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Z06 Master
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I took my Z to a dyno on Saturday to see what kind of power the stroker is making after 4K miles and this is what we found...





Great power, but look at the AFR. The original 21MC tune had the AFR @ 12.8.
The car doesn't throw codes. The only code I've seen is P1415 which has something to do with the A.I.R system. It seems like if it was an intake or exhaust leak, the AFR would be consistent. Not have a spike like that. Has anyone seen a problem like this before?
 

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The spike is a tuning issue and can be resolved with LS1 edit (and maybe HP Tuner).
I have had dynos with spikes on several occassions. Sometimes it was just wheelspin on the dyno and other times it was just additional tuning needed.
Also, as is obvious, your AFR is very lean almost all the way across the board.

Mike

(edited....I said rich instead of lean :blush: . Must start paying attention :crazy: )
 

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Ahhh...don't you guys mean pig lean? :lol:

Probably just a tuning issue Dan but I can't say for sure. Hell, I'm still trying to figure out how to get mine to idle! :lol:

Tom to the rescue!
 

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jub jub said:
Ahhh...don't you guys mean pig lean? :lol:

Probably just a tuning issue Dan but I can't say for sure. Hell, I'm still trying to figure out how to get mine to idle! :lol:

Tom to the rescue!

Yeah...that's VERY lean. I have no idea Dan...
 

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Jub, Your right on.. Pig Lean.. Get a good tuner to fix it up.. then you will see a jump in HP..

I wouldn't want to run the car the way it is now.. Way too lean for these temps..

Ernie
 

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Rich?

Jeez, that A/F wont let the car last the weekend. You need more fuel, asap.
 

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Was there any knock? Should have sounded like a snare drum.
My biggest concern is the spike at 3800 rpms on all 3 pulls.
If no knock then I would question the wideband. Greg's wideband as of late is reading much leaner than the onboard widebands of a couple of cars I have done recently that have them installed on their cars.
The car needs to be scanned while on the dyno, I do this with all cars, every pull.
What size injectors do you have? Have they been scaled back to take care of LTFTs and then run out of fuel prematurely?

I would think that if it was a lean condition caused by an air leak after the MAF that you would get codes while in closed loop.
 

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One more thing. You have seen my post about LTFTs.
Positive LTFTs will add fuel at WOT.
Lets say the LTFTs were adding fuel before the initial tune.
The VCM was then scaled to acheive the AFR of 12.8 without clearing the LTFTs, could explain that spike. Now you have been driving your car and the LTFTs are averaging near zero.
You now go into open loop and the LTFTs are not adding any fuel as it was during the tune. LEAN!!!!!!!!!!!!!!!!!!!

I always clear the LTFTs when scaling the PE table on the dyno just for that reason.
 

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22655TD said:
Yes the AFR is pig rich from 36 to 43. BADLY

I know you know better. :lol: Typo?
 

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Z06 Master
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Discussion Starter #12
FRC Tom said:
Was there any knock? Should have sounded like a snare drum.
My biggest concern is the spike at 3800 rpms on all 3 pulls.
If no knock then I would question the wideband. Greg's wideband as of late is reading much leaner than the onboard widebands of a couple of cars I have done recently that have them installed on their cars.
The car needs to be scanned while on the dyno, I do this with all cars, every pull.
What size injectors do you have? Have they been scaled back to take care of LTFTs and then run out of fuel prematurely?

I would think that if it was a lean condition caused by an air leak after the MAF that you would get codes while in closed loop.
Tom, I've never had any knock. The car runs great especially at WOT! The only problem I have is on warm restart. The idle hunts around a bit and then settles. It'll rev between 900 and 1800. I'm not sure what injectors are in there, but I know they're what 21MC deemed necessary for this motor.
It looks like I'll have to get it scanned and take it from there.

Thanks,
Dan
 

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Z06 Master
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Discussion Starter #13
Thanks for the input, guys :cheers:
 

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Z06phile said:
Tom, I've never had any knock. The car runs great especially at WOT! The only problem I have is on warm restart. The idle hunts around a bit and then settles. It'll rev between 900 and 1800. I'm not sure what injectors are in there, but I know they're what 21MC deemed necessary for this motor.
It looks like I'll have to get it scanned and take it from there.

Thanks,
Dan
Most cases a bit of scaling of the VE table between 1200 and 400 rpms takes care of that hunting idle. Scaling depends on size of cam.
 

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I wouldn't get too excited about that dyno sheet. I just don't see in reality the a/f going off the map lean (like that graph indicates) and not see some hicups in the power and tq curves. They look relatively smooth to me.

time for a bung and real a/f reader if you're losing sleep over this. Those tail pipe sniffers can act up.
 

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Z06 Master
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BLU-BY-U said:
time for a bung and real a/f reader if you're losing sleep over this. Those tail pipe sniffers can act up.
What a/f reader do you recommend? Do you put the bung in the header right before the cats? Which side or does it matter?
 

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Z06phile said:
What a/f reader do you recommend? Do you put the bung in the header right before the cats? Which side or does it matter?
Innovate makes a great AFR meter w/WB (LC-1). I have one here.

It's best to weld the bung before the cats, either side doesn't matter. There is also a way to use the wideband in place of the narrow band so you don't have to weld in a second bung.

http://www.efilive.com/forum/viewtopic.php?t=1736
 

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I like 12.8 at the rear pipe outlet
If you use bungs on the headers, 12.8 at the outlet would read 13.4 at the bungs. Usualy a .5 diffeance.
BUT.
On your graph (if it is correct) you need to adjust that hump.
 

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Call Andy at 21st and send him a copy of the dyno see what he says. Sounds like something is wrong with the dyno maybe.


Chris
 
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