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308 dyno-ed

Discussion in 'Technical Q&A' started by adesalos, Jan 10, 2004.

  1. adesalos

    adesalos Karting

    Mar 19, 2003
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    #1 adesalos, Jan 10, 2004
    Last edited by a moderator: Sep 7, 2017
    That's it!
    I got my 79 308 dyno-ed and it isn't pretty.. see pic below.
    I didn't have expectations (baseline, after buying the car), but now I have a good excuse to go next week to my mechanic to get my 60k service done.
    Any other suggestions of work to be done apart from the 60k, based on the dyno test result?
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  2. adesalos

    adesalos Karting

    Mar 19, 2003
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    By the way conditions for the test were as follow:
    52% humidity
    51 degF
    30.82 " Hg
     
  3. adesalos

    adesalos Karting

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    #3 adesalos, Jan 10, 2004
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    BTW, a guy (very nice, talkative and down to earth) showed up with his GT40 (a REAL one) to dyno. He didn't expect anything big since he considered his carb secondary jets too small, but still got 300hp. but the SOUND, my friend, the SOUND... that made my day!
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  4. ricrain

    ricrain Karting

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    Are the air/fuel ratio numbers real? If so, part of the problem might be the carburation (too lean most of the time). In fact, it's so lean by that graph, that I'd work about excessive EGT and knock.
     
  5. snj5

    snj5 F1 World Champ

    Feb 22, 2003
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    The A/F graph tells a lot of stories here. The US 79's were the leanest jetted 308s from the factory (emissions) and there is a lot of horsepower waiting for you with a very simple and inexpensive re-jet. Most power is made around A/F 13.2. If you look back at the two 3.2 with carb dyno post threads, I've just been through the same process, on a Dyno-Jet as well. Also remember that this jetting will effect your emissions testing if that is a concern. However, ricrain is right that I would be concerned about other damage from the lean A/F.

    The dyno jet should have corrected for the ambient conditions. If those are uncorrected (raw) numbers, you do have some work to do.
    Need to know:
    Was this test was made with the air filter on?
    Do you have stock USA jetting (125/130 mains, 220 A/C)?

    Assuming the answers are yes/yes, then would call Pierce manifolds (Mike) and suggest ordering after conferring with them as a first try:

    8 X 135 main jets
    8 X 200 air correctors
    8 X F24 emulsion tubes

    If you are really after more HP, Carobu Engineering published in Forza that a stock 308 carb's engine does better with 34 mm chokes (stock is 32mm). If you go to these chokes, may look at 140 mains.

    Every car is a little different and responds a little differently. Webers are easy and inexpensive to re-jet, then see where you are with the pulls.
    There are folks on this board who are very helpful, and you are going to see some improvement!!! I'm sure they will chime in here.

    Good luck and ready to help.
    best
    rt
     
  6. mk e

    mk e F1 World Champ

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    "In fact, it's so lean by that graph, that I'd work about excessive EGT and knock"

    No need to worry about knock, he's got it, and bad. That why the lines are jaged starting about 5500, That's what detonation looks like on the dyno and why the hp was so low.

    adesalos - I suggest you don't drive that car until you get the jets fixed. Putting the stock ones back in is the best place to start if the engine/exhaust is stock. If it is not stock, you need to go up at least 2 sizes, probably more like 3 or 4 across the board. There are several guys here including Russ with carb cars who can probably give yo ua good place to start. It's good that you found out now though.
     
  7. adesalos

    adesalos Karting

    Mar 19, 2003
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    Guys you are starting to scare my good here...
    What is the knock, and should I absolutely not touch the car before repair? Should I also check other part that could be or have been damaged because of this condition?
    I guess I will have my 4 carbs rebuild now, on top of my 60k service.

    BTW all the figures are corrected for ambient conditions...
     
  8. adesalos

    adesalos Karting

    Mar 19, 2003
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    Also, what does excessive EGT means?
     
  9. Tillman

    Tillman Splenda Daddy
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    Yes, I have one

    Knock, or preignition, is when the air/fuel mixture is igniting before the spark impulse is supposed to set it off. It's caused (usually) by hot spots in the cylinders which are in turned caused by poor air/fuel mixtures. I'm sure someone else will explain it better, but that's what I remember from dealing with hot rods. That's why we always tuned them very fat (rich) See http://www.superchargersonline.com/content.asp?ID=104 for a good writeup.

    The problem with detonation is that instead of a smooth power stroke, you get a random, jagged impacts on the rotating parts of the engine, such as the connecting rods, the crankshaft, etc. This can damage these parts, and in a very expensive way.

    You can hear this sometimes as a pinging in the engine under acceleration or load.

    High EGT is related. EGT is exhaust gas temperature. An engine that is running excessively lean runs hot, and generated much higher exhaust temps than normal. This can damage the exhaust system if not corrected.

    Fortunately, both can usually be corrected by adding fuel (oversimplification). So follow the advice you recieved earlier in the thread, and you should be on the right track.
     
  10. mk e

    mk e F1 World Champ

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    EGT is Exhaust Gas Temperature. Hot exhaust overheats the exhaust system and the engine bay.

    Good link on knock or detonation. The quick answer is that it means the fuel is exploding instead of just burning. If you continue to drive the car, the pistons will develop holes...if your lucky. It's very bad for the engine.

    Your car is very very badly out of tune. If it was mine, I would not drive it. You might be able to nurse it home if you stay off the throttle, but I don't think I would, your graph shows detonation present through the whole rpm band.
     
  11. atlantaman

    atlantaman Formula 3
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    to learn about knock and tuning--search for sites that provide "wideband o2 sensors" and EFI sites like Electromotive AEM. There are a lot of good articles there
     
  12. pma1010

    pma1010 F1 Rookie
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    I too strongly encourage you to increase the jet size. My guess is 1/2 or 1 step on the mains to 130 or 135. Stock jets in my 77 GTB were 135 mains, 55 idles, 220 AC and F36 Emulsion tubes. This was with the 4X series 40 DCNFs. I don't recall the series for the 78/79 milder cam cars (different series had different progression holes - 5X?) but I think this combination would get you close. Keep the old jets - you might need them for ignition. You'll get considerably more power with jetting that gets you closer to 13.2

    Mark, could the distributor (advance curve weights being off/weakness in the springs) be causing the variability in the torque curve?

    Adesalos, if it is going in for a 60K service, you might have the shop put the distributor on an advance tester. They'll pull them anyway to do the cam seals.
     
  13. mk e

    mk e F1 World Champ

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    "Mark, could the distributor (advance curve weights being off/weakness in the springs) be causing the variability in the torque curve?"

    Philip, A sticking distributor might be part of the problem down low, those lines are all over the place. I think it is so lean that cylinders are shutting down, a mis-firing cylinder sends unburned fuel and Oxygen out the exhaust. So, the O2 sensor reads as a lean condition because there is too much oxygen. From 5500 up, the only explanation I know of for the noise in the graph is detonation. It also looks like there are detonation spikes all down the graph, but not continuously like high rpm. It's pretty common in for detonation to begin at about the peak torque point, since that is where cylinder pressure is the highest, then once it starts the extra heat in the engine continues to cause it even though the torque is dropping.
     
  14. vette79

    vette79 Karting

    Nov 3, 2003
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    ****warning, long post****
    this is a ery long post but i feel something has not been addressed here that needs to be.
    you definitely need to increase your jetting, however i must caution you to be wary of jetting it too rich. this also applies to tillman as a car jetted slightly lean is better than a car jetted slightly rich as long as no detonation is present. all four stroke motors (any motor that burns straight gasoline and not an oil/gas mix) is like this. two stroke motors are a different type of motor alltogether, so this doesnt apply to them. back to cars. in car motor such as your ferrari, the piston is held in the center of the cylinder with three piston rings, one of these rings is an oil control ring. generally you will not want much oil on the cylinder walls, however some is needed to lubricate the engine and to decrease friction and heat between the piston rings and the cylinder walls. when you jet a car far too rich you saturate the combustion chamber and cylinder with gasoline, which causes an undesireable condition called "wash" or in more direct terms "washing down the cylinder walls." think about how gasoline will remove oil off of your hand. then apply that to your motor, as it does the same thing. not only will jetting your car far too rich seriously hurt fuel economy, throttle response and overall power, it will also cause some more serious problems due to the wash effect such as seizing the motor, which is what happens when there is too much friction between the piston ring and the cylinder wall. the piston gets stuck in the motor, usually in stroke change either at TDC or BTC and for some reason you find yourself with a motor that stops very, very quickly. if the car was say idling at the time sitting still(not likely), not only will you need a complete rebuild of the motor to see what damage was done, chances are you will have to hone the cylinder to get rid of the gouge that the piston made when it seized. it may even junk the whole engine block if the gouge is deep enough. now if you are driving the car, and on a high spirited run, the motor seizes and the back wheels stop turning. and right NOW. unless you depress the clutch immediately, not only will there be a chance the motor will be damaged even more, theres an even bigger risk of you losing control and crashing/rolling your car. I cant say ive got more experience in life as I am still relatively young (20) but ive been involved in racing carts, dirtbikes and cars including a lot of engine work for over 9 years now. ive seen the too-fat-follies played out too many times, and even though i am painting the worst case scenario, it is still something you should know that is a possibility. my experience has been that 80 precent of friends/neighbors/customers carb'd hotrods that i have looked at either new or old chevy or ford or exotic most of them are jetted rich. you want a car to be on the razors edge when it comes to jetting. you want it to be rich enough that you eliminate detonation under heavy acceleration, and lean enough that you are getting the most power and throttle response and fuel economy possible. first step it to ablolish the dreaded ping. if it needs be, a regular chevy or ford or whatever mechanic can ride with you as they will be able to detect pinging much much better than you unless you know exactly what to listen for. sometimes its loud and noticeable, sometimes you have to be looking for it and even then its hard to detect. anyway, once that is done, and you have eliminated the pinging problem and are confident that your car is running correctly and it wont hurt to flog it, take it somewhere that you can make a few hard passes. since i havent had any direct experience with your model, i cant say whether or not you can get to your spark plugs very easily. but it will be necessary for this. you may have to remove the valve covers to get to them, if i am remembering the 308 engine correctly. if you can get to the spark plugs, ill leave you to decide where, it would be nice to be somewhere its legal. what you are trying to do is run the car hard under full acceleration. make oh maybe two passes full throttle running the car hard through third gear and maybe into fourth. the pull over somewhere immediately. dont let it idle or run for much longer after your hard passes. shut it down, and do whatever is needed to get to the spark plugs. what you want to find is that they are colored a dull grey. if you decide to do this send me a pm and ill call you and give you what you need to be looking for. the way the sparkplug looks can determine many things. let me know what you end up doing, and good luck.
    Eric
     
  15. 348 Turbo

    348 Turbo Formula 3

    Jul 17, 2002
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    Nice post. This is why we have this board. Thanks for sharing, Mark!
     
  16. adesalos

    adesalos Karting

    Mar 19, 2003
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    #16 adesalos, Jan 11, 2004
    Last edited by a moderator: Sep 7, 2017
    well, I went to see my mechanic today, after verifying that it was in fact too lean (see white tip of spark plugs).

    He has 30 or so years with Fcars, so I tend to trust him well, and his explanation is: distributor is the 1st issue. Since there are 2 distributors, if they are not in synch, tuning the carbs will not make my problem disappear. After the distributors are set then he will take care of the carbs. He advised me not to change anything to the OEM settings (jet size or other). Ferrari know how to engineer a car and it is for a good reason that they did it this way.

    Interestingly, he also commented that only 1 type of gasoline was recommended for staying away from this kind of problem: Shell. Exxon being the worst.
    This is Texas experience, by a guy that has a 275 GTB, 275GTS, 250GTE, 365 GTC, GTC4, GTB spyder, 246.... in his shop, and no car older...
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  17. Mike328

    Mike328 F1 Rookie

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    adesalos,

    1. Were all the plugs as lean as the ones you took the picture of?

    2. No matter how much of an expert somebody is on a Ferrari, I would also weigh very heavily the actual experience and "owners consensus" from 308 owners like yourself about the car, since we've established things your mechanic might not know or otherwise care about.

    Like in the late 70s Ferrari was struggling to make their 308 line meet emissions requirements, requirements that the car was not necessarily designed to meet.

    Hence you see many changes along the way in the development of the 308--different cams, different stock jetting sizes, some of which were made in whole or in part to meet emissions.

    There is a range of acceptable mixtures in the cylinder. It's complex, but fuel economy, clean emissions, performance, engine gas temperatures, and prevention of detonation are all factors in determining this. If changing jet sizes gets you a better A/F more performance, then go for it if that's what you're looking for. But don't be shy about it... There's a range. 120 to 140 for you at sea level, let's say, for the main jets.

    One thing is for sure. The stock jetting size (125 mains, 220 air correctors I believe), with everything else in tune, will obviously not be the culprit in the problems you're seeing (problems lie somewhere else).

    HTH... Mike.
     
  18. snj5

    snj5 F1 World Champ

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    adesalos
    Would agree with your mechanic that the ignition must be right before tuning the carbs. It does not however, wholly account for those lean A/F numbers as clinically verified by your plugs.
    After you get the ignition close, would suggest the simple things first, stating the obvious here:

    Verify exactly what jetting you have in all 8 barrells; Some folks have been surprised - if your car came from a high elevation someone may have leaned the jetting for you previously.
    Verify float settings
    Verify fuel pressure at the carbs
    Be sure to do your A/F dyno pulls with the Air Filter on (makes the mixture a tad bit richer than open, a K&N while flowing more makes it a tad bit leaner than a stock paper). I like my dynos to be straight 4th gear pulls, but everyone is different
    Make sure no air leaks in the carb or vacuum take-offs

    As said before, Ferrari had really leaned that engine out for emissions, so it is prone to being lean. If you do correct with the 18% driveline loss factor, that does put you at 200hp flywheel, which is not far from the 205 or so factory claimed.

    Everything is a balance with hp and emissions. I feel pretty sure with better jetting you can find more hp, but at the expense of emissions. There is a great thread on the old board - search 'Re-jetting 308' on the old board. I'm going to predict that you will do better with 130s and keep the 220 correctors.

    good luck! We're rooting for you!!
    rt
     
  19. atlantaman

    atlantaman Formula 3
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    a bit of info on GAS

    first--all regular gas is the same, all premium is the same(except for AMOCO "white 93".
    it all flows thru 2 pipeline and when it is recieved at the distribution center (like here in atlanta) it is devided into large tanks owned my various gas companies--the companies then come and supply their own grades of additives that they like.

    but in essence--only the additives are different between exxon and shell, and BP and Citgo--etc.

    Also it is interesting to mention that the state govts will throw in some oddball regs occasionally on additives SO the gas in North Carolina BP stations is different form GA BP stations (additives only that is)

    This is the cool part---
    They will pump out of Houston 89 octane for say 2 hours, then ****ch to diesel for 1 hour, then to avgas for 1 hour--so on.. All teh downstream tank farms are on time clocks and will open valves on schedule to catch the various grades needed--cool huh---there is nothing seperating the different fuels--they use specific gravity to tell between them. And for the most part they do not mix up in teh pipes
     
  20. f355spider

    f355spider F1 World Champ
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    If you check the old F-chat archives you will find info on my 78 308 GTS which is identical to the 79's. My car was basically stock with the following mods: Crane cams ignition boxes with Bosch blue coils, K&N air filter and cat test pipes. Fresh 30k with new wires and plug extenders.

    On the dyno car was very lean (stock jetting). Shop progessively increased the main jets from 125 to 140. Car was still slighly lean, but they were afraid of getting too rich in they went to 145's.

    I would agree that further testing with the AC jets and emulsion tubes might allow for even better results. My shop didn't have them in stock, and results were so immediate and nice, that further tuning didn't seem necessary.

    Car went from (around) a corrected 190-192 hp at the crank to 214hp.

    The two biggest faults with the carb cars not making proper hp is the distributors not advancing properly and lean jetting. Your car is not that far off the mark, but slightly richer jetting will help.

    Russ has the experience here....listen to him!
     
  21. adesalos

    adesalos Karting

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    Thanks a bunch guys for all the information.
    I will put the issue of the jet size back on the table with my mechanic.

    Also, I forgot to mention that there is no more emission system on my car. Just a ANSA muffler exhaust (checked and the tail pipes aren't white).

    Would that also change things in the diagnostics proposed (especially on jets size recommandation)?
     
  22. f355spider

    f355spider F1 World Champ
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    Oops, I also had all the emmission controls removed on my car, forgot to mention it (air pump belt removed, charcoal cannister removed, etc.. I don't beleive it would change the adjustments, other than making sure you remove the cats. The richer jetting might damage the cats.
     
  23. snj5

    snj5 F1 World Champ

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    If it will help, here is a list of Weber jetting for 308s that I have polled from many 308 owners that they have found works well. All are stock 32mm venturi and F36 emulsion, so will just give the Main jet/air correction jet:
    140/195
    135/220
    140/210
    140/200
    135/220
    130/200

    If you're new to this, here are some simplified rules::
    The bigger the main jet, richer the mixture throughout the whole band
    Larger air correction jets lean out the high end (>5500) mixture
    A medium sized main venturi acts to give the air more velocity into the cylinder (good for response). Bigger venturis have more flow up high, but lower velocities down in the 2000-5000 range which make the response boggy but get more fuel/air in up at high rpm.

    For comparison, a stock street 206/246 Dino uses 125/220 with 32mm venturis; the competition version of that 2.4 l engine uses 160s/175 with 36mm venturis. The street version has a smaller venturi, requiring less gas (smaller main jet, larger a/c jet) but has a great response which is more important on the street. The competition Dino can flow a lot of air, therefore needs more gas (bigger main, smaller air correction) but does this at the expense of low end tractability, i.e., it would be a dog at low rpms but a screamer up high ( it's a race engine, duh) flowing large amounts of air and gas.

    All this gets back to why a few of us think you need a larger main jet, say 135 assuming you are running the stock 125s now. It will richen your mixture across the band, and is corroborated by other's experience. Main jets cost a few bucks apiece, and all eight could be changed in about an hour or less. I am beginning to think that your stock jets are dirty/clogged/gummed up or have been changed for high altitude. Would also be less than an hour to pull them, check the numbers on them and clean them out.

    Hope this helps; Mark or Philip or others can chime in if I've missed.
    good luck
    rt
     
  24. Mike328

    Mike328 F1 Rookie

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    One more. I'm running 125 mains with 200 air correctors. Works "ok" at 5000ft altitude. 55 idles, as well.

    I intend to try 130 or 135 within the next week or so.
     
  25. mk e

    mk e F1 World Champ

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    "Also, I forgot to mention that there is no more emission system on my car. Just a ANSA muffler exhaust (checked and the tail pipes aren't white)."

    OK, now we know what's wrong with your car. Removing the cat an installing a free flowing aftermarket exhaust will let the engine flow more air, BUT the carb MUST be rejetted or the engine will run very lean. The problem with modifing ANYTHING is that it will effect something else. If you want to use the stock factory jetting, you need to install the factory exhaust and emissions equipment. If you intend to keep your MODIFIED exhaust, you need to modify the carb to match. Your mechanic may not have realized that your engine was not stock.
     

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