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Octane Rating VS Knock

C

Cymaro

New member
Hey Guys,

I want to see a list of what octane fuel your running with your mods and how much knock you are seeing.

What are people seeing with 89, 91, 93, and 105(E85).

The reason I ask is I started out when I first got my car stock and ran premium 91 and saw around 5-6 degrees knock at some times WOT. After that I started blending in E85 to make 93 that had 10% ethanol with about 2-3 degrees knock. After a few tanks of that I have slowly worked up and my current tank is an E85 mix with premium that is 28% and 96 octane. I just did a run tonight and had zero knock. Car seems to like it and I've had no troubles so far.
Premium 91 here was $3.30/gal and me mixing to get 96 was $2.85/gal which was nice.
 


On e85 I could run 20* timing on a 3.0 pulley (full mods in my sig) with no knock. I've been on 93 for about a month now and on it I can only run a 3.25 and about 14* timing. See occasional 1-2* knock.


E85 ftw
 
It'll be tough for someone that tuned the car well to tell you how much knock based on fuel alone. Some throw more fuel at certain points to quell knock etc.
 
BillBoost37 said:
It'll be tough for someone that tuned the car well to tell you how much knock based on fuel alone. Some throw more fuel at certain points to quell knock etc.
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Exactly. With my current mods I would get 2-3 degrees at the top of second. After I tweaked JUST the PE numbers I get 0 knock anywhere, anytime.
 
chrsmi1 said:
On e85 I could run 20* timing on a 3.0 pulley (full mods in my sig) with no knock. I've been on 93 for about a month now and on it I can only run a 3.25 and about 14* timing. See occasional 1-2* knock.


E85 ftw
Click to expand...

So what is normal timing on a stock car? Also is timing just another word for ignition advance? On my aeroforce gauge it has one called ignition advance.
 


ignition timing advance has a lot of different values, the ones most worry about are when the car is in wot, and different years have different values. the 04+ timing tables are more aggressive, but on average, at wot, timing advance ranges from 14-16
 
SgtMarshal said:
ignition timing advance has a lot of different values, the ones most worry about are when the car is in wot, and different years have different values. the 04+ timing tables are more aggressive, but on average, at wot, timing advance ranges from 14-16
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Sorry I know a bit about engines but timing is one of those I know nothing about. So when chrsm1 said they could get 20* of timing is that better then the usual 14-16? Also is lower timing at WOT than the 14-16 retarding HP? One time at WOT I was showing around 9-10* timing and was still showing 0* knock. Kind of worried about my use of 28% ethanol on my stock car now haha. So what would cause that low of timing?
 
Do you happen to have DHP or HPT available to you? I have a dropbox with tons of differing tunes etc that you could peruse and get some more info from as well.
 
The ethanol isn't the problem. Your tune or lack there of is. If you're not seeing any knock you should be commanding more than 9 degrees of timing. If you're seeing less than 14-16 consistently then you're knocking or something weird is up.
 


more timing advance makes more power, but also increases the chance for kr. if you are knock free you have 2 options, smaller supercharger pulley and/or more timing advance. the idea is to get about 20* of timing advance knock free on the smallest pulley you can run. because you can run E85 you should be able to get more timing with a smaller pulley because it is more resistant to knock/detonation.
 
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