GTR problem

[toad]

hey everyone,

i know this is a subaru site but i thought id give it a go as im not part of a nissan one.

my mate just brought 1989 Nissan Skyline gtr running 24 pound at 506 hp on mild tune by a link g4.

Problem is the boost gauge (apexi) is set a 1.6 bar but when giving it s*** it jumps up to 1.9 bar but apparently the link is set to max at 1.7 bar. im unsure if this is normal. ive been told that it could be a seized wastegate spring? also when in 4th it will get to 4000rpm and the boost will hit 1.7bar and the boost cut out.

if any one can help that would be much appreciated.

[WRXONP]

shouldnt have a "boost cut" with a link..

sounds like either boost is spiking or boost is creeping

when you floor it does the boost go up to say 1.8 then down to 1.6 or does it go to 1.6 then gradually do up to 1.8??

wastegate isnt functioning correctly

[soopersubaru]

Boost cut not set on G4 either.

Be careful!!.Or blow it!! ;D..As The above person suggests......Waste gate issue probably

[WRXONP]

you need to figure out if its boost creep or boost spike..spike can be caused by allota things..

boost creep is the wastegate not flowing enough

you can set a MAP cut on the link which when the map sees a certain value (set by tuner) it will cut out

[toad]

it boosts from 1.6 and goes up to 1.9 bar. the wastegate is under the car. apparently the link is set to cut boost at 1.7 bar?

[WRXONP]

so you put foot flat and boost hits 1.6 but then slowly rises more??

if it is thats creap.. is it running an external?? is it tuned for that boost?

sounds like its a 38mm on a rb26??

is it single turbo?

[WRXONP]

BTW how do u get a mild tune on 24 psi LOL somewhat not mild

mild is 8 psi LOL

[soopersubaru]

Boost cut related to rpm usually in the G4...Rpm when at 1.9 bar is?

Could be a spike...However i would be concerned that the "cut" does not occur when 1.7 bar is exceeded.

Def not a normal occurrence.

Hook up a lap top and the you can log/see what is happening.

Can also check boost cut/rpm relationship.

[toad]

single turbo greddy t88, yup 38mm wastegate on rb26 plumbed back in, it has been tuned at 720hp at 32 psi lol but that maxed out injectors. yup boosts to 1.6psi then slowly rises

[WRXONP]

wastegate is too small / hasnt got enough flow to hold lower boost

obviously it could hold 32psi when tuned

basic rule of thumb

to hold lower boost solid you need a larger gate then comparing to holding higher boost as u can get away with a smaller gate when boosting more as it will be letting less out as more is needed to drive the ex wheel

what manifold is it could be the collector style

[toad]

front facing hks plenum. so wouldnt be just the spring?

[WRXONP]

hold on..it was tuned for 32 psi.. but its "boost cutting" lower than that? 32 is over 2 bar

[WRXONP]

 toad said:

front facing hks plenum. so wouldnt be just the spring?

lol

i ment exhaust manifold - the collecter where the gate picks the gases from??

how is it plumbed?? was it not plumbed before??

changing to a harder spring wont help....the wastegate needs to let MORE out to hold boost instead of creaping the boost higher and higher (not letting enough out)

[WRXONP]

got us a pic of the engine bay?? and wastegate / turbo setup?

[toad]

its from chch and they have 98 fuel, they detuned it to run 95 as thats the highest we got in invercargill. oh not sure what exhaust its all custom. its plumbed straight back into manifold. its allways been plumbed in. the bov is plumber back in aswell as the said it works better with the tune it has. softer spring?

[toad]

sorry not plumbed to manifold its on the bottom of the dump pipe

[toad]

will take pictures 2moro and post them k

[WRXONP]

the spring will not make it hold boost when it cant bypass enough away from the turbine

if you try lower the boost more the effect will get worse

[WRXONP]

the angle the wategate picks up from and the angle it dumps into the exhaust is really important...

but IMO a 38mm gate is too small for a RB26 especially with a single turbo of that size..

the rb26 head has ALLOT of flow and makes allot of exhaust gases..

get a larger gate and it will bypass more / hold boost solidly

tuner say anything about it not holding boost when it was tuned to the current state?

[toad]

got told not to lower the boost as its tuned for 24psi nothing else. nah he didnt mention anything

[toad]

the wastegate is connected to the bottom of the dump pipe and plumbs it directly back in just after the bend

[WRXONP]

when tuned you can allways lower boost more as its within the map..you never want to raise boost above what is tuned as it will lean out

so the tuner tuned it and said nothing about it creeping ??

[soopersubaru]

 WRXONP said:

wastegate is too small / hasnt got enough flow to hold lower boost

obviously it could hold 32psi when tuned

basic rule of thumb

to hold lower boost solid you need a larger gate then comparing to holding higher boost as u can get away with a smaller gate when boosting more as it will be letting less out as more is needed to drive the ex wheel

Re above.....Agreed waste gate too small for.....Therefore boost creep.

Still.......The boost cut rpm relationship is not correct if this is happening.

Hook up Laptop.....Best/only way

[WRXONP]

slam a bigger gate on..will probably need to change the manifold to suit so it has a larger diameter runner to the gate and a larger pipe going into the exhaust and a larger valve in the gate - which will let it be able to bypass more gases away from the turbo

sounds like it has a cheap chinese manifold off trademe with poor wastegate runner and small gate flange

[toad]

it was purchased from gun city in chch