car falls on it's face after 5k rpm

[MidnightSlide]

I just had an sr swapped into my car with these mods:

greddy o2 extension pipe5zigen downpipecusco flywheelexedy 3 puck clutchnismo mountshks hyper 85mm catback exhausthks intake filtervlsd

All the parts were brand new upon install, and didn;t come with the motor

I asked around, and it seems that it is reccomended to get a fuel pump, so i ordered one and it is on it's way. I was also told that unless i up the boost, it shouldnt be too necessary.

What i am worried about is, when i hit around 5k rpm the car seems to slow down.. like there is no more power.. just kinda levels off.. it feels kinda like it just stopps boosting. The boost is very strong up until 5,000 though. i was looking at my boost gauge the entire time and it shows a consistent 7psi...so i don't think that i am leaking boost.. i duno y it does that.. maybe it is just an sr trait.. i don't know..

Can anyone help diagnose my problem?

[extheflow]

it could still be leaking boost,say the bov will hold fine until 7 psi at wich time it starts acting like a wastegate. wait and see if it still happens with the new pump, or hook up a fuel pressure gauge in the meantime.

[MidnightSlide]

oh..another thing that i noticed, is that the car seems to go nowhere until 3,000rpm when it hits full boost. It seems kinda hesitational even.. kinda like i am bogging/flooding the motor.. it is really weird..

[gabossie]

check/replace your fuel filter.

[MidnightSlide]

hmmm...didn't think to do that yet.. thanks.. ima try that. Any other suggestions?

[Kenji180]

You are right.. you probably need a fuel pump for starters.. a walbro 255 should be plenty.. it sounds like the motor is leaning out around that rpm.. I would also check for any leaks/vacuum line leaks as well..

Good luck!

[MidnightSlide]

thanks.. i am going to try the fuel filter today, and the pump was supposedly shipped monday, so it should be here soon.

[240dreams]

i kinda have the same problem. the car seems "weak" at rpms lower than about 3.5k. is this natural?

[Cyberkreig]

Below 3.5k rpm you are driving a 2.0L N/A motor with a compression ratio of 8.6:1 & turbo cams. Not exactly a formula for speed.

[240dreams]

thats explains it all. thanks. i still love my sr tho.

[TurboB15Sentra]

The hesitation that you feel before 3K is most likely a bad o2 sensor.. and an exhaust leak throwing the reading off. At around 3K, the ECU ignores the o2 sensor and goes into open loop.Travis

[MidnightSlide]

aaah i see.. it performs really nice now that i put the walbro in. still knida slow til 3k rpm... ima have to look into the o2 sensor thing. I also just replaced the plugs with some denso iridiums...

[bootman]

i am having the same problem with my car it is strong up till 5000 rpm when i took it to the dyno it was super rich i am running the 300zxtt fuel pump i got a safc2 it helped a little but still super rich

[MidnightSlide]

i think ima get a fuel pressure regulator. That may help some..

[TurboB15Sentra]

If you still have the stock regulator in.. the car will run rich with the bigger fuel pump. The factory SR regulator isn't big enough to flow enough fuel out to the tank. So, the pressure spikes up a little and makes the car run rich.Travis

[MidnightSlide]

aaaah.. ok that is exactly what i was thinking. Ima go grab a nismo unit this week, along with the 300zx fuel filter... and hopefully a fmic, gotta find one cheap enough though...

[timmybgood]

hey midnightslide whats up with that kit

[TurboB15Sentra]

aaaah.. ok that is exactly what i was thinking. Ima go grab a nismo unit this week, along with the 300zx fuel filter... and hopefully a fmic, gotta find one cheap enough though...

email me with what you are looking for.. and your budget, and I'll see if I can help you out. [email protected]

Travis

[MidnightSlide]

thanks travis..i will be sure to do that..

[180crafter]

Will the nismo unit correct the fuel pressure spike??? The piping doesnt seem much bigger and even though I could raise the pressure, I wouldnt want the negative effects of the spiking. Not only that, would my increased boost and air/fuel still be affected by the fuel spike?

[TurboB15Sentra]

The difference is in the diaphram area... inside the regulator. It allows more flow.Travis

[DriftBandit]

The nismo unit is still on the stock 1:1 ratio, Like mentioned above it just has a stronger adjustalbe diaphram. Mine works great, fixed my fuel problem right away, Just be sure you get the right one for your motor.

Good Luck

-Jon

[Cyberkreig]

I command this thread to RISE!!

Since this thread i've been watching my boost graph carefully (greddy e-01). Obviously everyones setup is slightly different but i noticed a consistant boost drop off starting at 4500rpm. from my setting of 12psi boost steadly drops to the 9-10 range by 7krpm.

If you happen to have a boost controler with an RPM offset i suggest using it. starting at 4500 rpm i set my solinoid duty cycle at 10%. This helped to flaten out my boost curve above 4500 most of the way to redline. The car is noticeably faster. the upper rpm range still needs adjustment but its hard to get 7krpm in 3rdgear without a dyno.. safely that is.

my setup for reference: Stock S13 SR(motor/turbo) full 80mm exhaust, FMIC, Walbro pump. No tuning outside of the above. 12psi set by Greddy E-01. mix of 93 & 94 octane pump gas

[MidnightSlide]

hahaha definately... cmon sr gurus... give us some more opinions...

[MadSideways]

The stock intake manifold is very restrictive. You'll notice most dyno charts with the stock manifold tend to stop producing power at about 6300rpm...

Also, factory cams are designed to produce the most power at cruising speed, which would be between 3000 and 5000rpm...

Upgrading to the greddy plenum makes a huge difference in power above 5000rpm....but with added cams and a couple dyno runs to tune the ecu, you can almost rev to infinity, although you may blow your motor, there'll be no loss in the powerband...

Ofcourse, all of this is assuming you have full 3", unrestricted, intake and exhaust, and your turbo isn't passed its efficiency range.

[MadSideways]

This dyno chart shows a gt2540r with .86 A/R housing with and without a plenum/cams at 19psi:

[Cyberkreig]

wow, i thought the gt2540r would make more than that acorss the band.. especialy at 19psi. that graph talked me right out of one of those.

[MadSideways]

Yeah, I would say that the gt2540r pumps out about 380 with an internal wastegate, maybe 400 with an external wastegate...You can probably push it farther, but its going to get past its efficiency range and heat up...

If you go with the .64 A/R housing you'll get more low end power out of it, but it'll bring the top-end power down....

If you're wanting to break the 400hp mark, you'll need larger than 550cc injectors, and maybe a GT2871R, (420rwhp). Or goto a t3 style flange for a larger turbo, like enjuku racing, with their 512rwhp t3/t4....

[Cyberkreig]

this realy should be a differnt thread but whatever.. i dont see the point in bragging about having a 400whp car if its 401whp @7000 rpm. I mean its a good looking curve. i'd just like to see it bumped up 50 across the board.

[MadSideways]

If you want an even 50hp across the board, you're going to need a change in displacement. I mean 2.0L can only flow so much cfm at a given RPM, even with forced induction....

You can throw an oversized turbo on there and get more power under the curve, but you're going to sacrifice spool time....

Although, I think 300rwhp at 4800rpm rivals most domestics...