In an effort to actually make this a decent forum that has stuff other than **** talking here is a post I made on one of my tuning forums.

I have noticed that looking at many big cam dyno sheets that there is almost always a dip in torque from ~2000 rpm to ~3200 rpm. There is evidence that this is a physical characteristic of the engine. I just got done mapping my VE table, which is accurate to 0.5%. As many of you already know, VE is correlated to torque. If you view the VE table as VE vs. RPM with lines of constant MAP you'll see the general shape of your torque curve.

I have an MS4 cam in my car. Here are some specs: 239/242, .649"/.609", 111 LSA.

Here is my VE table both as a map, and as table data.
Map


Table Data - I have circled in red the dip in the VE table, which will also likely be a dip in the torque curve. This characteristic seems to be fairly normal for a cam of this size.



Then I started looking at stock tunes. I have done a comparison of a 2002 Z06 tune. I noticed similar behavior, and it looks like GM took some measures to reduce this behavior. I'll show what I think they did in a minute.

The Z06 VE map:


The Z06 table - Note the circled red flat. The Z06 cam is smaller, so it looks like this shows up as a flat as oppposed to a dip, but its still there.


To make the torque curve smoother it looks like they did two things in the region of of the flat. First it looks like they leaned out the commaned AFR curve in the PE curve.

Z06 PE curve - Note the area circled in red. You can see they leaned it out in the range of the VE/torque flat.


It also looks like GM added some timing in that same range.
Z06 Timing Map - Note the hump at the top of the "hill"



How does this relate to people with big cams?

Here is my PE table, which I think is plenty "lean" in that location of the dip, so I don't think I'll change anything there.
My PE curve:


My timing table - Note there is no hump at the top of the hill.



I was considering adding a hump to the top of the hill much like GM did on the Z06 tune. Hopefully this will minimize the dip in torque. Here is my proposed timing table (I have yet to try this out yet).


Your thoughts are highly appreciated!

 

Makes sense what you are trying. Add 2-3 degrees of timing in the 2800-3400 region and then log data and see if it gets you any knock in that area and see if then it wants more fuel in the VE table as well.

 

Good observations, however those dips in the torque in those areas really are just the way they with the bigger cams and no amount of timing or fuel is going to get rid of it.

 

I agree that no tuning will completely rid this, as its a physical characteristic, however, I think that it may be able to be minimized through tuning. Some other people commented that changing the header design can help tune out some things like this. I was talkin with a guy who had tried dozens of different intake manifold and exhaust manifold designs for a formula SAE car, and he showed me the data (torque curves) of each design. It was pretty amazing how much difference that stuff makes.