"Wet manifold" injector placement
Turbo Mini Forums

Afternoon all!
So I've got my beast running on the carb (I wanted to run in the cam / rings etc on a known working carb before fitting an injection system.

So - I've bought an alloy MGF 48mm throttle body, which has the advantage of a TPS and idle air bypass all for £16!

Next I need to figure out injector placement and which injectors to use.

I don't want to have to faf about with a cam sensor at the moment so think its best to run this as a wet manifold.

Is there any disadvantage to having the injector(s) BEFORE the throttle body? I understand that this will also help with atomisation.

Next, which injectors?
I am aiming for around 150-170 bhp, I have used a couple of online injector calculators and they state that im going to need something like 2x 650cc injectors, or maybe 1 frickin' mahoosive 1200cc?

Edited by Turbonator on 6th Nov, 2016.

"If its not broke, whack a turbo on it"

https://www.youtube.com/c/turbominitv

Personally I don't think it will work well at all with injectors before the throttle plate, especially at small throttle opennings.

If you look at the Specialist Components setup - which is probably the best "off the shelf" wet manifold setup - they have a pair of injectors after the throttle body.

And as you will just be running batch injection (no cam sensor and no point in sequential anyway on a wet manifold) the duty cycle can be as high as 85% so you should be able to use a smaller capacity than you have suggested. Which online calculator did you use ?
The one I have bookmarked says a pair of 440cc/min would be good for 180BHP at 80% duty cycle.
440cc/min just happens to be the MPI injector size, the difference in maximum power being that the MPI ran them in a sequential mode of port injection that would have severely limited their duty cycle.

The main consideration in choice (apart from size) is low z or high z.
Assuming this is going to be driven by Megasquirt (as you have implied in previous questions) is it fully built with low z capability ? (if you built it yourself you will know what I mean, if it was pre-assembled you should have had the option to specify whether the low z parts were installed).
Personally I prefer low z but I'm pretty much in the minority, most modern stuff is high z.

Schrödinger's cat - so which one am I ???

Morning Rod - thanks for your detailed reply, as always!
The injector location was something I've been thinking over and after certainly seems to be the best best, but not too close to the ports as the mixing wont be thorough - I'll have to figure out where to mount the injectors on the body i have coming (or buy a jenvey twin injector throttle body)

I assume im gong to want to run as many "squirts per cycle" as possible.

I'm running a Microsquirt V3, which I think wants high impedance injectors.
It has 2 injector channels, so guess it would be firing a sort of off-set batch (one then the other)??

"If its not broke, whack a turbo on it"

https://www.youtube.com/c/turbominitv

Sorry, forgot it was a microsquirt, they only do high z unless you add some sort of external driver board.
But high z seem to be most common now anyway.
For batch with any of the MS range I expect four squirts per cycle would be the best compromise on an A Series wet manifold. I'm not sure at what crank angle they would open in an un-timed (non-sequential) mode but at least it would be the same for each cylinder so charge robbing should be little worse than a carb, at least at high duty cycles.

Setting it to 8 per cycle "might" improve the mixing/atomisation but it's a trade off vs injector dead time compared to the duty cycle.

So far as I'm aware, if you set "Injector Staging" to simultaneous both chanels fire at once so you can just put one injector per chanel (assuming you use two injectors) and reduce the load on the driver FETs. If you set it to alternating (one then the other) without any phase reference (cam sensor) it would be random at start-up which one goes first so you may get some strange effects on whether cylinders 1 & 2 are preffered over 3 & 4.

But, I must stress, I've never tried this because I do port injection with the siamese code and, strange though it may seem, I find that a lot easier to understand.

Schrödinger's cat - so which one am I ???

Perhaps you could machine some injector bosses if you have a lathe and have them TIG'd into the the throttle body after the throttle plate. Or buy some secondhand injectors on ebay of suitable rating with a manifold, then cut it up for the bosses

While Rod is right that there might be some difference due to the random injector timing at each start up, I'm not sure that it will be significant if the injectors are close together and they are not intentionally aimed at a different specific intake port.

What will likely make a significant difference is the number of injection pulses per cycle for each injector. Using 4 squirts/alternating instead of simultaneous will mean that each injector only goes through 2 opening sequences per engine cycle instead of 4. That will result in larger (and more linear) pulses which will be more easily controlled and tuned.

This will give you a much larger dynamic range since this is effectively a staged injection setup without the hassle of tuning its activation parameters. That's because the alternating pulses can overlap so you will still have the full capacity of both injectors. This also has the advantage of providing a continuous fuel delivery as soon as you reach 50% duty cycle which should help fuel distribution.

I should add that you could remove any randomness on the injection timing by simply using semi-sequential injection. This way you will always get the same injection sequence. However, you still could get a fueling distribution difference due to injector placement and aim.

Jean

http://www.jbperf.com/

Thanks guys - That sounds very sensible Jean.
My intention is to run the standard "T" / "Log" style metro turbo induction manifold, and replace the carb with the new throttle body and injectors.
I'll need to make up some sort of intermediate piece to go between the manifold and TB with the injectors in. This should mean there is no "Aim" issues as the flow is split 50/50 as per the carb setup. So my aim is to get the most consistent mixture.

I COULD bring the injectors further away from the manifold too (and also the TB)

I'll do some plans of what I envisage and post them here in a bit.

Now for injectors...
The obvious choice appears to be 2x Bosch "Green Giant" 440CC injectors (12 ohm) 0 280 155 968

"If its not broke, whack a turbo on it"

https://www.youtube.com/c/turbominitv

Afternoon all!
Well I've been very busy with work so the injection has been on hold since my last message.

Anyway - this weekend I expect to be making the injection manifold, all the parts have arrived (stainless bends, AN6 fuel rail ends etc etc)
It will take some making as its 100% stainless, I don't have an AC TIG so cant weld aluminium at the moment.

MGF throttle body connected to 2x 2" 90-deg bends (sounds odd, but with good reason!)
2x Bosch "Green giant" 460cc injectors side-by-side spraying into the mouth of the standard metro turbo "log" intake manifold where the carb used to attach. I hope this should lead to a fairly homogeneous mixture at the valves.

Edited by Turbonator on 3rd Mar, 2017.

"If its not broke, whack a turbo on it"

https://www.youtube.com/c/turbominitv

Sorted!: http://www.turbominis.co.uk/forums/index.php?p=vt&tid=606484

Edited by Turbonator on 10th Mar, 2017.

"If its not broke, whack a turbo on it"

https://www.youtube.com/c/turbominitv

Update:
It works!!!!!!!

sort of.

"If its not broke, whack a turbo on it"

https://www.youtube.com/c/turbominitv

I have been cruising the site looking for an alternative to my throttle body injection that I am running now, & came across yours. The last post "It works" sort of...

What happened after this??

Cheers! Jason