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308 carb rejet

Discussion in 'Technical Q&A' started by chrismorse, Mar 14, 2004.

  1. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
    Full Name:
    chris morse
    A week age I purchased a 77 GTB with 22k on the clock. My first F car. Second owner had it for 19 years.
    I have a K&N on order and am planning to drop the smog equipment, including the thermal reactor/muffler, (will store it in the unlikely event that I have to resmog it in the next two years).
    I have done a moderate amount of research on exhaust options and am considering the series 80 flowmaster replacement, (as did millermon and a few others). I know this is near heresy, (not using a tubi, ansa, borla or stebro), but the cost is a big factor as I have to finish paying for the car and bringing many systems a little more up to date, (wheels tires, brakes, suspension bushings, headlights, and -gasp- a non stock right side rear view muirror).
    I would very much like to hear from anyone who has done a similar evolution, particularly jetting suggestions for sea level.
    (stock: M 135, F36 tubes, 220 ac and 55 idle).
    Maybe go to M140-145, 200 ac, and 60 idle?????
    Will a change from 32 to 34 venturis be worth doing ?
    I am looking forward to the developement, if I can just find a place to do so.
    On a related note, where is the best place to acquire jets, venturis, valve adjusting tools and an assortment of shims???
    I plan to drive the car frequently and quickly through the mountains and occasionally track the car.
    While removing the plugged up stock air filter, I noticed what looked like sound insulation inside the entry to the air cleaner. IMHO muffeling the sound of the webbers is a fairly egregious sin. Has anyone removed this stuff with good effect??
    While waiting for the K&N to arrive, I took my 19 year old son out for a 7700 rpm test drive without the air cleaner and we both just about wet our pants. and NO I am not going to let him drive it
    Big Grins,
    chris.
     
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  3. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    17,315
    USA
    Regardless of the changes, I hope your comment of "looking forward to the development, if I can find a place to do so" means a shop with a dyno. It will be required to confirm your changes. Also, be aware that many of the early 308's have issues with the advance mechanisms in the distributors. If you have any unexplained hp loss on the dyno, this is a the likely culprit.

    Of the early 308s (76 to 81) that have been dyno'd by our local club over the years, only 2 or 3 made even STOCK hp (mine included). All seemed to have carb, FI or ignition issues. My car just needed some larger main jets and the plug gap opened up. Those changes alone bumped by 78 308 GTS from 153 rwhp to 178 or so.
     
  4. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
    Full Name:
    chris morse
    Thanks Dave, I 've enjoyed reading your posts.
    I believe the po installed ngk platinum plugs as well as 2 MSD-5 boxes. Would you care to speculate on a plug gap other than .020 The po's mechanic said the car eats plugs. is this typical??
    I'm about 250 miles north of san francisco on the coast. The only dyno in the area is at the local state college, where i unoficially majored in auto shop.
    Don't think they will let me on. Besides that, I need someone a whole lot smarter than me to spec the changes - maybe a trip to portland??
    I'll have a good look at the advance mechanisms.
    As a side note - has anyone ever retrofitted a vacuum advance to improve fuel economy?

    thanks, chris.
     
  5. f355spider

    f355spider F1 World Champ
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    May 29, 2001
    17,315
    USA
    I'm no expert, only a backyard hack, and not a very good one. :)

    The common plug gap with electronic or MSD conversions is typically .032 to .034, often times a smaller gap will give you a distinct miss at higher rpms.
     
  6. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,366
    NY
    Chris you have me a little confused . There should not be any sound deading material in the air cleaner intake unless a mouse brought it in. I also use NGK plugs with a pertronix's breakerless conversion and 12v coils with no resistors. Time it at 7 degrees and let it rip. Got Ansa's on the rear and no smog equipment. Plugs have 10k miles on them and still are pretty clean after you blow it out. I don't use the choke as many others don't either so when you cold start it runs a little rich until warm. Once temp is up car runs great. I have left the carbs with the stock setup and it seems fine. Also you don't need to many "special" tools for a valve adjustment so don't waste you $'s. I did a valve check at 40k and they were all on so no need to get shims until you check and measure. Good luck and have fun.
     
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  8. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    There was a Forza back a couple of months where Tate Casey at Carobu Engineering (www.Carobu.com) re-jetted a Euro 308GT/4 with 34mm venturis and found they were optimal (i.e., more flow with not much hit on low end drivability). Great guy - would give him a call. While you definitely need a dyno with A/F to optimize your jetting, mains of 140 are quite common. I'd say an idle of .6 was a bit rich - shoot for .55 or .57.; 200 a/c are also common, but you really need a dyno to tweak the upper range.
    The best place to get weber stuff or ask questions is pierce manifolds (www.piercemanifolds.com); they certainly know my $... :)

    Also if you are re-jetting on a dyno, would re-jet with a K&N on and after any exhaust changes.

    Actually, some later 308s do have a larger throat with sound deadening where the air hose attaches. Don't think it makes much of a difference. (picture attached - note enlarged air entry)

    best
    rt.
     
  9. Wayne 962

    Wayne 962 Formula Junior
    Rossa Subscribed

    Nov 27, 2003
    448
    Not anymore. I've been testing a hand-held air-fuel mixture tool that plugs (clamps onto) the tailpipe of the car, so that you can record and measure A/F ratios while driving. Very, very useful. We're going to have it in the DriveWerks catalog this week, I'll post a link.

    Basically, you if you can tune and jet the carbs to get 14.7 (1.0 gamma) across most of the range, then you're in business, and only really need to spring for dyno time if you want to get that last 5%. The tool uses a wide-band O2 sensor, and I've used it on several cars (including my '79 308 already). I also have a CO machine (smog machine) in my garage, but that thing is hardly portable. By using this tool, you can verify that your carbs are dialed in.

    The problem I identified is that the mixture is *very* lean at anything but idle. I'm running in the 15-16 AFR range when on the road. Ironically, I don't get good fuel mileage either though (I would think with the carbs set so lean that I would be burning less fuel).

    I'm going to be taking some measurements (need an assistant to record while I'm driving), and I'll post them soon...

    -Wayne
     
  10. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
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    Russ Turner
    Wayne -
    Can't wait to see the pictures, sounds great. It's tough to measure steady state cruise A/F on a dyno-jet. I'm sure there will be an FChat introductory price... :)

    Wayne is right that, based on my experience, the Ferrari tolerates a lot of slop on the A/F ratio with respect to max numbers. While the Kjet seems to run right at 14.7, I do opt for a bit richer in the low 13's, but that's just me. What I have found is that the response to throttle is affected by the running A/F and accell jet.

    Hey Wayne, think there is an audience for you to do a follow-up to your Porsche book? "101 projects for your V-8 Ferrari..."

    best
    rt



     
  11. abarthracer

    abarthracer Formula Junior

    Dec 6, 2003
    373
    Falmouth, Cape Cod
    Full Name:
    david S.
    Wayne, please let us/me know when that meter is available. I could probably sell 3 of them right now, me and 2 friends who have been looking for something exactly like what you are talking about. Thanks
    David
     
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  13. Wayne 962

    Wayne 962 Formula Junior
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    Nov 27, 2003
    448
    I'm very green on these cars, but the more I look at them, the more they look just like other cars. It's just that the parts are expensive. On the scale of "super exotic," I haven't found too much unique or special about the 308, or the 308 engine. High performance, yes, but not like working on a 911 air cooled engine, or a Mazda rotary. Still, I doubt I would ever sit down to write a 308 book - it's just too much work. I'm working on 101 Projects for Your BMW 3-Series right now, (at this very moment - I'm sitting on my computer in the garage looking stuff up), and I think I might retire after this one. The hours are long, the pay stinks, and it takes forever.

    Anyways, indeed, this tool has been everything I've been looking for. Ever tried to tune an MFI (Mechanical Fuel Injection) car without a dyno? Pure guesswork, and honestly my guessing usually has a wide error bar.

    The tool can also map and record results directly to a laptop, although I haven't tried this yet. Mapping RPM vs. AFR would be key, but I'm not sure if the thing senses RPM. I'll let everyone know. Still, by itself, it's an extremely useful tool. I found it at SEMA (it was actually named new tool of the show by some organization), and was talking to the owner of the company who had read my books and was a customer!

    I asked the guys to toss it into the catalog, but I think they weren't exactly sure where to put it - it should be in there tomorrow.

    As for your numbers with AFR, if you ask the experts on this stuff, they usually will tell you that peak HP and fuel efficiency indeed is at 14.7. There are a few exceptions to that of course. The number one I can think of off the top of my head is forced induction - these engines typically generate maximum power at a bit richer mixture (14.2 or so off the top of my head), according to the "Engine Management Experts" I've talked to in the past.

    -Wayne

    -Wayne
     
  14. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
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    chris morse
    Thanks Dave,

    That has been my experience with most CD/Electronic systems.
     
  15. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
    Full Name:
    chris morse
    Steve, there is a fiberglass type material on both sides of the tapered air intake. It is retained by a perforated bit of metal. When I was a servicer manager at the local cadillac garage, a customer brought a seville back a couple of weeks after we tuned it and in a rather impatient boistrous manner implied that we did not do a good job, it ran poorly. We checked it out and found the entire perimeter of the air cleaner packed with dog foods - kibble!! It seems a mouse or pack rat liked the warmth of the engine, or maybe it was just the cadillac "ombiance". So, we bagged the kibble, smoke tested the cad and called the customer. Believe it or not, he was actually slightly humbled by the bag of dog food - didn't know why it was disappearing so fast.
    Probably wouldn't help much removing the fiberglass anyway.
    best
    chris
     
  16. Sean F.

    Sean F. F1 Rookie

    Feb 4, 2003
    3,004
    Kansas
    Full Name:
    Sean F
    Chris,

    Go to the archives (old F-chat) and do a search in the tech archives for a "308 carb rejet and rebuild".

    Don McCormick and many others hashed out a long thread on this very subject.

    If you dont' find it, I'll post a link when I get home this weekend. I've got it at home in my favorites.
     
  17. cavallo_nero

    cavallo_nero Formula 3

    Nov 3, 2003
    1,656
    colorado
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    Giovanni Pasquale
    #14 cavallo_nero, Mar 15, 2004
    Last edited by a moderator: Sep 7, 2017
    there are a lot of good mods to be had with the 308. I have the following:
    borgo hi comp pistons.
    electromotive direct fire ignition.
    krank vents
    deep sump oil pan
    SI clutch system
    and a true dual exhaust - probably the most noticeable improvement - even over a tubi - see pic.

    john
    78 308 GTS euro
    running at 6800 feet above sea level with 140 mains and 180 AC.
    soon to try 34mm choke venturies at the dyno
    Image Unavailable, Please Login
     
  18. Wayne 962

    Wayne 962 Formula Junior
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    Nov 27, 2003
    448
    Even with an exhaust like that, is it possible to get even, balanced length header tubes out the back of the car? The engine configuration seems to make this difficult...

    -Wayne
     
  19. cavallo_nero

    cavallo_nero Formula 3

    Nov 3, 2003
    1,656
    colorado
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    Giovanni Pasquale
    My car came from the factory with header tubes (euro spec). the header tubes are not all equal length, but pretty darn close. The set of 4 header tubes go into 1 collector for each bank. the piping from each collector to the mufflers are different lengths, but that is OK since each of the 2 mufflers has a designated bank of cylinders to scavenge. this true dual exhaust setup compliments the fact that the 308 v8 is essentially two 4 cylinder engines working independantly.
     
  20. Wayne 962

    Wayne 962 Formula Junior
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    Nov 27, 2003
    448
    So the exhaust on the bank that is closest to the rear - this loops around a few times in order make the length equal to the front one? I'll like to see a pic of that if possible...

    -Wayne
     
  21. abarthracer

    abarthracer Formula Junior

    Dec 6, 2003
    373
    Falmouth, Cape Cod
    Full Name:
    david S.
    Wayne, is it the one for $4045.00?! Wow, I would hope it would drive the car for you for that price. So much for the home mechanic having one. Oh well, I'll continue to do it by ear. Please correct me if I am wrong and maybe if you could provide a llink to it. Thanks
     
  22. Wayne 962

    Wayne 962 Formula Junior
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    Nov 27, 2003
    448
    No - this one is $339, and is worth every penny:

    http://www.drivewerks.com/catalog/shopcart/MISC/POR_MISC_INNOVT_pg1.htm

    I'll get together a coupon for Ferrari Chat members, but I want to make sure it's okay with Rob first...

    -Wayne
     
  23. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Wayne,

    I would like to purchase one of these devices if it will truly eliminate the need to make multiple dyno tests which it sounds as if it will. As I am currently setting up my engine and plan to put it in the car this spring I would expect to optimize the fuel/air ratio with this device and then make one trip to the dyno. Am I getting this right? What sort of discount do you think could be made available? Don
     
  24. Wayne 962

    Wayne 962 Formula Junior
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    Nov 27, 2003
    448
    Not sure yet - it may be a free gift coupon (I have lots of 1/43 Ferrari models that we like to give away as freebies).

    I need to wait for approval from Rob first. DriveWerks is not a FChat sponsor (it's a bit too expensive for us, as we are not Ferrari-specific), so I don't want to step on any toes.

    As for eliminating the dyno completely - nothing is better than a dyno. However, this tool will allow you to tune your carbs without a dyno and get yourself 90% there. It's really neat - I have a photo of it plugged into my 308 that I'll post tonite. I'm also going to get one of the RPM transducers (they are out of stock right now) so that I can record RPM versus AFR curves while driving. This will allow me to figure out and test which jets will work best to maintain the desired AFR of about 14.7:1.

    I've also used it to test my truck's fuel injection system, prior to having it pass smog.

    -Wayne
     
  25. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
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    chris morse
    Wayne,

    This really sounds like a time saver.
    How quickly does the meter respond? Slower means we will have to do the tesing at higher speeds or drag the brakes to allow the meter to stabilize and give us a good reading at WOT, at some rpm.
    How would one go about inputting the data to a lap top.
    and what type of software & how much??

    On a related note, has anyone ever used a manometer or a similar instrument to attempt to get an idea of the effedtiveness of the "ram air"??

    If we are really seeing a 5 or 10 percent iincrease in air box pressure at some kind of speed, will the carbs handle this or are we going to go leanor rich??

    curious?
    chris
     
  26. Wayne 962

    Wayne 962 Formula Junior
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    Nov 27, 2003
    448
    Answers: The tool responds instantaneously - there's no discernable delay. It's like the tachometer - basically instant. The unit comes with a cable to connect it to a laptop, and includes the software that you need to download the data (you can store up to 43 minutes of data).

    -Wayne
     
  27. Wayne 962

    Wayne 962 Formula Junior
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    Nov 27, 2003
    448
    #24 Wayne 962, Mar 16, 2004
    Last edited by a moderator: Sep 7, 2017
  28. rivee

    rivee F1 Rookie

    Jan 20, 2002
    3,726
    Nowhere important, USA
    Full Name:
    John
    Chris, as for your valve adjusting tools and shims: you can make the tools yourself if you look at somebody elses first you can see they are pretty basic. The same shims are used by many cars including Volvo, where I get mine. But check them first to see what sizes you'll need instead of ending up with 10-20 4.xx shims like I did.
     

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