Turbo vs. supercharger (splitted thread)

[beepbeep]

This was something a tought about posting in Marks thead but decided it will be better to keep it out of it,

Pete: we had this sort of discussions before so I wont go down in details too much but even if you nail few correct facts in your post you're wrong in many of them.

First of all: Laws of nature are still in charge. Compressed air is always going to be heated up according to ideal gas law, (even more so if using less efficient compressor-desings) so superchargers need intercoolers at least as much as turbos do. Superchargers (especially positive-displacement style Roots blowers) are inherently less efficient than turbochergers.

Second is that superchargers need as tight and fine tolerances as turbos do, but are physically bigger which makes them more expensive to manufacture and less reliable.

Then we come to real show-stopper when it comes to wider use of superchargers in production cars: Supercharger boost is always a function of revs, it's never linear and sometimes pretty steep (centrifugal turbochargers) which makes them hard to gear right. You either gear them high which means that they produce lot's of boost down low, but it also means that they'll just wisp around lot of hot air at high revs where all that excess boost will have to be reduced (effectivly robbing lot's of engine HP) or you gear them low so they reach correct boost at higher RPM but then you get torque that grows with revs and very peaky engine. You can soften this by using electric clutches and recirculating valves but it gets very messy and expensive.

All this is bypassed in turbo-installation with invention of wastegate. Turbo can work with full efficiency and boost controled by re-routing excess gases around the turbine and trough the wastegate.

All this is a reason you won't find but a handful of manufactors using superchargers in their nische-cars, compared to literally hundreds of manufacturers using turbochargers.

So yes, it's kind cool to have a supercharger but it's not superior in any way bar boost response.

P.S.

You should make a difference between boost-treshold and turbo-lag. Just having physically big turbo doesn't mean you must have high boost-treshold in case you have high engine-volume.

Actually, i bet Mark engine would be more efficient if he used one properly sized turbo than two small ones (if you read Garretts catalogs you'll find out that this is actually true, bigger turbos are more efficient) but he would have more turbo-lag. And turbo lag has nothing to do with boost treshold (which denotates revs at which exhaust flow is large enough to support positive boost pressure). With other words, big turbo can start boosting from 3000 RPM in slow acceleration but provide almost no boost at all in fast acceleraton in 1:st gear (common problem of 930).

Cheers!

[1fastredsc]

Also to add, most large turbo, or the turbine which is what's associated with there efficiency is usually due to large AR ratio turbine. A large turbine will not restrict the exhaust flow as much during high HP loads and therefore keep the heads cooler and create more HP (of course the compressor must match this high cfm characteristic). But of course for some people lag is a big deal, so the smaller more restricive turbine is usually chosen for production vehicles (a car like the 930 is an exception) to give them a more responsive feel in street driving. A good example would be that new dodge neon, picks up boost just shy of 2k rpm but starts loosing power dramatically after 5k rpm.
BTW beep, what you wrote was fantastic but i sort of disagree with the part of using two smaller turbines as opposed to one large one. Technically, splitting the work load of a large turbine into to two is just dividing the same energy, so therefore there's no real gain or loss. Just having the turbines strapped to really short headers is the gain with a fat $$$ tag attached to it. And as long as the compressor's produce the same amount of cfm while still being efficient at the given pressure, then it's the same as having one large wheel. Unless you know something i don't, but that's how it was explained to me. This is also why you don't see four bangers having two turbos strapped to them no matter how big the displacement.

EDIT: One more thing too, beep is definitely right about the intercooler thing. Ask me how i know. I got the bright idea one time to put my hand on the supercharger on a carrera after taking it for a run. It was only running 6psi of boost, but i still burnt the hell out of my hand.

[beepbeep]

Originally posted by 1fastredsc

BTW beep, what you wrote was fantastic but i sort of disagree with the part of using two smaller turbines as opposed to one large one. Technically, splitting the work load of a large turbine into to two is just dividing the same energy, so therefore there's no real gain or loss. Just having the turbines strapped to really short headers is the gain with a fat $$$ tag attached to it. And as long as the compressor's produce the same amount of cfm while still being efficient at the given pressure, then it's the same as having one large wheel. Unless you know something i don't, but that's how it was explained to me. This is also why you don't see four bangers having two turbos strapped to them no matter how big the displacement.

Exhaust-flow wise, it's just splitting energy in two, but smaller turbos tend to have slightly higher parasitic losses than bigger ones. Differencies are not big (and can probably be ofsetted in this case by advantage of short-headers) but you should remember that you have two shafts spinning at 160 000 RPM instead of one slightly bigger shaft spinning at maybe 100 000 RPM. It's easier to make aerodynamicaly clean desings if they are physically biger. Also, plumbing gets little more complicated/heavy with twin installation but it's often worth to trade little drop in efficiency for better responce, especially with boxer-6 desing where headers would be too long for single installation.

P.S. You can compare efficiency of big jet engines versus small ones.

[1fastredsc]

I understand, although technically i don't think two spinning at 160k rpm would be like one large one spinning at 100k rpm (maybe exagerated) since they are splitting the work load of one (maybe i'm just dense and don't get it). But having two seperate rotating masses as opposed to one slightly larger one, i'd see the loss in that therefore killing some efficiency but not a lot i think. I also understand making better design's with larger blades since the margine of slight imperfection will go down as the blades get larger. Either way, I do prefer one large turbo design over the two smaller ones. I like lag, i'm no dragger, and i prefer to keep the heads cool. Plus imagine the kind of bill you'd have to replace the turbos, especially if they are garrett GT's, as opposed to just one turbo.

[Pete Pranger]

Goran,

Yeah, this kind of looks familiar. I wasn't exactly finished last time but I didn't want to bore you anymore. But since I got started again, I hope you don't mind if I continue.

DISCLAIMER I am not trying to say that turbos aren't a very viable choice when it comes to making power, I have had very good luck with them. I am just trying to support the supercharger side.

That being said, here goes:

1. Those damn laws of physics. Yes, you are correct, if you take 2 volumes of air and compress them by the same amount, the temp will increase equally. BUT, if you compress one of those gasses right next to a turbine that is running about 1000 or more degrees F you will get some radiant and conduction heating of the air. This is what I mean about a turbo running hotter. I can put my hand on a centrifugugal blower while it is running and my roots blowers run about as hot as my intake manifold (maybe 150 degrees F ?).

2. As far as efficiency, I think we may be on the wrong page here. When I talk about efficiency, I am referring to the losses between what it "should" produce and what it "does" produce. Since a centrifugal blower is virtually identical in compressor design, to a turbo, I don't see how it can be less efficient. Now, a roots blower does have some losses in it due to its design (rotor tip at housing wall) but with the addition of teflon strips (ie. top fuel blowers but the teflon wears out in 6 passes you can tell in the loss of boost). For the street application, the rotors never make contact with the wall so as long as they stay clean they they see no wear. So, a roots blower may see some bypass in the housing, but that is easily accounted for with rotor speed (just turn it faster). I don't know if that's what you meant by efficiency or not.

3. As far as being less reliable, I just don't buy it. A roots blower has 4 bearings in an oil bath and it turns at roughly engine speed. There really isn't anything to wear out. A centr. supercharger is as reliable as a turbo without the heat. and the after shut down spool down. Do you idle your engine for a while after running it hard or do you have one of those after shut down oilers? You don't have to do that with a belt driven supercharger. I have changed my fair share of worn out turbos, but the only time I ever took a blower off of a detroit diesel was after the motor quit. And then, I took the blower and put it on a car. Stone axe reliability in my experience. Bigger? The belt driven ones are. More expensive to produce? Not in my experiece (but then I've never actually produced any.......). I can get a complete belt driven supercharger for 1200$ and a centrifugal supercharger for 2200$ and that's where the turbo kits start.

4. As far as production cars, you win this one with turbos hands down (especially european cars). I only know of a handful of supercharged cars made in the US and they are all roots blown, no centr. superchargers to be seen. That's the aftermarket and it's thriving. As far a linear production of power, it's linear with a belt driven supercharger (or gear driven for that matter), because each revolution of the compressor rotor displaces the same amount of air and since the compressor is mechanically linked to the engine, it will produce the same amount of air at each rpm level regardless. It has to. The turbo isn't spinning at the same speed at the same time ever really hence the output fluctuates.

5. Ahhh, the wastegate. Nope never seen one on a belt driven supercharger. I wonder if you could put one on and run say 12 lbs of boost from 2500 - 6500 rpm. I don't think it's ever been done, we (the roots community) just build the motor to eat full boost. I wonder though.......

6. Superior? I wasn't trying to imply superiority, just a different way to get to point B.

7. As far as single vs twin, you gotta admit twin turbos look cool. That's a valid argument isn't it?

And the controversy continues.........................

Thanks, Goran this was fun. Feel free to respond at your leisure.

Pete

[beepbeep]

Originally posted by 1fastredsc
I understand, although technically i don't think two spinning at 160k rpm would be like one large one spinning at 100k rpm (maybe exagerated) since they are splitting the work load of one (maybe i'm just dense and don't get it).

It seems obvious but it's not ;-). With twin turbos you have two shafts, two shafts generate more drag trough friction (BB turbos) or adhesive friction (oil film/plane bearing) then single one. Also, smaller turbos spin faster and frictional losses grow (non-linearly) with rotation speed.
[/quote]

But having two seperate rotating masses as opposed to one slightly larger one, i'd see the loss in that therefore killing some efficiency but not a lot i think.

Actually, no. As long as turbo is spinning at constant speed it doesn't matter if impeller i light or heavy...all energy will be used to overcome bearing-friction and compress air. But if you do a fast 1:st gear start, smaller turbo will pick up (and loose) speed faster and store less energy.

I also understand making better design's with larger blades since the margine of slight imperfection will go down as the blades get larger. Either way, I do prefer one large turbo design over the two smaller ones. I like lag, i'm no dragger, and i prefer to keep the heads cool. Plus imagine the kind of bill you'd have to replace the turbos, especially if they are garrett GT's, as opposed to just one turbo.

Well there are some really effective Anti Lag Systems (ALS) which can keep full boost @ "idle" by keeping throttle open, fuel flowing and delaying the ignition to make gas burn in the headers...keeping the turbo spinning. They sound pretty severe, and are generally non-streetable.

This is how it sounds and looks like on street car (if you are WRC buff you'll know what i'm talking about ):
http://hem.passagen.se/emilfrom/VR6TT-2.WMV

P.S. Talking about GT turbos, they aren't too expensive if you happend to find one from a lorry...a tad big maybe I hope this will work:
http://project911.luminasweden.com/log_images/IMG_1546.JPG
(that's 4 inch exhaust from turbo )

[beepbeep]

Originally posted by Pete Pranger
Goran,

Yeah, this kind of looks familiar. I wasn't exactly finished last time but I didn't want to bore you anymore. But since I got started again, I hope you don't mind if I continue.

On the contrary, i hope i will learn something. It's nice to have technical discussions.

DISCLAIMER I am not trying to say that turbos aren't a very viable choice when it comes to making power, I have had very good luck with them. I am just trying to support the supercharger side.

That being said, here goes:

1. Those damn laws of physics. Yes, you are correct, if you take 2 volumes of air and compress them by the same amount, the temp will increase equally.

Yupp, PV = nRT

BUT, if you compress one of those gasses right next to a turbine that is running about 1000 or more degrees F you will get some radiant and conduction heating of the air. This is what I mean about a turbo running hotter.

Unfortunately, that is not the case. There is very little heat transfer taking place trough a turbo shaft. Remember, there is impeller on one side and compressor on the other one, with oil- (and often watercooled) bearing housing a.k.a. CHRA. Impeller is made of aluminium-alloy and turbine of iconel, shaft is pretty thin and can be up to two inches long, passing trough (most often) plain bearing and is being lubricated by oil film. There is not much conduction being done that way.

Of course, turbos do run hot...upwards 900 deg. C, but on a hot side. If you compare turbocharger to a engine (which is not so bad considering both are basically air-pumps) compressor housing would be intake-plenum and turbine-housing would be headers. And you wouldn't put your hand on a header, would you?

I can put my hand on a centrifugugal blower while it is running and my roots blowers run about as hot as my intake manifold (maybe 150 degrees F ?).

Of course, it's hot beacuse it compresses the air and temperatures will be equalized between supercharger and intake by constant airflow.

2. As far as efficiency, I think we may be on the wrong page here. When I talk about efficiency, I am referring to the losses between what it "should" produce and what it "does" produce. Since a centrifugal blower is virtually identical in compressor design, to a turbo, I don't see how it can be less efficient.

Both right and wrong. True, centrifugal blower uses exactly same compressor-design as turbos (which are more effective than their positive displacement counterparts), but they are also mechanically driven and also need high operating speed that turbochargers need. This means it needs high speed gearbox and you know what happends with parasitic gear losses when rotation-speeds rise (those operate upwards 60000 RPM's). Also, it suffers from one bad trait compared to positive-displacement superchargers, it's flow vs. speed ratio is highly non-linear (it's almost logarithmic) leading to those kind of problems i was speeking about: either peaky engines or even more parasitic losses due to need for boost-limiting by either recirculation, pop-valve or magnetic clutch.

Now, a roots blower does have some losses in it due to its design (rotor tip at housing wall) but with the addition of teflon strips (ie. top fuel blowers but the teflon wears out in 6 passes you can tell in the loss of boost). For the street application, the rotors never make contact with the wall so as long as they stay clean they they see no wear. So, a roots blower may see some bypass in the housing, but that is easily accounted for with rotor speed (just turn it faster). I don't know if that's what you meant by efficiency or not.
3. As far as being less reliable, I just don't buy it. A roots blower has 4 bearings in an oil bath and it turns at roughly engine speed. There really isn't anything to wear out. A centr. supercharger is as reliable as a turbo without the heat.

Roots is much more linear than centrifugal one, but it too suffers from:

1. Need for very small tolerance seals, which drive the price upwards. Total area for those seals is much bigger than for turbochargers. Seals also tend to wear with age...maybe no super-fast but definately faster than for turbo that only have one high-speed oil-film lubricated bearing that basically never wears except at startup where blower has four bearings and much bigger sealing-area.

2. Compressor-design itself on Roots blower is inferior. They just use more energy to compress given amount of air, and they heat it up more by doing it. Ideal compressor would not heat up the air more than PV=nRT allows...big turbochargers have efficiency of over 80%.

3. Energy is being taken from the crankshaft...trough the belt...not good for efficienly either

4. It's very seldom to see some sort of clutch on compressors...so they need air-valves to limit the pressure. Imagine what happends when you lift the trottle at 6000 RPM: you'll have mechanically-connected blower still trying to shove all that air into closed throttle. It won't fit so valve will open and allow excess air to be whipped around-and-around the housing, being heated up during the process and buring extra gasoline. Turbo doesn't have this problem...it just opens the wastegate to limit the boost and excess gas flows around the turbo. (turbo does have another problem, it's stored mechanical energy , which trys to shove air into closed throttle...that's solved with BOV-valve which is somewhat similar to design being used in superchargers and not to be mixed up with wastegate)

5. It delivers pulsating stream of air.

and the after shut down spool down. Do you idle your engine for a while after running it hard or do you have one of those after shut down oilers? You don't have to do that with a belt driven supercharger. I have changed my fair share of worn out turbos, but the only time I ever took a blower off of a detroit diesel was after the motor quit. And then, I took the blower and put it on a car. Stone axe reliability in my experience. Bigger? The belt driven ones are.

Non-watercooled turbos last longer if cooled down by idling after hard driving. Watercooled (most modern are) aren't so picky.

More expensive to produce? Not in my experiece (but then I've never actually produced any.......). I can get a complete belt driven supercharger for 1200$ and a centrifugal supercharger for 2200$ and that's where the turbo kits start.

Well you still need pulley, belt, intercooler and extra fuel when you supercharge your engine, don't you? There are good efficient turbochargers to be had under 700$...how's that for comparision?

4. As far as production cars, you win this one with turbos hands down (especially european cars). I only know of a handful of supercharged cars made in the US and they are all roots blown, no centr. superchargers to be seen. That's the aftermarket and it's thriving. As far a linear production of power, it's linear with a belt driven supercharger (or gear driven for that matter), because each revolution of the compressor rotor displaces the same amount of air and since the compressor is mechanically linked to the engine, it will produce the same amount of air at each rpm level regardless. It has to. The turbo isn't spinning at the same speed at the same time ever really hence the output fluctuates.

Well there is one reasonably good supercharger desing called "Lysholm"-supercharger. It's something between roots and screw-type and gives pretty good efficiency and sooth flow of air, but it's pricey. Our swedish supercar maker called "Koenigsegg" uses centrifugal supercharger with intercooler on (Ford?) 32-valve V8. It produces heaps of horsepower on top but they got bashed for very peaky engine = bad acceleration for all that power. I think Mercedes uses some sort of screw-design...anyone knows better? I understand why centrifugal is popular...it's really easy to fit.

5. Ahhh, the wastegate. Nope never seen one on a belt driven supercharger. I wonder if you could put one on and run say 12 lbs of boost from 2500 - 6500 rpm. I don't think it's ever been done, we (the roots community) just build the motor to eat full boost. I wonder though.......

Please don't mix wastegate with BOV (blow off valve). Wastegate re-routes exhaust gases and has nothing to do with air-side. On the other hand, a variant of BOV is used on superchagers (as far as i know), to limit compressor-surge on part throttle by shorting the airpath and recirculating air around supercharger.
[/quote]

6. Superior? I wasn't trying to imply superiority, just a different way to get to point B.

They do have instant pick-up-and-go response that turbos lack though ;-)

[/quote]
7. As far as single vs twin, you gotta admit twin turbos look cool. That's a valid argument isn't it?
[quote]

Yupp...if i had 6 cylinders, i would go for twin-turbo, no doubt

And the controversy continues.........................

Thanks, Goran this was fun. Feel free to respond at your leisure.

Pete

It does! Thanx! I sure did respond!

[FasTommy]

How about the best of both worlds!!! sorry I don't have any details on how well this set up worked.. but definetly looks kool.

[1fastredsc]

You guys just really inspired me to finish my ME degree.
BTW, i feel stupid that i wasn't thinking in terms of friction, that makes the whole twin vs. single thing much more clear.
ALS that you describe sounds familiar. I believe when i had someone explain the tec 2 to me for the first time, they told me that sometimes non-sequential ignition was beneficial in turbo motors due to the second spark during exhaust valve openings. But i actually think lag is what makes turbo cars more drivable in the street, boost gets annoying when it trys to creep up while your in bumper traffic behind grandma. But when you do want it, it's just a simple down shift, then ludicris speed pays you a visit

[Pete Pranger]

Okay, just a few rebuttal points:

I never put a temp guage on the output air from a turbo or a beltdriven supercharger, so I will take your word on the heat transfer deal. And I occaisionally touch my headers, I have the scars to prove it.

I think we were thinking different things with the efficiency issue. I will agree that the mechanical losses are greater on belt driven blowers. I think BDS tried to build an electric test stand for their roots blowers and they would have needed a motot of like 100hp. On the other hand, (although I've never tried it) you can theoretically take the belt off of a motor running with a roots blower and it will work without the belt. Might be BS, but I don't know.

Okay a roots blower design is inferior to todays design. It was designed almost 100 years ago as an air pump. BTW I run my blowers "loose", they aren't sealed at all. I like at least 0.020'' between my rotors and case, nothing to wear out here. And with the throttle blades being "above" the blower, no extra air if the throttle is slammed shut. I like the newer "screw" type blowers (outlawed in the NHRA of course) very efficient and expensive. But even the roots blowers have a helical twist to the rotors (three lobe) that limits the pulses you got with the older two lobe straight cut rotors.

Water cooled turbos? Learn something new everyday I guess. Is this a factory thing or have I just lived under a rock for a while? Seriously, this is news (good news though) to me.

As far as the prices I listed, they were for the complete kit, pulleys belts everything. I imagine that I could put a turbo motor together for a little cash outlay (and a lot of work), I intend on trying very soon. The last blower motor I built used a 6-71 from a dump truck that I put together complete for under a grand - carbs to crank pulley. But I wouldn't recommend that route to just anybody.

Okay, you got me with the wastegate (and I thought you weren't paying attention ). Nope, it wouldn't (couldn't by design) work on a mechanically driven supercharger, guess thats why I've never seen one. I use blow off valves, but primarily to save the blower from a backfire.

Okay, here's one reason to go supercharger over turbo. I like carbs, and carbs don't like to be pressurized (unless of course you put them in a box and pressurize the box.............my next plan), and carbs fit better on blowers than they do on turbos . Oh, and the 3 inch drive belt sounds sick.

Pete

[beepbeep]

Originally posted by Pete Pranger
Okay, just a few rebuttal points:

I never put a temp guage on the output air from a turbo or a beltdriven supercharger, so I will take your word on the heat transfer deal. And I occaisionally touch my headers, I have the scars to prove it.

Take a look yourself:



2 is oil-cooling/lubrication galleries, 5 is water-cooling mantle, 1 are plain bearings, 4 is axial bearing, 3 oil drain.

Not much heat going trough that shaft...

I think we were thinking different things with the efficiency issue. I will agree that the mechanical losses are greater on belt driven blowers. I think BDS tried to build an electric test stand for their roots blowers and they would have needed a motot of like 100hp. On the other hand, (although I've never tried it) you can theoretically take the belt off of a motor running with a roots blower and it will work without the belt. Might be BS, but I don't know.

Of course it will work...it's like attaching a fan in front of vacuum-cleaner. The fan will turn beacuse of air-flow but it won't provide any power...om the contrary, it will rob engine of power.

Okay a roots blower design is inferior to todays design. It was designed almost 100 years ago as an air pump.

It was actually first invented by Roots brothers in 1859 as a waterpump, but it found it's use as simple way of deep mine ventilation.

BTW I run my blowers "loose", they aren't sealed at all. I like at least 0.020'' between my rotors and case, nothing to wear out here.

The better sealing the less blowtrough and the better efficiency.

And with the throttle blades being "above" the blower, no extra air if the throttle is slammed shut.

Yupp, but it also means that blower "sucks vacuum" at half-throttle which means raised pumping losses.

I like the newer "screw" type blowers (outlawed in the NHRA of course) very efficient and expensive. But even the roots blowers have a helical twist to the rotors (three lobe) that limits the pulses you got with the older two lobe straight cut rotors.

Yupp, NHRA usually outlaws everything that is technologically better...that's why they are still using pushrods and magnetos.
Lysholm screw-type compressor was invented in 1936 by Alf Lysholm of Svenska Rotor Maskiner that still hold patent for it. It's much better design than Roots, here's animation of how it works:
http://www.lysholm.se/howitworks_video.asp

It's marketed in U.S. as "Whipple Supercharger" under patent from SRM AB:

Water cooled turbos? Learn something new everyday I guess. Is this a factory thing or have I just lived under a rock for a while? Seriously, this is news (good news though) to me.

It's fairly old news as it's been around for at least 15 years...they just made new chanells in the bearing housing and attached coolant-pipes to it to keep it from overheating. It's developed to counteract cooked-bearing problem when people just shut off their red-hot turbos and oil cooked on the bearings, ruining them.

Here's picture of old Garrett T25 removed from our motor, you can see it has both oil- and water inputs:

As far as the prices I listed, they were for the complete kit, pulleys belts everything. I imagine that I could put a turbo motor together for a little cash outlay (and a lot of work), I intend on trying very soon. The last blower motor I built used a 6-71 from a dump truck that I put together complete for under a grand - carbs to crank pulley. But I wouldn't recommend that route to just anybody.

If you are handy with TIG and can fabricate some tubing it's not that expensive at all. Luckily, most are not :-) Intercooler is optional, but so it is for superchargers as well. Our setup is going to cost <1500$ for GT40 turbocharger and custom stainless headers.

Okay, you got me with the wastegate (and I thought you weren't paying attention ). Nope, it wouldn't (couldn't by design) work on a mechanically driven supercharger, guess thats why I've never seen one. I use blow off valves, but primarily to save the blower from a backfire.

Okay, here's one reason to go supercharger over turbo. I like carbs, and carbs don't like to be pressurized (unless of course you put them in a box and pressurize the box.............my next plan), and carbs fit better on blowers than they do on turbos . Oh, and the 3 inch drive belt sounds sick.
Pete

Carbs? As in carburators? Yuck! I wouldn't touch them with a six foot pole! They belong in 911T or something... On the other hand, it's probably easier to tune them if they are "suckers" (turbo don't like "sucking" air/fuel mixture too much). I never touched a carb in my entire life though so i don't know for sure... :-) Not intending to either :-)

[Pete Pranger]

You never touched a carb??????????Wow. I must be getting really old. I love my carbs, FI is okay for imports I guess (did I just say that? ), but for me hanging a 4 barrel or two now thats fun. I get called a dinosaur once in a while but I'm usually looking at them in my rear-view.

Okay, now repeat after me:

Pushrods are good
Carburetors are good
Magnetos are good...............for lawn mowers and chainsaws. Back in the 80s (early 80s but whos counting)magnetos were really the rage on "fast"street cars and I fell for it. Car didn't start worth a damn (I think I needed in impulse coupling) and I never got shocked setting the timing so much in my life. I got over that real quick.

Thanks for the cutaways, the only time I get to see the insides like that is when something bad happens..........

I am planning on running twin turbos on a 350 I am building, when I get a little closer if you don't mind, I would like to run a few combos by you for your opinion (apparently I haven't kept up with the times....), and if you ever put a big blower motor together, feel free to do the same.

Pete

[1fastredsc]

Well i wasn't about to scan all like 20 pages on the subject of turbos working with carbs but i figured i'd show some highlights since beep doesn't like them.

[beepbeep]

Originally posted by Pete Pranger
You never touched a carb??????????Wow. I must be getting really old. I love my carbs, FI is okay for imports I guess (did I just say that? ), but for me hanging a 4 barrel or two now thats fun. I get called a dinosaur once in a while but I'm usually looking at them in my rear-view.

Okay, now repeat after me:

Pushrods are good
Carburetors are good
Magnetos are good...............for lawn mowers and chainsaws. Back in the 80s (early 80s but whos counting)magnetos were really the rage on "fast"street cars and I fell for it. Car didn't start worth a damn (I think I needed in impulse coupling) and I never got shocked setting the timing so much in my life. I got over that real quick.

Thanks for the cutaways, the only time I get to see the insides like that is when something bad happens..........

I am planning on running twin turbos on a 350 I am building, when I get a little closer if you don't mind, I would like to run a few combos by you for your opinion (apparently I haven't kept up with the times....), and if you ever put a big blower motor together, feel free to do the same.

Pete

Hehehe...I'm relativly young (27) so I never had time to fool around with carbs, just watched my dad do it. If you start putting together twin turbo 350, i'll be glad to help you to my full extent .

Actually i just have a approximate idea of how magnetos work. It's something with spinning magnet inducing current in coil and firing pulses, right? I guess there is no advance-mechanism in them either? Interesting :-)

Injection is nothing bad, it's almost always better than carbs, even CIS...(wait, did i just say that? Gotta wash my mouth!). It's little more complicated than carbs but no rocket science in any way. I prefere EFI and ignition...no dizzys, magnetos and stuff...just one coil per plug and let the computer fire them when needed, with as much advance as needed. Add som adaptive knock- and boost control for good measure and you have very driveable car. :-)


Cheers!

/Goran

[GenX Porsche]

By no way am I as much of an expert as anyone on this post but I thought I would throw in an idea. Porsche moved to the concept of have two different sized turbos to produce the effect of having pull throughout the whole RPM range and aleviating the concept of having turbo lag. I currently have a post, in the engine rebuilding section, on the subject of building a early turbo engine with a twin turbo setup as I described. Just thought I would throw that concept in and watch it get beat around. So...have at it.
David

[beepbeep]

Originally posted by GenX Porsche
By no way am I as much of an expert as anyone on this post but I thought I would throw in an idea. Porsche moved to the concept of have two different sized turbos to produce the effect of having pull throughout the whole RPM range and aleviating the concept of having turbo lag. I currently have a post, in the engine rebuilding section, on the subject of building a early turbo engine with a twin turbo setup as I described. Just thought I would throw that concept in and watch it get beat around. So...have at it.
David

Well there is nothing to beat around. Porsche tried that concept on only one car: the 959. It gave pretty good response and power but nothing out of extraordinary. Japanese tried it too, on turbocharger RX7 rotary...it worked but all that plumbing was a tad cumbersome.

I hope you are aware that there are no cars being made with sequential-turbo setups anymore and that current 996TT's (as all other Porsche TT's bar 959) are just parallel designs. There were just two such desings: 959 and RX7.

There was one much more interessting concept: Rally Groupe B Lancia Delta S4 sucesfully used both turbo and supercharger, supercharger was used for low RPM response, then turbocharger took over and boosted at high revs. Engine delivered around 600hp as far as i remember, not bad considering it was less than 1.8L in size.



Also, there is swedish made Opel manta with both turbo and supercharger, but less sophisticated phasing system:
http://www.hilmersson-racing.com
.. it's interesting concept,but most of the time just not worth the hassle.

[Pete Pranger]

David,

I think what you are referring to is "sequential turbocharging" where you have a small turbo for the lower rpm ops and a larger turbo for the upper r's. I think I read about Nissan(?) developing a system about 10 years ago but I think turbo design has come far enough to make this unnecessary. I don't know its current state. I do remember it being a plumbing nightmare with some loss in efficiency. Kind of like the problems with multiple inline superchargers (like the above picture) I would speculate that reversion would be a problem along with the smaller turbo becoming a restriction. An actual twin setup doesn't fall prey to these problems because the turbos are seperated.

As far as the magneto thing, there are all kinds of setups, some with advance and others without, depending on application. If you operate in a very narrow RPM band (drag racing and aircraft) then you really don't need one. A lot of drag racers lock out the advance mechanism on a regular distributor to avoid high RPM fluctuations in timing. The only problem with that is starting the engine with such an advanced curve, you have to twist the dist before start up and retime when running (fun right?). The biggest problem with a magneto is the low energy produced by the very slow spinning magneto (hence the impulse coupling in airplanes, it uses a spring assembly to "snap" the rotor up to speed).

Pete

[JP911]

GenX-
You're referring to a sequential turbo setup as used on the 959. It's plumbed like a single turbo but with one small turbo for low-end power and one large turbo for upper end grunt. This is a great setup, but very challenging to engineer. As far as I know, Porsche has not used this setup on any other production cars. The 993 turbo and now the 996 turbos use two same-size turbos, one for each bank of cylinders.