I just put my car on the dyno a few hours ago. I have an 06' MT with Nismo CAI, headers and exhaust. After about 6000 rpms the HP falls off dramatically, and there is severe detonation/pinging. Although, my A/F ratio looks pretty good.

Has anyone experienced anything like this? I have heard two hypothesis so far,

1) I got bad gas (insert 3rd grader chuckle here), although I am usually using BP or Shell premium. I'm not buying no-name gas.

2) I need the ECU tuned because of the additonal air flow from the headers.

My problem with the possibility of #2 is that if that is the case Nissan should've made a disclaimer that an ECU tune should be done after the headers are added, but I've heard of no such thing. Plus all my work was done by the dealer and when I went back with my dyno print outs they were the ones that suggested an ECU tune. Well... WTF??? Shouldn't they definitively know one way or the other? It's Nismo parts for crying out loud!

Anyway, I'm going to run this tank of gas down and try another pull in a week or so when I have fresh gas (ha ha). But until then, has anyone seen HP numbers drop off like this? Unfortunately, the shop hasn't run any other Z's with headers so they don't know if this is tyipcal (it seems headers are one of the least common bolt ons, at least around here). Has anyone else added headers and done a dyno, without an ECU tune? If so, can you share your results? I'm curious if I'm the exception to the rule or if this really is an issue common with headers. Thanks.



BTW please forgive the dual postings, I really wasn't sure if this belonged in tuning, or exhaust.

 

That's normal for the HP to start falling off. Its your peak power. However I would suggest a tune (UTEC) if there is severe detonation!

 

Try switching the CAI for your stock airbox.

Also, if you still have stock cats on, the cats are a bigger restriction than the stock exhaust manifold. This makes a bigger difference at higher RPM as you can see with your dyno...

As for the detonation, stock cars ping all the time. It's just a way of life... the ECU detects knock and pulls timing, then slowly adds it back in.

If you want a good solution you need to tune...

 

Thanks guys.

HP fall off is one thing, but mine's a cliff, ~70HP drop. I haven't seen a lot of dynos but I have never seen anyone else's HP drop like that.

As for the detonation, I'll admit I'm still a newbie to cars, but considering everyone in the shop came running to the back to see who had "pop rocks" in their engine I think calling it severe is an understatement :-)

Regarding tuning, what should be looked at? My A/F ratio looks good, right? I'm in the 12's to 13's. Would it be EFI timing? Valves? What? Again I'm still learning, and reading, and searching as much as I can, but what might be tuned to solve this? Mostly when I read about tuning the main thing seems to be the A/F ratio.

As for the cats I have the nismo cat-back exhaust so I thought that meant new cats too. Or am I an idiot? :-(

FWIW, I'm going run the gas tank down, get a fresh tank and try adding an octane booster for my next pull. If it still pings then I can at least rule out bad gas. I'll post those results if anyone's interested.

I'm still hoping someone with headers on here has dyno'd pre-tune and can let me know if they had the same experience or not.

Thanks again for helping a new guy out.

 

Definatley need an ECU tune after a header install. When I got my headers/HFC's done, I felt no difference. Then I got it tuned and picked up 15whp and the car felt great. Your A/F should be in the low-mid 13's.

 

246 seem to be very legit . a flash is a good way to go though imo.

 

I think we're missing the point. Yes, it is expected that the hp will decline after the peak (or else it wouldn't be a peak), but to lose 50 hp within 500 rpms is very excessive. I don't think a lack of a tune would cause that much decrease that quickly. I have more mods than you w/out a tune and I picked up power across the board (the butt dyno says so!).

It may be that a tune is needed, maybe even an ecu reset would straigten things out. With you afr being good, you may want to look at why your ecu is, apparently, pulling timing. Perhaps the dealer didn't bolt something up tight or something is physically tapping/banging/vibrating against or within the engine causing false knock (this is unlikely, but it's worth looking at). There is A LOT of stuff that has to be removed to install headers, and it's possible that they forgot to tighten something.

I know, I'm pulling at strings here, but anything is worth a shot.

 

You DO have the OEM cats if your only exhaust mods are NISMO headers and Nismo cat-back exhaust. You have a rev-up, and probably not a lot of miles, and it could be that the cats are plugged, but it's unlikely. Your dyno does not show ANY gains over stock. Assuming a 17% drivetrain loss, you should dyno around 249. I seriously doubt it's for lack of tuning. Most our cars are rich from the factory, and breathing mods do not lean it out enough to cause a major problem. Look at my mods: I don't have ANY kind of tune, and although I never dynoed, I hit 6.5K a couple of times, and never heard any detonation. The power feels smooth, so I doubt mine dips that dramatically. I'm sorry I don't have any specific help on your problem, but don't use octane booster. Shell 93 V-power seems to agree with mine just fine for over a year. I looked at other dynos posted here and none have that big a dip, but most are close, and it may be within statistical reason. Are you sure it was detonation and not someone kicking a bucket around the shop or something vibrating on the car (heat shields, rattle, etc...)?

 

Thanks dTor, undrgnd, those are interesting ideas. After I got my headers installed I DO hear a slight tinny rattling sound in the lower RPMs. I've never ridden with anyone else that had headers so I don't know if that's normal or not. I once had a heat shield loose on my 94 Altima and it made a similar sound. But a guy at the dealer (where the headers were installed) said a tinny sound is typical with headers. He called it "that NASCAR Sound" and he's not fond of it so he won't put headers on his Z. Is this guy full of it? undgrnd, do you have any kind of tinny/rattle sound with your headers or is it smooth through all the RPMs?

I wish I knew someone else locally with headers that I could ride with. Before I dyno'd I had wondered if something wasn't tightened up correctly. Now with the HP drop could something be loose and at high RPMs exhaust is leaking by, dropping the back pressure and with it the HP? Could that be something to consider? (Again I am a car newbie, so I'm sorry if that sounds stupid, but my engineering mind is trying to come up with a solution. I can't stop thinking about this problem :-)

My next plan is to go fill up with 100 octane after I run the tank down, and do another pull. I'm hoping the problem was just bad gas, and that the knock sensors kicked in, retarded the timings, and resulted in dropped power. At least it's a hope, right?

BTW given the shear loudness of the pinging and that it happend on 2 of the 3 pulls, I believe it really was detonation. All the guys in the shop didn't even consider it being anything but detonation.

 

The rattling is a good indicator of a lose part. And it is quite possible that there is inaudible rattling at high RPM. If your knock sensors are "hearing" the rattling in the block, it will be interpreted as severe knock and pull timing accordingly.

Make sure everything is tight before you do your next pull and it may clear up.



.

 

Damn, that's a good thought. I suppose it is possible that the knock sensor is picking up the rattle and pulling timing. What the dealership guy is referring to is the whooshing or hissing sound of the exhaust flowing through the headers, but it's more prevalent with thin wall, long primary tubing, like you would find mostly on American cars. There is a hint of that on my car, but it's mostly masked by valvetrain, gear, throw-out bearing, and exhaust noise, however, I have no rattles.

 

That is what I was getting at last night. Glad to know my train of thought hasn't jumped track (yet).

 

Sorry it took me so long to get on here. Been swamped with school lately.

Anyways, yeah, when Matt's car was on the dyno, there was definately some weird **** foing on. We compared a few different dyno charts that were at the shop with his and none of them dropped off like his at all. Also, the detonation that could be heard all the way in the front of the shop was pretty insane. IIRC his A/F's didn't look bad by any means.

Also, Matt, you have the Nismo cat-back. Key words being cat-back. You should have stock cats on there still.

Sorry if this is all been posted before. I honestly didn't read through it all yet. I'm only on a short lunch break.

 

Here's an update. Ran my tank down to near empty and then went into the dyno yesterday with 100 octane. The pinging/detonation was gone and my HP leveled out like it's supposed to. I pulled ~246. On my last pull I must've had bad gas. So that's the good news.

Here's where it gets weird. We had four Z's doing pulls yesterday, most of us had some mods, mainly pop-chargers, exhausts, spacers, and an mrev. I'm the one odd ball with the CAI and headers. Here is where it gets interesting. The one guy (thloman81 see above post) that was 100% stock pulled almost 257. The highest out of every other Z with any bolt ons. WTF!?!?! Except for him we all had some collection of bolt-ons and we all pulled less than him. With mine being the worst at 246. Does this make any sense? What have others seen the Z pull at stock? Could ALL of us with bolt-ons be that far out of tune? Thoughts? Thanks.

 

Thanks for the dyno sheet. The person running the dyno let his foot off the gas before redline?

 

Get tuned, can't stress this enough

Also...there is more to the horsepower curve than the PEAK NUMBER.

Finally, intake temperature can make a big difference on the peak horsepower number.

If the "stock Z" was running cooler than the other cars for some reason, it could easily pull the highest hp number.