Empire

yeah, pretty much all nissan's (perhaps even all "modern" cars) do that at 1500 RPMs.
That appears to be where the fuel comes back and perhaps even where the IACV starts to open again so it can "catch" itself as the RPMs fall.
There are been a few people that have spent a good amount of time trying to tune that pop out and some have gotten it to be more quite, but never been able to get it totally gone.

SixCylinders

Thanks for confirming my suspicions. I've been trying to tune it out via the distributor (over a month ago) and I got the noise level down a fair bit but it seems like I've lost a little bit of power in the process or maybe it's just all this wonderful summer air.

Empire

yeah, i haven't ever seen anyone be able to get rid of it. I wouldn't mess with the spark time trying to get rid of that pop. That's a fuel issue. The guys that are running more rich than they should be will shoot fireballs out their tail pipes. But even the guys with a really awesome tune will still pop.
I would bet that even the stock cars pop, the difference is, they have a tight exhaust, and a cat, and a resonator, and a muffler to get rid of the sound.
If it is loud, usually, I would say, that you need to spend some time working on fuel maps. Maybe you're wasting a little bit of extra fuel that you don't need to be.

Loren

From the MS tuning I did on my Spitfire a few years back, going super-lean on decel (similar to DFCO) caused a lot more audible "blat" from the exhaust. That car had a very open exhaust, so it was prone to making such things noticable. I think the cause of that (in that case) was that I wasn't providing enough fuel to reach stoich and ignite... but, as soon as the fuel built up enough to ignite, it did, which caused a pop.

So, yeah... I think it sort of goes hand-in-hand with the DFCO concept and is a side-effect of that and an open exhaust. I guess the way to avoid it when DFCO hypermiling would be to simply downshift or clutch-in before the engine spins down to the RPM that fuel comes back on.

SixCylinders

Empire, I need to get Nistune before I can play with maps. It's definitely in the plans but more long term. I'm tempted to say that my y-pipe is what really brought the sound out, I didn't notice it much with the magnaflow and catback piping. Could have something to do with the capacity of the piping pre-cat...especially since I went with dual 2" to the Y where it merges into 2.5.

Loren, sounds like you've recreated my sound (to a louder degree). I wouldn't call my exhaust very open but it definitely would outflow the stocker by a substantial margin. One of these days I'm going to get a cut-out and see how it behaves without a cat and muffler behind it. I still unfortunately have my automatic so clutching in isn't an option....I could move the shifter up to drive or neutral but...not really worth it unless I've got a cop on my tail...in which case I just won't downshift.

SixCylinders

Seems like green motoring is dead....anyways I'll make a little number update incase you guys show back up. Got 32mpg on a 401 mile round trip the day before yesterday with a good amount of city driving dragging me down (and going against the wind both ways) and 500lbs of extra passengers. As far as the math goes for official record keeping I forgot to memorize the gallons at the pump but it was $40.98 @ 3.259/gallon and that comes out to 12.574 gallons.

Empire

awesome.
I wish I was getting anywhere near that.
I ended up replacing my DD corolla with a 4 door F150.
About to hit the gas station up to find out what I'm getting on the interstate.
My first full tank, (first week i owned it) all city driving, I got a whopping 12 mpg.

Loren

I was impressed last week. Spent the week tooling around North Carolina in my wife's 2007 MX-5. On the trip home Sunday, we were getting 38 mpg! Top up, cruise control at 72, 355 miles on 9.3 gallons. Totally unexpected.

SixCylinders

Dang that's driving 72mph? I need to test what my right foot can do with a 4 banger. Well...again, I drove a saturn SC2 once but didn't get any readings.

Loren

Modern fuel injection coupled with variable valve timing is proving to be great for fuel economy. The new MX-5 with a hard top is fairly aerodynamic, too, I'm sure that helps a lot.

Did I tell you about the trip back from Cedar Key a couple months ago in my Z4? I kept it below 60 and babied it, and it was reading 37.5 mpg on the on-board computer (which has proven to be pretty accurate) before I pulled off of the highway and started tanking it. It's damned difficult to drive that car in that manner, though!