Engine Power Curves: What is best for the various end uses? - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 18 (permalink) Old 01-10-2010, 06:13 AM Thread Starter
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Engine Power Curves: What is best for the various end uses?

Looking at the various Dyno graph outputs I have seen curves all over the place. This got me thinking what do we want the idle curves to look like based on end goal. By goals I mean Towing, Economy, Street Power, 1/4 mile, Competitive Pulling.

I have seen:

Tunes that: Torque shoot up at a sharp angle to a early RPM peak and the Horsepower jump up early as well and it flat

Others that have torque making a even arc up and down thru the RPM band peaking in the middle with HP making a gradual upward curve to a high RPM peak

Some with very flat HP and and torque curves

So what is "ideal" for what?

Also what about the trade off of higher torque peaks for broader HP bands or later torque peaks etc..

I also have seen it said a number of times to much toque to soon is not good. Sometimes I see much higher torque peaks for the same HP as a tune with lower peak but at a higher RPM thus the same or more HP

So what would we want to see for the various tunes we all tend to use:


Street Tune( general day to day use):

Towing:?

Economy:?

Race or Track( 1/4 mile): ?

Pulling(would this differ):?

What about one looking for the max HP regardless of usability Call it a Dyno Tune:?

Also how does Cylinder pressure and timing (SOI) play into all of this?

What is the safest for the engine?

Are there generally accepted curves patterns for each of these or is there large various in view points from tuner to tuner.

Where do we want to see peak torque come in. How much is too much?

what got me thinking about some of this was looking at a post by [email protected] PHP. He was posts some of the preliminary data from his blown engine questionnaire. One of the things he mentioned was that it seemed many of the engine failures had come from relatively stock motors and from use of what many tuners label the 80 HP Tow Tune. In thinking about towing a lower RPM peak torque would be beneficial but what would that mean from a engine stress or cylinder pressure standpoint. Now as that would also likely give a great seat of the pants feel to it for someone that decided to WOT it going street light to streetlight, many may like to use that tune as there general use tune or the one they leave it on by default. Then use that tune to really work the motor hard thru the entire RPM band @ WOT etc.. If torque to early tends to break stuff easier would that stand to reason this would not be a good thing. What tunes put the most stress on the engine if use for WOT. That then opened the door to what would be considered the ideal curves for these various end goal uses.

Also Diesel Power Magazine in the Feb printing release the article on its dyno and testing of 4 popular tuners tunes. It was a not to highly modified 97 F350. What was funny is they had Beans Stage 1 Sticks in it but did not try his tunes for the test? Unfair advantage maybe? Anyways for those that have not seen it. It was Tony [email protected] Diesel Performance, [email protected] Truck Shop, Tade [email protected] Diesel, and Jod[email protected] DP Tuner

Here is a link to the article:

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post #2 of 18 (permalink) Old 01-10-2010, 01:54 PM
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Re: Engine Power Curves: What is best for the various end uses?

Here is what a good dyno graph looks like when tuned right... All the dyno sheets in that artical would scare the sh!t out of me if they where on my truck other than BTS that one looked good.


1999.5 F-250 7.3l 4x4 6 spd Ported Heads, Head studs, valve springs, DI Push Rods, DI RR, 38R, Walbro fuel pump, 238cc Injectors from Nate @ Unlimited Diesel and Tuned by Matt @ Gearhead Automotive


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post #3 of 18 (permalink) Old 01-11-2010, 01:27 AM Thread Starter
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Re: Engine Power Curves: What is best for the various end uses?

That is rot of what I had thought i understood from what I had seen those on here that have experince with it basically say. I figured a nice long curve. Obviously the longer you extend out the torque peak in the RPM band the higher the HP but also as a higher RPM as well . But then seeing those got me to thinking about how possibly for different performance goals you may want the curves to be a bit different. Such as towing. What good is it to have a peak torque and HP so high up in the RPM band that you will likely never use it? Wouldn't a nice flat HP curve bee good for street cruising or DD. I know there is so much mroe than this that goes into tuning and this is simplifying it down to just the basic curve itself. I am not saying I support the above that I am asking questions about but rather is that legitimate reasons for manipulating the curve? For towing what does some of the big rig engine tunes set up for doing nothing but that look like?

I found it interesting if not a bit insulting that the author insinuated that Cales tune which we would consider one of the safer and better tunes was good if you were looking to win on a Dyno. To me that was basically hinting that other tunes were better for actual use. Not that I at all agree with this.

Then you had him report back what we have heard a number of times about TW tunes that they are very twitchy on the throttle which does tend to make them fun but at the same time harder for DD n certian conditions.

To me I would think you would want your HP to take a nice upward curve toward the RPM band max actually just slightly before that max. I coudl see how some woudl see that as a bit of a waste as it moves the torque peak up in the RPM band to where you would not be hitting it as much in the RPM bracket you would expect to. The thing is especially for modified engines they are putting out so much torque that even not at the peak they are producing more than enough for general use. To me that brings up another point do you tune curves differently for lower power engines than you do for higher HP engines. For a basically stock engine would it be better for general use to keep the torque peak a bit sooner and HP flatter as the torque is not so high as to be breaking things? That torque as an absolute number is lower and thus it would be of benefit at a earlier peak. But as you move up adding more power to the engine you need to move than torque peak up as the actual number itself woudl otherwise be so high as to cause reliability issues to the parts.

I found it interesting that taking into account he entire useful RPM band only Cales looked like what you would expect from performance vehicles engine power curve ie a performance race tune. Where you have HP climbing up to a max just shy of max engine RPM and torque making that typical fairly even arc. After all this testing in the Diesel Mag test was about which tune made the most power as in what would have the vehicle be the fastest. At least that is what I woudl assume as perf is usually shown on the 1/4mile track or top speed both of which Cales Tune would have taken the day IMO regardless of what the author stated. If what he said was tune then all drag race engine curves would look like TDP's.

Anyways comparing curves to what you see in typcial what are considered factory high performance vehicles it seems they sure look more like Cales tune.

Example here is dyno chart for an '08 Mustang:



Stock 2010 Camaro SS




Now a 09 ZR-1 Vett



Lastly a [email protected] 1/4 mile Dodge Viper



Now compare any of those to what were seen. Regardless of what the RPM total band is you can see the curves all basically have the same rounded torque curve and a steady climbing HP curve toward the RPM engine max or there about.

Now compare that to these:

















To me Cales is the only one that looks comparable as does yours Big_Stroker. The rest have basically flat HP curves and torque curves that race straight up to a early peak and then fall off at a more gradual angle similar to how Cales and Big Storkers HP curve climbs. I also looked at a couple race diesels and their tunes, 6.4 PS 5.9 C and a durmax, had similar curves as the perf gassers, Cale's, and Big_stroker's( Matts Tune) with steep HP rises to jsut short of max RPM and curves that made a gradual up and down curve

Now this of course is looking at these tunes from the perspective of race perspective. But what I see from those graphs is once you hit about 2400-2500 you are basically done with building power with the others. they do climb marginally from there to their peak which is still long before their red line max RPM. So is all that RPM is being left on the table so to speak. All the power and perf being bunched into that short performance band for engines that do to design and fuel type already have very short total RPM bands to being with? For a pure perf tune would you not want to use the entire band? Also the authors statement about the one building power the earliest being the one that would win the track, I woudl think it would have to be a very short track as I woudl think while that may be an advantage off the line it woudl hurt it as you wind thru the gears.

What I would also like to know beyond that is how does stress on the engine components come into play. I know I have seen posts on torque coming in to early and peaking being a bad thing as far as that is concerned.

Now also not forgetting the question of would any of this be changed for towing tunes or economy tunes?
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post #4 of 18 (permalink) Old 01-11-2010, 04:24 PM
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Re: Engine Power Curves: What is best for the various end uses?

I wish I could have singned up for that little magazine test but I digress....

The most average HP through the RPM band used to race will make the fastest truck. So the curve that makes the most average HP will be the fastest. A built motor like Blowby's can handle 1800 ft-lbs throughout the powerband and stay together. A stock forged rod engine should never be taken over 1200 ft-lbs IMO.

When towing, the power these engines can produce would break drivetrain parts if run at WOT anyway. You don't run an extreme tune at WOT when towing.

Look at those power curves in the magazine. You are dealing with stage 1 injectors that can't make good high rpm power because of a slow injection rate due to the stock nozzles. You also don't really have enough fuel to break any parts on a forged rod motor unless you really screw something up.

The Hybrid tunes I developed last year were designed to have the best of both worlds with an injector that has the potential to make better high rpm power and keep things safe for stock bottom ends. The faster injection rate allows for better higher RPM power (above 2600 RPMs). Nothing special here just a new thought or two 'injected' into this old game. Keep the torque safe and let it eat up top.
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post #5 of 18 (permalink) Old 01-11-2010, 11:18 PM Thread Starter
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Re: Engine Power Curves: What is best for the various end uses?

That is what I have come to understanding reading as much as I can on all of this.

So for stock bottom ends they are in two groups: Forged and PMR

For Forged you are saying the max torque that is safe is 1200 lb

For PMRs I am assuming it is lower but how much? 800lb maybe?

So, when you have upgraded injectors and turbo which can obviously produce torque way over this 1200 lbs the way you handle this is: You move the torque peak up in the RPM band as you also now have the abilty with the larger nozzles to get the fuel out fastest enough for correct SOI? This also stretches out the HP band and moves its max up in the band as well?

Looking at those dyno charts from the article I think it shows that. Look at any of the tunes other than Cales. They are running a tq peak much sooner with sharper curve and have higher actual tq. Cale has moved the torque curve up in the band which lowers it actual peak but has the effect of moving the peak HP higher and also extending the upward curve of both.

For towing would you want things to be flat?


So here is a question: Does torque peak location ( in the band regardless of the actual number cause more stress(whether its within parts tolerance or not) on engine parts if it peaks early in the RPM band or later? What puts more stress on the parts? 1000 lb @ 1600 or 1000lb @ 2400? I would think the early the sharper the curve up so...

Now I always also see tuners speaking of wanting to get the curve flat for towing. That to makes sense but at lower peakc, correct?

What really struck me with the tunes shown in the article was how completely different Cale's was to the others.

So of those tunes which one would you prefer ?

You said the power of this motor with forged rods does not make enough power to be breaking parts unless something like super advanced SOI etc .

So becasue of this they can afford to have peak tq come in earlier etc? But apply those same curves to a engine with more fuel and air and you will break things as the tq will be to high.
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post #6 of 18 (permalink) Old 01-11-2010, 11:54 PM
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Re: Engine Power Curves: What is best for the various end uses?

As simply as I can put it to apply to any diesel engine? It takes fuel to make torque, it takes injection rate to make that fuel make power at higher rpms. Why does a stage 1 injector make less power than a stage 2 injector when they are both 160cc?

Don't confuse the shape of the curve with the actual numbers. 600 ft-lbs of torque when you need (RPM) it is still more than 500 ft-lbs.

Imagine those curves with an injector capable of making 400 HP at 3100 RPMs but kept the same exact output as what you see in those graphs in the lower rpms. More is better bar none, the only tradeoff is durability.

My estimate is forged rods don't like more than 1200 ft-lbs PMRs don't like more than 900 ft-lbs. I'm sure DP knows the exact cylinder pressure that breaks rods since they invested so much money in the equipment to test it. It can easily be correlated to a torque output unless stupid SOI is being used.

Also on the infamous Big_Stroker dyno graph.... if I could have started the run sooner it would have made more torque for the dyno. Standard transmission trucks don't require you to make a "dyno only" tune that locks the converter and doesn't downshift like the auto trans trucks do.
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post #7 of 18 (permalink) Old 01-12-2010, 12:51 AM Thread Starter
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Re: Engine Power Curves: What is best for the various end uses?

Got it. I think I am only being limited right know by my knowledge or lack there of the tuning and the inner finer technical workings of the powerstorke engine and how they correlate to each other. Seeing how very drastically different Cales tune dyno run was to the others brought up lots of questions in my mind.
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post #8 of 18 (permalink) Old 01-12-2010, 01:02 AM
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Re: Engine Power Curves: What is best for the various end uses?

I wonder why the only ran certain tunes on the trucks... cale's tune would have beat everyone if he would have dial in some more fuel down low. Who knows it may have made the same power down low as the others but maybe there was a dyno operator error or the trans was downshifting sooner or something.
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post #9 of 18 (permalink) Old 01-12-2010, 01:34 AM Thread Starter
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Re: Engine Power Curves: What is best for the various end uses?

I can see that. My guess is if he had a chance to fine tune that tune it would have been that much better. He got more perf in the higher RPMS than the others were not even close to. The tq curve I am thinking woudl also have looked even better as well with more fuel.
One question a bit off track: Is it ICP that controls how touchy a pedal is off idle. You alwasy see those posts about how some race tunes are almsot to hard to drive reg as the pedal is so touchy and the power comes on to fast. Is that running high ICP? What if any negs are there from doing that? What does too high of ICP cause?
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post #10 of 18 (permalink) Old 01-12-2010, 01:37 AM
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Re: Engine Power Curves: What is best for the various end uses?

Quote:
Originally Posted by TARM View Post
I can see that. My guess is if he had a chance to fine tune that tune it would have been that much better. He got more perf in the higher RPMS than the others were not even close to. The tq curve I am thinking woudl also have looked even better as well with more fuel.
One question a bit off track: Is it ICP that controls how touchy a pedal is off idle. You alwasy see those posts about how some race tunes are almsot to hard to drive reg as the pedal is so touchy and the power comes on to fast. Is that running high ICP? What if any negs are there from doing that? What does too high of ICP cause?
Multiple things can cause touchy throttle.... The pedal is electronic and some tuners simply "juice" the pedal curve to make the tunes feel more powerful when it is mosly an illusion.
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