I ran across one of these while working on a large construction excavator today. Is anyone familiar with variable pitch turbos? Is this a new technology or something that has been around for awhile? What are the intended benefits from such a system. I suppose in theory the turbo could spool much more quickly using a mild pitch load on the vanes and then switch to a more aggressive pitch once up to speed? The Turbo i was in contact with today looked like the pitch was varied mechanically via a linkage coupled to a servo. I'm betting a turbo like this would be significantly higher in construction cost.

Ben Burris

86.5 Indischrot, AT. #1459

 

Yes. I think it was invented by Chevy or such in the past 3 years. Vanes that raise and lower centrifugally.

 

Which end do you suppose is varied the compressor side or the exhaust impeller?

 

Exhause afaik ... because it lies down flat when not used allowing far more efficient idle and low-rpm breathing

 

The technology has been in use in the aircraft business for decades. Garrett Air Research is a big pioneer in the field. Not sure how long it's been in use for automotive/racecar applications. Extremely expensive to produce. Each vane must be balanced perfectly. Faster the spin the more air is induced as the vanes pitch. More air, more boost. Allows for a smaller packaging size. Manually or computer operated pitch is common in use for helicopters and large machinery. Big bucks! Crude versions are even in use in heating and air conditioning systems. There has even been experiments with varible pitch vanes on root blowers for drag racing.

 

I recall a mention of a variable-pitch vane mechanism in turbos in a Road & Track article in the mid-80's. I believe the article was about aftermarket units specifically intended for Mercedes turbodiesels, but the discussion of the benefits was exactly as you pointed out. I recall a set of airfoil-shaped vanes placed circumferentially around the exhaust impeller -- I think the idea was to almost close the vanes together at low exhaust flow/rpm (to increase gas velocity, hence impeller rpm and boost) and open them up with increasing flow/rpm. The vanes on the impeller itself were fixed. I had a Saab turbo at the time and was immediately interested in the potential to help increase low-end boost and reduce turbo lag. I never heard of it again though!

 

Corky Bell talks a lot about the Aerocharger variable area turbo in his book, but I think they've since gone out of business. Here's a cutaway of one:

 

Bingo!!

 

The Aerocharger did not require a wastegate in the system. I think it was handicapped by low boost limits and poor reliability.

 

I saw someone explaining one this weekend on either Rides or Overhaulin. They stated with the vanes almost closed during initial spin up, there was virtually no turbo lag.

 

This concept is used on big rigs as well...usually an activator opens it up under heavy load. Some chrysler turbos from about 86 had a Garrett version. The Aerocharger was a unique concept and worked well but the bearings failed miserably and the company is out of commission....there is a patent but the guy won't sell the design out. I get that straight from Corky.