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March 2021
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  #1 (permalink)  
Old 01-23-2021, 10:14 AM
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Default EFI 8 Stack injector alignment squiggily tolerance?

As I continue to assemble, modify and redesign my 8 stack injection system (pics to follow later) I have a question about the injector alignment tolerance specs.

In other words, how perfectly aligned do the injectors have to be between the machined bosses in the throttle body and the machined bosses in the fuel rails?

The injector o-rings tight as they are in the machined bosses, are still a little squiggily.

I would like the fuel rails to be closer together, esthetics and packaging, which would put the injector boss in the throttle body about 1/4" off center relative to the injector boss in the fuel rails.

It doesn't seem like a lot and as I pore over various pics and installations of 8 stack systems here on this forum it seems (maybe camera lens parrallex) that the injectors on some are slightly canted (misaligned) between the bosses in the throttle bodies and the bosses in the fuel rail.

Any thoughts or expertise on this?????

Thanks for your help.

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Greg
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  #2 (permalink)  
Old 01-23-2021, 10:46 AM
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Not sure what you are saying but as long as you keep the nozzle centered it the hole it shouldn't matter. Just my thoughts.
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  #3 (permalink)  
Old 01-23-2021, 01:21 PM
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Hi hauss. The right and left banks of throttle bodies ar canted inward towards the centerline of the engine (CL fore and aft).

The fuel rails, with the injectors bottomed out in the throttle bodies and snug in the fuel rails above, have about a 1/2 inch gap between them. I would like to close that gap to zero. That would slant the injectors slightly in their machined bosses in the throttle bodies and the fuel rails.

The injectors are still bottomed out and snug, just canted a little.

Maybe the injector o-rings are meant to have a little give in them (to allow for expansion/contraction) and they are a little squiggly (they move around quite a bit even when bottomed out in their machined throttle body and fuel rail bosses).

A problem? I'm just wondering.

Cheers
Greg
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  #4 (permalink)  
Old 01-23-2021, 04:11 PM
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Yes, they are a little "loose" when installed. You will be able to rotate them, and move them around a little bit. As long as the two o-rings are fully seated, it won't leak.

The angle of the injector is kinda important. You want the injector to point directly at the intake valve. If it's too far off line, you'll be squirting fuel onto the walls of the port. And that's a bad thing.
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Old 01-23-2021, 04:13 PM
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Personally I wouldn't lean the injectors in the bore hole of the intake manifold for an esthetics improvement. Having some of the the atomized fuel recombined into a liquid by it ricocheting of the port wall will def cause a power loss and probably incomplete combustion.

Even if that does not occur the injector resting against the port hole edge will chaff into the injector housing when the engine is running.

Just my 0.02
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  #6 (permalink)  
Old 01-24-2021, 11:47 AM
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Thanks guys. I'll check out your suggestions/observations and let you know where I end up.

Cheers
Greg
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  #7 (permalink)  
Old 01-24-2021, 01:47 PM
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Hi guys. I stuck a 7/16 inch brass tube down through the machined injector boss in the throttle body and wiggled it around (the same amount of wiggling the injector seems to have) and the brass tube still has a very good direct shot at the intake pot/intake valve.

see pic.

And I have a little bit of port matching to do!

Looks like I may be OK.

Cheers
Greg
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Old 01-24-2021, 03:53 PM
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Perfect! I would leave that alone.
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Old 01-24-2021, 06:18 PM
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Bob's comment about proper alignment of the injector shot is a big deal for tuning but an even bigger deal is fuel leaks. When you cant injectors you compress the upper and lower o-rings more on one side than they was designed to be and not as much on the opposite side as they were designed to be.

There was a big name fuel rail supplier that unintentionally manufactured their fuel rails producing this same effect. Target zone for the injected shot not withstanding, the fuel leak that developed as the o-rings aged, flooding the top of the engine with gasoline was impressive. When the puddle got to the headers course you can guess what happened next.

Try to keep your injectors centered in both the manifold bore and also the fuel rail. With FI base fuel pressures in the 3BAR (43.5 psi) area you can get an impressive puddle of gasoline on top of a running motor very quickly. The ending is usually an unhappy experience.


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Old 01-24-2021, 07:12 PM
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Any o-ring fitting needs to be on the same axis as the bore it goes into.
ALL injectors in any vehicle are like this.
If you have some way of canting the injector body, then the injector to bore relationship cannot be correct.
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  #11 (permalink)  
Old 01-25-2021, 10:12 AM
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Thanks guys. Your concerns about o-ring integrity is a valid one. And I will carefully rethink my approach.

I do find it a little curious though, that inserting only one end of the injector (either into the machined bore of the throttle body, or the machined bore of the fuel rail) allows quite a bit of injector movement from side to side with little resistance from the o-ring.

I know I am using the right o-rings (size), but still curious.

Again, just an observation.

Cheers
Greg
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Old 01-25-2021, 11:30 AM
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It's all about what happens when you insert the other end of the injector into the other anchor point Greg. It is simply a significant fuel leak hazard because of the bind (misalignment) each side imposes on the other. Put 40+ psi of fuel pressure behind it and you have an accident looking for a place to happen. The place they "it" usually picks is somewhere on a highway, far from help.

A friend of mine bought a beautifully restored 1958 Covette two summers ago. Last summer while driving along the Pacific Coast Highway enjoying the beautiful view one of the two 4 barrels had a float seating issue and pumped gas over the top of the engine. He saw the smoke beginning to wisp out of the edge of the hood and come thorough the heater vents in the car.

By the time he got it pulled over to the side of the road, the whole front of the car was in flames and so were the soles of his shoes from all the liquid gas being sloshed around. He literally escaped by the skin of his teeth — and that fuel system only ran at 6 psi! Think about what a 40+psi fuel delivery system is capable of ...


Ed
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Last edited by eschaider; 01-25-2021 at 12:54 PM.. Reason: Spelling & Grammar
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  #13 (permalink)  
Old 01-25-2021, 12:27 PM
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Thanks Ed. You had me at accident and fire!!!!!!!!!!!!!!! Not LOL.

I'll ensure the injectors are perfectly aligned during my installation.

Thanks all for your advice and help.

Cheers
Greg
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