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308 carb airbox restriction discovered

Discussion in 'Technical Q&A' started by snj5, Feb 20, 2005.

  1. Spasso

    Spasso F1 World Champ
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    The stock 308 element measures 2 1/8" thick while the elements on my 240 measure 1 3/4" thick. I'll try to do some more digging in the K&N book or site today.
     
  2. Sean F.

    Sean F. F1 Rookie

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    Because you're still restricted as to how much air can be pulled into each carb by the air box. The hole is only so big while the surface area of the individual filters is much larger.

    Cutting your filter into four straight pieces, then attach one piece it to the opening you just cleared the baffels out of would have the same effect. The air has to go thru the filter regarless of where it is realative to the air horns.
     
  3. Spasso

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    Gutting the box is great but won't be used to it's full potential if the stock filter element restricts total flow potential.

    I haven't done a layout comparison (one large versus four small filters) but just looking at the setup it would seem that 4 individual filters afford MORE element area for the air to go through further reducing any possible restriction by the limitations of the stock filter area overall..
     
  4. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    Someone may know this better than me, but since we are getting all technical: someone told me last year that while there was more filtersurface area on the small filters, the pulsing of the vacuum had an effect. That is, the summation of all of the carb vacuum would yield a more smooth and steady vacuum and thus flow more across a smaller filter than the more pulsatile character of the larger individual carb filters. Something to do with the dynamics of airflow across a filter...
    It intuitively makes sense somehow, but anyone else heard this?
     
  5. senna21

    senna21 F1 Rookie

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    If you need to redesign the top to fit the air cleander housing give me the mesurements and I'll see what I can CAD up for you guys.

    Length, width, hight, positioning of he holes for securing it down ect...
     
  6. Spasso

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    Thanks for the offer

    One VERY important note. The 2 1/8" thickness is around the outer 2" of the airbox lid. Don't forget that the center section of the lid is raised that would allow a taller filter. I can't measure the difference right now.

    To fit a taller filter that 2" wide lip would have to be raised also. Get my drift?

    A taller filter, multiple or single may be for naught in light of Russ's postulation. I tend to agree that the constant flow through the filter would be more efficient than pulsating flow. I am not an expert in flow dynamics but it's logical to assume that any time you disturb the rate of flow, fluid or air, you disturb efficiency.

    Oh screw it, I'm buying a blower!
     
  7. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    Shouldn't this be in off-topic?

    Seriously, I think that for street work, the stock airbox may be pretty good now that it has been cleaned out. I would NOT have said that 2 weeks ago with the muffling. Certainly the sound is superior to my biased judgement compared to all I have heard before.
    One possible 'Ferrari' upgrade perhaps would be to a LeMans type box with dual air inlets - note that they seem to go for a plenum effect as well (Photo attached). For example, it would be interesting for DJ to weld snouts on both sides of one airbox, both sides vented to the scoop.
    Depending on weather, will drive the short and stock air horns back to back to see if any subjective difference.
    more this weekend
    rt
     
  8. Spasso

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    I know what your trying to do Russ and it's not going to work:p

    Sure would make a neat sound though.......................................................

    Besides, in order to run a snorkle out the left side I would have to move my coils and ignition boxes.
     
  9. hanknum

    hanknum Formula 3

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    I don't quite follow this. Are you recommending just putting a filter across the "snout" portion of the airbox? If you are, I think this would be the most restrictive oprtion.
     
  10. hanknum

    hanknum Formula 3

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    This is a great thread...I knew I should have paid more attention in my fluids class in college:)
     
  11. Spasso

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    I don't quite follow the reasoning either except that in answer to this question,

    ("So, we know that the four K&N filter set up pulls better air flow when the car is static. Why not just place these air filters inside the airbox and tighten it down? ....etc..........."),

    ...............Sean said it would be the same as placing a straight strip of element over the end of the "snout".

    In my mind running a gutted box with 4 separate filters in it would flow way more than placing a strip of element over the "snout" entrance. A lot more air can move through an unobstructed hole, even a small one, as opposed to one that has baffling or media.

    I still don't understand the analogy. Sean?
     
  12. robertgarven

    robertgarven F1 Veteran
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    #87 robertgarven, Feb 25, 2005
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  13. Artvonne

    Artvonne F1 Veteran

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    I remember years ago I seen a Fiat X19 with a snorkle that came up off the rear deck into a air scoop over the roof. Looked kinda wierd.
     
  14. Birdman

    Birdman F1 Veteran

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    No Way, that screen material is FAR too restrictive! You'll probably lose .00056 HP through that! ;)
     
  15. snj5

    snj5 F1 World Champ

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    #90 snj5, Feb 26, 2005
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    Been there, done that: not expensive, WAY loud, but a bit much for the street. But it's pretty dang cool - nothing looks better. :)
    How many concours points would those cost?
    :)
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  16. Spasso

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    I just fiinished the installation of my modified airbox and Kermit's Low Profile High Flow V-stacks.

    Some modification of two of the stacks was required because the base of the new stacks are larger than the OEM pieces and with the offset of the carburetors on top of the engine there was interference with the stock filter element. You can see the pictures here,
    V-Stack Installation

    I am still putting the car together and cleaning it up so I won't be able to take it out for a test drive for a day or two. I will post my impressions when I do.
     
  17. tbakowsky

    tbakowsky F1 World Champ
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    One thing I have always wondered..Why not make 2 individual airboxes for each bank of carbs..sorta like the LAmbo Jalpa set-up. That way you would be more directing air flow for 2 carbs instead of 4. Plumbing it would not be a problem, a 2 into one set up for the intake side would work very well. Any thoughts?
     
  18. snj5

    snj5 F1 World Champ

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    #93 snj5, Feb 27, 2005
    Last edited by a moderator: Sep 7, 2017
    Took the car on a brief back-to-back subjective comparison drive this afternoon. Short story is that the muffling removal makes the big difference, and the stack length adds character. Can somewhat feel the effect of the short stacks in the upper rpm range, i.e. >5500 rpm. While there may be an expectation bias, the low rpm response may be a bit better with the stock air horns. Will do a dyno a bit later.
    Sound is about the same - much more induction 'woom' and volume than the stock box but not the rawness of the individual filters.

    For those interested in the previous postings, enclosed is a photo of the Pierce filters seated in the stock airbox with the stock airhorns - they will not fit with the LPHV stacks due to interference with the mounting towers.

    And as an added bonus, here's a photo of my new low budget high flow mod - $5 of Home Depo screening for those of you who want to go 'A;fresco' for that 50's - 60's racer look. :)
    best
    rt
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  19. Birdman

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    Russ,
    I love the Home Depot air filter! Just enough filtration to keep out boulders and pocket change...but the FLOW!

    Birdman
     
  20. Matt Morgan, "Kermit"

    Matt Morgan, "Kermit" Formula Junior

    Nov 12, 2003
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    That is an interesting idea, putting 4 elements inside the stock shaped housing. I wonder what that would do for the power/torque curve? IMO it would act more like separate rather than any plenum effect, and would tend to show torque higher in RPM. I'm sure top end flow would be capable of more, as total element area would be increased, but at what point does the stock side scoop become a constriction?

    As the testing on the original went, I wasnt able to do it as detailed as I would have liked to do with time constraints. my baseline down, it showed leaner, yet more power. And while I was waiting for Air Correction Jets to arrive (thanks Russ), I gutted to air filter housing. As I had estimate it would take an ACJ change to get the mixture right, the added flow from gutting the unit took tha extra fuel and it wanted more, yet once again, it showed HP gains even though it was still lean. So I decided to go a full main jet change, and ran the final #'s the new mains in place. In hindsight (20/20) I would have liked to have done a run with just the insulation gutted just to see the differance in the flow. My "gut feeling" on this is if more element area were to be added another snorkle would become necesary.
     
  21. Spasso

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    I think it's time to find a good excuse to add another snorkle............................like a supercharger!
     
  22. snj5

    snj5 F1 World Champ

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    #97 snj5, Feb 28, 2005
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  23. Spasso

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    Good grief!
     
  24. Matt Morgan, "Kermit"

    Matt Morgan, "Kermit" Formula Junior

    Nov 12, 2003
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    I'd like to clarify my earlier post in the snorkle portion. I should have put down side scoop, as that, and the fiberglass duct to the bellows. (easily replaced with SMOOTH inner tube, (which probably isn't stocked @ Home Depot, LOL) The enlarged unit Dana built could easily be a bit more than the "upstream" rest of the flowis presently capable of. A double snorkle is a nice idea, but why not use a large single one, and keep the oil cooler (and the cost of moving it), in place? Take for example, the inne fender well. in reality, there should be a minumum amount of heat there than the scoop above it? Done right, with snap on mounting for ease of access to the front of the motor, it could be easily as wide as the original housing, and provide more flow that the motor could ever breathe. I believe someone had posted earlier on the side scoops efectiveness, and means of measuring the flow. Kinda gets the noggin workin'
    On a side note pertaining to the side scoop working, does the oil stay cool? HHHMMMMM
     
  25. snj5

    snj5 F1 World Champ

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    So far in this thread, we have seen that there can be recaptured rwhp (10+) from removing the flow restrictive sound deadening mesh and packing in late 308 GTB airboxes. This hp gain is added to further on the top end by using shorter velocity stacks.

    If we compare the earliest 308 airboxes, we'll see the GT/4 airbox has a very wide delivery area to the filter element, as do the first GTBs. I agree that for the street, a single wide area delivery airbox snout is probably good for up to 300 hp or so while the 308 LM boxes had dual delivery systems.

    Also notice that the approximate size of the air filter and 'resonant volume' around the intakes remains fairly constant throughout the 308 carb production, and that all of the injected models have a plenum approximately this size as well. I do not think this is an accident. The total runner length is also about the same between the carb and injected cars. A resonant plenum area is determined by runner length and other variables specific to each engine, and I think this is part of what is going on here. There is a very high end discussion of this on the other board and I've also been thinkin'.

    I now think that optimizing air delivery to the stock filtered 'plenum volume' as DJ has done is the best road to take for a broad powerband. The lower velocity stacks definitely increase high end flow as well, and give a larger volume of air over the intake which Webers have been shown to like in multiple applications.
    I'm wondering how modification of this volume affects peak hp and power band, but agree that max delivery of air to the stock filtered volume is probably optimal for a wide power band in the 3 liter V-8 while individual filters or open air horns is best for high end operation.

    Oh yeah, and the de-muffled open air boxes sound absolutely terrific! Classic Ferrari induction sound!
    best to all
    rt
     

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