Side by side fuel injectors in open manifold.

[PEW]

I have a fuel injection conversion project in mind, using either a Megasquirt or Canems programmable control system.

My old non-crossflow, 850cc four pot engine presently has a single semi-downdraught SU type carburettor. The carb is fitted on a heated swan-neck adapter which takes the mixture flow into the mouth of the main inlet manifold. The ports are arranged E-II-EE-II-E. The conventional cast ally inlet manifold has two horiziontal branches, feeding the two pairs of side-by-side inlet ports.

The main problem with this engine is its very small size and lack of space around the inlet ports and in the engine bay. It's a very tight fit in there, too small for any conventional throttle bodies, including motorcycle types, which are all crossflow. To keep the conversion simple, I'm therefore looking at the possibilty of fitting a single throttle body downdraught fashion, onto a vertical adapter bolted on the existing gas flowed and matched inlet manifold (i.e. replacing the heated swan neck adapter). This would allow me to fit two injectors into each of the manifold's two branches, one for each inlet port.

These would be fitted by welding in comercially available, push-in tubular injector adapters on the top face of the two manifold branches.

The inlet manifold branches have no internal walls and therefore act as plenums. This works very well on the carb setup. The injectors will be fitted side by side, at a 45 degree angle on the manifold, to fire directly towards the ports, only about 25-30 mm away from the face of the head casting.

I see no issue with this but I'd just like to canvass opinion here before I make an expensive mistake and ruin my specially made ally inlet manifold because I've missed something obvious.

Thanks in advance!

 

[WGJ]

This sounds like a BLMC 'A' Series engine, is that right?

- Siamesed inlets
- Simaesed exhausts on 2 & 3
- 850 cc


Bill

 

[LionelHutz]

From the description, I don't see why you would need 2 injectors.

The 2 injectors would likely work fine, but why not just install a single injector and fire it twice, instead of installing 2 and alternating their operation?

 

[BrianPetersen]

So you are proposing to have essentially one injector for cylinders 1 and 2 for that siamesed intake port, and another injector for cylinders 3 and 4 for that siamesed intake port?

Firing order for a 4-banger is either 1-3-4-2 or 1-2-4-3. In either case, that intake runner is seeing two intake strokes in a row followed by a full revolution of nothing.

Unless you do something rather unorthodox with the injection timing - and I'm not saying that's impossible - I'm thinking that whichever of those pair of cylinders is first in the firing order is going to be rich and the second one is going to be lean.

The original carb setup doesn't have this issue because all four cylinder pulses are taken away after the carb so that the flow through the carb is as constant as possible (or at least, as consistent for each cylinder as possible). Siamesed ports in which the valve timing overlaps are always going to have some interference between the two.

If you can fix it so that the injector fires coinciding with the early part of the intake stroke on each injector, you might get away with it. Each injector would see hit-hit-miss-miss with the other injector doing the opposite. The two hits in a row might not necessarily want the same duration. The duty cycle of the injectors would have to be kept low for this to work. No idea if the software you're proposing would allow this strategy.

 

[PEW]

No, this is a Reliant 850 engine. It has four cylinders and four separate inlet ports, not three as per the A series engine.

The proposal is for four injectors, two in each branch, or arm, of the manifold, i.e. one for each cylinder. There is no need for anything other than a conventional firing pattern, 1-3-4-2.

On other 4 cylinder setups I'm familiar with, the inlet ports have individual tubes leading to the port. The original inlet Reliant manifold is like this, albeit with cylinders 1-2 and 3-4 siamesed within the casting "branches". Unfortunately the inlet tubes are small in diameter and we've proved that more power is produced if the dividing wall is removed.

My manifold is an alternative cast ally design with a single oval interior common to both inlet ports. It's also extended to sit further away from the head as it was originally designed for a supercharger setup with a 4 branch tubular exhaust to fit beneath. It's big enough to house two injectors side by side in each branch. Hence my query.

 

[dgallup]

I think it would work OK as long as you use a very narrow spray angle injector. "Pencil" spray works very well for performance & driveability if the spray is targeted directly at the back of the intake valve. You might run into some problems at long pulse durations where one cylinder robs from the other.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[PEW]

dgallup,

Thankyou for your comments. I intend to arrange the fuel spray to go as directly into the port as possible, within the limitations of the physical space available. I know that many modern inlet manifolds house the nose of the injector in a small "archway" above each inlet branch directly at the port, which has a matching cutaway to help channel the spray. Unfortunately there is no room to do this on my manifold so the spray will go into the main airflow from above.

"Charge robbing" is one of my concerns. I think this will affect emissions rather than power. However, I'm sure that the injection conversion will improve the emissions of the SU setup. This has been an issue at annual MOT test (it's well known in Reliant circles) because there is no effective way of properly calibrating the mixture needle at idle.

Regards, Paul W

 

[NickJ67]

I'm a little bit confused here. You are saying it's got one inlet port per cylinder but also seem to be saying that there are two branches to the inlet manifold each feeding two cylinders. Is this because the manifold has no internal division between the paired cylinders?

If so, I think you need to be very careful as charge robbing is likely to be an issue. As you probably know, charge robbing does cause problems when injecting the A series (true siamese ports).

How to get around it?
- Position the injector as close to the head as possible, use narrow spray angle injectors and point them right at the back of the valves. Might be enough.
- Use a manifold that has at least some segregation. You can easily make a manifold from thinwall tubular steel (exhaust tube) and it works just fine. FWIW, I suspect you'll get better torque from a manifold with separate runners anyway. Maybe just not practical in the available space.
- Use either a single point injector for all 4 cylinder or a pair of them each to serve 2 cylinders.
Use sequential injection so you can time the shots (at low rpm at least where it will matter more). There are now versions of Megasquirt that can do sequential injection albeit at greater expense (still pretty reasonable) and complexity. Here's someone who's done it already

http://jbperf.com/sequential/Fuel_Injecting_the_A_Series.html

Don't know much about Canems but a little googling found this

http://www.canems.co.uk/siameseports.php

You might find this interesting too.

http://www.starchak.ca/efi/efi.htm

Hope you find this useful

Regards

Nick

 

[PEW]

I'm a little bit confused here. You are saying it's got one inlet port per cylinder but also seem to be saying that there are two branches to the inlet manifold each feeding two cylinders. Is this because the manifold has no internal division between the paired cylinders? [Unquote]

You are correct. The original design of the Reliant manifold has four narrow tubes/runners, two in each branch. This manifold is very small in diameter. It was discovered that more power was to be had if the "dividing wall" was milled away, leaving a single "hourglass" section tube now shared by both ports. This solved an uneven mixture problem on a particular Weber downdraught carb (34 ICH).

I now use a similar but improved design of manifold where the internal cross section is one large oval. The division in flow occurs only at the port face. My engine can no longer use the original manifold due to the inlet ports being enlarged sufficiently to cause a sealing problem at the head face. I use spacer blocks with an internal "hour glass" port on extended studs to get the new manifold on. Without them there is no room to get a spanner or socket in between the exhaust headers to tighten the nuts. Some of the fasteners are socket headed screws going directly into the head casting but not all are accessible with a hexagon wrench and a spanner has to be used.

To put the diminutive size of this engine in perspective, the head is only 13.5" in length (the car is only 10 feet long, think Austin 7 special). I cannot go back to a manifold with separate runners without downsizing the inlet runners again, so I would be as well to go back to the old restrictive manifold! But I cannot get injectors fitted to that because there is no space for them.

My reason for keeping the existing manifold is because of further space restrictions in the engine bay alongside the engine.

 

[not2fast]

Did you look at MS-Extra ? the code has fully sequential or Semi seq for Siamese setups, I realise this is not your setup but it may do what you want, btw you have full control over 720deg for the injection of fuel if that help with any charge robbing issues.

not2fast

 

[NickJ67]

Ok, thanks for the clarification. Then it seems like what you initially outlined is the only solution that will physically fit. I think it will work, but I do suggest that you proceed on the basis that charge robbing is a potential issue and pick an ECU solution that can deal with it. From familiarity, I'd suggest Megasquirt in sufficiently high spec to go sequential if needed, but there are doubtless others albeit at higher cost. Might depend on how comfortable you are with electronics?

Regards

Nick

 

[PEW]

Not2fast, I hadn't heard of MS-Extra, I'll check it out, thanks.

Nick, I'm OK with electronics provided the instructions are OK and having briefly looked through the downloadable manuals, Megasquirt seems pretty good in that respect.

Having taken the engine out of the car today, I've been looking at the manifolding issue again. It would be possible to weld in a simple "mixture containment plate" (my term) in the centre of each manifold spacer block. This might alleviate charge robbing to all intents and purposes.

The other way, as already suggested, is to convert to closed loop single point injection using the existing manifold. It might even be possible to convert the existing carb body; I know this has been done with Stromberg carbs.

My concern with that would be the duty cycle of the single injector.

 

[LionelHutz]

Brian - was that directed at me or the OP? I'd think a single injector would work if you trigger it at each intake event. Otherwise, one pointed at each intake valve could also work. I would definately want to use injector timing matched to the intake events as opposed to just triggering the alternating injector once per revolution or once per ignition event.

 

[PEW]

I'm slightly confused by some responses. Just to clarify, I don't propose using two injectors in total, but two injectors in each manifold branch.

As I said earlier, one per cylinder = four injectors, which would be fitted as close to the intake ports as space permits.

A single injector fitted at the engine end of the intake manifold would actually rely on charge robbing to work, not a good idea.

Alternatively, one injector fitted close to, or in, the single throttle body. Two injectors at that location would halve the duty cycle, which might work better.

 

[NickJ67]

Plenty of modern engines use single point injection with a single injector/throttle body. Whether any of these will fit nicely on your manifold is another question.

Examples that spring readily to mind are found on the Ford Ka (and probably older Fiestas which use that same venerable pushrod engine) and some of the smaller engined Vauxhalls from the 90s. Also some of the smaller engined Fiats. I expect there are many others too. These will be plenty big enough for your needs, maybe too big. I'm assuming you're UK based as the Reliant 850 can't be common elsewhere.

Charge robbing considerations aside, I'd prefer the multipoint, 4 injector solution.

Nick

 

[PEW]

Nick, Yes, I'm familiar with the smaller Fords, having had three Fiestas in the family over quite recent years. The Mk3 was the first type fitted with single point injection. Not a very good system in truth, the 1100 engine fitted with this produced less power than my tuned Reliant 850! By coincidence I have very recently bought a new Ford Ka throttle body to experiment with but it has no location for an injector. It would be of use to control the airflow on the 4 point as it has a throttle position sensor. Having said that, it is suprisingly large and it may get used on another project involving a Fiat 1500 and a supercharger...

 

[PEW]

I've been busy. Having tried a number of "mock-ups" using the actual manifold and cylinder head to suit various throttle bodies, I now think it will be best design compromise to use a one-off single point injection setup.

The throttle body will feed a simple plenum adapter fitted to the existing inlet manifold. I made a mockup of a simple plenum adapter (a simple truncated cone/frustum and bespoke end plates). There is room in this to fit two injectors side by side to halve the duty cycle (this requires a very simple, compact fuel rail). Megasquirt uses two injector ouputs so wiring should be very simple in this respect.

The actual adapter can be made from fabricated ally plate or may be done in CNC'd billet alloy, depending on how flush I'm feeling when the relative costs are finalised.

I've decided to retain the heated section swan-neck adapter as this will help in obtaining a very homogenous mixture.

Thanks for your ideas.

 

[mattsooty]

If I'm honest I really do not understand your concerns with charge robbing - unless this is some sort of dissertation or emissions compliance exercise. If I were you I would just hose fuel in, batch fire, and be done with it. The beauty of gasoline in SI engines is the broad spectrum of combustible AFRs that it exhibits.

MS

 

[BrianGar]

What is your goal,

Performance
Economy
or Emission friendly

You can only really have one without spending and thinking a fair bit.

The heated swan neck adaptor really only functions after startup, and until running temp is reached.

You'll find that the intake will conduct from head anyway - enough to re introduce fuel dropout back into intake air should the need arise. Fuel dropout is only a problem if the injector is far from ports, if its cold, and if your cranking speed is low.
Unless your intake is remote water fed, ie with hoses, from hoses, Id bin that bit because if its not hose fed, then its fed from a passage in the head - watch out if gasket starts failing under closed throttle. Give it extra choke/start enrichment on the tables if your having fuel dropout. I have always found manifold heaters of any kind, from electric hedgehogs, to water, to be a pain as things start to age.

Unless your trying to save the worlds emission problems, Id batch fire all four injectors, or however many at once. When the intake valve is closed, and piston is coming up to expel exhaust, the injector will again fire into tract, or near hot intake valve back. This will promote fuel evap further and will also allow you to run injectors at lower duty cycle % as each fire is 1/2 quantity that cylinder needs for combustion, this will make idle setup easier. But still, overall cc in tiny in comparison. Look into bikes/scooters for suitable injectors that you may score for free.

To be really honest, I wouldn't think too much about it. Ive seen some shocking intake(x4 injectors) or single injector setups that work very well, surprisingly. They drove fine too. Dunno about emissions or economy though, they were all test drives.
Remember a single carb works fine on an inline 6, with prehistoric runner design...

Answer the 'what is your goal' bit first, then Ill think some more!

Brian,

 

[BrianGar]

Matt got there before me!

Brian,