How to tune your engine (EFI) - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 45 (permalink) Old 03-18-2009, 12:03 AM
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Injector size, O2 readings, etc.

Brett,

Yes, I'm amazed by how much fuel my Nord engine seems to want, especially at low loads and revs (2-liter Nord with Megasquirt & Spica throttle bodies). Part throttle driveability suffers if I try to lean it out to reasonable, modern-car AFR values.

For the first several months, I tuned the engine without a functioning O2 sensor, and got the thing running pretty well by just "seat of the pants" and frequent plug chops (reading the spark plug color) at various rpm/load conditions.

Recently, I've gotten my PLX wideband controller (with Bosch sensor) to work, but adjusting my VE table to get "reasonable" AFR readings has made the car run poorly.

My wideband readings at idle and low-load conditions seem believable, but for some reason, I can't get the thing to read above aprox. 13.5:1 at full throttle and 100 kPA MAP. By 4000 rpm, my VE table values are already above 100, but I can't get it to read any richer. The sparkplugs come out black and the thing smells of gas, so I'm suspecting my O2 sensor or controller is giving me faulty or limited readings. Or, maybe my injectors are maxed out at high load conditions?

I noticed from a post of yours that you're running 35 lb/hr injectors, which work out to around 350cc/min, and seems awfully oversized by the calculations I've used. I've got 200cc/min injectors in mine, but maybe the traditional injector-sizing calculations don't aply to the Nord engine? How did you arrive at your injector size?

Sorry if some of this is getting a bit off the original topic. I suppose I can start a new thread...

George
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post #17 of 45 (permalink) Old 03-18-2009, 04:49 AM
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Originally Posted by gattia86 View Post
I noticed from a post of yours that you're running 35 lb/hr injectors, which work out to around 350cc/min, and seems awfully oversized by the calculations I've used. I've got 200cc/min injectors in mine, but maybe the traditional injector-sizing calculations don't aply to the Nord engine? How did you arrive at your injector size?
From memory, I originally calculated 26lb injectors, which would have supported about 180hp (I had plans for more engine mods) but then the Toyota injectors came up at the right price so I thought I would at least give them a try.
Oversized injectors are only a problem if the pulse width at idle is too low. ie less than 2ms. I still have some room to move at idle and can actually lean it out enough to cause the engine to stall. .

I also find that you can't go too lean on the run down because the engine will start to buck. I still get a lean tip in when going from off throttle back to light throttle, which I haven't been able to cure, so I occasionally get a slight buck.

I've decided that the best way to cure this is to install a V6, megasquirted of course and definitely no ITBs.

Bye for now.....
Brett.
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post #18 of 45 (permalink) Old 03-18-2009, 05:33 AM
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I also find that you can't go too lean on the run down because the engine will start to buck. I still get a lean tip in when going from off throttle back to light throttle, which I haven't been able to cure, so I occasionally get a slight buck.

I've decided that the best way to cure this is to install a V6, megasquirted of course and definitely no ITBs.
Sequential injector firing?

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post #19 of 45 (permalink) Old 03-19-2009, 03:39 AM
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Sequential injector firing?
Why?
With the less than ideal setup you end up with after converting a carb engine to efi, a batch system is all you really need.

Bye for now.....
Brett.
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post #20 of 45 (permalink) Old 03-19-2009, 03:44 AM
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With full sequential you will be able to fire the injector as the inlet valve opens. This means there is less chance for the fuel to fall out of the miniscule amount of air flowing past the valves and so hopefully less requirement to fun rich mixtures to get decent quallity idle and low speed running.

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post #21 of 45 (permalink) Old 03-19-2009, 04:44 AM
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With full sequential you will be able to fire the injector as the inlet valve opens. This means there is less chance for the fuel to fall out of the miniscule amount of air flowing past the valves and so hopefully less requirement to fun rich mixtures to get decent quallity idle and low speed running.
You really don't want to time the injectors to only fire when the valves are open. It's not a horrible idea, but all inall, outside of high or wide open throttle, the benefit does not really show up. For what you say, you do get a good amount of shear off the back of the very hot valve. For that matter, odds are that once the engine gets to full operating temperature, the injector is pretty much flash vaprorizing every injection. I've seen video from quite a few engines that show this.

One of the root problems with combustion instability is spark. The closer you are to MBT, the more robust the combustion will be to a/f errors. So on decel, when most of our engines don't advance the spark with low throttle (or MAP), your spark is a LONG way away from MBT at light loads, so you become very sensitive to a/f errors.

A better solution is to just turn the fuel off (if the system has decel fuel shut off), and then dump a bunch back in when the injectors fire again.

For idle, if you can, advance the spark to closer to 20 deg BTDC, and you'll need a lot less fuel.

There are two core issues with the Alfa combustion chamber- one is turbulance, or the major lack of it- so you don't get really good mixing. The second is the shape of the chamber- with a HUGE surface area and spreading the mixture out a lot (you'll note that the late Bosch cars with high compression had a small island on the top of the piston), it's really hard to get a good robust mixture right at the spark plug to fire at the right time. Better at MBT (if you can find it), but it's still a big, big problem on the older 4 cyl engines, and less of a problem on the V6's (even less so on the later TS motors based on the Nord block).

IF available, I would still go with sequential injectors. But that's what I know, too....

Eric
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post #22 of 45 (permalink) Old 03-19-2009, 06:45 PM
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With full sequential you will be able to fire the injector as the inlet valve opens.
Problem is that the injectors are a looong way out from the inlet valves.
A hang over from converting a cylinder head designed for carbs.

MS uses xtau to help with lean spots on initial accel and decel and it seems to work fine. Unfortunatly with ITBs and their irratic MAP signals xtau is often triggered during normal running, resulting in little spurts of over rich mixtures.

I could dampen the MAP signal more but then I lose responsiveness.

Oh the joys, not, of ITBs.

For the money, the ease of tuning and overall simplicity batch injection works just fine. Most manufactures used it for many years and many probably still do.

Bye for now.....
Brett.
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post #23 of 45 (permalink) Old 03-19-2009, 07:03 PM
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Oh the joys, not, of ITBs.

For the money, the ease of tuning and overall simplicity batch injection works just fine. Most manufactures used it for many years and many probably still do.
Manufacturers haven't been using it for at least 10 years, Nissan stopped using it in the late '80s.

Tuning wouldn't be any harder with sequential but the initial set up would be more involved.

Possibility of changing to TPS load sensing? A hot film air flow meter would be
the nicest way to sence load in this situation as long as all TB are attached to a common plenum.

Is the MS controlling the ignition timing too?

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Last edited by Duk; 03-19-2009 at 07:08 PM.
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post #24 of 45 (permalink) Old 03-19-2009, 09:24 PM
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Brett,

I'm looking to go with 38mm Hyabusa throttle bodies with the newest version of MS on my twinspark. Do you think the different intake ports between the Nord and the TS would change the MAP signal quality? Would this be affected by hotter cams?

On the MS Forums, it looks like a lot of people are running ITBs. Is there something unique about the Alfa engines? I believe you've been fighting this issue for some time, so I'd like to pick your knowledge prior to removing the Motronic setup.

Best Regards,
Lawrence
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post #25 of 45 (permalink) Old 03-20-2009, 12:15 AM
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All ITB setup have the same basic problem.
Rather low and pulsating MAP signals when compared with your typical plenum setup. Hot cams make this even worse.

Do some research on the MS and MS-E forums.

There are many solutions, like apha N mode (TPS vs RPM) or a blend of alfa N and speed density. There are also pneumatic and software dampeners, even multiple Map sensors feeding into a Hi selector circuit, aka synchroMAP.

All this tells me one thing. I ain't the only one to tear my hair out with this and by no means is my engine the worst either.

It's not unsurmountable though. I run SD only and the so called experts told me it couldn't be done.
Everyone who has driven the car remarks on how smooth and how responsive it is. Drives just like a modern car they say.

That's good enough for me but if I were to do it all again, no ITBs.

Bye for now.....
Brett.
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post #26 of 45 (permalink) Old 03-21-2009, 12:16 PM
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I have a question about injector timing after reading the following sentences on page 10-1 of the excellent Haynes Motorcycle Fuel System Techbook:

Quote:
Injection may start anywhere during the engine's expansion or exhaust phase but should finish before the intake stroke begins.

As the fuel requirement increases, the injector-open time has to increase, until the injector needs to be opened long before the intake valve opens. At this point, timed injection starts to lse significance. In fact, because the engine is going through the intake-compression-expansion-exhaust phases so quickly, it doesn't matter when the injector adds fuel to the air stream. Some systems switch to simultaneous injection (all injectors fire together) at this point. In simultaneous injection, each injector is fired once per engine revolution, arranged so that the pulse ends 60 - 90 BTDC on cylinder #1. The pulses of fuel will be delivered just before the intake valve opens on cylinder #1 (and on #4 in a n in-line four). Cylinders that are 180 out of phase (#2 and #3 on an in-line four) will have one fuel pulse during the intake stroke and another during the power stroke.
Now, granted our engines don't rev to 10-12,000 RPM like modern motorcycle engines do and injector timing may be closer to idling requirements in those motorcycles, I keep wondering what the best approach is. From what I read in this thread so far, the notion most people seem to follow is to open the injectors when the intake valve is open, which would be much later than described above. I couldn't find any information about what the optimal time is for fuel to atomize (i.e. fuel droplets dissolving into vapor).

So, my question is: Can anybody give advice on what the best injector timing is, given air and fuel temperature and atmospheric pressure, etc.?

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post #27 of 45 (permalink) Old 03-21-2009, 02:39 PM
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Originally Posted by turbolarespider View Post

One of the root problems with combustion instability is spark. The closer you are to MBT, the more robust the combustion will be to a/f errors. So on decel, when most of our engines don't advance the spark with low throttle (or MAP), your spark is a LONG way away from MBT at light loads, so you become very sensitive to a/f errors.

Eric
What is "MBT"???

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post #28 of 45 (permalink) Old 03-21-2009, 03:18 PM
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So, my question is: Can anybody give advice on what the best injector timing is, given air and fuel temperature and atmospheric pressure, etc.?
From what I've read and been told, with sequential injection the idea is to hit the back of the intake valve just as it begins to open. This helps to atomise the fuel as is is being drawn into the cylinder.
Many modern injectors, like mine, squirt two jets at slight angles which I assume is because they were designed for engines with twin inlet valves.

Fitting these injectors to older 2 valve engines in a position further away from the inlet valve (at least 4 inches on my engine) is not, I guess, ideal. But it works. Maybe not as good as a modern EFI setup but it's so darn close as to not matter, and whatever the case, its still way way better than smelly old carbs.

I'm also guessing that with these less than ideal setups batch injection may be preferential as there will always be a charge available when the inlet opens.

Bye for now.....
Brett.
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post #29 of 45 (permalink) Old 03-23-2009, 04:42 AM
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What is "MBT"???
I've heard many acronyms for it, but it's max spark advance for best torque. Ususally found with very high octane test fuel, and is a property (generally) of the combustion chamber.


As for timing. The real answer is that it depends. But you'll find that most OEM's time port injection to be done on a closed valve. 100% done on a closed valve. That way, you'll not run the risk of bore wash, where liquid fuel hits the cylinder wall, washing the oil away.

You can get some cooling advantage if you inject during intake valve open timing, and you see more of that happening as the injector spray patterns get more complex.

For vaporization, outside of the cold start and warm up phase, by the time your engine reaches full operating temperature, you are generally flash vaporizing 90% of the fuel just by injecting it.

Eric
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post #30 of 45 (permalink) Old 03-23-2009, 05:51 PM
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I will chime in. you want to load the hot intake valve. by feeding the fuel on the closed valve it will
#1 cool the valve (helps keep it from deting)
#2 heats up the fuel (may even go to a gas form)
#3 the puddled fuel work even out around the valve seat when it open you get a even ring of fuel entering.

So all and all you get better MPG and better emissions by blasting the closed valve.
now at higher RPM it does not matter as much as the valve will open before the fuel can get to the valve.

now for the Seq. injection has no advantage just look how much power is lost on a spica motor when it is timed wrong or out 180

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