New dyno sheet, weird curve

[janaka]

I went to a dyno day on saturday with a bunch of local guys (mainly imports, but cool kids). This is the 3rd time this shop has dyno'd my car, first was I6 then right after my swap and now this past weekend.

 

My setup:

2000 LS1- stock short block/heads

T56 transmission. all pulls in 4th gear

224/224 .567/.567" on 114LSA camshaft

upgraded springs/pushrods

FAST 90mm intake and FAST 90mm TB

sanderson 1 7/8" hugger headers

2.5" off collectors to 3" single exhuast (no cat or res but a small magnaflow bullet style muffler)

 

I'm pretty sure thats all the mods to the engine. Other details for those who care. Stock open R200 diff with 3.90 gears, aluminum driveshaft, Z31 cv axles, 245/45/16 rear tires, 1/2 tank 92octane (mix of 94 and 91 from last two fill ups)

 

Other pertinant info which may help explain some randomness.

 

I had a HUGE exhuast leak, also known as one header collector bolt went missing, arg. So I installed a new bolt on Friday afternoon and leak is fixed. My O2 sensor is right after the collector so it was driving a tad funny due to the O2 not reading properly. Dumb me didn't drive the car until the 15min drive to the dyno day so I don't think the PCM got to re-learn at all. Stupid me. The biggest concern is the weird peak/drop at 4200-4500rpm, then the trq continues to drop off but the HP curve picks back up.

 

Here's the dyno vid of the first run:

http://s282.photobucket.com/albums/kk268/elcamino-dude/dyno%20day/?action=view&current=040.flv

 

Peak HP 378

Peak trq 400

Thoughts? Comments? Concerns?

[Xnke]

that graph is not right...The Torque and horsepower curves have to cross at 5250RPM, due to the way horsepower is calculated. I think your dyno operator screwed up, or the machine is not setup correctly, or some other major error. Barring that, you're right, it's a weird curve, for sure.

[BRAAP]

Good eye on the HP/Trq cross over, though the HP and trq are represented on different scales, the numbers as lined up with their respective scales do jive.

I've seen before where the Torque and HP scales are not represented on the same scale which is sort of frustrating to those of us that use these graphs as tool, not just a pretty chart with colored arced curves to show off to extended family that wouldn't know what they are looking at any way. Somewhat annoys me when dyno operators present their graphs that way. It's nice to have both the HP and Trq figures represented/scaled the same, makes it easier to visualize what is taking place overall. especially when when wanting to compare to other graphs, previous runs, etc. Scaling the HP and trq graphs differently can alter the visual perception of how the power curve looks, but for what reason, I do not know.

 

Though that huge hump in the power curve that peaks at 4200ish is bizarre. No amount of false air to an O2 from an exhaust leak, or another error in the PCM could cause the engine to actually produce that large of a hump like that. Only explanation I can gather from that, especially seeing the lower trq figure immediately preceding that hump is tire spin initially and as the tire/s was/were regaining traction, the momentum of the drivetrain being slowed down by the rollers would show up on the dyno as a torque increase like that. Riding the clutch pedal could produce similar results. Or glitchy sensor on the dyno roller...

 

Edited April 20, 2010 by BRAAP
Typo's

[sq_creations]

Yup on dyno jets you have to turn on "Force Scaling" so that they line up at 5252. It looks like your real peak tq is 367 to me. The 400 run looks like the dyno freaked out for some reason.

[Blown77Z]

224/224 .567/.567" on 114LSA camshaft

 

What cam is that exactly?

 

Those numbers aren't bad at all !

 

Now put some better flowing heads on there and open up your exhaust for 420+hp

[Sideways]

that graph is not right...The Torque and horsepower curves have to cross at 5250RPM, due to the way horsepower is calculated. I think your dyno operator screwed up, or the machine is not setup correctly, or some other major error. Barring that, you're right, it's a weird curve, for sure.

 

Indeed it is. That said, the left is scaled to 400, the right is scaled to 450.

 

Edit: Doh went through, braaap beat me to it haha

Edited April 23, 2010 by Sideways

[SUNNY Z]

Not bad numbers. What front accessories are you running? Underdrive pulley?

 

Also, what did the car make before?

Edited April 24, 2010 by SUNNY Z

[janaka]

Sorry for the slow reply guys, baby at home getting all the attention (cute little bugger!)

 

anyway previous #'s were 363/353 (in sig) on the same dyno

Front accessories: Alternator and water pump (no PS, no AC, stock Fbody drive pulley)

 

The cam is a comps cam, pretty sure it was custom ground for the previous owner though. That said almost every LS1 store that does cams offers a 224/224 cam similar to the one I'm running. I'd probably go for the 228/228 version vs this as this is REALLY tame (i guess there's a reason they call it a baby cam, lol) I'd also opt for the 112 LSA for a slightly choppier idle. This is a great driver came though if you daily your car and not offenive to drive (my wife drives it with ease). They come up for sale on LS1tech.com all the time. Check any of their vendors and you'll find a similar cam. I'd LOVE to pick up a set of the 5.3L CNC'd heads which give a bump in compression and flow better than the stock heads I have now. They would be a great match to the cam, even the LS6 heads(243's) would be a nice addition if I got them milled to get a tad more compression. If I pull the heads off I'd have a hard time not pulling the cam for something a bit more aggressive though, lol. While I'm at it disease and all I have a friend selling a 3" electric cutout that I'm trying to work a deal on as well, dump it right at the collector and watch out!

 

Braap may have it right with the tire spin theory as I *think* I heard someone at the dyno day comment on the pass side tire spinning during the first pull. I'll have to talk to the guys and see if I remember correctly.

 

If that's the case 14trq and 15rwhp increase from intake and TB untuned. I think there is a few hp/trq in it with a tune (or at least straighten out the back end of the trq curve). Still not too shabby, moreso than just the #'s the car is waaay more fun to drive and dropped tons of time at the track. That's what I call a WIN/WIN!