Techsalvager

What wideband did you use to test with?

y8s

iTrader: (8)

Timing was optimized at both AFRs? Curious about how much difference in burn rate affects power that could be corrected by minor timing adjustments.

Ben

iTrader: (33)

My thought as well. You may have seen equal power with a little less fuel and a little less advance.

Savington

iTrader: (31)

Timing was optimized at 12.0:1 before I richened it to 11.6:1. If I was going to see equal power with less advance at 12.0, that implies that I had set the timing past MBT.

y8s

iTrader: (8)

MBT is not the same at 12:1 and 11.6:1 though.

And MBT timing should theoretically reduce BSFC (per Heywood).

Savington

iTrader: (31)

Am I missing something here?

If I set the timing to MBT-2* at 12.0:1, then that's essentially optimized. If I then decrease AFR to 11.6:1 by adding fuel, and the power goes up by 5whp, can either one of you explain to me how I could have somehow altered the timing at 12.0:1 in order to get that 5whp gain without adding the additional fuel?

I know MBT is different at 11.6:1, but it's irrelevant. I believe that MBT increases as AFR decreases (richer = slower flame front = more advance required to maintain peak pressure @10*ATDC), but let's look at both possibilities:

1. MBT is higher at 11.6:1, which means that I should have added timing to get closer to it, which would have increased power further
2. MBT is lower at 11.6:1, which means that I should have decreased timing to get closer to it, which would have increased power further.

I don't know why you guys think there's some trick to the idea that adding fuel increases power.

y8s

iTrader: (8)

I guess I'm just confused where all the extra fuel is going. I get that you need more than stoichiometric for best power because not all of the fuel is available for the combustion process, but is this a high boost issue? does the fuel condense so much that you need more to get to the point where power is maximised?

Faeflora

iTrader: (2)

11.6 to 12.0 is not that big a difference. That is a 3.4% difference in the amount of fuel.

I know you're reporting the the data as recorded Andrew, but that small a percentage difference could be within the margin of error for the AFR sensor or the calibration. Also, I don't mean to be a dick, but 5hp is not a huge amount. For a 350hp pull, that is a 2% power increase. That is small enough as well to be caused by a change in humidity/temp/trims/even tire pressure blah blah. Or something like a .2psi difference in the amount of boost.

Savington

iTrader: (31)

The richer-than-stoich is a combination of a few things - fuel will stick to the walls of the port, some will hit the back of the valve, some will be vaporized in the hot chamber (I'd say this is the most significant pre-combustion loss), and then whatever's left will light off assuming it's close enough to the proper number of oxygen molecules. I'm not 100% sure why it works like this at such a low boost level - I was surprised to see the power gain at such a low boost level. I used to tune cars leaner than that at 6psi, but this test changed that.

So your suggestion is that even though I manually enriched the VE table to alter the AFRs, what really happened was that the VE table alterations had no effect, the AFR gauge suddenly swung 3.5% richer, and the dyno read 5whp higher, all due to margin of error?

I don't mean to be a dick, but are you ******* trolling?

Faeflora

iTrader: (2)

No, that's not what I mean. I mean that your AFR gauge could be off. For instance, real AFR could have been 13 and you dropped to 12.5.

And yes, lots of things can happen between pulls.

nitrodann

If hes increasing the numbers in the fuel cells hes adding more fuel.

If he can increase the figures, do a pull, get more power, Then reverse, and repeat a few times, its working.

Dann

Faeflora

iTrader: (2)

Could some mod please split this fuel discussion out into a separate thread?

Braineack

iTrader: (62)

Why? this thread naturally worked itself into some awesome discussion. Why mess with greatness?

y8s

iTrader: (8)

Thread title updated.

Andrew: When you make counterintuitive discoveries that most people aren't comfortable with, you have to expect you'll be explaining them to some serious skeptics and dummies.

Just be glad it's us and not sjmarcy.

Braineack

iTrader: (62)

All I know is that if I had a dyno I dont think the car would ever be unstrapped.

Ben

iTrader: (33)

Haha, you were a little tough on our boy Fae (so I snipped that out), but there is some merit in what he said. A couple ponies can be within margin of error on a dyno. If you're talking about just a little difference, you do need to take multiple pulls to verify.

I still think that the extra fuel slowed down the combustion, and all things being equal (which they rarely ever are), less fuel and less timing would have made the same power. Was your air temp the same on both pulls? Was correction the same on both pulls?

There is another explanation though. The wideband calibration could be slightly off on the lean side.

I think the big picture lesson is that if you use the dyno to just hit a target AFR, you're doing it wrong.

Faeflora

iTrader: (2)

Yes that is what I have been saying.

FWIW my car made like 15hp more going from 11.5 to 12:1

JasonC SBB

I lost huge torque going from 11.3:1 to 10.5:1

Braineack

iTrader: (62)

I know the feeling.

18psi

iTrader: (76)

I lost a ton of power/torque going from 11.6 to 10.3 due to fuxorzed ait comp tables