What do you use to easily switch engine map from 91 octain to 100 octane?
 

I've been dead set on keeping some 100 octane race fuel around and have my SW chip setup for the high octane benefits.


But then I started thinking, what happens if I'm taking a road trip and have to stop to get gas and 91 octane is all they have???


Do I need to stop, pull out my SW chip and swap it for a 91 octane programmed chip every time?


Is there an easier way to change out fuel maps?

For a temp fix I would think retarding the timing is all that you would need to do. Pull 2 to 4 degrees out of it should get you in a safe zone.

That is hard to do on a Carrera. The timing is all set by the DME unless it is not a stock setup.

There is no straight forward way to do it. Easiest would be to pull the ECU out and change the prom, but if the ECU is still under the seat then it’s not a quick job.

I know Steve Wong can modify a 964 ECU for switchable programs, not sure about on the ‘87 28 pin prom.

If your dme has the fuel quality switch you could adjust it to pull timing.

I used to have exactly that for a 964 motor. No Bad Days and Ingo Schmitz programmed it. It was some kind of double-capacity DME chip with a switch we installed in the DME case.

So, while it's totally beyond my knowledge, it ought to be do-able.

The earlier, 24-pin (usually soldered-in) Motronic PROM only had room for a single map. The chip they used went obsolete, and the 28 pin chip they sourced instead was double the capacity (16K, I think- lol).

The older Motronic boards have the drilled through holes for the extra 4 pins; you can remove the old chip, solder in the DIP socket (and reflow anything on the board that looks like it was soldered by a drunken 9 year old in complete darkness while you're about it - there were puddles of flux and dull, grey, crazed solder pads everywhere you looked on the one I did).

So the later chip has room to hold two maps, and you can add a switch to select one or the other - FR Wilks (on this very board) used to offer exactly that for his 944 PowerPROM (hi-perf on one map, and either his "shudder-fix" or the factory in the other). Good idea to switch off the motor and re-start.

As an aside, I seem to dimly recall that, other than a tiny amount of motor-specific base code somewhere (probably for # of cylinders, motor configuration etc), a Motronic is a Motronic is a Motronic, (raising the possibility of re-purposing a used volvo or bimmer Motronic of the same basic type/era) - I posted a list of Motronic models on the 944 forum many years ago. But that's above my pay grade; talk to someone who knows...

For myself, I'd suggest you probably won't see as much difference between 90 and 100 octane as you expect - I didn't, with a CIS turbo. Kind of a surprise, but there you go.

Personally, I'd run the advanced timing and use a J&S Safeguard to detect knock/dynamically pull timing as necessary with the specific load/temperature conditions you're experiencing. And run full advance if it doesn't. Which also protects against a blocked injector causing one cylinder to run lean. Or leaving the switch in the wrong position. Or getting a tank of lousy gas.

i think your car will run just fine...

Ivan

I use standalone ECU with knock sensors to reduce timing per cylinder when knock should occur but it also has switchable maps if I ever need to use them.

What ECU are you using?

THIS^

the following thread explains what the switch will do -- http://forums.pelicanparts.com/porsche-911-technical-forum/254708-8-position-switch-d-m-e.html

I'd also bug steve wong on this if you're having him burn you a 100 octane chip -- see what/if he thinks the proper 91 octane setting would be.

Now I'm not a tuner, but I was collecting and looking at the data in the built LSA (supercharged) engine I had; and for the most part the octane boost that I needed was only necessary when I was really pushing the engine. Sure, I might have got a few more horsepower if I ran 100 all of the time and had the engine tuned for that, but my impression is that it wouldn't have been much. If you're in a pinch, I would think you would be fine with 91 as long as you aren't hitting it hard and causing it to knock (a lot).
Interested in other's comments, too.

A few years ago, Russell Berry was burning performance chips for 911s. He also made a switch that would allow you to switch between several different image versions. I believe it was called the multi-board.

For example, you could put a stock image on the chip, and assign it to switch position 1. You could put a Russell Berry image on the chip, and assign it to switch 2. You could put a Steve Wong image on the chip, and assign it switch position 3. At least that's how I remember it.

(I say you could, but Russell would have to burn it onto the chip for you.)

With the multi-board you were supposed to be able to go from a stock octane image, to a 93, 100, whatever octane or performance image with a flip of a switch. I don't know how well it worked; I do not have one.

Russell got his start with 944s, and is better known for his work with them. There are a number of threads dating back to 2010 in the 911 forum you can check, or look him up and give him a call.

I would not run 91 on a chip tuned for 100. That’s asking for detonation.

All motronic chips, other than the earliest, hold multiple maps. They’re selected through a dme coding plug, which is just a switch. Have Steve burn a 91 map in one of the extra slots. Then wire in a switch to trigger it. It’s really surprisingly simple.

I had this in my 85. the new owner was glad to know he could just switch it from 93 to 91 in case he was somewhere he could not get 93.

miss that car but needed funds for finishing my 78 930.

I have one of his chips in my 88. Russell was great to work with and I have had no issues with mine.

I use VEMS.

Yes, copy what most turbo streetable drag cars have nowadays and run a modern ECU like a Haltech with their flex fuel sensor that automatically adjusts the fuel and ignition maps to suit the actual ethanol content being delivered to the engine.

Use E85 (108 octane) when at the track, top up with E10 (87) or straight gas on the way home with no manual adjustment necessary to use fully optimised maps.

I have his chip in my 86 951 tack car. works great.

regarding his 911 chip, I replaced a AA chip with it. even though I was replacing a modified chip, I could still tell the difference based on my speed and shift points on the track.

FRWilk allowed switchable maps on his 944 chip by removing the altitude switch and using a removable jumper or two position switch. The chip would need to be set up for this though.