High Rpm Boost Lost

[Black_CSR]

Hi Guys.. got my Car Tuned today... Pretty pleased.. just curious as to why i start loosing boost towards high rpm.

Originally it was tuned for about 13psi or 13.5psi.. but the boost curve @ high rpm was tapering off low so we just got it tuned @ 11psi. At 11psi we lost only about 5-6HP which is not really much and made the curve smoother n more linear, So Avg boost is better near the top.

Today was 33'C so i don't know if i could of got a higher reading if it was a colder day.

So yeh what u guys reckons.. why it's loosing boost @ high rpm.. leaks, setup, etc..???

Ta

-SeS

P.S. mods R (3" Turbo back 5"Tip & HiFlow Cat, HD clutch, Hks Pod, Iridium Plugs gapped 0.65, Power FC, HKS EVC 5, CAI n DIY Pod Box , FMIC, GFB BOV, Bosch 910 Pump and everything else stock.. power mod wise.

Edited January 29, 2008 by Black_CSR

[BLK33T]

If you are running the standard turbo, which it sounds like you are, it is getting out of its efficiency range. Most standard turbos can't flow enough air at high rpm hence they become a restriction and constrict power past a given point.

There are a few solutions;

1. Turn the boost down until it stays flat (which you have done)

2. Get your turbo high-flowed and run more boost

3. Get another turbo

Anymore than 11 psi on the standard turbo is asking for trouble anyway stick with 11psi for now.

Hope that helps

p.s. you'll get more power on colder days at the same boost setting generally

Edited January 29, 2008 by BLK33T

[342Four]

plugs gapped at 0.65mm seems a bit small to me

but somebody correct me

i would have them around 0.75-0.8 from what ive read...but i could be wrong

[Al]

0.65 is very small, spark will not be very efficient. If you find that spark is breaking down when plugs are gapped to 0.8 then consider buying splitfire coil pack, as your std ones are worn.

What blk33t stated is spot on, but the plugs will also not be helping.

[BLK33T]

true didn't notice that ...

probally had to gap them that low because standard coils are getting a bit long in the tooth ...

I don't think that the boost dropping off would be the gapping of the plugs however, but I have been know to be wrong. Occasionally.

[BLK33T]

lol ... posted at the same time Al

[kingscorp]

TThere is nothing wrong, the Turbo running out of puff!, I think you will find Steve has turned the boost down on purpose as to not overdrive the Turbo.

Ambient air temp wont make a difference, when the Dyno is in shootout mode it compensates for the air temps.

Looks like an Auto, is it?

Ash

[342Four]

nup - mods list indicates HD Clutch

[Edge]

what are you actually using for the boost controller, perhaps try removing the restrictor on the tube going to the standard ebc?

I'm running 15 psi on my standard series 2 turbo and its fine with the fmic on.

[phenline]

what are you actually using for the boost controller, perhaps try removing the restrictor on the tube going to the standard ebc?

I'm running 15 psi on my standard series 2 turbo and its fine with the fmic on.

15 psi on a stock turbo ohh noeezz

[Black_CSR]

Ok so i guess it's pretty spot on... but he left the EVC on 13psi on A and 13.5psi on B. I'll have a play and get it running about 11psi.. or just over as u say yeh????? and get some coppers n gap em to 0.8mm??? reason i had iridiums in there n gapped to 0.65mm is cuz i had missfiring problems b4.. n that sorted it out.. but came back again.. n just use some injector cleaners to fix it... n it went away n that's when i had the Stock ECU in. Also used Silicon High Temp n covered them up...

Gave it a little squirt tonite and 1st n 2nd was pulling hard n going as high as 13.Xpsi or so... n hittin boost cut.. gotta play around wif the Map function of speed/throttle maybe.. or just Speed on the EVC n sort that out.. Haven't done 3rd or 4th Roll on though.

So i guess i'm maxing out my Stock turbo yeh???

-SeS

P.S. (Modifying Ain't Easy )

Edited January 29, 2008 by Black_CSR

[Black_CSR]

what are you actually using for the boost controller, perhaps try removing the restrictor on the tube going to the standard ebc?

I'm running 15 psi on my standard series 2 turbo and its fine with the fmic on.

Hmmm what do u mean by the restrictor??? i have the actuator directly hooked up to 0, 1 is tee'd off the original boost gauge line and 2 which is out goes to the nipple of the intercooler piping...

-SeS

[Chi100188]

good power Ses hahah i think i gotta make a cold air box too

[sidewayssam]

i have a similiar problem but its coz my hks electronic boost controller stop working so i temporarily bought a manual boost controller bleed valve thing, the manual boost bleed valve thing wont hold anymore than 17psi, so when it gets to 17psi and revs continue to go up it cant hold the boost and drops down to 14-15psi

[Edge]

Hmmm what do u mean by the restrictor??? i have the actuator directly hooked up to 0, 1 is tee'd off the original boost gauge line and 2 which is out goes to the nipple of the intercooler piping...

-SeS

well can't see any picture and my piping is onto a bleed valve but there is a restrictor in the tube going to the actuator on the turbo which should have had a restrictor removed, there should be a hard thing in the tube where a red or white mark is on it. It should have been removed already, but just a thought.

You could try a different tuner, it should be tuned while locked into 3rd gear. Boost leak anywhere? Any whistling noise from the turbo indicating broken fin?

not sure how boost is controlled by power fc, does it have a variable fast pulse rate that can be increased.

The series 2 turbo with its plastic impeller which is slightly stronger than the ceramic impeller on the series 1 turbo means that the series 2 turbo will run 13 psi at the track and is not known to have shear issues under this pressure.

series 1 turbo is good up to 12 psi.

Just to give an indication, I was suffering boost drop at high rpm as well, was fixed with replacing coils and replacing iridium v 0.8mm gap spark plugs at correct 5 temp rating.

Find yourself a good tuner, I took my car to three different places and each told me a different story two of which turned out to be false, first tuner charged me $980 for a tune, and two days later put it on the dyno and said it was a weak wastegate spring. Second tuner said it was the boost controller needing to be an electronic one instead of bleed valve. Third tuner said it was a coupple of the coil packs and said this is quite common in skylines, fixed + quick tune and now boost holds at high gear high rpm.

Measure whether the fuel mixture is running rich with a guage in your exhaust at the high rom and boost, don't just use the powerfc knocking light to tune, you need to check it.

If the fuel mixture is ok and the spark/coils arn't breaking down then put up with it or get a bigger turbo, cause at least you have fuel effificiency.

[SKYRYAN]

Sounds like a rat infestation. You need professionals in there asap. These virmin can and will chew through everything under your hood bro.

[Edge]

just took a look at the graph at the top you posted,

that tune you have looks like a good result, I wouldn't call that boost drop significant, the power graph looks fine.

cams or maybe just another adjustable cam wheel would fix it for the higher rpm boost.

Normally the engine looses efficiency over 6500 rpm with standard cams.

[kingscorp]

I dont think the engine would loose efficiency at 6500, the turbo will when trying to make 13psi.

I am sure Steve will give you the fuel graph if you ask

[Black_CSR]

It's Series 2 R33 GTST....

Ok Well my main issue is @ night when the air is denser n cooler.. it seems to cut out or boost cut @ 5G's on 1st n 2nd cuz it boost quite hard like 13.. peaked about 13.5 which is fine. I thought the lower the gears the lower the boost will be n hit full boost by 3rd or 4th.. not that i don't like it but during the day it's fine.. n hits peak boost @ 12.5 on 2nd.. n keeps pulling without hesitation. The front felt like it was goin Airborne haha

Had to adjust the BOV cuz it was too tight n seemed like it was choppin up the blades when it was fluttering @ low revs, that won't affect the Tune much will it???

I'll change the plugs first to Copper NGK BCP6ES n gapped down to 0.6mm n if it continues i'll get some splitfires in there..

I'll have a look @ this restrictor ur talkin about Edge n take a pic maybe...n get that fuel Graph for extra info..

Hmm i didn't think i needed Cams or Adjustable Cams for stock turbo... n all i needed was a bigger pump according to this forum

-SeS

Edited January 30, 2008 by Black_CSR

[Edge]

try this before you do anything else

get some 0.8mm gap spark plugs you want a bigger spark than 0.6mm...standard R33s2 comes with platinum for longer life between changes and more stable gap size. (and 1.2mm gap)

(it isn't too hard to change the plugs yourself - stress strongly you use a small socket driver and not a philips head where you have the option on the screws)

take it for a drive

then get it to the dyno and check your coil packs aren't breaking down (having spark run elsewhere instead of the proper spark plug gap)

if your coil packs are playing up just get second hand if you only need 1 or 2 otherwise you can fork out for a set of 6 new ones.

once this is sorted, get your tune tweaked to see if you can get a better result at high rpm.

cold nights result in more boost due to more power being generated by more oxygen in the denser air, resulting in an increased likelihood of spark breakdown.

You only need to replace fuel pump or install a rising rate fuel pressure regulator if you are running lean at higher rpm.

Other than that you don't need to waste money on cams which just enable a little more power from higher rpm range.

for much bigger bang for your buck, buy a turbo if you want more power...and then you might consider the cams.