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Power loss in air filter

Discussion in 'Technical Q&A' started by snj5, Jun 12, 2004.

  1. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    I am now noticing a typically 10+ hp loss using a K&N filter with a stock 308 Ferrari airbox over open carb trumpets on back to back same day chassis dyno runs. Paper filters are a little more yet by my dyno comparisons. The loss has varied on different days with different jetting/advance/exhaust, with as much as 20 hp this week. Is this everyone else's experience?
    I know the advantages of cool air from the scoop, but am really considering a different filtering system. My hyper experienced racing dyno tech said it was time for the hole saw. I have seen some 308 racers with separate carb foam air cleaners.
    Has anyone used aftermarket or custom air cleaners with success over the stock box?
    Any advice cheerfully considered.
    thanks
    rt
     
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  3. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Russ

    If you have this, I don't want to be redundant, but here's some data:

    The LM GT4 box was bigger and (I believe) taller than the stock. It measured 400 x 450 mm in top elevation. Single scoop (RHS). Velocity stacks were stock. No air filter.

    The Michelotto 308 that Rick Mancuso raced has two airfeeds, one each side from the two scoops into (what I assume) are open trumpets. (The oil cooler was mounted in the "mouth" [nose] of the car). The "box" was deeper than stock.

    Do I remember right that each 12 degrees rise in intake temp is worth 1 BHP?

    All the above is 308, not 328 sized as you know.
    Philip
    P.S., do you get the same impact when you lean it out a bit with the jetting?
     
  4. ham308

    ham308 Formula Junior

    Nov 3, 2003
    358
    NE Switzerland
    Full Name:
    Richard Ham
    In addition to getting cooler air, is there any ram-air effect from the air scoops? Or is it just very nice styling? :)
     
  5. 208 GT4

    208 GT4 Formula 3

    Dec 27, 2003
    1,699
    Brighton (UK)
    Full Name:
    Dan
    There is some good info on air filters on a thread here:

    http://www.pistonheads.co.uk/gassing/topic.asp?f=48&h=0&t=94546

    Follow the links in the Pistonheads thread. The K&N filter doesn't come out very well in the first one, but does better in the 2nd.

    I know these threads relate to other marques, but I believe if there were easy gains to be made through filtration, then Ferrari would have optimised the filtration/flow balance...Porsche certainly do...or so it would seem?
     
  6. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
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    Russ Turner
    Philip, Richard and 208 - many thanks.

    I think one reason for the power loss is the airbox height. While the K&N showed a loss of say 10 hp over open trumpets, I did a dyno run with a closed airbox and NO airfilter and lost 5 hp. The difficulty is the runners sit higher than stock, and the top of the airbox cannot be raised anymore. One idea was to run with NO airbox lid and let the bonnet act as the top of the airbox giving the maximum area possible and use seperate domed racing foam air cleaners for each carb mounted inside the topless airbox.

    I have driven aound with open trumpets and NO airbox, and doggone it did feel peppier. I know Superformance and Pierce Manifolds sell trumpets with screens. Man, that would look cool - perhaps this cold air thing is over rated. Perhaps not. In a mis-spent youth I had an Alfa 1750 with twin 40DCOEs with wire air screen trumpets that I would cover with KMart baby socks that worked pretty well - and holy #$%@ what a sound. Perhaps an answer would be to run the screened trumpets in a topless airbox sealing against the bonnet like a 250 SWB comp.

    will definitely look over the specs on the 308GT4 LeMans Airbox from the racing car. If it looks close, will try to make and fit a posterboard buck to test-fit.

    May just have to bite the bullet on this one for engine protection, however.
    best
    rt
     
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  8. Peter

    Peter F1 Veteran
    Rossa Subscribed Owner

    Dec 21, 2000
    6,387
    B.C., Canada
    #6 Peter, Jun 13, 2004
    Last edited by a moderator: Sep 7, 2017
    Russ, here's what the air-box looks like on the GT4 LM car:

    (By-the-way, please run a filter. After doing all of that work, why throw it away by allowing some piece of dust from the road/track getting in and scratching the s--- out of the bore...)
    Image Unavailable, Please Login
     
  9. ham308

    ham308 Formula Junior

    Nov 3, 2003
    358
    NE Switzerland
    Full Name:
    Richard Ham
    Russ, I agree with you. I've got the airbox off mine at the moment to fiddle with the tick-over, and the SOUND under full power, phew, it would almost make it worth wearing the engine out for. Well not really but it is awsome.

    More seriously, if you just let the carbs out into the space above the deck-lid, behind the cabin, isn't that a kind of low pressure area when you're going along? The opposite of what you want.

    And those sexy standard air inlets on the side of the car, they probably provide a positive ram-air effect. After all Ferrari used them for their subsequent designs; cheese-grater TR's and so on.

    Is there any scientific evidence that they work?
     
  10. parkerfe

    parkerfe F1 World Champ

    Sep 4, 2001
    12,887
    Cumming, Georgia
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    Franklin E. Parker
    I assume that these differences are AFTER you have adjusted the carbs for both "with the filter" and "without the filter". Otherwise, the car will either be running too rich with the filter or too lean without the filter depending on when you adjusted the carbs.
     
  11. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
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    Russ Turner
    Yes - good point, applicable primarily to carbs. All runs were actually made for A/F ratios and carb tweaking so the A/F were monitored. It's definitely a flow issue.

    Peter - many, many thanks - looks like the LM went for not only height, but volume. Kind of leans toward what I think is going on - will look at this some more. Agree in day to day use a filter would be smart.

    Ham - good question, not sure how much of a ram air overpressure is created.

    208 - perhaps my challenge is I am using an airbox originally designed for a 255 hp 2v to filter air for a 288 hp 4v engine....

    Many thanks. As Pooh would say, "this will require some thought".
    best
    rt
     
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  13. mk e

    mk e F1 World Champ

    Oct 31, 2003
    11,505
    The twilight zone
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    The Butcher
    Russ,
    10 hp sounds about right to me. If you see it change from 10 to 20 any any given day, I would guess that 10 hp is the mixture changing...if you are a touch leaner than perfect withou the filter, then you may be a touch richer than perfect with the filter and you see 10 hp, if it is already a touch rich without the filter, it will be even richer with it and you see 20 hp. You might get it down to 5 if you double the size of the filter....I find it's best never to make dyno runs without a filter so I'm not tempted to drive the car without it :)
     
  14. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Mark, et. al.,
    Many, many thanks. After plowing through the dyno graphs and other filter options, I think 10 hp or so is just going to be the "cost of doing business". I am vertically challenged spacewise and really do not want to modify my bonnet. I would like to keep the stock cold air ram (minimal as it may be). Interesting to note that, using Philip's numbers, even if my temperature delta was 48 (e.g. 70 ambient, 118 underhood) degrees, that would only be a 4 hp penalty assuming minimal resistance individual carb air filters. From a cost effectiveness standpoint, making another airbox wouldn't buy me that much on a street use car.

    As you and parkerfe well make the point, I do jet the carbs on the use of my car, which is on the street with a filter. However, as the graphs in previous threads have shown, the hp output does not change much at all for this engine under a fairly wide AF range of low 12s to low 14s (I've never gone above 14.5). My current jetting (40DCNF-12/36/140/190/55/F24*) on the chassis dyno will keep me pretty much between 14 - 13 under full load in 4th gear with a K&N air filter from 3000 tip-in to 8000 rpm (I have seen 3.2 Kjet dynos that hold the A/F at 14.5 or so the entire range under load, which is pretty impressive). On a recent trip between DC and Newport News, she got about 17 mpg cruising at 70 mph (+/- 10!) which I think is probably ok. She may be a bit rich at cruise as the family behind said it 'smelled' (and was loud, but not as loud as with the tubi). This mpg is almost what she got with the Kjet (closer to 20). Probably closer would be a 145/50 combo to correct for a possible cruise richness, but will need to buy one of those cool A/F doofers Pelican sells when I get resettled.

    So after it's all said and done, I'm pretty happy with the 20+ or so rwhp, reliability and DIY service improvement with the current set up. I've yet really to experiment with the advance as I am in the middle of a move, but will next do runs to max advance of 32 (stock), 34 and 36 degrees once I find a dyno in San Antonio; am still waiting on the cams after some tumultuous grinding events; Will look at rejetting when they go in whenever that works out (if ever).

    I will also pass on that, thank God above, the nuts that hold the airhorns on are magnetic - ask me how I know.

    best to all
    Russ

    * after many $$ dyno runs; donations accepted for passing these settings on. :)
     
  15. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    I inserted a hose in my air cleaner and taped it to the side of the car attached to a pressure gauge. This is a GT4, so you GTB/S guys may have different results. At 100mph, the needle was just barely off the peg. So there is *some* positive pressure, but not enough to generate extra HP. (1/10 PSI. Yippee!!) Got lots of stares at this redneck mod to my car.

    On a positive note: Many air scoops - especially on vintage cars - are located in areas where there is a slight vacuum. Much of the surface of a car is sort of wing shaped, thus giving the potential to 'suck rather than blow'. (OK, that was bad......) A notable exception is at the base of the windshield. So the mere fact that our scoops are located in a positive pressure area is of some benefit.
     
  16. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
    Full Name:
    chris morse
     

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