Guys,

408w, AFR heads, twin 67's

Got exhaust on the car, now I can hear everything. Whenever I'm giving it 100% throttle at 90-105 kpa, I can hear it rattle. When I first heard it, I backed timing way down, still did it. Then I noticed it running very fat, under 10.9:1. Got it to lean out, knock went away 90%. When the car was n/a it used 38° total timing, right now its less than 27-22 under full load under 105kpa. Above 100.kpa its dropped to 17*.

My friemds are telling me im not running enough timing and thats why it rattles. I am running autolite 3923's, which are one step colder than stock, just running 6 psi. Engine is 9:1.

Here is a pic of a plug, looks like its running really fat still.
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Ok, after doing a bit of research I found out that high load low rpm , detonation is somewhat normal and turbo cars. Any truth?

 

Not true. Who told you that?

 

Yes, boosted or not, lugging will cause detonation.

 

Thing is, I wouldn't consider 2,000 rpm lugging. But it does go into positive atmosphere, and I have to brake to get it to happen.

Is there a way to make this better?

 

What determines where it's lugging or not is the cam and DCR. With any kind of aftermarket performance cam, WOT at 2K could be right on the verge of lugging. How fresh is the fuel? And is it a decent octane?

 

We only have 91, filled up last week. It gets better when it is not as rich.

I Did put a smaller Cam in this year.

 

Take some fuel out and add some timing, and I bet it goes away!

 

When the car was na and using 38* timing, what was the cr and how much bigger was the cam?

 

Fuel does zero to control detonation. The tune has too much timing in the area where it is detonating.

 

I took it down to 10 °and we still got ping. I added about 5° to the original tune and knock went away.

Until that is, I drove it on a hot day. Once everything heat soaked, it came back. MAT correction was making it run just stupid fat. 13.0 at cruising and pegging the meter at wot.

So this weekend I'm building some heat shields, relocating the IAT from the lower intake to the charge piping, and switching to e85.

 

Also, try setting the timing to a fixed angle and free-revving it with a timing light on the motor. Make sure the timing isn't doing anything wonky at high RPM.

 

I definitely will Matt.

 

Dont ignore what it wants. To me it is apparent it is too rich by the fact that as you take fuel away it gets better. And the plug looks like hell. Its over fueled at cruise too.
However, if you where running real low timing it will cause the plug to look rich. Start with fresh plugs. Give it what it wants.

11.5 afr on pump gas is a good safe place to start. Not fat ,not lean. 6psi isnt much boost at all but its hard to know that kind of timing it will like in the end.
Use the plug as your guide and the wb as a reference.