Speedtoys

Probly the whole "Im in Florida" bit under his Avatar.

rgs944

17 pages of a supercharger thread and things are staying pretty calm. Fricken awesome! Thank you to a big variety of very smart 928 guys who are contributing. I am not going to go through the whole list of names but you know who you are.

Hilton

Probably European - TT is an ex-colony of Britain.

Never been to Trinidad - but Tobago was awesome.. great place for a holiday

Leon Speed

I remember getting gas in Venezuela for 10 cent per liter. Those were the days

WallyP

True "octane" ratings are the same world-wide - all adopted from the SAE work starting in the mid-twenties after Walter Chrysler started increasing the compression ratios on his cars. The two main ratings are "motor octane" and "research octane".

What you see on USA pumps is not an "octane" rating - it is, as shown on the pumps, an average of research and motor octane ratings. (R+M)/2 The 93 (R+M)/2 gas is at least 95 research octane, but it is tough to find any without the politically-correct, Federally-mandated, bribery-driven totally-green ethanol.

As a general rule, if "octane" is shown with no other qualifier, it is "research octane".

Cosmo Kramer

95 RON = 91 Octane in USA

jcorenman

Mark, without a Sharktuner and being able to look at the MAF numbers in the LH, there's no way to know how close to the limit you are. All you can do is guess and presume, and that's not always the best way to approach engine tuning.

The MAF signal, which is computed by the LH from the MAF voltage signal, is the "load" used along with RPM to address the fuel maps. Once the MAF signal reaches its maximum value, you are on the last row of the fuel map and you are done-- you are at 100%, and neither magic nor wishful thinking will get you more rows in the map. As Greg and John Speake have both said, that happens right around 380-400 rwhp. (It's not precise-- airflow and horsepower are linked by efficiency, and efficiency does vary).

Now that doesn't mean that the engine shuts down at 380hp, it just means that it won't be getting any more fuel above that. The LH is against the stops, and no longer operating as a linear device. Whether that is OK or not depends on how far past the 100% point the airflow is, and how much fuel that last row in the fuel map is calling for.

And if all you care about is power at WOT then all you need to do is fiddle with injector-size and fuel pressure until you get reasonable AFR's at WOT. It won't be ideal-- and the rest of the map will probably be pretty far off-- but it works fine for most racetrack stuff.

Where tuning gets interesting-- and where things go bad if your sensors are pegged against the stops-- is where you want good control and efficient running over the full throttle range. In that case the LH has to be running linearly over the full range range, i.e. controlling fuel accurately as the load changes.

Anderson's and Fan's cars use the sensing element from a standard MAF, but transplanted into a larger pipe. The stock MAF uses a one-inch (approx) hot-wire sensor in a 3.5" pipe. Moving that same hot-wire sensor to a five-inch pipe changes the calibration completely, providing the same MAF voltage for much larger airflow. The SuperMAF does the same thing electronically.

rgs944

What are thoughts about running a mixture of E85 to increase octane? Here the highest octane we have is 91 octane which is in effect 10% ethonal. So basically it is E-10. It would be nice to get to about 95 octane. Since E85 is 105 octane that could probably be done with about a 5 to 2 mix of the premium 10% ethonal gas and the E85. . Good idea or not? I know ethonal is harder on some fuel line parts but to get anything above 87 octane I need to use some ethonal anyway.

WallyP

91 (R+M)/2 is about 95 RON.

Going to E85 can get complicated - the LH doesn't understand that, so you get into some serious tuning.

Speedtoys

Ive been slowly working up to a 1/2 tank concentration of E85 over the last week with gobs of ST work.

I can now run the small pulley without IC and have <10 knocks in a 1/2/3 gear run.

Injectors are another concern..if I choose to remain on this path, I will need 48lb injectors without a doubt. Large swaths of the bottom-right quadrant of the fuel map cant quite get enough fuel on 36s.

In theory, I could run two coding plugs on the ECU..one for up to that 50% concentration, and one for straight gas.

I have to think about that...whether I want/need to.

BC

There is a bit of ethanol experience here on rennlist if you know where to ask. You will lean out on a sliding scale as you increase your useage of e85 in a given tank of gas. You will want to make damn sure you replace any old pressure lines that are rubber - old rubber. Newer FI stuff is usually okay. At 24lb injectors on an S3, I was at 17:1 AFR (petrol scale) at WOT (yes - i said it was THAT lean at WOT - but no detonation) and now that I have installed 36lb injectors I get the full effect of ethanol, but now I can't/won't use regular gas in the car at all.

It is 105 octane but much more that that if you use it properly.

jcorenman

The LH has two maps, they are called "cat" and "non-cat" but don't have to be used that way. One could be for regular pump gas, the other for your E85 blend. Two caveats: With the "cat" map selected the LH operates in the usual closed-loop mode, adjusting fuel in response to the NBO2-sensor feedback with a range of +/- 25%. With the "no-cat" map selected the LH always runs open-loop, and ignores the NBO2.

Three-way cats only work in closed-loop mode, they need the AFR to hover around stoich (14.7 for gasoline). What I don't know is whether they would be damaged if the AFR's get very far off.

But running closed-loop with the "cat" map would give you some compensation for differing ethanol blends. I you use the no-cat map then you are locked into whatever fuel-blend you tuned for. Flex-fuel cars use an ethanol sensor to tell the ECU what the fuel blend is.

The other wrinkle is that you need to select injectors for the most-fuel case, i.e. WOT with E85. Going back to gasoline, and tying to idle, means that the injector time will be very short. Some injectors are happier than others with very short-open times, and some experimentation with ST's opening-time parameter is going to be needed.

On the other hand, Colin swears by the 60# Siemens injectors even for a 5.0L N/A car, so that might be a good option.

And there is no need to swap coding plugs-- just wire the appropriate LH code pin to a SPST toggle switch somewhere. (And maybe another switch--SPDT-- to select among the three ignition maps).

Happy tuning!

victor25

Jim, because as you say our LH has the ability to adjust both +/- 25%... couldn't you find a happy medium, so that with gas it was subtracting 10 to 15% and e85 adding 10 to 15%. Then just disable your WOT, so that it is always using the O2 sensor in loop. You could also set the enrichment on acceleration up say 10% to account for having your foot in it.

Ohh... startup would be an issue though

jcorenman

Maybe... Let's see, if we invert the AFR for gas and E85, we get 0.068 lb of gas per pound of air, and 0.103 lb of E85 -- assuming the same airflow. Running E85 you would need 50% more fuel, so you would all of a -25% to +25% adjustment range.

In reality it is a bit more complex. First, there are two different "adjustments" used in closed-loop mode: The first is a short-term adjustment based on the NBO2-sensor reading, called "O2-adjust" in Sharktuner, and I think it is actually +/- 20% and not 25%. This is the adjustment that is always moving up and down around a few percentas the LH "hunts" around an AFR of 14.7 (or whatever stoich is).

The second "adjustment" is called "O2 adaptation" which is the long-term average of "O2-adjust". I think it also has a +/- 20% range (hopefully John will jump in here and straighten me out), and get stored in the LH memory. (When you disconnect the battery and reset the LH "adaptation", this is one of the values-- along with idle adaptation-- that gets reset).

Sooo.... if you did tune for the mid-point (a 50-50 blend of gas and E85) then I would expect to see O2-adaptation pegged at -20% with straight gas, and at +20% with E85, with the short-term O2-adjust making up the extra few percent. It might work.

Disconnecting the WOT switch won't help, because the LH goes open-loop on its own, at high load. The WOT switch just adds the extra fuel from the WOT map, if used.

Cranking fuel is fixed, but once it starts I think it might actually be OK, because the LH saves the O2-adaptation number and uses it all the time.

The drawback is that O2-adaptation is a slow average-- minutes-- and it might be difficult to keep the car running after switching fuel, until O2-adaptation catches up.

This sounds like a perfect science project for Jeff. Once it is tuned for the 50:50 blend (E42 ??) then enable O2-adaptation (hopefully disabled for tuning), and fill with straight gasoline and see what happens with O2-adaptation (it is shown on the fuel-monitor page, but not logged).

Cheers,

Speedtoys

Right now on about 10% fat in the cat map and the cruise map adjustment is running about 8% above that on a 75% mid tank of E85.

Theoretically, a straight tank of gas gas should pull down 10% or so just fine.

Will be able to bring down the mix slowly and observe after vaca the week before SF12.