domyz

iTrader: (6)

Here my issue:

Mods that matter:
IX Turbo ported
MAP o2 Eliminator DP Vband
MAP Short Runner Exhaust Manifold
ETS V2 LICP
ETS UICP
Milspec 100cell High flow cat
AEM Intake
CBRD Garrett 3.8" Intercooler
Speed density, 91 octane tuned.
And my catback exhaust consist of stock tubing, with a IX muffler modded for a little more flow (bypass holes has been drilled bigger). Still really a bottleneck.

I installed this weekend GSC S1 camshafts, the car's running strong, but after installation it started to knock everywhere from 5000 to 7000 RPM at WOT. Boost is set at a flat 24 psi. AFR is set at a flat 11.4AFR (avg)
The timing I was using (about 275 load taper to 255):



So obviously I had to retune the car to dial out knock for the new setup, and let just say this was really hard to get it completely gone. I ended up with 22 psi taper to 21 at redline, 11,4AFR and these adjustments to timing:
(about 255 load taper to 240)


I had to reduce timing by 2* and even 3* some places + dropped the boost by 2psi to eliminate knock. I almost lost all the power gained with new cams. I'm in the process of finishing my custom 3" catback, that will make my complete exhaust 3" in size, maybe that will solve the issue.

My theory: Engine is choked from too much backpressure and installing cams pushed the setup to it's limit. The fact that I'm able to hold easily 24psi with this turbo show that my exhaust is choking, I think. I'm guessing there is not enough scavenging/flow in the combustion chamber so that creates turbulence and knock.


It may be something else, but I have no other idea. There is no lifter noise.
Does anyone had this issue where cams caused the setup to knock everywhere ?
Does anyone had experience with reducing backpressure eliminated knock occurence?

I'm open to your experiences and ideas!

evoredy

iTrader: (7)

Seems like you don't have an appropriate ramp up for timing. Do you have the log showing peak timing and respective ramp to redline?

domyz

iTrader: (6)

I have a log at home, not really needed to show you the ramp though because as I said it follows the ramp from 255 to 240 load. from about 2* @ 3500 to 10* @ 7000. Knock was located between 5500 and 6500 (peak power).

The main problem is that I now need to run 6* at 6250RPM + 21psi which is really low compared to 9* and 24 psi before.

todd6027

iTrader: (10)

what does your mivec map look like ??

X Double Dot

subscribed

domyz

iTrader: (6)

Wish I had MIVEC

,,,Evo VIII



I should add that I tried
11.0:1 avg AFR all the way and it was knocking the same, maybe more.
I tried very low timing with 24psi flat: knock.
I tried normal timing with 21psi flat: knock.

The only way to dial it out was 22psi taper to 21, very low timing and just a tad richer (11.3/.4 average vs 11.5/.6)

todd6027

iTrader: (10)

sorry m8

domyz

iTrader: (6)

Ok so far no input. Maybe I'm the first with this issue on this pretty uncommon setup (full bolt-ons, cams, stockish modded catback)

I'll change the plugs, switch the 3" CBE and I'll update.

Biggy VIII

How did you figure out that you actually lost power after retune? Have you made any dyno runs or used VD to make sure that you lost anything?

domyz

iTrader: (6)

Not any.... I could feel it when I removed more than 2 psi and 2* of timing.
car was pulling really really hard before but was often knocking.

foxbat

Did you install springs & retainers along with the cams? I once had a bad case of phantom knock post springs/retainers installation.

I think that the stock pistons are temperamental with knock especially when using 91oct.

If I had such high load/rpm knock then I'd rather enrich AFR rather than having to drop timing & boost.

domyz

iTrader: (6)

No only cams with stock valvetrain.
It doesn't work, I dropped it to low 10s and it knocks. I replaced plugs and they didn't change anything.

I worked on a tune today, it peaks at 24, then quickly tapers at 22psi by 5500 and 21 by 6000rpm. My timing was only dropped by 1* from 6000RPM to redline: no knock.

mithrandir7533

iTrader: (1)

Do you have any racing gas (98 octane) to test your theory?

Biggy VIII

I would check on VD if you have realy lost anything.

Cams increased your VE, so you will experience some knock in the region where cams are most effective. Just tune it out and make a dyno run. ~2* doesnt lose so much power that you could feel it with a butt-dyno.

Just put you before and after logs in VD, make sure you gain or loose something.

domyz

iTrader: (6)

I haven't. But I think it would still prevent knock even if it's caused by backpressure/turbulence.

I have some Vdyno of before, I'll make one for after. Thanks for the input.
I knew I had to tune the car for new cams, but main problem is that knock caused me to nearly eliminate all power gained from cams.

I agree that butt dyno is really not the way to go .
But a difference 2* AND 2 PSI at peak power area is easy to feel on my butt dyno. I estimate it at about 20whp difference at my power level. I can even hear the engine sound drastically changing when timing is more agressive.

As you said, I'll test it on vdyno. I guess in the final tune, these cams gave me near 10whp, which is less than what I was hoping for. It's a VIII and GSC S1 have shown greater gains on this particular model (25+whp).