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E85 knocking with stock headers/cats

Oxford_5oh

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So ppl refer to E85 as knock proof or the holy grail but when the shop I used tuned my car after a paxton kit install the car was knocking at 20-22 degrees on E85 which kinda threw me off.
They said the stock headers/cats caused back pressure in the cylinders and is to blame, anyone have thoughts to support that claim and the need for long tubes and ditch the cats or should I be looking at something else for the cause?
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Jay-rod427

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21 degrees or so is about all you can typically get out of boosted coyote E85, so they're trying to push to hard and getting knock. This is why Coyote specific tuners are so good at what they do.
 
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Oxford_5oh

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Sorry I should of specified it was remote tuned by Lund at the shop, both sides saw about 2 degrees pulled and the final tune was20 degrees with the car being able to go up to 22 if the knock sensors are happy.
Just wanted the community's opinion on stock headers/cats being the bottle neck and if dropping the money for long tubes and dealing with a louder catless car was worth it.
 

Jay-rod427

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Sorry I should of specified it was remote tuned by Lund at the shop, both sides saw about 2 degrees pulled and the final tune was20 degrees with the car being able to go up to 22 if the knock sensors are happy.
Just wanted the community's opinion on stock headers/cats being the bottle neck and if dropping the money for long tubes and dealing with a louder catless car was worth it.
I can get 21-22 degrees at 15 lbs with mak cat deletes, never ran it boosted with the cats in. Catless has gains on it's own. And yes gets way louder on an already opened up system. LOL
 

Burkey

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It’s hard to say for sure without knowing a lot more about the setup and the tune.
Lund are right in what they’re saying (as usual).
How much boost are you seeing with the combo?
 

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MyLilPony

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I would say there is probably something there on stock headers/cats causing and issue. I sit at 22° and have seen higher with Lund when we were pushing it. I have catless headers, being you have the same type of blower, same tuner, I am assuming Fore fuel system and you tested your e85 before hand, your exhaust is causing an issue. I hope you tested your E at least to ensure that wasn’t an issue.
 
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Oxford_5oh

Oxford_5oh

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This was from the dyno pulls finish line (beefcakes neighbor) made on the local E85 they run in their cars and said its a tested source.
Car was seeing just under 12 lbs of boost but I haven't been able to run the car hard since I brought it home due to the clutch slipping at WOT above 6k rpm so a RST is sitting in the garage waiting install date.
 

Kona 18

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20* of spark is good for a car with stock headers and cats, you can't expect to push it as hard as you could a cat-less set up, Set the tune for 19* and let knock sensors add from there.
 
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Oxford_5oh

Oxford_5oh

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Thanks for the responses guys I trust lund and their tunes just wanted the community's comparisons on how their boosted setups respond to E85 timing.
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