TW720HVY

iTrader: (1)

Naturally aspirated O₂ verses super charged O₂, are they the same or should the different set ups have different desired O₂ readings?

Thanks

Whipple Charged

Yes, but you should provide some information on what you have so its easier to answer properly. But yes, normally a NA motor runs leaner than a SC motor, normally. That doesn't always equate to better fuel economy, but not sure where your going with this.

Philm

What would be ideal. Just picked up a handheld wideband to set the carb in my 598ci N/A. Thinking or shooting for around 12.5:1 at WOT? A little fat is better than any chance of lean. Have 10.2:1 comp on pump gas.

TW720HVY

iTrader: (1)

I have a naturally aspirated engine and a friend of mine has twin super charged injected engines and this weekend he was trying to figure out why his engine's plugs were fouling and actually wet with fuel. We talked about my engine's O₂ readings and I wasn't completely sure if SC engines needed to be leaner or fatter than non SC engines.

The guy who rebuilt the engines told him to look for 14.7 at idle. Again I don't know if this is right, it sounds too lean to me.

I just went through tuning and O₂ readings on our engine and I know there isn't just one simple answer. From idle to WOT a lot can change and happen.

He is using my O₂ but he is fuel injected.


Thanks for the help guys.

Advantage 575

iTrader: (3)

[QUOTE=TW720HVY;3730418]I have a naturally aspirated engine and a friend of mine has twin super charged injected engines and this weekend he was trying to figure out why his engine's plugs were fouling and actually wet with fuel. We talked about my engine's O₂ readings and I wasn't completely sure if SC engines needed to be leaner or fatter than non SC engines.

The guy who rebuilt the engines told him to look for 14.7 at idle. Again I don't know if this is right, it sounds too lean to me.

I just went through tuning and O₂ readings on our engine and I know there isn't just one simple answer. From idle to WOT a lot can change and happen.





I'd bet it doesn't idle to good at 14.7 to 1. My SCI 's like a little richer idle. Currently set to 12.25. Plane and cruise without boost I run it low 13's. Factor of most importance is EGT's throughout RPM band. Under boost I bring the ratio down pretty quick. Low boost up to approx 3lbs 12.5. But my high boost around 9.5 I'm in the 11.5 range. A true correct ratio is different for every engine. A lot of variables have to be known for proper set up. But 14.7 to one?

GPM

You might find something useful on this site, http://www.enginebasics.com/EFI%20Tu...%20Tuning.html

TW720HVY

iTrader: (1)

Thank you for the replies and information.

I completely understand that each engine is different. Even though we have a non SC'd engine we still took the engine and the boat to be tuned and it made a world of difference.

A friend is currently in the tuning stages with big engines and we just recently had a discussion about A/F ratios and I just wanted to make sure he has some good information. 14.7 seemed too lean.

Whipple Charged

boats are different than cars so throw all that out the window.

NA motors should idle about 13:1 to 14:1, especially with slower, older PCM's. New, Mercury based PCM's can't get away with 14:1 because there processor speed is so much faster that you don't have the occassional hiccup, but aftermarket ECM's or old OEM's could have issues. You also have to deal with proper cold start, accel enrichment, heat soak.... so the AF will vary. Low to mid range, an NA motor should be 13.5:1. Mid to high should progressively get richer. With aluminum heads, a good number would be 12.6:1 to 12.8:1 while cast iron needs to be roughly .25 to .50 richer. If erroring on the cautious side, the NA motor should be closer to 12.2:1 as there will be a variance in cylinders and banks.

A SC motor is similar, but richer and typically the same issues applies. Older OEM ecms or aftermarket typically have trouble with accel enrichment from low rpm, especially when its in idle control and even more so if its a positive displacement SC. We typically would set a aluminum head, pump gas motor up at 13:1 at idle, 13:1 in low to mid range and progressively get richer as manifold psi and rpm increase. Target, considering the motor has the right internal parts and were not fighting detonation, then target would be 12.0 @ WOT. But if its a stock motor, stock pistons, we would go to 11.6 to 11.8:1. If being agressive, 12.4 to 12.6:1 but almost never do that except for race gas. Cast iron needs to be .5 or more richer at WOT, same for idle and cruising.

You can almost always make more power on an SC engine by running a little richer, say 11.8:1 and more boost and timing vs less boost/timing and 12.6:1.

HaxbySpeed

x2

Good info Dustin.

Steve H

Old OEM's such as MEFI1?