NathanRX7

I want to get a compressor housing and attach a pulley to the shaft where the exhaust housing was. The main pulley on the motor is 6", and I could hopefully get a 1" pulley for the turbo, which would spin it at speeds ranging from 6000 RPM at idle to 48000 RPM at redline. What type of compressor would I need to make this work? I can get a good turbo from a Volvo or Subaru at the local junkyard for about $30. I'm not sure what these specific turbos spin at, but I am only looking to get about 4-5 PSI out of them. If that's not fast enough, I could setup another pulley between the turbo and the main pulley on the motor that had a 1" pulley on the side that hooks to the motor, and a 6" pulley on the side going to the turbo, so it would be a dual belt system to spin the turbo, giving me a range of 12000 RPM to 96000 RPM on the turbo. I am planning on mounting the turbo somehow to the P/S bracket because the pump in no longer there.

After looking at a bunch of centrifugal superchargers, it appears that all they are is a pulley driven turbo compressor. I know that some of them use gears internally to increase their speed, but this is not an option for me as I do not have a machine shop at my disposal or the money to just buy a kit.

I know all of this may be very silly, but please have an open mind and do not flat out tell me it will not work.

Tell me how I can make it work.

mazdaspeed7

Turbo compressor heating the air more than a supercharger? I think not. They are exactly the same design. The supercharger does have a cooler intake charge than a turbo, but partly because it isnt right next to the exhaust, and because it doesnt spin as close to its maximum speed as a turbo does. Turbos have a wastegate to keep them from overspinning, so they can be used close to the maximum speed more often, while a supercharger is designed to spin well below its maximum speed so if you do overrev the engine, you wont kill the supercharger too.

It is an interesting idea. Definately not conventional, but it could very well work. You also need to think about mounting it securely, and making sure the belts are lined up perfectly. That will be a pain to get perfect. An intercooler would be nice, but I dont think its necessary as long as you keep the boost low. You might want to get the turbo/supercharger working before you start worrying about an intercooler though. Its just another thing to complicate something that isnt going to be easy in the first place.

You also need to think about your fuel system. Also, you will need to use a TII MAF sensor from a car of the same series engine. The n/a MAF sensor might be fine, but then again, it is maxed out at 210-220 bhp.

Icemark

Hey, a belt driven turbo is a Super charger... not a turbo anymore.

You would need the compressor impeller running at around 8000+ RPM based on the size of the impeller wheel, to produce light boost at 3000 engine RPM for most turbos.

I personally don't think you are going to move enough air to make a difference. Go get a Lynsome <sp?> compressor off of a wrecked Millennia S instead. Same basic supercharger idea, with a proper sized compressor impeller. Betcha there are even Mazda brackets on that Millennia that might work with modification.

NathanRX7

This is what I like to hear!

Icemark: How sure are you of that 8000 RPM number being anywhere close to how fast it needs to spin? I have read many different places about turbos spinning at least 50,000 RPM. Don't get me wrong, 8000 RPM is definitely the number I want to hear, but is it accurate? Can anyone confirm or give me an idea of what type of turbo compressor I would need for this? Tell me it's one off of an old Volvo or Subaru! Thanks.

SoloRacer

I thought you were getting an FD in November? Why not just wait the month and save the money for mods to that car? I've been all the way through modifying a T2 and know that adding boost is not a band-aid job to get more power. It requires a fully thought out approach to avoid catastrophy. Here is what I have done to my T2 to get ready for more boost - and remember my car was a turbo to begin with so adding one to your N/A will be even more challenging:

3 mm apex seals
EGT & Boost Gauge
Wolf 3D
Malpassi Rising Rate Fuel Pressure Regulator
FD Fuel Pump
Larger secondary injectors
Racing Beat turbo back exhaust
RP Turbo Clutch

Now when I go to a T04 turbo I have to add the following to the list:

Upgrade the FD fuel pump
Add an additional injector rail
Front Mount Intercooler
HKS T04 Manifold
Tial External Wastegate

Now how much do think all this is going to set you back? Sure you may not need to buy everything here but you will need to address the fuel and ignition problem and that is going to cost money. You may not want to hear this but you are better off selling your car and buying a T2 if you want 6 lbs of boost in an FC. I strongly encourage you to read books like Corkey Bell's Maximum Boost and learn more about what is needed.

Guys, this guy is the same one who dreamed of adding a leaf blower to get 5 psi of boost. He does not seem interested in learning anything about even the basics of turbocharging. He is looking for the holy grail aka. "the $70 turbo charger that gives you 100 hp and is completely safe for your engine". If it were possible and made sense it would already be done somewhere. Trust me when I'm saying that these dreams are not rocket science - many have had the same ideas before I am sure. I'm not saying that adding a pully driven turbo (which is basically a really bastardized supercharger like was mentioned earlier) will not work. With ample time and money you probably could get it going. What I am saying is that it makes no sense from either a money point of view, time point of view or any point of view. And this guy seems more concerned about money. So from a MONEY point of view you are better off to pay the extra $2500 and upgrade your car to a T2. Then not only do you get the turbo power you also get the LSD, upgraded brakes, bigger rims, etc.

SoloRacer

One last thing before I go. Do you know anything at all about selecting a turbo for your car? Do you know that different compressors and housing sizes affect you performance? Do you know that just grabbing any turbo off of any car (Volvo, Subaru, etc.) is not the wisest thing in the world because they might not flow enough for our engines and you would end up with minimal gain if any? Why do you think most guys who upgrade their turbo's spend so much time selecting one with the correct specs?

So make sure you get a T2 turbo because at least you know that it was picked by the factory for our cars. Be prepared to give up $500 of your hard earned coin for a good one. Let the money pit begin!

skibum9199

Keep up the good thoughts Nate!

NathanRX7

SoloRacer,

I believe you are making quite a few assumptions about me.

We're buying an FD in November, but my FC is the car I will be driving until at least this summer, as the FD will be in Florida, and I'm at Chico State in California.

I know that adding boost in not a "band-aid job," and I have been in the process of thinking this out for the past couple weeks. You have done many things to your T2 to get it ready for more boost.

I have talked to quite a few people who know from experience or otherwise that the stock N/A fuel system can handle moderate levels of boost (talk to SuperchargedRex), and that is all that I plan to do. 4-5 PSI of boost is very minimal compared to a 1990 T2's stock boost, and you are talking about adding more boost to yours. I'm not talking about more boost, just a little.

Many people have told me I should sell my car and buy a T2, but there are a few problems with this. My car is worth more to me than I could ever sell it for because it's a salvage title after some jackass hit my car while it was parked and totalled it according to the insurance company.

Please do address me in my own thread as "this is the guy who...". I know perfectly well who I am.

I "dreamed" of a leaf blower, I told people what I was thinking of doing, and I researched the possibility of it working. I found that it would not work, and now I am on to other options. I like to learn things for myself. People told me the leaf blower would not work, and keeping that in mind, I researched it myself to find that it wouldn't.

I am very interested in learning all about turbocharging. That's why I started this thread by asking what type of compressor I might need to do this. It would be nice if I could use one from a junkyard, but if I can't, fine. I am here asking for advice.

No, I am not looking for any holy grail, nor am I looking to gain 100 HP. I am simply looking to get around paying for the supercharger companies' research and fabrication costs.

It is possible and it does make since, but most people would rather buy something that another company has put time, money, and effort into, and it bolts up with no fabrication needed. I am perfectly willing to do some of my own fabrication if I can save $3500 in the process.

Also, my car already has the LSD and upgraded brakes, and I like my 15" wheels.

Yes, I know different turbos affect performance, and no, I do not know anything about selecting the proper turbo for this application, and that is exactly why I started this thread. I am asking anyone who knows:

What type of compressor they think would be good for this application.

Thanks for anyone that is actually trying to help me instead of telling me to quit wasting my time.

Icemark

That is for very large impeller, to start actually making boost. KEY word START. You might get (again depending on the impeller size) get a half a lb at that RPM, maybe if you are lucky a full lb with a very large impeller.

But you are trying to use something that was well engineered to work off of exhaust driven... Off of air pressure... not a belt.

Frankly I don't think my message must have been clear. You are wasting your time on this approach to boost.

If you want a belt driven forced air induction, and you don't have money and it sound like you like too tinker, try using a supercharger off of a Millennia, or old MR2.

SoloRacer

I don't know if you will believe this or not but I am trying to help you. Sometimes telling a guy straight out that he is wasting his time is the right answer. Many shops will tell you to do this and do that and buy this and buy that and before you know it you have wasted a pile of cash and time on something you should have taken the time to learn about and talk to people who have been there and done that. Believe it or not 5 lbs of boost is a fair amount of boost. Believe it or not the stock 87 T2 only makes around 7 lbs of boost stock and hits fuel cut over 8. So what you are talking about is not "a minor amount of boost". You still don't understand anything about turbos. It is about FLOW not BOOST. A big turbo will FLOW more air at 5 lbs than a small turbo. I tried to explain that to you before but you weren't interested in listening.

Unless I'm mistaken November is only 2 months away. It will take you longer than that to get the problems sorted out with this car if you go the turbocharging route - especially if you are going from scratch with a pully driven turbo instead of a tried and true kit.

If you want to keep your car for nostalgia purposes that's great. We need more people like you. But remember there are limitations to what can realistically be expected and some decisions are not that smart to make. I own a 1953 Kaiser Fraser Manhatten that was restored by my late uncle. I enjoy driving the car even though it isn't the latest and the greatest. Now let's say I'm not happy with the power it gives me and even though I'm getting a really hot car in two months I can't wait and want to hotrod this one in the meanwhile. But I don't understand the first thing about hotrodding....hell I don't even know what a camshaft is because I've been using rotaries all my life. But I'm not going to bother learning anything about them and just jump out and slap something on. Maybe a set of Chev 350 camshafts will work in my ****** Continental engine....so what if someone tells me they won't work. Maybe I'll just get them machined to fit. But what did I expect them to do anyway? I don't know because I don't understand how these things work. Gee it's been two months already and look at the money I wasted buying the camshafts, machining them, etc. But look my new car is here. Good thing because my old one runs like **** now. But now I have no money to modify the new car because I wasted it all screwing around with my old one. Maybe if I put a leaf blower on the first turbo of my new RX7.........and the cycle continues.

Of course that is an exaggeration but you get my point. Maybe you should enjoy your car for what it is instead of looking for the cheap fix. There are cheap fixes you can do (Chris Ng's TID mod for example is a great thing that works well because he UNDERSTANDS how things work) but radical things will cost you MONEY.

I wish someone would have gave me this advice before I spent $14,000 modifying my T2. I might have bought an FD instead.

SoloRacer

Nathan,

I just read your post again and you say you are not looking for 100 hp. How much of a power gain were you hoping to make? The reason I ask is that there are many modifications you can make to an N/A such as porting, etc that will give you nice power gains. These are things that have been proven to work well. Have you considered making any N/A mods? I'm sure there are plenty of guys who can give you good tips on what works. Usually the only time you turbocharge a car is when you want more power than the N/A mods will give you. N/A power usually fairly simple and gives great throttle response. Turbos on the other hand require more maintainence, more complexity and worse throttle response. Or is it all about being the cool guy on the street with the turbo'd car that is important to you? I'm not slamming you or anything as I can totally appreciate someone having a trick car. I'm just confused as to why all the interest in turbo's and superchargers for small power gains when there are other options available to either make more power or get more power to the wheels.

racerfoo

I've got AC on my car.....is there a way to move that so i could fit the turbo in its spot for the belt? and then hook the rest of the turbo up to IC and all that....?

SoloRacer

Jef,

Bitter *lol* Who me? I guess I am. By the time I get my T04 installed I will be into this car for more than what a nice FD would cost. I should also have over 400 hp but even then, knowing now what I should have known then, I probably still would have preffered to buy an FD. I just didn't know it would cost so much to build a 400 hp FC.

I respect your opinion as you have been here forever and are knowledgable. Having said that are you ready to remove the turbo from your exhaust system and "belt 'er up"? I mean you have the parts right?

Also, I think Mr Wankle had at least a basic, if not complete, understanding of how the internal combustion engine worked before designing the rotary. I bet if he didn't have that knowledge we would all be rotary deprived right now.

BLUE TII

iTrader: (9)

If I were to build my own centr. S/C I would find a big turbo out of a diesel rig so I wouldn't have to spin it so fast and then use an intermediate pulley as you said.
I don't understand how you can get a turbo to work with that is in good shape for cheaper than you can get a S/C from an OEM application. I don't recommend the Millenia S/C as it would boost way too much for an NA and is relatively rare, but surely there are others that would give you lower boost. Thunderbirds used a mini rootes blower that can be found cheap on e-bay (although it is low boost it was on a bigger engine so mabye too much boost) , MR2s have been mentioned, but I think the S/C one is rare too. I think some Toyota Previas had a little S/C as well that can be picked up cheap. Search on e-bay for some S/Cs and then research those you find. If you find what boost and what displacement their original applications were you can calculate what you might get on your engine. You could also pick up a used centr. S/C and work w/ it.
Have fun and don't blow up your engine. I think that is why some of us try to get you to use the tried and true NA mods, they are safe, they work, they are cheap. Good luck

NathanRX7

SoloRacer:

It's nothing about being the cool guy on the street with a turbo. There are lots of turbo cars here, and I don't even race on the street.

There are tried and true methods of making more N/A power, and I will do all of them that don't require me to remove and rebuild my engine, but that does not mean that that is the only way to modify an N/A. This is a project for me, and if I can get something like this to work inexpensively and reliably it will be worth sharing with others. I fully realize that I need to do quite a bit of research, and that this may take a lot of work, but I am prepared for it. If it doesn't or cannot work, I'm not out of a whole lot of money.

David88vert

If you are looking for a cheap hp boost, and aren't looking for 100hp, then throw a 50 shot of nitrous oxide on the car. That will add the oxygen that you need to mix with the fuel to increase power. Use a wet system. Here are two articles that you might find interesting.

http://www.holley.com/HiOctn/ProdLin...ysteminfo.html

How Turbos Work (or: The Closest Thing to a Free Lunch)

Before we start, we have to take a second to review a little grade 10 physics - The Ideal Gas Law. In short, gas temperature, pressure, and volume are all related. Compress a gas (reduce the volume) and pressure and temperature goes up. Let it expand, and temperature and pressure go down. Increase the temperature, and the pressure goes up (in an enclosed space) or the volume goes up (it expands). Finally, gases want to flow from a high pressure area to a low pressure area, and the greater the difference, the bigger the push. (Pop a balloon, little bang. Pop a welding O2 cylinder, big bang) OK, a 4 stroke engine produces work by expanding a gas in a confined space where the high pressures created can push against a piston. Furthermore, that gas is heated by the process of creating it (unlike a steam engine) so you get even higher pressures - and more power. Unfortunately, most of that heat (which is the same as energy) is dumped overboard in the exhaust before we get any chance to use it. It's just not in the cylinder long enough to transfer all that heat into mechanical energy, and it's not practical to make cylinders "tall" enough to extract every last bit of work from that hot expanding gas. So, what can we do about it? well, we can point the tailpipes out the back to try and get some thrust - except that aside from some very rare circumstances, the gas volume isn't high enough to get any worthwhile push. (A few older Indy Cars actually created a couple of pounds of thrust from their exhausts, but that's not enough to be really useful) OK, how about sticking some sort of auxiliary engine in the exhaust flow? Steam engines did this for years... Enter the turbocharger, a turbine fed by exhaust gasses, connected to a compressor via a shaft that compresses intake air into the engine. More air in the cylinder means more fuel can be burnt per power stroke, more burnt fuel means more hot gas, more hot gas means more power - and more boost too. This is the closest thing to a free lunch you'll find in engineering, because you're taking heat (energy) that would otherwise be wasted and getting usable work out of it, with almost no tradeoffs. You gain a little complexity, and added manufacturing costs, but there is no real performance hit from adding a turbo. "But doesn't the turbo increase exhaust backpressure?" Under boost conditions, no. Here's why: when the exhaust valve opens, the pressure inside the cylinder is much much higher than the pressure at the turbo inlet. That cylinder pressure "blows down" very quickly, but we're on the exhaust stroke - the cylinder volume is decreasing very rapidly, and from the Ideal Gas Law, that tends to keep the cylinder pressure higher than the turbo inlet pressure. Finally, when the exhaust stroke is nearly done, and the pressures are nearly equal, the intake valve opens, the intake pressure (we're under boost here!) "blows down" into the cylinder, and presto! we have a higher cylinder pressure again. (I'll discuss backpressure - I _hate_ that term, it's misleading - in greater detail in a later post) That's enough bandwidth for today.


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Alright, yesterday we determined that a turbo was a device that could be used to get useful work out of otherwise wasted energy, to day we'll discuss how that happens in more detail. It is a common misconception that the exhaust turbine half of a turbo is driven purely by the kinetic energy of the exhaust smacking into it (like holding a kid's tow pinwheel behind your tailpipe) While the kinetic energy of the exhaust flow does contribute to the work performed by the turbo, the vast majority of the energy transferred comes from a different source. Keep in mind the relationship between heat, volume, and pressure when we talk about gasses. High heat, high pressure, and low volume are all high energy states, low heat, low pressure, and large volumes are low energy states. So our exhaust pulse exits the cylinder at high temperature and high pressure. It gets merged with other exhaust pulses, and enters the turbine inlet - a very small space. At this point, we have very high pressure and very high heat, so our gas has a very high energy level. As it passes through the diffuser and into the turbine housing, it moves from a small space into a large one. Accordingly, it expands, cools, slows down, and dumps all that energy - into the turbine that we've so cleverly positioned in the housing so that as the gas expands, it pushes against the turbine blades, causing it to rotate. Presto! We've just recovered some energy from the heat of the exhaust, that otherwise would have been lost. This is a measurable effect: Stick an EGT upstream and downstream of the turbo, and you see a tremendous difference in temperature. So, in real world terms, what does this tell us? All else being equal, The amount of work that can be done across an exhaust turbine is determined by the pressure differential at the inlet and outlet_ (in english, raise the turbo inlet pressure, lower the outlet pressure, or both, and you make more power) Pressure is heat, heat is pressure. Raising the inlet pressure is possible, but tough. Lowering the outlet pressure is easy - just bolt on a bigger, free flowing exhaust. I've seen a couple of posts from people who added aftermarket exhausts, who report "my turbo spools up faster now" Well, that's because by lowering the outlet pressure, you increased the pressure differential, and now the exhaust gas can expand more, and do more work. That increased work pushes harder on your turbo, and it spools up faster. You should also see less boost drop at redline, because if an exhaust system is flow-limited, once you pass the flow limit of the system, any additional gasses you try and force through it only raise the outlet pressure. Higher outlet pressure, lower pressure differential, less work, less boost. [note that the compressor side comes into play here too - that's another post DG] That covers Turbine Theory. Tomorrow - the Compressor Side.


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Having covered what a turbo is, and how the exhaust turbine works, we now turn our attention to the compressor side of the turbo. (If you thought yesterday's post was a little verbose, just wait 'till you see this one If you can extract work from an expanding gas via a turbine, then it stands to reason that you can compress a gas by driving the turbine shaft with a power source. In other words, the compressor side is just the turbine side driven backwards. The exact same physical lays apply, just now in reverse: we take a low pressure, low temperature gas, do work on it with the compressor vanes, and get a high pressure, high temperature gas at the outlet. That temperature increase is unfortunate, and will cause us problems later on - and we'll come back to it in a bit. While the turbine and compressor sides of the turbo are essentially the same, they are _not_ mirror images of each other, and the reason why is due to the chemistry of combustion. A given volume of air will burn an exact amount of fuel, in a ratio of air:fuel about 14:1. The volume of exhaust produced is much greater than the volume of the air used to create it, and the resulting exhaust pressure is much higher than the boost pressure will ever be, so the wheel and housing designs are completely different. Which leads us to turbine/compressor design. Turbines are wonderful devices. They are light, and _very_ efficient, but they also tend to suffer from a limited RPM range. That is, a turbine/compressor is very efficient at a certain RPM/flow capacity, but if you vary the shaft RPM very much, the efficiency drops. Run too fast, and the turbine blades cavitate and (aerodynamically) stall, and flow drops. Run too slow, and the blades aren't getting enough "bite", and flow drops. Here's an example. The M1A1 Abrams tank weighs about 55 tons, most of it in armor. (Steel and depleted uranium) It has a gas turbine engine that produces 1800HP at the wheels... er, tracks, which is enough power to move that beast at about 70 MPH. The turbine is amazingly small, and while I don't remember exactly how much it weighs, it seems to me that it's on the order of 300-500lbs. Compared to the weight of the rest of the tank, the engine might as well not be there! However, the design of the turbine was optimized for WOT operation. At WOT, the turbine gets better gas mileage than an equivalent diesel at the same power point, but at idle, the turbine efficiency drops, to the point where gas mileage (per minute of operation) is **lower** at idle than it is at WOT! Turbines are fantastic powerplants for vehicles that can run at a constant RPM all day - like tanks, boats, airplanes, IndyCars, etc. For vehicles that need to be run at different engine speeds, they don't work so well. (although if somebody invents a good infinitely-variable-ratio transmission, look out!) So, getting back to turbochargers, what does this mean? Well, a turbo is really a single speed device. We're only producing enough exhaust to generate boost at WOT, and we have boost-limiting devices to keep the turbo running at a constant speed (once it gets there) so, if we know how much boost we want to produce at WOT, and we know how much air we are consuming at WOT and full boost, then we can select a turbo (really, we're selecting a compressor wheel and housing combo) to maximize the turbine efficiency at that flow point. Well what does _that_ get us? A smaller turbo. That is better, because the smaller the turbo, the less rotational inertia you have to overcome, and the faster the turbo accelerates to it's WOT speed (and the associated boost level) The time delay between opening the throttle and the production of full boost is commonly referred to as "turbo lag" and is the single most hated "feature" of turbos. Ever wonder why the turbo on the 2G is so small? It's been exactly matched to the air consumption of the engine for the driving style of Joe Public - who rarely, if ever, exceeds 4500RPM. Reducing lag has another important side effect though. If you have a datalogger, and plot the boost curve of your vehicle, the area under that curve determines your transitional power band. Do a little calculus, and you find that increasing that area - even without increasing the peak boost point - increases the torque available to accelerate the car by a large amount. One of these days, one of our tuner guys is going to get a flow bench, and a dyno, and work out the air consumption of his motor at a certain boost point, and select a compressor wheel and housing combo that maximizes efficiency at that point (describing how is beyond the scope of this post - in a nutshell, you compare pressure maps) and go really, really fast. If the tranny stays together. Tomorrow: Wastegates and Intercoolers and BOV's - Oh My!


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The story so far: We have determined what a turbo is, how the exhaust turbine functions (and what affects its performance) what the inlet compressor is (and what affects its performance) and hinted a little at what selecting a turbo requires. Today: Intercoolers and Wastegates and BOV's - Oh My! So, yesterday we left off with high pressure air leaving the compressor outlet. Unfortunately, physics has worked against us this time, and the act of doing work to our inlet air to compress it has raised its temperature. This is bad. Not only are we reducing density, we're increasing the possibility of the great bugaboo - detonation. Remember, the onset of detonation is usually the limiting factor on the amount of power a given engine can produce, and that increased intake temperature (as measured at the intake valve) increases the chance of detonation. So we have to cool the air back down again, without losing any pressure. That's the job of the intercooler, basically a "air radiator" placed in the flow stream between the turbo compressor outlet and the intake manifold. There's really not much else to say about them, except: 1) The more you can cool the air flow, the better. This _normally_ means the bigger the intercooler, the better. (There are some smaller coolers that are better designed than the lower-end "big" coolers though, so size does not necessarily indicate effectiveness. 2) The cooler must be placed in a location where ambient air can flow through it. This means that your cooler must have an intake path and an _exhaust_ path. Mounting a cooler flush against a plate does no good! 3) There's always a pressure drop across a cooler. How much depends on the cooler design. Wastegates A turbo is a positive-feedback device. The more boost you make, the more exhaust you make, which makes more exhaust, which makes more boost... in a vicious circle. So we have to have some way of limiting boost. What we _really_ want is a way of keeping the turbine operating at a constant speed (see yesterday's post) so that we can maximize the compressor efficiency - remember that turbines like to run at a single speed. However, as measuring turbo RPM is not practical, and as boost level is directly related to turbo speed, keeping the boost constant is the wastegate's job. The wastegate is just a valve that opens when we have exceeded our desired boost level, and allows exhaust to flow around the turbine, instead of through it. This lowers the pressure differential across the turbine, less work is done, and the turbo slows down. The only "gotcha" with the wastegate is that it must be able to flow enough gas to let the turbo slow down. If it can't, then you get "boost creep" where boost levels slowly grow as the car remains under boost. Bad. BOV Everybody likes BOV's because of the nifty sneeze sound they make. However, a BOV is an evil device. It's taking your precious boost and venting it to someplace else. Bad! Unfortunately, it's a necessary evil, and we have to live with it. Here's why: You're under boost, the turbo is fully spooled, and life is good - then you shift. That means your foot comes off the gas - and the throttle plate slams shut. Suddenly, instead of flowing in a continuous stream through the engine, the intake air smacks into the closed throttle plate. The turbo, which is still spinning and producing boost because if it's rotational inertia keeps producing pressure, and the intake stream, caught in between a rock and a hard place, jumps in pressure. In fact, you get a high-pressure shockwave that travels from the throttle plate back to the compressor vanes, that once it gets there, is a little like poking a stick into the spokes of a bike wheel. The repeated shock is hard on the compressor vanes and the shaft bearings, and in any case acts like a brake, slowing the turbo, and requiring it to be spooled up again. The BOV sits in between the turbo and the throttle plate, and if it detects the shockwave created by a shift, vents it elsewhere - either to atmosphere, or back to the inlet side of the turbo. So, we lost boost pressure, but we kept the turbo spooled... tough to say without a dyno if that was a fair trade on a race vehicle. On a street vehicle, it was definitely a good idea, because we spared our expensive turbo a mechanical shock.


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In Summary:

For those of you who may have missed a part of the "Turbo Fundamentals" series, or those who may not have wanted to sift through all my Never-ending Sentences (TM) here's a summary of the last week's posts, plus the odd important point that may have slipped through the cracks last week. 1) Turbos reclaim energy that would otherwise been dumped overboard in the form of heat, by using exhaust gasses to spin a turbine, which in turn spins a compressor, which compresses the intake air. 2) Compressed intake air makes more power, because it allows you to burn more fuel per power stroke of the engine, and because it helps scavenge the engine. (The new, compressed, intake charge "blows out" the remaining exhaust gasses) 3) The amount of work done by a turbo's turbine depends on the amount of gas flow through it, and the pressure differential across it. 4) You can improve the turbine pressure differential by installing an exhaust system with a higher flow capacity than stock. It's impossible to have "too much" exhaust flow downstream of the turbo. 5) The intake compressor works best when it has been specifically sized for an engine's flow requirements and boost levels. 6) The best way to choose a compressor wheel and housing is to call the manufacturer of the turbo, and answer all their questions. 7) Intercoolers are our friends. They reduce the temperature of the compressed intake charge after the compressor has heated it. An intercooler is only as good as the air flow into it ***and out of it*** 9) Wastegates limit boost levels by acting as a "rev limiter" for the turbo. 10) "Boost creep" indicates a wastegate that is too small. 11) High boost motors require good ignition systems. Most top end stumbles and misses are ignition problems. 12) There's no substitute for a day on the engine dyno. There, that should about do it. Keep in mind that I've just summarized 80 years of turbocharger development and theory into a couple of pages over the last week. I haven't covered everything, and I've simplified a number of concepts where I could without losing the important stuff. (the physics of what goes on between the head and the turbine alone could make a book all on their own!) While my posts should help get you by, if you're really interested in this stuff, there's a lot of good books that cover this material better than I do.

Cap'nWankel

Not to be a stickler, but I believe the title is "Maximum Boost" If not, then get that one too... I am reading it right now, and it is absolutly amazing.

Evil Aviator

Correct. A belt-driven turbo is called a Centrifugal Supercharger. Hehehe, a "turbocharger" is technically a Turbosupercharger, but I won't get into that.

BTW, I don't know where you guys are getting your info from, but in most cases a turbo will feed the engine with cooler air than a supercharger, given the same boost level.

Corky Bell's new "Supercharged!" book is better, especially with respect to this subject.
http://www.amazon.com/exec/obidos/AS...937098-0223054

Josepi

Wouldn't the added stress of being belt driven on a compressor built as a turbo create some problems? I mean (it's still early granted), the belt has to be tight on the pulley, so what is going to be inside of the compressor to help keep it the shaft centered and not riding around on the bearings harder than it was designed to?

blu_gxl

first of all who the heck brought this thread back?

any way, who knows what kind of supercharger is on the mellenia? i believe it changed between 99-2000, but am not sure. also is it a roots type and the kit on superchargedrex's car is a camden centerfugal i think wouldn't a roots be harder to use? you would have to mount it directly to the intake monifold, or i'm thinking now you could fab up some kind of top plate that has an outlet such as the camden then you could route them the same. also the mellenia is only 5-6 psi right? hmmm this is starting to get more interesting.

james

splking

"Wouldn't the added stress of being belt driven on a compressor built as a turbo create some problems? "

that was my thought exactly. the fact that the impellers run off of bushings and not bearings should be a big concern. i dont think they were made to handle that kind of stress. from the belt tension i mean.

MasonX

If the turbo housing was attached with some sort of plate with a bearing setup on it which the shaft went through then you could relieve the stress on the bushings.

RETed

Blame Cap'nWankel!

I'm sorry, if we're talking about the stock turbo, it won't work.&nbsp The stock turbo is spinning an average of 50,000RPM.&nbsp There is no way you're going to get the stock compressor to spin that fast with a belt short of a 100:1 gear multiplier.&nbsp You'll need something on the order of a $2,000+ turbo compressor to run straight 1:1 ratio.

Not looking for 100hp increase?&nbsp Then you're wasting your money and effort with this idea.&nbsp You're much better off rebuilding, porting, exhaust, intake your engine to get "easier" power gains...



-Ted