While my last dyno "looks" healthy, there is a strange anomaly at the 3500rpm point. It's a dip in power below 350ft/lb. The dip did not occur prior to the cam. So either the culprit is in the valvetrain/cam or something related...

Fuel filter was changed, and air filter will be cleaned (K&N) to see if it's just dirt causing it...

I don't have a pic of it yet, the shop I dynoed at had printer issues, I will pass by during the week to get a copy.

As it stands from 2500rpm up, there is a steady climb with it peaking at around 350-360 ft/lb of torque around 3200rpm. It suddenly dips below 350 (like touching 349ft/lb at 3500rpm, then proceeds to climb steadily and consistently to 373 ft/lb peaking at 5000rpm what follows is a normal decline in torque until HP peak around 5800rpm.

The A/F is around 13 up until it does the dip, then begins to hit near perfect 12.7 a/f after the dip until 6000rpm when it climbs back to a/f ratio of 13.

How it drives on the road is strange too as I can "feel" the dip. It's like it loses power for a split second in the climb.

Numerous attempts to "richen" the fuel delivery below 4000 to match the after dip a/f didn't do much at all.

Any theories to why a dip at 3500 may occur?

Mods are as follows

Baseline
298HP/315ft/lb

SLP Lid
LS6 Intake
LS7 clutch/LS2 Flywheel
306HP/325ft/lb

QTP 1 3/4 Longtubes HVMC
3 Inch Magnaflow Cats
True Duals 2.5 Inch X-Pipe Over Axle
Solo Performance 3 inch mufflers
17x11 ZR1 Rims With Nitto 555R 315/35/17
Ported Throttle body
Tune
349HP/359ft/lb

TR224-112 0.563 Cam
Patriot Gold Duals with Titanium Retainers
Comp Cams 7.400 Chromoly Pushrods
LS2 timing chain
March Underpulley with overdrive alternator pulley
Nittos Replaced with BFG KD
Tune
380HP/373ft/lb

 

i was told to pull timming in that area and it would flaten out but for us truck guys it was like from 4200-4800 and pull like 2 degrees. just a thought.

 

I got the same dip in torque on my dyno graph after getting tuned. Here's my graph:

I don't have an explanation for it, I'll be watching this thread.

 

Or is that the 2 torque peaks that patrick g went over in one of his many threads?

But as I think about it that 2nd peak happened after larger peak torque.

 

I thought about it too after reading Patrick's thread, but the "2nd" peak was smaller and after the first peak... mine's not as dramatic as that pic, but it's still enough to "feel" it while accelerating.

also my first peak is like 355... and the second is 373... not far apart, but enough of an interrupt in the pull to make you go WTF?

 

You should have have a table top torque line with that cam. The tune is not right.
IT doesnt dip at all. It should climb and stay flat until it finaly falls off altogether.

 

I know what I should have, why else did I make this post?

The question is a matter of what's causing it? Too much timing? Not enough air? Fuel? Clogged MAF? It's easy to point at the tune, but after playing with the tune for 2 hours, various timing/fuel etc.. it was quite strange, we had the 3500+rpm dialed in perfectly, the drivability is near perfect smooth at cruising rpm, but the exact cause of the dip is an oddity....

 

I saw you comparing your results to Patricks and they wont be close to the same torque curve. His 238 cam will produce a much different curve , thats why I mentioned it.

If you had to much timing you'd know with the KR, how was the Kpa 100-105% if so then your getting enough air. Is it running lean at all? If not your getting enough fuel.

Any codes?

Also this isn't the tuning section. Might help to get your post in the right place.

 

How many miles on the valve springs? Are they single or dual? Dual springs are meant to cure harmonics.

 

He's got a solid valvetrain from what I can see but thats a good suspicion.

 

I've read a few threads that deal with this anomoly and it seems to always be in the tune. Midrange fuel delivery and timing need to be experimented with until you find the right combo.
If I recall correctly, you should try to fatten up the fuel mix and add a little timing in the midrange...but every car will behave a little differently.

 

I've got a very similar setup and the same "dip". I just recently started tuning it myself so we'll see if I can get it to "go away".

 

Quick question... why are you running dual springs on a TR224? That's quite overkill and is probably costing you some power.

 

I got a good deal on the Dual Springs new. A bit of noise for a bit of insurance in case of spring failure.

I suspect it's in the tune as well, but I won't be able to mess with it for awhile, albeit it accelerates like a raped ape...