Afr and knock are they related?

[selmerguy]

I have been messing around with my 1g latley and am tring to max out the fuel system as well as the tiny 14b. I installed a 3 inch o2 back exhaust and a hard uicp as well as a gm maft setup. I have a pocket logger and a wideband to monitor with and I have come to some intresting results.(at least to me) First at 18 psi my afr is perfect 11.6:1. I have the translator turned 2 clicks lean at wot. My idc is about 86%. The knock on the logger is not steady or predictable but the car seems to run fine. I have seen 36 a few times but the afr is good. I have never tuned a car with a knock sensor and I see alot of posts on hear where people actually use knock to tune. This makes no sense to me. So can you have a good afr and knock bad enough to hurt something? If so how and why?

 

[donmagicjuan]

I have been messing around with my 1g latley and am tring to max out the fuel system as well as the tiny 14b. I installed a 3 inch o2 back exhaust and a hard uicp as well as a gm maft setup. I have a pocket logger and a wideband to monitor with and I have come to some intresting results.(at least to me) First at 18 psi my afr is perfect 11.6:1. I have the translator turned 2 clicks lean at wot. My idc is about 86%. The knock on the logger is not steady or predictable but the car seems to run fine. I have seen 36 a few times but the afr is good. I have never tuned a car with a knock sensor and I see alot of posts on hear where people actually use knock to tune. This makes no sense to me. So can you have a good afr and knock bad enough to hurt something? If so how and why?

Assuming you're using pump gas, it's possible that you're actually a little lean for that boost level on a 14B. You might try richening things up a little bit to see if you can get rid of the knock. Forgive me if my 2G to 1G secret decoder ring isn't working properly, but I believe 36 counts of knock is quite an assload. Can you post a log with timing and AFRs from your runs? Remember, the goal of tuning your engine is to maximize the power extracted while minimizing knock. Taking the necessary steps to get rid of the knock is more important than dialing in what you believe will be the optimum AFR.

 

[GVR4592]

11.6 is too lean for what you're trying to do. You should richen it up until the knock goes away, you'll probably end up around 10.8-11.2:1.

 

[selmerguy]

I just did a pull in 2nd gear. I cant post my afr's with the timing cause all my wideband does is give afr right now. I cant make it work with my current logger. But durring this pull the afr from 4000 on was around 11.5 and never above 12.

rpm tima 02-r knock
2843 26 .76 0
3216 24 .68 4
3968 10 .78 15
4468 11 .74 14
5218 13 .76 13
6062 16 .80 19
6781 9 .78 24
7281 6 .85 36

 

[donmagicjuan]

I just did a pull in 2nd gear. I cant post my afr's with the timing cause all my wideband does is give afr right now. I cant make it work with my current logger. But durring this pull the afr from 4000 on was around 11.5 and never above 12.

rpm tima 02-r knock
2843 26 .76 0
3216 24 .68 4
3968 10 .78 15
4468 11 .74 14
5218 13 .76 13
6062 16 .80 19
6781 9 .78 24
7281 6 .85 36

Good grief, that is a lot of knock! Your timing curve should be a positive trend from the point of full boost to redline. By the top you should be seeing high teens to low twenties. Your ECU is pulling a LOT of timing above 6000. Until you richen things up, you're running a serious risk of damaging your engine.

 

[tstkl]

I think the main reason why people don't understand this stuff/how its all related is because they don't understand what is going on in the engine. The turbocharger creates more heat with higher boost (sometimes not too much more heat, sometimes a LOT more heat, this is why people say, "the efficentcy range of x turbo is y-z" because above z, the turbo is flowing a lot of extremely hot air that will cause more knock and do more damage than good. below y you just aren't flowing much air for it to be practical for you to be using that turbocharger. A smaller turbo with faster spool would suit you better) Higher intake air temperatures at the throttle body (the temperature outside effects this somewhat, but the biggest factor is the heat generated by the turbocharger, and disipated by the intercooler) will cause more knock. Leaner combustions will burn hotter, causing more knock. Super advanced timing will cause more knock as well. The three factors need to be taken into account when tuning an engine. With our cars, the largest benifits are seen from increasing boost and advancing timing, but again, every car is different, and running super rich with a lot of timing advance won't do you much good.

A good balance of the three normally comes from the following steps (obviously there are many, MANY different ways to tune, but this is my personal favorite.)

pick a boost within your turbocharger/intercooler's efficentcy range. For me that was 21 psi. (don't ask)

pick an afr that is somewhat conservative for your set up (pump go with 10.5-11.2, race go with high 11's, low 12's, again, this is all up to you, so don't get mad at me if your tune isn't producing the maximum power your setup is capable of) (for me thats 10.5-10.8 on pump)

increase timing throughout the rpm range until you see a tad bit of knock, then retard timing by 2-3 degrees to stay on the safe side.

if you can't tune your timing maps, obviously you must use the other two factors to control your timing, since your ecu uses the knock sensor to decrease timing, (and knock kill's engines) you want 0 knock at any given time in a pull.

remember kids, KNOCK IS BAD...

 

[Malero5]

I see 0-2 counts of knock on my setup. I have a really nice FMIC, fuel mods, dsm link, 93 octane, and my un ported 14b set at 18 psi. This is in 108 degree weather with my car's coolant at 205 degrees or so. my A/F ratio is 10.5. This is about the effeciency range of the 14b before you see knock due to high heat comming from the small turbo.

 

[Malero5]

oh one more thing...... I ran the 14b for a long time on the stock fuel system and I would not reccommend more then 16lbs of boost on that. 86 percent on IDC is going to screw you over. Not only will it destroy your injectors but it will not be enough fuel to keep down the knock. Although I am a bit paranoid so you might be able to get away with this setup at 17 lbs of boost with a lower A/F ratio. I always like to be below 85 IDC.

 

[selmerguy]

Yeah a did another log today after a bit of riching up the wot on my maft. Here is my log and I messed up when I told you guys that my idc was 86% I was looking at tps. My stuff is all messed up. My afr is good but my injectors are screaming more then my 14b here is the log knock is much better.

rpm knock o2 idc tim
3062 0 .17 3.9 39
3437 0 .09 16.4 31
4375 0 .17 45.3 30
4875 0 .21 70.3 27
5531 0 .25 90.6 19
6687 11 .27 139.8 21
7156 10 .27 121 14


I am going to turn down the boost and try to keep it at about 16 psi. My mbc is very touchy so this will be a challenge. The funny thing is that my afrs in this pull were richer at about 10.5 at wot and my stock o2 says lean. Oh well.

 

[Malero5]

yeah problem solved... look at your knock and your IDC. You need to turn down the boost to 16lbs untill you do some fuel mods.

 

[selmerguy]

yeah problem solved... look at your knock and your IDC. You need to turn down the boost to 16lbs untill you do some fuel mods.

But the boost feels so good!!!! I did a 16 psi pull today and the IDC was still stupid high. Do you think the maft can mess up the IDC numbers?

 

[slipstream808]

No, not directly, but the MAFT will mess with things because it does not give true airflow readings sometiems. BUT if you are doing good with your O2 readings, then you shouldn't have a problem really. But then again if the MAFT is reading too low taking you off of the top timing curve, then the ECU might be giving you too much timing, and that could cause the detonation.

 

[daren_p]

Wjats with your logs, are you just not posting all the info? Its hard to tell exactly whats going on since there are huge gaps between the points listed. Don's right in that first log you were seeing a tonn of knock. It looks like your probably still knocking in the second log as timing looks like its being pulled in the upper rpms. Can you post a log with alot more smaples?

 

[dnhieu]

Looks like a slight case of phantom knock. wouldnt he have kissed his motor goodbye with 36 counts of real knock?

 

[donmagicjuan]

Looks like a slight case of phantom knock. wouldnt he have kissed his motor goodbye with 36 counts of real knock?

If it were phantom knock, it would still be present after he changed his AFR and lowered the boost. If you are ever able to get rid of knock by using higher octane fuel or by richening the AFR, it is most likely the real deal.

 

[tstkl]

Although I am a bit paranoid so you might be able to get away with this setup at 17 lbs of boost with a lower A/F ratio. I always like to be below 85 IDC.

you mean a higher a/f ratio. remember, a/f ratio means, air/fuel, so if you don't have enough fuel, and you add more air, your a/f goes up...

if your seeing a value of more than 100% idc from the ecu, that means the ecu is ASKING FOR MORE THAN 100% OF WHAT THE INJECTORS ARE CAPABLE OF. Having a maft will effect that in no way. You can lean the car out and your ecu will ask for less fuel, because it thinks there is less air, then your idc's will be lower, but thats because you will be injecting less fuel. Your idc is a direct reflection of how much fuel your injecting.

If your still on the stock fuel system and you just HAVE to have more boost, you can do the following. I don't think you should, but I'll put it out there just so you can do it, at your own risk... and maybe it will work for you without any problems.

The stock fpr is a spring type fpr, so it can be crushed, just like the stock 1g bov. Get a fuel pressure gauge and crush it slowly until you get the base fuel pressure you want. (this means taking the fpr off and putting it on a bunch of times, although Im sure you could find some way to rig it up to an air compressor, as psi is psi no matter what is applying the pressure.) I personally went from stock (37 psi) to 46 psi. With the maft, I set the injector size to 520, but you would have to calculate it for whatever psi you ran at. And its not a liniar scale, so don't do it like 37/450=new pressure/new injector size. That DOES NOT WORK. I forgot the exact formual, but it can be found by searching around. A higher base pressure is less stable, so don't just slam your fpr as much as possible in hopes to get the most fuel out of your system. I wouldn't go above 46 psi.. but thats just me

 

[tstkl]

Looks like a slight case of phantom knock. wouldnt he have kissed his motor goodbye with 36 counts of real knock?

o no.......... you can go MUCH higher than 36 and not blow your engine......... and yes I have done a compression test recently...

 

[GVR4592]

The stock knock detection system on a 1g is crap, 5 counts could be a washer rattling somewhere on the engine, or a severe piston breaking detonation. That's why I have always tuned for 0 knock on 1g's.

But the boost feels so good!!!! I did a 16 psi pull today and the IDC was still stupid high. Do you think the maft can mess up the IDC numbers?
Today 12:51 AM

I guess we'll be seeing you in the Cylinder Head and Short Block forum soon....

 

[selmerguy]

The stock knock detection system on a 1g is crap, 5 counts could be a washer rattling somewhere on the engine, or a severe piston breaking detonation. That's why I have always tuned for 0 knock on 1g's.



I guess we'll be seeing you in the Cylinder Head and Short Block forum soon....

Only to ask what other people are running for internals. I know how to rebuild a motor. With that aside I did a long log today and made a intresting discovery. A few times in the log while just driving down the road the knock spiked to like 30. Once I was coasting at like 3700 rpm in third and the knock spiked. A buddie told me I should replace my knock sensor. He said it is a pita but I might try it. The IDC thing is funny too. I was told that the stock injectors were good to 16 psi. Why would my IDC be at 136% at 16 psi. The afr seems to be right on but the IDC is crazy high. I feel like when I step on it my injectors are screaming and giving me the finger. I plan to go bigger but I want to max out what I go right now.(Famous last words )

 

[GVR4592]

You're already maxing out what you have. IDC is 136........ is that registering?

 

[selmerguy]

You're already maxing out what you have. IDC is 136........ is that registering?

It regesters just fine..... I just dont understand that everything I have read and been told is that 16.5 psi is all you can run SAFLEY on a stock fuel system.. 136 IDC is not safley.

 

[GVR4592]

Did you hear that in the newbie forum? Because that's bs, every car is different. Some won't make it to 13 psi before they reach the limit of the fuel system. There are way too many variable to even guess where the stock fuel system stops doing it's job. That's where the datalogger comes in, your is telling you that you are maxing out your injectors. So turn down the boost, or upgrade.

 

[kraka]

Just wanna add, Im running a similar setup...

Im running my 14b at 17-18psi w/ fmic, 560's, safc +++

When I tune for 18psi, and I lean it out so my wideband reads in the low 11's at WOT, I get 10+ counts of knock...

Right now, I realize my safe zone is about 10.9 at WOT...I rarely get knock, maybe 1-5 counts at most, so my timing isnt being pulled but Im still not hella rich or hella lean...

11.8 is definitely too lean for pump gas...

I'll be running 100 octane pretty soon, so I might be now tuning for 11.0-11.3, I still wont go much higher than that.....The 14b really isnt effecient past 18psi anyway

 

[selmerguy]

Hey guys I am back after doing alittle more searching. I have another question but I didnt want to open a new thread. I am about to piece togeather my fuel setup and am looking at injectors. I have a 13109 afpr and a 255 walbro. My overall goal is to be at 350 hp or alittle more. I do plan on going dsmlink and my ecu starts with an E so I assume that means it is an eprom. But i have messed with a safc before on my 2g and it appears to do the same thing as the maft. The safc has 7 rpm points and the maft has idle, mid and wot dials. I cant see how using them togeather will do any good. Has anybody upgraded thier injectors and just used the maft to tune? How big can you go? Someone told me 650's but I read on here 550's.

 

[donmagicjuan]

When tuning with an AFC or MAFT, you start to run into problems with injectors larger than ~660cc. The reason, as you may know, is because these tuning devices do not provide the ability to compensate for the increased timing the engine will try to run with the perceived lighter load associated with drastically altering the MAS signal. Above this threshold, the timing can become advanced enough to cause knock at otherwise safe AFRs. If you're looking to make 350awhp, you will likely be close to maxing out a set of 660s, but it's probably still possible.