Centrifugal superchargers?? +/-'s
Discussion
So I picked up the latest "Engine Masters" here in the US which only deals with pushrod V8's mainly and I learned about something completely new. Perhaps, I had seen them in some after market tuner cars but what about the centrifugal superchargers?
An article discussed the various ways of spiking horsepower and it sounded as though (because it was not definitive) centrifugal was the best way to go all things considered. Yet, I don't know of any production car with this type of system. The article basically took "experts" from different racing divisions or long used methods roots blower, screw type blower, centri, and NO2 (unfortunately no one to represent turbo's). They also asked these people what their second choice was and more then one mentioned centri
So now I'm just day dreaming but . . . The application that I would be curious about would be a small v8 motor for an Ultima that would avoid the complexities of turbo charging or intercooling but allow for a smaller lighter weight engine with big horsepower though. Key to this idea is how much weight saving would there be, would it be meaningful, and if it would be an appropriate engine for road racing? (The magazine also had an interesting article on a SBC w/580hp and hydraulic lifters).
The article does mention the stress put on the front of the crankshaft, bearings, and "snout" of the engine. Aparently, it works well with efi applications and offers the easier packaging. Ultimately, I would lean towards a tweaked N/A engine with Ally block.
Any ideas or reflection on any of this?
>> Edited by pib on Sunday 14th August 21:46
An article discussed the various ways of spiking horsepower and it sounded as though (because it was not definitive) centrifugal was the best way to go all things considered. Yet, I don't know of any production car with this type of system. The article basically took "experts" from different racing divisions or long used methods roots blower, screw type blower, centri, and NO2 (unfortunately no one to represent turbo's). They also asked these people what their second choice was and more then one mentioned centri
So now I'm just day dreaming but . . . The application that I would be curious about would be a small v8 motor for an Ultima that would avoid the complexities of turbo charging or intercooling but allow for a smaller lighter weight engine with big horsepower though. Key to this idea is how much weight saving would there be, would it be meaningful, and if it would be an appropriate engine for road racing? (The magazine also had an interesting article on a SBC w/580hp and hydraulic lifters).
The article does mention the stress put on the front of the crankshaft, bearings, and "snout" of the engine. Aparently, it works well with efi applications and offers the easier packaging. Ultimately, I would lean towards a tweaked N/A engine with Ally block.
Any ideas or reflection on any of this?
>> Edited by pib on Sunday 14th August 21:46
The advantage of centrifugal blowers is small size and cheapness - since they basically use turbo technology but with a pulley and gear-up stage in place of the exhaust turbine. The disadvantage is the square-law rather than linear boost curve. This is fine on an engine that has a limited rev range (like a Merlin) but not what you want on a road car. There are some devices made which fudge around this somehow, apparently by having "gearing" which instead of teeth relies on the viscous drag of an oil film to transmit force, and allowing slip as speed builds up... sounds highly inefficient to me. I'd go for a screw-type myself.
The BRM V16 had a centifugal supercharger and was virtually undriveable because of the power delivery.
From what I can gather, the 'power band' of a centrifugal supercharger is problematical in practice...basically, you're talking about the compressor side of a large turbo, so you have similar problems with naff all boost at low compressor speeds, then the boost delivery rising very dramatically as the supercharger gets up to revs.
Good for engines that run at near-constant speed (the Merlins in WW2 Spitfires used them to great effect), but tricky to get the sort of smooth, progressive power delivery that most people want on road cars, whilst maintaining adequate efficiency.
Some of the smaller units used by people like Turbo Technics on their Elise conversions seem to work quite well, though.
From what I can gather, the 'power band' of a centrifugal supercharger is problematical in practice...basically, you're talking about the compressor side of a large turbo, so you have similar problems with naff all boost at low compressor speeds, then the boost delivery rising very dramatically as the supercharger gets up to revs.
Good for engines that run at near-constant speed (the Merlins in WW2 Spitfires used them to great effect), but tricky to get the sort of smooth, progressive power delivery that most people want on road cars, whilst maintaining adequate efficiency.
Some of the smaller units used by people like Turbo Technics on their Elise conversions seem to work quite well, though.
Im baffled as to why you say the power deliver of a CF blower isnt driveable ??
It has smoother more progressive power delivery than any other blower.
My old RV8 TT was pretty much useless in 1st, 2nd and 3rd due to its massive rush of torque midrange, when it made full boost.
It went quick, yes, but not that quick
My new engine, with a CF blower, has a LOT more power, is much faster, and more importantly, I can use 2nd and 3rd gear again. Wheelspin is on demand easily in 1st and 2nd, but it is so much more controllable now.
The fact a CF builds boost as the revs climb, means power deliver will be much more progressive. In fact, it really is just like having a much bigger engine.
It just depends what sort of power you want, and how your car is able to make use of it. IMO CF blowers are excellent.
The downside appears to be, they they use a bit of power to drive them. This means a good belt system must be in place to avoid premature belt wear, and slippage issues.
I'd say most manufacurers opt for turbos and rootes/twin screw types is that turbos are 100% tried and tested, cheap to mass produce, and produce superb results...in low boost form, for production cars.
Same with the other PD blowers. For a normal car the public will buy, in low boost form, these will give the gains that 90% of road users will be happy with. They dont want or need massive amounts of power. They want a nice torquey feel.
CF blowers dont give that so much. But they do give good gains, more so at the top end. Much more appealing to people who use the car properly.
It has smoother more progressive power delivery than any other blower.
My old RV8 TT was pretty much useless in 1st, 2nd and 3rd due to its massive rush of torque midrange, when it made full boost.
It went quick, yes, but not that quick
My new engine, with a CF blower, has a LOT more power, is much faster, and more importantly, I can use 2nd and 3rd gear again. Wheelspin is on demand easily in 1st and 2nd, but it is so much more controllable now.
The fact a CF builds boost as the revs climb, means power deliver will be much more progressive. In fact, it really is just like having a much bigger engine.
It just depends what sort of power you want, and how your car is able to make use of it. IMO CF blowers are excellent.
The downside appears to be, they they use a bit of power to drive them. This means a good belt system must be in place to avoid premature belt wear, and slippage issues.
I'd say most manufacurers opt for turbos and rootes/twin screw types is that turbos are 100% tried and tested, cheap to mass produce, and produce superb results...in low boost form, for production cars.
Same with the other PD blowers. For a normal car the public will buy, in low boost form, these will give the gains that 90% of road users will be happy with. They dont want or need massive amounts of power. They want a nice torquey feel.
CF blowers dont give that so much. But they do give good gains, more so at the top end. Much more appealing to people who use the car properly.
I said that the BRM V16 was undriveable...but that was a long time ago, with a small engine and a stupidly huge blower producing massive specific power output, for its day. I'm sure they are much better now and I certainly haven't heard that the TT Elise has a power delivery that is in any way unmanageable.
As Pidgeon says, the boost from a CF blower pretty much an exponential function of its operating speed. It is inefficient at very low revs, so you need to gear it up to be spinning fast enough so the boost starts to come through just as it picks up from idle. But then the rapid increase in boost means that by the time the engine is spinning at (say) 7,000 rpm, the blower is actually producing a lot more pressure than the engine can use, so it isn't terribly efficient in terms of power lost driving the blower...unless, like Pidgeon says, you use some form of viscous coupling or variable-speed drive, which is a complex and messy solution.
Not that I'm against them - quite the contrary; I like the idea of supercharging and a CF blower seems a nice, compact, simple solution, but if they really are the best thing since sliced bread, do you not think they'd have caught on by now? After all they are hardly a new idea - like I said earlier, this was considered routine technology in 1939!
As Pidgeon says, the boost from a CF blower pretty much an exponential function of its operating speed. It is inefficient at very low revs, so you need to gear it up to be spinning fast enough so the boost starts to come through just as it picks up from idle. But then the rapid increase in boost means that by the time the engine is spinning at (say) 7,000 rpm, the blower is actually producing a lot more pressure than the engine can use, so it isn't terribly efficient in terms of power lost driving the blower...unless, like Pidgeon says, you use some form of viscous coupling or variable-speed drive, which is a complex and messy solution.
Not that I'm against them - quite the contrary; I like the idea of supercharging and a CF blower seems a nice, compact, simple solution, but if they really are the best thing since sliced bread, do you not think they'd have caught on by now? After all they are hardly a new idea - like I said earlier, this was considered routine technology in 1939!
Granted there are no production CFSC AFAIK, but they do seem to be increasing their popularity in the after market pushrod V8 tuner crowd. Going by the article it sounded as if there were real advantages over roots and screw type blowers - linear power, wider selection of sizes, no huge loose of power down low or power surge threatening traction, fewer detonation problems at low revs thus octane less restrictive, fewer heat issues etc. etc.
But this is what the proponents were stating.
>> Edited by pib on Monday 15th August 00:40
But this is what the proponents were stating.
>> Edited by pib on Monday 15th August 00:40
CF's havent caught on ???? Take a look in Oz and the US.The things are absolutely everywhere.
I dont see their lack of boost from idle a problem. You gear/pulley them to make xx psi at max rpm. its quite simple.
The fact they dont make boost low down is part of what makes my car faster. If I had say 500lbft at 2000rpm, how much traction would that offer me ?
A PD blower may give the low down, but what they lack top end makes them a bad choice if you want a good high powered car. If its a good torquey road car, then a PD would be hard to beat.
A twin screw offers the best of both worlds. BUT...if you are wanting a high boost setup, then its back to traction problems. If you are running say 15psi from 2000rpm, its difficult to control power. Thats why A CF is so good.
Turbos are similar, but you could employ boost control, to reduce low rpm boost, and rise it as the revs climb to assist traction and make for smooth power delivery.
I dont know the Elise you talk about, but I can only think its a low boost, low power conversion. So traction and driveability should be good. If it was making say 400bhp, then it will be an issue.
I really like my CF blower a lot. I do miss the massive mid-range from a turbo. And I am considering going twin screw. But I think common sense is to stay with the CF, as it will be a faster road car, as quite simply I can get the power down better. If I had more torque that a turbo or twin screw offers, it would only go up in tyre smoke.
On a lowish powered setup like production cars are, it would be a major concern though, and a PD or turbo will work good. I'd go for turbo every time.
I dont see their lack of boost from idle a problem. You gear/pulley them to make xx psi at max rpm. its quite simple.
The fact they dont make boost low down is part of what makes my car faster. If I had say 500lbft at 2000rpm, how much traction would that offer me ?
A PD blower may give the low down, but what they lack top end makes them a bad choice if you want a good high powered car. If its a good torquey road car, then a PD would be hard to beat.
A twin screw offers the best of both worlds. BUT...if you are wanting a high boost setup, then its back to traction problems. If you are running say 15psi from 2000rpm, its difficult to control power. Thats why A CF is so good.
Turbos are similar, but you could employ boost control, to reduce low rpm boost, and rise it as the revs climb to assist traction and make for smooth power delivery.
I dont know the Elise you talk about, but I can only think its a low boost, low power conversion. So traction and driveability should be good. If it was making say 400bhp, then it will be an issue.
I really like my CF blower a lot. I do miss the massive mid-range from a turbo. And I am considering going twin screw. But I think common sense is to stay with the CF, as it will be a faster road car, as quite simply I can get the power down better. If I had more torque that a turbo or twin screw offers, it would only go up in tyre smoke.
On a lowish powered setup like production cars are, it would be a major concern though, and a PD or turbo will work good. I'd go for turbo every time.
Centifugal blowers are very popular in the US. just take a look at some of the corvette/ls1 foeums over there and you will see why they are populer to. the main reason i think is outlay. they are much cheaper than a turbo setup and can diliver similar levels of boost and power (roots/screw blowers are way behind on boots levels for street use).
also if you plan on using one in an ultima, the way they diliver thier power could be benifical over say a roots blower. this is because the voost builds with rpm. this take out a lot of the monster low down torque that can make high power/light cars harder to drive. also fitting the thing in would be easy. a little rerouting of things and you could have a nice D-sc1 ProChager cappable of about 900bhp on your engine.
id go for a porcharger over the vortech beasue of the location on the SBC (its a little further back) but both seem to produce the numbers!
please keep us posted on what you feel about them. be nice to see someone try it.
thanks Chris.
also if you plan on using one in an ultima, the way they diliver thier power could be benifical over say a roots blower. this is because the voost builds with rpm. this take out a lot of the monster low down torque that can make high power/light cars harder to drive. also fitting the thing in would be easy. a little rerouting of things and you could have a nice D-sc1 ProChager cappable of about 900bhp on your engine.
id go for a porcharger over the vortech beasue of the location on the SBC (its a little further back) but both seem to produce the numbers!
please keep us posted on what you feel about them. be nice to see someone try it.
thanks Chris.
Dont forget Eliot, you have 4wd.
And people going for big power in the US, do often use turbos, but again, they use huge slicks.
For a road car, on road tyres, where you want big power, and good power delivery, a CF blower is hard to beat.
There is little to choose between Paxton, Vortech and Procharger. I'd say they will all yield similar results, for a given size. Procharger does seem to have the largest range though.
I have a Vortech YSi on mine, and Im quite happy with it. Its the biggest "small frame" blower they do. Its rated at 1200bhp, although I think it would be very very hard pushed at that on pump fuel.
Forget SBC's, go LS1.
And people going for big power in the US, do often use turbos, but again, they use huge slicks.
For a road car, on road tyres, where you want big power, and good power delivery, a CF blower is hard to beat.
There is little to choose between Paxton, Vortech and Procharger. I'd say they will all yield similar results, for a given size. Procharger does seem to have the largest range though.
I have a Vortech YSi on mine, and Im quite happy with it. Its the biggest "small frame" blower they do. Its rated at 1200bhp, although I think it would be very very hard pushed at that on pump fuel.
Forget SBC's, go LS1.
pib said:I think as mentioned above people looking for the engine characteristics delivered by a centrifugal blower opt for a turbocharger, I suppose the only major advantage is that there isn’t any lag (although there is less power available at the flywheel and a higher moving mass in the engine).
Any ideas or reflection on any of this?
I seemed to remember reading somewhere that they used them on aircraft with gearboxes to keep the boost up.
I reckon that the boost levels rising exponentially to revs are a bad idea. I thought that's why people didn't like turbos. I suppose it depends on how your engine's set up. If you have a big power spike and loads of gears, great. If you have a 4 speed box with big gaps in the ratios, not such a good idea. It seems that people are getting good results with undersized turbos with broad torque curves. Personally, I'd run a screw blower if I had any choice but stick with a rootes for the moment. I'd never run a centrifugal blower. Worst of both worlds.
totally disagree.
Say you want a 5-6-700bhp road car ( or indeed more ).
With turbos, thats going to mean massive torque, and massive wheelspin once the boost kicks in. You could try and tame it by mapping boost vs rpm, but its still going to be tricky.
With a twin screw, similar scenario.
With a CF blower, mild boost at low rpm = less torque, more boost up top, more torque, and more power.
It works superbly in my opinion.
I honestly do miss that massive mid range boost feeling turbos give, but I know for certain if I had it, it would probably make my car slower on the road than it is now. So its rather pointless.
For a high powered road car, a CF blower is an excellent choice.
Say you want a 5-6-700bhp road car ( or indeed more ).
With turbos, thats going to mean massive torque, and massive wheelspin once the boost kicks in. You could try and tame it by mapping boost vs rpm, but its still going to be tricky.
With a twin screw, similar scenario.
With a CF blower, mild boost at low rpm = less torque, more boost up top, more torque, and more power.
It works superbly in my opinion.
I honestly do miss that massive mid range boost feeling turbos give, but I know for certain if I had it, it would probably make my car slower on the road than it is now. So its rather pointless.
For a high powered road car, a CF blower is an excellent choice.
stevieturbo said:
For a high powered road car, a CF blower is an excellent choice.
Wouldn't you recommend a turbo in that situation though? More work to fit I suppose, but once fitted I can't see any advantages of the CF blower over a turbo (apart from the lack of mid-range torque, and tbh I struggle to see that as an advantage).
Examples, using my own car obviously.
4.6 Rover V8 twin turbo, making say 500bhp ?
1st, 2nd were totally useless in the dry due to wheelspin. Very uncontrollable. Once boost starts to build, even modulating the throttle is difficult to hold it back.
Even 3rd gear on most surfaces resulted in very bad wheelspin.
When it did grip, it felt great....
In the wet it was useless in all 5 gears.
New engine, CF blower, and I'd be confident to say over 600bhp.
1st is useless. 2nd on a good surface is controllable. 3rd grips.
The car is a lot faster, and more useable. It puts the power down a LOT better.
Another example. Calders 1000bhp+ Supra. True its a race car, but it can smoke ET Streets most of the way up the 1/4 mile. It has broken into the 9's, but mose usually it runs mid-10's
Last I seen them claim was like 1200+bhp.
On road tyres, it can smoke the tyres for the full 1/4 mile. It would be mid 11's on road tyres at best.
It would be totally useless on the road.
Then take A friend ( hes on the viper forum ) who has a proven 920rwhp CF blown viper.
It too runs mid-high 10's, very repeatable, and on road tyres ( albeit softish ones ). It is 100% a road car, and can run consistent 10's. Calder's much lighter, more powerful, and almost slick shod car occasionally runs faster times, but most of the time its nowhere near its potential, due to wheelspin. Wheelspin is on tap in teh Viper up to 3rd gear in the dry. But its just as easy to put your foot down gently, and for it to grip. It can be driven with an element of control at all times.
You simply dont have that same torque control on a turbocharged car.
A twinscrew would probably fall somewhere in between the 2.
>> Edited by stevieturbo on Wednesday 17th August 20:12
4.6 Rover V8 twin turbo, making say 500bhp ?
1st, 2nd were totally useless in the dry due to wheelspin. Very uncontrollable. Once boost starts to build, even modulating the throttle is difficult to hold it back.
Even 3rd gear on most surfaces resulted in very bad wheelspin.
When it did grip, it felt great....
In the wet it was useless in all 5 gears.
New engine, CF blower, and I'd be confident to say over 600bhp.
1st is useless. 2nd on a good surface is controllable. 3rd grips.
The car is a lot faster, and more useable. It puts the power down a LOT better.
Another example. Calders 1000bhp+ Supra. True its a race car, but it can smoke ET Streets most of the way up the 1/4 mile. It has broken into the 9's, but mose usually it runs mid-10's
Last I seen them claim was like 1200+bhp.
On road tyres, it can smoke the tyres for the full 1/4 mile. It would be mid 11's on road tyres at best.
It would be totally useless on the road.
Then take A friend ( hes on the viper forum ) who has a proven 920rwhp CF blown viper.
It too runs mid-high 10's, very repeatable, and on road tyres ( albeit softish ones ). It is 100% a road car, and can run consistent 10's. Calder's much lighter, more powerful, and almost slick shod car occasionally runs faster times, but most of the time its nowhere near its potential, due to wheelspin. Wheelspin is on tap in teh Viper up to 3rd gear in the dry. But its just as easy to put your foot down gently, and for it to grip. It can be driven with an element of control at all times.
You simply dont have that same torque control on a turbocharged car.
A twinscrew would probably fall somewhere in between the 2.
>> Edited by stevieturbo on Wednesday 17th August 20:12
stevieturbo said:
You simply dont have that same torque control on a turbocharged car.
That's very interesting. My own (very) limited experience of turbos has been that the turbo tends to counteract the throttle and I seem to be fighting it all the time to get as much torque as I want, but I assumed that was just because I wasn't used to it. Maybe this calls for some sort of throttle-by-wire system to deliver torque in proportion to throttle position?
Not as simple as that.
Once a turbo engine has the ability to create full boost, it will pull almost as hard at half throttle, as it does at full throttle.
Im not talking low powered engines here.
So its almost like an off/on switch with power delivery.
One second you are making say 0psi, and have 100bhp. The next you can very easily be making 300bhp and with a lot more torque.
Ive driven both. I love turbocharged engines. The rush is awesome. But in practical terms, unless you have very good traction to make use of it, it isnt always going to be the faster car.
CF blowers have power delivery that is very user friendly. I do like mine a lot. Once I have more power, it will be even better, but its looking like I'm near my limit with my current 600cc injectors.
I'm going to have to get the bigger ones to work, although a stroker kit over the winter will help.
Once a turbo engine has the ability to create full boost, it will pull almost as hard at half throttle, as it does at full throttle.
Im not talking low powered engines here.
So its almost like an off/on switch with power delivery.
One second you are making say 0psi, and have 100bhp. The next you can very easily be making 300bhp and with a lot more torque.
Ive driven both. I love turbocharged engines. The rush is awesome. But in practical terms, unless you have very good traction to make use of it, it isnt always going to be the faster car.
CF blowers have power delivery that is very user friendly. I do like mine a lot. Once I have more power, it will be even better, but its looking like I'm near my limit with my current 600cc injectors.
I'm going to have to get the bigger ones to work, although a stroker kit over the winter will help.
stevieturbo said:
totally disagree.
Say you want a 5-6-700bhp road car ( or indeed more ).
With turbos, thats going to mean massive torque, and massive wheelspin once the boost kicks in. You could try and tame it by mapping boost vs rpm, but its still going to be tricky.
With a twin screw, similar scenario.
Not at all. With a positive displacement supercharger the boost never "kicks in". It's there all the time. The closest analogy to fitting a positive displacement supercharger in terms of power delivery is fitting a straightforwardly bigger N/A engine. It might be desirable to fit a spiral throttle quadrant so the pedal is less sensitive at smaller throttle openings, but you don't get that thing of fighting to get to the power at first and then fighting to get rid of it when it all arrives in a lump (unless you've got some sort of mental cam, which you don't generally want with a supercharger anyway).
I do get the impression from your posts on this thread that your driving style is rather different from mine... it sounds like you are happy to drive on revs, and therefore get on well with peaky engines, whereas I like to keep the revs in the middle of the range, so I prefer engines with flat torque curves. Perhaps it's a result of me being brought up on long-stroke British pushrod designs.
Not at all. I dont really rev mine past 6000rpm.
In fact every 1/4 Ive done so far, even on my new engine, I was shifting at about 5800rpm. Its something I need to experiment with, as mine is probably peaking at more like 6500rpm. Shifting at 6k just feels right though.
But there isnt much point in having say 500bhp/500lbft of torque at say 2500-3000rpm if it goes up in tyre smoke.
Im definately not wanting a big revvy engine. I simply want to make in and around 750-800bhp, and be able to make use of it on a road car. Thats never going to happen with a turbocharged engine in a 2wd car.
Ive tried and realised at much lower power, its a futile excersize.
In fact every 1/4 Ive done so far, even on my new engine, I was shifting at about 5800rpm. Its something I need to experiment with, as mine is probably peaking at more like 6500rpm. Shifting at 6k just feels right though.
But there isnt much point in having say 500bhp/500lbft of torque at say 2500-3000rpm if it goes up in tyre smoke.
Im definately not wanting a big revvy engine. I simply want to make in and around 750-800bhp, and be able to make use of it on a road car. Thats never going to happen with a turbocharged engine in a 2wd car.
Ive tried and realised at much lower power, its a futile excersize.
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