Less Boost= More Power

[GWS]

So, if I'm getting 44lbs boost at WOT with my stock turbo, how do I adjust my boost down, and to what pressure?

 

[Amianthus]

(Guys, steer me right if I am wrong on this. ) Here's how I understand how this subject works.



If your turbo is puting out 40 psi of boost, that's roughly a charge air temperature of 400F. Now if the aftercooler has the capacity of removing 85F across it, you still have 320F charge air. Now if you are getting 30 psi boost you are getting roughly 300F charge air and 215F post-aftercooler. This will allow for a more dense air charge as air at 215F is more dense than air at 320F.

There is a point at which the gains of more boost are overcome by the temperature of the incoming air. Thus causing excess heat in the cylinders during burn. This is compounded by the backpressure of the turbine exhaust housing. If the housing is too small, you will get more retained heat, and cause the turbine to spin faster. That in turn will make the problem (high charge air temp) worse.

On a bigger turbo, the exhaust gasses are allowed to spin the turbo at a speed more suitable for a proper air charge temp. And still allow the exhaust gasses to escape with lower back-pressure.

Someone fix me if I'm wrong.



BTW, GWS post your sig. Then we can start to tell you where to begin.

 

[R.ebel]

maybe we could run expansion pipes

Now that would be cool, wonder if its ever been tried on a diesel

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[McDowra]

Amianthus

thats what i was trying to say. more boost doesn't always mean more air.

 

[Ted Jannetty]

Boy this is great!

This is exactly what I have been saying all along.

Here is a list of facts I have collected and would like to share.



A 12cm2 housing flows like a 12cm2 housing with the wastegate blocked off.

a 12cm2 housing flows like a 16cm2 housing with the wastegate operational.

Hence back pressure is kept to a minimum.

Blocking or disabling wastegates hurts efficiency, hurts power, increases charge air temps, creates way too much back pressure, etc.

Every turbo has a efficiency map, or boost range.

Running them out of that map just generates a ton of heat the intercooler can't get rid of.

34 lb. boost will support 485 hp, so if you have less than that, you should have less boost.

Less cold boost is better than more Hot boost.

Every turbo has a CFM rating at efficent turbine shaft rpm, spinning them faster just generates heat.

Don't get me wrong you can raise boost some without going out of the efficiency map say 4-8 psi, but you only want to add enough boost to have a clean tail pipe under load.



Turbocharger sizeing IS ROCKET SCIENCE! and there are only a handfull of people outside the factory's that know how to do it right, buyer beware!



The moral of the story is Don't Disable wastegates only adjust them as necessary to match additional fueling.



For the HX 35 I would stay below 34 psi.



21 psi will support 350 hp on 24 valve engines, you need about 24 psi on 12 valves because of the cyl. head design.



EGT can go higer with too much boost, You might ask, how much is too much?

Answer; anything more than you need to achieve a clean tail pipe with your given fueling.



You will reach a point where the cyl is full and can't possibly burn all the fuel that is put in, that is when you get black smoke, and excessive EGT, with no more power.



I believe, that it is 485 hp on the 24 valve engine.



We can burn more fuel than that, if we use Propane or Nitrous to speed up the burn process, then 600 hp is within reach.

 

[GWS]

Is the boost adjusted (down) by backing off the allen screw inside the brass wastegate elbow?

 

[Diesel Freak]

Originally posted by GWS

Is the boost adjusted (down) by backing off the allen screw inside the brass wastegate elbow?

Yes, that is exactly how I did it. Turn the screw out 1/4 turn at a time.

 

[hdm48]

Lots of very good info here. all of this should be saved for future cummins owners.

T. Jannety, I'm curious, what els are you going to do with your ski-doo's and forman? the reason I ask is I own Miller Racing Engines and I do m/c and atv motors. we have some great hill climbs and grass drags. are you a racer or just a fun rider?

I'm just nosey.

 

[Marco]

Good post Ted!



I think the wastegate blocking story started to "see" the actual power increase a certain mod could provide. The more boost = more power became then a common thought. Like you're saying, that's not true.



Finally we're starting to use our brains instead of the muscles here!



Talking about efficency, what about adding a fan or even more than one in front or behind the intercooler? That would surely rise the efficency range of the intercooler. Water injection?

What else?



I'm more than convinced that we all togheter can find new ways/mods to raise the efficency of our engines!



Marco

 

[Ted Jannetty]

I think a fan would get in the way of air flow through the intercooler.

A water spray bar in front of the intercooler would work Very Good to cool it, You know, Evaporative cooling!



I believe if we stay with in the limits everything just works better.



hdm48, I just ride for fun, and like to make improvements where necessary, also like to experiment!



I did run a snowmobile at a dragstrip on asphalt back in 97.

I also did the grass drag circut in New England in 98 and 99.

Had alot of fun but too much like work.

 

[GWS]

Even with the MAP sensor power derating taken out of the picture with the boost module, the ECM will defuel the engine in the event it is informed by the IAT that intake air temps are above the allowable limit (whatever that is). So if all this excess boost is increasing intake air temps how come we never hear of anyone setting a DTC for it?

 

[Alan Reagan]

That's a good point GWS. I'm looking at a modification now where I need to know the temp in the charged air system. I don't know if the air temp goes up 10* per lb of boost. I am beginning to believe it doesn't. When I did the IAT measurements Marco suggested in another thread, the IAT runs out of measurement capablity pretty quickly.

 

[Powder Extreme]

What the hell I'll thrown in my 2 cents worth. I have a SPA gauge that reads the intake air temp right above the intake manifold (in the elbow from the intercooler line to the engine) I just got back from a trip to Maryland, so I've seen all sorts of altitudes and temperatures. At normal cruising the intake air temp is 5 degrees more than the outside temp, very consistant boost reading 3-7 lbs. Climbing a hill or racing that show off hot rod in the slammed Dakota with the "worked over" 360 the intake air never got more than about 30 degrees hotter than it was outside, boost maxed at 34 lbs. Running the air conditioning while cruising would give me a 10 degree difference in air temps, also very consistant altitude didn't seem to affect these readings. While running 75 in a strong head wind for about 50 miles, boost reading 15-20 lbs the intake air was running about 25 degrees hotter than outside with the A/C on. Suprisingly when the temp would go up while climbing a hill, it would stay cooler and cool off faster if I left the Horton fan clutch turned off. On this trip I saw outside temps from 45 degrees to 105 degrees. My opinion is the intercooler works much better than we are giving it credit for. The intake air will heat up, but it's gonna take quite awhile at full throttle, which with these beasts just isn't necessary.



Sorry for the long post, hope it sheds some light

Jerry