BLITZ Supercharger
#26
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Originally Posted by Sputnik
One of the major drawbacks to an SC (of any type) is that it is locked into the engine rpm, and so it's efficiency band is rather narrow. In this case, the standard Renesis engine with it's large rpm range exagerates that limitation, so a turbo would offer a broader power band.
For example, check out the dyno results of an S2000 with a centrifugal SC. The SC actually hurts performance in lower rpms, has only modest increases in the middle rpm band, and doesn't really "kick in" until the upper rpms. While this is acceptable in a road course race track, or during "canyon carving", where you will always have the car in the upper rpm bands anyway, this is perfectly acceptable. But for around town driving, this will actually make the "gutless" feel of the engine at low rpms even worse. It depends on what you're looking for, but it can be very disappointing to spend all that money for "peak" power, and actually have worse performance around town. While one might not have "turbo lag", they will have "rpm lag", which can be just as frustrating, and is something that you have to work around just as much as turbo lag.
Meanwhile, a turbo can "cover" that rpm range better. It is still affected by the greater rpm range (for example, a turbo will have to pump about twice as much volume of air at 8k rpm, than at 4k rpm, to maintain the same boost level, so one will need to size accordingly), and there will still be some trade-offs in response vs. peak power, but not quite as much as with an SC.
But at the same time, the lower rpm limit of the auto-Renesis might make it more feasible for a roots-type SC, which while it has some drawbacks, is still quite effective in the 7k rpm limited Miata. And the lower rpm boost that the roots type gives will make up for some of the lack of low end grunt of the Renesis.
Anyway, I would choose turbo vs. centrifugal SC vs. roots SC vs. other upgrades on what I wanted out of the car, and for my money. While there are cases where one of the SCs would be fine, a turbo seems to be a better fit for the RX8 in the majority of cases, including peak HP and broad power band.
---jps
For example, check out the dyno results of an S2000 with a centrifugal SC. The SC actually hurts performance in lower rpms, has only modest increases in the middle rpm band, and doesn't really "kick in" until the upper rpms. While this is acceptable in a road course race track, or during "canyon carving", where you will always have the car in the upper rpm bands anyway, this is perfectly acceptable. But for around town driving, this will actually make the "gutless" feel of the engine at low rpms even worse. It depends on what you're looking for, but it can be very disappointing to spend all that money for "peak" power, and actually have worse performance around town. While one might not have "turbo lag", they will have "rpm lag", which can be just as frustrating, and is something that you have to work around just as much as turbo lag.
Meanwhile, a turbo can "cover" that rpm range better. It is still affected by the greater rpm range (for example, a turbo will have to pump about twice as much volume of air at 8k rpm, than at 4k rpm, to maintain the same boost level, so one will need to size accordingly), and there will still be some trade-offs in response vs. peak power, but not quite as much as with an SC.
But at the same time, the lower rpm limit of the auto-Renesis might make it more feasible for a roots-type SC, which while it has some drawbacks, is still quite effective in the 7k rpm limited Miata. And the lower rpm boost that the roots type gives will make up for some of the lack of low end grunt of the Renesis.
Anyway, I would choose turbo vs. centrifugal SC vs. roots SC vs. other upgrades on what I wanted out of the car, and for my money. While there are cases where one of the SCs would be fine, a turbo seems to be a better fit for the RX8 in the majority of cases, including peak HP and broad power band.
---jps
If 60 hp is about the most that the Renesis/RX8 can generate safely it might be a better fit for a Roots, as the kit can probably generate that quite easily, if there is no upside (turbo can turn up the boost). The Celica Blitz unit is priced at $5K on Hop Up racing, but if the RX8 unit really is $7K I would seriously doubt if they would sell many of them. At $5K (and if they could generate 60 hp, not 50hp that they are currently claiming) I would consider it, but at $7K, dont think so.
#27
Still too expensive at 5k for 60 hp.
Need more like 100hp
We need a better ratio of return on investment.
Hell for that price you can port and polish and get 40 hp for less than half the price.
Need more like 100hp
We need a better ratio of return on investment.
Hell for that price you can port and polish and get 40 hp for less than half the price.
#30
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Originally Posted by Fanman
I believe you are a bit off on this. The centrifugal SC (which looks like half a turbo marketed by Vortesh, Paxton, etc.) does make boost in a linear fashion, but the Roots/Lysholm SC's make a substantial amount of boost right off idle. Those are the ones marketed by firms like Jackson Racing, Blitz, Comptech (except the S2000's). This might be a good alternative for the RX8.
...The turbos usually generate their boost at around 1/3 of the revs (in this case I would expect it to have boost around the 3500 rpm & up range)...
...[turbos] are usually a bit more complicated to install, and can be more expensive (though from this Blitz kit...YIKES !), and needs more tuning...
...If 60 hp is about the most that the Renesis/RX8 can generate safely it might be a better fit for a Roots, as the kit can probably generate that quite easily, if there is no upside (turbo can turn up the boost)...
And turbos also have a side benefit for those of us at altitude like Denver. Like a normally aspirated engine, an SC will only draw in a certain volume of air at a certain throttle/rpm combination, so it will draw in thinner air at higher altitudes. But as long as your turbo is big enough, it will draw in a larger volume of air at higher altitudes to end up at the same boost levels. Turbo lag does increase (and you have to watch octane levels), but other than that, you basically get the same power. For example, if you are high enough in altitude that a NA engine is only making 80% of power in the thinner air, a 250 HP engine will be making appox. 200 HP. A bolt-on SC kit that increases power by 25% at sea level will give that same engine appox. 250 HP at altitude. A bolt on turbo kit (with a big enough turbo) that increases power by 25% at sea level should pretty much give that engine appox. 310 HP at altitude. That's a very general calculation, but you get the idea.
---jps
#31
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You're wrong in many places but the one that really interests me is your altitude compensating turbo.
I think you need to move up to some higher math. It is published on this forum more then once. Try searching.
Not only would your system interest me I can name a couple of aero engine mfg that want to hire you.
![Confused](https://www.rx8club.com/images/smilies/confused.gif)
Not only would your system interest me I can name a couple of aero engine mfg that want to hire you.
![Wink](https://www.rx8club.com/images/smilies/wink.gif)
#32
the blitz supercharger looks the same as the toyota design used back in the 80's (?)
it also looks like the smaller version used on the 1.6L and there was a longer higher displacment on for the 2L.
these SC had straght lobes not helical. they did have a little lag and were said to come on boost 1000rpm from idle. I have heard of people using the 2L SC on 3.6L motors with good results with low boost but if blitz are using the smaller version (which displaces about 1.4L per revolution from memory) I don't see how it can keep up with the rotary's need for air.
one thing they have a clutch on the front of this SC and can turn it on and off. if they over drive it for low rpm then they can turn it off to stop it spinning to fast and damaging it's self.
blitz would have considered all these and i'm sure the kit is half decent.
it also looks like the smaller version used on the 1.6L and there was a longer higher displacment on for the 2L.
these SC had straght lobes not helical. they did have a little lag and were said to come on boost 1000rpm from idle. I have heard of people using the 2L SC on 3.6L motors with good results with low boost but if blitz are using the smaller version (which displaces about 1.4L per revolution from memory) I don't see how it can keep up with the rotary's need for air.
one thing they have a clutch on the front of this SC and can turn it on and off. if they over drive it for low rpm then they can turn it off to stop it spinning to fast and damaging it's self.
blitz would have considered all these and i'm sure the kit is half decent.
#33
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Well, I've always heard that turbos tend to suffer less from "thin air syndrome" then superchargers or normally-aspirated cars. I thought it had something to do with the thinner air causing less resistance to the spinning turbo impeller however.
jds
jds
Originally Posted by Richard Paul
You're wrong in many places but the one that really interests me is your altitude compensating turbo.
I think you need to move up to some higher math. It is published on this forum more then once. Try searching.
Not only would your system interest me I can name a couple of aero engine mfg that want to hire you.![Wink](https://www.rx8club.com/images/smilies/wink.gif)
![Confused](https://www.rx8club.com/images/smilies/confused.gif)
Not only would your system interest me I can name a couple of aero engine mfg that want to hire you.
![Wink](https://www.rx8club.com/images/smilies/wink.gif)
#34
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And it's thinner coming out also. On top of that it is colder outside and therefore there is less in the way of volume to spin the turbine. No free lunch here.
A variable stator might help but still never gonna get anything for free.
How come they only used SC in WWll on the aircraft. There was one turbo by the ***** but unsuccesfull compared to SC engines. They did use nitrous though on the fighter planes for hi alt dog fighting. But they couldn't carry enough to use it except in emergency.
Also of note should be that they had an inert gas to pressurize the nitrous to a given press. Not reliying on just the natural press which varies with amount left and temp.
Not aware of any rootsblowers ever used on these engines. There were some tests by Allison for turbos but I don't know what came of it. There were some multi stage centrifugals as on the Griffin. 2222 cu in V-12 Rolls Royce used in some transport planes.
A variable stator might help but still never gonna get anything for free.
How come they only used SC in WWll on the aircraft. There was one turbo by the ***** but unsuccesfull compared to SC engines. They did use nitrous though on the fighter planes for hi alt dog fighting. But they couldn't carry enough to use it except in emergency.
Also of note should be that they had an inert gas to pressurize the nitrous to a given press. Not reliying on just the natural press which varies with amount left and temp.
Not aware of any rootsblowers ever used on these engines. There were some tests by Allison for turbos but I don't know what came of it. There were some multi stage centrifugals as on the Griffin. 2222 cu in V-12 Rolls Royce used in some transport planes.
#36
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The thing about a turbo system that makes it appear to work better at higher altitudes isn't the turbo itself but rather what boost level is regulated at. If the wastegate is set to open at 8 psi, it is irrelevant how hard the turbo is working to et there as long as it does. At a lower altitude where the air is thicker, the turbo doesn't have to work as hard to get that 8 psi. As the altitude rises, it becomes harder to get that pressure since there is less of it. The turbo just works harder since the wastegate doesn't work as soon. The wastegate does allow the turbo to still hit 8 psi so it appears that turbos do in fact compensate for altitude. However this is only true to a point. As the turbo works harder to get the same boost it would at a lower altitude, it also heats the air up more so there is a drawback. The same basic mentality is used as an excuse by many people to keep their air filters in the hot engine compartment. They assume that the turbo will just spin faster to make up for the less dense air which is true but it is still much hotter. From this standpoint I will agree that a turbo does have an altitude advantage over a geared supercharger. A supercharger that is geared for 8 psi at sea level will not make 8 psi in Denver. A turbo will but it is also working harder and producing less power than the same 8 psi at sea level. It would still have an advantage but by no means is it a be all end all altitude compensation. There is always a tradeoff.
For street use this is probably one of the only areas that I will rule in favor of the turbo. When it comes to other things such as reliability, heat, etc, I won't.
For street use this is probably one of the only areas that I will rule in favor of the turbo. When it comes to other things such as reliability, heat, etc, I won't.
#37
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RG, tell me is the waste gate working in gauge pressure or absolute. It seems to me that they work on gauge pressure which means that if it makes x psi over the ambiant it still does at higher alt.
Thus it is only x higher then the now lower absolute pressure which is what the SC does. +/- that is. Clear as my usual explaination, right.
Prey tell why would you not look to the aerospace industry for advanced engineering. They have alot more money and stricter rules. require more testing and if something fails they cannot get out and push.
Thus it is only x higher then the now lower absolute pressure which is what the SC does. +/- that is. Clear as my usual explaination, right.
Prey tell why would you not look to the aerospace industry for advanced engineering. They have alot more money and stricter rules. require more testing and if something fails they cannot get out and push.
#38
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You don't know what you're talking about, I read it in Makes and Models so I know its true :D
jds
jds
Originally Posted by Richard Paul
And it's thinner coming out also. On top of that it is colder outside and therefore there is less in the way of volume to spin the turbine. No free lunch here.
A variable stator might help but still never gonna get anything for free.
How come they only used SC in WWll on the aircraft. There was one turbo by the ***** but unsuccesfull compared to SC engines. They did use nitrous though on the fighter planes for hi alt dog fighting. But they couldn't carry enough to use it except in emergency.
Also of note should be that they had an inert gas to pressurize the nitrous to a given press. Not reliying on just the natural press which varies with amount left and temp.
Not aware of any rootsblowers ever used on these engines. There were some tests by Allison for turbos but I don't know what came of it. There were some multi stage centrifugals as on the Griffin. 2222 cu in V-12 Rolls Royce used in some transport planes.
A variable stator might help but still never gonna get anything for free.
How come they only used SC in WWll on the aircraft. There was one turbo by the ***** but unsuccesfull compared to SC engines. They did use nitrous though on the fighter planes for hi alt dog fighting. But they couldn't carry enough to use it except in emergency.
Also of note should be that they had an inert gas to pressurize the nitrous to a given press. Not reliying on just the natural press which varies with amount left and temp.
Not aware of any rootsblowers ever used on these engines. There were some tests by Allison for turbos but I don't know what came of it. There were some multi stage centrifugals as on the Griffin. 2222 cu in V-12 Rolls Royce used in some transport planes.
#39
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Originally Posted by Richard Paul
RG, tell me is the waste gate working in gauge pressure or absolute. It seems to me that they work on gauge pressure which means that if it makes x psi over the ambiant it still does at higher alt.
Thus it is only x higher then the now lower absolute pressure which is what the SC does. +/- that is. Clear as my usual explaination, right.
Prey tell why would you not look to the aerospace industry for advanced engineering. They have alot more money and stricter rules. require more testing and if something fails they cannot get out and push.
Thus it is only x higher then the now lower absolute pressure which is what the SC does. +/- that is. Clear as my usual explaination, right.
Prey tell why would you not look to the aerospace industry for advanced engineering. They have alot more money and stricter rules. require more testing and if something fails they cannot get out and push.
While a supercharger will give you say 8 psi over ambient pressure, the wastegate on a turbo will allow you to get 8 psi over sea level pressure.
Last edited by rotarygod; 01-06-2005 at 01:03 AM.
#41
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Originally Posted by rotarygod
...If the wastegate is set to open at 8 psi, it is irrelevant how hard the turbo is working to et there as long as it does. At a lower altitude where the air is thicker, the turbo doesn't have to work as hard to get that 8 psi. As the altitude rises, it becomes harder to get that pressure since there is less of it. The turbo just works harder since the wastegate doesn't work as soon. The wastegate does allow the turbo to still hit 8 psi so it appears that turbos do in fact compensate for altitude...
...However this is only true to a point. As the turbo works harder to get the same boost it would at a lower altitude, it also heats the air up more so there is a drawback... A turbo will but it is also working harder and producing less power than the same 8 psi at sea level. It would still have an advantage but by no means is it a be all end all altitude compensation. There is always a tradeoff...
Originally Posted by Richard Paul
...How come they only used SC in WWll on the aircraft...
---jps
#42
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If you look at a "supercharger" on a B-17, it is nothing more than an exhaust driven turbocharger with a very large pilot controlled bypass valve (wastegate). This is how they could just turn on the supercharger at higher altitudes. The pilot also had to manually increase the richness of the mixture. Thank god for modern computers!
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