The Silver Buick's 1969 Firebird OHC six project.

[Paul S]

Yep, Q. My. "in so far as is possible" was a concession to not wishing to try a compound angle in the 'prototype' system-now on the road 8 or so years.

Sequential does permit cylinder adjustments though I am not sure I'm smart enough to avail myself of the opportunity--the plugs all color identically and well and the two AFRs (one in each downpipe) run very well together. Naturally, those ob01servations are somewhat crude...

My preferred scheme is to use fast actng, low impedance injectors and inject only when airflow is established into the cylinder--very possible in my lean burn philosophy (remember, my high CR engine runs well at 19+ AFR) . Of course, there is a vast controversy on this subject. I have found some of the data opposing such an approach somewhat contradictory, as you might suspect.

Paul

[TheSilverBuick]

On my Buick 455 in the Skylark I am running sequential. I've done some math based on my cam specs. what my injector duty cycle is at idle and cruising and what the point of peak air demand by the cylinder should be (point of the quickest piston speed) and if it all times out right and I programmed it right, during idle and cruising speed the injectors don't spray fuel unless the intake valve is open and the exhaust valve is closed (after overlap). Just this week I shaved another 1.5 AFR off the cruise, taking it from 15:1 average to 16.5:1 average. I did likewise with the idle, but decided to kick the idle back to 15:1 from a drivability stand point.

My excel charts haven't gotten sophisticated enough to account for variable RPM so I've used a fixed cruising RPM (~2300) and fixed idle RPM (~900) which I recorded the engine pulsewidth and duty cycle and then adjusted the sequential timing to put the entire pulsewidth in the time frame the intake valve is open and exhaust is closed. As I lean it out it only widen's the window between stopping fueling and intake valve still open.

So a break down of the criteria I used to mathematically set my injector timing, which is timed at the point the injector stops spraying. At idle I started with the peak cylinder demand is at 74* ATDC of the intake stroke, so I centered the pulsewidth so 74* occurs in the middle of the injection**. Then as fuel demand increases I leave it alone until the point I think it is spraying when the exhaust valve is open, then I start letting the injection process end later so it continues to start after the exhaust valve closes up until about 5* before the intake valve closes. Ultimately locking the end of the injection to 5 crankshaft degrees (720) before the intake valve closes. Any fuel the cylinder needs will be injected prior to that point. I also actually have it set so that in theory it will inject as soon as 3 crankshaft degrees before the exhaust valve is closed to get the process going.

Of course all that is based on "if" my math is right and "if" I am actually programming this thing correctly, LOL! DieselGeek here does tons of dyno tuning for individual cylinder AFR's and global injection timing phasing and will say (correctly in my opinion) that this is purely academic without dyno testing as he says lots of time the injection timing isn't what you'd expect for max power. In any case it makes me feel better, LOL and I think it is tough to go wrong at idle and cruising if your intake valve is open longer than the injectors (or so I think...). I was able to drive the car at ~300 or so RPM lower when I went to sequential from batchfire. Before it didn't like being driven below 1,500rpm, now I can put along around 1,200rpm when I haven't overly leaned it out.

**I make it sound much more complicated than I've implemented. Looking at it I actually have it much more simple than that. I end injection every time at 106 crankshaft degrees (intake closes at 222*) from idle through cruising as the window is more than large enough. I also take into account I'm not injecting after the piston hits BDC unless the rpm's are up above 4,000rpm for some ramming effect, though for some reason I have the end of injection stopping 15* before the intake valve is closed (which the piston is well on it's way up, 28* ABDC). Hmm.

[Bamfster]

What do you mean? On the Oldsmobile engine? That's how they came from GM. Early experimentation in EFI I guess before they decided on a hard straight rail that is less likely to crack and leak.

Yea .... the Olds .... I've always liked the look of hard lines over the stereotypical rail ....

[Paul S]

Great post, TSB! Thank you.

You may recall a long discussion in the MegaSquirt site on this subject a few years ago. The conclusion then was that an SAE paper correctly pointed out that 'cylinder wall washing' was an issue for those benighted yahoos who tried to time their injection in the manner you so well discussed--for no apparent benefit. I read the paper and didn't get that point exactly.

Recently pointed out in Hot Rod magazine, was that one of the benefits of Direct Injection in gasoline engines (article related to the new 2014 LT1) was the charge cooling effect on VE and detonation tolerance (adding up to an increase in CR of 1-1.25 units). The sequential port injection scheme is not nearly as clean as DI but I can't help but think that some of the benefit shown there is available-and a 2,000+ psi pump isn't needed...

BTW, I implemented sequential on an inverted, alum., 406cid V-8 and it ran beautifully before I ran out of money and time. It-Electromotive TECIII-had to be 'tricked' to get the injection timing the way I wanted but there seemed to be no problem with it. It had 12.5 CR, a short duration, high lift 'truck' cam and it idled so quietly you could talk over it and it had just stub exhaust stacks--but when you opened it up...

Paul

[TheSilverBuick]

You may recall a long discussion in the MegaSquirt site on this subject a few years ago. The conclusion then was that an SAE paper correctly pointed out that 'cylinder wall washing' was an issue for those benighted yahoos who tried to time their injection in the manner you so well discussed--for no apparent benefit. I read the paper and didn't get that point exactly.

You lost me a bit here. Should I be more concerned about how I have my injector timing? I did a quick search of the MSEFI forums and didn't come up with anything substantial relating to sequential, cylinder wash or SAE paper?? One post mentions spraying the intake valve before it opens could result in raw fuel hitting the cylinder wall and washing oil off, but that is impractical on two ends, one is if the engine is cold enough for the fuel to stay raw in the chamber I'm not revving it high enough to pull fuel in until vacuum is peaked (and best chance of vaporization) and two, eventually the situation will occur if you are hitting 75+% duty cycles simply to get fuel into the chamber. I'm a bit confused.

[Paul S]

TSB, the info was in the Mega Manual under Sequential Injection. I have, in my files, some vectors to those areas but they are not now available. I have part of one of the Mega Manuals and the following is an excerp from Sequential Injection:

"So the effect of sequential timing is relatively minor, and applies mostly at low rpms. The OEM manufacturers use it mostly for emissions reasons (most of the OEM fuel injection systems up to the mid-90s were bank fire). However there is a real benefit in sequential systems in that you can do individual cylinder tuning (if you have the time, skill, and equipment)."

This does not address the issue in as much detail as I know it has and I will continue to look in my files and on line. I may have kept the SAE paper and will look for it as well.

[Paul S]

Hi TSB:

I have looked high and low for the SAE paper to which I referred earlier with no luck. Please let me go back to the beginning and try to summarize what I've been kicking around here.

I started looking at this 9 years ago when I was designing a v-8 for an aircraft application. At that time Bowling and Grippo, of eventual MS fame, had some words about the sequential injection issue and it may well have even been on their "efi332" site, if you remember that one.

They argued then, as they did in their later Mega Manual, that sequential wasn't necessarily good for all out power but if you happened to care about fuel economy or-who knows-emissions, you might consider it. They didn't like the idea of injecting with the intake valve open. One of their 'exhibits', along the way, was the SAE paper that discussed washing the oil off the cylinder walls when the raw, unvaporized fuel entered the chamber. Given that the performance improvement was not significant, in their view, 'sequential' was downplayed at the time.

For the restricted case of my aircraft engine (narrow operating envelope), I didn't buy the argument.

That was then and now "everybody's doing it". We can't even find the discussion these days, as it has, apparently, become moot, IMHO.

So, TSB, I feel that with the OEMs using sequential and the wide variety of people and aftermarket systmes using it as well, your scheme is completely acceptable.

Paul

[TheSilverBuick]

Thanks Paul for taking the time to look for it. I've seen a bit of the history of aftermarket sequential and it is interesting to see the reasons 'for' and 'against'.

[DanStokes]

Paul - I'm an SAE member and if you're interested I could see if I can find that J-paper. If you can remember (more or less) the title and/or the year it would help in the search.

Dan

[Bob Holmes]

Observing cylinder to cylinder O2 readings will show that there is performance to be found in sequential fuel injection. I would think that in this application that it would certainly be true. Given the significant differences in the induction paths for each cylinder, they can't possibly have the ability to induct the same amount of air for each cylinder.

When we went to tuning the EMC V8 as 8 individual single cylinder engines, we found significant gains. I still think we could have pushed it further given time and $$$. There has to be individual curves given the twist in the crank and cam.

Oh well, there is only some much time in the day and money to spend on such pursuits.

[TheSilverBuick]

For the record, I feel mentally out gunned compared to a couple of you =P

[greenXpress]

For the record, I feel mentally out gunned compared to a couple of you =P

I feel that way every day.

[Monk]

For the record, I feel mentally out gunned compared to a couple of you =P

Yep.......like they're talking in tongues.

But I dig this thread.

[silver_bullet]

Ditto...

[Paul S]

Ditto...

Hi Guys:

Let me assure you that you are not, as TSB said, "mentally out gunned". I have eaten so much 'humble pie' over this conversion of my '68 LeMans to EFI, I ought to weigh 600 lbs! It took me 4 iterations of fuel system to get one that is quiet, feeds all the time and is bullet proof (I hope!), for example. Another example, I recently, got a coolant leak from the region of the head gasket. I realized that I had not retorqued the head after having R&R's it! "Mentally out gunned"? I think not! (Fortunately, I caught it early with no harm to the engine!)

I go to car shows and stand in awe of what other guys can do.

That all honestly and humbly said, I'll keep looking for that paper, Dan. I just can't imagine that I dropped it, though it's possible.

Also, Bob, on the airplane engine--inverted v-8--I was going to install EGTs on every cylinder-a common aviation practice-and do what you outlined. The time was mid 2008, BTW, hint, hint.

As it is, I have a PLX Devices EGT gauge (1 only, of course) to optimize the spark timing for my OHC6. My scheme is to get good lean performance with as much advance as I think it needs (too retarded and it misses, BTW) then jiggle the spark to minimize the Exhaust Gas Temperature. The cooler the EGT, the lesser amount of energy is going out the exhaust pipe and the most going into the crank.

Some may think that I will blow the head off my 6 with detonation, but at these very lean-18-19-air fuel ratios, it has never detonated and I don't expect it to (there's a cool way to estimate the point of detonation...). As long as I can stay our of lean misfire, leaner is good, IMHO.

Have a Merry Christmas and Happy Holidays, Guys. The blizzard has stopped here in the Great Plains, so we're off to Denver.

Paul