I've been getting alot of knock/spark retard in my LT1 lately, thought it may be false, but it turned out to be real. I ended up removing about 6-8 degrees of timing in the 4000-5000 rpm range and 90-100 KPA from what the stock tables had to get all of the knock out.

I'm wondering why my tuned LT4 with larger cam can tolerate 8-10 degrees more timing than my stock LT1 at the same rpm/KPA without knock when the LT4 has a higher compression ratio???
The LT1 has about 90k miles on it, maybe some carbon buildup...maybe because the LT4 is in my heavy truck so the motor has more of a load on it at those rpms...maybe the overlap of the intake/exhaust valve timing in the LT4??

 

What DCR are you currently running?. Also, did this just start happening?.

 

It's all completely stock original. Had the car 8 years, when I transplanted the LT4 into the truck I got DM scan sw, so I hooked it up to the TA, and was seeing some knock, 2-3 degrees..I alter the timing table and fixed it, this was about 3 years ago..never had a reason to scan it again until recently at the track with it for the first time and it was getting 8-9 degrees just at 4-4.5k rpms again, not even on the shift but in 3rd gear (its an A4).

I'm about to do a head/cam swap, but wanted to get a good clean base line with no knock first. I filled the tank with 104 unleaded to determine the knock was real, it went away with the 104. Also tried a LT4 KM that didn't seem to matter either.

Now in the main spark table, most all cells in the area mentioned (4-5k rpms/90-100KPA)are set to 30-31.5 degrees.

 

any ideas??

 

the LT4 has a bigger cam with more overlap and less DCR. Thats why on average you're gonna have less knock on the LT4. Then theres probably some carbon buildup in your LT1. I'd use some form of carbon removal to get rid of it.

 

ah, thanks, been educating myslef on DCR. Usually everyone only speaks in terms of static compression...since the LT4 has a higher SCR than the LT1 I couldn't figure this out....now I understand DCR...that explains it cause the cam does have alot more overlap... thanks

Probably carbon build up and less quality gas than 10 years ago probably explains why the stock timing was creating knock too.

 

Also the quench on the LT4 is more optimized.