Hello,
I built this engine from used parts just for fun. Nothing was much worn but used. So the compression is not perfect... I mean its fresh engine with around 100 miles on it so it still havent settled down so hot starts are impossible.
What the engine has are:
Extended secondary intake and exahust ports. Intakes are much larger, exhaust ports are approx the same as on 6 port plates.
And as a standard new Plugs coils and wires.
New MAF.
All other is standard.
Checked all selenoids and valves for correct work.

Problem:
Right now i started to slowly use engine in mid rpm. But as soon as i pass 4k RPM mark with light throttle it begins to missfire. It shows with engine flashing on dash but no celcodes . It flashes only with light throttle. When running WOT it does not flash on dash but has not much power up until 5k rpm when it picks up. I haven t spun the engine faster than 5.5k RPM since it is very fresh.

Now do i need some sort of tune? Or things like this are not suppose to happen due to porting?

This isnt my first rx8 also not first engine more like 20+ engine i did. But until now i did only factory default engines.

 

The SSV opens the secondary intake ports at 3750... so likely it has something to do with that. Either it's not opening for whatever reason, or is opening and the porting is not playing nice with the stock tune.
Need more data to narrow it down, see if you can get AFRs and fuel trims from OBD when in both the high load and low load condition you described.

 

I did few runs. What i found out it missfires as soon as it open SSV no matter what. Only if running WOT dash starts lighting bit later but thats it. For whatever reason if not at high load it opens at 4000RPM. I attach a log its a bit long but if you look trough it you can see STFT adjustment stops as soon as abobe 3200 RPM. When missfire happens (right above 4000rpm) i can see only lower engine load (Retarded timing due knocking?).

Otherwise for whatever reason it is nearly impossible to start the car even when cold. It took me good 30 Seconds cranking until it fired up totally cold at amb temp of 25°C.
Interesting is that before the misfires started when i was driving only until 4k RPM it would start cold and hot without problem. So i am thinking that the missfire has damaged some internals. But on the other hand idle is rock solid and even if rpm drops to approx 400 rpm (when doing manuvers while parking the car) it always picks up and runs never dies.
So right now i am thinking it would be maybe better to open it up. Do you have other suggestions?

 

You didn't record AFRs or long term fuel trim or airflow. Might bave to do this again. I don't know that the problem is internal to the engine, if it's not dying on you and starting performance is equally bad cold and hot, those are reasons to think it's not the keg. Things to check:
- jet air
- ssv operation
- with afrs and fuel trims see if you need a tune.
- compression test before you go tearing it all down. that will confirm if the engine is in trouble.

 

Ok but i need few answers first. JET air : what it is? I dont understand the expression.
I can check AFR on catalizer O2 sensor but since i have good working CAT what afrs should i be looking for? Or it would be better to switch in one which is gutted? I mean it will give me voltage ratings from lambda so some base numbers would be good to know what should i look for.
Well... nobody does here compression tests for wankels. I have available only standard equipment for POT engines. Do you know what to look for with it? for example how many Bars off pressure should be archieved for given cranking rpm??

Thanks for info

 

Jet air are 2 small tubes that feed air from the intake directly to the intake ports, bypassing the manifold. They held start and hold stable idle.

The front O2 is the wideband one, so get AFR from there. Bank 1 Sensor 1. Don't get voltage, it's not voltage based, get the actual AFR/lambda value. It's available via OBD.

Like any engine you're looking for AFRs around 14.7 most of the time, 12.xx under load. Leave the cat alone, if you're sure it's in good shape.

You can google the compression standards for a renesis, there are plenty of results. There are also YouTube videos for how to test with a regular compression tester. It's not the best, but enough to get some information on this problem.

 

"Jet streams" You mean the one hose that goes to the back of intake and it splits to 2 small tubes that are fed to both primary ports? I will blow trough it air with compressor hope it helps something.
About readings. I bought Torque pro. And this one found something as commanded and metered AFR. Other than that i have only volts for bank 1 sensor.
Today i found out It missifires even in lower rpm approx 3200 rpm on second gear with very light throttle.
Here is a list of time stamps where misfire occoured:
16:31:50.764
16:33:41.166
16:36:55.564 2nd gear approx 47 KM/H
16:38:20.965 2nd gear low load

I dont know... It runs rich or stech in those areas. Not lean at all.

I also attached vid how it holds rpm when trying to move without adding throttle.
https://drive.google.com/file/d/1Od_...ew?usp=sharing

 

The drops to 20 Measured AFR are when you let off the throttle and decelerating. This is normal.
The logs look fine though there is something weird with how Torque logs rpm. It goes in chunks, instead of a different number every row. Not critical, but weird.
Also in the video, there's something up with your speedometer. It's reading 0 while you're clearly moving. Speed is collected from the wheel speed sensors, and if one of those is acting up, that couuuuld play into this issue.

TBH I think it's a combination of your porting and no tune to account for it. Get the compression tested, even if with regular tester if you have to, just to make sure that's not the problem.

If nobody there has a compression tester, then who did the rebuild and porting? What template was used?

 

In the logs i always left throttle once it shown missfire on dash. So afr 20 is understandable after it.
Data in chunks is normal since i use bluetooth adapter and it was set to 0.2 second refresh date. Thats quiet lot of data so it was in chunks.
In video i was barely moving od not moving at all. This is like 5th rx8 i driven and all weree same with speedometer. There is little lag and slow movements are detected only when you move the car sustainely for at least few seconds.
So all in all nothing found yet.

I do a compression test with standard meter. I found perfect video on youtube for it.
As i said porting was done by me as a first try. Its a large streetport. I have hold myself to grooves made by side seals and extended the port to at least half lenght of aux port of 6 port block. Sad that i dont have photos i would have posted it here.

Then if may ask does somebody know if there is some chinese clone for reading the ecu of rx8 and also some naming file for these ecus?
I did tune all of our cars but they are all vw cars.
Since mazda uses different ecus i need different HW for it.

 

MazdaEdit and VersaTune are the current options for tuning.

 

So compressions are as follows:

ROTOR FACES PSI
47 49 49 Highest PSI 49 REAL PSI ---> 48 50 50 Final Score BAR 4,02 4,2 4,2




ROTOR FACES PSI
46 49 50 Highest PSI 50 REAL PSI ---> 47 50 51 Final Score BAR 3,94 4,2 4,28

I dont know for an engine That has approx 120 miles now and is from used parts that were OK. I dont think it should have so big problems starting cold.
One thing i found starter turns only about 190 rpm with disconnected 1 plug and in other compression meter.

 

Errr those are not great numbers. How exactly was it rebuilt? Did you replace any big parts (housings?). The slow starter is definitely not helping you, you need something to get up to 250-300rpm.

 

I had like 20 used housings so i used ones that had best surface. Used new Apex seals and used Side seals. All springs new.

I found out what is causing the problem in theory. I extended secondary ports so much that they actually cause shorter stroke of rotor thus lower compression. I have extreme blow by trough secondaries when it starts up. THE SSV is very noisy as it clicks.
The 6 port engines has a workaround for it. Its APV which can close and hold the compression better then SSV.
Secondly low start RPM and weak battery adds to it.

Newermind it was just an engine for test. I will now pop it out and will continue with my hybrid engine setup with turbo.

 

you will only waste more effort and money with the hybrid, just as posted on here and on RX7Club.

I also warn people about porting, but as the saying goes ...



.

 

There isn't enough room to extend them that far ! What did you do exactly ?

If I were in your position theres two things I'd do before condeming the engine
1/upgrade the starter (no renesis will start well at 190rpm)
2/Take it on a long road trip .....minimum 300miles then retest compression.

 

As i said above about port size. This is not the only problem. It is misfiring on light loads and high +light loads above 4000.
I wont hasle with it anymore.

Continuing with hybrid.

 

It needs tuning .... I've run engines on compression that low or lower without those kinds of issues.

 

I had same issue..Changed CAT..Problem solved