twin chargeing a FC?
09-13-07, 08:42 PM
#26
Rotorhead
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http://www.aeromanagement.com.au/blown3rotor/index.html
09-13-07, 09:23 PM
#27
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No.
They are not bolt-on.
Twin HT-12's, so it's two same sized turbos.
No, they are technically not one per rotor, as the STUPID turbo exhaust manifold layout is really bad.
-Ted
They are not bolt-on.
are the gen 3 twins a big and a small turbo, or one turbo per rotor?
No, they are technically not one per rotor, as the STUPID turbo exhaust manifold layout is really bad.
-Ted
09-13-07, 11:44 PM
#28
Great Scott!
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Actually this is an idea I have had and have been working on for a while cermet coated housings with really low compression rotors and a whipple twin screw are in order right now and once that gets together will figure out what to do about the turbo.
09-14-07, 12:24 AM
#30
More long posting...
In a truly fair comparison between a nice turbo and a twin screw supercharger, everything being as equal as it can be, the turbo "should" make more power. While a turbo is an exhaust restriction to some point and this is always true, it also utilizes some wasted energy to make boost. A supercharger uses no wasted energy to spin so it's completely parasitic.
Now saying that, anyone with n/a experience knows the power difference between a crappy designed stock box like exhaust manifold and a properly designed header. The power difference is very big across the total powerband. Exhaust makes a huge difference. I'd be curious to see a turbo exhaust manifold bolted onto an n/a engine and then on the outlet side of the manifold instead of a turbo, a small orifice the total area of the turbo exhaust inlet size be installed and then dynoed. If you've ever looked into the exhaust housing of a turbo, it necks down pretty small in there and this isn't even taking into account the blades being in the way. A TII turbo has a VERY small opening in there. If this hole size were used as a pipe off of a turbo exhaust manifold on an n/a, how much power would the engine make compared to a nicely done header system? I'll bet it's significant. Ever wonder how a stock TII only makes 182 (or 200 fwhp depending on year model) yet a stock port n/a engine with good tuning and a good exhaust can potentially hit this? Why is that? The losses through the turbo are larger than many think they are. Of course the argument would be that a better flowing exhaust system after the turbo would free up power too but it still is proof that a turbo is not always a nicely flowing efficient device.
I'd like to see a twin screw supercharger installed on a properly built TII engine with a nicely done collected header system. When not under boost such as in cruising, this engine would hand a TII it's butt all day long as off boost power would be much nicer. That's where you drive most of the time anyways so yes it's important.
Then we can also get into the arguement about porting. Boost may be boost but timing between a turbo engine and a supercharged engine should not be done the same way. The best porting on a supercharged engine is one with no overlap. While this isn't possible on a 13B, it is possible on a Renesis. They key to making power on a supercharged engine does not lie in added port timing as in bridge or peripheral ports. On a supercharged engine, you always have more intake pressure than exhaust pressure. During overlap, you will always blow some of this intake charge out the exhaust which is a waste. With no overlap, you use it all.
A turbo engine on the other hand is different. On an n/a, scavenging is so important because exhaust gasses dilute the incoming intake charge at lower loads and rpms due to the fact that the exhaust has more pressure than the intake side. We rely on scavenging and inertia to overcome this. On a turbocharged car, you always have more exhaust pressure than intake pressure which means you always have exhaust gas dilution. It is actually possible to have more intake pressure on a turbo than exhaust pressure but the turbo gets pretty large and streetable isn't anywhere in there. The I also need to mention that a larger wheel will eventually get so heavy that it's mass now contributes back to the restriction issue even though the outlet is large. This is why twins work well and decrease backpressure when designed properly. This also has to be quantified by stating that this is after a certain point and also isn't ALWAYS true at every boost level. There's alot to think about. A huge mammoth turbo with a huge heavy exhaust wheel on a peripheral port would drive that engine crazy as as tried to idle.
Before I go on, I know someone is going to jump in here and say that this is impossible. If you are just focusing on air in/air out I'd agree. However it's all about energy in and energy out. The energy going into the engine is air and fuel. The energy going out is air, heat, and power. By having less exhaust pressure than intake pressure on the exhaust, you are not doing the impossible. Indy cars did this for years. Keep in mind that this is highly improbable and practically an impossibility on a street driven engine that needs good turbo response. Then again something is only impossible until someone does it!
Now back to the timing issue. Since a turbo will almost always have more exhaust pressure than intake pressure, and even in the best case scenario still less of a pressure difference favoring the intake that a supercharged engine, we don't really have the problem of a high overlap engine such as a bridge or peripheral port blowing boosted air out the exhaust. It doesn't happen. It's all usable. If we had 2 brideported engines, one turbocharged and one supercharged, and both units were comparable, the turbo would walk all over it all day long. It's not because the turbo is more efficient than the supercharger. It's common sense which apparently isn't all that common. As we have seen from others, turbocharges can work very well with high overlap engines. If we took one of BDC's beautiful half bridge engines and substitued the turbo for a supercharger, we'd see him on here the next day complaining what a piece of crap it was. Now you know why. With high overlap on a turbo engine, you still get the disadvantages of a high overlap n/a engine as well and these are seen at low loads and rpms, not to mention emissions and gas mileage. On both engines once load increases, they both overcome those deficiencies and get quite fun. A supercharger would not be this way with high overlap.
Now saying all of this, it poses the question as to how would the perfectly designed and ported engine work with a supercharger as compared to a more agressively ported engine with a turbo? One engine while having less overlap isn't suffering from the amount of exhaust gas dilution that the other is and all of it's boost is being used to take up all of the available airspace as a result. It also would have an exhaust that helps make power. The other engine being a turbo with higher overlap would have more time for air to get in but it isn't benefitting from exhaust gas scavenging to help make power and it has more exhaust gas recirculation to the intake side to take up space and heat up the air somewhat.
Which would win? I'd actually still lean towards the turbo engine for all out race use and looking at forced inducted race car technology, this appears to be true. However 99% of us here don't have race cars even though 50% of the people think they do! For street use I'd bet the supercharged setup would be very nice and very streetable. I have no doubt that you could build a streetable 400 hp supercharged engine. The largest variable is cost. You can go faster for cheaper with a turbo and due to such a price difference, it's very easy to justify some compromises as long as you still get the performance that you want. If it takes a few extra psi and reduces mileage a little bit, so what? Power is power regardless of what the boost gauge says and mileage differences may be justified through price so the turbo is the obvious solution to most people.
I'm bolting on an archaic TII turbo on to my 1st gen btw. Why would I do this if I really don't like that unit? I already have it which makes it free and I really only want about 250 hp which that unit can do. I've just justified it. I know my mileage will fall from it's current n/a collected exhaust state but I've only put 3000 miles on that car in the last 5 years so that isn't really an issue either. If I had more money to spend on my car, I'd definitely try the twin screw. I am helping a friend with a twin screw setup on his V8 right now though so at least I still get to play with one somehow!
My whole point in this is never to say a supercharger is better than a turbo. As with anything out there, suspension setup, porting, etc, it depends. That's a fair answer. You can never absolutely state one is always better or more efficient than than the other without a LOT more detail right down to how the car will be driven. I encourage anyone to go out an build a nicely done supercharger system. I'll bet it would be nice.
In a truly fair comparison between a nice turbo and a twin screw supercharger, everything being as equal as it can be, the turbo "should" make more power. While a turbo is an exhaust restriction to some point and this is always true, it also utilizes some wasted energy to make boost. A supercharger uses no wasted energy to spin so it's completely parasitic.
Now saying that, anyone with n/a experience knows the power difference between a crappy designed stock box like exhaust manifold and a properly designed header. The power difference is very big across the total powerband. Exhaust makes a huge difference. I'd be curious to see a turbo exhaust manifold bolted onto an n/a engine and then on the outlet side of the manifold instead of a turbo, a small orifice the total area of the turbo exhaust inlet size be installed and then dynoed. If you've ever looked into the exhaust housing of a turbo, it necks down pretty small in there and this isn't even taking into account the blades being in the way. A TII turbo has a VERY small opening in there. If this hole size were used as a pipe off of a turbo exhaust manifold on an n/a, how much power would the engine make compared to a nicely done header system? I'll bet it's significant. Ever wonder how a stock TII only makes 182 (or 200 fwhp depending on year model) yet a stock port n/a engine with good tuning and a good exhaust can potentially hit this? Why is that? The losses through the turbo are larger than many think they are. Of course the argument would be that a better flowing exhaust system after the turbo would free up power too but it still is proof that a turbo is not always a nicely flowing efficient device.
I'd like to see a twin screw supercharger installed on a properly built TII engine with a nicely done collected header system. When not under boost such as in cruising, this engine would hand a TII it's butt all day long as off boost power would be much nicer. That's where you drive most of the time anyways so yes it's important.
Then we can also get into the arguement about porting. Boost may be boost but timing between a turbo engine and a supercharged engine should not be done the same way. The best porting on a supercharged engine is one with no overlap. While this isn't possible on a 13B, it is possible on a Renesis. They key to making power on a supercharged engine does not lie in added port timing as in bridge or peripheral ports. On a supercharged engine, you always have more intake pressure than exhaust pressure. During overlap, you will always blow some of this intake charge out the exhaust which is a waste. With no overlap, you use it all.
A turbo engine on the other hand is different. On an n/a, scavenging is so important because exhaust gasses dilute the incoming intake charge at lower loads and rpms due to the fact that the exhaust has more pressure than the intake side. We rely on scavenging and inertia to overcome this. On a turbocharged car, you always have more exhaust pressure than intake pressure which means you always have exhaust gas dilution. It is actually possible to have more intake pressure on a turbo than exhaust pressure but the turbo gets pretty large and streetable isn't anywhere in there. The I also need to mention that a larger wheel will eventually get so heavy that it's mass now contributes back to the restriction issue even though the outlet is large. This is why twins work well and decrease backpressure when designed properly. This also has to be quantified by stating that this is after a certain point and also isn't ALWAYS true at every boost level. There's alot to think about. A huge mammoth turbo with a huge heavy exhaust wheel on a peripheral port would drive that engine crazy as as tried to idle.
Before I go on, I know someone is going to jump in here and say that this is impossible. If you are just focusing on air in/air out I'd agree. However it's all about energy in and energy out. The energy going into the engine is air and fuel. The energy going out is air, heat, and power. By having less exhaust pressure than intake pressure on the exhaust, you are not doing the impossible. Indy cars did this for years. Keep in mind that this is highly improbable and practically an impossibility on a street driven engine that needs good turbo response. Then again something is only impossible until someone does it!
Now back to the timing issue. Since a turbo will almost always have more exhaust pressure than intake pressure, and even in the best case scenario still less of a pressure difference favoring the intake that a supercharged engine, we don't really have the problem of a high overlap engine such as a bridge or peripheral port blowing boosted air out the exhaust. It doesn't happen. It's all usable. If we had 2 brideported engines, one turbocharged and one supercharged, and both units were comparable, the turbo would walk all over it all day long. It's not because the turbo is more efficient than the supercharger. It's common sense which apparently isn't all that common. As we have seen from others, turbocharges can work very well with high overlap engines. If we took one of BDC's beautiful half bridge engines and substitued the turbo for a supercharger, we'd see him on here the next day complaining what a piece of crap it was. Now you know why. With high overlap on a turbo engine, you still get the disadvantages of a high overlap n/a engine as well and these are seen at low loads and rpms, not to mention emissions and gas mileage. On both engines once load increases, they both overcome those deficiencies and get quite fun. A supercharger would not be this way with high overlap.
Now saying all of this, it poses the question as to how would the perfectly designed and ported engine work with a supercharger as compared to a more agressively ported engine with a turbo? One engine while having less overlap isn't suffering from the amount of exhaust gas dilution that the other is and all of it's boost is being used to take up all of the available airspace as a result. It also would have an exhaust that helps make power. The other engine being a turbo with higher overlap would have more time for air to get in but it isn't benefitting from exhaust gas scavenging to help make power and it has more exhaust gas recirculation to the intake side to take up space and heat up the air somewhat.
Which would win? I'd actually still lean towards the turbo engine for all out race use and looking at forced inducted race car technology, this appears to be true. However 99% of us here don't have race cars even though 50% of the people think they do! For street use I'd bet the supercharged setup would be very nice and very streetable. I have no doubt that you could build a streetable 400 hp supercharged engine. The largest variable is cost. You can go faster for cheaper with a turbo and due to such a price difference, it's very easy to justify some compromises as long as you still get the performance that you want. If it takes a few extra psi and reduces mileage a little bit, so what? Power is power regardless of what the boost gauge says and mileage differences may be justified through price so the turbo is the obvious solution to most people.
I'm bolting on an archaic TII turbo on to my 1st gen btw. Why would I do this if I really don't like that unit? I already have it which makes it free and I really only want about 250 hp which that unit can do. I've just justified it. I know my mileage will fall from it's current n/a collected exhaust state but I've only put 3000 miles on that car in the last 5 years so that isn't really an issue either. If I had more money to spend on my car, I'd definitely try the twin screw. I am helping a friend with a twin screw setup on his V8 right now though so at least I still get to play with one somehow!
My whole point in this is never to say a supercharger is better than a turbo. As with anything out there, suspension setup, porting, etc, it depends. That's a fair answer. You can never absolutely state one is always better or more efficient than than the other without a LOT more detail right down to how the car will be driven. I encourage anyone to go out an build a nicely done supercharger system. I'll bet it would be nice.
Last edited by rotarygod; 09-14-07 at 12:33 AM.
09-14-07, 12:40 AM
#31
Yeah all things being equal the turbo should always be slightly better. It's just not night and day as many imply it is though. I was really referring to the people that think just because it's a turbo that it must be better than any random supercharger just because it's a supercharger and this isn't true. If I compare a large AX series Whipple to a TD-05H, I'd be foolish to say the TD-05H makes more power by sheer virtue that it's a turbo. That's the types of comparisons that people seem to make when they speak against superchargers. Of course we need more information such as what sized supercharger and what boost level, etc... At a low boost level on a small 4 cylinder engine, that may very well be true. At higher boost levels however... you get the point.
09-14-07, 01:11 AM
#33
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Yo rotary god I'm building a nice twinscrew set-up... the only thing I need some help with is porting as I'm not sure what to do... fluid-dynaimcs wise it seems to me a well done streetport would be fine as this isn't going to be a track only car and I want it to be driveable... any tips on streetporting would be appreciated... btw its a sixport and I choose it over a four port on purpose before everyone starts being gay about how much worse they are to port... cause in reality if you want smooth power they are not worse at all... And if anyone tells me to do a monster port (joining the aux. and secondaries) I will murder them. I will be running about 25 psi.
09-14-07, 08:31 AM
#35
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an old nissan march had a turbo and supercharger setup...and it was incredibly complicated...and a watse of time...
IMO i would just stick with turbo/s....less complicated, less parts to fix, and your saving yourself lots of $$$.
btw dont superchargers take away some top end revs?
IMO i would just stick with turbo/s....less complicated, less parts to fix, and your saving yourself lots of $$$.
btw dont superchargers take away some top end revs?
09-14-07, 08:53 AM
#36
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I agree with most of what you said rotarygod but theres more to be said for testing. the other day i read something on a mustang forum or in a book (i dont remember which) (also im not claiming this for fact as i dont remember all the details, its just to prove a point). someone had a 700HP NA mustang and a dyno and put a supercharger on it with the intake off (just hooked up the belt) and dyno'd before and after. after it lost nearly 200HP with just the belt on, was running like 500HP. they hooked up the intake and made almost 1000HP with the supercharger. even if this was completely fake (but i dont think it was) theres something to be said for testing.
i believe a turbo blocking your exhaust would still not make this much of a loss. the real test would be to hook a good super and turbo charger (with the same boost levels, and efficiency) up one at a time, dyno it with the intake off and on with both. this isnt going to happen though so we're all stating opinion.
i believe a turbo blocking your exhaust would still not make this much of a loss. the real test would be to hook a good super and turbo charger (with the same boost levels, and efficiency) up one at a time, dyno it with the intake off and on with both. this isnt going to happen though so we're all stating opinion.
09-14-07, 09:36 AM
#37
I agree that there's no substitute for testing. Theory and homework can get you in the ballpark of your goals but it's testing that takes you the rest of the way. That's how every successful race team in the world does things and why they are always out on the track testing. They've built the car with certain goals in mind and have based their designs on those goals. They just have to tweak it for each track to get optimum performance.
A supercharger is definitely going to rob power from the crank. That doesn't surprise me at all. Remember a top fuel dragster's supercharger requires something like 1000hp to spin at the speed they need it to. I also agree that all things being equal, a turbo will still rob less power from the engine than a supercharger will. I can't deny that. A supercharger spins through usable engine power. A turbo while also consuming some usable power also runs on waste exhaust and by default should be more efficient in that regards in a perfect world.
Unfortunately my old flowbench has gone the way of the dodo and I haven't built a new one yet. I'd be curious to strap various turbos to it to see what kind of a restriction they pose on the exhaust system. Of course there is no true way to be 100% accurate with this number as it isn't accounting for air trying to be forced into an intake system but I'd still like to get a general idea of what various turbo restrictions are in relation to standard pipe size flowrates. What if I strapped on a stock TII turbo and found that the flow losses were equivalent to running through a 1.5" pipe? That would be significant. Keep in mind I made that number up so don't think it's a fact. If this were true then the next step would be good old testing. Strap a 1.5" pipe onto a turbo manifold outlet and hook it up to the rest of the exhaust without a turbo. Now dyno the engine n/a and get a base power reading to see what exhaust restrictions only are. At least it would get you in the ballpark. Then compare this to a properly setup collected exhaust system. This still isn't taking into account power loss due to the compressor working but it would be useful information. Different turbos obviously have different flow loss levels.
In the same fashion, various superchargers will also have varying amounts of drag on the system. I'm sure a large supercharger spinning at speeds capable of 1000 hp would have some pretty large losses and 200 hp worth seems believable. Nothing is free. It's all about compromise. Was it a roots blower btw?
By comparison, it's not impossible to install a nice exhaust system on a nonturbo rotary and pick up 30 hp over stock. I guarantee that a stock TII turbo doesn't flow as well through the exhaust wheel as the stock boxlike exhaust manifold of an n/a does which would mean it would rob power over the n/a manifold. Let's be nice and say it only costs us 10 additional horsepower in restriction over an n/a manifold. If we can pick up 30 over a stock one and the stock turbo robs 10 (again I made that number up), that's a 40 hp difference right there! We aren't talking about a 1000 hp engine either. We are talking sub 200 hp. Multiply that times 5 to attempt to make some comparison to 1000 hp and we get a 200 hp difference. It probably wouldn't scale up exactly the same but you get the idea when it comes to comparable loss.
Obviously no one here has tested these systems to get exact numbers but the principle absolutely applies. Then of course we've got other variables such as the various compressor efficiencies and the speculation can go back and forth indefinitely. My whole point is not to proclaim the superiority of the supercharger. Not at all. Superchargers do have their place though and they aren't always a worse choice than a turbo. They also aren't so hard to spin that a rotary can't do it. Unless of course we are talking about a huge dragster blower! I wouldn't try to pull a tractor trailer with an RX-7 either so it's all about using the right tool for the right job and even then understanding the compromises neccessary to do it that way.
A supercharger is definitely going to rob power from the crank. That doesn't surprise me at all. Remember a top fuel dragster's supercharger requires something like 1000hp to spin at the speed they need it to. I also agree that all things being equal, a turbo will still rob less power from the engine than a supercharger will. I can't deny that. A supercharger spins through usable engine power. A turbo while also consuming some usable power also runs on waste exhaust and by default should be more efficient in that regards in a perfect world.
Unfortunately my old flowbench has gone the way of the dodo and I haven't built a new one yet. I'd be curious to strap various turbos to it to see what kind of a restriction they pose on the exhaust system. Of course there is no true way to be 100% accurate with this number as it isn't accounting for air trying to be forced into an intake system but I'd still like to get a general idea of what various turbo restrictions are in relation to standard pipe size flowrates. What if I strapped on a stock TII turbo and found that the flow losses were equivalent to running through a 1.5" pipe? That would be significant. Keep in mind I made that number up so don't think it's a fact. If this were true then the next step would be good old testing. Strap a 1.5" pipe onto a turbo manifold outlet and hook it up to the rest of the exhaust without a turbo. Now dyno the engine n/a and get a base power reading to see what exhaust restrictions only are. At least it would get you in the ballpark. Then compare this to a properly setup collected exhaust system. This still isn't taking into account power loss due to the compressor working but it would be useful information. Different turbos obviously have different flow loss levels.
In the same fashion, various superchargers will also have varying amounts of drag on the system. I'm sure a large supercharger spinning at speeds capable of 1000 hp would have some pretty large losses and 200 hp worth seems believable. Nothing is free. It's all about compromise. Was it a roots blower btw?
By comparison, it's not impossible to install a nice exhaust system on a nonturbo rotary and pick up 30 hp over stock. I guarantee that a stock TII turbo doesn't flow as well through the exhaust wheel as the stock boxlike exhaust manifold of an n/a does which would mean it would rob power over the n/a manifold. Let's be nice and say it only costs us 10 additional horsepower in restriction over an n/a manifold. If we can pick up 30 over a stock one and the stock turbo robs 10 (again I made that number up), that's a 40 hp difference right there! We aren't talking about a 1000 hp engine either. We are talking sub 200 hp. Multiply that times 5 to attempt to make some comparison to 1000 hp and we get a 200 hp difference. It probably wouldn't scale up exactly the same but you get the idea when it comes to comparable loss.
Obviously no one here has tested these systems to get exact numbers but the principle absolutely applies. Then of course we've got other variables such as the various compressor efficiencies and the speculation can go back and forth indefinitely. My whole point is not to proclaim the superiority of the supercharger. Not at all. Superchargers do have their place though and they aren't always a worse choice than a turbo. They also aren't so hard to spin that a rotary can't do it. Unless of course we are talking about a huge dragster blower! I wouldn't try to pull a tractor trailer with an RX-7 either so it's all about using the right tool for the right job and even then understanding the compromises neccessary to do it that way.
09-14-07, 09:48 AM
#38
I agree, except I do know of one modern supercharger installed on a rotary engine. Unfortunately, the car is nowhere even close to being streetable, most of the remainder of the car is far from modern, and one high-dollar example will not exactly start a trend on this forum. Much like you, I am still waiting to see somebody do this correctly on a street car.
http://www.aeromanagement.com.au/blown3rotor/index.html
http://www.aeromanagement.com.au/blown3rotor/index.html
That page does bring up one bad thing about a supercharged rotary and that is the noise. A turbo is a decent muffler on it's own. A supercharger isn't! We all know how loud an n/a rotary can get. Now imagine trying to quiet this noise down with twice the energy coming out of it! Again, there are advantages and disadvantages to everything.
09-14-07, 10:02 AM
#39
Lives on the Forum
IF you go here they've got some comparison dyno charts of some very similiar turbo and supercharger cars using twin screw superchargers.
http://www.flyinmiata.com/tech/dyno.asp
While they're not rotary, it does give you an idea of the differences and how good a properly done supercharger can be.
Now for twin charging: increased effort, complexity, weight, etc >> benefits compared to a turbo or supercharger alone
http://www.flyinmiata.com/tech/dyno.asp
While they're not rotary, it does give you an idea of the differences and how good a properly done supercharger can be.
Now for twin charging: increased effort, complexity, weight, etc >> benefits compared to a turbo or supercharger alone
09-14-07, 10:17 AM
#40
That's actually a nice site and they don't seem to be biased towards one or the other as they understand advantages and disadvantages based on intended use.
It is interesting to note that they are not using intercoolers on the supercharged kits but the turbo dynos do have them. At least the ones I saw did. That will make a difference too of course. They are also using Eaton roots blowers and they say that they are more efficient than a twin screw at lower boost levels which they did used to use. They do have a few twin screw dyno charts up. I have heard that elsewhere and again it's all about compromise. The newest Eatons have actually gotten to be fairly nice and are a far cry from the old M60 units that people like to get off of old T-birds. I'm still a fan of the twin screw though and it should also be pointed out that of course they will try to get you to favor the Eaton as that's what they sell. They admit that it's a cost issue. Just something to think about. Did they actually change for performance reasons or was it price? Their supercharger outlet doesn't look like it's got the best shape to it. If you look at the old T-bird Eaton units, they had an outlet shaped similar to this and the aftermarket responded with a much better one that made more power. Of course I've never tested their unit so I'm jsut speculating.
There is at least one dyno in there of a 300 hp supercharged setup so that's pretty good from a 2 liter Miata engine. They do also state that they feel that ultimately a turbo could make more power if that was your goal and I'd generally agree with that as well. I need to stare at those charts more.
It is interesting to note that they are not using intercoolers on the supercharged kits but the turbo dynos do have them. At least the ones I saw did. That will make a difference too of course. They are also using Eaton roots blowers and they say that they are more efficient than a twin screw at lower boost levels which they did used to use. They do have a few twin screw dyno charts up. I have heard that elsewhere and again it's all about compromise. The newest Eatons have actually gotten to be fairly nice and are a far cry from the old M60 units that people like to get off of old T-birds. I'm still a fan of the twin screw though and it should also be pointed out that of course they will try to get you to favor the Eaton as that's what they sell. They admit that it's a cost issue. Just something to think about. Did they actually change for performance reasons or was it price? Their supercharger outlet doesn't look like it's got the best shape to it. If you look at the old T-bird Eaton units, they had an outlet shaped similar to this and the aftermarket responded with a much better one that made more power. Of course I've never tested their unit so I'm jsut speculating.
There is at least one dyno in there of a 300 hp supercharged setup so that's pretty good from a 2 liter Miata engine. They do also state that they feel that ultimately a turbo could make more power if that was your goal and I'd generally agree with that as well. I need to stare at those charts more.
09-14-07, 01:27 PM
#44
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thats my point. i like turbos because of the boost adjustability too, its something you can do on the fly instead of changing a belt. overall i believe its just a cheaper solution. you can bet if superchargers were cheaper id have one though, just be alot easier to setup, instead of fabricating abunch of exhaust pipe for a turbo.
09-14-07, 02:25 PM
#45
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As we have seen from others, turbocharges can work very well with high overlap engines. If we took one of BDC's beautiful half bridge engines and substitued the turbo for a supercharger, we'd see him on here the next day complaining what a piece of crap it was. Now you know why. With high overlap on a turbo engine, you still get the disadvantages of a high overlap n/a engine as well and these are seen at low loads and rpms, not to mention emissions and gas mileage. On both engines once load increases, they both overcome those deficiencies and get quite fun. A supercharger would not be this way with high overlap.
I'm staring down the barrel of a rebuild for my 90 NA, and am very interested in including a SC system while I've got it open. I have no doubt in my mind that I'm getting in *way* over my head, but I love tinkering around and time is not an issue.
09-14-07, 02:51 PM
#47
thats my point. i like turbos because of the boost adjustability too, its something you can do on the fly instead of changing a belt. overall i believe its just a cheaper solution. you can bet if superchargers were cheaper id have one though, just be alot easier to setup, instead of fabricating abunch of exhaust pipe for a turbo.
I never addressed the original thread question. I personally don't think it's worth the effort to do both a turbo and a supercharger together. I say pick one.
09-14-07, 05:26 PM
#48
Lives on the Forum
They used to use Lysholm superchargers, and that's what the "Ubercharger" is, but ran into problems with availability and who owned the design when them and Corky Bell went their seperate ways. Now they use the Eatons because they can actually get their hands on them.
09-14-07, 07:46 PM
#49
Rotorhead
Join Date: Feb 2001
Location: Charlottesville, Virginia, USA
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They used a PSI "B" series twin screw supercharger:
http://www.psisuperchargers.com/viewproduct.php?id=29
http://www.psisuperchargers.com/viewproduct.php?id=29
