You guys are all pretty knowledgable and I know a few of you have Z's.

Anyway, I posted a dyno comparo here before: https://acurazine.com/forums/showthr...highlight=dyno

Now, I have recently installed headers and here is a post I placed on the Infiniti sites with an update and asking for help:


I've had my Strup headers on for a week and a half. Had the car dyno'd and it was disappointing to say the least. That said, I swear there is a problem. Even more of a problem, my dyno guy had massive computer problems and the email file he sent me of my plot I am having a hard time getting translated to post here.

Suffice is to say, the plot shows a peak gain of 3.7hp to 249.7 and a peak torque gain of 2.2tq to 227.2. However, in some areas I have dropped torque--especially around 3500 rpm's down to 205tq and the curve has gotten more wavy. However, the hp is still entirely steady and peaking, not losing power, and is at least one or two hp higher throughout the range until the peak. Further, the a/f is well over 14 until higher rpm's where it is back to where it was before, though it dips in the 3200-3750 range where my tq curve is dipping, too.

Now, I SWEAR I HERE A PROBLEM, but the car is not throwing a code at all and it isn't a massive 'wooshing' air leak kind of sound. To me, and now maybe my mind is playing tricks on me, the left side of the exhaust sounds louder than the right.

When my shop did my headers, they ordered a whole new gasket from Infiniti and they did tell me one of the header studs gave them massive amounts of trouble on the passenger rear--to the point of having to back it out or something. I guess my questions come in where I have no code present to alert of an issue, and secondly, I don't hear a typical leak one would normally hear, it just sounds really odd at lower rpms--almost like a coffee can with air running through it. Not raspy or anything, just weird in a not good kind of way. I've had headers in other cars of various iterations, this just sounds odd.

Now about the dyno: I only got two pulls in 3rd because the third he wanted to do in 4th for his own edification flapped up his machine in some way (still odd to me, but the car made 212hp/261tq in 4th!!!). Both were virtually identical. My VDC was off, but the slip light (LSD)came on for the second run and stayed on until the car left the machine and I drove it down the street and it then reset. It was 79 degrees outside per the weatherman though the car showed 84 in the shop and it was near 100% humidity. This was almost 20 degrees warmer and I know this makes a difference. Also, the dyno was over 25 miles in stop and go traffic from when I left my office to have it done, contrasting with the 5 miles I drove straight over early in the mornings the last 2 times. It was virtually boiling when dyno'd this last time as opposed to pretty cool the last times.

Now, I did not expect huge gains, but I would have thought to have seen more--especially in the torque gains, and certainly, gains in USEABLE power rather than peak.

Now I also have to say the guys at Stage 6 here is Jax are awesome. Dwight did the install and he also does Titan's work in Orlando on their Supra(s). He has done a couple of Z's, just not a G, but is more of the Supra guru. My dyno guy is a Mustang man and is the Vortech distributor here, he saw nothing out of the ordinary. Both have not deeply looked into the car post install because the car has been hot, but neither sees or hears and obvious problem and both think the code would cause the engine light to come on. The dyno knows of Strup products and thinks that there is some sort of problem, though-likely a leak.

Any thoughts from you guys? So far, others seem to think that it is indeed the stud that had to be backed out that is not making a secure fit and that is likely the leak source. I simply thought this would cause a code to flash, or the leaky sound would be more obvious. Additionally, how could this one stud area cause that much of a peformance change? I dunno...

Lastly, my only other planned mod until FI is going to be an exhaust (and I plan to go with the Vortech s/c kit), so I will want an exhaust to work with the s/c. I really wanted to keep the Strup headers with the s/c install, so my question is: before FI, do you see an exhaust opening up more gains post header install--as if the stock exhaust is limiting the benefits of the aftermarket headers as is? I was thinking the Borla or the true dual Stillen exhaust, or exhaust and a/m Y pipe like Nismo--any thoughts???

Sorry about the ramblings and sorry for the lack of the dyno plot, but thinking of all this is driving me nuts this morning...Just needed to unload.

I really thought it was a dyno variance issue, but the sound has me all flapped up as does the wavy torque curve with some loss here and there, and the really high a/f (I would have thought it higher when cooler, not warmer).

Any help would be greatly appreciated...

 

Check all the bolts and make sure they are tight. The rule iof thumb with header installs is to heat cycle the gaskets once or twice to get them seated properly. Once they are seated, retorque the bolts. Also, most headers have thinner walls than the factory manifolds, so you will here some more valve train noise. That could be your source of sounds. A leaky header or exhaust will have more of a tick than a woosh. Now for the dyno, was it a dynojet, a mustang dyno? To be sure about the dyno, I'd get the car redyno'd elsewhere. What type of gaskets did you use, were they stock or the crappy gaskets that usually come with headers? Was the flange surface flat on the headers? There are a lot iof questions to be asked. Also that small gain sucks, but do you feel any seat of the pants increase? Race a stock Z and see how you hang.

 

I ran an '05 convertible MT Z and also a neighbor who has an '03 MT G with a CAI. My car was faster than both...
It was a dynojet--the same dyno on three different runs over the stretch of 2 months. The first set of mods made large (15-20hp) useable gains in several places. The headers only mirror the previous modded run, except the loss of torque as noted and the waviness of the torque plot. Lastly, I hear no tick per se and the gasket was a new one ordered through Infiniti...