Knock Reading Rockets With Extra 2 Psi Of Boost, Although Car Is Fully Tuned..

[Dose Pipe Sutututu]

Hi guys,

Recently bought a R33 GTS-t, tuned with a PowerFC, problem is when I hit the limiter knock jumps into the region of 60~80 Knock which is dangerous. Rev Limiter set at 7000rpm

The question is, why does it only get those numbers @ 18psi although at 16psi, even hitting the limiter I don't get more than 50 Knock?

I've read posts here and there that its normal to get high knock when hitting the limiter, and others say it's dangerous and regardless of revs/rev limiter knock should always be low.

Boost vs Knock in my case:

18psi - 80 Knock

16psi - 40 Knock

14psi - 30 Knock

10psi - 20 Knock

Would this be because of the tune? I looked at the ignition map, looks like the tuner hasn't even touched it, looks identical to the stock ignition map that PaulR33 has uploaded to his FAQ thread.

I'm not going to mention who tuned it, but I noticed that the injection pulse/latency is wrong. all injectors are set at 70% with 10ms, although running 450cc S15 injectors should give a value of 0.85%..

Regardless the tune is relatively safe, with A/F ratios around 11.75:1 but kind of jagged producing 245rwkW at 18PSI.

Thanks GUYS!

[R31Nismoid]

Erm... its you hitting the limiter thats setting the knock sensor off. Ive seen mine hit over 100 knock on the off chance i hit the limiter (seen it do it once)

It probably wont actually be detonating, its more the violent cut in/out caused by hitting the limiter and the knock sensor is picking this up.

Just like a starter motor can trigger the knock sensor reading high and so on...

Why would you be hitting the limiter regularly anyway, thats not exactly the smartest thing to be doing

If your hitting the limiter, and its knocking, id say its more to do with you as opposed to the tune - so stop doing it

[89CAL]

well it depends really on what boost ur car was running when it was tuned. If it wasnt seeing 18psi while it was being tuned and the tuner just left the afr's and timing maps how they were in the regions on the map that your car wasnt hitting then that would explain the knock.

I'd say if you think the tuner has barely touched it and just tried to steal some cash off you, take it somewhere else. If you've upped the boost since the tune then as i said he may not have accounted for that. But if its just when ur up around the limiter then you shouldnt really be hitting the limiter all that often anyway

EDIT: R31Nismoid got in just before me. It could be just noise sense from the limiter but mine doesnt knock that much on limiter, cant give you a number cause havent hit the limiter for a while now but i dont think it was terribly high. Id say talk to someone who does tuning and see if they think the tune is a bit out

Edited January 16, 2009 by Boostin96

[Mr. Untouchable]

along side getting it tuned again, maybe try different tuner and get second opinion on maps etc.

Maybe you should drop 100 rpm and set it at 6900 RPM. (if your a limiter abuser )

and i think you will find s15 injectors are 480cc items? JDM items anyway

i think ADM are 370ccs? maybe someone can verify.

have you got a big fat cooler? also which turbo? Fuel pump?

cheers

[EFI Performance]

EXTERNAL gate's can put the ECU into its knock map if set up.

[Dose Pipe Sutututu]

R31Nismoid: Well I try not to, but there's will circumstances where it hits the limiter, I'll eventually will take her to a drift day/motorkhana of some sort and that would involve alot of rev bashing to keep the back out around corners.

Boostin96: The car was tuned at 18PSI, knock reads relatively low from low rpm all the way to 6xxxrpm, but once I hit the limiter, the knock count goes a tad crazy

Mr. Untouchable: Myth that S15 injectors are 480cc, it depends on the fuel pressure, they're actually 450cc, I've got a decent sized cooler, fuel pump, and a HKS2535, so all the supporting mods. I will get the car road tuned once I got the time & money, prefer to get the A/F ironed out, and slightly more lean, also would like the car tuned for cruise and medium load. It runs stupid rich, getting around 350km/tank and flames up on the over run.

[joeyjoejoejuniorshabadoo]

just set the limiter to 10,000... then you'll only ever hit it once...

[DRIFTER]

[89CAL]

lol im trying to remember if i hit my limiter last night or just dreamt it. 1 or 2 other cars i was with did so who knows haha

but the only time i get bad knock atm is when im doing quickshifts on 12psi (for example like racing at the drags that sorta shifting)

[paulr33]

mythbusters ahoy!

more boost -> more heat -> more heat -> more detonation

its as simple as that

the more pressure you stuff in, the harder you make the compressor wheel work, the more heat gets mashed into the engine

theres a point where adding more boost doesnt yield any more airflow, this is when the compressor is out of efficiency

at this point, it throws in lots more per PSI increase and jack all airflow, ie no more power, and crap loads more heat, ie detonation city

[89CAL]

mythbusters ahoy!

more boost -> more heat -> more heat -> more detonation

its as simple as that

the more pressure you stuff in, the harder you make the compressor wheel work, the more heat gets mashed into the engine

theres a point where adding more boost doesnt yield any more airflow, this is when the compressor is out of efficiency

at this point, it throws in lots more per PSI increase and jack all airflow, ie no more power, and crap loads more heat, ie detonation city

Makes sense paul

so this may be a silly question i dunno, but what your saying is cause of a smaller size turbo, it reaches its max efficency at x amount of boost which is only x amount of airflow. So for example the heat generated inside his turbo at 18psi yielding x airflow will be more then the same amount of airflow from a bigger turbo at less boost.

Btw, and im not trying to hijack this thread here lol, but can u shed any light on my problem with knock on quick gear changes (as mentioned 2 posts above)

Cheers

[Dose Pipe Sutututu]

Could someone like read my first post and answer my question? I know more boost means more knock, but I don't get much knock unless I rev bash the motor.

Back to the discussion, I've read where people rev bash their car all day and still get next to nothing knock.

[Swiper the Fox]

Could someone like read my first post and answer my question? I know more boost means more knock, but I don't get much knock unless I rev bash the motor.

Back to the discussion, I've read where people rev bash their car all day and still get next to nothing knock.

the std gts-t timing map in a power fc is a timing timebomb.

way too much ignition advance, and the further down the load cells you go the worse it gets, as putting more boost in it makes it access the load cells further down in the map. Do a run with the map tracer on each boost setting and you will see what i mean.

dont kid yourself...just because the afr's are ok does not mean its a safe tune...afr's are only half the battle.

as a quick test go into the ignition/injector correction screen and pull 5 deg out of it (very simple to do) put it on 18psi and see what happens...ill bet its ok as far as knock goes. Caution though as this correction only lasts while the ignition remains on, when car is off this value goes back to 0.

can you copy up the afm settings...i.e. voltage and percentages...ive got a feeling i know who 'tuned' this one.

Edited January 18, 2009 by DiRTgarage

[Dose Pipe Sutututu]

I'll do it tonight I'll manually look and type each cell into a spread sheet lol..

I might invest in the cable & software soon...

[W0rp3D]

Can anyone tell me what is safe-moderate-dangerous knock levels?

I hit the limiter once which showed just over 60, most of the time its around 25 but one other time i have seen it at 45 with out hitting the limiter.

[R31Nismoid]

25 is more than fine. I sit 20-30 just putting around.

60 off a limiter is to be expected really as there is so much influence around what can cause knock off a limiter.

If you've seen 45 cruising around, its probably just a wayward few cells. Try remember the rpm/load/gear you were in and your tuner should be able to work that out easily and fix it

[W0rp3D]

The 45 was most probably when i was giving it a boot, didnt notice it till after, when ever i have been driving normally its usually 15-25.

[R31Nismoid]

Ye thats totally fine. under full noise i never see over 30 on mine.

[DECIM8]

get a shift light... the engine light is not the shift light

[W0rp3D]

get a shift light... the engine light is not the shift light

Really, WOW never knew that.