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Weber Velocity Stacks Filters or No?


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Is it bad to run these without any kind of filter on them? I see all the JDM youtube videos and almost every one of them dont have filters.  I drive mine maybe about an hour or so a week if that, and only when the weather is good. Its not a daily driver, but some of my local datsun club guys are freaked out I do this and think Im going to ruin my engine. If Im not tracking it where its going to get rubber bits sucked up, I dont see the harm.

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I ran mine for two years without filters, driving it two or three times a week. If you keep up on your maintenance, wiping them down frequently and plan for a rebuild at shorter intervals, you can run without filters. Don't drive on dirt roads or in the rain. After two years, there was starting to be visible build up in the throats. You just have to careful and think about where you drive.

Edited by ctc
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Given that 95%+ of your time with the car will be with the hood closed, wouldn't you rather avoid the risk of sucking in debris and damaging your engine?  I went with a large single ITG filter that covers all 3 carbs on my engine - if I am at a car meet and want to show off the stacks, it takes me 5 seconds to turn 4 clips and lift it off.  

Better safe than sorry IMO.  

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This car isnt a DD. I drive my Titan through all kinds of crap. Comparing the two isnt really a good comparison IMO... My Z see's a lot of driving when the weather is awesome, with no long trips.... maybe about 300-500 miles a year on it and only during the Arizona Fall/Winter months. I do like the idea of the quick removable air filters tho...

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You wouldn't run them because "they look very restrictive"? Not a great reason, is it?

I can relate the following from a compressor startup I did this past weekend in Vincomin Vietnam. It was my first startup where I was able to measure a drop on a 'witch's hat' startup strainer.... These particular strainers are made in China, and are sized to fit in place of our standard expansion bellows on the inlet piping of the machine.

 

I am familiar with witch's hat strainers, having used them for the past 25 years during commissioning. A standard witch's hat strainer usually is put in place of the "maintenance spool" a piece of pipe 4' long on the inlet to allow removal of casings, etc. That hat strainer will look like a dunce cap, almost 4' long--a long cone with lots of surface area.

 

The new strainer is 18" long.

 

It looks restrictive to me, compared to traditional witch's hat strainers.

 

In testing this weekend, at full flow, the shorty strainer had the water manometer almost sucked out into the inlet. And at minimum flow, closer to 10" of Inlet Restriction (the maximum allowable with plugged inlet filters!)

 

A standard witch's hat strainer with finer mesh is usually no more than 10" at maximum flow...

 

So chances are good, it it looks restrictive, chances are it is, and testing will quantify it. Those Pierce strainers are not "filters", they're rock strainers. They serve no purpose other than keeping a piece that will catastrophically fail the engine out... Simply scoring cylinder walls from dust and sand will still happen. They're a vintage-look throwback for the racing cars of old. They are no substitute for a proper filter which will be more effective, and less restrictive.

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That's really not enough for me to go on. I have those strainers on one of my Zs, and once it's sorted I plan to hit the dyno and see just how restrictive they are (all filters will have some restriction). I don't know if I can do a filter comparison since my horns stick out too far to get a K&N pod on there. The strainers are my best option as far as space, I'd have to buy shorter horns to run a filter.

 

Again, I'll have actual numbers when I go to the dyno.

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I also think they look very restrictive and wouldn't run them either. I've suggested before that someone could do a simpler test if you have a wideband; just see if taking them off makes a difference on the AFRs. I used an ITG filter on my triples, FWIW.

 

For your actual numbers, you will need to actually tune the carbs to see what the actual difference is. That's a lot of screwing around. The AFRs gives an immediate answer as to whether they restrict flow or not.

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I also think they look very restrictive and wouldn't run them either. I've suggested before that someone could do a simpler test if you have a wideband; just see if taking them off makes a difference on the AFRs. I used an ITG filter on my triples, FWIW.

 

For your actual numbers, you will need to actually tune the carbs to see what the actual difference is. That's a lot of screwing around. The AFRs gives an immediate answer as to whether they restrict flow or not.

You didn't get it. ANY filter restricts the intake. The point of testing is to find out how much of a restriction it presents. Tuning these carbs is very simple, if you know what you're doing. Changing 6 main jets, if need be, is not difficult.

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Yeah, I think that old argument about checking AFRs was based on an advertisement that claimed no restriction. FWIW, I didn't find them that easy to tune, and I messed with a lot more than main jets. 

 

I enjoy tuning triples and it's pretty straightforward now that I've amassed some knowledge over the years. If the AFR noticeably changes when removing the filters, the only tuning change needed would be main jets, at least to determine power loss at WOT.

Edited by Leon
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You didn't get it. ANY filter restricts the intake. The point of testing is to find out how much of a restriction it presents. Tuning these carbs is very simple, if you know what you're doing. Changing 6 main jets, if need be, is not difficult.

Just six main jets? And when do you change them?

 

I'd be interested to see restriction numbers, not AFR or jets changed... What do they restrict compared to a proper filter box? Restriction is pumping loss...

 

Those Strainers restrict only the VENTURI. Ambient pressure is still on the float bowl...

 

A filter will cover the float equalization hole, so as filters plug, the pressure present at float bowl is relatively similar to the Venturi, so the car does not start to run progressively richer as the filter / strainer plugs!

 

The phrase "if you know what you are doing" indeed applies.... This is a most basic carburetor principle of proper filtration, that float bowl is vented to the same ambient pressure as Venturi throat. The relative delta p across that strainer is different at idle and at 7,000 rpms WOT. I WARRANT it results in enrichment.... And depending on fouling factor, variable enrichment at that!

 

All filters cause restriction, yes.

 

But not all restriction is the same!

Edited by Tony D
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Just six main jets? And when do you change them?

 

I'd be interested to see restriction numbers, not AFR or jets changed... What do they restrict compared to a proper filter box? Restriction is pumping loss...

 

Those Strainers restrict only the VENTURI. Ambient pressure is still on the float bowl...

 

A filter will cover the float equalization hole, so as filters plug, the pressure present at float bowl is relatively similar to the Venturi, so the car does not start to run progressively richer as the filter / strainer plugs!

 

The phrase "if you know what you are doing" indeed applies.... This is a most basic carburetor principle of proper filtration, that float bowl is vented to the same ambient pressure as Venturi throat. The relative delta p across that strainer is different at idle and at 7,000 rpms WOT. I WARRANT it results in enrichment.... And depending on fouling factor, variable enrichment at that!

 

All filters cause restriction, yes.

 

But not all restriction is the same!

 

That's a good point, although I'd imagine it would be difficult to "foul" these strainers, especially considering your previous statement: "Those Pierce strainers are not "filters", they're rock strainers."

 

Now that I think about it, I can test the strainers/filters on my other Z given that it fits those horns. The horns are 1.5" shorter so that I can get a filter housing over them. I was already planning to dyno test after getting the car back on the road (should be soon) in order to quantify filter losses and effects from the air horns, so I can add testing those strainers at the same time.

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