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308 carb airbox restriction discovered

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

  1. thecarreaper

    thecarreaper F1 World Champ
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    #51 thecarreaper, Feb 23, 2005
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  2. Birdman

    Birdman F1 Veteran

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    I don't know about other years, but on the '77 you can disconnect the top of the stick that holds the boot up and raise the boot another couple of inches. That makes enough room to get the airbox out easily.

    Birdman
     
  3. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    Brief Summary so far

    1. Many carb airboxes have a meshed baffled silencer in the snout that may obstruct against the air filter, severely restricting flow path and available filtration area not allowing maximum flow. This has been approximated in the 10+ hp range and consistant on at least two dynos by different people.

    2. Several instances are shown removing the baffling and mesh in as little as 20 minutes with a Dremel, clearly opening up the airflow around the filter. Excellent photo documentation by DJ (Spasso)

    3. Although a confirmatory dyno is pending, a subjective evaluation showed remarkable improvement based on more ram flow of cool outside air to the carbs. De-muffled airbox sound sound is resonantly musically smoother in character than in-your-face competition engine sounding seperate filters ( :) ), and not much louder than the stock muffled airbox with comparatively nil induction sound.

    4. Discussion of merits of shorter velocity stacks and how they may possibly help improve flow further.

    5. 308 owners now have 3 choices: Stock box, opened and unmuffled stock box, individual Pierce Filters

    Coming soon: Dyno possibly in March by the Spassmeister
     
  4. snj5

    snj5 F1 World Champ

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    And in a Mondial it just lifts right out as there are tons of room... :)
     
  5. Spasso

    Spasso F1 World Champ
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    I am guessing that the perforated metal and sound deadening material may be less of an issue on the early (pre 1978) boxes, being less intrusive and restrictive than the later emissions boxes with the vacuum operated intake flap.

    I did have to remove material from the '76 GTB box that I modified but did not make comparison measurements between the two boxes concerning filter element clearance and intake snout restrictions. A moot point when gutting the assembly anyway...............

    The comparison photos show the element clearance in the gutted '76 box and the restriction of the unmolested '78 box. This should really make a difference.
     
  6. Spasso

    Spasso F1 World Champ
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    Another great tip! Thank you,
    DJ
     
  7. chrismorse

    chrismorse Formula 3

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    Thanks Birdman,

    Great idea. i have always sweated it trying to get the box off without bumping it hard enough to let one of those sleeves fall out of the rubber carb gasket into the intake. Makes me nervous, always check to see if any are missing when i get the box on the bench.

    Any hints for affixing them or where to get replacements.

    thanks,
    chris
     
  8. robertgarven

    robertgarven F1 Veteran
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    #58 robertgarven, Feb 23, 2005
    Last edited by a moderator: Sep 7, 2017
    Another reason for loving the gt4 :) On the gt4 airbox there is lots of room around the filter as it sits real close to the trumpets and seems to have a taller cover. I like kermits shorter stacks but that would take all the fun of getting all those nuts off the trumpets ;-)
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  9. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    Actually, Ferrarichat's own 'Legend of Rock N' Roll' Robert Garvin makes a great point. In installing and removing the mounting nuts you have to be WAY WAY more careful not to drop them down the carb. From my experience, one needs to buy a magnetic socket or something...
    OBTW, the GT4 cover is the same size as the GTB, only the snout is different. Another reason to love the GT/4 :) :)

    Will test side by side with the stock air horns this weekend,

    best
    Russ
    The US Air Force version of Dee Snyder...
     
  10. hanknum

    hanknum Formula 3

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    Yeah, I got rid of the nuts and pulled the studs and am using bolts. I also see that some in their pix replaced with allen head bolts. Looks like I'm going to Lowe's this weekend to find some of the allen head ones.

    One thing I don't like about the "snout" of the GT4 airbox is that it is angled back. This makes the path of air make a severe bend. One more reason to love my GTS/B :)

    Eagerly awaiting your report Russ.

    Henry
     
  11. Birdman

    Birdman F1 Veteran

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    Chris,
    Just put some tape over the tops of the carbs, or stuff a small rag into each one (gently) before you pull the airbox.

    What a great idea! No studs to get in the way at all!

    Birdman
     
  12. pma1010

    pma1010 F1 Rookie

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    Use a little (clear) silicon sealant. Holds them in place.
     
  13. ham308

    ham308 Formula Junior

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    Great thread and thanks for the summary Russ.

    Looking forward to the dyno results..

    Richard
     
  14. don_xvi

    don_xvi F1 Rookie

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    Two notes on recent topics in this thread:
    1) I'd suggest leaving the studs in place in the locations where they're easy to do, it'll minimize the risk of running those bolts into the Aluminum. I have a few (in the rear as I recall) that I've changed to bolts, but left studs where things are easy to do.

    2) I think it's funny that people are trying to SECURE the rubber gaskets to the airbox and removing the rear bonnet to do the install, I lift the airbox the little bit that it can be and then slide the gaskets in/out to remove/install! I'm likely to eventually tear up the gaskets, but I can do it in 10 minutes now.
     
  15. cavallo_nero

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    #65 cavallo_nero, Feb 24, 2005
    Last edited by a moderator: Sep 7, 2017
    i permanently anchored those 16 gasket 'collars' to the top of the carbs with blue permatex, they have not budged in 4 years. i yank the air box with the rubber gaskets still in place on the airbox......
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  16. GavC

    GavC Formula Junior

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    I removed the baffles in the airbox on my 308gt4 1977 euro spec over 8 yrs ago. It made it sound nicer was told to do this by some race techs I don't think that it adds 10 bhp maybe 1-3 but does increase the flow caused by the venturi effect. I am very interested in the shorter stack that are available(nothing available in UK like this)and look forward to the dyno results. Please post your jet/needle/air correction sizes as well if possible.
     
  17. Spasso

    Spasso F1 World Champ
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    A great thing to pickup on all of these tips and tricks for getting the airbox on and off without popping the hatch, especially if stuck out on the road. I will try them the next time I need to pull the box.

    This time around it was necessary to pull the hatch for easier access to all of the fuel and vent lines that I replaced above, between both tanks and along the forward firewall. Rejetting is also easier.

    It only takes me 20 minutes to pull the hatch as it is and the access to the engine is much easier.
     
  18. 1975gt4don

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    excellent thread guys! Nice work Robert G, SNJ5 and SPASSO. You guys rock.
     
  19. Matt Morgan, "Kermit"

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    #69 Matt Morgan, "Kermit", Feb 24, 2005
    Last edited by a moderator: Sep 7, 2017
    If it is any help, I fabricated this nut driver out of a sheet metal (Tek Screw) driver, usually used with a cordless drill. It is 5/16", which fits the nuts, and has a magnetic insert to keep the nuts from droping. I turned the OD down to more easily fit the stock horn tool relief on the top,and the LPHF screw holes.
    As I had a piece of knurled aluminum stock on hand, it made the perfect handle. With a dimple on top for the forefinger to guide it, it took seconds to remove the nuts (Dyno time is not cheap, so get it done).
    Do not try it on Stainless Steel however, as it won't pick it up.
    There is a dyno chart with the baseline and final run, transposed onto one on the website.
    HTH
    Kermit
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  20. Spasso

    Spasso F1 World Champ
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  21. senna21

    senna21 F1 Rookie

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    #71 senna21, Feb 24, 2005
    Last edited by a moderator: Sep 7, 2017
    I'm surprised no one has brought up this fix (or I may have overlooked it). Use both methods.

    Spasso and others are right in the fact that the stock air box brings in cool air from the outside with a slight Ram-Air effect while at speed. This will get you better hp than having the engine try to suck air that's already trying to escape from the bay through the louvers. Don't forget hot air rises. It's not going to want to go directly into those carbs. They'll have to suck all that hot turbulent air in.

    Sure with the open set up on the Dyno it'll make better HP but in real world application I'll bet it doesn't.

    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? The air will flow from the intake easily into the now open chamber housing the four air filters. If they're too high you can modify the top of the air cleaner to fit (make it higher).

    Here's a half A$$ed photo shop of what I'm talking about
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  22. Spasso

    Spasso F1 World Champ
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    I like it! Great idea, DAMN good idea!.

    Best of both worlds. Hey Carreaper, can you take some measurements?
     
  23. Birdman

    Birdman F1 Veteran

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    You know, it's funny, that very thought crossed my mind the other night, but I was thinking the individual filters wouldn't fit inside the stock box. Could be wrong. The box lid surely won't go all the way on, but then again, who cares? So it gets some air through the intake and some comes over the top. I would love to hear if this works.

    Birdman
     
  24. snj5

    snj5 F1 World Champ

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    I tried this once a year or so ago. As I remember, the Pierce filters would not clear the carb tops/mount towers and seat well. May be different for you guys. In this mutiple filter installation would lose any plenum and flow effects, but hard to quantify.
    In my installation with longer runners, there is a bonnet clearence problem.
    Good luck, hope it works for you!!
     
  25. Spasso

    Spasso F1 World Champ
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    .............not those particular filters but I think K&N makes a shorter version than those. I have a "thin" set of K&N's on the side draft Webers for my 240 but they are oval. They appear to be the right thickness for a 308 airbox, if not, pretty close. I'll measure them on Friday morning.

    I am thinking K&N may make a rectangular version of the "thin" element that I use. If so these could fit in the stock box under the stock lid and give maybe twice the element area than the stock one.

    SK also makes filter housings that accept K&N filters, rectangular ones.

    Time to do some more investigating......................
     

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