Putting NA2 injectors on a NA1 motor

**Viper Driver** · 12-29-2004, 17:44

I've done a lot of small mods to my engine (I/H/E, straight pipes, SOS Stage I ECU, SOS Big Bore throttle body, SOS tuned intake manifold) and my last two dyno sessions have shown an ever-increasing lean condition that I feel is robbing my car of some hosepower and possibly creating a dangerous situation. It's apparent that the problem is somewhere in the fuel delivery, since Chris (SOS) says that they did not modify any of the fuel maps from OEM on the Stage I ECU.

I tested the fuel pressure with a gauge borrowed from Chris, and there is plenty of fuel pressure. I changed the fuel filter for good measure and changed out the spark plugs to NGK Iridiums. Finally, I've been running BG44K through the fuel system in an attempt to clean the injectors and hopefully fix the problem. However, I got an idea recently and I think I'm about to act upon it. I figured that I would post here to see what others think, and see if someone else has actually done the same thing before.

With all of my supporting mods, my car should be putting out greater than NA2 horsepower. Since there is about 15% greater fuel flow from the NA2 injectors, why not install them in a modded NA1 car? I've read the threads here that say the NA2 injectors are backward-compatible with the NA1 motor......so why can't I find any threads where someone else has actually done this? Wouldn't this be a better solution than having to worry about having pristine clean NA1 injectors that (best case) are approaching 100% of their flow capacity? Can anyone think of a reason not to put NA2 injectors on a slightly modded NA1 car?

Anyways, I now own a set of NA2 injectors and plan on installing them in the next few days. Just looking here for input beforehand just in case there is something I haven't thought of. Barring any unforeseen roadblocks, I'm going to dyno the car on the 15th and see if I get any improvements to the A/F and horsepower.

Thanks!

Chuck

**Briank** · 12-29-2004, 18:16

Doing a couple of searches here it looks like you can put the newer injectors in the older engines. But there is a problem with putting older injectors in a 97 or newer.

http://www.nsxprime.com/forums/showt...ight=peak+hold

http://www.nsxprime.com/forums/showt...ight=peak+hold

**Viper Driver** · 12-29-2004, 19:14

I know.....I've already seen that. I was wondering if anyone has actually gone out and done it!

**Briank** · 12-29-2004, 20:03

Originally Posted by Viper Driver

I know.....I've already seen that. I was wondering if anyone has actually gone out and done it!

Going to larger injectors is common with the FI crowd. Specifically using the 3.2 injectors in place of the 3.0 part, I don't know

I think you could just put in an adjustable FPR to tweek your AFR.

**Viper Driver** · 12-29-2004, 21:10

What's with the

?

An adjustable FPR means TUNING, a word which I do not associate myself with. My simple caveman brain tells me that the NA2 injectors are a plug-and-play solution.

**D'Ecosse** · 12-30-2004, 23:52

Originally Posted by Briank

Going to larger injectors is common with the FI crowd. Specifically using the 3.2 injectors in place of the 3.0 part, I don't know

The difference is that with the FI guys you are also changing the driving signal via some modified means, whether piggy-back or stand-alone controller (the exception being the Comptech S/C)

I would expect that when you install bigger injectors, the ECU is gong to want to compensate & will re-teach itself to satisfy the conditions determined by what it sees on the O2 sensor, regardless of what size injectors you put in there.

IOW - it only makes sense to change the injectors if you modify the tuning from stock ECU - maybe at this point it would be a "better" investment to just retain the stock injectors, but switch to an AEM (for example - mainly as the best cost option) and tune it to match your new conditions. I would expect with your mods, you should probably still have enough o/head to drive them harder, although at that point you can always change to bigger if you desire.

**Larry Bastanza** · 12-31-2004, 03:50

Any change is this area will most likely require tuning. Once you alter components of the system, things change. Your present ECU has no idea about different injectors, etc.

Have you sent your injectors out to RC Engineering for flow testing?

HTH,
LarryB

**Viper Driver** · 12-31-2004, 10:11

Before I start, I really appreciate your responses to my questions.

Originally Posted by D'Ecosse

I would expect that when you install bigger injectors, the ECU is gong to want to compensate & will re-teach itself to satisfy the conditions determined by what it sees on the O2 sensor, regardless of what size injectors you put in there.

Well, that would work fine any time the throttle is not at WOT, but I believe that the ECU does not even look at the O2 sensors when the throttle position sensor is at WOT. What does the ECU do at WOT? I suspect that there is a mechanical issue with the fuel delivery, and the stock injectors are at or near their full capacity. Even if I sent them off to RC Engineering, I would still have this problem again sometime in the future as they get re-clogged.

Would you put NA1 injectors in an NA2 motor (if you could)? With my motor making NA2 horsepower, it makes sense to upgrade the injectors to deliver enough gas instead of taxing the NA1 injectors to near their maximum.

IOW - it only makes sense to change the injectors if you modify the tuning from stock ECU - maybe at this point it would be a "better" investment to just retain the stock injectors, but switch to an AEM (for example - mainly as the best cost option) and tune it to match your new conditions.

I already own the NA2 injectors, so that is not a problem.

I suspect that the AEM would be a solution if it were a software/engine management issue. However, I believe that it is a "hardware" issue. There's no way the stock ECU is supposed to allow upwards of 15:1 A/F ratio! My solution is to get slightly bigger injectors so that they aren't working as hard to spray enough gas into the motor.

I may have already fixed the problem since I haven't dyno'd the car yet, but the final link in the fuel delivery chain for me to address is the injectors. Even if it isn't necessary to do so, doesn't it make sense to put an injector with a more appropriate fuel flow rate into my car?

Am I off base on this? I think that my reasoning is sound.

Thanks for the posts and inputs guys!

**satan_srv** · 12-31-2004, 11:08

doesn't make sense to just add 15% more fuel across the board. Sure you can do it, but there is no guarantee your result will be better, other than being less lean...too much fuel the other way and you will also lose power.

Have you checked your MAP sensor voltage?

**D'Ecosse** · 12-31-2004, 11:27

Well first, just from just an interchangeability standpoint, if you research the links Brian provided above, you will see that the injectors operate differently & are not compatible - I don't believe you can swap them with no other changes.

Now as to the ECU functionality - yes, it is correct that at WOT the injectors are "open-loop" however any corrections the ECU has "learned" from the "closed-loop" conditions will be applied. Simple case - if 10% bigger injectors are installed (assuming the ECU has ability to resolve the difference) then the drive will continue to be adjusted down until the O2 sensors are "satisfied". Then this resultant ratio change will be applied as a constant even in WOT conditions.

If you were lucky enough to find it "just-right" when you re-install the new injectors, then you should try re-testing it after another month or so & see what the difference is. To avoid the ECU re-learning & adjusting you would have to constantly be resetting the ECU by removing the clock fuse (or running with it removed!)

If you research (the F/I forum is a great resource for this topic!) you will find many experiences of the learning process of the ECU causing issues that were thought to have been accommodated.

**robr** · 12-31-2004, 11:57

out of curiosity, what are your dyno results with those mods? i have I/H/E/straight pipes on my 91 as well and am wondering what the SOS Stage I ECU, SOS Big Bore throttle body, SOS tuned intake manifold gained you. Last dyno had me at 270RWHP.

**Viper Driver** · 12-31-2004, 12:20

Originally Posted by robr

out of curiosity, what are your dyno results with those mods? i have I/H/E/straight pipes on my 91 as well and am wondering what the SOS Stage I ECU, SOS Big Bore throttle body, SOS tuned intake manifold gained you. Last dyno had me at 270RWHP.

I've dyno'd my car 3 times......

The first was with I/H/E, the second added the SOS ECU, and the third added the Big-Bore throttle body and intake manifold. I showed modest gains up until the last dyno, and all of them have been showing a progressively lean A/F ratio. Not even my last dyno has come close to yours....I believe it was 255.9 RWHP with an A/F varying from 14:1 all the way up to greater than 15:1. What was your A/Fs on your dyno plot?

D'ecosse:

From what I have read (and Brian Zublin seems to be confirming in one of the threads above) is that the NA2 injectors WILL work on the NA1 cars. Conversely, though, the NA1 injectors are not forward-compatible to the NA2s.

Satan_srv:

I'm not talking about adding 15% across the board. Like D'ecosse says, the ECU will meter the fuel to achieve a set parameter during non-WOT, so there won't be any increase in fuel going to the motor at all. It's when the motor is at WOT that concerns me (when the demands on the fuel delivery system are the most strained).

And no, I haven't checked the MAP sensor voltage yet....something I'll try to do today.

Chuck

**x15** · 01-01-2005, 03:27

Originally Posted by Viper Driver

The first was with I/H/E, the second added the SOS ECU, and the third added the Big-Bore throttle body and intake manifold. I showed modest gains up until the last dyno, and all of them have been showing a progressively lean A/F ratio. Not even my last dyno has come close to yours....I believe it was 255.9 RWHP with an A/F varying from 14:1 all the way up to greater than 15:1. What was your A/Fs on your dyno plot?

Have you tried flow testing your standard injectors? The reason i am speculating that this might be an area to look at is that i had a similar situation when i put the car up on the dyno when i first bought the car.

On the dyno, at 5,800rpm, it was in the mid to high 14s and even flashed a low 15 AFR at about 6,800rpm. I then thought that being a 13 yo car that the injectors or fuel filter might be a little blocked, seeing that the mileage was pretty low (ie about 80,000kms), due to under usage.

I then replaced the fuel filter and pulled the injectors out and did an untra sonic bath and flow tested the injectors.

The results of the injector flow test showed that 1 injector was flowing quite a bit more (almost 10%) than the other 5 (we do not know the exact flow rates etc of the injectors, and did the standard flow test of flowing the injectors for 60secs at x amount of fuel pressure and seeing how many ml of fuel the canisters collected).

I ordered a new injector from Honda Australia and when it arrived, i decided to flow test the new injector to see how much the standard one was supposed to flow. To my surprise, the 1 injector that flowed more than the other 5, was flowing the correct flow, and It was the other 5 that were flowing less than normal. This showed that over time, 5 out of the 6 injectors in my 1991 engine became clogged up by about 10%.

This may be a cheaper option for you by flow testing the standard injetors (it cost me AUD$22 per injector to get it flow tested and cleaned), rather than changing to NA2 ones, as i believe they are not a straight swap. Even if you do get the NA2 injectors to fit, there would be a need for some sort of tuning to get the AFRs spot on.

Just out of curiosity, if you have the SOS stage 1 ECU, wouldnt you be able to get that re-programmed to richen the mixtures, considering you have increased the airflow into the engine with a larger throttle body, and intake manifold volume? Running lean doesnt necessarily mean the injector duty cycle is maxing out, but could mean that the ECU is not supplying the correct fuel parameters to the engine.