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dyno'd my car yesterday

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knuts

Probationary Member
13
0
Aug 15, 2002
Bismarck_ND
ok well I put a big16g ported, unclipped. 660cc injectors, 2.5 dp, 3"exhaust, ported 2g manifold, ported 02 housing, 255 fuel pump, etc.

Well he got 268.8 .. a/f 12.0 across the board, 92 octane, im running stock side mount IC.. about 5 minutes later the last pull was 261 with a/f 11.9..... my intercooler was pretty toasty...temp in shop about 65 i spose... now im assuming that it was at 12psi because he never touched the mbc under the hood when he got out and thats where its at so...

I have a question about my knock sums... on my way home i hammer it and the pocket logger reads like 30 plus knock......with the a/f ratio like that across the board why would my knock be so damn high? it was cold outside and i was driving like 60 through freezing rain and the IC was COLD...

Im thinking next mod will be an indy race core..

what do u think of the numbers? is there more to be had out of a little big 16g?

Thanks guys, this is my first dyno experience and im still a newbie OMG
 
I was in the same exact situation.

Here's the problem: You are running lean. If he tuned it to 12.0:1 at the dyno session, you can bet that your logger is putting out O2s that are indicative of a lean condition. I bet they aren't .92-.94 in range.

Solution: tune the car with the datalogger at night. You will match the ratio but be too rich in the hot weather.

After I took out my car last night, I was still knocking and had to add even more fuel to bring the knock down.

In theory, once you get rid of the knock, your car will be putting out more HP on the street than at that dyno.

-M
 
Why on earth did he tune the thing to 12.0:1 A/F on pump gas???? Thats insane imo, your just asking for trouble. Luckily you were not running alot of boost. I've always heard that 1g's O2's will have a lower O2 voltage than .92-.94 for ideal a/f. I've learned that O2's are worthless personally.
 
Originally posted by Violater101
Why on earth did he tune the thing to 12.0:1 A/F on pump gas???? Thats insane imo, your just asking for trouble. Luckily you were not running alot of boost. I've always heard that 1g's O2's will have a lower O2 voltage than .92-.94 for ideal a/f. I've learned that O2's are worthless personally.

Yea, that was a little dumb.

My suggestion would be to enrichen the fuel till you eliminate knock at the rpm that is knocking. Look at the O2 readings when the knock is gone to see how much you enrichened the fuel. My fuel trims are as follows:

Hi-118%
Mid-103%
Low-118%

Very rich to get rid of knock..

-M
 
aren't ft's over 100% indicative that the ecu is having to add fuel??? you still need to add more.
 
Originally posted by nine5raptor
aren't ft's over 100% indicative that the ecu is having to add fuel??? you still need to add more.

yes, fuel trims mean the ECU is adding fuel. But that's correct if you are using a SAFC to richen up the fuel.

-M
 
fuel trims are based on 02 input.

if you add fuel with and afc/afc/maft, your fuel trims will drop due to the change in a/f mix.
 
Originally posted by nine5raptor
fuel trims are based on 02 input.

if you add fuel with and afc/afc/maft, your fuel trims will drop due to the change in a/f mix.

Or rise. Enrichening will raise the fuel trims and leaning will lower the fuel trims.

-M
 
hmmm, i must've been thinking the 1gs acted like the 2gs (still learning about your guys' car, im solely a 2g guy).

say my fuel trim is 17%, I ADD 20% fuel to get the ft to ~ -3%-0% since positive ft's mean the ecu is adding fuel to get things back in line. if they are neg, the ecu is taking away fuel.
 
Originally posted by nine5raptor
hmmm, i must've been thinking the 1gs acted like the 2gs (still learning about your guys' car, im solely a 2g guy).

say my fuel trim is 17%, I ADD 20% fuel to get the ft to ~ -3%-0% since positive ft's mean the ecu is adding fuel to get things back in line. if they are neg, the ecu is taking away fuel.

Hmm.. I'm not sure what you are saying.. A fuel trim reading of 100% means that the ECU doesn't have to adjust for any fuel increase or decrease and you have a fairly good mixture. If you are below 100%, the ECU has had to lean out the mixture to keep things in line. If you are above 100%, the ECU has had to add fuel to keep things in line.

Taking up your fuel with the SAFC will do this. If you have bigger injectors, then leaning out the SAFC will cause a lower than 100% reading.

This is the way I understand it. I can't say for a 2G.

-M
 
If your fuel trim is at 118% then you are lean.
 
Originally posted by Phoenyx

If you are above 100%, the ECU has had to add fuel to keep things in line.
-M

ok, for mine: 0% is a perfect ft., if it says 17%, then the ecu is adding 17% more fuel than it's base, so I add 20% with the maft and the fuel trim goes to -3% as I have added more than enough fuel to get the ft centered on 0% and the ecu needs to take some away.

based on what you said, if your fuel trim is 118%, then you are above 100% and the ecu is needing to add fuel. therefore if you add fuel yourself (by lowering the air reading via afc) then your fuel trims will LOWER.

so you need to add more fuel, you are lean (you need to lower the amount of air the ecu sees).
 
Originally posted by nine5raptor


ok, for mine: 0% is a perfect ft., if it says 17%, then the ecu is adding 17% more fuel than it's base, so I add 20% with the maft and the fuel trim goes to -3% as I have added more than enough fuel to get the ft centered on 0% and the ecu needs to take some away.

based on what you said, if your fuel trim is 118%, then you are above 100% and the ecu is needing to add fuel. therefore if you add fuel yourself (by lowering the air reading via afc) then your fuel trims will LOWER.

so you need to add more fuel, you are lean (you need to lower the amount of air the ecu sees).

This is not the way I understand it nor is it in practice.

My fuel trims were:

Hi - 110%
Mid - 100%
Low - 110%

My SAFC-II settings were:

2000: 0%
3000: -6%
4000: -8%
5000: -18%
6000: -8%
7000: 0%

This caused my car to knock like hell and my EGTs would peg at 1650F in 4th gear.

According to you, I'm not running lean but at about the right ballpark (100%-110% is a good range according to what I've read).

So, from that you can see that the SAFC was lowered (meaning the amount of air coming in that the ECU sees is less than what's actually there). But guess what? When the ECU sees lower air, it also injects less fuel, so the fuel trims would indicate this. However in practice, although the fuel trims were in a good range, I get knock due to my actual O2 being lean.

Now after I turned up the SAFC-II settings to this:

1000: 0%
2000: +3%
3000: +8%
4000: +9%
5000: +10%
6000: +11%
7000: +12%

I'm getting this for fuel trim:

Hi: 118%
Mid: 108%
Low: 118%

And guess what? Hardly any knock at all! And EGTs in top of 4th =>1450

The SAFC in the plus range means that it is adding more air into the system, but the ECU will then add more fuel! Which is what I want! So yea, the ECU "thinks" I'm running lean and so it adds more fuel to compensate for that.. althought I'm not really lean because of my O2 readings and knock being non-existant.


To clarify that I know what I'm talking about, read this FAQ (under Airflow and Fuel Trim):

http://www.vfaq.com/TMO/Tuning-Tips.htm

Under normal circumstances (without a SAFC to trick the computer), you would be 100% correct that I would be running lean naturally. But this isn't the case..

-M
 
For God's sake, will you PLEASE do some research on how a DSM ECU works before you go arguing with people? You're wrong AGAIN.

If your fuel trims are 118%, then you are running lean. Actually, you are running about perfect, because that is the point of the fuel trims.

If you enrich the SAFC (add fuel) then the fuel trim numbers will go down.

Let's say the ECU sees 30 counts of air. It looks into the tables, and they tell it to inject 2 counts of fuel. It does this, and then looks at the O2 sensor. Now, let's say that the O2 sensr tells the ECU that it is still too lean. The ECU will eventually get to where it has to add, say 2.2 counts of fuel to be right at stoich, according to the O2 sensor. The fuel trim would be at 110%, because 2.2 is (1.1*2).

Now, say you bump the SAFC up to +10% in that rpm range. Now, the ECU will "see" 33 counts of air, although the motor is still only getting 30. The ECU willl look to it's tables, and it will see that 33 counts of air requires 2.2 counts of fuel. When it injects this 2.2 counts of fuel into the actual 30 counts of air, then the O2 sensor will read to the ECU that the mixture is perfect. It doesn't have to add extra fuel, or subtract fuel, from the values defined in the stock maps. This is a 100% fuel trim.

Thus, by increasing the correction on the SAFC (enriching the mixture, adding fuel) we bring the fuel trim from 110% to 100%. SAFC goes up, fuel trim goes down.

Now, you say that you increased the corrections on the SAFC, and your fuel trims went up? Well, the corrections you are changing are on the HI THROTTLE map. You use the hi throttle map to tune for WOT performance (by knock). You use the LO THROTTLE map to tune for idle and cruise, and these settings are determined by the fuel trims. You need to increase your lo throttle corrections a little bit, to make the fuel trims come down.
 
what he said.

actually thanks for jumping in kyle. you are a 1g and afc guy, i am a 2g and maft guy, so not quite the same, although fuel trims are fuel trims.
 
lower the number on a 1g, like 86, you're running rich
a higher number say 118, you're running lean.

every car is different....
 
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