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Post by Zed on Mar 14, 2018 16:09:25 GMT
More of a how to understand it than how to do it, but if you understand you don't need instructions and understanding is your only real hope of getting it right for your particular combination of carbs and engine. I was minding my own business, idling, loafing, lounging and reading a few weeks ago when I came across a thread on the samba about AFR. Previously I'd thought a wideband kit was a bit expensive and I seemed to be able to tune and jet ok by semi-educated trial and error, but reading this thread turned a few of my beliefs on their head. Posts by "john@aircooled.net" were the ones. I'm going to quote a few here and a link to the thread. I hope he won't mind, he seems keen to inform. The thread is here. www.thesamba.com/vw/forum/viewtopic.php?t=293837&postdays=0&postorder=asc&start=20Here's the first one about how many of our asumptions are wrong and why... I'm an idiot, ignore me, everyone else does (and runs 13:1 all the time, MORONS). For those that are interested in knowing, if you keep leaning out the engine the engine will run cooler and cooler as power is dropping off, until the engine just dies since combustion will not occur with too lean a mixture. Only airplane guys have a clue on ROP and LOP tuning. I'm an engineer that reads too much. The automotive guys are 40 years behind the times. Most guys would just stare at you if you told them (and were correct) that 15:1 runs cooler than 14:1, and 16:1 runs cooler than 15:1, etc. The problem is guys that know just a little bit, and think they know a lot. These are the guys that will tell you to run "32 degrees of total timing" for example. With that much timing, you have to run a richer mixture for the engine to get out of it's own way. There are only 3 guys I know of that TRULY understand that ignition timing and A/F are not independent of one another. The problem is they are ADJUSTED independently, but their affect on one another is dramatic, and guys do not get it. Most guys set the timing to 30-32 total, then tune the WOT to produce best power. All they have done is found best A/F for THAT timing. In fact, most engines will make MORE power and run clean if you'd lean it out, and pull out some timing. You have to follow an iterative process to find the sweet spot. Find A/F, set timing, find A/F, set timing, Find A/F, etc. Most guys are so rich they have to run a lot of timing, since the burn happens so slowly because it's so fat. But they don't see that they'd need less fuel IF they'd run less timing, since "all motors make more power with more timing". This can be seen on your engine if you run super rich (like 10:1), you need to run WAY too much timing (another 10 degrees), but it will actually run "OK" and you wouldn't know it was so far out of tune by how it ran. But if you can convince them (which is difficult/impossible most of the time, because they are tuning the wrong way) to lean and retard, the engine wakes up! An example of being properly tuned is seen with that guy in San Francisco in a recent thread with his IDFs (edit: oh yeah, that's THIS THREAD LOL). When he started getting close running a LEAN cruise, he had to pull out ignition timing, which allows him to run leaner still, and maybe pull out even more timing. That sucker is going to run cool and return some fantastic MPG when he's finished. I think 40mpg is not difficult, but some "experts" talk like 25mpg is the Holy Grail or something, when in fact it's a joke. Hopefully the average Joe will have a clue on tuning in 10 years, just like the average Joe NOW is not 009 brainwashed, at least not like they were a decade ago. John Aircooled.Net Inc.
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Post by Zed on Mar 14, 2018 16:21:55 GMT
Here's a graph. Johns explanation... The bottom line on that graph in a nutshell is engine efficiency. Power from fuel used. Ideally your gearing would be such that you were at the peak of that curved line (1/BSFC) at your cruising speed. Note that this point is 50F COOLER than peak EGT, and it's also leaner than stoic (1 Lambda = 14.4:1 on gas). Note that once you hit Stoic, the leaner you go the cooler the engine runs. BUT, there is a point of diminishing returns, since you have to use more pedal (and more fuel) to regain power that you lost by being lean. There is a point where if you lean out more your MPG will go DOWN (1/BSFC is decreasing, sloping down), since efficiency is decreasing. But note that the area at the top of the 1/BSFC curve is very flat, you have a good deal of room to play around (tune) with. You want to target the peak of that 1/BSFC curve for max MPG. And surprise surprise it runs cool. DUH This info has only been around for a short period of time, like 75 years..... John Aircooled.Net Inc.
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Post by Zed on Mar 14, 2018 16:33:31 GMT
Setting idle speed and mixture...
You do NOT want the highest RPM you can achieve at "idle". While this may be the most "efficient" idle setting, it's very unstable and will not hold RPMs steady, ESPECIALLY as engine temps change.
Everyone I've ever seen has their carbs adjusted via the wrong method. They MAY be adjusted right, but via the wrong method (they got lucky). To get the proper idle, AND to make sure that the carb is setup so IT WORKS LIKE IT WAS DESIGNED TO, do this.
For reference, LBI (Lean Best Idle). How I do it is to back out the idle mixture screw a bit, then turn it in until you hear the engine miss on that cylinder. Now back it out until it picks up. Back out to fastest idle, find the sweet spot. Once you do, go out another flat (1/2 turn). Repeat for the other 3 cylinders. This is how to set idle mixture. It's actually 1/2 turn richer than lean best idle, but my setting (1/2 turn richer than LBI) is more stable than actual LBI under real usage conditions (where temps will change from what it is when you adjusted it).
Also, only do your adjusting on a warm (HOT) engine. That's how you drive it, so don't do the setup when it's not warmed up.
So do to your engine, set idle timing to around 7-8 BTDC. Get idle speed around 800. Sync the carbs. Set idle mixture. This is the initial setup ONLY.
Now, you must get the throttle plates in their proper position. If you have vacuum advance, put a gauge on the vac advance port, or if you do not have one put a hose on and "listen to it". Turn the idle speed screw in until you get a vacuum reading (or a sucking sound on the hose). Now back it out until it disappears (no vacuum). Now match the other carb to that one. Now NEVER EVER TOUCH THE IDLE SPEED SCREWS!!! Any change in idle RPM you make now will be via the air bypass screws or ignition timing.
Make sure both barrels on the same carb flow the same. If they don't, you may have a bent throttle shaft. Go to carb Doctor ACE or Harney.
Adjust to LBI.
So what is your idle speed? If it's too high, you need to remove idle timing, then reset the idle mixture again
If it's too low, you have a couple options. If your idle timing is close to 7-8BTDC, the first thing I'd try is to open the idle air bypasses. Do both the same so both barrels flow the same. You only get so much adjustment on the air bypass screws. If that doesn't do it, you have to add idle timing which will bump up the idle speed. Add timing until you are at your desired RPM. I do NOT recommend timing over 12 degrees at idle, if you need this much you likely have something wrong somewhere. If you need more than 12 degrees at idle, something is wrong. The exception is centermount carbs; those MAY need more air to get the idle speed up. Do that by backing down on the timing, then open the air bypasses or drill the plates a little at a time (and reset idle mixture) until you are at the desired idle speed.
Be aware that optimum idle timing has NOTHING to do with optimum full advance. So if you are using a non adjustable distributor you will have a problem, since idle timing dictates your full advance! If you want 28 total, and adjust your idle from 12 to 8, your distributor advance must be changed so you adhere to both conditions. If you have a Mallory it's a 5 minute job, it's trial and error if you have a Bosch or GOOD LUCK if you have a Chinese 009 or something.
This will allow the carburetors to work properly. If you have a centermount carb, you MAY have to drill the throttle plates, but only do this after you have done the basic setup first. It's critically important to have the throttle plates just below the progression holes at idle!!!!!! I can't stress this enough. Obviously the carb setup WILL be different at different elevations, and with different engines. And in fact, idle speed WILL be affected by the oil you are using, 50W is going to slow the idle down more than 0-20 for example.
Note that any time you make an idle jet, idle speed, or ignition timing change, you have to go back and reset the idle mixture!!!
John Aircooled.Net Inc.
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Post by Zed on Mar 14, 2018 16:42:00 GMT
Combustion is a LOT more complex than most folks realize.
You can have a plug that looks "lean" yet the wideband reads rich. WTF?
When you have a situation like this it's because the fuel is under-vaporized, and the combustion completes in the exhaust pipe instead of the chamber.
So the cylinder is lean but the O2 sensor is rich. You think that will throw guys off their tunes? And their solution is to throw more fuel at it, which makes the problem worse! You see this all the time with guys running less than .8 Lambda, and they do not realize the chain of events this causes. One obvious one is rings that go away and blowby increases dramatically.
You have to understand that the available fuel at the time of IGNITION is what you see on the spark plug if you are reading plugs. A Wideband reads the total fuel load that you are putting into the cylinder but it doesn't tell you the completeness of the burn IN THE CHAMBER, it only tells you the total ratio coming in and out.
An awful lot of performance VWs do not have enough heat or energy to gasify (vaporize) the fuel load being put into it. If less fuel is metered out, the heat available will be absorbed by less fuel and a higher gasification (vaporization) level will be achieved and the plug will color brown. In other words, the given heat in the engine is a constant for the amount of fuel we are putting in it. We want to vaporize the fuel completely, yet a lot of guys are tuning rich to "run cooler", and it kills their performance and they do not even realize it.
Many VWs are running 11.* A/F or even richer, and when run this rich the combustion temp as an average is "cold", and that's why they need so much ignition timing, cold A/F mixtures are slow to combust. Things are also hurt by cooling systems with no thermostat (running too cold), etc.
I'm sure this went right over the heads of a lot of guys, but this could take a LONG time to digest, just think about it a while and when it clicks you will be on another level of tuning prowess.
Hella Buggin leaned the engine out and all of a sudden it woke up and responded to his tuning changes properly. It did not respond before that because he was too rich (cool). When I'm referring to temps, I'm referring to temps pre-combustion, which is what vaporizes the fuel properly.
John Aircooled.Net Inc
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Post by Zed on Mar 14, 2018 16:54:32 GMT
Now some carb tuning aimed at weber idf and dellorto drla, he explains better elsewhere, I'll edit this post when I find it... The easiest way to see when the mains come in is to put an overly-large main jet in (like a 160), and it will immediately swing rich when they come in. Driving with NO main stacks in to get a feel for progression, then this process for the main transition, will let you tune the main tip in (via the air jet) so the transition is seamless, without excessive nor inadequate overlap. Then you tune the main circuit last with the main jet to aim for target A/F (usually 13:1ish) and you are done. the order should be idle jet (no mains, for lean cruise tuning) Air jet with overly large main (for transition tuning) main jet (for load tuning). John Aircooled.Net Inc Me again. What he says is. 1) IDLE JETS Remove your main stacks completely and drive. You will only be able to use partial throttle, too much destroys the vacuum - you'll soon find out how much. If it doesn't like it go up an idle jet size until it does. If it's happy go down sizes until it isn't, then back up to the smallest happy one. After each change reset your idle mix. You now have the leanest idle jets. If you have afr meter there are numbers, go read the samba thread, only 100 pages! IDLE TRANSITION Still with main stacks removed, drive for a week, get used to how much throttle you can use, the revs it manages under different conditions. You will find it's load, not revs that determine where the transition to mains occurs. The transition holes are fed by the idle jet only. The size of your air jets changes where the transition occurs. You don't want the mains coming in late or it will be lean in transition. You don't want them early or it will be rich. Sooooo, stick an oversize main jet in and drive. There are numbers for afr and if you have one you'll see it all happening, if not you'll just have to judge based on your week of driving just on idles. The big mains are to make it obvious. If the mains come in too early (rich transition), you need to reduce the air net size. If there is a lean transition (mains too late) go down an air size. If it seems perfect and you don't have afr hou may have to bugger about like this to prove it to yourself. If you do have afr you'll see it. John says "progression runs on throttle position and vacuum, NOT RPM. Just start with a huge main and small air. You should have a lean hole (BOG). Keep upping airs til it lessens and lessens, and finally goes away. When mains come in it will swing to ~11:1, the exact # isn't important, what's important is it's not "progression A/F". Once you get no lean hole, leave the air jet alone and lean the main to get 12.8-13:1 and you are finished." MAIN JETS Now you really need afr and aim for high 12's/low 13's but otherwise lean it until it pinks then rich it up a bit. Confused? Go read the samba thread.
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Post by Zed on Mar 14, 2018 17:25:53 GMT
More wiseness from John
The question is "what is the load?".
If you insist on driving 70-75mph in a bus, you have a significant LOAD and will never run on progression, so you'll be on mains and should be 13:1.
That is why it's so important to KNOW where your progressions are, by driving around with the mains removed (deactivated). Progressions are for LIGHT LOAD (lean tune), mains are heavy load (Power tune). Do not confuse them.
However, I will say the most common problem is people tuning progression for 13:1, which is a huge mistake (even in a bus). If you jet the carbs like I recommend, the carbs will adjust the A/F for the load you give it. Load = throttle position.
The only time this is a real problem is if the carbs are oversized for the application. The would end up with a situation where the carbs are barely open (progression), but the engine is close to maxed out. Like dual 48s on a stock 1600. You can tell because if you open the carbs more the engine doesn't go any faster. Very Happy
If the carb(s) are too SMALL, you'll wind up on mains very early, since the engine is starving for air.
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Post by Zed on Mar 14, 2018 19:50:19 GMT
This may be of interest...
Pinched from another samba thread, author S.G. Kent.
(1) why does raising the compression ratio increase the efficiency of an engine and make more HP?
A. It increases the temperature of the combustion creating greater thermal efficiency. More heat gets used which means more torque. Torque x RPM / 5252 = HP. More torque means the bus accelerates faster. Greater thermal efficiency means better MPG.
(2) In what ways does raising the compression ratio create a challenge for VW bus engine owners?
A. VW buses are already heat challenged. Gene Berg felt that a compression ratio in the low 6's was the only way to make a VW air cooled engine last. There are lots of challenges to a VW engine as the heat increases - piston scuffing, detonation from hot spots, cracking due to uneven thermal expansion and cooling, head leaks, pulled studs, dropped seats etc. Cooling becomes the greatest challenge. The balance between heat and power ends up with a C/R somewhere between 7 and 8 on most buses. VW chose around 7.3:1 based on their experiences. If the owner is willing to give up some engine life, and burn premium gas a 8.0:1 will give more power and efficiency. The trade off is greater risk of piston scuffing in a bus. On a 411/412, 914-4 or 912E that would not be a problem because of the lighter load on the engine.
(3) In theory, how does cam overlap and timing affect the amount of air and fuel that can be burned?
A. The air and fuel moving into a cylinder, and the exhaust coming out are pressure waves - they act like a child on a swing, moving back and forth in the intake and exhaust. The cam can harness this extra energy and supercharge the cylinder thru valve timing - much like pushing at the right time can push the child higher and higher on the swing. The same is true for the exhaust. Opening the valve at the right time can create super scavenging, allowing more space and a lower pressure that helps draw in - super charge the incoming air and fuel. The timing and over lap needed change as the RPM increases. It becomes greater as the RPM increases and less as the RPM falls. Thus, each single profile cam lobe has an optimal RPM that it is most efficient at. Changing intake and exhaust lengths have the same effect as lengthening and shortening the chain the child is swinging on.
(4) How does the increasing of the duration and overlap affect a VW bus engine? Pros and Cons please.
Longer duration cams work better at higher RPM. Shorter durations work better at lower RPM. When one uses a shorter duration cam the torque peak is greatest at lower RPMs. When one uses a longer duration cam the torque peak is greater at higher RPM's. Since HP is RPM X torque \ 5252 the effect is more HP is the engine torque peak is increased. Lightweight racing cars that rely on speed and RPM to go fast, often having many gears to keep the RPM up, benefit. A heavy bus however is built to longevity. Running around with the engine at 5,000 + RPM in a bus all the time would kill a motor. That's Ok on a motor that gets rebuilt every race. It is not Ok on a bus engine that the owner expects to last 50,000 to 80,000 miles. The best cam for a bus is one that makes a torque peak in the range that the bus is driven mostly - somewhere around 3,500 to 4,500 RPM.
(5) Why do semi-rough intake and exhaust ports allow more flow than polished ports?
A. Laminar flow. Once a polished port has a separation of laminar flow it doesn't have enough turbulence to recover to the full size of the port. This reduces the size of the port and therefore reduces the flow into the cylinders. A lightly rough port has enough turbulence to recover and adhere back to the port walls, where the entire cross section of the port can be used,
(6) How does the cross sectional area of a port affect flow, torque, and horsepower?
A. The size of the port helps determine the velocity of the charge. There is a balance between the velocity and size of the port, combined with the cam duration that allows the maximum charge to be pushed into the cylinder."
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Post by Zed on Mar 14, 2018 20:04:25 GMT
More from John, it's good to repeat same thing with different words until it sinks in. The progression circuit operates on throttle position, when the throttle is only open a little bit (<1/3) the manifold vacuum is very strong to the progression holes, and it pulls air/fuel out of the progression holes. This progression circuit is necessary because airflow at low throttle settings is insufficient to initiate the main circuit. You can prove this by removing the mains/emulsions/Airs (jet stacks) and drive around on the progressions to see how they work, and under what conditions they do and do not. I strongly recommend doing this for several HOURS (not blocks) to get a really good feel for how they function. It is true that by using bigger idle jets the progression will be extended, but not the way most think it does. This is because the engine becomes too rich at low throttle settings, and as fuel metering tapers off it still stays above a "combustible" level. It makes no sense to make the entire progression circuit too rich just to fix a small lean hole at the end of progression/beginning of mains. Why fix a 500RPM band and ruin a 2500 RPM window, when you can fix the 500RPM band you are lean in, instead? IF there is a lean hole between progression and main, MOST put bigger idle jets in to cover up the hole, but this makes no sense. This is because it richens up ALL OF PROGRESSION (to too rich), just to fix a lean hole right at the end. The proper solution is to make the mains come on earlier. That's why I recommend to do some extended driving on progression ONLY (Main stacks removed), to get a feel for the progression. Change jets as needed to get the lean cruise you desire (which is NOT 13:1). Then you put in a "too big" main jet, so that when the mains come in you see it on the A/F or 5-gas, because it swings way rich (it's very obvious). Change airs to get the transition (lean hole) to just disappear. Start with a small air jet, as the lean hole will be biggest and most apparent. As you go bigger on the airs, the mains come in earlier and earlier. You stop with the air jets tuning once the transition has NO lean hole. Then you change the main from the one that's too rich, to the one that's just right. DONE. If you can't get main tip in correct with air jet tuning, you have to mess with the emulsions, which sometimes requires emulsion modification (it's easy), not just changing them. Float level also changes when the mains come in, and these are not properly adjusted out of the box, you MUST do this. I have done a lot of weber/dellorto tuning, and can simply say that 65s are too big for IDAs, UNLESS you have installed a much larger than "normal" idle air, like a 135+ (stock is 120), because what matters in the progression circuit is the ratio of idle fuel to idle air. You can use a 50 or even a 45 idle fuel if you have a small idle air, like an 80, to maintain the ratio. This is not easily adjustable on IDFs or DRLAs because they have a fixed orifice, but IDAs it's adjustable and tunable, which USUALLY means enthusiasts screw it up because they don't know what they are doing. But my point is that if you have 48IDAs with 37mm venturis and change to 40 or 42mm, the idle jet tuning will not be affected AT ALL. You WILL have to change the mains and airs, since the mains will come in at a later time with the larger venturis, since the signal is weakened. So air jet tuning will have to be done to keep the mains coming in at the right time. This is why the size of the venturi changes the size of the air jet needed, the bigger the venturi the bigger the air jet. That's why 28mm venturis use smaller airs than 32-36mm venturis with the SAME F11 tube and same 45mm Aux Venturi.
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Post by Zed on Mar 14, 2018 20:29:34 GMT
One more thing, you must disconnect you pump jets when sizing your jets, leaving them working will confuse the issue. By doing that, when it's all wrapped up, you should find you barely need them.
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Eoin
Full Member
Posts: 101
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Post by Eoin on Mar 14, 2018 20:37:12 GMT
Of course, get FI and timing you can map and everything is an independent variable and much easier to set up to work right, whatever the load / revs.
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Post by Zed on Mar 14, 2018 21:13:53 GMT
Of course, get FI and timing you can map and everything is an independent variable and much easier to set up to work right, whatever the load / revs. I can't be arsed and Dellortos are things of beauty that I love very much. If I wanted pure performance yes, but it's a bslance of engineering and style for me. More mpg and snappier response will do me just fine. The engine is strangled to give heaps of torque anyway.
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Post by VW Toast on Mar 15, 2018 15:57:45 GMT
Holy mindfuck Zedman !!!!
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Post by Zed on Mar 15, 2018 16:43:34 GMT
Holy mindfuck Zedman !!!! Indeed. My afr kit arrived today. Now I need someone to weld the fitting to the exhaust and also need to extend the cable. Long cable price takes the piss, it's just 7 core 20swg wire. A towbar multicore will probably suffice.I may even solder the connections!
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Post by paradox1001 on Mar 15, 2018 17:37:04 GMT
Holy mindfuck Zedman !!!! I read the whole thread on the samba over a couple of days I kept having to stop for a while as it certainly takes some getting through. I do like threads that I learn from like that though. I’ll be following along with zed aswell as I’ve got a set of kadrons to go on my engine some time in the future When it comes to jetting them I think I’d be better of doing it myself this way. Rolling road time doesent come cheap.
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Post by paulcalf on Mar 15, 2018 18:11:10 GMT
Can't believe you lot didn't know all of that already.
Simple stuff!
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