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Part throttle knock- tuning help

AWDPower

Well-known member
Joined
Feb 28, 2011
Messages
107
Location
Vacaville, CA
I'm having a hell of a time getting my GVR4 dialed in. I've been having an issure with part throttle knock. As soon as I build any boost at part throttle, the knock counts jump up. I can peg the knock counts at 43 with 2psi on the gauge, and about 30% throttle. I don't think it's phantom knock, because I can repeat it at will. With heavier throttle, I usually get minimal knock. I'm running a 20G at 20psi with 750's a 3G (#482) MAS, and a SAFC on 91 octane. I know that the set up will not be easy to tune, but this part throttle knock started fairly recently. I've tried adding and subtracting fuel. My fuel trims are just over 100 for the mid and low, low 80's for the high. The power delivery on the car is aslo very choppy when I go WOT. It's worse in lower gears. When I step on it in first gear, I get a brief surge of power, then it falls on it's face while you can hear the turbo spool, then it takes off again. The car is very inconsistent, but it usually feels good at mid throttle, then falls flat when I floor it. I've checked for boost leaks, and swapped out the knock sensor. Any ideas? I've been working on this for the last couple months and I'm getting nowhere.

Thank you.
 

EMX5636

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Joined
Jun 28, 2008
Messages
1,631
Location
Bucks County, PA
I haven't had to tune a SAFC car in a while, but you might want to try backing the base timing closer to 0* instead of the stock 5. What spark plugs are you running? They could need replacement, or be gapped to big.
 

AWDPower

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Joined
Feb 28, 2011
Messages
107
Location
Vacaville, CA
NGK BPR7ES, gapped at .028. I'll try backing off the timing, I know I'm getting way too much.
 

ktmrider

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Joined
Sep 10, 2007
Messages
3,128
Location
Tempe, AZ
Quoting EMX5636:
I haven't had to tune a SAFC car in a while, but you might want to try backing the base timing closer to 0* instead of the stock 5. What spark plugs are you running? They could need replacement, or be gapped to big.

This suggestion is good, Keydiver documented this issue well. Stock timing curves are way too aggressive for just an SAFC at that boost level.

Would also think about some BR8's too.
 

AWDPower

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Joined
Feb 28, 2011
Messages
107
Location
Vacaville, CA
Thanks guys. I backed the base timing down to 0*. At first, there was no difference. But I quickly figured out that the too much timing was causing me to add too much fuel. With the reduced timing, I was able to take out a quite a bit of fuel, and the car woke up. It now pulls strong and smooth, with less knock. I'm still getting a lot of light throttle knock, but it is less frequent and takes more effort to trigger. I know I still am running too much timing, and a bit too rich, but the car is running a lot better.
 

turbowop

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Joined
Apr 29, 2001
Messages
11,971
Location
Yakima, WA
Find a used copy of DSMlink v2 and sell the SAFC. I picked up a used version for 503 for $250 and then sold my SAFC on Ebay for $210. I had no idea they went for that much used, but it damn near paid for DSMlink. Once you do that you can dial in your timing however is needed.
 

EMX5636

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Jun 28, 2008
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1,631
Location
Bucks County, PA
Mark has the best idea, (plus add a wideband if possible).

You can have rich knock as well. My car doesn't like extra fuel, it shows all kinds of weird knock. Just something to consider. You also might want to bring the plugs down to .022-.025
 

AWDPower

Well-known member
Joined
Feb 28, 2011
Messages
107
Location
Vacaville, CA
I plan on going the DSM link route in the future. I'm rebuilding the engine in my daily driver, and was trying to make due with what I have for the GVR4 for now. I had no idea SAFC's were worth that much, I have an extra one. I'll also try closing the gaps on the plugs a bit. Thanks for the help.
 

turbowop

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Joined
Apr 29, 2001
Messages
11,971
Location
Yakima, WA
For what it's worth, the SAFC I sold was the SAFC-2. I think the older ones don't quite go for that much, but apparently SAFC's in general are worth something to all the Honda guys out there. I was about to sell it to a coworker for $100 but he didn't have the cash at the time, so on Ebay it went. Glad I did that since I doubled my money. /ubbthreads/images/graemlins/rofl.gif
 
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