charge be directed for better flow.... of corse if you had a flow bench you could test all kinda shapes to find what works best than....have them injection molded or cast & sell the crap out of them!!! |
AS for the tangs to keep the filters from moving/sliding inward, one side of the lip has a small rib that I suppose will help prevent that, but the new short filters won't do that cause they are new and flexible and naturally want to stay round and the older ones are molded to to be oval and won't do to any other shape.
I wish I had access to a flow bench( and a motor/chassis dyno also), I would have used it many times! The cone thing seems like a decent idea, tests on either previously mentioned devices would be many and interesting. The flow assist device will be something to think about and consider, I could screw it to the lid to make it removable and maybe do some butt dyno testing and if I ever get a new sensor for my WB, some checks with that. |
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Frankysfree Samba Member
Joined: April 16, 2012 Posts: 179 Location: Fort Worth, Texas
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Posted: Sun Jun 19, 2016 10:44 am Post subject: Re: Velocity stacks and filter heights |
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Is there a big disadvantage to only running filters without velocity stacks? When i got mine it had 40 IDF's with no stacks, only filters. I understand the reason to run the stacks just wondering if it will lose a significant amount of power or tq by not running them or will it be slight. Are there any dyno sheets to show the power difference? _________________ 1967 Bug
1969 Bug thats getting a Hayabusa engine
2008 Harley Nightster
"You can't know where your going until you know where you've been" |
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Sun Jun 19, 2016 11:30 am Post subject: Re: Velocity stacks and filter heights |
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I haven't seen any dyno comparisons, but the stack or any stack will aid the directional control of the air going into the carb, reducing the turbulence in the carb throat and improving the "vacuum signal" at the venturies and make tuning more consistent. At least that is what I have found in the reading I have been able to find in various forums and articles. But, it is all on the internet, so who knows. There is mention of some tests on kads w/ and w/o stacks in various threads, and w/ stacks was better. |
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tattooed_pariah Samba Member
Joined: April 24, 2006 Posts: 2047 Location: El Cajon, CA
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Posted: Sun Jun 19, 2016 11:44 am Post subject: Re: Velocity stacks and filter heights |
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ps2375 wrote: |
Here's where I'm starting from, about 1-1.25" from top of stack to the lid.
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Sooo, I've been trying to follow along and understand, but I get sidetracked easily..
This is what mine look like right now. Would having this little amount of clearance be the reason I'm having such a bitch of a time jetting my carbs? I get really close, but never quite "right"
Right now, it runs strong, but cruising anywhere from 3000-3500 rpms it pops occssionally, is this due to lack of air because of the height restriction?
IIRC I'm running 1.15 Main's, which is what I've always ran, should I ditch the velocity stacks or bump up my mains? _________________ -pariah (just a novice from "that other VW site")
'72 Volksrod "Effigy"
"Never worry about stepping on people's toes. People who get their toes stepped on are either sitting down, or standing still on the job."
-Admiral Arleigh Burke, USN(ret.) |
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dsrtfox Samba Member
Joined: August 25, 2009 Posts: 443 Location: Phoenix
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Posted: Sun Jun 19, 2016 12:33 pm Post subject: Re: Velocity stacks and filter heights |
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Maybe you could shorten the stacks ? |
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Sun Jun 19, 2016 12:44 pm Post subject: Re: Velocity stacks and filter heights |
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With my current config, the motor runs well and I don't notice any problems, I just know that the stand-off fog washed the plasti-dip off the undersides of the lids. From what I gather, the extra room won't fix a tuning issue, but might help with consistency of jetting and could effect the tune a little. |
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cliveawn Samba Member
Joined: December 07, 2010 Posts: 481 Location: Southern Sweden
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Posted: Sun Jun 19, 2016 12:50 pm Post subject: Re: Velocity stacks and filter heights |
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Interesting thread,do running stacks reduce induction roar?
My motor roars a bit and it does get annoying on long trips. _________________ ---------------------------------------------------------
Green 78 Westfalia Helsinki,
2056 with 41 x 34 valves,ported heads
Fully balanced
8,5:1CR
JPM Custom made cam
JPM 7075 dual taper pushrods
IDF 40's with 28mm venturi's
Python CSP 42mm exhaust.
115 HP
Daily driver 2017 Volvo V60 D5 hybrid
Rica stage 2 tune 345hp.
''Funny thing about common sense is that its not very common''
Seismic gun mechanic |
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ps2375 Samba Member
Joined: April 24, 2014 Posts: 2471 Location: Meridian,ID
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Posted: Sun Jun 19, 2016 3:57 pm Post subject: Re: Velocity stacks and filter heights |
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cliveawn wrote: |
Interesting thread,do running stacks reduce induction roar?
My motor roars a bit and it does get annoying on long trips. |
No. BTW, that is music, not noise. |
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