Banks Big Head

[More Power]

<a href="http://www.thedieselpage.com/reviews/bighead.htm" target="_blank">Banks Big Head
More Boost for the LB7 Duramax 6600 </a>

The key ingredients to more turbodiesel power are more fuel and higher boost pressures. The Banks Big Head incorporates an adjustable turbo wastegate linkage, allowing you to raise boost pressure to get that power increase.

[Jim Brzozowski]

Got a question. There was a comment about hiting the dreaded 39 psi and causing turbo overspeed in the article..
How would increasing the boost cause turbo overspeed. Wouldn't the intake side of the wheel be pushing against more pressure resulting in slower turbo speed, unless of course the exhaust gas was flowing a so much higher speed due to restrictions in the exhaust? I don't think I understand enough about this. Also, If one installs that BIG Head, will the computers compensate for fuel flow etc, without setting codes?

[More Power]

I've heard from two separate individuals over the past couple of years who each said their turbo disintegrated at 39 psi. One had a turbine wheel come apart and the other a compressor wheel failure. It is the centrifugal force at very high turbine speeds that cause the damage. A high EGT could also affect the turbine wheel side, contributing to its disintegration.

Yes, it takes a lot of fuel to get to 39. I don't have the mod details for each truck used in the above examples, but that figure of 39 psi for two separate instances was enough for me to suggest a problem at that boost pressure level.

Now, I have heard that there are a few intrepid Dmax owners who are running with their LB7 wastegate wired shut. Lord, have mercy on their souls..... :D

Personally, I am choosing to use nitrous to pick up the slack when more boost might improve performance.

I'm still not quite to 30, but no codes yet... I'm told the ECM can only read to 26, so you'll need a mechanical boost gauge to see what's really going on.

MP

[Seth McKinney]

Does the bighead do anything for setting 3 juice -- setting 2 predator?

I guess is it any benefit to us that don't have wicked crazy mods?

Thanks -- this looks interesting.

[More Power]

Does the bighead do anything for setting 3 juice -- setting 2 predator? Most of the popular power boxes/programs are engineered to work within the limits of the stock boost pressures and Allison torque limits (at least for a while). Even with a competition Edge (150) (http://www.thedieselpage.com/reviews/attitude.htm) or VanAaken (150) (http://www.thedieselpage.com/reviews/dsgbanaaken.htm), the amount of exhaust smoke doesn't really beg for more boost. However, more boost would likely reduce exhaust temps for those who tow heavy.

The BH is prolly most beneficial to those who are pushing the limits with big programs or boxes (200+). ;)

MP

[Seth McKinney]

Figured that...

Maybe next year I will go for another Tranny. I am about tapped out for the year.

Any recomendations for a good tranny smile.gif

[madmatt]

Any recomendations for a good tranny
Proloc or ATS.

[More Power]

Seth, I agree with Matt, and would add that you should pay attention to what the 12-second (or faster) trucks are using - in so far as transmission durability is concerned. There is an increasing number of options in trans upgrades these days, and perhaps we'll discuss some of them in an upcoming article.

I'll be visiting with the folks at BD (http://www.diselperformance.com) shortly, where I hope to interview their trans builder and shoot some photos. Proloc (Suncoast) has been in the forefront of Allison upgrades, and ATS has been an early pioneer that pays attention to those who are putting down serious power. A trans from any one of these builders would do a good job.

Lil Red (http://www.thedieselpage.com/features/project2-16.htm) will be getting a performance Allison in the next few weeks - probably a Kennedy/ATS. Making power with the Duramax is easy. Getting it to the ground is a whole nother story. :D

MP

[BMDMAX]

I have been pretty happy with the Big Head wastgate on my truck so far. I got it set initally per the instructions and then fine tuned it on Kennedy's Superflow. Having the boost mapped on the dyno plots was a great plus in getting it dialed in.

I run mine at 35 PSI, the highest spike registered has been 37.5 pounds. I have been running it in that fashion for close to a year now. It is right on the bleeding edge of the risky side but sometimes you just gotta push the envelope.

Best diesel only dyno pass to date is 539 HP so it does help with the bigger programs. :D

[rjschoolcraft]

Originally posted by SoTxPollock:
Got a question. There was a comment about hiting the dreaded 39 psi and causing turbo overspeed in the article..
How would increasing the boost cause turbo overspeed. Wouldn't the intake side of the wheel be pushing against more pressure resulting in slower turbo speed, unless of course the exhaust gas was flowing a so much higher speed due to restrictions in the exhaust? I don't think I understand enough about this. Also, If one installs that BIG Head, will the computers compensate for fuel flow etc, without setting codes? The compressor uses rotational speed to impart centrifugal acceleration to the air. This is how the work is done to get compression, or increased outlet pressure. The speed of the air exiting the impeller is usually reduced by a diffuser section or duct to increase static pressure and reduce losses associated with high flow velocities.

The pressure ratio across the compressor is a function of rotational speed and mass flow rate. The volume flow rate, in this case, is determined by the engine speed. For a particular volume rate of flow (engine speed), the only way to increase pressure ratio is to increase the rotational speed of the compressor so that the mass flow rate increases. If you plot lines of constant engine speed on a map for varying pressure ratios, you'll see that the lines are diagonally inclined up and to the right on the map.

All turbomachinery parts have a maximum speed limit for mechanical integrity. Centrifugal stresses can eventually overcome the strength of the material and a burst will occur.

The "maximum boost pressure" before burst will vary for different engine speeds, since that affects the needed impeller speed for a particular pressure ratio. If you look at a compressor map, the constant impeller speed lines curl downward as the flow rate increases. This is because you are moving farther away from the peak efficiency of the impeller. Therefore, at higher engine speeds, the burst speed of the impeller (or turbine) will be reached at a lower pressure ratio than when at lower engine speeds.

The 39 psi limit is good for only one particular engine operating speed. If one knew what that was, we could get an idea of what the curve looks like.

[Jim Brzozowski]

ronniejoe, excellent response, backs up my idea that as long as you don't mess with the rev limiter one shouldn't be able to have enough engine speed to spin the turbo too fast, of course any kind of imbalance would always be pretty quickly catastropic. Is there a vibration sensor near the shaft of the turbo, like in the big fuel gas turbines? I also tend to cringe when I think of someone blocking their waste gate and then get into a situation of engine overspeed on a very steep mountain pass somewhere, I would never think about doing that. Everything has its purpose. Thanks to responses like yours, we all know a little more about the turbo now.

[rjschoolcraft]

Thanks for the kind words, but it looks like I need to add a little more information here for clarification.

When I said that engine speed dictates volume flow rate, I did not mean to imply that controlled the speed of the turbocharger. The engine speed and displacement of the engine determine how many CFM it will move. Now the density of those Cubic Feet passing through each minute can vary significantly.

Think about a gas engine with a carburetor. If you are running along at 75 mph, say at 2500 rpm and suddenly let off the throttle... what happens? Well, the throttle plates close creating a very severe restriction in the inlet flow path. The engine, at the instant the throttle plates close is still spinning along at 2500 rpm. Let's assume this engine is a 350 cid Chevy, for grins. At 2500 rpm, the postive displacement pump that is our engine is pumping 253 CFM. When the throttle plates close, the engine is still pumping 253 CFM at that instant, but the air is very low density. In other words the volume flow rate stayed the same but the mass flow rate dropped significantly. Each cubic foot now weighs significantly less than when the throttle plates were open.

In our turbo diesels, the compressor controls the mass flow rate, while the engine controls the volume flow rate.

The compressor is driven by the turbine in the exhaust stream. While there is some expansion that occurs across the turbine, the primary driver for these is turbine inlet pressure (or back pressure in engine terms). This pressure is determined by several factors, including engine speed, combustion temperature, etc. For a constant engine speed, say 2500 rpm again, the turbine inlet pressure (TIP) can vary significantly. Consider the same scenario as above. In the case of the diesel, when you let off the go-pedal, you are controlling fuel flow directly and the flow drops to idle setting. This will immediately lower the TIP and cause the turbo to slow down, making less boost.

If you were to run your truck on a chassis dynamometer, the control could be set to hold a constant speed no matter what the torque out put of the engine is. For instance, you could run the engine up to 2500 rpm with very little reaction torque supplied by the dyno. This would require very modest accelerator pedal application and very low fuel flow. The engine would hum along with some very low level of boost pressure, say 2 or 3 psi for grins. Now begin to mash the pedal down. The dyne controller has been told to hold speed no matter what, so it increases the reaction torque to do just that. Now the engine is laboring at 2500 rpm under load. Fuel flow is signficantly higher and boost pressure is now higher as well, say 15 psi. Push down further (to the mat), and the dyne will increase reaction torque to hold speed. The engine is now making all the torque it can at that point with significantly higher fuel flow and significantly higher boost pressure, maybe 25 psi.

In the first condition described above, the turbo is loafing along at, say 80,000 rpm (these are all just made up numbers, but representative none the less). At the second condition, turbo speed is up to, say 100,000 rpm. At the third condition, the turbo speed is up to 120,000 rpm.

All this happened at a constant engine speed. The volume flow rate did not change, but the mass flow rate changed significantly as a result of the faster spinning compressor impeller. This is possible because by adding more fuel, the combustion temperature goes up, the cylinder presssure goes up and therefore, the TIP goes up. This spins the turbo faster.

Hope this makes things clear as mud! ;)

[Jim Brzozowski]

Totally clear, sure cleared up my misconception about engine speed control. Thanks again.

[Kennedy]

Originally posted by BMDMAX:
I have been pretty happy with the Big Head wastgate on my truck so far. I got it set initally per the instructions and then fine tuned it on Kennedy's Superflow. Having the boost mapped on the dyno plots was a great plus in getting it dialed in.

I run mine at 35 PSI, the highest spike registered has been 37.5 pounds. I have been running it in that fashion for close to a year now. It is right on the bleeding edge of the risky side but sometimes you just gotta push the envelope.

Best diesel only dyno pass to date is 539 HP so it does help with the bigger programs. :D We also added a little doo-dad to help the Big Head more yet...

[Jim Brzozowski]

I'd ask what that dodad was, but I don't think I could afford it. Was that 539hp with the VA-200only?

[chris duncan]

is there a version for the LLY Duramax

[Kennedy]

Originally posted by chris duncan:
is there a version for the LLY Duramax No wastegate on the LLY turbo...

[chris duncan]

Originally posted by kennedy:
</font><blockquote>quote:</font><hr />Originally posted by chris duncan:
is there a version for the LLY Duramax No wastegate on the LLY turbo... </font>[/QUOTE]Kennedy

Thanks, I am still learning about my Duramax truck.