Is anyone else seeing what I see at 5k RPM (switchover point for MEVI) (Blue Graph)

Good news is, the Stillen Exhaust+WSP B-Pipe definately helps.

Need to figure out if I've got something set up wrong.



Thanks,
IanS

 

Looks pretty normal to me. Since you've got a blower, the VIM switchover is occuring as boost is really starting to come on line. The switchover causes a slight drop on power, more so with the blower I'm sure. The dyno shop sucks though because they aren't correcting the graph to look smoother. That graph is very hard to read.


Dave

 

Damn, I scanned the wrong graph...

Hold on a sec, I'll put the SAE one up there.

IanS

 

Ok, the SAE Graph is up.

IanS

 

I'm assuming the top graph is your reference. I disagree with Dave, you are dropping 30+ hp That is WAY too much.

Are you auto, is there a shift in there? Otherwise check it out!

 

Ian- it would seem to me that the switch over point should be coming on later than 5000 rpms.

Did you do a pull with it stuck "open" and one with it stuck "closed"?

If so, where did the lines intersect?

 

Well, if you look carefully, it only drops for 100-200RPM. This is the switchover point for the MEVI.

We tried raising the RPM in which it opens, to 5300, then 5600. Both times, the hp dropped justl ike that.

If you look at the red graph, you see an earlier run I did at 4800RPM switchover.

Same result.

It's not a huge deal to me because it only lags for 200RPM or so, but I wanted to know if others with these mods are seeing this temporary drop.

Yes, I am Auto, but I do not shift there.

IanS

 

wtf is wrong with your dyno?!

well then again the rpm range that the x axis is on is smaller than normal. but you should NOT be jumping all over the place like that! :P


what spark plugs are you on?

whats your fuel disc ratio?

whats your pulley size?

 

could your MEVI be taking a long time to cross over, causing a temporary loss in power?

 

1 step colder NGK Coppers

No Disc, Cartech Adjustable FMU - If you look at my A/F Curve, it looks pretty consitant and good.

3.25"

Blitz BOV

Custom CAI

 

5000-5200RPM is the drop. That's about .2 seconds. That's pretty fast. I just want to know if others with SC_MEVI (mardisgrasmax?) see this temporary drop.

IanS

 

Whenever you have a dramatic change in airflow characteristics, such as when the MEVI switches over, it's likely that you're going to have a bit of turbulence inside the manifold and that its overall efficiency will drop momentarily (100-200rpm or so) until it stabilizes and the turbulence is gone.

The same thing happens on a lot of other cars with variable intake manifolds.

Note the VI x-overs at 3800rpm on all three of these dynos (02 Max 6spd, 02 Alty 5spd, 03 CL-S 6spd). There's a little dip in all of them.

http://mywebpages.comcast.net/stevte...anceMagcom.jpg
http://mywebpages.comcast.net/stevte...anceMagcom.jpg
http://mywebpages.comcast.net/stevte...k_Astroboy.jpg

Just for reference, VTEC engages on the CL-S at 4800rpm. I guess you can switch cam profiles faster and with less "disturbance" than you can switch an entire air supply (intake manifold runners).

 

We need to enroll some of you back into to school to be able to read graphs He's not loosing 30fwhp on the switchover, he's loosing about 10fwhp and 10fwtq. The axis' are different, that's also why the TQ and HP curves don't cross at 5252.

When testing my VIM on the dyno, I opened the butterflies at 4500rpms which was too low. This caused a drop of quick drop of ~12fwhp and tq until it recovered by 5100rpms. On my second run I opened the butterflies at 5000rpms and the curves were nearly perfect. There was only a 2hp/tq drop on switchover.

Like I was saying earlier, since Ian's boosted, it's quite possible that the airflow of the runners gets turbulent as the VQ is coming under boost and the butterflies open at 5000rpms.

If those graphs are truely corrected (ie smoothed out), I'd hate to see the orginals. You really shouldn't be bouncing all over the place like that once they smooth out the graphs. Most dyno graphs look like that initially and then the shop runs a Dynojet correction program to smooth out the graphs for easier reading. Are you sure they did that?


Dave

 

Nope, not totally sure.

He's sending me the data files this week so i can use the Dynojet software myself and tweak the graphs a bit.

I'll see what happens then. The good news for me is that apparently the loss at switchover is expected.

Now I need to figure out this:
If I truly am jumping aorund like that, then what the hell is causing it?

My A/F Curve looks good, so I don't think it's a fuel problem.

Spark Plug fouled? Bad coil? kitten in my intake?

 

Meow.

 

That's funny!
Your dyno graph looks pretty good, especially the air/fuel curve. I know you've tried all different setting for MEVI switch over, but the switch point just doesn't seem right. I know MardiGrasMax is switching over at 5600 rpms. Just my 0.02!

 

Heh...that reminds me of the Office Assistant Kitten.

I hate that little bastard. I wish I could get the Office Assistant Dog to eat him. Or the Office Assistant Einstein to blow him up.

Or maybe I'll just shove the Office Assistant Paperclip guy up it's azz.



IanS

 

What's up the the curves?

 

Tried it since I got the SC at 3800, 4400, 4800, 5000, 5200, 5500, 5600, 5800.

All of them showed this drop. 5000 worked the best out of all of them....(least amount of drop, most hp gain at top end)

MardisGrasMax set it to 5600 because of his N02. he was worried about leaning it out too much or something.

IanS

 

Any ideas?

 

As Dave mentioned earlier, the curves look jacked because your y-axes are zoomed in so much. Put those curves on your standard 0-xxx axis and the curves will look pretty normal. Your worst drops are on the order of 5-10 ftlbs. The 10 ftlb drop is from the MEVI switchover, which is perfectly normal...just look at a 2002 dyno plot and it's ~3800 rpm VI switchover (~10 or more drop). The 5 ftlb drop earlier in the rpm range may be due to a spark issues. Either plugs not gapped quite right (spark being extinguished...ie need less gap) or there's a coil or two flaking out...or your engine sensor grounds need to be cleaned. I'd look at that first. Easy to do.

 

Keven97SE makes sense...
Are you running 1 step colder plugs with the correct gap?

 

he's running one step colder NGK coppers

 

Gapped to .034

IanS

 

You should data log the car. I wonder how much timing the ECU is pulling or how much knock retard your getting. Its too bad you can't change the timing curve, otherwise it looks like the ignition timing isn't set optimally.

 

I hooked an ODBII Sensor computer to it a few weeks ago...

(All recordings are at idle)

MIL Codes - None
Intake Air Temp - 141 degrees
Engine Load Value - 17%
Short Term Fuel Trim - 11.7%
Long Term Fuel Trim - 9.3%
Short Term Fuel Trim 2 - 12.5% (not sure why there's 2...maybe Left and Right banks?)
MAP Sensor Vacuum - 9in Hg
Fuel System - Open Loop
Idle - Fluctuating between 700-730
Ignition Timing - Advanced 11-15 fluctuating, mostly at 15
Air Flow Rate - .37lb/min
O2 Reading Section 1, Sensor 1 - .05
O2 Reading Section 1, Sensor 2 - Varied - .1 - .5
Fuel System 1 & 2 (Once agian, Left and Right banks, I think) - Open Loop
Coolant Temp - 200 degrees

 

I was absent that day.. lesson.. never post before your morning coffee and the slidebar is your friend.

 

Anyone want to comment on my timing above?

Is that normal?

Of course, who knows what it's doing at high boost.

IanS

 

Your timing is fine. Kevin97se's suggestions seem reasonable, "coil or two flaking out...or your engine sensor grounds need to be cleaned", but I think the coil would throw a CEL and ditry engine ground for a little itsy bitsy spark shouldn't matter...IMHO.
What does your tuner have to say?

 

My current tuner, while he's a very cool guy, knows far more about Mustangs than Maximas.

Here's another symptom, however:

I can only get 15Hg Vacuum in Park at idle. I've tested this with 3 calibrated gauges at 3 different spots on the manifold.

I also tested Engine Compresion
Front Bank: 210 210 210
Rear Bank: 190 190 190

IanS

 

You could always borrow one of our (mine, eb's, etc) coils and see if it makes a difference, I know mine are not going out... just a suggestion...

 

That is one flakey curve. Mine dosent drop any HP, just ~5tq. IIRC my switchover is ~5300??? I'll check my Harlen switch later. Timing is fine, 15 degrees is good, but it shouldnt jump around too much. Coil packs maybe an issue, try an reseat the grounds for the coil packs and the injectors, its the two 10mm bolts with all the wire's attached to it bolted to the front of the lower intake manifold. Other than that, maybe your auto trans is going and the clutch packs are starting to slip? Thinking out the box here.

 

If you drop 5tq at 5000ish RPM, then you'll drop 5hp as well. Maybe there was some smoothing or averaging applied to your curves, though.

 

I'll try the coil packs. However, with a bad coil pack, wouldn't you think the car would idle funny? It's pretty steady.

The tranny feels pretty good, except for on the Dyno boosting at full throttle at the end of 1st gear, the sucker goes CACHUNK! pretty hard.

This seems to be pretty normal, however, as I have the VB Mod, and the shifts are hard anyway.

IanS

 

Yes they are smoothed out

 

So everyone:

What gap should my plugs be at with this amount of hp? I'm using Copper NGK's 1 step colder.

Thanks
IanS

 

From the NGK WEB SITE TECH TIPS (http://www.ngksparkplugs.com/techinf...ps.asp#gapping):


3. Gapping

Since the gap size has a direct affect on the spark plug's tip temperature and on the voltage necessary to ionize (light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the vehicle that the spark plug is intended for. Those with modified engines must remember that a modified engine with higher compression or forced induction will typically require a smaller gap settings (to ensure ignitability in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need.

A spark plug's voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap yet still provide a strong spark.

With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme. Be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think.


I thought I remember reduce gap by one step (1mm or ~0.004") every additional 50HP the motor makes...in your case, 2 steps (2 mm or ~0.008"). Since Nissan recommends an 11-series (1.1mm or 0.044") gap on the Maxima plugs, you'd want to reduce that to 0.9mm or 0.036".

On a technical "why is this necessary" note, when you increase the power of a motor (without increasing displacement), you are achieving this by increasing the pressure in the cylinders. This increased pressure increases the dielectric constant of the air/fuel mixture between the electrodes of the spark plug. This means it takes more voltage to arc across the gap. You can either add a higher power ignition system (increase V) or decrease the gap. Reducing the gap brings the voltage requirement back down so that the same V yields the same ability to spark.

 

thank for that explnation

makes alot of sense

 

Sweet! Great explanation.

That's exactly what I gapped them to when I installed them, just double checking.

I'll take my plugs out anyway and look for any fouling/problems, and re-check the gap just to be sure.

I'll also borrow someone elses coils, and see if I notice any difference, although this is probably best done on a Dyno.

IanS

 

Finally got the data files. This is what it looks like on scale, SAE Corrected, smoothed out to 3 out of 5......

Opinions?