Why do our engines keep blowing up?

[JayDee]

I have had both my cars over 160 more times than i can remember and not just for a short spurt as at totb.

Yes I witnessed this:D

Max,

Do you connect the motec to the datalogit, have you checked logged readings against readings if you ran the motec separately?
In the pfc if the Air temp sensor  is heat soaked it takes alot fuel out, but once you are moving the air going into the engine is cool, therefore you get a leaner condition.

claaizy rx7

are you sure its blown 6 times

[maximtaylor]

The motec is connected to my datalogit and has been set up correctly so that the display matches with the logged values.

Yes, I had considered the matter of the air temp sensor in the equation, affecting both fuel correction and ignition timing.

From recollection, does fuel not go up and ignition get retarded with high intake temps? My FCEdit sofware is at home

I\'ll have a look tonight.

Regards

Max

[JayDee]

The fuel decreases the hotter the intake and yes the ignition is retarded at whatever temp you set it to.

Jason

[bill shurvinton]

There should be 2 things happening with a good ECU. Up to a point the speed density equation will reduce fuel to cope with reduced air density. However there should also be maps to richen up in case of excessive intake temperature. This latter is missing in some cases.

Haven\'t looked at the FD but there does appear to be a design flaw with the air temp sensor if it does heat soak badly.

[JayDee]

The PFC has 6 points from -30 to +80C, so yes you can richen the high temp.
The sensor is the problem, you have to stop it from heat soaking and to react faster.

Json

[Fish]

I have sort of been following this, in my OWN personal opinion a lot of this is down to the mapping of the cars.

Trolling though the US forums, I came across this new forum on water injection. http://www.turboice.net/forum/

Hopefully this forum will take off, and lots of useful information will be posted on there. Sadly I don’t think much of it will be about rotary engines.

Once the ECU gets replaced on my FD, I will be speaking with Carl (the nice gent who built my engine) to make sure that he is happy with each of the steps on the mapping project.

I have said for a long time that I don’t trust the Apexi as an ECU! I just don’t think it’s as good as people keep rating it. I am using it just to make sure that the engine can be run in properly, even the base map if so rich that it shouldn’t blow up. And then keep the engine running until funds allow for a proper ECU to be installed and mapped. Even might be going for the bench dyno mapping way, but then when re-fitted back in the engine bay it will require further mapping.

Max, although heat is generated by having to much fuel in. My understanding is that it can also work for having to little fuel in! One easy way of checking is to have EGT probes fitted, how many cars do have them? Not many.

I know the reason for one of the engine failures, and it didn’t appear to be a mapping problem.

Dan
Reading with interest.

PS. Claaizy, be careful about comments like that unless you can back it up.

[maximtaylor]

Hi Fish

Yes, I must get a pair of EGT sensors - one for each rotor....

The beauty of topics like this is that there are so many opinions! You just need to look around on the US forums for that. It would be so easy if everything we read was always correct!

It could be my mapping that caused my pop, but my timing map is a little less aggressive than a stock map to (hopefully) allow for 98 ron fuel as opposed to the 100 it is supposedly mapped for in stock form.

My fuelling according to my O2 sensor was bang on (although I accept that a pair of EGT sensors would have told me if I was lean in one rotor).

Some kind of temperature correction to timing or fuelling may have assisted the failure, hot weather, hot sensors, hot everything! I could throw in another spanner and mention plugs?..........

But I go back to the safety margin issue, which higher octane fuel and WI assist with.

Just moves that danger area further away!

Why don\'t you trust Apexi ECU\'s Fish? Plenty of cars run with it. Who\'ve you been talking to

Regards

Max

[Fish]

Max you know me, I talk to almost everyone. They say its good to talk.

I have never really liked the Apexi, and those that know me know that. I have never kept it secret. They are ok at the fuel and ignition adjustment, but they cannot control boost properly even with an uprated map sensor. Thats why everyone runs a boost controller along side it. Some are using the Apexi unit, some the Blitz, HKS, etc. but it appears that once you change to single turbo setup, it cannot handle it.

I agree with the two EGT sensors, but you could get away with running just one on the rear. As we all know that is the one that runs lean and thus hotter.

Dan

[claaizy rx7]

It has blown up 6 times due to crank sensor issues I think, there was some kind of problem with the motech sensor.  I just cant believe people would just keep rebuilding a engine and blowing it again, its just claaizy!!
And Mr Fish, why dont you trust the Apexi?

[Fish]

Some like McDonalds, some like Burger King. I just dont like Apexi, its a personal choice.

Thanks for the bit about Phil\'s car.

Dan

[bill shurvinton]

Couple of notes to think about ( bit short of time as usual)

1. Most turbo\'d road cars do not have a cooling system that can cope with WOT operation for more than about 30 seconds. Mainly because you are unlikely to need more than that on the open road.

2. When you are running twice stock this will become worse.

3. An air-air intercooler is not a good idea for TOTB type applications. An air-water is better with a nice tank of iced brine in the boot. See the Ruf porsche that they used for the ring record or any bonneville racer for examples.

4. with racing you really should drain the water and refill with just water and water wetter. Antifreeze lowers specific heat capacity.

5. The vehicle cooling system becomes critical. Personally I prefer an EWP to the stock water pump as you can run it full chat when idling. Seperate water circuit for the turbo is worth considering. The FMIC WILL reduce the cooling ability of the rad. ( plus all the housing mods to help heat removal). If it were me I might even get the housings tapped to measure local water temp in between the plugs.

6. If the air temp sensor heat soaks then that needs fixing. Easy enough to do.

7. Heat shielding between exhaust and inlet needs addressing. As does airflow past the turbo. Extra fan worth thinking about or some ducting.

8. Twin widebands are very useful. EGT is useful additional info, but really too slow to save you. Problem is the only person who build a WB that you could put pre-turbo is dead.

9. A workable knock detector would be a god send. I am working on it, promise.

10. Higher octane fuel, but looking at the failure mode, its definately heat build up related, as the engine will have passed through 6000RPM at WOT at least 3 times before the big bang.

Once you have looked at all these holistically then the tuning and water injection follow. As you know I am a great believer in WI, even on NA motors. Tuning is not a black art, its being methodical and thinking it through.

Oh and log anything and everything you can.

Hope this helps

Bill

[20B_boy]

Originally posted by claaizy rx7
It has blown up 6 times due to crank sensor issues I think, there was some kind of problem with the motech sensor.

Hmmm...who told you that then? \'I think\' you are rather misinformed...chinese whispers, hey...

Originally posted by claaizy rx7
I just cant believe people would just keep rebuilding a engine and blowing it again, its just claaizy!!

Claaizy indeed :bandit

[Glenn Butcher]

Hi all,

Good thread Max.

I personally think that tuning is the key - hell these engines ran and won the 12hours at Bathurst 4 years running.  You can\'t tell me that they are not WOT for long periods of time!

What we really need, and I haven\'t been able to find out there on the internet in all these years - is a good reliable source on the following, (I have picked 350 Flywheel Horsepower as it is probably most common - but anything up to 700hp for a 13B should have similar principles applied I would have thought):

So for the 350FWHP turbo rotary...

1. Timing for the Leading plugs (across the rev range)?
2. Timing for the Trailing plugs (across the rev range)?
3. Timing Split between the two (across the rev range)?
4. Primary Fuel injector pulse timing (based on different injector sizes - i.e. flowrates)?
5. Secondary Fuel injector pulse timing?
6. Auxiliary Fuel injector pulse timing?
7. Fuel supply system required? based on horsepower required?
8. Optimum Intake temps? (from reading books like Corky Bells he thinks that things like water injection is doing a job that the intercooler should be doing i.e. the intercooler isn\'t efficient enough).
9. Perfect AFR to aim for across rev range?
10. Perfect EGTs to aim for across rev range?
11. Spark plugs to run based on combustion temps?
12. I\'m sure there are other things - but this should be a start???  We can also look at things like the Timing and AFR on a standard rotary, as we know that it has to be like that for reliability.

The above would really be about getting all the secrets from a good rotary tuner - but there is some good info. out there on the Net.  I think we should try and compile what we can here?

The hotter weather would increase the intake charge temps. the knock sensor may not pick this up to retard timing.  When you have a good ECU you can do things like retard the ignition based on air intake temps. or have the boost level lowered based on intake temps. etc. - can Apexi do this?

What size wastegate are you running? and what boost? Rotaries need LARGE wastgates to get rid of excess boost efficiently.

One of the main reasons that your engines are popping on high speed runs is because the critical detonation point is at peak torque (around the 6000rpm mark).

More fuel will certainly help cool down the combustion temps. but if you aren\'t adjusting timing along with it then problems can occur.

Afterall, if your EGT\'s are really high then the Apex seal won\'t be far from melting point along with all the forces of it going around at 6000rpm also.

Here is a very good thread on timing etc. from some of the best rotary tuners in the world - well worth the read: http://www.rx7club.com/showthread.php?s=&threadid=101226

.ps I\'ll keep searching around - I know that Ezio from //www.cityperformancecentre.com) would have all these secrets, I\'ll see if he can part with some

[Carl]

Hi Glenn,
small point,the cars that raced in the 12 hours at Bathurst had stock power levels.
So what with higher than stock outputs being the ones that are blowing up the engine can and does reach higher stress levels than the Bathurst cars.Generally it could be said stock cars do not keep blowing up.
I am in complete agreement with you that tuning is critical on the modified engines, but so are many other things like fuel,how the car is driven,maintenance,boost control,temperature control of coolent,temperature control of intake charge,injector sizes,fuel pressure both from the pump and regulator,sparkplug quality ................and  the list goes on.
On top of this is how well or badly the engine has been built and modified can have a direct effect on how reliable an engine is.
Turbo sizing is also important.
So it is a combination of factors that can cause a problem with engine failure.
It must be said though that there are many high power engines that are still running ok here  that have spent days on open pit lane track days so some of us must be doing something right too.
Kind regards
Carl:guinness

[Glenn Butcher]

Hi Carl!!!

How are you?  (I\'ll reply to your email later).

The Bathurst RX-7\'s weren\'t quite standard    they had larger exhaust systems, larger intercoolers, and the engines had been rebuilt before each race.

Either way - I know they were running them very rich for reliability.

I know that the RX-7 that Ezio/Alec prepared for one of the races had around 350FWHP - pic. here: .

Yep - the list is endless, further to my previous post - port timing of course will effect ignition/fuel etc.  so you could only use the stock ports as a guide.