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

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.

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

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

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.

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?

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

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.

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:


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.

Why?