drop in torque curve

[mgilvan]

I was reading the DT headers thread and I notice there is huge drop in the torque from 1800 to 3100
https://forum.ih8mud.com/threads/dt-headers-dyno-result-thread.514381/

I s there a reason why there is drop in torque is there any way to correct this?
Should the torque curve look like this ?

 

[OregonLC]

Welcome to the world of exhaust tuning. The header length is critical in timing the exhausts pulses. Looks like the DT header is optimized for higher flow above 3000 at the expense of tuning at lower revs. I imagine there's only so much you can do in the space we have.

 

[mgilvan]

oh ok i see, but this is the stock engin's graph . i found it odd for engine to lower its toque

 

[OregonLC]

My bad, had assumed it was the DT curve. Same theory applies though. The exhaust pressure pulse must be tuned to align with valve timing to maximize combustion charge. Higher pressure in the header when trying to exhaust and you're going to have some burned material remaining on the next event. There's a lot more going on than just throttle position and rpm when it comes to making power.

 

[OregonLC]

In thinking about this more, I'm now wondering if the early spike in torque may just be the TC locking up?

 

[Sandroad]

And it's not really a huge drop; maybe less than 25 ft-lbs on this scale. TC lock-up may explain it, since in the real-world there is a small drop in "pull" right at lock up.

 

[jLB]

is there any way to correct this?

Yes, trim off the left side of the graph below 2400 RPM. Just like the Tundra graph in post #18 of the original thread.

 

[mgilvan]

@Sandroad i tought the tc (torque convertor) is engane as soon as you put the transmision in D
and yeah its 25 lb/trq but with my driving doing 65ish the rpm is usualy at 2200 ish

 

[jLB]

@Sandroad i tought the tc (torque convertor) is engane as soon as you put the transmision in D
and yeah its 25 lb/trq but with my driving doing 65ish the rpm is usualy at 2200 ish

The torque converter is an inline part of the drivetrain from the moment the transmission is put into gear, but it is not direct drive (it allows slippage between the engine and transmission). If it were direct drive, you would stall when you came to a stop while in gear. Most modern toque converters have a lockup clutch to eliminate slippage once you reach cruising speed.

 

[mgilvan]

ic , thanx man