Supercharging - Why cant we have more cars with this?

[Robin Plummer]

Supercharging is a thing of past, is it a thing of the future. Why don't more pruduction and racing engines have it (Drag Racing aside?. The best example I have seen is the Lancia Delta S4 rally car that had low pressure boost supplied by a roots charger and high pressure boost by a turbo. Discuss.

[Peter Mallett]

Being a fan of all things MG I have read quite a lot about supercharging. Back in the 30's MG produced more production cars with this than most of the other manufacturers. (They won a lot of records in the up to 750cc classes). The K3 Magnette was a fine example of a small supercharged sportscar, which was driven by, among others, Nuvolari and Count Gianni Lurani.

The problems with supercharging are really based upon the amount of drag on the drivetrain that the supercharger imposes. It is however quicker to respond to the throttle than a turbo.

The turbo, is more economic in terms of energy usage but falls down in response time (throttle lag). That's why the Delta S4 had both.

Of the two the turbo is the better because a) its lighter and b) its easier to fit.

That's my understanding anyway. If Frank were here he'd no doubt tell us that these things were tried by LSR car builders before the egyptians built the pyramids!!!

(PS. You can edit that last bit out if you like Sparkster).

[KC]

A lot of the arument concerning supercharging versus turbocharging comes from what you are attempting to do. Turbochargers were developed by Porsche to create more upper range horsepower for their small displacement engines in sports car races. Races where they typically faced larger displacement machines with higher torque. Superchargers, roots type as opposed to centrifigal, generate low end torque and have been highly developed in US drag racing circles where rpm was thought to be less important than stump pulling torque. The centrifigal supercharger was used quite a bit in Indy cars on the Offenhauser engines where the rpm was kept more or less constant. The Pontiac Bonneville and Buick Regal in the US employ superchargers to build more torque from the fairly weak (as compared to most import 6 cylinders) GM V6 powerplants. Most factory turbocharger applications in the US are seen in large diesel semi trucks where rpm is usually constant. Both Ford and Dodge also offer commercially designed turbo-diesels in their light truck lines for increased torque.
I have heard of dual super-and turbocharging methods where the supercharger is used to develop low end power and then passes on to the turbo for improved breathing on the top end. Superchargers, being a relatively low speed pump, begin to face heavy thermo losses at high rpm and do not work in the upper ranges nearly as well as turbos. Also, superchargers will cost some level of power as they must be mechanically driven whereas the turbo system uses the exhaust gas.

[Leo]

A example of the drive-train losses of a supercharger: the supercharger on a Jaguar XJR engine delivers about 120 HP at maximum. Since the XJR is about 80 HP stronger that the regular 4.0 litre Jag, it's quite obvious how much HP it costs to drive the supercharger.

I want to speculate on a possible application of supercharger however. I see a possible use in small cars like the Smart. You can fit a relatively small and low-power engine, which is very economical. Then if you add a supercharger with its own clutch (so it can be switched on and off, like the Mercedesses from the thirties), you can add power only when needed. You don't have to drive the supercharger unnecesarilly (like is city traffic, traffic jams and so on). If you combine this system with a continious variable transmission (CVT) and design the proper software, you can run the system fully automatic, and so that you achieve maximum performance and economy.

By the way, aren't the current high-compression-ratio, low-boost-pressure turbo's (used by Volvo, Saab) a good alternative for superchargers??

[Slowcoach]

In 1992 Aston Martin introduced the Virage Vantage (I believe their most powerful production car upto that point) boasting a 550 BHP engine , still using the trusty V8 but with the addition of twin superchargers . A few years later , with the limited edition Le Mans version , the power was upped to 600 BHP . My point is this - for the new DB7 Vantage AM chose to develop a brand new 6-litre V12 engine rather than using a smaller existing engine with supercharger/s , surely if such a marque (considering their American ownership) were prepared to go the route of a new engine ( although I wonder if , dare I say it , it was actually 'borrowed' from elsewhere in the group ) then surely the supercharger is indeed a thing of the past.

[KC]

I am not sure if the European car market got the supercharged Toyota MR2 (previous styled body) that we got here in the US, but they used a similar setup to what Leo was referring to. The mounted a small displacement supercharger to their low torque 1.6 liter engine and used a modified A/C clutch to engage the system. It only worked when the throttle sensor picked up the demand for it. As Toyota did not produce the system for very long I am not sure how well it actually worked.

Another method used by Subaru in their WRX competition machines a few years ago was a small electric drive motor attached to the turbocharger shaft that kept it at a minimum speed so that after a throttle life off and subsequent wastegate dump, the boost was reapplied quicker as the turbo accelerated faster.

Most production based engines have switched to smaller displacement turbos because of the latest advancements in ferro-ceramic coatings and high temperature bearings allow the turbo to be more efficient than the supercharger. CART also uses small turbos becase they react faster and shorten the turbo-lag to a minimum.

One thing I never understood concerning forced induction systems is why not use an accumulating system? The turbo or supercharger can be used to pressurize a boost bottle and the extra induction pressure can be employed via a throttle sensing solenoid. The nitrous power boost kits available today use this type of method but with nitromethane for a fuel boost. Why not just use the compressed air charge for the same?

[Peter Mallett]

Originally posted by KC
Turbochargers were developed by Porsche to create more upper range horsepower for their small displacement engines in sports car races.

I think you'll find that turbochargers were initially developed by Daimler Benz in the thirties to improve the power of diesel engines. It was this idea which led Whittle down the jet engine route. At least that's what I read last week.

[enzo]

KC :

You'd have to have a HUGE bottle to hold enough compressed air to give a boost of any meaningful duration, & the power requirements to compress enough air to high enough pressure would far out weigh any gains.

Just think for a second of how big a tank is used for a typical 5 HP shop air compressor, how long it takes to get that tank filled to 120 psi, and then how fast it drains down using a single 10 cfm air tool.

Doesn't mean that it can't be done - it just would have a packaging problem in your typical small car !

[KC]

I think that most of the turbocharging technology was originally developed by Daimler for the German military in the Luftwaffe. I knwo they used turbocharging and nitrous injection in various long range bombers.

As far as the volume required for a accumulator, if the boost was only applied for acceleration and not for continuous duty I think a relatively small bottle at very high pressure could be used. If used in a 1.0 liter engine a temporary boost of say 20% more horsepower could increase the driveability without destroying the efficiency. The bottle would have to be large and the compressor section would take up too much power to make a continuous duty accumualator feasible.

[Robin Plummer]

This may be irrelvant to Supercharging but people have knocked Skoda cars for some time. But did you know why one of the reason's Hitler invaded Cheqzslovakier (cant spell!)? Because he wanted the Skoda factiores as they had the technolgy to build his Panzer tanks powered by damiler-benz engines!!

[yelwoci]

As PM mention Lancia S4 used a twin system which wasn't always two separate devices but they tried a combined unit called a 'Comprex' I think. The belt drive provided teh low speed power and a clever pulse wave assistance during the mid phase and then full turbo thereafter.
I believe it was better than a pure supercharger, but not as effective as a turbo at full power.

VW's G-charger uses a scroll pump, which is supposed to be quieter and more efficient than the Rootes or straight centrifugal unit.

IanC

[Michael M]

The supercharger was invented by Swiss Alfred Buchi in 1905, it was a mechanical driven centrifugal compressor. The first racing cars to use these types of superchargers were American Chadwicks from 1907. They ran in the Vanderbilt Cup Races and the Savannah Grand Prize, proving fast, but unreliable.

Centrifugal supercharges had been widely used in aero engines in WWI (and of course also in WWII), because they increased the inlet air pressure, which decreased at higher altitudes. Don't know about any turbochargers used in aero-engines, but would not exclude any research work in this direction.

In the early 20s Daimler-Benz did a lot of R&D to apply the aero-engine supercharging to automotive engines, and concluded that the centrifugal supercharger was unsuitable, they used instead rotary-wing type superchargers (Roots system). Centrifugal compressors are more effective, but the additional power is only available at high revs, and it comes like a "bang", whereas Roots type compressors are more smoothly, with power increase over the whole rev range. The BRM 1.5 ltr V16 e.g. used a centrifugal supercharger, this was the reason for its phenomenal power, but also for its undrivability.

Development in the USA went into another direction, centrifugal superchargers had been found more efficient for oval racing, where most of the engine operation is performed at more or less constantly high revs (Miller, Offenhauser).

All these superchargers, whether centrifugal or rotary-winged, had been driven mechanically from the engine itself, so there was of course a limit of efficiency when the power needed for their operation exceeded the power they produce.

The exhaust turbocharger was not invented by Daimler-Benz, but also by Alfred Buchi as early as 1915, and the first turbo in an automotive engine was introduced in 1938 in a Swiss Saurer Diesel truck engine. Since today most turbochargers are used in Diesel engines, because there they achieve the best efficiency.

However, the first gasoline engine with an exhaust turbo was of American fame, in 1962 the Chevrolet Corvair Monza and the Oldsmobile Jetfire had been the first passenger cars using this system. It was not fully developed and unreliable, so dropped very soon again. The next serious attempt came from Germany, in 1973 the BMW 2002 Turbo, and in 1975 the Porsche 911 Turbo. On the racetrack, the first exhaust turbo driven engine appeared in 1972 in CanAm, the all-mighty Porsche 917/10.

Coming back to Robin's initial question of using (mechanical) superchargers in modern racing and production engines. Mercedes is using the supercharger since a few years again in their production models, the SLK 230 and the E 230 are available with this option. Just read that the next series of 2 litre engine in the standard E 200 saloon will be available only supercharged (Kompressor). They use the old Roots system in developed form, with 3- instead of 2-winged rotaries. Leo's idea of supercharging for micro cars looks interesting, but I think the main hurdle for such a system will be a financial one. Microcars are sold with economical argumentation, and such system would increase the production costs considerably.

Talking about competition engines, in case technical regulations allow forced induction, the turbocharger will be always more efficient than both mechanical systems.

Peter, also one more word to MG. Did you know that MG was indirectly involved in the development of the Mercedes-Benz M154 3 litre GP engine? The German driver Bobby Kohlrausch received in 1936 from Abington "EX 127" to participate in the German "Speed Week", where he set the new record in class H (750 cc) to 225 km/h. DB bought this car in 1937, and tests showed 115 HP at 7000 rpm. This was 153.3 HP per litre, equivalent to 460 HP for a 3 litre engine, and was the target set for the M154. Interesting to mention that this figure was only achieved in 1939 with the latest version of the 3 litre GP engine (M163).