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Upping the boost causes a lil problem...

Old 10-30-2008, 08:12 PM
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Default Upping the boost causes a lil problem...

My setup is a lil different from most of the ones here, so I'm not expecting any CONCRETE answers...but a lil insight wouldn't hurt. For the past several months I've been running around 8 or 9 pounds of boost. During that time my car has run pretty well...My afr's are generally in the 11's, sometimes spiking to a low 12 at around 3-3.5K rpms(car has generally run a lil lean in that area since I boosted it). My fuel/management setup consists of SRT4 499cc injectors(the black and blue ones), an AFC NEO, and a LC-1 wideband,STOCK fuel pump, NO afpr. When I first boosted my car I had to pull a good amount of fuel in order to keep the car from running real rich. My corrections were generally in the -30 to -20 range. The ECU in my car(05 SpecV) is a pretty adaptive unit however and the tune does quite a bit of drifting from time to time. As time has progressed and the temp and humidity increased this summer I was having to add fuel quite regularly in order to keep the car from running lean(in boost at WOT). It had got to the point where I had my corrections up to -5 at 500rpms and from -5 to 0 the rest of the way across the board(up to 6500rpms, my redline is 6250). I'll also add that recently I upgraded from a t3/t4 with a .48 a/r exhaust & 50 trim compressor to a t31/t4 with .63 a/r exhaust housing(it's been machined to fit the 76trim stg3 wheel) and 60 trim compressor. I also upgrade from a 2.5" maf housing to a 3" housing, BECAUSE the maf maxes out at around 14 or 15 psi when using the 2.5" housing. ANYWAYS, just recently I decided to turn the boost up(I use a perrin mbc), and see how the car responded. It just so happens that around the time I did this we had a full days worth of rain and the outside temps dropped significantly(from 70-80degrees to 50-60degrees daytime temps). I assumed that running more boost I would PROBALY need to add some fuel to the equation, BUT when I started driving the car after increasing the boost(was hitting 13psi), my car was running EXTREMELY rich. At WOT I was seeing 9.7-9.9 at low rpms and it was never climbing much higher than low 10's(10.2-10.4 etc. etc.). The car was pulling OK until I hit max boost and then I was experiencing a light buck-hesitation like the car will do when it's running extremely rich. I started pulling fuel and it helped SOME...I actually had one or two 3rd and 4th gear pulls where the car would pull pretty smooth up to 6k at 13psi, but for the most part the hesitation was there once you achieved 13psi. I'm pretty sure that my car just needs retuning and I need to just pull alot of fuel because that's how this crazy *** ---- does from time to time. I've actually already pulled a considerable amount of fuel, but I haven't been driving the car very hard whatsoever. I'm goin' tomorrow and getting another set of plugs, because I'm pretty sure I've fouled at least one of mine out and that maybe a contributing factor. I'll take a pic of one of my old plugs when I'm replacing it and post it up. Like I said I know alot of you hear don't use the hack and aren't familiar with nissan setups, but anybody(JD, Xeno) who has done some tuning on MAF(my car uses the same MAF sensor found on the 350z's) equipped cars let me know if there is anything else I meet need to take into consideration.
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Old 10-30-2008, 08:33 PM
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Default Re: Upping the boost causes a lil problem...

holy wall of text batman
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Old 10-31-2008, 11:53 AM
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Default Re: Upping the boost causes a lil problem...

spark plug gap?
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Old 10-31-2008, 01:14 PM
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Default Re: Upping the boost causes a lil problem...

Originally Posted by 98vtec
spark plug gap?
Yup, or he's nipping against MAF cut. The AFC deal lowers the signal to maniulate fuel, yes, but it also keeps the MAF voltage from going high enough to hit fuel cut.

Two things:

1) Stage 0 thru either 2/3 SRT4 injectors are "577" cc injectors. In a return system they are good to 350+ at 12:1 and a little less power if run richer. They are found on eBay for <$45 shipped and are an easy fit into a Honduh fuel rail despite what the Riceboy Brigade claims. (Hold a set next to a stock Honduh injector sometime, boys, you will giggle. Stupid, stupid ------- riceboys)

2) With this economy now is the BEST damn time for you to upgrade to a better setup than an AFC. My friend just picked up a NIB AEM F/IC for $175 from a local dumbass... the F/IC is currently the only piggyback you can trust. You can clamp the MAF voltage where the transition into boost occurs and the F/IC controls the injectors for you so the AFRs under boost don't drift, unlike the OBD2 ECU fighting the AFC tune. The F/IC also intercepts the cam/crank pickups and delays the timing there to induce ignition retard, so the ECU doesn't freak out when it sees power pulses (measured through some crankshaft fluctuation sensor like a Honda, or by intellient monitoring of the cam/crank sensors) out of time with the ECU-specified igniton event - basically, in common person speak you don't throw a bunch of random misfire codes.

I know you don't have a Toy/Lexus, but log onto www.my.is sometime and have a look see through their engine management forum. What I want you to see here is 1,001 posts about various OBD2 CELs and OBD2 ECU-related shitfits those cars are subject to as it's a VERY complex and picky OEM ECU, and then I want you to read some of the F/IC intro threads dating back a couple years where you get through the sixth page with multiple people reporting 6+ months of CEL-free boosted enjoyment in posts dating back to '06 - it's not new bandwagon BS, it's a known quantity.

Also, the F/IC logs AFRs for you via one of two analog inputs. You can configure the gauge to read whatever you want, it's entirely user configurable.

Now, just be careful which one you get vs which one you need. There are a couple uncommon F/ICs for the 8 cyl market, but the the common ones control up to 6 cyls and are either a PN 30-1910 or 30-1911 depending on whether you have digital or mag style cam/crank sensors.
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Old 11-01-2008, 09:07 PM
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Default Re: Upping the boost causes a lil problem...

Ehhhh, I'm not gonna bother with any other piggyback. I've already been in contact with someone at UpRev about the osiris software. I'm just gonna stack up the bread, $900-$1k, for that setup. I'll have to go to a local(Marietta) dealer so they can get a copy of my ecu rom...I'm hoping to do this around the end of the year or possibly tax time next year. I put a new set of plugs in my car, and pulled some of my fuel and the car seems to be running better...but I did turn the boost down to about 10.5psi. I'll probaly turn it up a lil more again tomorrow since I have it running pretty decent again right now, and it has a fresh set of plugs in it. I have the SRT injectors, so my logic(it may be flawed) has just been to run SRT spark plugs as well. They come pregapped at .050, should I be setting them at anything different?? This is a newbish type question, and I'll be doing a search here momentarily, but what should I go by when it comes to what gap I should be running on my plugs?? And JD, the larger MAF housing I am using(3" compared to 2.5") is SUPPOSED to allow me to run up to at least 20psi with maxing out the maf sensor. A friend of mine(who's reasonably knowlegded when it comes to FI) doesn't see how that would make a difference, but I've READ that other ppl have had success with it.
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Old 11-02-2008, 05:51 AM
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Default Re: Upping the boost causes a lil problem...

1) Spark plug selection depends on your engine and how hot it likes to run. SRT-4's run 5's, dude, which would kill a mild naturally aspirated B-series that want's a 7, bordering on an 8. Plug gap, in a similar fashion, depends on your ignition system. Since you are boosting a factory NA setup you definitely need to run a tighter gap than stock.

2) A MAF, whether hot wire or karmann-vortex, measures the mass density of the air coming through it. Now, what is more dense, 300 whp worth of air passing through a 2.5" hole or the same mass of air passing through a 3" hole? You guessed it. For the hotwire meters the air isn't as dense in the bigger MAF, resulting in the hot wire not being cooled as much as stock MAF diameter so the ECU is fooled into thinking there is less air going through the engine. For the karmann meters, they operate on air vortexes that change with velocity and density across the meter... they are affected in exactly the same manner.

3) A completely different MAF, wierd spark plug selections, AFC and no MAP clamp... you scare me sometimes.
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Old 11-02-2008, 12:49 PM
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Default Re: Upping the boost causes a lil problem...

Originally Posted by N/A mike
holy wall of text batman
i lol'd hard
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Old 11-02-2008, 04:25 PM
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Default Re: Upping the boost causes a lil problem...

Originally Posted by Joseph Davis
1) Spark plug selection depends on your engine and how hot it likes to run. SRT-4's run 5's, dude, which would kill a mild naturally aspirated B-series that want's a 7, bordering on an 8. Plug gap, in a similar fashion, depends on your ignition system. Since you are boosting a factory NA setup you definitely need to run a tighter gap than stock.
What plug and gap would you recommend?? This is a 2.5L, 9:5:1 compression ratio...I think I've listed most everything else in my setup, let me know if you need to know anything else. I was told recently that I need to be running a .030 gap...that sound about right?? I'm trying to get this thing to run smooth in the 12-13psi range...
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Old 11-02-2008, 04:38 PM
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Default Re: Upping the boost causes a lil problem...

Answer a couple Q's and I'll spit out a plug number for you.

Do you have to run a resistor plug due to COP?

What is the factory (NGK) plug temp for your QR25?

Do you have any plugs that were in the engine that are colder than the 5's you have now? If so, look at the ground strap and try to discern the "heat mark" which is the rainbow band where the ground strap's temper changes from combustion heat. The ideal is to center that bad in the middle of the 90 degree strap bend... too close to the tip is too cold a plug, too close to the base is too hot of a plug. If the whole tip of the well of the plug, and even a thread or two down, have a rainbow color to them because that's where the heat mark has moved HOLY ---- you're lucky to have a engine. Anyway, look at a plug and try to tell me what you can. :P

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