Detroit Steel

At first glance you might be inclined to write off this rare 1978 C3 as just some wild experimental design concept. But if you look beneath the cover, it’s packed with 880-horsepower and capable of going from 0 to 96 km/h in 2.5 seconds.

Read the rest on the Corvette Forum homepage. >>

Richard454

I remember that car for back in the day...

Although the new version of larger "Centerline" wheels make it look like a Hot Wheels Car...

REELAV8R

Which nozzle at the gas station provides JetA?

Mike Ward

I know(knew) the car very well

http://www.ncrsquebec.com/events/jet.html

My boss at work in 70's was the chief design engineer for the Indy Turbo that this car got it's engine from. An old buddy of Granetelli too.

jr9170

That is wild vette. love the old school Centerline wheels,although the new style are badazz...

REELAV8R

Cool. What can you tell us about it?
What is the primary difference between the St6 and the Pt6 turbine engines? Still reverse flow? Free turbine it sounds like in the clip.
How was it coupled to the transmission? Through a high stall torque converter?
The article alludes to the brakes being of some special purpose. Is that how you modulated the speed of the car with the engine "idling"?
Idles at what? 60% t0 70% or something then you have throttle for the rest?

Priya

The wheels make the car look awkward.

Mike Ward

The ST6 and PT6 are essentially identical engines, only differing in certification requirements which made the ST6 more affordable to the non-aviation market. All PT6/ST6 are of reverse flow free turbine design. The free turbine feature means that no transmission torque converter is required or actually desirable. The engine and transmission input shaft are directly coupled. When is car is stopped, so is the power turbine section. When the brakes are released, the free turbine will begin to rotate, much like taking the brakes off a wind turbine.

As the gas generator section idles (out of necessity) at around 60% speed, it's still providing enough energy to the power turbine section to propel the car at around 60 MPH. Although the stock brakes are enough to stop the car, they would be subject to fade as the driver is required to 'ride' them to keep the car at around-town speeds. Aftermarket brakes were selected for that reason.

One of the most common questions was about the big rectangular 'filter' or 'radiator' on the top of the engine. This was actually the evaporator for the air conditioning, nothing to do with the engine.

The first of the two videos was shot the same weekend as the pictures linked in my post. The car had been brought back to Pratt to have some engine repair work done and Cliff, the owner agreed to keep it on site to coincide with the open house. I organized a visit by the local Corvette clubs which resulted in about 60 cars showing up. I took those who were interested on a shop tour afterwards. There was a cutaway engine on display as shown in the pics- lots of question as it's not always easy for a pistonhead to grasp turbine stuff.

Gordonm

Mike is that a numbers matching car?

groovyjay

That car needs to be lowered big time!

3JsVette

That's better.

Priya

Wheww, those wheels look dumb.

Mike Ward

Yes, 100%. The number the buyer offer matched what the seller would accept. Definition #8 I think.

jr9170

REELAV8R

Thanks Mike. Interesting way to couple to the transmission. Seems like there would plenty of lag initially until the inertia of the stationary power turbine section plus the transmission/powertrain is overcome.
I know I can jam the throttles full forward and it will take a good 3 seconds or more before full rpm is achieved and the power section is already rotating at 70 to 80 % of it max rpm.
I figured the large "filter" on top was some type of heat exchanger. Air to air with an expansion turbine?

Mike Ward

There is. This car is not much of a performer off the line. The interia is not the main issue, a stalled turbine produces very little power but once rotating the output increases exponentially with speed.

The remainder of the AC system was pretty much stock GM as I remember.

Garys 68

So it is a manual (4 speed) trans?
Also, what was used for gear reduction? The turboprop unit?

Mike Ward

The stock GM turbo 400 autobox was used. The engine had it's own planetary reduction gearbox to reduce from 30K turbine speed to about 6K input to the transmission.

REELAV8R

You mention that a torque converter is not desirable in this app. Wouldn't a high stall converter have allowed the power turbine to continue to rotate eliminating some of the lag when power is applied from a stop?
It seems it would have allowed for less brake wear as well if the stall was somewhat above the idle rpm of the output shaft.
Heat would be an issue but could be managed? Too much torque for the converters of the era maybe or physical space constraints?

Mike Ward

With the understanding that turbine output increases exponentially with speed, the problem with integrating a torque converter (or any device that allowed the power turbine assembly to rotate) would be finding a way of absorbing the additional energy produced- the last thing you'd want if the goal is to slow or stop the car.

If the car was single-purpose for drags, then yes your idea would work but given that the car was intended for around town driving some compromises had to be made.

Something similar occurs on your aircraft- much easier to keep the plane still with the prop in feather rather than with the condition lever fully advanced- even though gas generator speed does not change.