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Precision Raceworks MPI Rail Injector Seating. What about CTS, APR and Iroz?

staying_tuned

staying_tuned

Drag Racing Champion
Location
Poconos
Car(s)
2016 Mark 7 Golf R
So thanks to the forum and a few prompt responses from Gilbert at PR my MPI install wen't smoothly. One thing I couldn't mentally grapple is why the injectors aren't seating in what appears to be a perfectly cupped seat with guide notch and grove.

Anyone with the PR kit knows what I mean and I'm wondering if this is the case with the CTS, Iroz and APR kit as well. In the first photo you can see the rail mounting point (upper left) is fully seated on the manifold posts yet the injectors have a good 1/8" to go before being fully seated.

Aside from what can visually be seen here, the base of the injector with the bottom cupped shaped gasket (see pic) and bottom of these injector holes appear to be designed to mate together like two cups stacked. With the space, there is no contact, just a void of air. I'm worried less about a leak than I am about the impact this has on air flow and the resulting spray pattern. With the nozzle being 1/8" or 1/4" higher in the manifold there must be cases where actual drips of fuel are formed along the inside of the manifold as opposed to a clean mist. See second photo where I've represented the air pocket. I'd also wager that the upper gasket alone was not designed to hold back 30+ psi long term, the two gaskets are most likely designed to work together.

Is this the case with the CTS kit as well?

I've got an email out to Iroz & APR to see if they'd sell just their rail. I'd love to see photos of how the injectors are seated post install but their install guides only show a top down view, not the actual final seating position.

Does anyone know if any rail other than PRs seat the injectors fully? Call me paranoid but I'm making it a point to scrutinize everything along the way and this just seems like a potential area of concern. Thoughts?

Thanks in advance!

Follow-up info: APR’s rail is $194 and part number Z1002866. Awaiting word back from Iroz.

Fully seated rail yet injector floating high 1/8" or more:

precision-raceworks-mpi-rail.jpg




Resulting pocket created:

air-pocket.jpg



Injector gaskets with bottom one being nulled out by gap:

injector.jpg
 
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staying_tuned

staying_tuned

Drag Racing Champion
Location
Poconos
Car(s)
2016 Mark 7 Golf R
Diggs24 said:
Mine look like that and work perfectly.
Click to expand...

I know this solution works for many folks, myself included when everything comes together. I'm more wondering if this is intended, or the lack of a few more iterations on the design life-cycle.

What would be your reasoning behind why two items perfectly designed to mate (injector tabs, manifold injector tab channels, lower gasket, cupping in manifold injector port base for lower gasket, etc) don't?
 
staying_tuned

staying_tuned

Drag Racing Champion
Location
Poconos
Car(s)
2016 Mark 7 Golf R
Diggs24 said:
Because the OEM injector dimensions are not the same as the Bosch being used.
Click to expand...

Ah, gotcha. That makes sense for PR's kit with the 925cc injectors they are using. Andrew at APR just confirmed there is no gap with their 980cc based kit but he couldn't confirm if my 925cc PR supplied injectors would result in no gap using their rail which they do sell separately (updated OP). I'm anxious to see close-ups of both the CTS and Iroz injector array post install. Scoured videos, posts etc. and no luck yet. It's doubtful that I'll yank my rail based on this alone unless I need to pull the mani again.

At this point the logical conclusion is PR found that the 925cc injectors would work well enough and switched to increase margin. Their price is no cheaper than the CTS 980cc equipped kit. We have confirmed that there exists a 980cc kit with OEM like injector seating via APR, possibly even CTS but I haven't found close-ups yet. I suspect Iroz's kit wouldn't leave the gap either, still TBD. Unless there is something uniquely magical about the 925cc injector specifically that only PR knows about, increasing bottom line without revising the design makes the most sense especially given their history with avoiding costly design iteration i.e. heated press inserts before going with threaded inserts, no injector clips which they now include, etc. They still have work to do IMO.

Clearing this up as it seems I may have jumped to conclusions too quickly. The gap isn't an awesome outcome but there are more factors in play than I'm unaware of due to my general ignorance on injector fitment, manufacturing variances, spray patterns etc.
 
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staying_tuned

staying_tuned

Drag Racing Champion
Location
Poconos
Car(s)
2016 Mark 7 Golf R
staying_tuned

staying_tuned

Drag Racing Champion
Location
Poconos
Car(s)
2016 Mark 7 Golf R
vw671 said:
APR "rail" is a OEM ROW rail. I'm not using the APR kit but I'm using the OEM rail.
Click to expand...

Ah, good to know. Was thinking damn they went to greats lengths making it blend in haha.
 
M

Mosquito

Go Kart Champion
Location
FL
I noticed the slight variance in injector sealing too. In my case, injector #1 is slightly higher with #2 slightly lower eventually trickling down to #4 which is just about perfect.
I am using a new EU manifold and the left rail insert is maybe 2-3mm higher than the right one and barely sticking out the plastic fastener. I played around with it and attributed the variance to that.

In the case of those doing drilling and inserting on a NA manifold for instance. I would probably attribute any variance to a manufacturer tolerance on the metal fuel rail itself, more so than the injectors since the fasteners can now be fully screwed in the plastic and making it flush. In that case, grinding down the metal rail holders a couple of mm should do the trick. At the end of the day, the variance is quite small, the PR injectors are extended tip (or so I understand) and use the metal runners to break up the jet once inside the intake valve chamber vs the wide spray CTS/APR use by default (also hit the runners).

In the end, there should be no issue so long as there no leaks and the variance is very small. But yes, it could be perfect it would probably increase manufacturing cost of the rail on PR by quite a %. +/- 5mm variance on metal manufacturing vs +/- 2mm changes pricing considerably. Plastic is nice and much closer to perfect for mass production but requires tooling and molding, this alone is several thousands alone, just for the set up. This is why you don't and won't see aftermarket redesigned PCV valves for high boost use.
 
M

Mosquito

Go Kart Champion
Location
FL
vw671 said:
Click to expand...

Very clean!
OEM ROW rail, black fuel line T (could only find shiny ones), Spulen PCV with CC and no loss of washer fluid capacity! You did your homework.
Only issue I could find is, the Spulen N80 valve hose is weak as hell by default and collapses under vacuum, sometimes triggering a purge flow error. I replaced mine with a stiffer hose and inserted the check valve there.
All is good.
 
V

vw671

Autocross Newbie
Location
San Diego
Mosquito said:
Very clean!
OEM ROW rail, black fuel line T (could only find shiny ones), Spulen PCV with CC and no loss of washer fluid capacity! You did your homework.
Only issue I could find is, the Spulen N80 valve hose is weak as hell by default and collapses under vacuum, sometimes triggering a purge flow error. I replaced mine with a stiffer hose and inserted the check valve there.
All is good.
Click to expand...

My Spulen has been on for over a year, no issue with that hose.

Fuel T: https://www.holley.com/products/plumbing_an_fittings_and_hose/hose_ends/vapor_guard/parts/782405ERL
 
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