rcwilbur

I have Texas Speed 5.3 heads and 224R cam in LS1 Corvette with Manual transmission. AFR is 12.5 at WOT and I'm getting a lot of knock retard. PCM is taking away as much as 10 degrees timing. I started with stock tune which had about 26 degrees of timing at WOT and have steadily reduced timing in about five different steps. Last run I set timing to 16 degrees at WOT. It doesn't seem to matter what the timing map is set at, the knock retard is always removing about the same thing 10 degrees.

I've tried carbon cleaner, but am at a loss as to what to look for next. Is there something I could have done wrong installing heads/cam that would cause this?

outkast6991

iTrader: (34)

Throw some 100 octane unleaded in it. If the kr doesn't change then its probably a false condition. Might have better responses in the tuning section too

outkast6991

iTrader: (34)

Also what is your compression?

rcwilbur

Compression is 10.9 to 1. Thanks. I will try some higher octane gas and see what it does. I'm thinking its false knock because it seems to show knock irrespective of the programed timing. I will try this in the Programming section too. Thanks for pointing that out.

LS1T56FTW

iTrader: (3)

With those heads, his compression will be right around 11:1. My car actually couldn't take much timing either, I think it is partially due to the baby cam. I have a 228/232 with 111LSA and the MOST timing we could get my car to run was 25* and that had to climb in the RPM range to get to 25 too, it started at like 22 or maybe even lower. Don't get too caught up on throwing a ton of timing at these cars, my car put down 470WHP with those heads so you shouldn't be too down on power. Like the above guy said, maybe it is false knock, try out some higher octane, or maybe your wideband is incorrect and you are actually leaner than you think. If you can get around 18-20* timing I wouldn't worry, but you are a little low with only 16*.

outkast6991

iTrader: (34)

My car is only taking 24-25 as well before showing kr

rcwilbur

I would be okay with 20 timing, but problem is when I put 20 in for wot I get almost ten degrees of knock retard. When I reduced it to sixteen I still get almost 10 degrees of knock retard and you can feel the loss of power.

I'm really at a loss. I think it must be false knock, because no matter what I've done to timing or fueling it always shows similar levels of knock at WOT.

LS1T56FTW

iTrader: (3)

Start looking for places that could make false knock then. Bad motor/trans mount(s)? Loose heat shield? The sensors have to be picking up noise from something. If you are dropping timing and the KR is staying consistent, that would lead me to believe that the timing is not causing the issue.

Exidous

iTrader: (11)

I use 25-26* from 4k and up. 228r cam and same heads. Unmilled I think. 92 Oct E10 gas. E85 is about 108 Oct. Cannot get E85 on island yet :-(

I'd look elsewhere for your issues.

What gasket thickness you use?

rcwilbur

Its the MLS GM Gasket. I don't see the headers rubbing anything, but I know when I installed the LG street headers I could hear a lot more valve train noise (even before I installed the new heads and cam.)

I am tuning the car on the street so I can't really look into the engine bay when it is running at 4000 RPM--not safely anyway

rcwilbur

Thanks. I installed LG Street headers before I did the head cam swap. I went back and looked at some of the logs for those tunes and I guess I had some knock retard then. I am new to the tuning thing and thought as long as I didn't increase timing I didn't need to look at those maps.

I don't see where the headers are hitting anything? Is it possible that the headers themselves could create that much additional noise that they are triggering the knock sensors? Just wondering, because it was louder inside the car after the install.

outkast6991

iTrader: (34)

what motor mounts are you using? also if the exhaust is rubbing anywhere that could be an issue as well

rcwilbur

Motor mounts are the stock mounts--didn't change anything there. I can't see where the exhaust is physically rubbing anything, but I'll take a closer look today.

LS1T56FTW

iTrader: (3)

Put in some polyurethane motor and trans mounts. Not only are they sweet (because your car shakes like a true muscle car), but it should stiffen everything up tight enough that nothing would rattle/hit. Take a look at this dyno video:

I think this pull I made 462/415ish:


Motor doesn't even move.

Old Geezer

iTrader: (3)

Maybe, try posting in the tune/diagnostic forum???

garygnu

whats the lsa ,was the cam advanced when degreed ?what timing chain did you use ?maybe you have carbon build up in the chamber .

4merlt1user

iTrader: (1)

I had the same issue on a fresh build with the knock sensor upgrade, didn't matter what timing I threw at it at 3200 rpm's it would pull 10-12 degrees of timing, unplugged the sensors and it still pulled timing just not as much.

Rechecked everything replaced grounds and the only thing that made it go away was to zero out the table

But that will change now that I'm going with more cubes so we shall see what happens

rcwilbur

Cam is 114 LSA and was installed straight up. I'm sure there was some carbon, but I ran sea foam through it to try and take the carbon out.

I looked the car over to see if I found the exhaust rubbing anywhere and it isn't. I looked at past logs and saw that I was pulling timing after I installed the headers, but before the heads and cam. I think the headers are somehow introducing more noise to the sensors.

I think I've solved the problem. I ended up backing timing down to where I knew it was safe (about sixteen and I could actually feel it pulling a lot of power when the knock retard kicked in). I desensitized the knock sensors until I was not getting any retard and then started bringing the timing back up.

Interestingly, on the LS6 engines GM put in higher knock levels for the sensors, so I started with those. I haven't finished yet, but this seems to be the right path and the car is starting to open up at WOT.

Thanks to everyone for their input.

rcwilbur

Thanks, I did post over there too, but must not be as much traffic, because got no response there

LS1T56FTW

iTrader: (3)

Good to know about the LS6 motors/knock sensors.

Also, the thing pulls like a freight train now doesn't it? 4000-6500 is insane now, right?