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Discussion Starter · #1 ·
I've been meaning to compile this information for some time now, after seeing somewhat of a surge in ITB interest, and a few people on the ITB Facebook page realizing that the Jenvey ITB "kit" requires you to either make compromises, or do some problem solving on your own, I decided it was best I put this out there as coherently as possible.

Hopefully I can shed some light on some of the questions people are having.

Before I start, I want to make it very clear, It puts a bad taste in my mouth that these Jenvey ITBs are advertised as a kit, cost as much as they do, and are this incomplete.
 

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Discussion Starter · #2 ·
The first thing most people do when they get these is throw the horns on them, marvel at how cool they look, and take a short victory lap.
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Once you begin to think about actually installing them, you realize there are some things you need to figure out. The first and most glaring issue, is the issue of where you are going to draw vacuum from.

The Jenvey ITB "Kit" Does not come pre drilled and tapped for your vacuum fittings. There are areas where they could have added vacuum ports, but left the rest of the work up to you.

completely unacceptable for a "kit" that costs this much.
I have seen some people defend them by calling them "motorsport grade".

Motorsport grade is code for junk.
 

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Discussion Starter · #3 · (Edited)
I have seen a lot of people ask questions about the different screws, dimples, etc on these.

The manifold has two sets of dimples that can be made into vacuum ports.

These smaller dimples on the bottom of the manifold are most commonly used for adding fittings for an IAC valve. I do not have an IAC valve on my setup, but I will add information in this section about IAC valves in the future.
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These are your fine adjustments for your throttles. Do not touch these. And do not remove them to use these areas as a vacuum source. I have seen a couple people try and do this. The ports are too small to get good vacuum readings from, and you also lose the ability to balance your throttles.

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The larger set of dimples which I have poorly circled in red, are the ones in which you should* use as your vacuum ports for MAP readings and your brake booster vacuum.

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The holes circled below (covered by the plastic caps in some other pictures) are the injector holes in the throttles where your injectors will go if you choose to use the Jenvey supplied fuel rail / fire hazard.

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The Allen screw circled below, is what you will use to adjust your idle. This screw opens or closes the throttles to control how much air is allowed by.

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This photo below shows the throttle linkage that you will connect your throttle cable too eventually.
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Discussion Starter · #5 · (Edited)
Now that you've got a lay of the land, lets talk about the two options for sourcing your vacuum for MAP and the brake booster.

1. Use the Jenvey fuel rail as a vacuum rail
2. Drill and tap the large dimples for vacuum ports.


I see a lot of people using option number 1 for their vacuum. A lot of people who buy this "Kit" buy it because they assume that for the price, it will be a plug and play ordeal with no compromises. Many people who buy these kits, simply do not want to drill and tap their manifold for vacuum ports, and I absolutely do not blame them.

Below is a photo I stole from the ITB Facebook page of a Jenvey fuel rail functioning as a vacuum rail.
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This abomination is connected to a vacuum block where the vacuum is distributed to a brake booster, and MAP reading.

Please don't set your ITBs up like this. If you are in the US and are hesitant about drilling and tapping your manifold, message me and I will do it for you. Hopefully ill provide enough info to where you feel comfortable doing it yourself.

Below is what a correctly drilled and tapped manifold looks like.
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I also was tired of seeing people use a vacuum block poorly mounted in the engine bay somewhere and draping all the vacuum lines across the engine bay. Below is the vacuum block bracket I came up with.
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I 3D printed the bracket for test fitting
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And finished product here machined out of aluminum
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If you want to set yours up this way and want one of these brackets, Ill have some more made.

Here is a diagram of what goes to where.
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MAP means manifold air pressure (goes to ECU)
FPR means fuel pressure regulator.
 

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Discussion Starter · #6 ·
Here I will detail the drilling and tapping process and what I used to do so.
These are the vacuum fittings I used.
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These fittings are 1/8 NPT.

The drill bit you will need is a 21/64''
The tap you will need is a 1/8-27 NPT.


You can find both the necessary drill bit and tap on amazon.
 

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Discussion Starter · #7 ·
First you will want to center punch the center of all of the dimples. Center punching them just helps make sure you drill straight and true.

Before you start drilling, please wear a mask or respirator. Whatever material this is cast out of floats around in the air when you start drilling.


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This was a good bit of drilling to get to this point, and there's still plenty of material to get through. I went through two or three drill batteries drilling 4 of these out.
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These holes are seriously deep.
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You will feel it in the drill when you get close to puncturing through. Go slow, and switch to a smaller bit if you feel you need more control. Here is a shot of a finished hole. At this point you'll want to grab a file and lightly clean up any rough edges.
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Here are the finished holes from the top side.
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Once your holes are drilled, you're ready to start the tapping process. If you've never used a tap before, watch a few YouTube videos or maybe defer to a friend who has. Go slow. I used engine oil to lubricate the tap.
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When you install your vacuum fittings for the final time, make sure to put some thread sealer on the threads.

This is a shot from the inside of the runner of how the vacuum fitting looks installed.
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I was pretty happy with the result, and the MAP readings I got from sourcing vacuum here were very consistent.
 

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Discussion Starter · #8 ·
Now that the vacuum is sorted out, lets discuss the options for fuel rails.

If you have a 1990-1993 1.6L, you will have to use the Jenvey supplied fuel rail and can not use the OEM fuel rail. The OEM fuel rail for the 1.6L cars is attached to the intake manifold.

If you have a 1994-2005 1.8L, (Note The intake manifold pattern is different for 94-97 and 99-05) you can use either the Jenvey rail, or you can use the OEM fuel rail.
 

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Discussion Starter · #9 ·
If you use the Jenvey supplied rail, you will have to figure out a fuel pressure regulator. If you use the OEM fuel rail in the head, that is the easy button as it has the fuel pressure regulator as part of the fuel rail. My "kit" came with a SARD fuel pressure regulator. It was junk and leaked at all of the fittings.

if you want to use the OEM fuel rail, you will have to plug the injector holes in the Jenveys. You can do so with these injector plugs meant for a 4AGE. These are from Techno Toy Tuning.
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Discussion Starter · #10 ·
Now lets talk about the Jenvey fuel rail. What an absolute disgrace for a "kit" in this price range. Instead of sending a fuel rail already set up and ready to go for a miata. They sent me a "one sized fits all" fuel rail. You are in charge of cutting the fuel rail to length yourself. Seriously? SERIOUSLY?

Not only do I think a 2 piece fuel rail is a stupid design from the beginning, but having your customer cut the fuel rail to length themselves? That's asking for trouble. I was skeptical about leaks from the beginning, and I was correct.

Behold, the absolute travesty this is.
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If you weren't already displeased with your purchase, you probably are now when you start cutting your fuel rail to length.
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If you have one of these fuel rails and for some reason you're still interested in using it, i measured the final length that needs to be cut.
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This fuel rail feels flimsy, and it is. It ended up leaking at the fittings in the middle.
 

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Discussion Starter · #11 ·
It should be noted that Jenvey does now make a one piece fuel rail. I'm not sure if they are including it with their kit now, of it is an optional extra. Regardless, I would be skeptical of its quality.
 

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Discussion Starter · #12 · (Edited)
If you want to use your stock injectors in this fuel rail, or really any injector, you're in for some more fun.

Jennvey again, supplied a universal fuel rail spacer. Not specific to any injector. Once you go to test fit the fuel rail with the supplied hardware, you will find that, the spacers they supplied are too big, and the bolts they gave you are too long.

here are the spacers they provided, and in the background is a SolidWorks model i made for a spacer of the correct height.
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On the left is the 3D printed spacer I used, and on the right is the one size fits all Jenvey garbage that came with your "Kit"
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Here you can see how tall of a spacer you will need.
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Once you get your spacers to the correct height, youll then need to either cut the supplied bolts to length, or get new bolts of the correct length. I was already very much over this project and just decided to cut mine to length. Below is the length you will need.
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Here is the finished product.
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My RX7 yellow top injectors I was never able to get to fit. The purple injectors out of a VVT engine I was able to get to fit, with the correct O ring. I bought an insane amount of O rings, and Jenvey never was able to tell me what O ring I should be using if i wanted to use OEM mazda injectors in their fuel rail. I eventually found an O ring size that sort of made for a snug fit in the rail, I believe it was from a specific Bosche EV6 injector.

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Even after i got a snug fit, how these were setup combined with the leak at the fuel rail, and the SARD regulator being completely worthless. I decided to just use the OEM fuel rail and call it a day.
 

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Good feedback. Keep it coming. Sorry to hear the Jenvey kit is really more of a DIY project with some dubious quality parts. That’s a real bummer. It seems all the ITB kits require some engineering, although the Maruha Motors kit might be the most complete option today.

One thing I really liked about my TWMs is the integrally cast passageway that connects all 4 intake runners to a big hose nipple for vacuum supply. Makes it super easy to connect a vacuum distribution block.

As for fuel injectors, the Jenvey FAQ says,

“What type of injector?

Dimensions: All Jenvey injector mountings and fuel rails will accept either the standard 'O' ring mounted injectors for 14mm bores as supplied by Bosch, Weber, Lucas, etc (64mm between 'O' ring centres) or the shorter 'Pico' style injectors (38mm between 'O' ring centres).

There are a number of other injector types, using the same 'O' rings but with different lengths. These can be used on our twin throttle bodies with ease, but may require different fuel rail mountings on individual bodies. Please specify which you are using when ordering throttle bodies and fuel rails.

Flow-rate: When fitting our throttle bodies to an otherwise standard engine bear in mind that increased power means increased fuel demand and the original equipment injectors are therefore usually inadequate.
Therefore, the fuel rail spacer dimension was probably engineered with the standard Bosch EV14 injector in mind. Bosch also makes 3 other length EV14 injector housings (w/ Extension, Compact and Long) so be careful there. This was honestly one of the more frustrating parts of my project as TWM/ Borla supplied my injectors but the specs they provided didn’t cross reference to any Bosch part numbers or technical data like flow rate @ X psi.
 

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made for them by Jenvey I believe....

Rich.
I thought so, too, but the Maruha branded parts do look more compete and well finished as far as I can tell. I put Maruha right up there with Toda and OS Giken in terms of craftsmanship and quality.
 

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Triggering my ptsd from when I purchased a Jenvey "Kit" from one of the revered vendors (the ecu wasnt even for the right car and it was missing pieces. The "IAC" was just a fucking tube...)

Everything the OP is saying is correct/true. It's ridiculous that this is marketed and sold as an application specific kit. I remember going through the same issues- blocking the injector ports, manifold hitting fuel rail or something (needed longer manifold studs/spacer), cable/linkage is garbage (ended up modifying it to work with oem cable), length between valve and throttle plate causes issues as well.

**** is endlessly frustrating and stupid. T3 manifold and 4A 20v throttles are the way to go.

With all that said, I really like your VAC manifold mount and the way you got around the issues with the kit!
 
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