107hp, 194.8lb/ft torque at the wheels.

1980 240D 3.0VNTi 215k miles
Modifications: OM617.952, 4-speed manual, GT2256V VNT turbo, air-air intercooler, W115 300D intake, 3.46 diff, ALDA/EGR removed, Pyrometer/Boost/Exhaust psi gauges, bypass oil filter and Mobil-1 5W-40 synthetic oil.

The second picture shows how much boost I have at idle, it drops to 0 when I open the vanes.

Post your dynamometer results if you have some.

Any idea how that boost curve looks compared to a stock turbo? Doesn't look like much boost below 2100 or so like the stock turbo.

Here is my sheet from 2-13-06 with the KKK K26 turbo.

The boost curve is nearly opposite. :D

I notice now that the boost starts at 7 psi, thats pretty impressive. Did they not load the engine below 2000 rpm?

Did they not load the engine below 2000 rpm?

Just whatever it took to keep the rollers moving until he mashed the throttle.

Here is the graph where the vanes were set always open. Notice how the boost curve has a slightly more concave shape to it and starts at only 2psi.

Once I fix and sell the '79 I'm using the cash to upgrade and am aiming to beat that 107 HP. :D

Good job!

Here is the graph where the vanes were set always open. Notice how the boost curve has a slightly more concave shape to it and starts at only 2psi.

Also notice how your low end torque fell. The higher boost gave you about 4% more torque.

I'm not grasping why the maximum torque is only at 2300 rpm with a boost level of 8.5 psi.

Something is not right. There is no reason that this engine can't produce peak torque at 2800 rpm. Randy and others have dyno runs that confirm this.

This engine would have significantly more than 107hp if the torque peak could be shifted to the right.

Are you positive that the cam timing and IP timing are correct? Is the lift on the cam to spec?

Something needs adjustment.

I'm very happy. Almost 200lb/ft of torque down low where its useful and a broad flat HP curve. All without opening up the pump or using additional fuel through water injection. I can't wait to get that extra 30% when I remove the rack limiter and tweak the torque capsule. :D

VIDEO (http://www.youtube.com/watch?v=xMgVuGDf8xQ)

I'm not grasping why the maximum torque is only at 2300 rpm with a boost level of 8.5 psi.

Something is not right. There is no reason that this engine can't produce peak torque at 2800 rpm. Randy and others have dyno runs that confirm this.

This engine would have significantly more than 107hp if the torque peak could be shifted to the right.

Are you positive that the cam timing and IP timing are correct? Is the lift on the cam to spec?

Something needs adjustment.
Its probably mainly due to the VNT and possibly the w115 intake manifold. You may notice that the dyno run where the turbine vanes are held wide open it does move the peak torque to the right. The peak is lower, but it is more to the right. This just illustrates the advantage the VNT has at generating efficient boost over a wider range of rpms. The longer intake runners probably shift the peak torque a little lower too.

Here is my sheet from 2-13-06 with the KKK K26 turbo.

The boost curve is nearly opposite. :D

Now, there is a good looking set of curves. If the shape of the curve could remain the same and the torque peak raised...........it would be fabulous.

Now, there is a good looking set of curves. If the shape of the curve could remain the same and the torque peak raised...........it would be fabulous.

Yes, but the engine always had an early torque peak, it just never had a turbo that could supply air for it show.

I got 65lb/ft more torque, 10hp more power and much better drivability from only "bolt-on" changes with no additional fuel above stock, with better fuel economy on top of it!

Let me dust off my old PeeCee and see if I can get an overlay of my oldest and most recent graphs. Superflow does not have a Mac version of their dyno chart software.

I got 65lb/ft more torque, 10hp more power and much better drivability from only bolt-on changes with no additional fuel above stock, with better fuel economy on top of it!



Yes, I can see why you're quite pleased.

But, I'm still baffled by the inverted torque curve........it's just not common on these engines.

But, I'm still baffled by the inverted torque curve........it's just not common on these engines.
Well, neither is a variable geometry turbo. ;)

Well, neither is a variable geometry turbo. ;)

The VNT certainly explains the increase in torque down low.........but, it doesn't explain the falloff in torque from 2350 onward. It's my understanding that the VNT functions like a very small turbo at low rpm's and then, with its vanes open, functions nearly identical to the stock turbo at higher rpm's.

but, it doesn't explain the falloff in torque from 2350 onward.

Ah, that is the job of the torque control capsule. It reduces fuel with RPM since the engine's volumetric efficiency goes down as RPM goes up.

Ah, that is the job of the torque control capsule. It reduces fuel with RPM since the engine's volumetric efficiency goes down as RPM goes up.

You adjusted that setting during the tuning for the VNT?

The torque curve looks like the new mercedes diesel (of a couple of years ago) felt when I drove it. A boat load of torque almost from idle and just full huge power on up through the rpm range.

I am wondering if the 115 intake runners choke it off and limit the power as the rpm rise? Small runners I believe I have read increase response down low but would limit it up high. That's why newer engines often have variable intake tube lengths, I believe.

Tom W

The torque curve looks like the new mercedes diesel (of a couple of years ago) felt when I drove it. A boat load of torque almost from idle and just full huge power on up through the rpm range.

I am wondering if the 115 intake runners choke it off and limit the power as the rpm rise? Small runners I believe I have read increase response down low but would limit it up high. That's why newer engines often have variable intake tube lengths, I believe.

Tom W

Maybe it's quite normal. With the VNT, although the torque is falling constantly throughout the range from 2300 onward, it's still higher (135 lb.-ft) than the stock vehicle (125 lb.-ft.) at 4000 rpm.

The very high peak torque available down low with the VNT might make for a strange looking curve.........but, it just might be typical.

You adjusted that setting during the tuning for the VNT?

No, I have not even removed the back cover of the pump to touch any of it's innards.

I am wondering if the 115 intake runners choke it off and limit the power as the rpm rise?

Thats definitely possible. I'm fine with sacrificing some top end power for increased low end torque in daily use. Absolute screaming horsepower isn't what I'm going for.

No matter how you analyze it the increased area under the curve is quite phenomenal. To bad Forced isn't a member of the ASME. He could do a great paper on "What is possible when you tell the EPA to stuff it!" :D

Thats how I would imagin the torque curve on a CDI would look. Very interesting thread, I bet you can get more with some adjustments.

Forced,

I have been comparing your earlier run to this last one and I don't think the power drop off is due to the torque control capsule. You have the same IP and the same adjustments (minus the ALDA of course) but you don't make the same power at the top end. I think it might be possible that your compressor is choking.

Just a thought

Forced,

I have been comparing your earlier run to this last one and I don't think the power drop off is due to the torque control capsule. You have the same IP and the same adjustments (minus the ALDA of course) but you don't make the same power at the top end. I think it might be possible that your compressor is choking.

Just a thought

The original setup gave 95hp @ 4000.

The VNT gives 107 hp @3900.

It's difficult to argue that the compressor is choking. The curve looks a bit strange, but the absolute numbers are up across the entire range.

Maybe the VNT did was it was designed to do........boost torque in the low end while leaving the high end "relatively" unaffected.

I might have to consider one of them..........the results are quite dramatic.

At 4250rpm in his 2/13/06 run he had about 95 HP and drops to about 80hp at 4500rpm. On his latest one it drops below 80hp before it gets to 4250 rpm and 4500rpm is no where to be seen. Considering the wide power band he has right now I think its very easy to argue that the compressor wheel is choking at the top end. A slightly larger trim compressor wheel might just give him a little more area under the curve at the top end and shift the torque to the right some.

Of course he may not want this because he has already stated he loves the low end torque.

At 4250rpm in his 2/13/06 run he had about 95 HP and drops to about 80hp at 4500rpm. On his latest one it drops below 80hp before it gets to 4250 rpm and 4500rpm is no where to be seen. Considering the wide power band he has right now I think its very easy to argue that the compressor wheel is choking at the top end. A slightly larger trim compressor wheel might just give him a little more area under the curve at the top end and shift the torque to the right some.

Of course he may not want this because he has already stated he loves the low end torque.

Yes, I agree........above 4200, the power falls off a cliff with the VNT.

But, as you mention..........he's not interested in more torque in that area.

Lance, I've been mulling over that curve for the last few days.

Can you explain how they run the test? Do they start in fourth gear and apply the power from 1000 rpm and let it rip? I presume that this must be the case because there's a relatively smooth torque curve. If they ran it through the gears, there would be steps in the curve at every shift.

One additional question concerns the interpretation of the results. The stock 617.951 puts out 184 lb.-ft. at the engine. Knock off 30% for the driveline and you've got about 135 lb.ft. at the wheels. However, with a 3.2 axle this would provide 432 lb.-ft. at the rolls. So, does the software require the axle ratio and the tire diameter to provide a "corrected" rear wheel figure based upon engine torque?

With these results, would you agree that a slightly larger compressor might increase the overall horsepower? Is such a turbo available in a VNT?

Can you explain how they run the test? Do they start in fourth gear and apply the power from 1000 rpm and let it rip? I presume that this must be the case because there's a relatively smooth torque curve. If they ran it through the gears, there would be steps in the curve at every shift.
...
So, does the software require the axle ratio and the tire diameter to provide a "corrected" rear wheel figure based upon engine torque?

They do all their vehicles in second gear, settle at the start RPM and floor it up to redline. I'm not 100% on the math behind it but they assured me that it is accurate. You should contact them with specific questions about their dyno: www.carzcustom.com/the-dyno.shtml

With these results, would you agree that a slightly larger compressor might increase the overall horsepower?
I'd have to say "maybe". This is the first VNT installed on a 617 so there really isn't much to compare it with for me to give a definite yes/no answer. The exhaust pressure ratio is close to 2:1 at full output. I'm not sure if that is due to the inherent inefficiencies of the VNT vanes altering the path of the exhaust or the turbine working to push the compressor. A larger wheel will be closer to the efficiency islands at full power so there are probably a few ponies to gain from a larger wheel.

Is such a turbo available in a VNT?
There are gobs of VNT combinations that can work on a 617, it all depends on your power goals, how deep you are willing to dig in your pockets and your sheer luck finding some them. Garrett GT2056V, 2059, 2060, 2256, 2259, 2260, 2359, 2556, 2559, 3063, 3571, 3788 and larger and some overseas models/sizes I've likely not even seen yet.
Holset HE341VE, HE351VE, HE431V and HE531V

Some like the GT2256V (Sprinter) and GT3788V (Powerjoke/Intertrashional) are common as dirt in the states. The GT2359V from the E320 CDI occasionally pops up. Others like the GT2260V and GT2559V (Both BMW) are common in Europe/UK but will break the bank to get one over here. Some like the GT3063V are extremely rare anywhere.
The Holset HE351VE (6.7L Cummins) is becoming common, but it is well in the Myna pump HP range.

Well, I contacted the dyno outfit in an attempt to clarify exactly what they measure.

Since the test is done in second gear, some data input to the software of axle ratio and gear ratio would be required if the graphs are going to represent engine output.

But, in typical fashion, I get a bunch of nonsense:



We generally run the vehicle in a gear in which we will be able to gather consistant data. If we were to run the test in first gear the teat would be over in 3 seconds and would be hard on the straps hoding the vehicle in place. If we test the vehicle in 5th or 6th gear it would overheat and cause engine damage. We try to find a happy medium where the test is going to take anywhere from 8-20 seconds. SuperFlow dynos are different from other dynos. They DO NOT measure acceleration vs. time however they measure actual torque that is being applied to the rollset which is on an axis. We normally do not load the vehicle unless needed to. Being an AWD dyno we have 4000 pounds worth or inertia roll which is more than enough for most vehicles however a modded diesel pick up truck requires us to apply load in order to spool the turbo. As a general rule of thumb we experinence a 10% loss through manual transmissions and 30% loss through automatic transmissions. We can also hold any vehicle at any RPM in any gear, it's just a matter if your engine or tune can handle it. We have some fans that are capable of blowing winds of 70MPH+.


If they are measuring actual brake torque to the rollset, the vehicle must be stopped at discrete engine speeds via load from the dyno. Due to the 8-20 second claimed time.........I'm fairly sure that this is not being done and the torque measured while rolling through the various rpm points is not accurate.


Further attempts to get them to clarify exactly what is represented on the output graphs did not generate any response.

So, I conclude that these guys are clueless and that the data presented is meaningless on an absolute basis. As a comparison between "before" and "after" runs, it might be valid.........but, the parameters of the dyno would need to be identical. No assurance that this would be the situation.

It's another sad commentary that the people who provide the service have absolutely no idea what they are providing to the customer.

If they are measuring actual brake torque to the rollset, the vehicle must be stopped at discrete engine speeds via load from the dyno.
Why?

Why?

The torque value to the rolls when accelerating will be a bit lower than the full brake torque if the vehicle is held at a discrete rpm by the dyno. I don't think the difference is significant..........but, if you're measuring brake torque and not deriving torque from acceleration..........it's the proper way to make the test.

I'm sure they could do it in this fashion, but the engine would be at maximum power for at least one minute..........could be problematical.

I ran some calculations and had another think about that dyno.

The machine doesn't need any gear ratios or final drive ratios for the calculations. It only needs to know torque at the wheels, wheel speed, and engine speed and it can provide a proper printout.

So, the only remaining question is how they accurately measure engine speed on a diesel?

So, the only remaining question is how they accurately measure engine speed on a diesel?

Reflective strip on the crank damper and optical pickup.

Reflective strip on the crank damper and optical pickup.

Perfect.

The printouts will be accurate.........although the operator doesn't have a clue why that will be so.

Perfect.

The printouts will be accurate.........although the operator doesn't have a clue why that will be so.

Sadly, that's the case with most services of most varieties, at least in the U.S. People seem to be content to just do what the various manuals say and never ask "why?".

Its been nice to learn a little more about how a dyno works:D

http://i3.photobucket.com/albums/y71/kartek/Truck%20Stuff/dyno_pull_2.jpg

Oh wait, you wanted Mercedes dyno sheets... :D