Some time ago we had a discussion about the difference btwn superchargers vs blowers vs turbochargers.

Here's the video I wanted to show then but couldn't find. Now I've found it and can no longer find the discussion thread!

Anyway, this is a TRUE supercharger. I believe this one is a 3-71, made by GMC, but several other companies copied this style so that might not be accurate.

Please note that the carburetor (not fuel injection system) is sitting ON TOP of the supercharger. The air/fuel mix is actually COMPRESSED inside the body of this SUPERCHARGER, then forced into the engine under pressure.

This SUPERCHARGER is belt-driven, which takes a few horses to drive it. These usually added about 50 'bolt-on' horsepower to the engine.

http://www.youtube.com/watch?v=YBwWXD_Rq7Y


Frank

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1970 240Z

That is a "roots" supercharger. The actual definition of supercharger is a device that increases the pressure of the fuel-air mixture in an internal combustion engine, used in order to achieve greater efficiency. Technically a turbocharger is a type of supercharger. Most consider any compresor that is belt driven by the crank to be a supercharger and when driven by exhaust to be turbos. Technically they are all "true" superchargers. There are just many types of them. Twin screw, centrifugal, roots, turbocharger - they're all superchargers.

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Rob
1971 240z

i've seen this video many times. pretty sweet until it failed.

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Mike Tubiak
1978 Datsun 280Z - HLS30-438694

Too much pressure or too much heat. Superchargers compress fuel/air which makes their 'breath' much hotter than the ambient temperatures. If it 'breathes' too hot into the engine, a number of bad things can happen. This one blew a head gasket, probably more because of pressure than because of heat.
That's one advantage of a BLOWER over a 'wet' supercharger ~ all the blower moves is air. It has heat issues too, but not like a vane-type (roots) supercharger does.

ALSO, these belt-driven true superchargers didn't create a huge amount of pressure (only in the neighborhood of 8 PSI), while some of today's turbochargers can pump out 20psi with the turn of a knob.

But these Roots style 'chargers pumped out BIG volumes of air under less pressure. The designation (3-71, 4-71, 6-71 etc) indicates how many 1780cc cylinders can be scavenged in a single turn of the supercharger impellers. If this was a 3-71 charger, it could pump out enough pressurized air to completely scavenge (3) 1780cc (71 cu in) cylinders each time it revolved. That would make 5340cc (or 5.4L) of air volume, which is greater than the 2800cc (2.8L) engine he tried to put it into. So his supercharger would have to compress the air at least twice normal pressure to get it all in there.

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1970 240Z

Well the problem with heat with any forced induction system is a matter of physics/chemistry. There is a law governing "ideal" gases...PV=nRT where p=pressure, v=volume, n is the universal gas constant, r=gas quantity (in moles, which is 6.02x10 to the 23rd power of gas molecules) and t=temperature in kelvins. Basically this equation means that if you double the pressure, you double the temperature of the gas ON THE KELVIN SCALE, which starts at absolute zero. In other words, if you run a lot of boost, the temperature of the air (or fuel/air mixture) as it enters the cylinder is already really hot. It is therefore very prone to pre-detonate and destroy pistons, rings, rod bearings, and head gaskets with great ease.
The problem is controlled with retarded ignition timing, lower compression ratios, alcohol or water injection systems, and intercoolers. An intercooler is really just a radiator that the compressed gas is run through in order to cool it down. The l-series turbochargers were not intercooled, so the amount of boost you can run on a stock system is limited. The same problem exists with the system shown in frank's video....that supercharger is feeding fuel/air mix straight into the intake manifold without any intercooling, and this is asking for trouble.

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71 on a rotisserie, two more in pieces in my shed...and a 69 1600 waiting for me to get to it

For example, the rule of thumb on the l28et is that you need an intercooler if you're running more then 10 lbs of boost, stock is around 7. (... my Z is intercooled... )

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Phil
1981 280zxt - Now in the care my son!
2014 370Z Sports Touring Roadster

now you've got me curious Phil...what do you get out of your car, hp-wise?

A manageable amount Filipe, I'm guessing about 250 hp. Never had it dyno'ed though. Once you're on the dark side, hp gets very addictive.

Stock hp is 185 at 7 psi. I run a 3" SS mandrel bent exhaust from the downpipe back, hi-flow cat and Magnaflow muffler which has a documented 24 hp increase. Currently running 12 psi (14 occasionally). Each additional psi = 10 hp. So, 185+24+50=259 hp. Of course you have to subtract some for the 96,000 mile, 32 year old motor.

The next step would be to increase fuel. I already run a Porsche 911 twin turbo fuel pump and could install larger injectors or a raising rate adjustable fuel pressure regulator, which has been sitting on a shelf in my garage for the past 3 years now. Or go the Megasquirt route.

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Phil
1981 280zxt - Now in the care my son!
2014 370Z Sports Touring Roadster

!!



....we should look into getting a drooling smiley face...

That thing is Huge. I have seen one at a show before, and it was much smaller and still used the SU carbs. I would be interested in finding one if possible. Not sure if it was home made, but sure looked cool and probably alot safer.

Latham and Judson made a series of excellent belt-driven impeller ("wet") superchargers for sportscars in the 1950s, which didn't blow things up. I recall seeing a good number of 4-cyl MGs with tiny little Latham units on them back in the day. Drivers complained that low speed performance was poor because those superchargers needed higher engine speeds to be efficient, but they always required a few horsepower to drive them even when they weren't giving anything back. Once the impeller speed built up to a certain range tho, it would increase the engine output by more than 50%.

In the mid-'50s and early '60s, Studebaker used one or two Paxton "superchargers" (technically blowers) to boost their cars and set quite a number of records. They were marketed as 'superchargers' because it sounded more socially acceptable than the proper SAE designation of 'blower', but that's what they were ~ they moved nothing but air, and forced it into the top(s) of the carburetor(s), rather than receiving air/fuel from the carbs, compressing it, and forcing it into the cylinders. They greatly improved volumetric efficiency which resulted in horsepower boosts and much greater performance.
I might be able to find pictures of both......

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1970 240Z

Here's a sweet-sounding little MGB on the Dyno with a tiny twin-screw type supercharger (made by Moss Motors) which boosts its horsepower almost 100% (70whp stock, 140 whp supercharged) and requires no intercooler.

This is a 4cyl, OverHead Valve PUSHROD engine. No guess what RPM he's hitting here, but it doesn't even sound dangerous.

http://youtu.be/B2idec1U2JA

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1970 240Z

If I can recall, the one I seen, bolted right to the L-series engine intake flush to the Head, then the intake runers and carbs bolted to this. Sleek and cool looking.

I found a few pictures of supercharged L-6 engines Paul ~ maybe the one you remember is among them?

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1970 240Z

those all look sick!

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Mike Tubiak
1978 Datsun 280Z - HLS30-438694