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Sbc MFI A/F ratios
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DRR Top Comp
Picture of Curly1
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I depend on my O2 and trust them but use common sense to like Bucky and Triple Nickel both said your goal is to get best tune and fastest ET. Tune to those then use your O2 as a reference to track changes in weather etc.

Just like using someone else's tire gauge, weather station or timing light they may not be the same and could lead you away from where it needs to be.

I have seen similar tire gauges read almost 1 pound different at 6 PSI, seen different timing lights a few degrees different and I know one guy whose weather station always reads about 1000 feet Density Altitude from what mine does.
O2 sensors could possibly read different to and what is good for your car may not be for mine.

These are some reasons why you do not tune to O2 number you tune to ET. Even those numbers can mislead you a little, if you are running too much timing you can run it a little fatter and it will run same and plugs look good. My thinking there is it may swing more in weather changes so I try to keep tune up closer. From my experience most people run way more timing than they need any way.


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Posts: 4065 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
DRR Pro
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quote:
Originally posted by C Hodge:
All 4 of my O2s are reading 4.8 for the car to be consistent. It’s a 421 running 0 pump with kinsler nozzles flowed to what my 33 Ron’s are and 92 kinsler main pill. I do have to run a high speed leanout to get the 330 and backhalf numbers consistent


What brand 0 pump do you use? Are you over driving it? Sounds more like a 0/ 1-2 pump.
 
Posts: 2504 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Sportsman
Picture of C Hodge
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It’s a Ron’s pump. When I bought the setup I started with the 0 1/2 pump and couldn’t get the car consistent. I changed to the 0 and Tuning got much easier. I am running a lot less psi than what’s suggested with only having 56 psi at the finish line but it’s working great.
 
Posts: 235 | Location: Tennessee | Registered: December 18, 2006Reply With QuoteReport This Post
DRR Pro
Picture of Alaskaracer
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I tuned mine by the plugs and mph, and looked at afr after to use as a reference....I'm at about 5.0-5.4 afr on mine....if I go one pill (4 numbers) to either side, the car will slow....Not sure a high speed would make much difference on mine though.....


Mark Goulette
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Posts: 1503 | Location: Back home in Alaska! | Registered: February 13, 2011Reply With QuoteReport This Post
DRR Pro
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Something I found going from MFI to EFI last month. Thought it might be of interest to some.

Here’s two runs overlapped that are identical 60’ and 1/8 ET to the thousands. The solid line is EFI (mpfi on 8-1-21) and the dashed line is MFI (6-2-21). Exact same engine, throttle body, fuel pump and intake manifold. The AFR of the EFI is held at 5.2 and the AFR of the MFI is 5.2 and dips to 5.1 at the very end of the run.
https://i.imgur.com/f9rXfmN.jpg

 
Posts: 2504 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Pro
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quote:
Originally posted by C Hodge:
It’s a Ron’s pump. When I bought the setup I started with the 0 1/2 pump and couldn’t get the car consistent. I changed to the 0 and Tuning got much easier. I am running a lot less psi than what’s suggested with only having 56 psi at the finish line but it’s working great.


Do you recall the finish line psi with the 0- 1/2 pump ??
 
Posts: 2504 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Sportsman
Picture of C Hodge
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I didn’t have the racepak on the car when I had the 0 1/2 pump
 
Posts: 235 | Location: Tennessee | Registered: December 18, 2006Reply With QuoteReport This Post



DRR Sportsman
Picture of Stephen Hughes
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Quick update, went down 8 numbers on the bypass pill to try it this weekend making a big enough swing we could tell something. A/F was 5.2 down to just dipping in the 4.9 range at the finish. Car only moved .007 in 6 runs from about 6 pm until 2:20 am. Seems as if it liked the change...now if my driver would wake up and not decide to be .032 4th round, we might have had a shot.


The Pull-Out....for when you want to work smarter, not harder!!!
 
Posts: 336 | Location: Texas | Registered: September 12, 2005Reply With QuoteReport This Post
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