stiff valve train and large cams cause faulty knock reading?

[gtrjon]

So guys i have a fully build head:
Tomei procams 270 duration 10.25mm lift
Supertech dual valve springs with titanium retainers
supertech valve guides/seals
Greddy Timing belt
Arp Head studs
tomei 87mm 1.2mm head gasket (and full tomei metal gasket kit)
Oem nissan gasket kit
tomei adj cam gears
5 angle valve grind!

Basically ive spent hours on hours tuning my car and so far have achieved 512awhp @18psi on rgs mustang dyno. One problem. I am running a power fc djetro for my engine management and during my last tune my knock count started reading 70-100 regardless of how much boost or timing was pulled. Tuner basically said that knock sensor must be gone or cracked. So last week I swapped out the knock sensors for a working set and knock count is still the same. Reads 100+ at start up and 60-110 after a full boost pull. So after talking to a few tuners again we have come to the conclusion that due to my stiff dual valve springs and my decently sized large cams the knock sensors cant read accurately. Which sucks since there is no aftermarket alternative for measuring knock and kinda makes tuning for high boost (i am bumping up to 29psi) hard since we have to listen manually for detonation. just wondering if anyone has ran into this problem before or have any other possible theories?

[gtrjon]

http://youtu.be/yuHKhKUQgVQ

http://youtu.be/u5lOiuKLawY

she moves a bit

[GTRADDICT]

First vid is awsome! Warp speed! The oem valve train is super loud, I bet your right with stiffer springs and higher lift it could make more noise. Wouldn't the EGT's be a good alternative way to detect if something is wrong when tuning for Highboost? idk if Knocking will increase EGT's... I'm just babling.
Car sounds mean!!!!

[NismoS-tune]

What's your AFRs like? EGTs? I'd say you have legit knock there but it's might be something loose in there?

I run very similar springs/cams but have had no knock. I'm running a knock box though. OEM knock sensors and PFC are fine. I had a buddy who was around the same power as you with similar setup (minus head work) who regularly saw 40-60 knock on his pfc. Drove it till it blew up (too much boost killed a rod bearing, excess cylinder pressure vs N1 oil pump, crushed the bearing).

[pmdawg]

There is an aftermarket solution go with this:

http://www.jandssafeguard.com/

Lots of Drag GTRs are using J&S KnockGuard Systems to monitor knock.

[gtrjon]

What's your AFRs like? EGTs? I'd say you have legit knock there but it's might be something loose in there?

I run very similar springs/cams but have had no knock. I'm running a knock box though. OEM knock sensors and PFC are fine. I had a buddy who was around the same power as you with similar setup (minus head work) who regularly saw 40-60 knock on his pfc. Drove it till it blew up (too much boost killed a rod bearing, excess cylinder pressure vs N1 oil pump, crushed the bearing).

your missing the point. my afrs are good. mid 11's wot . mid 12's at idle and 15+ cruising with no misfire. i am running 18psi with meth there is no/minimal knock. any knock count over 20 you can head audibly and anything over 31 causes damage. im reading 100+ meaning if it was accurate i would have spun all rod bearings at once. there is "nothing loose in there" although i do like the idea of using egts as a way of measuring knock. i am not currently monitoring them.

[gtrjon]

There is an aftermarket solution go with this:

http://www.jandssafeguard.com/

Lots of Drag GTRs are using J&S KnockGuard Systems to monitor knock.

i wouldnt call it an aftermarket option since it utilizes the oem knock sensors reading. kinda defeats the purpose

[NismoS-tune]

your missing the point. my afrs are good. mid 11's wot . mid 12's at idle and 15+ cruising with no misfire. i am running 18psi with meth there is no/minimal knock. any knock count over 20 you can head audibly and anything over 31 causes damage. im reading 100+ meaning if it was accurate i would have spun all rod bearings at once. there is "nothing loose in there" although i do like the idea of using egts as a way of measuring knock. i am not currently monitoring them.

You are correct, I'm out to lunch though I don't recall reading anything about what your AFRs were, just a guess. My bad. Good luck sir! I'm just a friendly guesser, not a mechanic. I'm one of those guys that can afford lots but knows nothing about what he buys a money pit lover I guess.

[collector240sx]

Are the knock all across the board or in specific area, have you check for anything loose that could be knocking against the engine, chassis. Like metal pipe, part of the harness not attached properly, even over flow line with the metal loop.

Knock's don't have to come from the engine, sound travel really well trough solid material.

Good luck.

[Terrh]

crappy transmissions can cause phantom knock too.

On my RX-7 I never even ran knock sensors, monitor AFR's and EGT's and keep the timing safe and you're good to go. (yes, I realize this isn't ideal but it works)

[MarusGTR]

i wouldnt call it an aftermarket option since it utilizes the oem knock sensors reading. kinda defeats the purpose

From an engineering standpoint the sensor isn't your problem, it's the signal that's being misinterpreted. Theoretically, if you'd find a system with some built in filters that could cut through the white noise you'd get proper knock aquisition and proper knock control with the stock sensors.

But this is all theoretical of course. Maybe pmdawgs's controller has those filters.

[Dragon Humper]

I don't think audible knock is at a 40 count on the PFC, I regularly saw 30 to 40 on my feedback at all times above 4000rpm and I have never heard a thing. That could have been just the engine tackle and my base. I run rediculously good fuel for the street as well and even at only .9 bar the counts were the same. They only increased about 5 counts at 1.5 bar. I think it was just ambient engine noise (valve train and such). Unfortulately my Knock Sensors have stopped reporting and I haven't figured out why yet.

It's a glitch, maybe torque the sensors to 75% of factory spec and see if that makes a difference.


Jon.

[RSTuning]

Get something called knock ears. listen to them, at which point you can determine if its valve train noise or tuning related.

PS, New knock sensors would be a good idea. not used.

[ZinnZ32]

Things like this can be dealt with when tuning. I know some really good companies out there use a sophisticated "Knock Listening" System when tuning cars on the dyno, with headphones, sensors, etc. Really, that is the best way to do it, and I don't see why more shops don't have more simple tools, to provide more information when doing such an important step in the process of getting power out of a car.

For those that don't know. Not all knock is 'audible' by the human ear. Mostly, that is heavy detonation that people refer to when they can hear it. There is also light detonation, which many peopl have, but will not notice. Heavy detonation (usually audible) can kill a car quickly, or take up to 6months, to a year in some cases. Light detonation can slowly wear the car down, taking 2 years or more in most cases.


I really think, there is some factors tuners need to be more cautious about. It's really a job where you need to take responsibility and care for every single car that comes in, and be absolutely sure, without any doubt that it is going to be safe when it leaves. You would think that'd be obvious, but there are a very few shops out there I would personally trust to take my car to the limits of tuneability.

[Dragon Humper]

For a built engine (forged pistons and properly gapped rings) small amounts of detination won't do very much, if anything. Chevy 4.3l V6s in mid '90s trucks would rattle like a bastard climbing every hill they came to on 87 octane and would last at least 250,000kms. All the while with glass-like hyperutectic pistons. Det. under boost isn't any worse contrairy to what some info. floating around the web would suggest. The peak cyl pressures are vitually the same boosted or not. Nitrous on the other hand is a whole different animal when it comes to det., the chemical comp. of the mixture is far more volatile and peak pressures are much higher.

If you have light det. that you can't hear the worst that can happen is the conrod brgs will get beat on a bit. If you are running a good oil and the clearences were set right to begin with it shouldn't really be an issue.

I find there are 2 types of tuners, the ones that have no idea what they are doing and blow up many more engines that anyone should and the ones that are FAR too conservative and are leaving buckets of power on the table.

The ones that find that balance and impress me are few and far between.



Jon.