After, oh, about a year after I wrote the software so I could datalog the usual ALDL stuff at a more reasonable 8 fps I finally did some meaningful WOT datalogging. My car was having one of those extremly rare and unusual moments where everything was working properly and it wasnt broken down or in pieces. Even after nearly three years of owning this car, I can still count these moments on one hand with a few fingers missing .

Anyway, the performance was less then stellar. 3-63 MPH (cant do standing starts w/o wheel spin) in 6 secs flat. Looks like that BONE STOCK 2.8L V6 exhaust and cat that I have might be holding me back, just a little bit...

The only thing that stands out is how much the MAF and MAP outputs vary. I wouldve thought they would be more smooth. Wonder why that is? Timing issues, maybe? No audible or reported knock so that rules that out. Looks kinda funky, but maybe thats just the way its supposed to be.

 

Oh, the engines specs are: 350 w/ vortec heads and a performer plus cam .420/.442, 204/214 112 LSA.

 

MAF and MAP are both sensing things that are affected by acoustics in the intake tract -- the sound waves oscillating in the intake cause (a) pressure fluctuations (sound waves are pressure waves) and thereby cause (b) fluctuations in the particle velocity which the MAF senses. These are in addition to the ever-present electronic noise effects riding on the outputs from both sensors. You always get more noise on the MAF sensor at WOT than at cruise because the throttle blade(s) are fully open so you get a lot of sound traveling upstream from the heads/intake manifold back to the MAF. At cruise, when the throttle is nearly closed, the path is nearly choked off so you only get some of the lowest frequency sounds traveling upstream.. so the MAF sensor should look smoother at cruise. FWIW.

 

Another thing is that the O2 volts seem to fluctuate a little as well. Dont know how much that means from a NB but it would seem to suggest that the actual AFRs could fluctuate a couple of points with the MAF. This is definatly some sort of intake tract thing. Its at least somewhat steady under low load. Another thing is that due to the limited A/D resolution, the minimum step size around those flowrates is something like 2-3 g/s.

 

Gears and stall?

I'm hoping with the BFG KDW's, a tune and my 1.6RR's I'll be 5 flat.

. . . maybe better?

 

Heh, not worth mentioning, really...

2000 stall (stock as far as Im concerned) and 2.77's. The stall matches teh engine combo alright but 3.42's would work better on the gear side of things. Sounds like the engines on a brake engine dyno when I accelerate, especially in OD. It still has pretty good pickup, none the less, but better gears would help.

 

Got my 3" exhaust on today. The up side is the car is much better up top. Really hauls. The downside is that its too big for the current setup. The motor is really limp at low to mid RPMs now. Before it was like I had a turbo-diesel and it would take off as soon as I touched the gas. So, basically the reduced low end torque sort of negates the increased top end power.

Anyway, I got another datalog for comparison. The 5-65 time for the current setup is 5.75 seconds. Getting better...

I also noticed there is a standing wave forming in the large pipe that serves as teh intake. Its much more pronounced then it was before. kdrolt was right on the money about the 'noise' being acustical waves. Its a sinusoidal 4 hz wave.

 

Now that I mention it, Im really pissed about the exhaust. I was hoping it would be a home run, and not a more here, less there sort of thing. especially considering that the headers, cat, and catback where nearly $700. And, it doesnt even really sound any different.

For this setup, a mandrel bent 2.5" exhast wouldve been better. Oh well...

 

Demented, don't be to critical on the exhuast system you just installed. I belive there must be something else going on that you just haven't seen yet. You can't dispute the results most everyone gets after installing a header back 3" exhuast system expecially after retuning the chip. Do you have access to a wideband to see where you are in the low to mid range? You know the usual questions, I just think you're overlooking something. Keep playing with it I'm confident you'll find your lost power and then some.

Steve

 

The torque loss is around 1000-2000 rpms. With better gearing/stall, it wouldnt be a problem. Its really mostly at part throttle, which is kinda why it annoys me. With this transmission and gears, 1000-2000 is where the car spends most of its time on the street. Its a little sluggish at low rpms at WOT but once it gets going, it really presses me back in the seat. I was really pleased with that, which is why a 3" exhaust is necessary Even in third it still flies. Its never been faster. It just needs some help down low (read: gears and stall). I also have maf, which wont need as much attention as SD will. Ill will still keep an eye out, though, for potential issues.

Theres no denying the fact that I needed it, though. The car is many times faster at higher rpms. It was really sluggish with the 2" exhaust. Not only that, but the tail pipe off the muffler was kinked over when it was bent, so it was a severe restriction at high rpms.

 

[QUOTE]

 

Huh? Looks like some of your post got lost in transit.

 

In racing though, I don't think my car sees between 1-2k for over a second or even that (launch at 3200). Have you messed with the part throttle timing/fueling at all after the exhaust swap?

 

After driving my taurus (sanity check), the camaro feels like a normal car now. The torque starts off low at idle speeds, and rapidly builds as the engine speed increases. The car really isnt having any problems at part throttle, but it was such a stark contrast to the old exhaust with the shift happy 700-R4. Came out swinging but got out of breath real early. As far as the timing, Im afraid to push it any harder. Im running a good deal of timing. When I first was stuck with that old exhaust, my first 0-60 time was 7 seconds. I ramped the timing up to around 36+ degrees of SA at WOT and it dropped down to 6 secs. Ive actually pulled some at various areas as I dont have the exhaust gas leftoverization that I had before. I get apparent knock at higher rpms.

I also got rid of most of the massive bog that I had from having too much AE. That part of the fueling still changes. Now I can let it have it from a standing start rather then roll in initially. I suspect that it would easily knock a quarter of a second off the 0-60 times, even more since Id be able to start from a standstill.

As far as the fueling goes, FWIW, the BLMs havnt changed much with the MAF system and it doesnt feel much different. This was sort of the whole driving force behind me converting over to MAF for the fueling in the first place. No more VE tuning sessions after every mod. The fueling is much easier to rough in, but not as precise as a good SD setup with fine VE tables (what I had before). Basically what I have now is a computer model of a 650 CFM carbeurator with a vac advance HEI dist. Basically after a mod its: tune the AE/timing, and go out and enjoy. I am ordering a Innovate WB kit so I can have the WB-O2 readings in my datalogs (I think the base model does that). I really need it for AE. Ive been tuning it by sticking my head out the door and watching the exhaust for black smoke while observing how the engine is running when I hit the gas.

Overall, the more I use the car, the more I really like how it runs. It really produces large ammounts of actual tangible acceleration when I get on it. I guess Im really being too critical. When I first put the 350 in, the car couldnt even pass one of the crappy throttle body injected civics.

Next step is to hit the real dyno and see what its really doing across the board rather then trusting the butt dyno. Id suspect around 275 in chassis crank HP. The cam I have is really lame and I have a cat so Id be surprised if it got more then 300 HP.