10 replies to this topic

[Dodgefan10]

I think Speedy said something about this in print once however, I have been diagnosed with CRS. (can't remember shit) What is the best F/A ratio for the 5.7 Hemi in an N/A car? Need it safe, need reasonable gas mileage, and like power across the curve, not just peak(s)....Thanks for you input guys...

[Hemi31]

around 12.5 at WOT. It will always hunt 14.7 at part throttle.

[Dodgefan10]

Thanks much Hemi31. Gotta' hook up to a wide band sensor and monitor F/A in case I can squeeze a little more power out.... Gotta' get ready for CF2......

[Plumkrazy]

you can go a few clicks lower maybe 12.7 12.8 if it isnt revving crazy high

[Speedy]

If you're gonna start messing with the tune I'd do it like this.

Get some time at a dyno shop. The runs will be cheaper than a wide band. For a NA car I don't think you need a wideband gauge installed, but the dyno shop should have one on hand to use for your tuning. Just make sure the reading is taken BEFORE THE CATS to be accurate. They may have to add a bung to your exhaust. Not a big deal as it can be capped of when done.

12.5 is a good value to shoot for at WOT. The important thing is to try to make it stay as close to 12.5 throughout the entire rev range as possible. It can't be perfect, like it may start off a tad more rich (12.2) or a tad more lean (12.8) when you first hit the pedal, but it should stabilize and ride out at a constant value.

Once you get 12.5 dialed in, you can try to lean it up a hair and see what happens. See if it makes more power on the dyno and see if you get any ST KNK. If it sees any KNK and starts to pull timing you've shot yourself in the foot as the timing pull will cost you A LOT more power than the tick or two leaner air fuel ratio (AFR).

You might can get 12.6 or 12.7 and find it's a sweet spot but all motors are different. Yours may like 12.3 or 12.4. You won't know until you start tweaking and testing.

[Andy@PWR]

Different cars have different fa requirements. Tune the car on the dyno. Don't go any leaner than 13.0. As erik said, you can't adjust part throttle fa so don't worry about mileage.

[Dodgefan10]

Thanks much gentlemen....Will buy the dyno time.....True Street charges $375 for a Dyno tune....Have a custom tune from Johan in the car but, email tunes are not quite the same as dyno tunes....Like the tune thats in it alot (much better than the canned tune) but, wanted to see if I could pull a little more out without it being unsafe....

[HemiSam]

If you're going through the expense of welding a bung in the midpipe ahead of the cat, and paying for custom tunes, I'd seriously consider investing in something like this. Weather affects AFR materially, as an example, and you can tweak fuel and timing at WOT within a band. That means you can tweak your customer tune but I wouldn't do it w/o being able to see your AFR.

But that's just my two bits...

http://www.innovatem...products/db.php

HemiSam

[Dodgefan10]

Thanks Hemi....Have considered a dual gage pod (pillar) with an aeroforce interceptor gage and f/a gage....unless the interceptor will monitor f/a too? Could do two of them....(oh no, another mod...)

[Jay6spdRT]

Does the Trinity have a virtual gauge to monitor A/F ratio? I don't think I've logged this.

[Speedy]

The Interceptor has an analog input that you connect your wide band sensor to. So yes it does have the ability to display AFR, but not from the OBDII port as that data is not available in the car. You'd need to have the sensor like LC-1 to feed it.

Trinity is the same way.