Tuning and exhaust back pressure

[HD-tech-NH]

I tried the H&S HD300 today. I've been running spartan 275 for nearly a year now. Before spartan I used innovative. First impressions are good. The 300 pulls harder than the 275 did but falls off during gear changes. The innovative tunes were the same way. Does anyone have a theory as to why this would be? Lastly I'm planning on running a 75 mm RCD atmo with a stock hp. Any ideas as to how much of a drop in ebp I'll see?

 

[sideactiondiesel]

None .

 

[Groomzybanshee]

:whs:

 

[HD-tech-NH]

No drop in back pressure? I have my alert set at 82psi which goes off regularly on full throttle pulls. My baro is typically at 17psi. Should I start making plans to install a waste gate?

 

[sootie]

yep...sooner rather than later

 

[Pan4905]

If anything, ebp will increase.

 

[powerstroked08]

Your ebp will only drop with a vgt change. And that's if it has a different turbine.

 

[sideactiondiesel]

:whs:

Your ebp will only drop with a vgt change. And that's if it has a different turbine.

 

[B585Ford]

I tried the H&S HD300 today. I've been running spartan 275 for nearly a year now. Before spartan I used innovative. First impressions are good. The 300 pulls harder than the 275 did but falls off during gear changes. The innovative tunes were the same way. Does anyone have a theory as to why this would be? Lastly I'm planning on running a 75 mm RCD atmo with a stock hp. Any ideas as to how much of a drop in ebp I'll see?

I assume you mean as you shift and lose most of your boost that it takes a little longer to spoil back up? If so, I would guess this tune doesn't fuel as hard at lower RPM or vane position is different at lower RPM at WOT. What version tune are you running and what LBF are you setting it at?

 

[HD-tech-NH]

I assume you mean as you shift and lose most of your boost that it takes a little longer to spoil back up? If so, I would guess this tune doesn't fuel as hard at lower RPM or vane position is different at lower RPM at WOT. What version tune are you running and what LBF are you setting it at?

LBF @ 3
latest version
And your assumption is spot on.

 

[B585Ford]

LBF @ 3
latest version
And your assumption is spot on.

I always ran LPF 0 or 1 and was happy with spool up. Maybe, I didn't realize what I was missing since I have never ran Spartan tunes. If you have the unlock codes, you could make changes with MCC or get a hold of Matt (GH) and get him to make you some tunes.

 

[Morgan@Midwest Diesel & Auto]

None .

:whs:

If anything, ebp will increase.

Your ebp will only drop with a vgt change. And that's if it has a different turbine.

:whs:

Please tell me why ebp will not be lower, or why it will go up....

Please explain why adding an atmo with a larger turbine than anything else out there is going to add BP?

I agree you need a gate, but I absolutely disagree with any statements that BP will stay the same or get worse when adding a RCD 75.

 

[powerstroked08]

The only reason I'm saying that the ebp will not change untill a larger vgt turbine is added is because the vgt to my understanding is the "bottle neck" both up pipes go to it first and then dump to the atmo. Now I guess if there is less pressure in between the atmo and the vgt then technically the ebp can drop some. But not as much as with a larger turbine in the vgt. But that is only my opinion and how I have wraped my head around this.

 

[Morgan@Midwest Diesel & Auto]

Yeah I understand. But from experience getting the back pressure away from the vgt will drop some across the board. Helps the vgt get rid of its pressure.

The reason the vgt is the biggest bottle neck is actually on the tiny compressor side. Think, your trying to shove the air from a huge 75x102mm atmo though the tiny cast 52mm vgt...

 

[B585Ford]

Yeah I understand. But from experience getting the back pressure away from the vgt will drop some across the board. Helps the vgt get rid of its pressure.

The reason the vgt is the biggest bottle neck is actually on the tiny compressor side. Think, your trying to shove the air from a huge 75x102mm atmo though the tiny cast 52mm vgt...

IMO predicting EBP with compound turbos is one of the most difficult things to do so I am glad you chimed in....seeing 2 or more very knowledgeable people disagree is always good for learning/understanding. As you stated, the compressor on the VGT is relatively small and as mentioned earlier, I always thought the compressor on the VGT acts as a bottleneck. To me, that would suggest that ANY atmo turbo that flows more air than the stock atmo will increase EBP because the VGT is compressor is the problem. If the 75 would produce an equal or lesser EBP, there obviously has to be other factors involved. As Powerstroked08 said earlier and you eluded to, if there is less EBP coming from the atmo turbo (less pressure in the intermediate pipe), then total EBP may come down. If I following your logic and/or real world results correctly then the total EBP is more dependent on the EBP coming from the atmo than the EBP produced by the small compressor (bottleneck) of the VGT. Is that correct? I guess another factor which may be present and seems impossible to predict is the flow rates. By that I am referring to velocity each turbo allows to flow through the turbine. I am basing that off the results from the Stead Speed exh manny and up pipes. In that case, although there appeared to be less restrictions on the flow of the exhaust gases (based on the less abrupt turns and larger diameter plumming), the velocity of the exhaust gasses actually slowed and caused the EBP to rise while producing less boost. Is that a factor regarding just changing the atmo?

 

[sootie]

the RCD 75 stands alone because the turbine is larger, thus lowering backpressure.

 

[B585Ford]

the RCD 75 stands alone because the turbine is larger, thus lowering backpressure.

??? so you disagree with everyone else that the VGT acts as a bottleneck??? Or the bottleneck of the VGT has minimal effect even with a much larger compressor than stock?

 

[sootie]

??? so you disagree with everyone else that the VGT acts as a bottleneck??? Or the bottleneck of the VGT has minimal effect even with a much larger compressor than stock?

nope-not sure if you meant to quote me, i never once said that. My point was that of all drop in atmo chargers on the market today, only the RCD has a larger turbine which does lower backpressure.


obviously we arent changing the exhaust side of the vgt even if we do a larger drop in however; the boosted are from the atmo must pass thru the vgt on the compressor side therefore if it is larger, it requires less work on the atmo's part to get that boosted air thru thus potentially lowering back pressure (still maxes out the stock sensor on mine tho...so i dont really have exact pressure difference from stock HP)

 

[Morgan@Midwest Diesel & Auto]

Ok, I think I will make this easier to understand.

Exhaust back pressure is the restriction to flow through the turbine housings.

All vgt's using a stock turbine will have the same ebp readings on the same truck regardless of the compressor. You can only flow so much through the stock turbine wheel and housing. The only one that will lower ebp through the vgt is the elite 59 with larger turbine which is different than their standard 59 drop in.

The same goes for all atmo's using a stock turbine. Except the rcd 75 which has a larger turbine. So, the only drop in atmo that will truely lower physical ebp is the RCD.

So just like anything if you add a 75 to a any vgt it will reduce intermediate backpressure on the vgt. Which will in turn lower total ebp.

Then if you combined the large turbine elite vgt with the large turbine 75 then you would have the most flowing setup. That is all on the exhaust side.


The compressor side is totally different. The air comes in the atmo, then the atmo pushed the air through the compressor of the vgt. At a rate of more that the vgt can flow by itself. That is why they are compounds. If the vgt could produce enough, air then we wouldn't be shoving air from the atmo, and it would be used as a single. In any compound setup, you lose efficiency of the atmo from forcing air through the hp turbo. In a 6.4 with a large atmo and stock vgt then them you are further restricting the percentage of the atmo's capability. Going to a larger free-er flowing vgt compressor allows the atmo to push more air through it easier. Therefore gaining higher volume of airflow in the engine. Upgrading the vgt doesn't actually make more power, it allows the atmo to make more of the power it's capable of making.

 

[Morgan@Midwest Diesel & Auto]

Any turbo is more efficient as a single than as if it was an atmo in a compound setup. That is due to the parasitic energy lost out of the exhaust by turning two turbines/compressors versus one and the loss from forcing the larger volume charge air from the bigger turbo through the smaller turbo compressor.