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Less Boost= More Power

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EZ setting for ETH and factory injectors

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yep you read that correctly.

I was pushing almost 38 Psi on my HX-35, and I decided to slowly drop it down. Now I am at 28 psi and it pulls MUCH better at higher rpm's.

On a more interesting note, I was doing some testing, and when I pulled up to the line (yes this was on the street :D ;) )I sure got some interesting looks. After my tire warming session I was starting to draw a crowd. I made one solo pass and when I got back the other gear heads could not believe that I was running a diesel. One guy in a Supra asked to race, but chickened out after I told him what my max boost pressure was.

I am sure he would beat me, but he would not budge.

Ricers are just way too much fun to screw with.



The Illegal Street scene is way too much fun!



-Cliff
 
I've thought about this alot and it seems like when an engine has extreme boost, that it would run lean, unless modifications were made to supply enough fuel to go with all that air. If you can't supply enough fuel to get the fuel/air mixture to the optimum, then reducing boost theoretically would give more or at least optimized power. Wouldn't it?
 
On a diesel, there really is no "lean or rich". Excess fuel will just go out the stack black. Going back to some other resent posts, the IAT defuel seems to be the culprit in this scenario. Hi inlet air temps running above the turbo map= ECM defueling and timing retard to compensate. Lowering boost 15psi would drop intake temps about 120*. Defueling probably starts around 220*/240* at the IATS. Marco should know what the actual "cutback" temp is... T
 
The IAT sensor is used for fine tuneing the fuel/timing. In other words the IAT output is used by the ECM only at a steady load.

At WOT the IAT output isn't used by the ECM. That's one of the reasons a bad IAT kills MPG.

Marco
 
Ynot, I know what you are saying about lean and rich. What I'm trying to say is that there should be an optimum point at which the fuel air mixture produces the peak power with the least effort. If black smoke is coming out, then the engine is running "rich" and if the engine is defueled it is operating in a "lean" condition if you use the gasoline engine analogy. I don't know what other terms to use. The optimum or peak performance is a specific volume of air and specific volume of fuel to go with it. I would think that's why they have the MAP and IAT sensors so that the engine can get as close a possible to a complete burn, good power and reduced emissions. I have all of this as statements but really, I should have question marks afterwards cause I'm speculating.
 
Let me throw another theory in the pot for consideration. It takes work to drive the turbo to produce airflow (boost). Once boost is above the theoretical level required for optimum combustion, the additional air is just blowing through the combustion chamber, but work is being expended on the exhaust side (i. e. , the turbocharger's turbine) to compress this unused air. By lowering maximum boost via the wastegate, pre-turbo exhaust back pressure will also be lower since (1) a greater percentage of the exhaust is flowing through the wastegate and (2) mass flow of the exhaust and the resulting pressure drops are lower since mass flow of the intake air is lower. This will reduce pumping losses of the engine - the work required to push the spent gas and excess air into the exhaust manifold.



Rusty
 
Rusty, That's where I'm trying to go. That's what I meant about "optimum power with the least effort". If you take it to the extreme, why set the compression ratio at 16 or 17:1? If compression is a good thing, double it. Problem is, bearings go bad. The amount of work required to compress at that ration exceeds the benefit. And it you are putting 38 lbs of pressure in the cylinder before it compresses, aren't you making the engine work alot harder? The "effect" analogy of lean and rich is to ask, "when the engine is blowing black smoke (too much fuel to burn) is it performing better? When there is no smoke is the engine performing better?" I think the answer is between the extremes. I know mine seems to perform better when she smokes a little.
 
now that my turbo is running in it's efficiency map, everything is running cooler.

Intake air is cooler, EGT is unchanged, Top end responce and power is better.



an engine performs best when there is no smoke at all. If there is smoke then all of the fuel is not being burned. The soot you see in the clowd behind you is carbon particulate. All the hydrogen in the fuel has burned off but not all the carbon has been ignited.



Those of you with plugged boost ports or incorectly calibrated boost elbows may want to lower your boost pressure back into the efficiency range of the turbo. The result will bring a smile to your face. I know it did with me :)



-Cliff
 
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If we could just optimize the timing so the engine performs like it is built to perform we would probably have zero smoke, better mileage and longer lasting engines. Somehow tho we have to retard the timing to the point where only certain pollutants disappear. My old boss used to say that you could tell when a diesel was set up just right. No smoke on the flats with just a haze starting on pulling hills. If you ever try to stay with a tractor trailer set up that way, you'll see what I mean.
 
Alan,

I've played a lot with the timing of the ISB. With a "perfect" timing you get a better ( a little ) mileage, lower EGT's. I agree with you.



Smoke is another question though! With the pumping ability at low RPM's of the VP it's possible to over fuel the engine. Thus you get SMOKE. Believe me when I say, been there, done that!:D



Marco
 
Alan, to answer your first question with the numbers you're looking for, all internal combustion engines operate at peek efficiency between 12. 5 and 14:1 from what I've seen. That doesn't really equate with diesels, tho. Peek efficiency comes with medium compression and charged air, hence the turbo. For high HP's, lower compression and more boost works better for temp and load reasons. For mileage, no smoke is best, granted. For high HP, unburned fuel cools the cylinder and adds extra lubricity for the cylinder top and valve guides... T
 
Interesting! How come they dont moniter the exhaust carpon coming out of the chamber and control fuel by that . Seems you would get max efficiency?
 
let me throw a different idea at you. How about you get more air at the lower boost . The reason being at the higher boost the compressor wheel is cavitating, which heats the air. We sell a turbo for 425 Cats, it lower max boost by about 3-4 lbs Egr's are lower and Hp goes up. It drops inlet air temps over 200 degree's. Higher boost doesn't always mean more air. This is why clipping the fins on a turbo looks like it reallys speeds the boost up, but in reality gets you less air then a unmodified turbo.
 
One word....Backpressure

Diesel,



At 38 lbs boost, the backpressure or turbo drive pressure is probably close to double the boost psi. Your small turbo housing is choking the engine at higher boost psi. In other words@ 38 lbs boost your exhaust manifold and turbo exhaust housing has 75 psi of back pressure!. I don't know why more of us dont blow out our exhaust gaskets at high boost with the OEM turbo. The engine is struggling to get the spent exhaust out of the cylinders. Its corked up on the exhaust side.



This is why the Holset HX-40 16cm2 is killer at 40 lbs of Boost & high rpm's. Its drive pressure is close to its boost pressure. This is where you want to be. :)



Good article from Bruce Malinson: (below) :)



"The compressed air or intake manifold pressure enters the combustion chamber and forces out the burned hydrocarbons or exhaust. This process is called scavenging the combustion chamber. Now, what happens when all of the exhaust doesn’t get evacuated out past the exhaust valves and through the turbocharger? Simply put if the exhaust backpressure is greater than the intake manifold pressure, the exhaust will enter the intake manifold once the intake valve opens during valve overlap. This is not a good situation and you certainly don’t want this taking place in your engine. The results of excessive backpressure are high exhaust temperatures, poor fuel mileage and a tight running engine. What do I mean by a tight running engine? If your engine feels like you always have to push it, your foot is always into the throttle, the engine feels as though its being choked at highway speeds it just doesn’t want to glide along the highway, this is what I call a tight running engine. Too small of an air cleaner can also cause this problem, however in this article we are going to concentrate on the turbocharger and exhaust system. In today’s society everybody wants more boost or intake manifold pressure and to obtain more boost you decrease the size of the turbine housing (exhaust housing) of the turbocharger. Now that the exhaust has to pass through a smaller orifice or turbine housing, the velocity of the exhaust increases and the turbine wheel (exhaust wheel) spins faster which in turn spins the compressor wheel forcing more air into the intake manifold. Now all of this may sound good so far however once the size of the exhaust housing is decreased the piston on its upstroke must now work harder to force the exhaust out of the combustion chamber through the turbocharger. "
 
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Originally posted by McDowra

The reason being at the higher boost the compressor wheel is cavitating, which heats the air



Uh... I think you need to look up the definition of cavitation..... it does not apply to gases... . only liquids.



-Cliff
 
Sorry for butting in here But you guys are into a subject that has been a hot topic for a long time. so your making a lot of boost, great, but is that boost happening when you want it? Is the volumetric e' value of your engine able to flow that volume? Just go to a tractor pull and look at the smoke from a modified class machine. the balance should be for power and milage on a street machine. Racers don't care about milage or if they scorch a motor. If you are making lots of boost and no power you've gone beyond the design parameters of your engine. you need to check the cam timing, actual valve lift, flow CFM of your head, intake system and the flow of your exaust system. what is the actual compression?. mass produced engines vary a lot. also the pump may not be able to keep up with the demands. Alot of boost in the manifold is a cool thing to look at, but is the engine actualy breathing that mush air? I have driven trucks that when you pull a long hill and back off the throttle a little it will pull harder. some cummins and cats will do this and nobody can explain why. I don't know maybe it's something to do with the total mass of exaust at any given time or exaust pulse harmonics causing a loss of scavenging at the exaust valve just like in one of my race motors. I do this on purpose to flaten out a torque curve. maybe we could run expansion pipes?

Well that's my 2 cents worth for now. keep this topic going please. I love to learn new stuff. thanks for listening.
 
Ynot, I think I understand. Maybe that's why my old boss liked a bit of smoke on the the hills..... he probably understood the cooling effect of the unburned fuel. Hemi Dart, your post explains why the IAT sensors are carboning up on some of these trucks. Now the question would be, if the engine is not using an exhaust brake, why is there so much back pressure as to cause carboning in the intake?



HDM48, I agree on the boost. More is not necessarily better. I think most owners want it for the cooling effect I know with a Cummins 350NTC I used to drive, backing off WOT almost seemed like you were stopping the engine from "flooding" (to use a gas engine term).



Diesel Freak, look what you started. These are informative posts.
 
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I have had my "EZ" on for over a week now. Would you guys recommend that I put the stock Boost Elbow back on to try?



I don't have any gauges yet, and I don't want to increase the EGT's. Am I correct that the "EZ" puts in more fuel, and with lower boost preasures, my EGT's could get out of hand on a hard pull up hill?
 
Get gages first. I am not familiar with the EZ, but I hear it fuels like the VA and Power Puck. EGT's can get out of hand so I strongly suggest a set of gages before tweeking boost down to an efficient level.



-Cliff
 
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