Hesitation At 6000 Rpm

[910trx]

i never get to drive the stagea like it should as i have a missus stapled to the passenger seat 99% of the time.

yesterday she had a lift home with a friend so i wound down the windows and have it a couple of full throttle runs .

it works fine and goes like a rocket after the new exhaust has been put on a month ago (3 inch front pipe, the highest flowing cat i could find and a fujitsubo cat back 3 inch)

but i noticed everytime at 5500 to 6000 it hesitates for a second then keeps on going to redline where the auto shifts, the exhaust makes the nicest craclke and pop sound while engaging second and continues strong in the next gear.

only noticed it recently and if it is on 50-80% throttle it wont do it - only at near or full throtle.

drives beautifully none the less, just curious to the cause

the exhaust stuffed things up?

sign of something on the way out?

[scotty nm35]

Running rich or lean by the sound of it. Any engine mods you know of?

[910trx]

nope , not that i know of

Std everything except the exhaust

also just added fresh oil and running on 98

Edited November 26, 2009 by 910trx

[KiwiRS4T]

Exhaust won't be doing any harm but you may have noticed an increase in boost. Do you know what state your plugs are in? A new set of coppers might fix the problem. Ideally your next mod should be some means of tuning the engine.

[910trx]

in all honesty i have not ever changed the plugz

i aim once i get back to adelaide (see long trip in stagea thread) and doing an new waterpump, plugs and cam belt as i have tools, mates, second car and plenty of places to get parts from

once i get back i'll swap in some newies and retry - this is the extent of all planned modifications, goes fast enough and reliability is the top priority, not power.

[QWK32]

Completey normal for a RB25, mine also does it and so I know a few other people with the same thing. The VVT changeover is at about 5000rpm so we're probably experiencing the increase in torque from the high rpm lobe. At first I thought it could be a tuning issue with the stock ecu running too rich, but I've pulled my mixtures back to an acceptable afr and still feel the torque increase around 5500-6000rpm.

I think you'll find if you look at some dyno sheets of RB25's running stock VVT cams and control points you would see this flat spot on the torque curve.

[910trx]

i'm guessing it is just more noticeable in a lower gear and without the backpressure of the old standard exhaust dampening its effects.

its hard to test it in 2nd and third gear safely for obvious reasons, and its likely i'll never do it again for another 3 months...

just had me a bit worried thats all

thanks

[kidafa]

coil packs arcing....

[910trx]

^^^ exact same engine with lesser an exhaust

it is pretty obvious the dip in performance which matches what i feel, almost looses power before making more.

some with bigger injectors, powerfc and exhaust cams have overcome this

not for me but looks common although i'll never go that far.

Coilpacks, well could be - it happend at the exact same rev range though, thought arcing packs woild be a bit more sporadic.

Edited November 26, 2009 by 910trx

[Chasey]

Hey i had a series 2 RS4 stagea with RB25det engine... had the same problem, i went through every thing, coil packs, spark plugs, air flow meter. i couldnt work out what was wrong till about 4 months later it got worse and worse, turned out it was the fuel pump. put a new fuel pump in it and it went great

[pyro-ns]

^^ your pic's a bit small mate.

doesn't the neo have Continuous Variable cam Timing, as opposed to some form of variable timing??? there shouldn't be an overlap at all (in theory) with cvt??

edit:

i've also noticed since putting a boost gauge in the girl's stag, the (stupid) dual stage boost doesn't work too great. in the second stage it spikes to 7 and then bleeds back out to 5 again :S

Edited November 26, 2009 by pyro-ns

[910trx]

yeah i know its small - but seems irrelevant now

whats a good pump worth these days?

Edited November 26, 2009 by 910trx

[Chasey]

yeah i know its small - but seems irrelevant now

whats a good pump worth these days?

Just put a 2nd hand one in... should set you back around $100.... or i think you could get a walbro for around $250 new.

it will only be one of these 3 things thats wrong, coil packs, spark plugs or fuel pump. see if you can borrow some one elses parts to check what is wrong

[wolverine]

I have a 2nd hand one lying around if you need one.

[910trx]

i'll wait untill i get back and start doing the things that i know it needs and the cheapest first

so probably plugs, pump, then packs

thanks guys really appreciate it

i'm still clueless when it comes to efi turbo - throw me a carby and i'm fine...

[QWK32]

i paid $170 for a brand new walbro GSS342. 500hp rated.