Discussion
Sorry have to dissagree with the above post, yes the ones favoured on the post are much easier to fit due to the way they produce air flow, but are not true superchargers they are mechanicaly driven turbos which means they are in fact high speed fans. We did the original TVR350SX supercharged car and have been supercharging engines for more than twenty years. The mechanicaly driven turbo is much easier to use because it can be fitted to blow in front of the throttle body and can be controlled by the throttle between the head and the turbo. Thich means it does not have to be matched to the engines requirements nearly as closely as a proper supercharger which is not a fan but a compressor which would blow the trottle spindle straight into the engine if it was closed quickley at high revs. Proper supercharges have to be controlled at their inlet. The turbo type are much cheaper and can produce the power but have the same power delivery as an exhaust driven turbo. A proper blower gives much more instant air at low revs which improves the bottom end power and torque hence there use in the drag racing scene. At the moment we have a Procharger blown Mustang engine in the workshop which we have tested against our twin screw conversion on the same engine, we were asked to change the engine because the owner did not like the power delivery, nothing below 3000rpm until the fan spooled up. TVR and others used the turbo type units and got the power which is ok if you want to rev the engine and give your gearbox a hard time.The screw type give low end grunt and keep on doing it all the way to the rev limit which means much less use of the gearbox with a reduction on shock loading for the box. One day I will get round to building a speed six with a proper blower but up until now the internals were not good enough. YAHOO and I have often talked about doing an engine for his car.
If you want to rev your engine all the time and enjoy that type of power delivery then the fan type of blower is fine and will give you all the power you want but at the cost of engine and transmission life.
If you want to rev your engine all the time and enjoy that type of power delivery then the fan type of blower is fine and will give you all the power you want but at the cost of engine and transmission life.
Edited by scooterscot on Saturday 9th February 18:21
I'm using the same logic - a relatively low peak power but very broad power band (4.6/M112) to reduce the number of gear changes needed, less time coasting, fewer shock loads on the transmission, less disturbance to the balance of the car, less workload on the driver. In my case I'm sticking with a relatively cheap bottom end too.
But I can see the advantages of the centrefugal blower. They are far easier to package, tend to be more efficient (safer for a given boost level), and I think it could really suit a revvy engine which you want to be docile at the bottom of the power band and pull like a train when you rev it.
But I can see the advantages of the centrefugal blower. They are far easier to package, tend to be more efficient (safer for a given boost level), and I think it could really suit a revvy engine which you want to be docile at the bottom of the power band and pull like a train when you rev it.
it is a very interesting subject,i was looking at a twin screw but but i was put off by the ammount of work needed to fit one and also the power delivery,a few people have commented that with a twin screw you hit maximum boost a 3000rpm which would suggest a lot of low down torque tapering off at the top end , with a centrifugal blower boost comes in around 3000 depending on the set up.
is it possible to run a twin supercharged engine with a twin screw and a cenrifugal charger to give boost all the way through the rev range ??
is it possible to run a twin supercharged engine with a twin screw and a cenrifugal charger to give boost all the way through the rev range ??
tuscandom said:
it is a very interesting subject,i was looking at a twin screw but but i was put off by the ammount of work needed to fit one and also the power delivery,a few people have commented that with a twin screw you hit maximum boost a 3000rpm which would suggest a lot of low down torque tapering off at the top end , with a centrifugal blower boost comes in around 3000 depending on the set up.
is it possible to run a twin supercharged engine with a twin screw and a cenrifugal charger to give boost all the way through the rev range ??
What would IMO make a lot more sense is either turbo on its own (they seem to be getting a *lot* better at avoiding lag these days, and you're talking about a relatively low boost solution here) or compound super/turbo charging with the supercharger just to overcome the turbo lag and then the more efficient turbo taking over. But at these low boost levels I wouldn't have thought all that effort was justified.is it possible to run a twin supercharged engine with a twin screw and a cenrifugal charger to give boost all the way through the rev range ??
tuscandom said:
was talking to someone who was fitting a turbo away from the engine bay near the back end of the exhaust to avoid the heat..interesting
I thought the conventional wisdom was to keep the exhaust temperature and speed as high as possible upstream of the turbo and keep the pressurised volume in the intake and exhaust as low as practical. Putting the turbo on the tail pipe would seem to go against all that. It might be fine once you've got everything spooled up, but I can't help thinking that you're making life much harder than it needs to be. People seem to get by fine just shielding the exhaust and turbo, running much higher boost levels in much more cramped engine bays than yours.A good twin screw blower such as the Opcon will give good power and torque all the way to the rev limit. Our conversion on the 2 valve 4.6 Mustang engine fitted to the MGZT260 takes the power up from 260 to over 400hp.The torque 435 lbs is almost flat from 1600 to 5500rpm with max hp at about 5600 rpm. This is achieved using only 9psi (intercooled) The blower can go to 15psi with ease and over 550hp on the same 4.6 engine.The unit is a 2.1 litre blower and it would easily take the speed six up to 600hp. Many of the American twin screw kits only give power up to 3000rpm because of the top gear ratio which is usualy in the region of 50 mph per 1000rpm. On the MGZT260 MG changed the top gear ratio for a 29 mph per 1000 rpm from the 50mph one which ment that the Rouch Eaton twin screw prototype engine which I have in my workshop had the all below 3000 set up. When we tried it on the road it was not very nice to drive due to its power delivery and it ran out of puff at 3000 rpm. This is the classic American set up, we decided to use the Opcon which is by far the most efficient blower(about 84% against most others less than 50%)in doing so along with very careful matching of the blower size and drive speed we get a smooth delivery all the way to the 6000rpm engine rev limit.Over the same distance this 1900kg five seater can reach 147 mph against the Tuscans 152mph, just shows it is all about torque.
If you would like to see the conversion have a look at www.dreadnoughtgarage.co.uk
If you would like to see the conversion have a look at www.dreadnoughtgarage.co.uk
The Eaton will do the job but it has to be a little bit of a compromise to get the supply to match the engine demand. It will be a great help if you have very good intercooling as the Eaton output temp goes up much more than the Opcon when you ask it to work hard.The dyabatic efficiency of the Opcon is about twice that of other makes. I cost of the Opcon is much higher, but I think it is worth in our case as we are blowing engines for other people and the better we get it the happier our customers are. Dennis Priddle showed me a charge cooler that he made which was fitted in place of the standard unit on a Jag, the engine made more than 30 bhp with the same blower. We are going to use the trick charge cooler on our prototype 1800 K Series engine figures say we should get 280 plus bhp.
Once we have blown up the 1800 K a few times and got it right we might look at the speed six. The speed six will be a tough nut as it has a very special feel to it and the blower will have to be very well matched to keep its character.It might need two kits the revy one and the grunty one
Once we have blown up the 1800 K a few times and got it right we might look at the speed six. The speed six will be a tough nut as it has a very special feel to it and the blower will have to be very well matched to keep its character.It might need two kits the revy one and the grunty one
scooterscot said:
I must be out of touch, could you give me an example would like to look at the reasons.
see here on procahrgers web site.http://www.procharger.com/racing-news/07update-aug...
Got dirt? Brothers Scott and Mike Bracken from Lee’s Summit, MO churn-up plenty of it with their twin Hemi 7,200 Modified tractor puller. After recently switching from roots blowers to ProChargers, the Hemi torque output was increased by more than 25%, and horsepower by more than 45%. Running in the Missouri State Tractor Pulling Association events, the Bracken Brothers are a force to be reckoned with. Equipped with a ProCharger F-3R 139, each Hemi puts out more than 2,000 hp and a dirt-churning 1,638 ft. lbs of torque. At the August 18th event at Oak Grove, MO, the Brackens came in second with a pull of 331 feet. And then, a week later at the El Dorado Springs, KS event., took home the win with a pull of 395.01 feet
also here is a thread on the advantages/disadvantages to both.
http://www.ls1tech.com/forums/showthread.php?t=860...
from what i have heard top fuel guys would be running turbo now if they could but the rules dont allow them! would be much easier to tune the engine for the power they needed when they needed it (ie not all off the line like they have now!!).
as for what the bigger guys are running, the best i have seen form a ls type engine is 800bhp and similar torque. these number, inc the torque, are much easier to achive with a paxton or procharger F-1A than they are with a Kenne Bell twin screw.
Cheers
Chris.
Hi Chris have to agree with your post but tractor pulling is a bit different from road work. If you fit a bigger output unit you will make more power but that is not what I was talking about. You also compare different installations, I was talking about the types of blower and their performance in respect of power delivery in a road car. In tractor pulling you put your foot to the floor, hang on and wait.
scooterscot said:
Hi Chris have to agree with your post but tractor pulling is a bit different from road work. If you fit a bigger output unit you will make more power but that is not what I was talking about. You also compare different installations, I was talking about the types of blower and their performance in respect of power delivery in a road car. In tractor pulling you put your foot to the floor, hang on and wait.
you right but lets take the style of cars TVR's are. ie light rear wheel drive cars.now we all love torque, it the thing thats puts you into the back of your seat no matter what gear you are in. using a roots type blower you get all the boost (and thus torque) at about 1000rpm. thats great, but having a shed load of torque from 1000rpm onwards in a TVR would be useles. its like dropping a 502BBC in there. yes it would be very fast if you had the grip, but on uk roads i cant see it working!
now with a centrifugal setup you actually push the power and torque curves up and to the right. this means there is now a constant increase in power and torque across the whole rev range. i have seen many torque curves on centrifugal superchargers that are nearly as flat as well tuned N/A engines. its a much smoother delivery than a roots supercharger or even a turbo. yet you still get the big hitting numbers at the top end like a turbo would. having spoken to some guys drag racing using these type of superchargers they say its much easier to control and actually get the power down and they say its more like driving a NA car than and other power adder.
as said before though there is no right or wrong way to supercharge anything. i think it would be an inresting package, and VERY fast, if you put a positive displacement supercharger (please make it a twin screw) on a speed six engine! however i thing a rotex or procharger would be more suited to the characterisitcs of the car.
Chris.
What you say is correct but the throttle is not used like a switch on a road car. You can't have too much power or torque but you can give too much throttle for the gear you are in and the grip you have. The drag race cars are well over 3000hp now and this sets very different delivery needs,sticky goo on the track,slicks that act like tracks as they go flat at the contact patch etc.
If I do a speed six it will be with an Opcon and we will then see what its like on the road, the TVR has a special character and that may be lost with a blown engine.
We have fitted a lower final drive to get a feel of more torque and the car responds well to that.
If I do a speed six it will be with an Opcon and we will then see what its like on the road, the TVR has a special character and that may be lost with a blown engine.
We have fitted a lower final drive to get a feel of more torque and the car responds well to that.
Interesting to read this topic. Having driven a procharger supercharged S6 I can say that it does suit the car very well and as chuntingdon has commented it does pile on the power very progressively and enables the car to be dragged from the lights, whilst also remaining useable in the wet without being a traction loosing nightmare to control. IMO due to their light weight the S6 cars are not exactly in need of huge amounts of low down torque that a positive displacement compressor would give. (By the way a centrifugal is still a compressor, Jumbo jets wouldn't fly otherwise and natural gas would not be exported at pressure down pipelines). Scooterscot does hit on the main point tho, the engine needs serious mods to be able to cope with the heat and the stress, my first attempt went very wrong due to poor fueling application and set up, inadequate components for the job and poor assembly practice, but S6SFX has detailed that debacle. Supercharging is a very expensive route to gain more power from the S6, but if it works out this time around it will still be worth it as it just enhances the superb characteristics the S6 already has. For those of you whom have ridden a high performance 4 stroke bike I am sure you will agree that the S6 has a similar acceleration curve through the rev range (of course its not as fast as bike tho), it just keeps on pulling to the last gasp. I can tell you that the Centri blower helps the car get to that last gasp that bit quicker. scooterscot, I would be very interested to see you guys roll a car out with a Positive displacer, I hope you do and wish you all the best with it.
G
G
Gassing Station | Speed Six Engine | Top of Page | What's New | My Stuff