Is it a good idea to put one of those larger oil-sump deals on your bus? It sounds like a really good idea, but is there some technical reasons that it would be harmful?
I've never seen a deep sump that didn't leak, apparently because the sump-plate studs -- even when replaced with longer units -- were never meant to carry such a load.
Reduced ground clearance, while never a problem on the drag strip, can cost you an engine in daily driving. I've seen several crankcases with chunks knocked out of them as a result of hitting something with the attached (and quickly detached) deep sump. I've also seen a couple of engines lost when the oil pick-up extension came adrift, started sucking air.
With a filled deep-sump, the oil takes forever to warm-up. And of course you have to keep the thing filled if you want your dip-stick to work :-) Drag-racing, we ran the engine with the minimum of oil, pouring in fresh for each run. It never showed up on the dip-stick because the dip-stick does not extend into the deep sump.
We used to call these things the 'Poor Man's Dry Sump'. Getting the liquid oil out of the crankcase gave us extra rpm, always important when you're trying to catch a clock. For roundy-round, rallys and road courses, we had a better results -- and less expense -- using a windage tray and fabricating extenders for the push-rod tubes. Running at speed, we thought the deeper sump would keep the oil from pooling-up out in the head... and maybe it did, for a few seconds. Fact is, running at speed the extra capacity of the deep sump doesn't mean squat -- we just ended up with an extra quart of oil in the outside head. Live and learn :-)
I thought the added surface area of the deeply finned (and properly fabricated sumps, such as the one Gene Berg made) would result in cooler oil temps. It didn't. The oil took longer to come up to normal operating temperature but once there, it was about as hot as before. Apparently the oil cooler is about twenty times as effective at cooling the oil as any form of sump --- you'd need about five times the surface area of the typical deep-sump before you saw an appreciable drop in your engine's oil temp. There's bound to be some variation here. I'm talking about using a deep-sump in California. Veedubers in Finland probably swear by the things :-)
All of the guys who claimed miraculously low oil temps after bolting on a deep-sump usually had chromed valve covers, chromed push-rod tubes, no thermostat and so on -- they were already running near the red-line before they bolted the thing on -- and most of their claims were based on only a few minutes of run-time -- the extra oil hadn't even warmed up yet.
Deep sumps are suicide off-pavement... or on-pavement for that matter, if you have to negotiate the occasional rough alley or railroad track.
Deep sumps tend to get in the way when you need to drop your engine, forcing you to raise the vehicle higher (bugs) to clear the rear apron and to use a different scooter (buses).
Finally, most of the deep sumps I've seen were very poorly made, the exception being the ones Gene Berg used to sell (I've not seen his most recent offering but I understand it's aluminum. It used to be magnesium and beautifully made, too.) The deep sumps sold locally are bubble-packed crap, cast in Taiwan and have casting inclusions and lots of CASTING SAND RESIDUE. (Someone on the Type2 List... [Thom?] ran into this problem.) It would be suicide to bolt such a thing on an engine.
The bottom line? Deep sumps first appeared on the drag strip. Kiddies bolt them on because they can and because they look kewl and because all the tits & ass VW magazines say it's the thing to do. I ran them on the strip but found them impractical on the road, sought other -- more effective -- solutions.
Your engine, your decision.
-------------------------------
Want to increase your oil capacity? Add a full-flow oil filtration system. The big FRAM PH-8A canister holds nearly a quart of oil, the hoses about half a pint.
-Bob Hoover
-1995
Wednesday, November 29, 2006
VW - Oil Contaminantss
.
All engines provide some form of crankcase ventilation, normally drawing air in through a filter and exhausting it by means of a road draft tube or engine vacuum. On older American cars the inlet filter was in the oil filler cap and periodically replacing the cap -- and the filter it contained -- was a normal maintenance item. In the Volkswagen, air is drawn in around the fan pulley, exhausted to the air breather. There is no filter.
When building a Volkswagen engine, to insure dependable operation under all conditions the nose of the engine is machined to accept a shaft seal that fits around the hub of the fan pulley, the hub being modified to provide a smooth sealing surface. A filtered air inlet is provided elsewhere on the engine, typically on one of the valve covers. The filter is located on the firewall, plumbed to the engine with hose. The better breather filters provide for moisture trapping. The normal outlet is unchanged. The seal is commonly called a sand seal since it is a virtual necessity when running off pavement.
Without such a seal, whatever is in the air will be drawn into your engine. Even when running a full flow oil filter, it's wise to replace your oil periodically to get rid of chemical contaminants picked up from the air being drawn through the crankcase.
-Bob Hoover
-1995
All engines provide some form of crankcase ventilation, normally drawing air in through a filter and exhausting it by means of a road draft tube or engine vacuum. On older American cars the inlet filter was in the oil filler cap and periodically replacing the cap -- and the filter it contained -- was a normal maintenance item. In the Volkswagen, air is drawn in around the fan pulley, exhausted to the air breather. There is no filter.
When building a Volkswagen engine, to insure dependable operation under all conditions the nose of the engine is machined to accept a shaft seal that fits around the hub of the fan pulley, the hub being modified to provide a smooth sealing surface. A filtered air inlet is provided elsewhere on the engine, typically on one of the valve covers. The filter is located on the firewall, plumbed to the engine with hose. The better breather filters provide for moisture trapping. The normal outlet is unchanged. The seal is commonly called a sand seal since it is a virtual necessity when running off pavement.
Without such a seal, whatever is in the air will be drawn into your engine. Even when running a full flow oil filter, it's wise to replace your oil periodically to get rid of chemical contaminants picked up from the air being drawn through the crankcase.
-Bob Hoover
-1995
VW - The By-Pass Solenoid Trick
St. Muir and the By-Pass Solenoid, or "Soul y noid? We don' need no stee-king solenoid!"
This one really gets me hot under the collar, first because it ain't a by-pass-anything, and second because the usual method, using an old Ford starter solenoid a la St. Muir is dumber than hell, partly because it ain't a solenoid at all but a contactor, and finally because you just don't need a starter contactor for this particular job.
The problem is that Volkswagen feeds their starter solenoid 12vdc by way of China. They run the juice all the way up to the front of the vehicle, through the starter switch which isn't all that reliable to begin with, then all the way back to the solenoid -- which is where the juice started its journey to begin with.
By the time those 12 volts have marched up front, squeezed through the switch terminals and hiked all the way back to the solenoid about of half of them are dead and the others have blisters. They jump inside the solenoid, put their electronic shoulders to the wheel but find they're played out by the trip. If the solenoid moves at all it does so sluggishly, often not strongly enough to close the contactor terminals that provide juice to the starter motor.
The fix is to keep those 12 volts from wasting their time and energy on that useless hike by putting in a relay. That's what that Ford contactor is pretending to be. The joke is, the contactor uses almost as much juice as the VW solenoid! A wiser choice is a headlight or horn relay. Cheap, easy to find and easy to mount. Screw it to the fender well inside the engine compartment to help keep the terminals clean.
What the relay does is tell those 12 volts when to go to work on the solenoid. You wire your relay with the same wire originally used for the VW starter solenoid but you install new, heavier wires -- with a shorter run to the battery and solenoid -- from your relay. Since a headlight relay only needs an itty-bitty amount of power to pick or transfer, the original wiring provides more than enough energy despite its long run. And since your new, heavier wiring provides a shorter, neater, cleaner, prettier, healthier and politically more correct run between the battery and the VW starter solenoid, it fires right up every time.
This isn't a new problem. In fact, Volkswagen came out with a fix for it years ago. Their solution? A simply relay packaged as a completely wired kit, including instructions. The part number was something like VK-1 and you could buy it from any dealer for about two bucks.
I understand Gene Berg started selling Ford contactors because he got tired of trying to explain to St. Muir deciples that St. John didn't know very much about elektrissity. I know a whole bunch about elektrissity and I'm still alive, even though I use a headlight relay to pick my solenoid and a horn relay to turn on my back-up light and an itty-bitty microampere relay out of a short-wave radio to tell my external cooling fan when to turn on, although a Ford contactor would have done the job -- sorta -- in each and every case and would have, if St. Muir had thought of back-up lights and cooling fans. ("Back-up lights! We don' need no steeeking back-up lights!")
Sermonette
Cold weather brings home the problem of the voltage drop in the long wiring runs common to a Volkswagen bus. If you want reliable starts and brighter headlights you need to know more about heavier gauge main buss wiring and the use of relays. You are the mechanic-in-charge of your vehicle. Sometimes that calls for you to be an electrician as well.
-Bob
-1996
Ed. Note: I've heard Gene Berg Ent. now offers the original VW relay instead of a Ford contactor. Check their catalog.
This one really gets me hot under the collar, first because it ain't a by-pass-anything, and second because the usual method, using an old Ford starter solenoid a la St. Muir is dumber than hell, partly because it ain't a solenoid at all but a contactor, and finally because you just don't need a starter contactor for this particular job.
The problem is that Volkswagen feeds their starter solenoid 12vdc by way of China. They run the juice all the way up to the front of the vehicle, through the starter switch which isn't all that reliable to begin with, then all the way back to the solenoid -- which is where the juice started its journey to begin with.
By the time those 12 volts have marched up front, squeezed through the switch terminals and hiked all the way back to the solenoid about of half of them are dead and the others have blisters. They jump inside the solenoid, put their electronic shoulders to the wheel but find they're played out by the trip. If the solenoid moves at all it does so sluggishly, often not strongly enough to close the contactor terminals that provide juice to the starter motor.
The fix is to keep those 12 volts from wasting their time and energy on that useless hike by putting in a relay. That's what that Ford contactor is pretending to be. The joke is, the contactor uses almost as much juice as the VW solenoid! A wiser choice is a headlight or horn relay. Cheap, easy to find and easy to mount. Screw it to the fender well inside the engine compartment to help keep the terminals clean.
What the relay does is tell those 12 volts when to go to work on the solenoid. You wire your relay with the same wire originally used for the VW starter solenoid but you install new, heavier wires -- with a shorter run to the battery and solenoid -- from your relay. Since a headlight relay only needs an itty-bitty amount of power to pick or transfer, the original wiring provides more than enough energy despite its long run. And since your new, heavier wiring provides a shorter, neater, cleaner, prettier, healthier and politically more correct run between the battery and the VW starter solenoid, it fires right up every time.
This isn't a new problem. In fact, Volkswagen came out with a fix for it years ago. Their solution? A simply relay packaged as a completely wired kit, including instructions. The part number was something like VK-1 and you could buy it from any dealer for about two bucks.
I understand Gene Berg started selling Ford contactors because he got tired of trying to explain to St. Muir deciples that St. John didn't know very much about elektrissity. I know a whole bunch about elektrissity and I'm still alive, even though I use a headlight relay to pick my solenoid and a horn relay to turn on my back-up light and an itty-bitty microampere relay out of a short-wave radio to tell my external cooling fan when to turn on, although a Ford contactor would have done the job -- sorta -- in each and every case and would have, if St. Muir had thought of back-up lights and cooling fans. ("Back-up lights! We don' need no steeeking back-up lights!")
Sermonette
Cold weather brings home the problem of the voltage drop in the long wiring runs common to a Volkswagen bus. If you want reliable starts and brighter headlights you need to know more about heavier gauge main buss wiring and the use of relays. You are the mechanic-in-charge of your vehicle. Sometimes that calls for you to be an electrician as well.
-Bob
-1996
Ed. Note: I've heard Gene Berg Ent. now offers the original VW relay instead of a Ford contactor. Check their catalog.
VW - Volkswagen Ignition System
Early VW's used an ignition system based on the Kettering patents from the 1920's, in which the battery voltage was stepped up to several thousand volts through the use of a transformer, the thing we call the coil. But transformers only work when the voltage is changing. (Alternating current 'changes' 120 times a second (ie, 60 cycles) so transformers work just fine.) To use a step-up transformer in a car you'll need something to cause the voltage to change. Just turning it on and off will work. Henry Ford used a magnetic-reed oscillator, a kind of vibrating switch. Boss Kettering (he ended up running General Motors) had the genius to connect the ignition transformer through a mechanical switch driven by the engine. Opening and closing the switch provided the changing voltage needed to make the transformer work. The switch of course is the ignition points.
How the Coil Works
The reason a transformer works lies in the physical properties of electrical current. When a current flows through a conductor it generates a magnetic field around the conductor. Conversely, when a conductor is moved through a magnetic field, a voltage will be induced in the conductor. A transformer takes advantage of those principles of inductance by winding one coil over the top of another. At low frequencies you can focus or concentrate the magnetic field by winding the coils around an iron core. And since you can't move the coils relative to one another, the changing voltage in the primary winding serves as the 'movement' needed to induce a voltage in the secondary winding. And as you've probably guessed, the voltage in either winding is proportional to the number of coils in the inductor; if there are more turns in the secondary, its induced voltage will be higher than the voltage in the primary. But there's no such thing as a free lunch, the total amount of energy remains the same. If you pump in 120 watts (that is, ten amps at twelve volts) to develop, say, 30,000 volts in the secondary (about what you need to jump the gap of a spark plug under worst-case conditions) the amperage can't be more than about three-thousandths of an amp (.003). Actually, things never work out that neatly in reality because there are losses in the coil's iron core, etc.
Why The Capacitor is Needed
Those same principles of inductance create a kind of paradox, because when you stop feeding juice to the coil, that is, when the points open and the magnetic field collapses, inducing the 30,000 volt current in the secondary, it also induces a current in the primary as well! It's not very much because there are only a few windings in the primary, but it's enough to jump a small air-gap, such as the one between the just-opening points in the distributor. That tiny spark is enough to erode metal away from the points and if there is any oily vapor inside the distributor, any oil on the points will become carburized; you'll 'burn' the points.
To keep your points from burning as they open and close, you'll need to provide something to absorb that spike of counter-current, something more attractive, electrically speaking, than the air-gap between the points. That's a job for a capacitor. To the counter-current, the capacitor looks like a black hole, an attractive one. The spike of current dives right in. And the points don't burn.
The points have a tough job, switching up to eight amps of current many times per second at highway speed. Indeed, as engine speed increases the efficiency of your ignition system decreases, thanks to heating problems and fundamental electrical laws. This declining efficiency has a serious effect on your spark voltage and results in poor high-speed performance, incomplete combustion and a host of other ills.
But us humans are tricky rascals. To see how tricky, read the articles covering electronic ignition systems.
-Bob Hoover
-1995
(Ed. Note: This article deliberately ignores more sophisticated resonant frequency explanations of the coil-condenser relationship as being unnecessary with regard to vehicle maintenance.)
VW - Let There Be Light!
.
So there you are, purring across the desert in the cool of the night and there's a funny sound from the engine room and the purr gets a little quieter and that damned red light comes on. You just lost the fan belt.
No big deal; you've got a spare. And the lug wrench is the same size as the fan pulley nut and you've even got a screwdriver to keep the pulley from turning while you take off the nut. But the flashlight has those Civil War surplus batteries and gives you one last good-bye glow like a tiny red worm and dies. You're fresh outta light.
Doing it in the Dark
If you got a bug, changing your fan belt in the dark isn't too bad. You've got your flashers going of course, and they throw a little light into the engine room. But let's hope you don't drop anything, you'll be pushing your bug back and forth, playing patty-cake with the ground hoping all those stories you've heard about night-time desert creepy-crawlies aren't true. (They are.)
But you have a neat little trouble light in your kit. It's your static timing light. Connect it up, change the fan belt and you're on your way.
Sure is nice to have the right tools when you need them, eh? What? You say it's back at the house? I don't think that's a very good idea, do you? Why don't you keep it in the door pocket with your fuses.
Whatdaya mean, 'What fusess?'
Reality Check
Most good cars provide a light under the hood, another in the trunk, one in the glove box, a couple under the dash, one by the ash tray... Good cars provide good lighting; they assume you'll drive at night now and then. Cheap cars don't do that, assuming you'll stay home glued to the tube when the sun goes down. The Volkswagen is a cheap car (or usta be!). The only lights you get are the ones required by law.
My 1973 Datsun pickup has a little light under the hood, positioned so you can check the oil. It's a very smart kind of light. (Only after praising the Datsun people for their thoughtfulness did I learn that such a light was a legal requirement in some countries where 1973 Datsuns were sold.)
Letting in the Light
I've got four lights in the engine compartment of my 1965 bus, two in the engine compartments of the Ghia and sedan, two on the baja.
On the Ghia and bugs I put one of the lights on a bracket pop-riveted to the blower housing, positioned so as to illuminate the distributor and that side of the carb. The other light is mounted on the base of the generator tower so I can see the dip stick and the timing marks on the pulley.
The light fixtures I used are high quality new-surplus items manufactured by Grimes, the aviation people. They are solid nickel-plated brass jobbies that cost a couple of bucks each. Pretty small; Grimes calls them 'panel lights'. They use the commonly available #1816 12vdc lamp. (That's the GE number; it cross-references to others that will fit.) The lamp is small, about like a flashlight bulb. If you want more light than it provides there is a halogen replacement.
I got the light fixtures from American Science & Surplus (3605 Howard St., Skokie, IL 60076. (708) 982-0870 ) The part number for the lights is #10572. Cost was about two bucks.
(Ed. Note: About two weeks after I posted this in 1995 people reported the fixture I used was no longer available. Which doesn't change the purpose nor value of this message: You need light in order to do useful work, and other fixtures are available. Nowadays [2006] I'd recommend using LED's rather than incandescent lamps.)
Screwing Them On (or up, your choice)
When mounting the lights on the engines I made up brackets from sheet steel or aluminum. On the bus, I used aluminum angle stock and mounted the lights on the overhead of the engine compartment. In all cases I gave the lights their own fused circuit, installing the fuse and the light switch on a small panel tucked up out of the way. The panel is aluminum, shaped to fit, installed with either screws or pop-rivets.
Since I was running an auxiliary circuit I figured I might as well run a good one, going directly to the battery with a 10 gauge wire. This is easily done in the bus and Ghia, where the battery is in the engine compartment. On the '68 sedan I snuck the wire under the body, fastening it securely at several points and protected inside of black polyethylene tubing, the stuff they use for drip irrigation systems. On the '67 baja I pulled the wire through the body channel with the other wiring.
Why such a big wire? For the cigarette lighter. Or rather, for the cigarette lighter socket. (I smoke a pipe; kinda hard to get going with a cigarette lighter.) The socket is fused with a 25 amp circuit breaker. I use it to power a 12vdc air compressor or a trouble light or a camping lantern or a ham radio or... or whatever you might want to plug into a cigarette lighter socket. I guess the thing would even work as a cigarette lighter, although mine comes with a big red plastic plug to keep out the dirt. (Baja-dust is special stuff, capable of penetrating six inches of steel plate.)
(Ed. Note: The cigarette lighter socket proved its worth on the run to Inuvik when it was used to power my 12v soldering iron with which I repaired a cracked plastic recovery tank on a water-cooled Vanagon.)
No one ever notices the auxiliary lights, unless they see them on at night. The lamps are hooded; the light shines where you're looking, not in your eyes, and on the bus each of the four fixtures is behind a rib or strut. The wiring is wrapped in looms and the looms secured with aircraft-type wiring clamps, secured to the chassis with stainless steel sheet metal screws. The switches and panels are out of the way; you have to look for them to see them. No chrome, no colorful curly wires; everything is built for the long haul and so far, has worked exactly as intended.
Sermonette
I plan to keep my Volkswagens until I fall apart. Until that happens I'm going to keep doing what I like to do, which is to head for places well off the beaten track. The lights and the auxiliary power outlet make things safer and more convenient, and enhance the usefulness of my vehicles. Installing them took a bit of work but if properly done it's a one-time thing, good for the life of the vehicle. Such things are worthy improvements for early Volkswagens.
-Bob Hoover
-1995
So there you are, purring across the desert in the cool of the night and there's a funny sound from the engine room and the purr gets a little quieter and that damned red light comes on. You just lost the fan belt.
No big deal; you've got a spare. And the lug wrench is the same size as the fan pulley nut and you've even got a screwdriver to keep the pulley from turning while you take off the nut. But the flashlight has those Civil War surplus batteries and gives you one last good-bye glow like a tiny red worm and dies. You're fresh outta light.
Doing it in the Dark
If you got a bug, changing your fan belt in the dark isn't too bad. You've got your flashers going of course, and they throw a little light into the engine room. But let's hope you don't drop anything, you'll be pushing your bug back and forth, playing patty-cake with the ground hoping all those stories you've heard about night-time desert creepy-crawlies aren't true. (They are.)
But you have a neat little trouble light in your kit. It's your static timing light. Connect it up, change the fan belt and you're on your way.
Sure is nice to have the right tools when you need them, eh? What? You say it's back at the house? I don't think that's a very good idea, do you? Why don't you keep it in the door pocket with your fuses.
Whatdaya mean, 'What fusess?'
Reality Check
Most good cars provide a light under the hood, another in the trunk, one in the glove box, a couple under the dash, one by the ash tray... Good cars provide good lighting; they assume you'll drive at night now and then. Cheap cars don't do that, assuming you'll stay home glued to the tube when the sun goes down. The Volkswagen is a cheap car (or usta be!). The only lights you get are the ones required by law.
My 1973 Datsun pickup has a little light under the hood, positioned so you can check the oil. It's a very smart kind of light. (Only after praising the Datsun people for their thoughtfulness did I learn that such a light was a legal requirement in some countries where 1973 Datsuns were sold.)
Letting in the Light
I've got four lights in the engine compartment of my 1965 bus, two in the engine compartments of the Ghia and sedan, two on the baja.
On the Ghia and bugs I put one of the lights on a bracket pop-riveted to the blower housing, positioned so as to illuminate the distributor and that side of the carb. The other light is mounted on the base of the generator tower so I can see the dip stick and the timing marks on the pulley.
The light fixtures I used are high quality new-surplus items manufactured by Grimes, the aviation people. They are solid nickel-plated brass jobbies that cost a couple of bucks each. Pretty small; Grimes calls them 'panel lights'. They use the commonly available #1816 12vdc lamp. (That's the GE number; it cross-references to others that will fit.) The lamp is small, about like a flashlight bulb. If you want more light than it provides there is a halogen replacement.
I got the light fixtures from American Science & Surplus (3605 Howard St., Skokie, IL 60076. (708) 982-0870 ) The part number for the lights is #10572. Cost was about two bucks.
(Ed. Note: About two weeks after I posted this in 1995 people reported the fixture I used was no longer available. Which doesn't change the purpose nor value of this message: You need light in order to do useful work, and other fixtures are available. Nowadays [2006] I'd recommend using LED's rather than incandescent lamps.)
Screwing Them On (or up, your choice)
When mounting the lights on the engines I made up brackets from sheet steel or aluminum. On the bus, I used aluminum angle stock and mounted the lights on the overhead of the engine compartment. In all cases I gave the lights their own fused circuit, installing the fuse and the light switch on a small panel tucked up out of the way. The panel is aluminum, shaped to fit, installed with either screws or pop-rivets.
Since I was running an auxiliary circuit I figured I might as well run a good one, going directly to the battery with a 10 gauge wire. This is easily done in the bus and Ghia, where the battery is in the engine compartment. On the '68 sedan I snuck the wire under the body, fastening it securely at several points and protected inside of black polyethylene tubing, the stuff they use for drip irrigation systems. On the '67 baja I pulled the wire through the body channel with the other wiring.
Why such a big wire? For the cigarette lighter. Or rather, for the cigarette lighter socket. (I smoke a pipe; kinda hard to get going with a cigarette lighter.) The socket is fused with a 25 amp circuit breaker. I use it to power a 12vdc air compressor or a trouble light or a camping lantern or a ham radio or... or whatever you might want to plug into a cigarette lighter socket. I guess the thing would even work as a cigarette lighter, although mine comes with a big red plastic plug to keep out the dirt. (Baja-dust is special stuff, capable of penetrating six inches of steel plate.)
(Ed. Note: The cigarette lighter socket proved its worth on the run to Inuvik when it was used to power my 12v soldering iron with which I repaired a cracked plastic recovery tank on a water-cooled Vanagon.)
No one ever notices the auxiliary lights, unless they see them on at night. The lamps are hooded; the light shines where you're looking, not in your eyes, and on the bus each of the four fixtures is behind a rib or strut. The wiring is wrapped in looms and the looms secured with aircraft-type wiring clamps, secured to the chassis with stainless steel sheet metal screws. The switches and panels are out of the way; you have to look for them to see them. No chrome, no colorful curly wires; everything is built for the long haul and so far, has worked exactly as intended.
Sermonette
I plan to keep my Volkswagens until I fall apart. Until that happens I'm going to keep doing what I like to do, which is to head for places well off the beaten track. The lights and the auxiliary power outlet make things safer and more convenient, and enhance the usefulness of my vehicles. Installing them took a bit of work but if properly done it's a one-time thing, good for the life of the vehicle. Such things are worthy improvements for early Volkswagens.
-Bob Hoover
-1995
AV - Flow-Bench vs Reality
--- In AirVW@yahoogroups.com, CaptonZap asked:
> Have you ever heard of a flow bench that pulses? -----------------------------------------------------
Some fluidics applications -- gates and the like -- are tested using a flow-bench that emulates real-life situations. But I've never heard of such being applied to an automotive flow-bench.
---------------------------------------------------
>I don't know if the difference in > flow would warrant the trouble to make a pulser for the bench. Any thoughts?
--------------------------------------------------
The original purpose of the flow bench for head work was to provide a measure of merit rather than quantified data. But it wasn't long before we saw flow-bench figures converted into purely notional units of cubic feet per minute (what you actually measure is the pressure differential) and used to sell junk to the Kiddie Trade. The same sort of 'bigger is better' hype is used to sell cams, valves, cranks, jugs and so-forth.
After my second tour in Vietnam I built a rather elaborate flow-bench. Over a period of about seven years the most valuable thing it taught me was how little I knew. And I'm not just talking fluid dyamics :-)
As you've already guessed, measuring the flow of air can only provide a measure of merit -- this head flows more (or less) than that head. But fuel-air does not behave the same as air alone. Smoke or other benign suspended colloid, in the proper ratio with air, provides a more realistic test -- and often produces results significantly different than when using air alone.
The idea that a simple measure of merit is good enough for selecting the 'best' heads is only valid for dragsters, where fame & fortune is based on a run-time of six to ten seconds. As soon as you add durability to the equation -- and measure it in hundreds of hours rather than tens of seconds -- you may as well throw away that huge pile of heads you've been working with and start all over. If you do that, don't be surprised if your best efforts looks remarkably similar to the heads off existing aircraft engines :-)
An even tougher test is to discover that after a thousand hours of work you've managed to confirm what Sir Harry Ricardo defined in his book... in 1920.
---------------------------------------
Lemme give you an example of why the flow-rate thing is mostly hype. Let's use a 2180cc engine having a volumetric efficiency of 100% (yeah, I know -- impossible -- but work with me here). 2180cc times 0.06102 equals 133.0236 cubic inches. But were talking a four-cylinder Otto cycle engine so the actual displacement per revolution is just half that or about 66.5 cubic inches per rotation of the crankshaft.
Now pick an rpm, something seriously silly for an airplane, such as 3200... because you want to make the prop horribly inefficient and wear out the engine quick like a bunny. Or whatever :-)
66.5 cubic inches times 3200 rpm is 212,800 cubic inches. Divide that by 1728 and you've got 123 cubic feet per minute.
That's a totally fallacious figure because at that rpm your VE won't be anywhere near 100% but lets use it as a bench mark... or even round it up to 125 cfm just to make the figuring a tad easier.
Keep in mind, that's the also flow through the carb for the entire engine -- all four jugs.
Now take a look at all those trick heads they sell to the kiddies. Huge valves... which run hot and seal worse than smaller valves... but a nice match for the huge ports and cut-away valve guide boss... that gives you flow rates per cylinder as high as 350 cfm. Wow! Gotta be good, eh?
If one jug can flow 350cfm, with four-cylinder Otto cycle engine that means it has the potential to pump 700 cubic feet of air per minute! Gosh! Is that great, or what?
Did anyone notice that the maximum amount of air the engine can use is only 125 cfm? Apparently not, because hi-flow heads sell like hot-cakes :-)
Wanna build an engine for a replicar like the Beck 550 Spyder? Then you want something that can spin seven grand and hit one-forty on the straight-aways. That's when you go for hi-flow heads, six pound flywheel, titanium valves and four 40mm Dellortos.
But not to sling a prop.
The airframe dictates the prop and the prop dictates the engine. That's when you discover that the actual flow-rate of your engine is something less than 90cfm and that even Single-Port heads can give you that. Of course, you put your stock SP heads on the flow-bench and clean up the ports and swirl-polish the valves and attend to a host of other minor chores and come up with a marked improvement in your volumetric efficiency for nothin more than a bit of labor.
Why the interest in volumetric efficiency? Because in a normally aspirated engine peak VE tends to coencide with peak torque. And despite what the hucksters keep yelling, with a fixed-pitched prop mounted directly to the crankshaft the key factor in producing thrust is how much torque you have available at that particular rpm.
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Which prolly isn't the answer you expected, although you did ask for 'any thoughts' :-)
-R.S.Hoover
> Have you ever heard of a flow bench that pulses? -----------------------------------------------------
Some fluidics applications -- gates and the like -- are tested using a flow-bench that emulates real-life situations. But I've never heard of such being applied to an automotive flow-bench.
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>I don't know if the difference in > flow would warrant the trouble to make a pulser for the bench. Any thoughts?
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The original purpose of the flow bench for head work was to provide a measure of merit rather than quantified data. But it wasn't long before we saw flow-bench figures converted into purely notional units of cubic feet per minute (what you actually measure is the pressure differential) and used to sell junk to the Kiddie Trade. The same sort of 'bigger is better' hype is used to sell cams, valves, cranks, jugs and so-forth.
After my second tour in Vietnam I built a rather elaborate flow-bench. Over a period of about seven years the most valuable thing it taught me was how little I knew. And I'm not just talking fluid dyamics :-)
As you've already guessed, measuring the flow of air can only provide a measure of merit -- this head flows more (or less) than that head. But fuel-air does not behave the same as air alone. Smoke or other benign suspended colloid, in the proper ratio with air, provides a more realistic test -- and often produces results significantly different than when using air alone.
The idea that a simple measure of merit is good enough for selecting the 'best' heads is only valid for dragsters, where fame & fortune is based on a run-time of six to ten seconds. As soon as you add durability to the equation -- and measure it in hundreds of hours rather than tens of seconds -- you may as well throw away that huge pile of heads you've been working with and start all over. If you do that, don't be surprised if your best efforts looks remarkably similar to the heads off existing aircraft engines :-)
An even tougher test is to discover that after a thousand hours of work you've managed to confirm what Sir Harry Ricardo defined in his book... in 1920.
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Lemme give you an example of why the flow-rate thing is mostly hype. Let's use a 2180cc engine having a volumetric efficiency of 100% (yeah, I know -- impossible -- but work with me here). 2180cc times 0.06102 equals 133.0236 cubic inches. But were talking a four-cylinder Otto cycle engine so the actual displacement per revolution is just half that or about 66.5 cubic inches per rotation of the crankshaft.
Now pick an rpm, something seriously silly for an airplane, such as 3200... because you want to make the prop horribly inefficient and wear out the engine quick like a bunny. Or whatever :-)
66.5 cubic inches times 3200 rpm is 212,800 cubic inches. Divide that by 1728 and you've got 123 cubic feet per minute.
That's a totally fallacious figure because at that rpm your VE won't be anywhere near 100% but lets use it as a bench mark... or even round it up to 125 cfm just to make the figuring a tad easier.
Keep in mind, that's the also flow through the carb for the entire engine -- all four jugs.
Now take a look at all those trick heads they sell to the kiddies. Huge valves... which run hot and seal worse than smaller valves... but a nice match for the huge ports and cut-away valve guide boss... that gives you flow rates per cylinder as high as 350 cfm. Wow! Gotta be good, eh?
If one jug can flow 350cfm, with four-cylinder Otto cycle engine that means it has the potential to pump 700 cubic feet of air per minute! Gosh! Is that great, or what?
Did anyone notice that the maximum amount of air the engine can use is only 125 cfm? Apparently not, because hi-flow heads sell like hot-cakes :-)
Wanna build an engine for a replicar like the Beck 550 Spyder? Then you want something that can spin seven grand and hit one-forty on the straight-aways. That's when you go for hi-flow heads, six pound flywheel, titanium valves and four 40mm Dellortos.
But not to sling a prop.
The airframe dictates the prop and the prop dictates the engine. That's when you discover that the actual flow-rate of your engine is something less than 90cfm and that even Single-Port heads can give you that. Of course, you put your stock SP heads on the flow-bench and clean up the ports and swirl-polish the valves and attend to a host of other minor chores and come up with a marked improvement in your volumetric efficiency for nothin more than a bit of labor.
Why the interest in volumetric efficiency? Because in a normally aspirated engine peak VE tends to coencide with peak torque. And despite what the hucksters keep yelling, with a fixed-pitched prop mounted directly to the crankshaft the key factor in producing thrust is how much torque you have available at that particular rpm.
-----------------------------------
Which prolly isn't the answer you expected, although you did ask for 'any thoughts' :-)
-R.S.Hoover