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High Compression Turbo Help

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Old 04-10-17, 09:50 PM
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High Compression Turbo Help

So I need a bit of help...

I was lucky enough to receive my RTEK 2.1 recently, and I've installed it in the car and set up the basic stuff. I am, however, brand spankin' new to tuning. I've gone through every single seemingly-relevant thread in the RTEK forums, back to the oldest page, but I am monumentally unclear as to what I should do about my particular situation.

My engine is a S4 Turbo, streetported, using S4 N/A rotors. Stock turbo, 550cc injectors, 3" down and mid-pipes into a 2.5" Racing Beat N/A catback. Stock airbox and TID, aftermarket BOV, FD fuel pump, no twin scroll, no emissions nonsense, etc.

The only things I've done so far with the ECU was select my injectors, lower the staging point to 3,100, altered the hot-start fuel map and added between 5 and 12% of fuel between 4,000rpm - 8,000rpm in the range of 4 to 14psi. I have not touched the timing.

I do understand that the fuel and timing corrections go hand-in-hand. I have also gathered that on the high-compression builds, it's important to back off the timing quite a bit more than you would with the standard turbo rotors.

I'm not going for crazy power, I just want it to be tuned safely and be reliable.

My boost generally runs from 8 to 10psi, depending on how cold it is outside. I do have a wideband, though it is not connected to the ECU currently for logging purposes (I'll get to it eventually..)

Additionally, within the next few months I'd like to install my Hybrid turbo and 720cc secondaries (May pop another set of 720's into the primary location at this point as well.)

Basically what I'm looking for is a fuel and timing map on which to copy into my RTEK that is generally recognized as safe for my high compression engine given the porting, exhaust and current limitations of the fuel system. Certainly they must exist...? I'm a little surprised that I haven't found them yet as I'm sure my 'build' has been done before many times over. So where are they hiding?

If you do post maps, please explain why these changes are necessary.

Learn me some tuning!
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Old 04-11-17, 03:03 PM
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Give this thread a read: https://www.rx7club.com/rtek-forum-1...g-maps-885556/
Should at least point you in the right direction
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Old 04-12-17, 04:51 PM
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Here's a question.. On the 'high compression ' timing maps, in vac, I guess I expected those to be negative numbers to retard the timing.. One member posed the question himself, and then posted later saying he inputted the maps as they were shown and said all was well. The question was never technically answered, so I'm asking it now.

Also, I intend on using those timing maps... But for fuel, the only thing I can find are solareon's fuel map. I assume it's safe for me to utilize that as a starting point and adjust the fuel further based on what my AFR's are doing?

Are these timing and fuel maps even safe to be using with my 550cc injectors?

I feel like I need Aaroncake's input. :-D

Last edited by Acesanugal; 04-12-17 at 04:56 PM.
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Old 04-16-17, 03:00 PM
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I guess this being the Rtek forum here, I'm not terribly surprised at the lack of response... But really? Rtek has been around for a long time, surely someone must have input.
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Old 04-19-17, 05:42 PM
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You have to start somewhere. Perhaps use Solareon's fuel map, drive gently staying out of more than a few PSI of boost, and see if AFRs are anywhere in the ballpark (like 13).

If you have the air pump, the wideband O2 sensor will read erratically lean in vacuum and cruise areas of the map.

550cc Injectors: You might be fine. The stock turbo will choke airflow at redline, so you don't really need more fuel than stock. I'd be more concerned about the area where boost hits, if you are planning to run 10+ psi. As you remove fuel and add boost, read you RTek logs to check the injector duty cycle. You'll see if you are in the 80-90% danger zone.
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Old 04-22-17, 08:02 AM
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Originally Posted by ColinShark View Post
You have to start somewhere. Perhaps use Solareon's fuel map, drive gently staying out of more than a few PSI of boost, and see if AFRs are anywhere in the ballpark (like 13).

If you have the air pump, the wideband O2 sensor will read erratically lean in vacuum and cruise areas of the map.

550cc Injectors: You might be fine. The stock turbo will choke airflow at redline, so you don't really need more fuel than stock. I'd be more concerned about the area where boost hits, if you are planning to run 10+ psi. As you remove fuel and add boost, read you RTek logs to check the injector duty cycle. You'll see if you are in the 80-90% danger zone.
u got afrs wrong, 13s will pop a turbo engine, high compression even worse.

12.5 under 250hp
12s 250-300, 11.5s up to 450
11s to 550, then add water and go back to 11.5-12.
ball park.
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Old 04-22-17, 08:59 PM
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I'd be happy with 270hp. But that is a saga for another time.

Meanwhile, across town...

I reconnected the o2 sensor and added a bit of fuel to the cruising portion of the map and that brought the closed loop AFR's down to 14.3-15.1 depending on load. However, the problem of it not going into closed loop at appropriate times still remains as I figured it would.
According to my Rtek logs, the o2 sensor appears to be operating in the correct voltage range.
My TPS is dead on at 20%, but I feel like the TPS is the problem.. While it may be adjusted properly, I feel as if it's range is not as linear as it was many moons ago. My theory is that because of this, it does not indicate to the ecu that the engine is 'cruising' at a physical throttle position where it would indicate so if the sensor was working properly. Meaning while the physical throttle position is correct, the indicated throttle position at that point is telling the ecu open loop is appropriate. I could be way off here, but to me it sounds logical. Thoughts?

Additionally, I have another question... My AFR's under full boost are richer now than they were when I was running the stock timing maps. As you know I am now using timing maps much less aggressive than stock because my engine has S4 na rotors. Can running less timing than stock cause the engine to run more rich with the stock fuel map? I'm hesitant to pull fuel with the Rtek because it seems backwards to me.. But if running less timing means you also need to dial back your fuel a bit, then I will do so. I need an expert. Where's arghx at? It's his timing map I'm using :-P

I'm shooting for 11.1 to 11.3, leaning more towards 11.3 under full boost based on the research I've done. 10.6 to 10.8 seems a tad rich to me, and I've read of some horror stories in the 10's on high compression turbo applications....
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Old 04-23-17, 06:01 PM
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Originally Posted by lastphaseofthis View Post
u got afrs wrong, 13s will pop a turbo engine, high compression even worse.
Part throttle. Your numbers are correct for full boost.

Originally Posted by Acesanugal View Post
I reconnected the o2 sensor and added a bit of fuel to the cruising portion of the map and that brought the closed loop AFR's down to 14.3-15.1 depending on load. However, the problem of it not going into closed loop at appropriate times still remains as I figured it would.
According to my Rtek logs, the o2 sensor appears to be operating in the correct voltage range.
My TPS is dead on at 20%, but I feel like the TPS is the problem..
Check for a continuous sweep. If it's reading right, it's reading right.

Originally Posted by Acesanugal View Post
Can running less timing than stock cause the engine to run more rich with the stock fuel map?
I haven't heard of that. Maybe if there was a lot of incomplete fuel burn or misfires. In any case, I would still adjust for target AFRs.

Originally Posted by Acesanugal View Post
I'm shooting for 11.1 to 11.3, leaning more towards 11.3 under full boost based on the research I've done. 10.6 to 10.8 seems a tad rich to me, and I've read of some horror stories in the 10's on high compression turbo applications....
You want to be rich as you are adjusting the map. What stories are you referring to?

Also, I was not able to achieve 0.2AFR accuracy on an RTEK, especially at the injector transition point. Maybe 1.0 AFR during the changeover. The technology is older and not as precise as the modern stuff.
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Old 04-24-17, 09:06 PM
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After talking to a friend, I guess I'll be making some negative corrections to my fuel map this weekend.

I also believe I've got the closed loop situation figured out and adjusted to a more reasonable afr.

No doubt I'll come up with more questions soon.
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Old 04-25-17, 09:48 AM
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Just saw this thread.

1. Replace your o2 sensor. Get a new one, it's 30 years old. Those old 1 wire o2 sensors weren't very accurate in the first place. Go on Rock Auto and order it, it's $24 from NTK (NTK is the original manufacturer, use them).

2. Does the car drive funny? If it reads that lean under low load but it drives ok, I wouldn't worry about it, unless you care about NOx emissions.

3. If you have the money, replace the TPS too. I'm not sure if you need to go to the dealer for this, but Rock Auto has them for around $200. If you don't want to spend, confirm the resistance sweep is ok (as has been mentioned already).



The boost based timing maps are actual spark timing for the leading side, they aren't correction maps. On the leading side a negative number isn't some relative value like the fuel correction maps; it is an actual spark timing command. The split is set relative to the leading. If you use my high compression split maps, don't worry about changing them. Just put that map in there and leave it alone.

For the leading side, tune that on a dyno only. Otherwise, leave it alone.

The closed loop staging - if the TPS and airflow meter are ok, and it drives fine, don't worry about it. You're not going to damage anything. But you need to have good sensors. If you really want to tune the part throttle/closed loop area, ok, do that, but I personally would leave it alone.

I tend the give stock tunes a lot of credit, although that applies less and less the more mods you have. That's my point of view.

Last edited by arghx; 04-25-17 at 10:49 AM. Reason: lean under low load isn't dangerous
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Old 04-25-17, 09:54 AM
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I used both the leading and split timing maps that you labeled for use with a high compression 9.4 engines. So you're saying I should have only used that split map?

My o2 sensor is a bit over two years old.. And turned out to be operating within range.

Initially when I inputted both timing maps and left the fuel map as stock, it was reading into the 16's in closed loop and I did feel some hesitation cruising down the highway. I added a wee bit of fuel in the cruising portion of the fuel map which brought the numbers back down to where they should be and it seems to be fine now.

However, after I installed the leading and split maps, I noticed my AFR's were reading a lot richer at wot at full boost.. Down into the mid to lowish tens at their lowest, which I'd never had happen on stock timing and stock fuel. My question now is should I make negative corrections to those boost areas of my fuel map to lean the AFR's back out to 11.1?

Last edited by Acesanugal; 04-25-17 at 09:58 AM.
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Old 04-25-17, 11:27 AM
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Originally Posted by Acesanugal View Post
I used both the leading and split timing maps that you labeled for use with a high compression 9.4 engines. So you're saying I should have only used that split map?
No. You're fine. What I'm saying is, leave those maps as-is, unless you are on a dyno tuning spark. When you do tune the spark, tune the leading only, unless you have a really good reason to mess with the split.

My o2 sensor is a bit over two years old.. And turned out to be operating within range.
Ok, good to know.

Initially when I inputted both timing maps and left the fuel map as stock, it was reading into the 16's in closed loop and I did feel some hesitation cruising down the highway. I added a wee bit of fuel in the cruising portion of the fuel map which brought the numbers back down to where they should be and it seems to be fine now.
That's fine. The stock ECU might have been expecting the air pump to be running in that area, but you don't have that installed. The air pump sends air from the airbox to the exhaust ports, before the O2 sensor. Only in a narrow operating range does it send air to the cat.

However, after I installed the leading and split maps, I noticed my AFR's were reading a lot richer at wot at full boost.. Down into the mid to lowish tens at their lowest, which I'd never had happen on stock timing and stock fuel. My question now is should I make negative corrections to those boost areas of my fuel map to lean the AFR's back out to 11.1?
To answer your question directly: Yes. You should make changes to your fuel map to meet the guidelines I posted about in this thread about target AFR:

https://www.rx7club.com/rtek-forum-1...tables-890528/ . You can use the moderate map. Conservative map is for protecting the cat.

Here is some more background info:

Changing the spark may have changed the exhaust temperature which changed the boost. Or changing the spark changed the relationship between throttle and torque - my map is a lot more conservative than the stock ECU for safety. So that ends up changing the relationship between engine airflow/boost and engine torque, and so you end up in an area that runs richer. The enrichment in the ECU is scheduled based on engine load, which is proportional to airflow divided by rpm.

The fuel correction map is based on boost and was inserted into the ECU fuel calculation by the makers of the Rtek, to make changes on top of the factory fueling based on airflow (AFM signal)

Last edited by arghx; 04-25-17 at 11:32 AM.
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