RDX Tune... a couple of questions

naaman · 27 March 2014

I've been trying to figure out if the principles in the RDX tune can be applied to another car, and was researching some newer injectors for my 98 LS1 powered vehicle.

The nuances of the combustion process are a little bit mysterious to me so if someone can lay out the key factors in semi-layman's terms, I'd appreciate it.

Here's what I'm trying to find out:

How do we know that the gains on the RDX/ProSpeed tune have anything to do with the injectors? Couldn't the tune itself be responsible for most or all of the gains?

Do we have any relatively recent dynos of stockish/light bolt-on C30s with a tune without the RDX mod? What kind of gains were achieved?

What is it about the injectors that did the trick? Spray pattern?

dablackgoku1234 · 27 March 2014

RDX injectors are nothing new. They've been retrofitted onto all types of Honda 4 bangers with positive results. Only recently did it exist on the NSX. When the concept was first introduced here, the person was flamed and laughed at...until he proved everyone wrong. It is the superior spray pattern and leads to a cleaner combustion, and thus, better power.

Honcho · 27 March 2014

Prospeed tunes cars without RDX and the gains are 10-20 whp, depending on mods. What I would be interested in seeing is a car with brand new or freshly cleaned/balanced OEM injectors vs RDX. I had my injectors done as part of my head gasket rebuild and the car is noticeably stronger.

naaman · 28 March 2014

dablackgoku1234 said:
RDX injectors are nothing new. They've been retrofitted onto all types of Honda 4 bangers with positive results. Only recently did it exist on the NSX. When the concept was first introduced here, the person was flamed and laughed at...until he proved everyone wrong. It is the superior spray pattern and leads to a cleaner combustion, and thus, better power.

Sure, but doesn't it require a tune, as well? How can we eliminate the tune as the source of most/all of the gains?

Honcho said:
Prospeed tunes cars without RDX and the gains are 10-20 whp, depending on mods. What I would be interested in seeing is a car with brand new or freshly cleaned/balanced OEM injectors vs RDX. I had my injectors done as part of my head gasket rebuild and the car is noticeably stronger.

L_RAO's stcok injectors did improve once they were cleaned, though they were not compared after being cleaned.

A.S. Motorsport · 28 March 2014

I do for see it not being that difficult to retrofit the RDX injectors in a LS engine you'd need a connector & fuel rail adapter to suite the GM fuel rail and wiring harness.
I recall seeing it done be fore with different types of injectors.

I did have both here earlier this week but they just shipped out :frown: so can't check it out anymore.

dablackgoku1234 · 28 March 2014

naaman said:
Sure, but doesn't it require a tune, as well? How can we eliminate the tune as the source of most/all of the gains?

The before and after dynos were based off of Prospeed tunes, not OEM vs tune. Unless you are saying the base Prospeed tune wasn't done to full potential and that the RDX tuned was...I guess that could be a possibility.

For the cost of an injector clean ($25), you're almost at the price of new injectors ($40).

naaman · 29 March 2014

A.S. Motorsport said:
I do for see it not being that difficult to retrofit the RDX injectors in a LS engine you'd need a connector & fuel rail adapter to suite the GM fuel rail and wiring harness.
I recall seeing it done be fore with different types of injectors.

I did have both here earlier this week but they just shipped out :frown: so can't check it out anymore.

I'm not so much concerned with using the RDX injectors themselves (though, if they are the "best" injectors, it might be worth a shot). What I'm more concerned with is the principle: Does the tune account for most/all of the gains, or do the injectors?

dablackgoku1234 said:
The before and after dynos were based off of Prospeed tunes, not OEM vs tune. Unless you are saying the base Prospeed tune wasn't done to full potential and that the RDX tuned was...I guess that could be a possibility.

For the cost of an injector clean ($25), you're almost at the price of new injectors ($40).

??? Where can you get a set of injectors for $40?

I thought the baseline run was NO tune with just some basic bolt-ons. It was 247whp, a little higher than typical for a completely stock 3.0. Was baseline, infact a tuned NA1?

A.S. Motorsport · 29 March 2014

The tune will aid any base line OE setup.
The injectors offer far better atomization vs traditional injectors. don't know exact gain ratios but for example.. 40% gain would be from fine tuning the system and 60% would be by more exact AFR control and ratio.

I do know a tuned ecu C32A or C35A engine (SOHC non V-Tec) running its stock injectors vs RDX injectors is 10whp and 10ft lbs across the whole band.

naaman · 30 March 2014

A.S. Motorsport said:
The tune will aid any base line OE setup.
The injectors offer far better atomization vs traditional injectors. don't know exact gain ratios but for example.. 40% gain would be from fine tuning the system and 60% would be by more exact AFR control and ratio.

I do know a tuned ecu C32A or C35A engine (SOHC non V-Tec) running its stock injectors vs RDX injectors is 10whp and 10ft lbs across the whole band.

I'm sorry, I don't understand. Can you explain the difference in what you mean between "fine tuning the system" and "more exact AFR control"? Those two sound like the same thing to me.

The second part of your post:
Just to clarify: you're saying that stock plus tune yields +X horse power, and RDX + tune yields X+10 horsepower?

RagingAngel · 2 April 2014

I think the answer here is in two parts:

1) The RDX injectors have a much larger capacity at 410cc. The OEM NSX injectors are reportedly the same as the B-Series/D-series at only 240cc. While they can be pushed to work with higher fuel pressure, this causes their efficiency to drop.

2) The superior spray pattern that everybody loves.

My experienced is based off B-Series motors but I'd like to think it is just as relevant. Compared to other similar 410cc injectors, the RDX with the SAME tune can yield more power due to its finer mist pattern and also response time. This gives the tuner the ability a wider window to work with in terms of the AFRs.

naaman · 2 April 2014

Interesting. Are the RDX injectors typical of a modern injector, or are they somehow different from other injectors today? For example, does the spray pattern do the same thing on a Toyota Corolla or a ZR1 Corvette? Or, conversely, do the NSX injectors just suck?

RagingAngel · 2 April 2014

I believe the RDX injectors are a little special and they were commissioned by Honda to be built to their specifications because the RDX was the first recent production Turbo motor for Honda in about 2 decades. The last was the Honda City IIRC.

As they are designed in this specific fashion, their spray pattern will be the same on any motor they are used on. I believe their intended fuel pressure is around 51psi.

The NSX injectors are inadequate in general for the motor (when used in VTEC) and it was believed they were used primarily for efficiency so the NSX could evade the gas guzzler tax when it was initially released. Another positive notch for an otherwise superior supercar back in the day.

Honcho · 2 April 2014

RagingAngel said:
The NSX injectors are inadequate in general for the motor (when used in VTEC) and it was believed they were used primarily for efficiency so the NSX could evade the gas guzzler tax when it was initially released. Another positive notch for an otherwise superior supercar back in the day.

Also they went with the 240 to improve idling and starting performance- it was intended as a "usable" supercar. It's no accident to me that the current problems with this mod on the NSX relate to idle and starting.

Also, the 240 was adequate for the stock engine. It is once you start modding and increasing airflow that you run into problems. Still, even the CT supercharger manages to get enough fuel out of these "undersized" injectors. It's all in the tune.

One the bugs are worked out, I am definitely interested in it, though.

naaman · 3 April 2014

RagingAngel said:
I believe the RDX injectors are a little special and they were commissioned by Honda to be built to their specifications because the RDX was the first recent production Turbo motor for Honda in about 2 decades. The last was the Honda City IIRC.

As they are designed in this specific fashion, their spray pattern will be the same on any motor they are used on. I believe their intended fuel pressure is around 51psi.

The NSX injectors are inadequate in general for the motor (when used in VTEC) and it was believed they were used primarily for efficiency so the NSX could evade the gas guzzler tax when it was initially released. Another positive notch for an otherwise superior supercar back in the day.

So are the results unique to the NSX, then (I know other engines are seeing "gains" of 4 HP or what not)? If the injectors on the NSX were designed to restrict it, then it makes sense to assume that the principles applied here would probably not translate to a different platform (my LS motor, for example). Essentially, "upgrading" injectors won't work on my LS1 becasue the injectors it is equipped with are not deliberately restrictive to begin with. Correct?

Honcho · 3 April 2014

naaman said:
So are the results unique to the NSX, then (I know other engines are seeing "gains" of 4 HP or what not)? If the injectors on the NSX were designed to restrict it, then it makes sense to assume that the principles applied here would probably not translate to a different platform (my LS motor, for example). Essentially, "upgrading" injectors won't work on my LS1 becasue the injectors it is equipped with are not deliberately restrictive to begin with. Correct?

The principle would apply if the stock LS1 injectors do not atomize the fuel as efficiently as the RDX 12-hole design. The reason this appears to work so well on old Hondas is that they use a pintle-type injector, which is a relatively old design (1970's), and does not create as clean a burn in the combustion chamber. In addition, Honda heads are much better designed than the injectors, with good flow and positive swirl, so they react well to a more consistent/efficient fuel vapor.

Thus, it's not an issue of "restriction," but instead efficiency. As I noted above, you can get the stock 240cc injectors to deliver enough fuel for a supercharger. However, as fuel pressure goes up to meet flow demand, the quality of the spray pattern goes down. On the LS1, I have no doubt GM sized the injectors appropriately for the airflow, so there is no restriction issue.

naaman · 4 April 2014

Okay, so it's essentially like I thought to begin with: If I can determine that:

1) LS1 stock injectors have room for improvement
2) There is a better (patterning) injector that will fit
3) The combustion chamber can support/will benefit from the improvement

Then I should see gains due to more complete combustion, since a finer mist is easier to ignite evenly than a high pressure "blast."

It will depend upon how good the stock injectors perform relative to whatever replaces them.

To know whether the experiment worked on my car, I would need to complete the following steps:

Clean the stock injectors, and then, all in the same day:

-Dyno the car as it sits now for a baseline.
-Have it tuned to maximize what it can do right now
-Install different injectors and a quick tune for smooth operation
-Dyno with new injectors
-Fine tune
-Dyno

RagingAngel · 4 April 2014

I think the main issue with the RDX injectors not performing well (idle/starting) on cars NSX or not is as Honcho stated: It's in the tune.

I don't see the RDX suffering from these problems.

Experienced tuners will tell you that tuning for part-throttle, idling and starting can be one of the most tricky things while tuning only for WOT is relatively easy by comparison.

I'm certain that 240s can work for a multitude of applications but it's not ideal when compared to a more modern injector such as the RDX.

Injectors that will show these "RDX gains" can be bought directly from Denso or Bosch or if you prefer aftermarket brands, grams and ID (injector dynamics) have been fueling some of the fastest cars out there...but are seldom offered smaller than 550cc....which takes us back to the issue with properly idling.

With larger injectors, they seem to require adequate pressure to mist the fuel but if not trimmed properly for idle, well....now I'm just talking in loops haha...

A.S. Motorsport · 7 April 2014

naaman said:
I'm sorry, I don't understand. Can you explain the difference in what you mean between "fine tuning the system" and "more exact AFR control"? Those two sound like the same thing to me.

The second part of your post:
Just to clarify: you're saying that stock plus tune yields +X horse power, and RDX + tune yields X+10 horsepower?

All my points have been explained in above post,

For example fine tuning your stock clean system will push power to the maximum envelope of the system in it's current form.
Adding the RDX injectors allows you to better atomize fuel air mix, and offers you a larger injector so you have a more than sufficient flow rate.

Then re-tuning the system with the RDX will raise the envelope that you set with the stock tune, due to the advantages pointed out above.

That simple calculation i gave was what has been documented to happen on C32A and C35A engines, the NSX having far more efficient head will react differently, perhaps gain more due to it's superior design.
The better and cleaner AFR ratio you have the safer you can tune the ignition and thus the more compression and boost you can run.

This can be easily seen with modern direct injection cars, for example current Mazda's now are capable of running 14:1 compression on a street car with out requiring special fuel.
a decade ago that would have been unthinkable in a mass produced car.

Nero Tenebre · 8 April 2014

I would agree the rdx injector idle problem is with the tune. I have them on my obdii car with custom time and don't have any such problems. They run like stock but it feels like I added headers again.

naaman · 9 April 2014

A.S. Motorsport said:
All my points have been explained in above post,

For example fine tuning your stock clean system will push power to the maximum envelope of the system in it's current form.
Adding the RDX injectors allows you to better atomize fuel air mix, and offers you a larger injector so you have a more than sufficient flow rate.

Then re-tuning the system with the RDX will raise the envelope that you set with the stock tune, due to the advantages pointed out above.

That simple calculation i gave was what has been documented to happen on C32A and C35A engines, the NSX having far more efficient head will react differently, perhaps gain more due to it's superior design.
The better and cleaner AFR ratio you have the safer you can tune the ignition and thus the more compression and boost you can run.

This can be easily seen with modern direct injection cars, for example current Mazda's now are capable of running 14:1 compression on a street car with out requiring special fuel.
a decade ago that would have been unthinkable in a mass produced car.

Nero Tenebre said:
I would agree the rdx injector idle problem is with the tune. I have them on my obdii car with custom time and don't have any such problems. They run like stock but it feels like I added headers again.

Okay, so on a stock engine, I can see gains from a tune, but I'm pushing the limits of the system (the injectors). With better injectors, I can have the same gains in a safer set up. Right?

Nero Tenebre · 10 April 2014

IIRC you should not run more than 80% duty on any injectors for safety. If you need more fuel than that it is better to step up to a bigger injector which will run within it's efficiency range.

Honcho · 10 April 2014

Nero Tenebre said:
IIRC you should not run more than 80% duty on any injectors for safety. If you need more fuel than that it is better to step up to a bigger injector which will run within it's efficiency range.

Not necessarily true. Honda typically runs its factory injectors at 95% or more, including on the NSX.

A.S. Motorsport · 10 April 2014

naaman said:
Okay, so on a stock engine, I can see gains from a tune, but I'm pushing the limits of the system (the injectors). With better injectors, I can have the same gains in a safer set up. Right?

Yes and no Nero is right with that statement, but you should also take in to account the much better atomisation from the RDX injectors giving a better AFR that burns more efficiently in the combustion chamber.

naaman · 13 April 2014

A.S. Motorsport said:
Yes and no Nero is right with that statement, but you should also take in to account the much better atomisation from the RDX injectors giving a better AFR that burns more efficiently in the combustion chamber.

That's what I've been trying to get to the bottom of. My assumption is that better atomization results in a more complete burn which means that more power should be produced. However, there are many who say that any "gains" would be negligible or not noticeable, and that the 20ish horsepower could easily be had from a tune alone (and that the injectors are not contributing to that number).

How does better atomization allow for a "better" AFR? I assume you mean that when the ECM does it calculations, the actual burn equates to what the ECM is trying to achieve, rather than leaving unburned fuel that was designated based on metered air (i.e. "better" AFR is actually more complete burn with the same AFR). Is that what you're saying?

Also, are the RDX injectors unique in their ability to improve power? Or are they typical of modern injectors? That is, do other modern injectors work the same way as the RDX injectors?

Nero Tenebre · 13 April 2014

Honcho said:
Not necessarily true. Honda typically runs its factory injectors at 95% or more, including on the NSX.

Well if they are running at 95% it definitely makes sense that larger injectors could help take advantage of better breathing via mods!

OP there is really only one way to find out the answer you want and that is with hard data. I was going to tune with base injectors and then retune with rdx to answer this but the problem is you pay for two tunes. I was not throwing down an extra $500 but for someone with a shop they can do back to back tunes with the control group.

RDX Tune... a couple of questions

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