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!

 

[PEW]

Brian, this is a link to a photo of the manifold:

And the original (which was found to be restricting overall airflow):

 

[PEW]

Brian, yes your photo shows a Reliant manifold, albeit for a 750, rather than the 850.

Those manifolds have 21mm diameter runners, too restrictive for my engine (the runners are much smaller in diameter than the ports in the head so we stopped using that type some years ago). It would actually be very difficult to fit injectors, as they would all have to face in different directions. A fuel rail would be very difficult to align.

Also, the 4 branch exhaust now fitted to my car means that manifold can no longer fit my engine because the length of the side branches is too short to reach the head. The original cast iron Reliant exhaust manifold is very small too and of very poor design. It went in the bin a decade ago and there is absolutely no prospect of me fitting that so I can also fit a more restrictive inlet, too.

This is the main reason I wanted to use the existing inlet manifold, which is wider across the side branches, so the two pairs of injectors can sit alongside and be parallel to each other.

I'm now going back to the idea of a larger, single injector in a single 38mm diameter Jenvey throttle body, retaining all the existing manifoldery. Effectively this would just replace the existing carb. Having downloaded drawings of the Jenvey item, I've now got as far as designing an adapter plate so it will fit straight on to the heated swan neck. The plate will also locate the outer throttle cable.

I'll forgo the long individual inlet runners for what should be excellent fuel /air mixing, i.e. same set up as with the existing carburettor. It will also make a very simple, uncluttered, installation and look pretty good good under the bonnet.

 

[BrianGar]

All Id be worried about is that the large runner cross-section would hinder airspeed at lower rpm, thus hurting torque.

Brian,

 

[PEW]

Brian, that doesn't seem to be a big problem in this instance; we've done well in trials with this manifold fitted, using the present SU carburettor (we won a class awards last time out and came second in the whole trial).

 

[potteryshard]

Have you looked at the GM TBI? This is a throttle-body injection complete in one package which contains two injectors located immediately atop the throttle plates, fuel pressure regulator, throttle position sensor, and an idle air control motor and valve. Old technology, but millions made, readily available, and quite reliable and simple. Injector location atop the throttle plates is intended so that at small throttle openings, the air shears around the edges, and so allegedly mixes better than if squirting into the interior of the manifold.

 

[PEW]

potteryshard,

Thanks, and no I've never seen a GM TBI in UK. I've now looked these up online and it seems the smallest unit made was for 2.8 to 3.1 litre engines, is this correct? My engine is just 850 cc and therefore I think one of the GM units will be unsuitably large, in respect of intake gas speed and low throttle opening controllability, which is often important for a trials car (we need to carefully control the engine power output to avoid wheelspin, especially on section starts/restarts).

However, I have considered other smaller single point injectors available here, from the previous generation of smaller cars (Fiat, Ford, Suzuki etc). I don't know if they are tunable and from experience I know the Ford ones are unreliable with age.

Thanks again to all, this is a really interesting topic for me (even if for no-one else).

 

[patprimmer]

I think around 1988 a Vauxhall Cavalier had a throttle body injection unit as an option. Certainly the Aussie version did in 1.8 EFI "unleaded fuel" format.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[PEW]

Thanks Pat. Not many of those old buses around these days.

I've just bitten the bullet and bought a set of three throttle bodies from a '99 Triumph Speed Triple 955i, a cheap Ebay deal at just over £50 delivered, injectors, fuel rail, TPS, linkage all included. I reckon about a sixth of the cost of a new Jenvey setup?

This bike uses three completely independent 42mm throttle bodies with injectors, linked together by simple pressed steel rails, so they can be very easily dismantled. These are unlike most other bike setups I've considered, which seem to be made to operate as a unit.

The "master" one houses both the throttle linkage and the TPS, so I intend to use just that one on the original manifold system and see how I go with it.

I'll need to modify the fuel rail, but this looks easy enough as it's billet alloy with a screwed plug in each end. I can shorten it then re-drill and tap the "new" end to close it off, using the original plug. I think I may need a slightly larger flow injector but that will need further research before final setup is done.

A long way to go yet but I'm looking forward to the challenge of making this work.

I'll report back at some stage. Thanks again for all contributions here; just realised how many there have been.

 

[BrianGar]

'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'

Where theres a will theres a way I guess...;

B,

 

[PEW]

Brian, the normal motorcycle injection setup is for a throttle body for each cylinder; usually fitted via a short spigoted adapter, in close proximity to the cylinder head face.

What I meant was that that type of setup can't be done on this small, non-crossflow engine (I don't know of any non-crossflow, fuel injected motorcycles).

The proposed setup is to use a single motorcycle throttle body on the existing carb manifold and heated swan neck adapter, which keeps the TB well away from the cylinder head and the heat of the exhaust manifold. The single throttle body will replace the existing SU type carburettor.

 

[BrianGar]

I see, I hope you see gains then. I really feel the manifold, and airspeeds still could be the holdbacks - but I hope Im wrong.

Ive designed and cast a lot of custom manifolds for different setups, Its amazing what you can fit in a space if its tailor made. See how the single tb fairs I guess, It sounds a pretty simple, and cost free swap should it not show gains so go for it,what have you to loose!

Brian,

 

[PEW]

Brian,

If this doesn't work out I'm considering an engine swap for the only other engine that will easily fit in our tiny car's engine bay.

This is the Suzuki G10A, coupled to a Suzuki Jeep 5 speed gearbox (this little front wheel drive engine rather surprisingly bolts straight on to the 4wd jeep gearbox). This conversion is now being supported by the designer of the car, Peter Davis, who has come out of apparent semi-retirement (at least as production of car kits is concerned), to help owners who have struggled to get the Reliant engine to perform sufficiently well.

I've just realised an unintended bonus of buying the Triumph triple throttle body setup: The Suzuki G10A is a relatively modern, three cylinder, crossflow ported, 1 litre engine. It uses a single point injector in standard form and produces just 52 bhp. The Triumph triple bike setup might well bolt on to it very easily and release quite a bit more output.

 

[dgallup]

Let me get this right. You are going to use just one of the Triumph multipoint throttle bodies and injectors in a single point setup? I don't see this giving decent fuel distribution and atomization at all. As noted above, single point injection systems normally inject above the throttle plate. The injectors typically have a wide cone spray that impinges the throttle plate and at small openings the air/fuel flow through the gap promotes evaporation and mixing. We made the injectors for that 99 Speedy, it does not have a wide cone spray.

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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]

Surely the fuel atomisation can't be any worse than with the original SU carb on the same manifold. The fuel spray will travel through the coolant heated plenum before entering the inlet manifold proper, which also picks up exhaust heat.

I'm not committed to using the Triumph injector, it may actually not be big enough in flow capacity, so a change might be required in any case.

When you said "we made the injectors", may I respectfully ask who "we" is?

Thanks, Paul.

 

[dgallup]

I've been in the same plant for 27 years. The ownership has changed so many times I've lost count. We were SAGEM back when those injectors were made.

It's not just droplet size. Cone angle and targeting are all wrong for single point application. You can change the injector but you can't fix the targeting. I still think you would have fewer problems with individual port injectors.

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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,

Thanks for the advice, much appreciated and I can understand what you are saying. However, I can't fit single port injectors for practical reasons already explained. In an ideal world I would do so, that was my original idea put forward here.

The inlet tract on my setup is 13 inches from injector output face to the ports, all of it heated. The Triumph injector will actually fire directly at the hottest part of the heated swan neck (toward the outside wall of the upper downward bend where the coolant input joins it, i.e. the "back of the swan's throat"), which will hopefully provide sufficient fuel vapourisation.

The SU carb worked well for many thousands of these little engines, using the (same) swan neck on a similar manifold but with an inner dividing wall to give as long a runner as would fit in the engine bay. This made the flow division occur less than half that distance from the ports. One engine tuner found a "glitch" (quite severe charge robbing) when the heated swan-necked plenum was removed to fit a Weber downdraught carb for his racing series (Rebel Racers). Two cylinders (one in each pair) ran weak. Removing the inner wall in the manifold cured the problem.

I used this setup for some time but found another, hot starting problem instead. I've gone back to the SU type carb on a purpose built, wider bore manifold. The plugs run very evenly coloured using this setup so it appears the swan neck is heated for good reason.

I've been in touch with Jenvey, who make high quality throttle bodies. They make single point throttle bodies not dissimlar to the Triumph type. I was going to fit one until I found the Triumph setup at far lower cost.

Jenvey said they thought a single point setup should work well. Obviously, the proof of the pudding is in the eating! This is experimental stuff after all. If the single point injection doesn't work out, I can always think again. I regard the main bulk of the project to be in fitting the electronics and associated other stuff, sensors etc to make it all work. Both Megasquirt/Microsquirt or Canems can control either application.

If this project gets completed, I'll post the results here, either good or bad.

 

[BrianGar]

I cant understand how there is room for the oem manifold, but not for ITBs? Lets say for one second you were to cast, or tig, or whatever a new, or refab the existing one, surely you could incorporate an injector to each runner? And just mount the aircleaner/Throttle plate where the carb goes c/w electronic pot on the side?

You could also mount butterfly's in the oem manifold after the injectors and before port/head face. Much like the Toyotas variable intake butterfly's near valves.
Surely this is possible and you could even use parts from the V.runner Toyota manifold?

I feel when you gutted the divides out of the ports, it was possibly better fuel/air mix you were getting, and not more air. The total twin port/runner cross section now seems insane for such a small engine.

Brian,

 

[BrianGar]

I forgot to add, I realise Toyotas butterfly's are for inlet tract geometry change and not for throttle control, but you get the idea.

Brian,

 

[PEW]

Brian, I've never heard of a Toyota "v.runner". A Google search of that expression brings up only "4 Runner" on the USA Toyota website but that's a large 4 x 4 and I'm in UK anyway. I presume you mean something else.

The problem with space/size is two fold. Again, I'd like to emphasise that this is a tiny 850cc, non-crossflow engine. The total head face is just 13" long, shorter than the head width on my Honda CB750. There are eight ports on the same side. The Reliant OE manifold is only 8.75" long and about three and a half inches from front to back. Each of the two mounting flanges, where it bolts to the head, containing two inlet runners, is just over two inches wide. The original fit for both the Reliant (and the Liege) has a single 1.25" SU carb sitting above the rocker cover (I mean right above it).

The standard inlet ports are only 21mm wide. I've done extensive research and no-one makes a small capacity four cylinder motorcycle with ideally small individual throttle bodies - at least not for the UK market. I bought a set of four TBs from a modern (small by UK standards) 650 Kawasaki for a look see; the TB unit is larger than the cylinder head itself and the outlets are 42mm in diameter, twice that of the inlet ports.

Apart from very limited physical space on the engine itself, the engine bay is very narrow. Fitting stuff alongside the engine means I can't access the battery, which sits alongside the engine, or the alternator drive belt adjustment. I had twin SUs on the car to begin with but it proved totally impractical and I had to remove them. It was almost half a day's work to check and top up the battery level or to adjust the fanbelt tension.

Obviously, anything is possible if enough money is thrown at it. Unfortunately I cannot justify production of a new, one-off manifold casting.

Regards, Paul.

 

[BrianGar]

v = variable.

If you are to swap over to efi, and want to see gains, then I dont think there is much point in doing so unless you get serious about the manifold.
Generally, well In my eyes, power would come first, adjusting ancillary(s) would be far down the list.

Look into tig welding something new of you cant afford casting. Where theres a will, theres a way.

Brian,