News

308 carb airbox restriction discovered

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

  1. Spasso

    Spasso F1 World Champ
    Silver Subscribed

    Feb 16, 2003
    14,612
    Land of Slugs & Moss
    Full Name:
    Han Solo
    Thanks Dave,
    The plugs I pulled today are BP 6 ES. I cleaned and regapped them at .032" for the run up north tomorrow. I usually run them at .035" in my 240 when new but seeing as these are used and worn somewhat I thought I would tighten things up a bit. Just a little hedging and guessing on my part.

    I'll pull them tomorrow night and see what they look like.


    Another note; After my drive Thursday morning the 308 idled smoothly with no popping. A good sign.
     
  2. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Remember, to get a read of the plugs at say 6000 rpm, you have to run it hard at this level for 15 - 30 seconds and then cut ignition and fuel. Don't pull over and then turn it off. You'll read will be corrupted by the idle condition. Allen Bishop does quite a nice piece in his book on how to do it.
    Philip
     
  3. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
    5,379
    NWA
    Full Name:
    Paul
    Actually, you dont need to cut fuel, you couldnt do it with a carburator anyway. Just cut the ignition under power, clutch, neutral, roll to a stop and check the plugs. They used to do that on the back straight at Daytona, and Iam sure they still do. Sounded odd that a car wide open loud one second, would suddenly go silent the next and come rolling around headed for the pits.
     
  4. robertgarven

    robertgarven F1 Veteran
    Rossa Subscribed Owner

    Feb 24, 2002
    5,055
    Ventura, California
    Full Name:
    Robert Garven
    #129 robertgarven, Mar 5, 2005
    Last edited by a moderator: Sep 7, 2017
  5. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
    5,379
    NWA
    Full Name:
    Paul
    Yes, some are harder than others. I can get to mine (77 GTB) without to big of headache. I dont know what a GT/4 is like. Maybe that lunch basket is more like a pretty red with drawers?
     
  6. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    I think you have to drop the engine to get to the front plugs in a GT/4...just kidding.

    I've often heard that the stock gap is good with the stock coils, but should open up to 32 or so with MSD or better coils.

    Have had some time to think about Spasso's airbox application. Historically on this board and the FList, GT4 and carb GTB folks have often reported having their car run better after just upgrading to 140 main jets keeping everything else the same. Now considering that was with the stock air box, I now think that 140 is probably the minimum neccesary with the increased airflow in DJ's new set up. Would not be surprised if one size smaller a/c jet as well as what Kermit reports. Definitely better to be a little richer at the high end of the range.

    Philosophically IMHO, being a bit lean down low (< 3500 ) is not as critical as being around A/F 13 at 4K and above. The accel bump may cover any dumping the throttle, so will probably be ok with current idle jets.

    Philip, if you're on here, could you briefly comment again on changes in jetting and sound when you first went to P-6 cams?

    Another factor also is that with Spasso's mod, we will be using the entire air filter and not just passing all the dirt at one small area, so should increase filter life theoretically.

    Best to all, and thanks for all the great advice.
    rt
     
  7. maurice70

    maurice70 F1 Rookie

    Jan 25, 2004
    3,885
    Sydney
    Full Name:
    maurice T
    GT4 front bank plugs are not that difficult to change.I got a long spark plug socket wrench and I find it quite easy to do.All 8 plugs would take less than 1/2 hour to do
     
  8. Spasso

    Spasso F1 World Champ
    Silver Subscribed

    Feb 16, 2003
    14,612
    Land of Slugs & Moss
    Full Name:
    Han Solo
    After a 180 mile run today I pulled the plugs on the rear bank and the electrodes are very clean with a light brown discoloration at the end of the center insulator. This is with the 135 mains. It pulls pretty good up to about 7,000 RPM then seems to run out of breath (fuel).

    It pops at light throttle too so I am pretty sure I need to go to the 140 mains.

    I am hoping my friend Peter GT4 can help me with this. Peter, where are you?

    Anybody else have some 140's they can Fedex me before next Saturday?
     
  9. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    I might have some spare 190 A/C's if you want to enrichen the top end for that final pull over the 7000 rpm top. I do have some 145 mains, but that would probably be too much. Will check, PM address if interested.
    Sounds like great progress!
    Great work. We're rained in here in Texas, so no testing today.
    best
    rt
     
  10. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Paul, yes I mis-spoke. I meant turn the key off which, as you know, also kills fuel pump. Anyway, 'nuf said, appropriate correction.
    Philip
     
  11. Spasso

    Spasso F1 World Champ
    Silver Subscribed

    Feb 16, 2003
    14,612
    Land of Slugs & Moss
    Full Name:
    Han Solo
    Russ, You have mail.
     
  12. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Russ
    When I put in the P6s, I also increased venturi size and since changed carbs etc. That said:

    First step was increasing the mains and the idles - I think we went to 145 F36 185 60s with the 34mm/40 DCNFs. The challenge with the race cams is getting them to work below 4000 or 4500 rpm. As you know, I've tried upteem combinations and am now running 52 idles, 145 mains, F24 emulsions and 185 (I think) e-tubes with the 44 DCNFs. Also, 200 needles which I'll pull down to 175. The goal has been to get the idle and overrun lean for snappy throttle response and the WOT 4500 rpm+ A/F around 13. Top end is still a bit rich. Bottom end feels great.

    Sound is louder and deeper.

    Imagery is flames out the Tubi on the downshifts.
    Does this help?
    Philip
     
  13. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
    5,379
    NWA
    Full Name:
    Paul
    Philip~

    Do you know where you were at with the 40 mm carbs before moving up to the 44's? I will be running 10.4:1 compression with the P6 cams, curious of your setup. I was thinking of opening up to 36mm venturies. With the now gutted airbox, even 140's are sounding a bit lean, thoughts?
     
  14. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Yes, I think you'll need to go to 145 or higher with f36 emulsions. Lean is quick, but you want to start with a margin of error. With 36mm venturis in the 40s, I ran 145 or maybe even 150 mains, f36, 60 idle, 185 ACs. I think you should start with 145s. Have some 150s in the box and do a plug cut if you don't have a wide band AF. If you change the e-tube it all changes.

    I put in a wide band AF meter to help me understand what was going on. Not much help low down (there's so much reversion and unburnt gas you'll get a poor read), but very helpful above 3500 rpm or so. The carbs are a bit harder to sync with the P6s as there's so little vacuum. Nonetheless, be patient and you'll get it to idle at 850 pretty evenly and to pull from about 3000 rpm up. Below this you really need to ease into the throttle. Stomp on it at 2500 and it chugs and falls on its face. When it picks up at 3500 or so, it'll put a smile on your face.

    FYI, when we put on the 44s we had a hell of a time to make it run well. I've had idles up to 70, ACs of 165 and 155 mains...all trying to sort out an issue best dealt with by e-tubes. Norwood advised me to trade them for some 42s. Nonetheless, perserving (I have a large collection of jets!), we have got the car to run very well with the bigger carbs and I wouldn't go back.

    On venturi size, I've 36s and 34s in both 40 DCNF and 44 DCNFs. I believe the car is quicker in the mid range with 34s and quicker around most tracks. The 36s only seemed to come into their own at 6500 or more. That said, try them. You can get a set for the 40s from Pierce for $150 or so I think or I'll sell you mine. PM me if interested.

    Where did you time the cams and what clearances have you set?
    Hope some of this helps
    Philip
     
  15. hanknum

    hanknum Formula 3

    Nov 1, 2003
    2,043
    Santa Barbara
    Full Name:
    Henry
    I'm thinking the restriction here is the limited size (necking down from the insulation) and not from the small filter area that is intially seen by the incoming air. Once this filter area is clogged up with dirt the air will be "routed" around the rest of the filter. What does everyone else think?
     
  16. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Since we are talking of airboxes flowing better and jetting change to take advantage of getting more air to the carbs, our new readers need to know that changing main jets, emulsion tubes and air correction jets is easy easy easy, and takes about 30 minutes or so. Don't be put off by doing it, even I can do it!
    Here is an article (with pictures!!!) showing just how it's done !!

    http://ferrarichat.com/forum/showthread.php?t=42363&highlight=changing+weber+jetting

    As far as using the rest of the air filter to spread out the filtering as Henry is saying, I've already noticed some detritus making its way to the back of the air filter. Mission accomplished!

    Philip - The imagery of flames coming out the back of a tubi sounds exciting!
    I've actually had this happen myself, but it was from losing one side on the Marelli ignition and the dead bank was still getting gas pushed in from the K-jet and lighting off in the catalytic converter. This was exciting as well, but in a bad way! It happened 3 times actually, and that's why I have a single Unilite distributor today....
     
  17. Spasso

    Spasso F1 World Champ
    Silver Subscribed

    Feb 16, 2003
    14,612
    Land of Slugs & Moss
    Full Name:
    Han Solo
    Simply put, Yes.
     
  18. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    #143 snj5, Mar 6, 2005
    Last edited by a moderator: Sep 7, 2017
    So far in this thread, we have seen that there can be recaptured rwhp (10 - 12+) from removing the very flow restrictive sound deadening mesh and packing in late 308 GTB airboxes. This hp gain is added to further perhaps on the top end by using shorter velocity stacks.

    The sound deadening mesh with it's fiberglass packing is easy to remove, and several FChatters have already done so. Spasso, a well known Tech Section overachiever, even brilliantly built a beautiful air snout extension (documented early in a thread later hijacked: http://ferrarichat.com/forum/showthread.php?t=50136 ) to further promote cool airflow. His initial driving impressions did indicate a possible secondary lean situation with the stock jetting that he is addressing. He described 'running out of umph up high, which would be consistant as that is where the flow improvement would be most notable.

    With the removal of the sound deadening material, the Weber induction sound is much more pronounced, over the stock box, but not as loud or raw as the individual carb filters.

    Webers are well known sensitive to the amount of air above the air horns. Shorter velocity stacks act to increase this area allowing greater high end air flow, possibly at the subjective cost of a little lower end umph. Dynos were posted suggesting around a 5 - 6 rwhp improvement.

    With the increased airflow comes the possibility that the carburators will need to be richened, probably by going to 140 main jets at a minimum. The proceedure to do this is documented here:
    http://ferrarichat.com/forum/showth...g+weber+jetting
    I personally would add a richer (smaller, e.g. 190) air correction jet for the top end where the flow difference will be most pronounced.

    Among the several side discussions, the positive effects of cool air ram vs the popular individual carb filters has been discussed, as well as the possible plenum effect of the airbox and the fluid dynamics of aggregate vacuum producing a smoother flow across a filter element. And, Henry also identified that after the mod there would be more available filter element area available to pick up the dirt.

    Right now, we are imbroiled in the proper re-jetting of the carburretors to take advantage of the increased air flow, and waiting anxiously to see if Spasso will get his 140 mains installed before his dyno appointment next Saturday....

    Pictures of before and after below. Back to our story.
    Image Unavailable, Please Login
    Image Unavailable, Please Login
    Image Unavailable, Please Login
     
  19. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    A great photo essay of Spasso's clever airbox mods are in post #23 of this thread.
     
  20. Spasso

    Spasso F1 World Champ
    Silver Subscribed

    Feb 16, 2003
    14,612
    Land of Slugs & Moss
    Full Name:
    Han Solo
    Hey Russ,
    Any luck finding those 190 A/C jets?:p
     
  21. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Yes I did - if still interested PM.

    And for everybody else, here's my Weber jetting yard sale:
    Main jet sets: 145s, 150s
    Emulsion tubes: F36s
    A/Cs: 220, 210, 175(yowsa!!!! For that LM spec engine...)
    idles: 60s,55s,50s
    accell jets: 60s (!!!!!!)
    Step right up!
    :)

    Just took the bambino out on a run. The airbox mod makes a difference in sound and power, folks. Sure sounds better than every street Ferrari injected V-8, period - 360 tubi schmoobi I say, there's no substitute for those eight singing organ pipes playin' Italian High Mass at 6000 rpm....
     
  22. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Russ
    Good thread.
    My belief is the stock cams run at of "oomph" at 7,000 due to lobe profile/overlap design etc. That said, efforts that result in increased airflow will raise BHP.
    Philip
     
  23. Spasso

    Spasso F1 World Champ
    Silver Subscribed

    Feb 16, 2003
    14,612
    Land of Slugs & Moss
    Full Name:
    Han Solo
    Max power on my dyno pulls last year were about 6750 to 6800 RPM with an air/fuel ratio of 14.5:1 but it still ran right up to 8,000 without skipping a beat.

    When I said running out of breath at 7k I meant it started to fall off quickly and didn't feel as willing to rev much more.

    Russ,
    Ultimately it sounds like there may be the possibility I might need the 190 A/C's but I want to run the dyno with just the 140 mains so I can get an A/F plot on the entire run. That should give me enough info for the next move.

    The carb popping at anything but full temp gets really annoying after a while so I am thinking of moving up to .60 idle jets as well.

    Can you sit on those items until Saturday night?:p

    Much appreciated if you can,
    Thank You,
    DJ
     
  24. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    This is exactly what I meant. Two notable changes of the P6: more oomph across the range, particularly from 3500 andit pulls strongly all the way through red line and beyond.

    I have a reve limiter set to 8000 out of deference to 28 year old valves etc. If (when?) we rebuild the top end, I'll have the motor built to withstand 8500 to get the max out of the cams.

    I do not mean the response to be a "celebration" of P6 profiles (in this day and age, there are much better ones), merely that the cam profile has a big impact on the engine breathing.
    Philip
     
  25. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
    5,379
    NWA
    Full Name:
    Paul
    Has anyone dynoed an engine with P6 cams and decent compression to plot where it makes HP? Just curious what kind of animal I am building over here.
     

Share This Page