Sean H

well that is where the arguement begins... to still keep it basic, superchargers can make torque easier and turbos can make HP easier, and i am sure somebody will come back and argue that too.... they both can be tuned to produce either... they both are a compromise of sorts... i think turbos have more upsides with modern efi/computers, superchargers (gear driven style...) have the edge with carb setups.... then you have centrifugal superchargers which act like turbos driven off the crank....

basically any of them will/can work and in the marine industry right now superchargers rule.... but who knows what is next?

Reed Jensen

Turbochargers work by capturing the lost energy in the form of heat and expanding gasses.So they are more efficient than a crank driven roots type or screw type blower. There is a heat drop in the exhaust temp downstream of the turbo. This energy is then transmitted through a shaft the connects the turbine wheel to a compressor wheel. The compressor wheel pressurizes the intake system for more air and fuel to be forced into the cylinders... more charge into the cylinders... more pressure and heat from the exhaust... the horsepower and pressure build exponentially until the waste gate opens and diverts the exhaust away from the turbine wheel. On some models the nozzle from the exhaust through the turbine area is large enough that it limits the amount of pressure that the compressor can make... then there is no waste gate... but there is a loss of efficiency. Turbo systems on cars have a gulp valve that allows the engine to draw air from around the turbo system to lessen the amount of turbo lag at low speeds. But... once the system is fully pressurized.... the engine has to used the fuel and air that is in the system before the engine slows down.. so there is lag coming on the throttle and lag coming off the throttle... but coming off it's not as noticable.

Michael1

Having worked at Pontiac during the development of the Turbo Trans Am, and having looked at dyno data on that engine, the atomization was NOT terrible. In fact, it was better than any other engine in production at the time. Cylinder to cylinder air fuel ratios were within 0.1 from highest to lowest even at full throttle, while the non-turbo engine would be up to 2 points highest to lowest. It was as good or better than fuel injected engines. One interesting tidbit, is the fuel did slightly erode the compressor blades over time.

Also, blow through systems do not "blow all of the fuel in the carb into the intake", any more than driving from Pikes Peak to Death Valley is going to blow all of the fuel in the carb into the intake. The boost pressure is equalized on the bowl and venturi sides. Blow through systems actually have a tendency to run lean on boost, just like your car runs leaner at low altitudes. That's why guys like Gale Banks added fuel nozzles to their blow through carbureted systems, which were run by an electric pump while on boost.

Finally, the "lag factor" is nothing to worry about. You might have 1/2 cu. ft. of volume in the carburetor box on an engine that draws 800 cu. ft. per minute. The box would only represent 0.04 seconds of air. There is more volume in the tubing and intercooler of today's injected automotive application.

Roby, stick with us! We'll get you educated on turbos!

Michael

robyw1

Well if you're using the correct AR ratio and you have your compressor wheel properly clipped/trimmed for your given application, then it will create more torque than a supercharger will at any RPM. At RPMs above 1000 the Turbocharger's torque numbers jump out on the supercharger and skyrocket from there. The Torque curve of a Turbo is very high and very flat. A supercharger's torque curve ascends to a peak as the RPM's rise then taper off when the supercharger becomes inefficient. There is only one way to make a supercharger provide more low end torque than a turbo and that is put such a small pulley on it that creates boost at idle. Even then that advantage is short lived..... Very Short Lived.

To address what Reed said I assume he is referring to a Blow-off valve (BOV) As soon as the throttle blades are slammed shut you will experience what is known as compressor surge. If a BOV is not installed then this surge is forced back through the compressor wheel and out the airbox. This will act as a huge brake for the turbo shutting it down in a hurry. If a BOV is used between the compressor and the throttlebody being actuated by manifold vacuum behind the throttle body, the BOV opens up allowing this surge to escape into the atmosphere or where ever you decide to direct it. (The sound this makes is unmistakable) Anyway the use of a good BOV will not allow the surge to slow the turbo. This is why I say when your shifting gears in a car or your on & off the throttle of a boat you will NOT experience any lag if you are using a good BOV.

The downside to a turbo if there is one is that your exhaust between the engine and turbine housing is somewhat restrictive. Because of this cam timing on the exhaust side has to be specifically designed for a turbo to achieve the best results. There can be no overlap because the added backpressure with a turbo will magnify your existing reversion problem. The cam timing on the exhaust side has to be very quick to open and close while having to be able to exhaust an increased amount of spent gasses at the same time. This is not an easy task and is usually aided by using higher ratio rockers on the exhaust side. However your good marine cams are a good start because of their design to reduce water reversion.

Roby

Sean H

i volunteer my boat for a test boat.... who's got some motors?

robyw1

I would like to see those test results of the "improved atomization" of the draw-thru system. As I understood it the thing (80 TTA) ran so hot the fuel turned to vapor when it hit the compressor housing. That's not what I mean when I say atomization.

Also could you explain the function of those 3 stages of Turbocharging those cars had? Wait let me get my inhaler incase I laugh too hard

Roby

robyw1

Just so you can see the system were talking about.

Qball

This is a really good thread boys.....lets keep it that way. It would be great for all of performance boating to dig deeper into this. Let's not get this thread into a pissing match.

robyw1

It is all in good fun. I mean no ill will

Roby

Phknlwyr

And what affect does the increased atomization have on the seventh pfizter valve?