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Longblocks and planning

Joined
11 July 2014
Messages
1,432
Location
Chicago, IL
So, I have what one may call a high-mileage NSX. It has over 330K on the clock on the original motor. The motor still hums along fine, and even has that throaty roar at times.

I am planning for the inevitable...the day I need to drop my motor and swap in another. That thought process leads me to wonder where I am going to source a long block and what that will look like in terms of whether it is rebuilt or just a low-mileage core.

For those of you that did replace your motor, did you rebuild or buy a built motor? Did you elect to stay completely stock? If you bought a built motor, are there vendors that are more known for this work? I don't know the C30A's tendency on wear. Do you find that the heads, rings and bearings are the only thing (typically) needing replacement or is there cylinder wall machining that needs to be done?
 
Have you consider one of the package offered by SoS? Rebuild stage 1,2,3... May be a better option then swap? Since everything will be brand new.
 
a built motor has some liability vs a completely stock oem one.My first motor cooked a bearing so acura good willed me a short block and we built up the top end with the comptech iem package...that motor went south due to spring failure..so I ran 150 miles home from the glen on 5 cylinders...my final replacement was a complete used engine I found on prime. every now and then a good one pops up .
 
I'm sort of in the same camp as you .. although not quite as high on the mileage number (I'm at about 200k). But I was discussing this very same topic at the recent NSXPO with Larry B and Source1 since I'm proably due for a new TB/major service in the next 12 months or so and was wondering if a 'refresh' was advisable at the same time. The surprising advice I got was that both effectively said "stick with the OEM engine rather than a refresh" as long as a leakdown test was fine. Brian even mentioned that they'd just put a supercharger on an engine with over 300k miles (might have been you) and it was running just fine. On the other hand, I also hear that the C30A head gaskets are a weak spot. Maybe Brian's comment was for a C32.
 
I'm sort of in the same camp as you .. although not quite as high on the mileage number (I'm at about 200k). But I was discussing this very same topic at the recent NSXPO with Larry B and Source1 since I'm proably due for a new TB/major service in the next 12 months or so and was wondering if a 'refresh' was advisable at the same time. The surprising advice I got was that both effectively said "stick with the OEM engine rather than a refresh" as long as a leakdown test was fine. Brian even mentioned that they'd just put a supercharger on an engine with over 300k miles (might have been you) and it was running just fine. On the other hand, I also hear that the C30A head gaskets are a weak spot. Maybe Brian's comment was for a C32.

Ian,

No, I don't have a supercharger. Mine stills sounds nice and throaty (OEM exhaust) and I love it. It pulls strong.

I have noticed a rumbling/vibration between 1000 and 2000 rpms. I replaced the crankshaft pulley when I had the TB/WP done. I also had the valves adjusted and new plugs installed. None of that helped. I may (not sure yet) spring for a set of new injectors (not sure they would cause rumbling, but it couldn't hurt, right?)

The only negative in the motor (rumbling aside) is that when I hit above 6000 rpms a decent puff of smoke (not sure how to describe, but it seems like oil burn). It happened a couple of times under hard acceleration. I am curious if I have worn enough valves (the NSX tech did say my cams and valve train was quite worn, but still in spec.)

I suppose I could run this thing another 50K or even more. I thought that if I ran across a nice enough C30A that I would snap it up and have it rebuilt for swap out later.
 
Ian,

No, I don't have a supercharger. Mine stills sounds nice and throaty (OEM exhaust) and I love it. It pulls strong.

I have noticed a rumbling/vibration between 1000 and 2000 rpms. I replaced the crankshaft pulley when I had the TB/WP done. I also had the valves adjusted and new plugs installed. None of that helped. I may (not sure yet) spring for a set of new injectors (not sure they would cause rumbling, but it couldn't hurt, right?)

The only negative in the motor (rumbling aside) is that when I hit above 6000 rpms a decent puff of smoke (not sure how to describe, but it seems like oil burn). It happened a couple of times under hard acceleration. I am curious if I have worn enough valves (the NSX tech did say my cams and valve train was quite worn, but still in spec.)

I suppose I could run this thing another 50K or even more. I thought that if I ran across a nice enough C30A that I would snap it up and have it rebuilt for swap out later.

Better to have your injectors cleaned and re-balanced- they will flow the same as brand new for a fraction of the cost. Based on what I saw with my job here, I think a full intake manifold, throttle body and injector service should be done every 90k miles. There was over a cup of motor oil and blow-by in the bottom of my manifold and the EACV port was almost totally blocked. You will not believe the difference in throttle response and idle after this service.

Sounds like your valve seals are going. I had mine replaced at 90k with the TB job, as the tech noticed the tops of the valves were wet. Though, I had no smoke yet.
 
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Better to have your injectors cleaned and re-balanced- they will flow the same as brand new for a fraction of the cost. Based on what I saw with my job here, I think a full intake manifold, throttle body and injector service should be done every 90k miles. There was over a cup of motor oil and blow-by in the bottom of my manifold and the EACV port was almost totally blocked. You will not believe the difference in throttle response and idle after this service.

Sounds like your valve seals are going. I had mine replaced at 90k with the TB job, as the tech noticed the tops of the valves were wet. Though, I had no smoke yet.

Honcho

Check out my intake. Apologies for the iPhone photos. I was out of light! The TB was dirty. I am going to tear that all down and clean it up. Am still looking and reading up on the RDX and other injector threads. Am really hopeful to learn if there is a new-technology (multi-nozzle/jet?) for our existing computer setup. Ideas are appreciated. In the meantime, off to RC will go the existing injectors.

Thanks!Butterfly closed and dirty.jpg

Butterfly slightly open really dirty.jpg
 
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I'm hopeful that the RDX injectors are a real performance gain. As it stands, we don't have any data (that I know of) comparing a fresh set of OEM (91) injectors with a newly installed RDX + tune. It's reasonable to speculate that the RDX "upgrade" shows gains because it's being compared to old, clogged, not-optimized stock injectors (as well as having the computer tuned for performance). Still, the theory seems legit: better, finer spray = better burn.

Some say that the RDX injectors are not responsible for the gains; only that the tune itself would achieve the same results on stock (refreshed) injectors.
 
The injector clean will work wonders and RC will only keep them for a day, two at most. I would suggest getting new o-rings when you refresh your injectors. The throttle body/manifold clean is a very good thing to do also.
 
The injector clean will work wonders and RC will only keep them for a day, two at most. I would suggest getting new o-rings when you refresh your injectors. The throttle body/manifold clean is a very good thing to do also.

Thanks for the response. I have new O rings, etc. (thanks to Solidol).

One thing that has been of interest to me is how do we expand our (okay, my) collective knowledge around our injectors. It seems to me that our ability to purchase injectors from other cars and make them work as the OEM intended would be a nice start. What I don't get is why is it so hard to find data on our injectors and then compare them to other injectors and if that matters (I have read posts on here that suggest spray patterns - needle or cone - matter to our intake manifolds). A handful of injectors from a Legend is under $25 if self-pulled. Sending them to RC would be the next step. How cool would it be to have a dozen perfect injectors and not having down time?

Now THAT would be interesting to me.

BTW, I am ready to buy six new injectors. I just prefer to be thoughtful about how I spend my NSX budget. :)
 
One of the issues with injectors, is matching the exact flow rate and dead time. I think the flow rate is not that difficult to match, but the dead time is.
The dead time is the time it takes an injector to open and close. The flow rate is the injector wide open. When the ECU completes the circuit and the injector starts to open, it takes a period of time before fuel starts to flow. This is the biggest part of dead time. If the ECU commands 20 milliseconds (ms) of fuel, (lets just use 1 ms =1cc of fuel) but the injector takes 1 ms to open, the engine only gets 19cc of fuel. Now let's ask the injector to open 10 times for 2ms each time, the engine will only get 10cc of fuel because it took the injector half of the commanded time just to open.
Pulse width is the amount of time the ECU commands the injectors to be open.

The ECU has two modes, closed loop and open loop.
In closed loop the ECU uses the o2 sensor to help determine if the pulse with is correct for that moment. If the sensor reports lean, then the ECU adds time to the pulse width. If the o2 sensor reports rich, the ECU removes time from the pulse width. So no matter what the injector dead time is, the ECU will compensate for it.
In open loop, full throttle say, the ecu ignores the o2 sensor and for the power setting, the ECU just commands a fixed pulse width from the look up table in its chip. So it doesn't know exactly how much fuel is going to the engine, it is relying on the data whoever programmed put I the chip.

There are so many variables with modern injectors vs 23 year old units, like spray patterns and angles, dead time, flow rate, working pressure. High impedance or low impedance.

So in short putting in injectors that have the same flow rate should work in closed loop, they might not work that good in open loop. Idle and off throttle requires the smallest pulse width and thus is effected the most by dead time. 1ms is 25% of 4ms, but 1ms is only 2% of 50ms. So the ECU needs to know this.

This only is the Thumb Nail version, and YMMV. There are much more knowlagable people out there than me that have written some great information, it just takes time to read it.
 
One of the issues with injectors, is matching the exact flow rate and dead time. I think the flow rate is not that difficult to match, but the dead time is.
The dead time is the time it takes an injector to open and close. The flow rate is the injector wide open. When the ECU completes the circuit and the injector starts to open, it takes a period of time before fuel starts to flow. This is the biggest part of dead time. If the ECU commands 20 milliseconds (ms) of fuel, (lets just use 1 ms =1cc of fuel) but the injector takes 1 ms to open, the engine only gets 19cc of fuel. Now let's ask the injector to open 10 times for 2ms each time, the engine will only get 10cc of fuel because it took the injector half of the commanded time just to open.
Pulse width is the amount of time the ECU commands the injectors to be open.

The ECU has two modes, closed loop and open loop.
In closed loop the ECU uses the o2 sensor to help determine if the pulse with is correct for that moment. If the sensor reports lean, then the ECU adds time to the pulse width. If the o2 sensor reports rich, the ECU removes time from the pulse width. So no matter what the injector dead time is, the ECU will compensate for it.
In open loop, full throttle say, the ecu ignores the o2 sensor and for the power setting, the ECU just commands a fixed pulse width from the look up table in its chip. So it doesn't know exactly how much fuel is going to the engine, it is relying on the data whoever programmed put I the chip.

There are so many variables with modern injectors vs 23 year old units, like spray patterns and angles, dead time, flow rate, working pressure. High impedance or low impedance.

So in short putting in injectors that have the same flow rate should work in closed loop, they might not work that good in open loop. Idle and off throttle requires the smallest pulse width and thus is effected the most by dead time. 1ms is 25% of 4ms, but 1ms is only 2% of 50ms. So the ECU needs to know this.

This only is the Thumb Nail version, and YMMV. There are much more knowlagable people out there than me that have written some great information, it just takes time to read it.

GraemeD

Thanks for the thoughtful response above.

Where does this leave us with interchangeable injectors then? And what about those rebuilders we see in the vendor section or on ebay? Are they using the exact OEM injector or just using something similar that matches a few of the factors you listed?

Seems to me that the safest way to go is to buy new, OEM injectors after all.
 
I believe the RC ones are identical to Honda OEM dead times, just with different flow rates. After all, RC is based on Torrance, CA, which can't be a coincidence. Thing is, the limiter here is the stock ECU. If you go to a full solution like the AEM Infinity, you can use whatever injectors you want because the ECU can be programmed to fit whatever is in there. If you're sticking with the stock ECU, you should stick with the stock 240's or use RC.
 
I believe the RC ones are identical to Honda OEM dead times, just with different flow rates. After all, RC is based on Torrance, CA, which can't be a coincidence. Thing is, the limiter here is the stock ECU. If you go to a full solution like the AEM Infinity, you can use whatever injectors you want because the ECU can be programmed to fit whatever is in there. If you're sticking with the stock ECU, you should stick with the stock 240's or use RC.


Thanks, Honcho.

I was thinking of those guys on Ebay that sell OEM refurbished injectors (complete with appropriate part numbers). I was curious if they are really using OEM or another maker and just letting the ECU correct for the variables GraemeD mentioned.

As to the ECU, I am learning that this 1991 model car has some design "quirks"...as in ECU. So much to learn about and the ECU may be next.

BTW, I am not opposed to using RC. In fact, I plan to send mine there when I pull them.

Thanks to all who have responded.
 
Morgan, what's your compression numbers?


Solidol -

I have not run them. Nor have I run a leak down test. The motor in this car (and really the whole car including both front compartment and engine bay) appears to be as original and clean/tidy. However, it has over 335K miles on it. I am resolved to a rebuild but have not noticed anything that concerns me yet OTHER than a puff of grayish smoke under heavy and high rpm (I wonder if I am buying some carbon off?)

I am in the beginnings of a major tune up. I just did plugs, timing belt, water pump, some other small odds and ends. While I was tooling around with the rubberized air tube between the throttle body and air cleaner (to get at the VSS easier), I noted that the intake valve on throttle body opening was not very clean. It had quite a bit of carbon build up. I suspect that the intake has it's fair share of carbon as well.

I tell you this because I want to do the basics of a tune up (and do the injectors for this season). After I can locate a fitting spot to do some real work, I will pull the entire intake off and clean both it and the throttle body (professionally).

Long answer but thought I would put out my reasoning for staying on the injectors.

Speedmaster (the Omega watch, not the car)

- - - Updated - - -

Morgan, what's your compression numbers?

Solidol - I just realized that I went off my original thread title with the injector piece. You were asking about my compression (and probably next, leak down). Since I already mentioned that I have done neither, I should mention that I tend to jump ahead several steps. I.e. when I sense something should be at the end of their useful life, I will start lining up information to be ready. This beast could run another 100k miles for all I know. To your point, I will make it a point to get both done if for just reporting out purposes for the general Prime membership. Thanks.
 
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Before anything else I would get compression readings first. Don't jump into conclusions too fast. If you see low numbers do leak down and figure out which cylinder(s). If compression is healthy look at valvetrain and pcv
 
Before anything else I would get compression readings first. Don't jump into conclusions too fast. If you see low numbers do leak down and figure out which cylinder(s). If compression is healthy look at valvetrain and pcv

+1 totally agree. Santa got me a nice KTC compression tester kit this year. An annual test is a good way to monitor the health of your very expensive engine. :D
 
Before anything else I would get compression readings first. Don't jump into conclusions too fast. If you see low numbers do leak down and figure out which cylinder(s). If compression is healthy look at valvetrain and pcv
Solidol-do you know what standard compression is? I looked at the manual and it gave a number that I presume you divide by six (about 225 psi)
 
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