mods- 35r, streetport, 1300cc sec, 255fp. 12psi pfc

As the weather has turned cold I have been out checking my a/f and knock readings. I cant seem to get my knock readings down as low as they have been in hotter more humid days. As I accelerate through 5000 to 6000 rpm in 3rd I am gettin 2 to 3 knock spikes in the 50 to 80 range. Above and below that rpm there is little to no knock but through my torque/hp cross I am getting sum ping. My a/f are in the 11 to 11.3 range and my trailing timing is set at n13-3 n14-4 n15-4 (5200,5600, 6200@12psi)with a 10deg split. I had been driving the car like this with out any issues for a few months

I tried pulling 3 degrees timing from n13 to n20 across p15 to p 20 to try to get the knock readings down but didn't seem to help. also played with a/f ranges from 10.5 to 12 to c what happens( like to keep it at 11.3 ish) but still ping ping.

Any Ideas on what could be causing my problem?? I am leaning towards cold dry air or maybe sum crappy 93pump gas. Wish I had AI going on, one day...

 

I do not understand what your timing is in the affected area.
3-4 degress IGL with 10 split????????

 

no. thats what the trailing timming is

 

So IGL is 13-14 deg.
IGT is 3-4 deg.

I ran the car like this with very little knock until it got colder. I would c sum knock but it stayed in the 20's.

btw. its a timing map i got from a real cool guy in slidell,La

 

Certainly sounds like a safe map. Timing isn't aggressive, AFR's are fine. Try going from 10* to 12* split. What heat range plugs are you running?

Peak torque (pressure) is in those rpm areas so it's expected that the knock would be there, but hard to say whats causing it. I guess whenever your tank is about half full try topping off with more premium. Or if you have access to a couple gallons of race fuel you could try putting that in to see if it helps.

 

I was thinking it was on the safe side as well. I opened the split to 14, seems to be about the same knock wise.

I have 9's all around.

When the tank gets empty I am going to fill up on sum non ethanol fuel. I wonder if that 10% is getting the best of me....

 

What octane is the ethanol fuel?? Ethanol fuel would make it run a little leaner but it doesn't sound like it's running lean. Maybe it's just poor quality fuel.

 

I have been using 93 with up to 10% ethanol.

Found a filling station that has non ethanol fuel. When the roads dry up I am going to use whats left, then fill up there and add sum 112octane. let ya know if the ping goes away

I am betting/hoping on crappy fuel. In the last few months I have seen many gas stations in my area pulling their tanks.

A friend of mine got a tank of water(paid for gas) the other day. Couldn't even leave the station cause his car wouldn't run. I don't like hearing things like this....his v8 and 150shot wouldn't have liked the extra H2O either.

 

The norm is to list IGL with split, not IGT with split!
Your listed 12psi timing is about what I run at 10psi boost with a GT35R T3 1.06 with mild porting. And it was also used on a GT35R T4 1.06 with PineApple medium ports.

I say you are 2 degrees too hot for colder weather. Maximum winter timing is less than maximum summer timing.

 

Changed the gas and no different. 93 oct non 10%ethanol

Pulled 1 to 2 degrees off the leading map in the 4800 to 5600 rpm. Kept the trailing as is and the knocking went away. The highest recorded knock was 22 after 10 or so 3rd @ 4th gear runs

It seems as i raised the split by lowering the trailing timing the knock got worse. With a 12 to 13 degree split the knock nubers hit over 100 (ouch) through 5000 to 6000 rpm. btw this is at 12psi of manifold pressure.

With an 8 to 9 degree split through peak compression pressure no high knock numbers. So I conclude less split at PCP=smother combustion burn smoother. btw this is at 12psi of manifold pressure.

2 degrees was bout right. good call.


Does this have some thing to do with flame propagation across the rotor face?? like pages 44 and 45 of Kenrichi Yamamota book.

 

Thanks for posting your experience. Would you mind sharing some of your datalogs? I would like to check them out. I'm having some strange knocking as well. Thanks.