Re(2): change timing


Given that I have now investigated and worked with EFIs and programmable timing for the past 10 years, first with one of the most sophisticated systems on the market on the Allisons of the Green Monster Team and lately with the most simple one on the market for my turbo LS engines, I probably qualify to answer.
The first time we played with EFI was about 20 years ago, back when you still had to burn chips for any change you made. Turned out rather quickly, there was no way to get enough fuel into the Allison (unless you put like 5 injectors per cylinder on it and ran like 5 individual systems per engine to operate all those injectors). So we skipped that rather quickly, We had an engine run on EFI on Idle sometime in the very early 2000s, but that was that.

The reason why we went back to EFI with the Allisons probably another 10 years later, was because we put a different blower wheel into the Allison supercharger and when trying to get the fuel system to run, it turned out the mechanical system couldn't really follow the boost curve (at least so I thought). It could have probably been possible to do it mechanically, but as I was in charge for the fuel system back then, I decided to have a look at how the EFI technology had progressed.
I found big enough injectors, a box that could operate 12 of them on one engine and a Pro Mod guy willing to work with us. The blower wheel went on the attic and is probably still there...
We had the Dragster guy over here a couple of times to get it all dialed in.
It all looked pretty promising and easy form the very beginning until we hit a very steep learning curve.
This was less because things were electronically controlled but more because we got a data logger with the system, which basically monitors every single combustion in the engine.
We quickly had to learn that all those "auto settings" are pretty useless and you'll find yourself manually building your fuel and ignition tables based upon Lambda values, intake air temperature and EGT values you got from the runs you've already done. So "turn key" is pretty much BS. And don't think you can adopt a drag tune into a pulling engine. You'll face issues you've never thought of.

But the question was about timing:
Actually on a blower engine you would run a pretty static timing and we actually also have a pretty "static" timing with the superchargers, too. We do compensate maybe 1 to 2 degrees between cylinders to make up for different cylinder fillings, so to not "over stress" the cylinders with a better filling. But that's pretty minor.

We have not even thought about "traction control", but we had to think a lot about "keeping the engines cool enough during the run", so, same as what many mechanical systems do, we kinda start too rich off the line and let them smooth out during the run and hope they ain't melting by the end of the run (which you might face when running a dragster tune).

Where has the EFI been a benefit?
As we run radial blowers (same as what a Pro Charger would be), we are faced with the fact, they don't supply air gradually but the air supply goes up by the square in relation to the rpm. Means compared to roots type blower charged engines, they are totally gutless in the lower rpm range. At the other end, at top rpm, there is a point where those blower wheels run into stall speed (an original Allison supercharger wheel does this at app 37000 rpm) and will not feed any more air, but create crazy amounts of heat (which they actually already start to do once you get over 3200 rpm - oh surprise --- that's what they were made for). So you have to work with a pretty narrow rpm range between actually getting boost and feeding your engine 900F hot air (which at 25 psi of boost doesn't contain much oxygen).
What does this have to do with EFI?
Well, the typical approach is to "add fuel when the EGTs get hot". If you e.g. set up your Allison Fuel system to have good EGTs at 4000 rpm, you give it a) enough fuel to run and b) add another 35% - 40% of fuel wich does nothing but cool the 900F Intake temperature.
These extra 35% - 4% of fuel is what then kills you in real life with a mechanical fuel system in combination with a radial blower (and turbos belong in that category, too), if the engine drops rpm. As rpm drops the supercharger get's back into its designed operating rpm, intake air temperatures drop and the fuel demand drops DRASTICAlLLY, as you don't need as much for cooling purposes anymore. Our experiences with the existing, mechanical systems were, that we could set the systems to work well in between 3700 and 4200 rpm, but as soon as any load hit the engines they would fall back to 3700 rpm (where the blower was delivering its maximum amount of oxygen) and then with any more load would fall flat flat on their faces once it dropped below 3500 rpm - because we simply over-fueled them with the fuel we had added for cooling purposes. So we basically had to gear down on tough tracks, where the blower guys just happily stayed in their gear and ran away from us.
So with the EFI we were able to match the fuel curve (by having a drastic change in fuel delivery between 3000 and 4200 rpm) and this actually resulted in the fact we could stay in the "high gear" and a completely busted driveline I think 5 years ago. We had gained torque, because we could reduce some of the effects that came out of the combination of running the mechanical systems as we knew them in combination with the original Allison supercharger.
Bascially, as our triple still runs with original Allison superchargers, that was enough to keep it competitive with the 4 x 14-71 blown Hemi guys here for now. The new blowers like the M5 and alike have brought the Hemis another step forward now, so that's back to the drawing board for us.
Would this have been possible with a mechanical fuel injection? Probably yes, but it would have gotten crazy complex and expensive and would have taken A LOT of time on the track with trial and error. Time we don't have. We need to make progress quickly just to keep up with the V8 technology. We're a handful of ordinary guys with Allisons working against the R&D budget of NHRA.
It took us long enough to figure all this out the way it went and to change the fuel curve, all we physically had to do was punch in some numbers (which was the easy part).
After having a closer look at what's happening with the "Alky burner engines", following pretty closely what Willem Veldhuizen has been doing with his twin John Deere Alky engines in the mod class (which sure isn't short on power) I would think, the turbo guys face some similar issues. There was this interview on pullingradio network with him, where he stated, the torque range" of the blower engines" is just so wide, they can basically get away with much faster gear ratios than him, as he has to work in a pretty narrow rpm range, that he has a hard time competing with them.
In my opinion, the turbo motors on mechanical injection run way to fat at anything but full boost and rpm, because it's #### difficult to get "big steps" in the fuel supply done mechanically.
This doesn't become visible much when everybody runs the same kind of set up in the super stock classes, but in mods and minis, this is an issue.
I found it pretty interesting at Ahoy last March, when the "Maximum Risk" made everybody else (including the Gallots) look like beginners in the super stock class. The fact the tractor coughed bucked loads of water and the rumor it runs one electronically controlled fuel circuit was a hint to me they must have been thinking about the relation of intake air temperatures & fuel mixtures quite a bit. I'll add the video link below.
So, practical benefits of EFI - in my opinion:

It's easier and much faster to tell it what to do instead of adjusting valves and doing countless runs on the track, changing "one thing at a time".

You still need to know what you are doing though (and when you come from CFI and go to EFI, you basically start all over).

Modern EFI systems come with "safety features". You can e.g. tell it to shut one cylinder down its EGTs get too high.

Ignition: If you have a strong bottom end, the ignition timing for tractor pulling is actually turning out to be pretty static in the end. We run WOT and full boost. Boost and rpm require the exact opposite timing -- and if both rise which each other (which they do in a tractor pull), they cancel each other out. Still you can do stuff like idle rpm control or adjust the timing on individual cylinders. But that's pretty much the same as running different compression in different cylinders and then you better work on your air intake.

SS Ahoy 2017

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