If you are interested in turbos, you want to go fast.  Being able to tune a turbo can help you go faster by letting you quickly and easily change the turbo’s behavior to best suit conditions.  At Borowski Race Engines, Inc., all our customers want to go fast so we wanted to learn more about Bullseye Power LLC’s NLX tuneable turbos.  This blog will share with you what we learned.

First, a little background.  A turbo’s performance is defined by what is referred to as its compressor map.  The outer limits of performance are largely set by the conditions at which the turbo will either surge or choke.  Surge occurs when the compressor is pushing against a higher pressure than it can produce.  The most frequent occurrence for turbo surge is when the blade of the throttle body closes.  Suddenly, the air has no where to go.  Another surge inducing condition is when the engine is not capable of ingesting the amount of air which the turbo is attempting to supply. Surge from whatever cause necessitates the use of some type of pressure relief to prevent damaging the turbocharger.  Blow-off valves between the turbo and the throttle body are one means of venting excess pressure.

It was learned many years ago that a turbo’s surge parameters could be changed by incorporating a groove between the inlet air bell and the base of the housing.  This groove allows some air to escape as the turbo is approaching a surge condition.  By doing so, it changes the compressor map.  The groove has therefore been dubbed a MAP groove.

Until Bullseye’s Bill Devine filed his patent application, no one had ever thought through the potential advantages of being able to adjust the width of the MAP grove.  Being skilled in the art of turbochargers, he knew any width change should theoretically affect the compressor map and therefore change performance of a turbo on any given engine.  His ideas were subsequently confirmed with bench testing.  The  embodiment of Bill’s invention is now Bullseye’s NLX line of tuneable turbochargers. The air inlet bell and turbo housing are threaded so that the groove can be quickly and easily opened or closed.  It is secured in place with 4 set screws.  Simple, as the best inventions often are.

We here at Borowski Race Engines, Inc. wanted to move from theory and bench to practical by running a series of dyno pulls to see the results for ourselves.  Our test protocol was straightforward. We coupled one of our 402in³, hydraulic roller, LS engines with a Bullseye 76mm NLX turbo and ran a series of back-to-back dyno pulls on E85 at different MAP groove widths in random order.  Each rotation of the threaded bell is 1/16^th of an inch.  We ran pulls at 0, 2, 4 and 6 turns thereby varying the MAP groove width from zero to 0.375”. 

The video below tells the tale:

Turbo Tuning with MAP Groove Width from Borowski Race Enterprises on Vimeo.

As described by Bulleye's David Hall, overall best performance as indicated by average horsepower across the rpm range was achieved with a midrange MAP groove.

Peak power for any dyno pull was 1,172.8 hp at 6,100 rpm with the MAP groove closed.  We at Borowski Race Engines call peak power a “hero number” because it’s what people want to talk about. More power across the rpm range is what wins races.  The 40+ horsepower spread between 4 and 6 turns was a surprisingly large difference to us.  It told us that its worth our time to find an engine’s sweet spot when we are running it on the dyno.

How else can this tuneability help a racer?  There were big differences in bottom end torque. 

As any racer knows, track conditions vary.  While you might want maximum power most days, a slick track might give better ETs coming out softer so that you can hook up.  With this tuneable turbo, you can adjust this engine’s torque at 4,500 rpm by 50+ lb-ft to best adapt to your needs at that moment.

In conclusion, we saw significant differences in performance between MAP groove settings.  We believe the tuning differences can be exploited by racers to find their overall performance sweet spot and adjust at track-side accordingly if conditions change.  Overall, this quick and easy tuning capability looks like a real winner.

Reference

1. United States Patent 9,932,885; Tunable turbocharger compressor cover; William Devine; Bullseye Power LLC; Muskegon MI