Hi guys, I'm new to turbos and efi but have a question I'm hoping someone can help me with. I'm building a 56 Chev gasser with a BBC and twin turbos, I want to use one of my tunnel Rams on it and convert it to efi. I want the tunnel because they look cooler and bit more like a gasser than single plane would.
i know most times the injector is placed pointing towards the valve, but am I able to run them up the top where my finger is pointing? ( hopefully pics work). I'm looking for some where between 700 and 800hp at the crank.
i have read the old posts where it says the injector being to high ruins idle and power under 1800rpm, but also that having the injector facing air flow could increase better distribution of fuel.
Like I say this is new to me, but if the engine is boosted wouldn't the fuel be forced down the runners no matter where the injector was placed? And how does a carb supply enough fuel to run low rpm on a tunnel ram if it's squirting small amounts from the top.
thank you for any help.
Jason

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Hello Jason!

Well, I won't say that it will not work, but I do have a few questions on the position.

Will the injector be mounted perpendicular to the center line of the inlet hole? So, will it look like your picture with your finger?

How far into the air stream will it penetrate?


I would imagine that spaying from parallel (or near parallel, i.e. >=30 degrees) with the air flow, in the center of the inlet would be the best way to go. But I've not done much research on it exactly.

I set up an injection system on a V8 with ITB's and had them set up to spray in the downstream direction offset from the centerline so that fuel wouldn't puddle on the throttle blades. Car ran well, but that's mostly anecdotal buttdyno sort of analysis. HAHA

 

Hi Vr4drive92, thankyou for your reply. Like I say I don't know much about efi, but yes I would position the injectors like my finger. 90 degrees to flow I guess you would say, also they would be above each runner .
I'm not sure how far into plenum area they would need to be but that's not hard to do if this position would work.
This will mainly be a street car, with few trips to the track a year.
Thanks
Jason

 

Nope. Imagine your tunnel ram functioning exactly like it does on a naturally aspirated engine, but with much denser air.

Depositing fuel on the manifold walls (wall wetting) is a big consideration here and personally, I would avoid placing the injectors perpendicular to the airflow as proposed. Pointing them down the ports would be an improvement and placing them down by the head like a production EFI intake would be better still. I would not point the injectors upstream. The thing is, air flow in each port is pulsed, not constant. Unless the EFI system can do sequential injection at the specific point in each cycle when the port can pull the fuel in, then there's a strong possibility of simply shooting fuel up or out of the port otherwise. Also related is the topic of injector spray pattern. A fan spray mounted up high is going to increase wall wetting, but might suspend more fuel in the air quicker. A pencil stream with good aim might get fuel down the port sooner. This is all speculation on my part; I'm only trying to introduce concepts and considerations.

The wall wetting issue is also going to directly affect your acceleration enrichment ("pump shot") settings much like a carb. Putting the injectors close to the head/valve will allow the tunnel ram to function like a modern "dry" EFI intake with the benefits of long runners and a large plenum (better driveability). Not sure if that matters for your application.

One modification-free option is to get a pair of aftermarket 4bbl TBI throttle bodies.

 

Hi 65ShelbyClone,
Thank you for your reply, what you said makes sense to me and I can see it would have been the wrong choice. I watched the video clip of the tunnel ram with a perspex plenum and runner and like you said the pulses were pushing up and down the runner.
I ended up putting the injector bungs in the bottom, but because of the style of bung I had to put them in at around 80* instead of straight up. I'm guessing this isn't perfect but hopefully will still work fine.
I am going to make an aluminium plenum to bolt on top and have bought 2 75mm Mustang throttle bodies that I will run facing forward. I was going to use a 90mm throttle body but the CFM of two Mustang ones added together came to about the same as a 90mm and they were cheaper.
Any thoughts on stacking them on top of each other rather than side by side? I thought I might help provide better air distribution inside the plenum with the help of a divider.
Thanks
Jason

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I agree that your final position was probably the right one.

At one time, some racers I know and talk to occasionally installed two sets of injectors (for a lot of Horsepower) one position was where yours is and the other position was on the opposite side of the runner also pointing downward.

They did install 4 Injectors backward to help with cooling the boosted air some distance before the throttle body. Methanol engine.

20 Injectors total. Picture attached

Tom V.

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dual mechanical injectors
methanol
same manifold you have

- - - Updated - - -

Hi Tom,
Travis has removed those 4 injectors

ash

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Just recently saw a youtube a video where a well know turbo engine builder designed a custom high rise intake and had two sets of injectors running down the middle underneath. Very trick.

 

Agree ASH, he also cut out and welded up the injector bosses near the roof of the intake (YEARS AGO) when he tried to spray methanol across the plenum. Lots of changes to that inkae over the years vs the very early picture. Tom V.

 

Is wall wetting the issue with having fuel sprayed against the air stream and/or further upstream by the plenum roof or throttle body?

 

Wow, a 6 year old thread! Its never too late to learn something, right?

Good question. I'm interested in that too. One advantage of injector placement as far away from the valve as posible is the fuel has a longer time to vaporize. However, is that defeated by other issues that net a loss in power?

 

Wall wetting is always an issue. Looking at modern OE they are spraying the back of the intake valve, using a pattern that closely matches the valves. This gives fuel the best chance of getting into the cylinder. Even though it is a known problem it can be calculated and compensated for. OEM tunes have a feature called transient fuel, which accounts for fuel that will be stuck to the walls when demand starts, and fuel that remains stuck to the walls after demand ends.

I have seen some high level race engines that put injectors far up the runners to aid in charge cooling, but I think they may be methanol guys.

 

Not clear on what you are saying Ben.

On a carbed system you move the throttle quickly and the fuel in the plenum is sucked off the walls of the plenum. So the Accelerator Pump replaces that fuel so you do not have a "lean miss" in the engine.

Same deal happens with EFI but typically the injectors are closer to the intake valve so you can fill in that lean spot when the extra fuel is along with that extra air.

But the EFI engines still have some runner and plenum wall wetting as the engine ALWAYS has a reversion pulse back toward the atmosphere.

Under steady speed conditions, I had video (camera inside the intake) that showed that some runners have
flow streams of fuel to given runners at varied RPM points, especially with Charge-Air Intercoolers mounted near to the intake runners.

Tom V.

 

I think we are saying the same thing. I am calling it transient fuel in EFI, you are calling it accel pump shot. Although, they aren't exactly the same: the transient feature only accounts for runner wetting/drying, the instantaneous demand is carried out via throttle position airflow modeling, delayed via manifold volume.

This is 2 generations ago Ford systems. I haven't messed with any of the direct injection stuff.

 

That film would be nice to see, Tom.

Are you suggesting its best to place the intercooler away from the intake ports if possible?

 

Film was made in Ford Research to solve a distribution issue in the intake manifold.
I have not worked for Ford Research for 6-1/2 years. Also it was their property.
So nice to see but impossible to accomplish.

Tom V.

 

Filming inside an intake is something I have always wanted to do. Is it possile you could give some ideas on how to do it without disclosing any Ford IP? Equipment, smoke, lighting, frame speed, anything . . . ?

 

1) Small LED light mounted inside the intake up high from the floor of the intake on one corner, opposite from the Throttle Body location on the intake.

2) Small "spy" camera (like the scum bags use to film women's dressing rooms).
No clue where to get the thing but one of the workers was into filming small animals entering a
box trap so that they could be relocated in a different location in the swamp in Florida.
He had a source which we used for the testing.

Tom V.

 

Thanks, Tom
I goggled "scum bag camera" but didn't come up with much. LOL, but have some other ideas.

 

Why not a bore scope?