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Discussion Starter · #1 ·
I'd like to get a thread together with information on side feed injectors, stock and larger replacements. Trying to avoid top feed injector swap info here, but if it is relevant, go for it.

So, the stock fuel system runs at 55psi. The fuel pressure is regulated in the tank, which means this setup has only 1 line from the tank to the motor. (the feed line)

Facts:
Gen 1 stock injectors - 25lb/hr (black tops)
Gen 2 stock injectors - 29lb/hr (red tops)
Internal fuel rails in the intake are -8 AN (1/2")

A good side feed injector upgrade is the Subaru yellow top injector. They will flow close to 60 lb/hr at 55 psi. The down side is that they are really expensive new. Cost at the dealer is 150 per injector, which is 1500 for injectors plus tax. If you look on the Subaru forums, you can get 4 shipped for 150 - 200 bucks. This will require new injector connectors, and obviously some kind of engine management to compensate for the extra flow.

The Subaru injectors aren't a direct drop in, I believe that an O-ring swap from the original injectors would be enough. I'm also thinking that the tip may need to be filed down a bit to fit.



Here you see (left to right):
1) late model Nissan 300ZX TT injector. 370cc
2) Subaru yellow top injector 550cc
3) Stock Gen II injector 305cc
4) Nissan Maxima injector 240cc

These are all high impedance injectors, and all should fit without too much issue.

Soooo, why is the Maxima injector there you might ask? Well, I got 24 of them for 100 bucks. I wanted to try resizing the injectors to flow more and had some success thus far. I had some pics, but they are super fuzzy, so you'll have to imagine it.

The bottom of the injector has a plate micro welded to the injector with several small holes in it. This atomizes the fuel as well as limits the amount injected. If you remove the plate, the flow goes from 240cc to 550cc. Obviously the pattern isn't as good anymore, but it is similar to the stock Viper injector now. I rigged up a flow bench to test the flow rate before and after, and initial testing is good. I modded 20 of the 24 and plan to flow them all and see what the variance is between them.

I was thinking if there was a wide spread, I can use the individual cyl trim in the VEC to compensate for them.

I realize that this isn't for everyone, but I will give it a try and report back.

As a neat note, the TT 300zx injectors can be modded in the same way, but result in the same end flow rate. Nissan probably used the same base, just changed the restrictor plate and color. They are also really expensive too, so the Maxima injectors are the obvious choice for this test.

Alright, have at me.. :)
 

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Great post !!
I flow injectors and if you need me to double check/back up your results between the different injectors I'll be glad to do so at no charge. This might really help some folks out.
 

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Great post. Paolo and I were talking about side feed injectors the other day and I had brought up the Subaru ones, but I really didn't know much about them. Thanks for the solid info. I'd be very interested to see your results with the Maxima injectors.

I checked out your website...great to see you DIY'ing stuff. We need moar DIY'ers on here.
 

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great info. I wonder at the accuracy and tunability of the hogged out Maxima injectors at light and partial throttles though given the atomisation will be worse.

Also, if you go to the expense of an aftermarket ECU, why not go for low impedence injectors that are more precise over a wider range?
 

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Discussion Starter · #6 ·
Thanks guys!

1TONY1 - I may take you up on that offer. I wouldn't mind a second opinion from someone with more experience flow testing injectors.

The Former PFR - I will DIY anything I can, even if it takes me a few revisions. Working on getting away from the hack and slash mentality though.

Torquemonster - I have a feeling that driveability will be lessened to some degree, will need to test to see how much. The spray pattern should be similar to the stock viper injectors as they have a single hole as well as the modified maxima injector. Yes it is not ideal, but we'll give it a shot, and if I can live with the results, I have saved a lot of money and have helped out the community.

As far as the aftermarket ECU, it all depends what you are using. Myself, I'm using a VEC, and the only way to use low impedance injectors is with a resistor box. Just because I can use low-z injectors in this manner, doesn't mean I get the benefit of them, it just means I can treat them as saturated injectors without frying the injector drivers in the VEC. Also, I am not aware of any low-z side feed injectors either (doesn't mean they don't exist, just saying I haven't seen any).

Later,
 

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great info. I wonder at the accuracy and tunability of the hogged out Maxima injectors at light and partial throttles though given the atomisation will be worse.

Also, if you go to the expense of an aftermarket ECU, why not go for low impedence injectors that are more precise over a wider range?
Viper injectors are the worst I have seen for atomization...or lack of would be a better way to say it. Basically it's a stream. If you look at the intake around the injector a well atomizing injector might be spraying onto the intake wall before it gets to the main runner. I have wondered if those injectors were picked or designed just for that reason.
 

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Subaru injectors can be modified up to 850cc. There are also non-modified 850cc sidefeeds based off the Subaru injectors.
The Subaru injectors have good atomization up to ~75psi. I ran 55psi on 850s with no issues in my STi. The flow rates are based of 43.5psi.

Incorrectly clipped Subaru injectors suck (atomization) and can lead to sticking open. I had a set of Subaru modded 816cc injectors, one was stuck open and hydrolocked my engine. That company no longer produces injectors.

If anyone's interested in the Subaru, let me know. I can get very good pricing on them.

Nick
 

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Aren't you dong a TT on your viper? If so, I assume you'll be having to go in and be forced to modify your fuel pump arrangement anyway, no? Why not redo the system to the more common return with top feed injectors at that time? It just seems (IMO) like the more logical approach in the long run if you're going to be making a lot of power. Also, you've obviously run the numbers, but aren't you going to be fairly limited with 5XXcc injectors with FI?
 

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Discussion Starter · #11 ·
No Name - Yes, I am building a mild TT system as we speak. These 550's should flow between 600 and 620cc at 55psi, which should give me a safe limit of 800whp which would be the most I'd want to run on a stock forged motor.

I am planning on dual walbros in the tank with 2 inputs into the intake fuel rails and 1 return from the front. With this setup I could run higher base pressure if I needed to, but I think 800whp would be a good all around daily driver.

Later,
 

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We've gotten side-feed "60's" from ROE for under $1000. Tops were yellow and required massaging of the aluminum hold-down brackets to fit right. They worked like a champ with triple-255 pumps and return-style modified fuel passages in the intake. Even came with the new injector pigtails...


 

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Discussion Starter · #13 ·
We've gotten side-feed "60's" from ROE for under $1000. Tops were yellow and required massaging of the aluminum hold-down brackets to fit right. They worked like a champ with triple-255 pumps and return-style modified fuel passages in the intake. Even came with the new injector pigtails...


What engine management are you running? Do you have any numbers for that setup? Thanks!
 

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Viper injectors are the worst I have seen for atomization...or lack of would be a better way to say it. Basically it's a stream. If you look at the intake around the injector a well atomizing injector might be spraying onto the intake wall before it gets to the main runner. I have wondered if those injectors were picked or designed just for that reason.
that makes sense - they're bouncing off the wall to get atomization - otherwise car would not be so smooth down low nor get such reasonable mpg at cruise... though modified Vipers with better injectors can get much better mileage
 

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No Name - Yes, I am building a mild TT system as we speak. These 550's should flow between 600 and 620cc at 55psi, which should give me a safe limit of 800whp which would be the most I'd want to run on a stock forged motor.

I am planning on dual walbros in the tank with 2 inputs into the intake fuel rails and 1 return from the front. With this setup I could run higher base pressure if I needed to, but I think 800whp would be a good all around daily driver.

Later,
FYI, there are 650cc, at 43.5psi, variations of the Subaru (yellow top) injectors

Nick
 

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AndyMac said:
What engine management are you running? Do you have any numbers for that setup? Thanks!
Stock computer with a "Split Second" fuel/timing box. At 12-13psi, it did 746/745 on a dynojet. Drove like stock otherwise.
 

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Discussion Starter · #18 ·
james111 - I was thinking about hacking one up to see what would happen.

White Out - That might be a bit on the big side for the VEC, but I would try them if/when I need more injector.

coupe - Impressive!
 
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