reactor2

C7Z, 770whp / 799ft/lbs
14.1 psi, 93 Octane and NO METH w/ 13.0 AFR

How is this motor not all over that parking lot?
What am I missing?

The tuner seems to know what he is doing so I'm certain I'm missing something.

stevieturbo

Simple...some information is clearly inaccurate !

And if it is direct injection, I've seen a lot of reports that widebands may not always read as you expect they would...and this can also depend on whether there are cats fitted and where any wideband is located.

reactor2

In the video, the tuner said the AFR was right around 13.0-13.1. I thought he may have just misspoken. However, if you zoom into the dynojet dyno graph you can clearly see that the AFR is right around 13.0.
There are no cats on the vehicle and I assume the tuner is using a tailpipe sniffer.
As you noted, it must be the direct injection. Surely this tuner knows his stuff.

ysb02

I think stock the lt1 targets 12.8 afr at wot with e10 so 13 seems a bit high for a pd blower but isn't crazy I guess.

SBCGENII

If he is using a tailpipe sniffer it would mean the opposite.

stevieturbo

Except as everyone should know, a wideband does not measure actual AFR.
It measures excess oxygen and gives an estimate based on that. In most cases there is a very good correlation with AFR...but absolutely not always.

So just because the wideband says 13...doesnt necessarily mean it is 13 as would be measured on a proper gas analyser.

but if the engine runs, makes power and doesnt blow up, the numbers dont matter.

SBCGENII

I think a richer mixture keeps things cooler. With DI you may be able to run closer to stoich because of where the fuel enters. If you were only doing 1/4 mile passes and letting the car cool down between passes you might be able to run even leaner.

stevieturbo

I think the difference in reading is simply down to more efficient combustion that anything else ?

it isnt to say the mixtures are different....just that what the sensor sees is different. Which isnt the same thing.

Again, the sensor is not measuring AFR. I've never worked on any DI stuff but have read reports of some guys saying widebands can read very lean on them, but in reality they may not be as lean as they indicate. ( or perhaps they are !, but if the engine works and doesnt go bang...all good )

SBCGENII

I think we would need to know the mass of air entering the cylinder and the mass of fuel added to find out. I certainly won't be suprised if a newer engine could burn more oxygen at a leaner ratio. Would be cool to have a test with a Gen IV and Gen V engine and set them up for the same air and fuel mass per and see the AFR difference.

stevieturbo

I'm sure there I'd seen another thread somewhere ages ago too with more info

http://efi101.com/forum/viewtopic.php?t=8938

SBCGENII

I just read that post and some others and I am just glad I got port injection and have a good idea where I need to be lol. I think when these Gen Vs came out quite a few were blown up because they keep making good power gains until they blow.

stevieturbo

When a lot tune DI engines, they add port injectors anyway. Trying to get lots more fuel from a DI system would be very very expensive.

And long term DI is ***** anyway, as intake etc internals get gummed up with all sorts of ***** unless you can ensure the air ingested is 100% clean ( ie no crankcase ***** allowed to get in )
Many end up looking like dirty stinking diesels inside the intake !

there's no doubt they can make power and are probably more efficient....but there is a cost.