EFI injector mounting "outside the box"

[KobaltBlau]

These photos of the work of Domenic Beninca's in australia got me thinking. He works mostly on ALFA stuff.

Here's a slide throttle on a 2.0L alfa four, with efi injectors mounted. Mounts are obviously fabricated (brazed):



This reminds me of the MFI injectors mounted high on RSR stacks, but it's even more like the Jerry Woods "madonna" Setup pictured in Bruce Anderson's book.

Here are a couple of photos of the same type of system set up for a V6:



Here's the idea: use MFI stacks and fabricate some mounts to mount a fuel rail like this above the stacks on each side. anybody think this is a good/bad idea? This would avoid the cost of TWMs and also perhaps be more effective. I realize that above a certain engine displacement/rpm the MFI stacks become less suitable, but I don't want to worry about that here.

[ValveFloat]

Well, it looks like TWM thinks its a good idea
http://www.twminduction.com/ThrottleBody/ThrottleBody3006.html#highmount
Sounds like something worth trying to me, as long as that fuel spray doesn't ignite in your plastic stacks.

[David]

This is good for max hp but I don't think it works too well on a street car that needs to idle well.

[KobaltBlau]

Originally posted by ValveFloat
Well, it looks like TWM thinks its a good idea
http://www.twminduction.com/ThrottleBody/ThrottleBody3006.html#highmount
Sounds like something worth trying to me, as long as that fuel spray doesn't ignite in your plastic stacks.

Nice, Joe. That's a new product, I didn't know about it.

In case anyone else has name service problems, here is the IP based link:

http://66.34.33.121/ThrottleBody/ThrottleBody3006.html#highmount

It is really interesting to see that those TWMs have the high mount injector and a low mount injector. They don't explain why (that I saw).

Originally posted by 125shifter
This is good for max hp but I don't think it works too well on a street car that needs to idle well.

Why? perhaps because the intake pulses push the column of air up at lower RPM? The standard low mount injectors would allow air to be pushed up somewhat and still not escape the stack, but the above-mount probably wouldn't behave well if pulses were going up while the injector was open ...

[KobaltBlau]

I am adding some TWM pricing for reference, this is just the basic weber-compatible throttle bodies, not the fancy ones linked to above:

3003-3038 Linkage kit for 3bbl 246.38
3003-4003/L Throttle body 3 BBL 602.25
3003-4003/R Throttle body 3 BBL 602.25
3003-4403/L Throttle body 3 BBL 602.25
3003-4403/R Throttle body 3 BBL 602.25
3003-4603/L Throttle body 3 BBL 602.25
3003-4603/R Throttle body 3 BBL 602.25
3003-4640 Manifold for 3003, 2 bolt. 465.38
3003-4642 Manifolds for 3bbl, 3 bolt 423.00
3003-4803/L Throttle body 3 BBL 651.52
3003-4803/R Throttle body 3 BBL 651.52

so here's an example shopping list, everything but the throttle bodies seems to be cheaper from PMO, assuming the linkage and air horns are compatible (I know the manifolds are):

1 pr throttle bodies from TWM, size 40, 44, or 46 $1205
ported 911 intake manifolds from PMO, pair $350
linkage kit from PMO $125
velocity stacks from PMO, set (TWMs don't come with these) $90

so that's $1770 for the base induction setup. These are "retail" prices, particularly the TWM ones. I do not have any idea how much cheaper it is possible to get these things. It may certainly be possible to find things like the linkage kit, velocity stacks (air horns), and intake manifolds used from a weber setup. That would help.

Of course, you still need engine management, but if you use MegaSquirt it ain't that much. These TWMs have MAP sensor ports. I'm not sure if they could be used with Megasquirt or if you'd have to go to Alpha-N. It seems like you could write some code to clean up the MAP output if it's all over the place due to intake pulses, and add that to the megasquirt code, if someone hasn't already done that.

[KobaltBlau]

I just noticed the velocity stack/air cleaner mounting is slightly different on the TWMs according to their website. They use 6mm studs that are 1mm farther apart than the weber. I'm not sure what size the studs on the weber are, but it seems like it ought to be possible to modify the weber horns to fit. Hopefully, since the TWM horns (full-radius) are ~$60 each.

I still don't know for sure if you can use a weber linkage.

[KobaltBlau]

Bump ... can anyone give more information on this below, or any other comments?

The below is related to the fact that TWM decided to include low mount and above trumpet mount injectors on their top kit.

Originally posted by KobaltBlau

Why? perhaps because the intake pulses push the column of air up at lower RPM? The standard low mount injectors would allow air to be pushed up somewhat and still not escape the stack, but the above-mount probably wouldn't behave well if pulses were going up while the injector was open ...

[KobaltBlau]

Here's a snippet I found in TWM's FAQs:

Q: Why are the injectors positioned in the TWM throttle bodies and not in the manifolds, like original equipment EFI systems?

A: Original equipment EFI systems are configured to meet very stringent emission regulations and to provide "soft" driveability characteristics. Positioning the injector as close to the inlet valve is beneficial in this respect. Maximum power however, is usually obtained by moving the injector away from the inlet valve, some racing engine manufacturers going as far as to mount the injector high in the velocity stack and others installing two injectors, designed to operate at different RPM. When TWM designed the throttle bodies our engineers were not in favor of having high pressure fuel on the atmosphere side of the throttle plate, although this could have resulted in some power increase. We compromised by mounting the injector as far from the cylinder head as possible while still maintaining the safety afforded by keeping the fuel downstream of the butterfly.

The question now is, why does positioning the injector close to the inlet valve improve emissions and "soft" driveability characteristics? Let's assume everything is under the throttle plate.

This seems like a fuel distribution issue: with the injector low, atomization isn't as good, but the fuel can be easily timed to get into the cylinder and not sit on top of the intake valve.

Certainly when the injector is higher, the fuel has more time to atomize. This is good. But perhaps when the injector is higher, the distance or intake pulses make it difficult to ensure that the fuel is injected at the right time for the intake cycle ... ?

I know I'm missing something here, can anyone clarify?

Thanks in advance.

[David]

I thought I recalled an idle problem due to the injector being on above the butterfly, but maybe it was a safety issue with being above the butterfly. On our 3-rotor Sprite AutoX car, we run an injector above and below the slide valve.

[KobaltBlau]

did you use the above-slide injector just at higher RPM? was that the purpose of it?

Thanks David,

[David]

The second injector does come in at higher RPM, but I didn't do the programming so I don't remember when it comes in. Since the 3-rotor only has 6 injectors, this wasn't hard to do. For a 911 to run 12 staged injectors, they would have to run in batch mode. It's my understanding that it's better to run 6 injectors with sequential mode which is what I'm doing on my 930.

We ran staged injectors so we could run the 3 stock injectors and 3 new low flow injectors to get the fuel we needed to make 400+ hp.

I haven't purchased the injectors for my conversion yet, but I expect they will be about $100 each due to the 55 lb/hr flow rate.

[KobaltBlau]

Ah, OK david. so the need for 6 injectors probably took precedent over the desire to mount 1 injector high and 1 injector low.

still wondering this, though:

Originally posted by KobaltBlau
The question now is, why does positioning the injector close to the inlet valve improve emissions and "soft" driveability characteristics? Let's assume everything is under the throttle plate.

[KobaltBlau]

bump

[David]

This excerpt is from A. Graham Bell's "Forced Induction Performance Tuning". It's a great book as are his other books like "4-Stroke Performance Tuning" and "2-Stroke Performance Tuning". Now that I've given him a shameless plug so he doesn't sue me, here's the piece on injector location:

[David]

Here's more (it wouldn't take in the last post and I had to resize them?):