New Injector Innovation for NSX

So while i was perusing the top end of the motor i figured i would clean and service the injectors. After nearly 160k miles i can certainly say they were not "clean" but they weren't terrible. RC Engineering wants $150 to service the OEM injectors ($25x6) plus my cost to ship, lets call it $160. What the Heck. You only live once. lets try something new

I found some 4-hole Bosch injectors from this company called OsideTiger. California based and in the fuel injection game for almost 17 years, Charlie has been messing with CRX and 90's Honda models for awhile. He informed me that the 250cc 3.0L C30A injector is common for a few different models, they have successfully adapted the 4-hole Bosch units which work perfect.

He told me they were working towards a 12-hole Denso UC solution (apparently more holes, finer atomization, cleaner burn etc. etc.)
My understanding is that the OEM injectors are essentially late 1980's technology and there have been some major improvements since then.

These 12-hole type injectors are essentially what are provided in modern cars, providing the cleanest stream/atomization. The kit includes everything needed to install, even wiring adapters that allow no-cutting. The stock ECU can handle these injectors no problem, just reset and let it relearn.

I have had them installed and running in my 1995 NSX for 100 miles, so far no problems. Idle seem smoother, starts faster, i "certainly feel" a bit more power or torque from 4k onwards. It feels "better" at low speeds around town (its like i can feel the bite point of the clutch easier now?). I will update again as soon i put more miles, hopefully this is something that can benefit the NSX community.

update: 200 more miles (now 300 total). I am definitely getting better MPG, i need to figure out how much by running a tank through it at once.

install notes:
-REPLACE Fuel line 12mm crush washers x2 (90428-PD6-003) where fuel line meets fuel rail or risk burning your $60k car to the ground over $10 (ask me how i know:tongue
- ziptie adapters to vacuum line for fuel pressure regulator so it will still fit under injector covers
-i used 1mm washer/shims to push up the fuel rail a bit. These injectors are 1mm taller. I think Charlie will start including these now, but if not they are like 12 cents at home depot.
-make sure the wires for the adapters are not touching the valve covers
-align injectors with marks on fuel rail
-put just a SMALL amount of clean motor oil to lube the injector O-Rings to go in easy on both ends
-prime fuel pump 2-3x before initial start as fuel rail will be empty
-let the engine warm up completely to temp before driving off for the first time, pull over every so often to check for leaks and carry a fire extinguisher just to be extra safe! leave intake manifold cover and fuel rail covers off during this process.

*this is great time to clean or replace the Intake Air Temp and if your feeling cheeky remove/clean the Throttle body as well following Larry Bastanza's article in the NSXCA magazine.

advantages for this to me:
-plug n play- no cutting
-will work with stock ECU (im sure even more benefits with aftermarket engine management)
-includes all needed harness adapters (the stock connectors suck to get off, get a pick or really small flathead screwdriver ready)
-relatively high reward, low impact project
-easily reversible
-removes a large-unsightly box in the engine bay
-better MPG
-relatively "cheaper" than $160 ($150+10ship) just to clean my OEM injectors from RC Engineering.
-100% genuine Denso, I confirmed this with Charlie at OsideTiger. OsideTiger remanufactures/cleans them etc. He has been excellent to work with.

I will really only know 100% with live data once i get this thing on a Dyno and my SOS AEM V2 installed, but for now.....it works pretty damn well:biggrin:






UPDATE 2/7/2019


Ok so the first 12-hole Denso 270cc injectors i tried popped up lean codes towards the end of a tank of gas (300+ miles). The car idled and ran fine but this worried me so after speaking with Charlie he thought to go up a size on the injectors because i have some performance modifications. The codes didnt pop up when i was accelerating just around town or normal 3rd gear, 50-60mph conditions.

P0171: Fuel System Too Lean (Bank 1)
P0174: Fuel System Too Lean (Bank 2)

The first time i cleared the codes (just pull the clock fuse under the hood) thinking it was just a freak occurrence or maybe something was left loose, the codes came back after another 150 miles or so. I promptly limped the car back home, took apart the airbox/throttle body and triple checked everything to make sure i was not having any air leaks to cause a lean code.
I arranged a new setup from Charlie to try.

So now we are on variation 2 of this modified injector setup. Now I am running Bosch 18-hole 315cc 14mm injectors with 11mm adapters into the fuel rail. These injectors seem to have solved the lean issue and because of the very fine atomizing of fuel from the 18-hole setup, this increase in flowrate does not seem to have any detrimental effect. These injectors spray in a cone pattern, the car idles and runs fine all the way to redline, so far no complaints after 300 or so miles. From what i understand the OEM 250cc injector (91-96) and 270cc (97+) is small and it is run at a high duty rate.

Im sure there are more scientific ways to go about this but im just trying to share what i have learned messing with injectors etc.

Flowrate is measured at how much fuel an injector flows at an industry standard 43.5 psi, because the OEM injectors are older needle style injectors they do not atomize as well as a modern 4,12, or 18 hole injectors so they shoot "two streams" which is a dated technology. The game nowadays is how fine/dense of a mist and small the particles of fuel can get. The fuel rail/fuel pressure regulator controls this ~43.5psi condition for the injectors so flowrate can be varied to a certain extent when increasing how finely the fuel is atomized. My understanding is that as we increase the atomization efficiency and mist density of fuel in the motor we can safely run a slightly larger flowrated injector. The ECU cannot physically see the larger flowrate but because the difference is not much it compensates in the fuel table. I am running a Uni-Filter, DF scoop, and full SOS exhaust setup, so i believe these modifications make the case for larger injectors even more convincing.

For example the Prospeed RDX injectors are 410cc flow rated at 43.5psi, this is too much a of a difference for the stock ECU to handle. it cannot effectively trim the fuel tables enough to compensate for the increased flow. Hence there was a chip for 91-94 and additional tuning required for 95+.

Im sure someone more versed than me will correct me on some of this, but hey at least im out here trying.

Some notes about installing Osidetiger's RC-DEVIL Bosch 18-hole kit:
-3 washers now shimming up the fuel rail on each post (12 total), this is the max height possible anymore and the nut wont have enough to thread on.
-use a bit of fresh motor oil when pressing in o-ring (14mm to 11mm) adapters into fuel rail
-ziptie adapters to fuel pressure regulator vacuum line
-use new crush washers on fuel line
-you must rotate the front bank of injectors 90-degrees to plug in as the plugs foul against a harness. Injectors spray in a perfect cone so it doesnt matter the position (no need to really align with marks on the fuel rail like OEM injectors)

I have 400 miles on this setup and so far no codes or problems. Im pretty happy with this setup however i dont have any great data besides, i installed it, ran it, pullled the spark plugs and "read" them with a nice light brown color. Everything seems to be operating/burning fine and it seems to make power everywhere. I have not done air/fuel ratio as the original OBD2 o2 sensors are not wideband so they do not show that information. I think this setup is pretty darn good and the motor runs like a sewing machine.

So far i know for sure this setup will work on 1995-1995 NSX for sure, im fairly certain it will work on 91-94 NSX with the same injectors just send Charlie pictures.


left: Blue old 270cc Denso injector
right:Gray 315cc Bosch injector and new adapter



Notice there are 3 washers stacked to shim up the fuel rail on each post. (4 posts, 12 washers total).
shown here is the rear bank, on the front bank you will rotate the injectors 90 degrees to get them to clear the harness.


Left:
blue 12-hole Denso

right top:
gray 18-hole Bosch

RC-DEVIL said:

...

I found some 4-hole Bosch injectors...

He told me they were working towards a 12-hole Denso UC solution...

Click to expand...

Just to clarify, did you install the 4-hole Bosch or the 12-hole Denso injectors?

I installed the 12-Hole Denso, however my initial contact was through the 4-hole Bosch solution they have listed on ebay.

I am the first to install this 12-hole solution as far as i can tell.

Nice writeup. This may be a good route for me. I have 134K on my injectors (I think) and was considering the RC process (I have done it before on my other NSXs.)

Now, since I have not done this job myself, I need to read up on the process. Seems fairly straightforward. I will break out my manual and get ready. Thanks.

Nice write up, i took out my injectors for cleaning at 100k miles. Took it to a local high performance shop that work on drag cars , they let me observe the cleaning process. They were in good shape, cleaning was not necessary but I paid for their service and peace of mind.

Speedmaster said:

Now, since I have not done this job myself, I need to read up on the process. Seems fairly straightforward. I will break out my manual and get ready. Thanks.

Click to expand...

Morgan,

I'm sure there are local shops in Chicago that can clean them for you if needed, saves time and money for shipping

RC-DEVIL said:

I installed the 12-Hole Denso, however my initial contact was through the 4-hole Bosch solution they have listed on ebay.

I am the first to install this 12-hole solution as far as i can tell.

Click to expand...

Very cool you're trying this out. The common ProSpeed RDX injector swap here is for 12-hole Denso injectors, but they are nominally rated at 410cc/min unlike the ones you're using that are OEM ECU friendly (only flowing about 12.5% more than the OEM 240cc/min injectors).

The nice thing about the RDX Denso injectors is that they have a split-flow spray pattern of about 25-30 degrees to match ports with two intake valves. If these 270cc/min Denso injectors have the same split flow, then that is awesome and I'd like to try them out. I assume that they do, otherwise your informal test results probably wouldn't be as favorable.

Can you please confirm what spray pattern these injectors have, or do you know what kind of engine these are spec'ed for OEM-wise?

Thanks!

Mac Attack said:

Very cool you're trying this out. The common ProSpeed RDX injector swap here is for 12-hole Denso injectors, but they are nominally rated at 410cc/min unlike the ones you're using that are OEM ECU friendly (only flowing about 12.5% more than the OEM 240cc/min injectors).

The nice thing about the RDX Denso injectors is that they have a split-flow spray pattern of about 25-30 degrees to match ports with two intake valves. If these 270cc/min Denso injectors have the same split flow, then that is awesome and I'd like to try them out. I assume that they do, otherwise your informal test results probably wouldn't be as favorable.

Can you please confirm what spray pattern these injectors have, or do you know what kind of engine these are spec'ed for OEM-wise?

Thanks!

Click to expand...

from what i understand the OEM injectors are 250cc for the 3.0l NSX, properly running and cleaned they flow at 250cc/min. I am honestly not sure on the spray pattern but i put another 200 miles on this setup today, everything seemed to operate perfectly fine and i had power everywhere, So i am assuming they are split flow. I believe Charlie said these were formerly Toyota injectors but i might be wrong you will have to ask him.

Any air fuel ratio testing or logs?

drew said:

Any air fuel ratio testing or logs?

Click to expand...

nope, just my butt dyno so far :redface: but it seems to work fine. I will only know 100% with data if i put it on a dyno and get the AEM installed.

as far as i can tell the car reacts perfectly fine with the stock ECU on my 1995 NSX.

My data is basically i installed it....ran gas through the car and everything played nice haha

Hass said:

Nice write up, i took out my injectors for cleaning at 100k miles. Took it to a local high performance shop that work on drag cars , they let me observe the cleaning process. They were in good shape, cleaning was not necessary but I paid for their service and peace of mind.



Morgan,

I'm sure there are local shops in Chicago that can clean them for you if needed, saves time and money for shipping

Click to expand...

Thanks, Hass. Mine are probably fine. (I went through my receipts last night, making one of those "owner's books" full of receipts, data and such and found a receipt for RC Engineering at 66K miles.) Still, I like the idea of a more efficient injector (if it does indeed help). Maybe if we could get the specs and decide for ourselves? Might be worthwhile.

Dyno would be nice with AF ratio. If all checks out, this is a good option since the Prospeed RDX injector/chip kit is no longer available. Also good for 95+ ODB2 cars as the RDX setup was 91-94 only.

This is quite possibly my favourite mod. Better fuel efficiency and a noticeable bump in hp/tq. Much better return on investment vs I/H/E.

Will be following this thread! Nice to see new product for NA NSX!

This is officially on my grocery list too. ��

Would these 12 hole Denso injectors work for a 1991 and its ECU? Would the 91 ECU be able to be reset and learn as you indicate the 95 will?

Interesting! I might just have to do this too, as I was gonna have mine cleaned as well. I assume these would work on the later 3.2s?

Somebody should do some AFR logging to ensure compatibility. Just a little due diligence. Pull a cat, get a test pipe, put in a wideband O2 sensor and drive around for a day.

Way back when I installed my CTSC I wanted to minimize down time, so I purchased similar year Legend injectors and sent them off to RC for cleaning. I figured the injectors should be close enough and are physically an exact match. I installed my CTSC, begin the the tuning and verification process. My AFR's are are all screwed up and running mostly lean and yet the engine sounds great (WTF!). I check everything and eventually decide to put my old original injectors back in and the AFR's go back to normal. My engine would have been junk if I ever left my garage. I eventually get my original injectors to RC and no problems for at least a decade.

These new injectors are probably awesome and great, but a basic verification would be nice.

the nice thing about the obd-2 cars is it will throw a lean code...

docjohn said:

the nice thing about the obd-2 cars is it will throw a lean code...

Click to expand...

Be careful with that approach. While in closed loop operation the ECU will attempt to correct the AFR back to the target value - typically 14.7 on an emission controlled car of NSX vintage. The fuel trim correction may be able to correct the AFR on a lower flowing injector with the result that you don't get a lean code or generate a code indicating that trims are excessive. However, at high engine load the ECUs typically go into open loop with no O2 correction. The wide open throttle dyno runs on stock engines typically show AFRs less than 14 because of this. The ECU may not throw a code at wide open throttle if it isn't in monitor mode and even if it does, it might be too late.

Best not to rely on closed loop operation to save your butt. Confirm that the replacement injector flow rates are correct.

damn open loop.....:redface:

Old Guy said:

Be careful with that approach. While in closed loop operation the ECU will attempt to correct the AFR back to the target value - typically 14.7 on an emission controlled car of NSX vintage. The fuel trim correction may be able to correct the AFR on a lower flowing injector with the result that you don't get a lean code or generate a code indicating that trims are excessive. However, at high engine load the ECUs typically go into open loop with no O2 correction. The wide open throttle dyno runs on stock engines typically show AFRs less than 14 because of this. The ECU may not throw a code at wide open throttle if it isn't in monitor mode and even if it does, it might be too late.

Best not to rely on closed loop operation to save your butt. Confirm that the replacement injector flow rates are correct.

Click to expand...

Thanks for the wisdom Old Guy. Who would be in the best position to confirm the flow rates? The vendor that the OP is working with (seems logical since he/she does this for a living)?

If you know the original part number, there is a website that lists a whole pile of factory data for different injectors.

http://users.erols.com/srweiss/tableifc.htm

They list by Honda / Acura and they list by Nippon Denso. However, the Honda/Acura table is mainly empty except for part numbers. The Denso table is populated.

If the vendor knows their business, they should know the flow rates. If they don't know the flow rates I would not be listening to anything they have to say.

If you have one of the unknown injectors, you could send it to RC, or WitchHunter or somebody like that to be 'cleaned'. After cleaning they test the injectors to confirm the flow rates so you could get the data that way. Maybe RC would cut you a deal on just flow testing or maybe there is a local cleaning shop that could do the flow test for you.

Something to watch for when comparing flowrates. The de facto standard for specifying fuel flow rate through an injector is a pressure differential of 43.5 psi across the injector. The 1991 NSX fuel pressure regulator operates with a base pressure of 46-53 psi. When comparing flow rates of a new injector to an original NSX injector, just make sure that the flow numbers you are using are for the same base pressure. When you get injector test data back from somebody like RC, they usually provide the flow rates at the de facto standard of 43.5 psi. Its very easy to correct the 43.5 psi flow rate to reflect the slightly higher base pressure in the NSX system.

Ok so the first 12-hole Denso 270cc injectors i tried popped up lean codes towards the end of a tank of gas (300+ miles). The car idled and ran fine but this worried me so after speaking with Charlie he thought to go up a size on the injectors because i have some performance modifications. The codes didnt pop up when i was accelerating just around town or normal 3rd gear, 50-60mph conditions.

P0171: Fuel System Too Lean (Bank 1)
P0174: Fuel System Too Lean (Bank 2)

The first time i cleared the codes (just pull the clock fuse under the hood) thinking it was just a freak occurrence or maybe something was left loose, the codes came back after another 150 miles or so. I promptly limped the car back home, took apart the airbox/throttle body and triple checked everything to make sure i was not having any air leaks to cause a lean code.
I arranged a new setup from Charlie to try.

So now we are on variation 2 of this modified injector setup. Now I am running Bosch 18-hole 315cc 14mm injectors with 11mm adapters into the fuel rail. These injectors seem to have solved the lean issue and because of the very fine atomizing of fuel from the 18-hole setup, this increase in flowrate does not seem to have any detrimental effect. These injectors spray in a cone pattern, the car idles and runs fine all the way to redline, so far no complaints after 300 or so miles. From what i understand the OEM 250cc injector (91-96) and 270cc (97+) is small and it is run at a high duty rate.

Im sure there are more scientific ways to go about this but im just trying to share what i have learned messing with injectors etc.

Flowrate is measured at how much fuel an injector flows at an industry standard 43.5 psi, because the OEM injectors are older needle style injectors they do not atomize as well as a modern 4,12, or 18 hole injectors so they shoot "two streams" which is a dated technology. The game nowadays is how fine/dense of a mist and small the particles of fuel can get. The fuel rail/fuel pressure regulator controls this ~43.5psi condition for the injectors so flowrate can be varied to a certain extent when increasing how finely the fuel is atomized. My understanding is that as we increase the atomization efficiency and mist density of fuel in the motor we can safely run a slightly larger flowrated injector. The ECU cannot physically see the larger flowrate but because the difference is not much it compensates in the fuel table. I am running a Uni-Filter, DF scoop, and full SOS exhaust setup, so i believe these modifications make the case for larger injectors even more convincing.

For example the Prospeed RDX injectors are 410cc flow rated at 43.5psi, this is too much a of a difference for the stock ECU to handle. it cannot effectively trim the fuel tables enough to compensate for the increased flow. Hence there was a chip for 91-94 and additional tuning required for 95+.

Im sure someone more versed than me will correct me on some of this, but hey at least im out here trying:redface:.

Some notes about installing Osidetiger's RC-DEVIL Bosch 18-hole kit:
-3 washers now shimming up the fuel rail on each post (12 total), this is the max height possible anymore and the nut wont have enough to thread on.
-use a bit of fresh motor oil when pressing in o-ring (14mm to 11mm) adapters into fuel rail
-ziptie adapters to fuel pressure regulator vacuum line
-use new crush washers on fuel line
-you must rotate the front bank of injectors 90-degrees to plug in as the plugs foul against a harness. Injectors spray in a perfect cone so it doesnt matter the position (no need to really align with marks on the fuel rail like OEM injectors)

I have 400 miles on this setup and so far no codes or problems. Im pretty happy with this setup however i dont have any great data besides, i installed it, ran it, pullled the spark plugs and "read" them with a nice light brown color. Everything seems to be operating/burning fine and it seems to make power everywhere. I have not done air/fuel ratio as the original OBD2 o2 sensors are not wideband so they do not show that information. I think this setup is pretty darn good and the motor runs like a sewing machine.

So far i know for sure this setup will work on 1995-1995 NSX for sure, im fairly certain it will work on 91-94 NSX with the same injectors just send Charlie pictures.


left: Blue old 270cc Denso injector
right:Gray 315cc Bosch injector and new adapter



Notice there are 3 washers stacked to shim up the fuel rail on each post. (4 posts, 12 washers total).
shown here is the rear bank, on the front bank you will rotate the injectors 90 degrees to get them to clear the harness.


Left:
blue 12-hole Denso

right top:
gray 18-hole Bosch

Can you hook up a scan tool and find out what the long term fuel trim is ( LTFT) ?

james0933 said:

Can you hook up a scan tool and find out what the long term fuel trim is ( LTFT) ?

Click to expand...

This seems like a good idea to me; with an OBD2 car, looking at the fuel trims is really easy using a relatively cheap dongle and a phone app.

RC-DEVIL said:

. . . the car idles and runs fine all the way to redline, so far no complaints after 300 or so miles. From what i understand the OEM 250cc injector (91-96) and 270cc (97+) is small and it is run at a high duty rate. . . . The ECU cannot physically see the larger flowrate but because the difference is not much it compensates in the fuel table. I am running a Uni-Filter, DF scoop, and full SOS exhaust setup, so i believe these modifications make the case for larger injectors even more convincing.

Click to expand...

In closed-loop operation (i.e., at idle and low-throttle, low-RPM conditions), the ECU will compensate using the aforementioned fuel trims (that's why it's handy to look at the trims). But at full-throttle (and I think high RPM), the ECU switches to open-loop mode without any trims applied; thus, in open-loop you will see the change from the injector size. The fact that the NSX ECU doesn't apply any trims in open-loop is what makes it work better than other cars with a piggyback fuel controller like the AEM F/IC. Looking at the fuel trims will give you some idea of how the injectors are flowing relative to the OEM injectors but you would need AFR logging to see what things look like at high RPM. This does seem like a great way to use modern injectors with an ECU/piggyback that can control fueling.

Haven't tried my TL injectors method yet?