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DIY Fuel injection thread.


yoeddynz

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Will be fine pre throttle I think but I would run sequential with a big enough injector you can get all your fuel in within the intake valve event. Transient fueling with wall wetting/pooling issues might be a bit more varied when cold. Still gonna be a ton better than a SU carb haha.

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2 hours ago, scooters said:

Been thinking.. 

You can do it pre throttle. 

I still think you will tear you hair out trying to tune it. 

like this but without the fire risk . 

 

 

227QE0L.jpg

Setups like that often run two sets of injectors, or they simply don't give a shit about low rpm drivability so still not suited for a road car

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So I tinkered with having outboard injectors, about 3/4 of the way up the runner. 

And its an absolute shit of a thing, because of wall wetting like BobbyBreeze says.

You are wetting this absolutely massive area of the intake runners with fuel, and some of that fuel takes time to evaporate and end up back in the air/fuel mix and into the engine. 

So for a real life example of why this sucks. 

Lets say you tune your car in 4th gear, at the rate of accelleration you are going. Some of the fuel that you spray in at 4000rpm doesnt get into the engine until you're doing say 4250rpm. 

So if you get all of your air fuel ratios correct, it only suits that one rate of accelleration because you are actually tuning "Ahead" slightly. 

So now when you are in 2nd gear, your air fuel ratios are now a mess because the fuel you spray in at 4000rpm, ends up in the engine at 5000rpm. (or whatever) 

And the transient throttle is just shit.

It will work okay if you keep your entire intake manifold as hot as possible to minimise wall wetting, mine was insulated from the head so stayed quite cool. 

But I found it was more of a headache than it was worth so just went back to normal port injection and my throttle response was night and day difference. 

I was using 8 injectors total so I could blend between them as desired but found it still wasnt really worth it even just for full load high rpm.

Other people have tried the same with greater success so perhaps it was my choice of injector, or the angle, or whatever. But yeah it sucked.

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On 01/09/2018 at 11:07, mjrstar said:

Anywhere that has potential to pool fuel is total poison to tune. I had an encounter with a supercharged pinto which was injected pre supercharger.

Could tune it fine on song and at idle but the transition off idle when it gulped the pooling fuel was a disaster and the idea eventually was scrapped. 

Get those injectors as close to the head as possible...

the runners are pretty short. -6cyl datsun

On 01/09/2018 at 11:13, scooters said:

@fletch  Best bet is after that throttle blade bud.

 

The fuel is just going to hit that blade at idle and cause you endless drama. 

 

although I can see what your trying to do (hide the injector) Most other set ups are after the throttle for good reason.

its got to be better than a SU carb right? at idle the fuel already dribbles past the throttle plate

On 02/09/2018 at 08:45, yoeddynz said:

@fletch You could point the injectors up from underneath after TB so then hidden? (but if this is going into a trumpet?  then its a no go unless one wanted a melted mess of injector all over exhaust manifold..)

i hope to turbo it so much heat, there is a ton of room in the top of the hat to put the injectors. putting them up from below would work too, but would lose the carb heat circuit

 

On 02/09/2018 at 11:30, BobbyBreeze said:

Will be fine pre throttle I think but I would run sequential with a big enough injector you can get all your fuel in within the intake valve event. Transient fueling with wall wetting/pooling issues might be a bit more varied when cold. Still gonna be a ton better than a SU carb haha.

i am fitting 2x 550cc ev14 short injectors into each carb. there is a good heat circuit through the carb floor, and intake floor.

 

 

here is a diagram of some filthy U.S TBI carb, im doing the same thing but sideways.

315423558_caddytbi.jpg.f350e3c3c43419657779f82f908ec8c1.jpg

 

heres a kit for a similar carb

CarbAdapters.jpg.4f2b342da462d1a8e0c4ada84df92fc4.jpgCarbsNeedInjector.jpg.060c60be4a5120aee3b7d6237af3852b.jpg

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If you don't have an engine that is going to be revving up at 1,000,000 rpm per second then you should be fine. As you say it isn't really any different to how a carb does it. Just make it do like 4 squirts per cycle or something instead of 1 or 2 squirts per cycle. That will reduce the wall wetting and pooling.

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firing injectors into a hot port set up helps vaporize the fuel without question.

Firing A injector into a throttle plate is not ideal. Having said that....just make sure its sequential to get the best posible outcome. 

again you would never know the difference between batch and sequential injection  at 4500 rpm 

its just the low end and idle quality is better. 

Remember a common missoma is that sequential injection is tied to valve timing and fire when the valve is ope or about to open.

Lets say your injectors are at 85% duty way the fuck up in the load cells.. well a lot of that fuel will be sprayed while the valve is shut anyway. 

@fletch

 

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19 hours ago, scooters said:

Remember a common missoma is that sequential injection is tied to valve timing and fire when the valve is ope or about to open.

Lets say your injectors are at 85% duty way the fuck up in the load cells.. well a lot of that fuel will be sprayed while the valve is shut anyway. 

I agree however the further you have the injector from the head, as is being propositioned. The more relevant injector timing becomes because you have inlet harmonics trying to push fuel back out top of the runners. Which doesnt really matter when the injector is right by the valves, but a very big problem if they arent.

I have found that on a cold start the engine will start waayyyy nicer when you use an injector timing that sprays when the valve is open, in order to minimize wall wetting. As it takes so bloody long to evaporate when engine is cold.
A friend of mine tried the same thing with E85 which is notoriously awful for cold start and found massive improvements.

The recent idling improvements that AJG193 recently found by going to 2 squirts per cycle is basically a crude way of circumventing the problems of batch injection's asymmetrical injector timing.

If you have your engine idling and slowly advance through the injection timing range it makes such a difference it can either make your engine rev a lot higher or make it stall. As the combustion quality changes so much.

When I tried having a fuel map using 100% staged outer injectors (even though fully sequential) it was an absolute shit show for idle and transient conditions, even after a lot of time trying to optimize it.

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1 hour ago, Roman said:

I agree however the further you have the injector from the head, as is being propositioned. The more relevant injector timing becomes because you have inlet harmonics trying to push fuel back out top of the runners. Which doesnt really matter when the injector is right by the valves, but a very big problem if they arent.

I have found that on a cold start the engine will start waayyyy nicer when you use an injector timing that sprays when the valve is open, in order to minimize wall wetting. As it takes so bloody long to evaporate when engine is cold.
A friend of mine tried the same thing with E85 which is notoriously awful for cold start and found massive improvements.

The recent idling improvements that AJG193 recently found by going to 2 squirts per cycle is basically a crude way of circumventing the problems of batch injection's asymmetrical injector timing.

If you have your engine idling and slowly advance through the injection timing range it makes such a difference it can either make your engine rev a lot higher or make it stall. As the combustion quality changes so much.

When I tried having a fuel map using 100% staged outer injectors (even though fully sequential) it was an absolute shit show for idle and transient conditions, even after a lot of time trying to optimize it.

Wasn't me that found that. I've been running 2 squirt since day 1. Tried one squirt for a minute once and instantly regretted it. I think 4 squirt would get me too far into nonlinear range at idle.

 

edit: actually went 2 squirt in December, it was the simultaneous thing that I only tried once 

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4 shots per cycle make much more sense to me since with only two shots, one injector per batch will be firing say on valve opening event, while the other will fire with the valve closed 360° out. With 4 shots you'll be firing half and half, meaning each cylinder will see the exact same fuel conditions.

Just make sure you adjust your req_fuek to suit or you will be running twice as much juice and mess everything up.

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