Timing in my LT1 vs LT4, why does the LT1 not like as much?
04-09-2006, 08:51 PM
#1
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Timing in my LT1 vs LT4, why does the LT1 not like as much?
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??
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??
04-09-2006, 11:10 PM
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Re: Timing in my LT1 vs LT4, why does the LT1 not like as much?
Originally Posted by MEAN LT1
What DCR are you currently running?. Also, did this just start happening?.
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.
04-11-2006, 09:45 AM
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Re: Timing in my LT1 vs LT4, why does the LT1 not like as much?
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.
04-11-2006, 03:05 PM
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Re: Timing in my LT1 vs LT4, why does the LT1 not like as much?
Originally Posted by LiENUS
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.
Probably carbon build up and less quality gas than 10 years ago probably explains why the stock timing was creating knock too.
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