Well, I blew the engine earlier today. A couple of weeks ago, we took the car to the dyno and did some pulls at 21-22 psi. Everything looked pretty good, except the power wasn't quite as high as we had hoped for (457 whp). Air fuel was a tad rich at 10.8, so this morning, I leaned the air/fuel out to 11.3. I did a 3rd gear pull and at about 7000 rpm it sounded like I hit a rev limiter. So, I immediately let off of the gas. When the car came down to an idle, it would only idle at about 2" of vacuum vs. the normal 10" and sounds pretty rough. EGTs on one rotor dropped to about 300 degrees Farenheight while the other was at a normal 900 or so. Verdict..........toast.

Luckily, I was trending the run and got some good data.

First, some specs.......
13b-re
GT42 Turbo
Haltech e8 ECU
C16 Leaded Race Gas

The air fuel looked great at a flat 11.3 (Yellow Trace), however the boost was 27 psi (blue trace)! I checked the boost controller's open loop duty cycle and it was 30%, just like when we were pushing 22 psi on the dyno. The only difference is that when we dynoed, it was around 95 degrees and this morning it was in the high 60's. I knew boost varied by temperature in open loop, but I never thought by 5 psi! Looks like I better get closed loop working next time. I was expecting to only be hitting 22 psi, so I left the BUR9EQ plugs in for this run. If I knew it was going to boost that much, I would have swapped to some 10.5 race plugs. Not sure if too hot of a plug caused the engine to detonate, but I'm only running 10.5 plugs from now on!

Intake air temps were normal at 100 degrees when the engine blew (green trace).

Ignition timing was very conservative at 6 degrees BTDC (Dark Red Trace).

Ignition split was 15 degrees.

I'm not sure if the EGTs were high or not, but the one that blew was at 1894 degrees (Purple Trace) and the other was at 1843 degrees (Pink Trace).

The part that really has me concerned is that exactly when the engine blew, the data trend flatlined for about 3/4 of a second and again a couple of seconds later. Not sure what the ECU was doing and if this caused the engine to blow, or something else.

Let me know what you guys think. Air fuel was on the money and the timing was conservative. I'm at a loss as to what caused the engine to blow. I don't mind rebuilding the engine, I just want to learn from this incident to make sure I fix whatever caused this.

 

sorry for your loss but given the circumstances as you set forth the result was predictable.

you were probably making close to 600 rwhp w a GT42 at over 25 psi in coolish weather.

that's over 4 FWhp per cubic inch!

and you were running 9 plugs?

gasoline only? all gasoline, including C16, autoignites at 458 degrees F

1894 call it 1900 F EGT?

way too much CCP (combustion chamber pressure/heat) to live.

and yet 2 rotor motors can make 1100 rwhp for a number of trips down the quarter. they do it on methanol and their egts are around 1700.

you need to cool it.

run any decent 93 octane pump and between 1200 and 2000 CC/Min of methanol along w 10.5 to 11.5 plugs and you won't be phoning your engine builder.

howard

 

C16 is not normal gas, and alcohol is not the only way, never ever has been never ever will be. Take a look here at this car for a local proven example http://www.jigsawrx7.com/main.html you can see the AFR in video's and times speak for them selves as does the dyno on 38psi on C16 only. You will see in the videos page its running 13:1 AFR and richest it goes is 12.5:1 in 4th gear at end of run.

SPECS:

Under the Hood
RP street port, Extude Honed upper intake manifold, Extrude Honed Ground Zero Lower Intake Manifold. 3mm
seals, modified Greddy T-88 turbo, Apex front mount intercooler, Greddy Type R BOV, Greddy aluminum intake
elbow, Koyo aluminum radiator, Jet-Hot coatings, Custom radiator hoses, Evans 0-pressure waterless coolant,
Summit oil catch can, Greddy 4" downpipe, 3 3/4" Greddy Power Extreme Japanese spec racing exhaust, Odyssey
Racing battery

Engine Management
Haltech E6K Stand alone system, Greddy Profec B boost controller, 2 Stage launch sequence system, Wideband
O2 air/fuel analyzer, Moroso master cut-off switch, Jacobs Pro Pak Ignition, Jacobs Leading coil, Jacobs high
energy plug wires, NGK-R racing plugs

Fuel System
Weldon 2025 high flow fuel pump, baffelless custom sumped stock fuel tank, 850cc primary injectors (2), 1600cc
secondary injectors (2), RP limited edition secondary fuel rail, -8 Russell stainless steel fuel lines and fittings, SX
engineering fuel pressure regulator, Twin SX high flow fuel filters, custom flow design return system, VP C16 race
fuel

1993 Mazda Rx-7
Nickname: JigsawRx7
Best Quarter Mile Time: 9.87 @143mph
Best 60ft: 1.36 seconds
Current HP: 631whp
Current Weight: 2674lbs including driver

More C16 only cars from this tuner > http://rx7.com/images/street_heat.pdf

Also there is an endless list of gasoline only RX7's in Japan that run 9's on street tires at over 140mph. All I can do is show you history proves many capable people have done what you are trying to do and done it very well. Hope you sort out the problem what ever it is and don't get too much wrong advise off the forums laying the blame on things for no reason.

 

Tuning with EGT is new to me, and a search revealed that there seems to be no general consensus as to what the target EGT should be. How would I lower EGTs? I know adding fuel will lower them, but 11.3 afr doesn't seem lean at all compared to what others are doing. What about timing?

 

Did you lose the seal/seals or did they stay intact? I lost a motor last night myself! I'm going to pull the turbo to see if there's any good news...

I was going to make the yearly post in the 3rd gen section to remind everyone to be careful. I with these nice low IAT's "it's the most wonderful time of the year."

 

I lost mine yesterday Too

 

not an expert by any stretch, but my $2...

plugs are too hot.

EGT is too hot, ideally they should be under 1700

27psi is a lot of boost, it might have been too lean

air temps? water temps? oil temps?

 

OP, I'm running ngk/greddy race plugs, 10 L and 10.5 T at ~20 psi boost. Those 9s definitely aren't doing you any favors with your setup.

Lance brings up a good point, this seems to happen every year...... cluster of blown engines as it cools off and tunes and boost levels change.

 

Air temps - see above
Water Temp - 180 degrees
Oil Temps - 150 degrees

 

You blew your motor because you forgot to check this box:



Why are people so hard headed about overboost fuel cut?! This isn't directed at anyone specifically. Why do people think it's bad for the engine? 100% guaranteed you would still have your motor right now if you had set a fuel cut for 23psi. There's a reason why just about every car with a factory turbo has an overboost fuel cut of some sort. I've hit fuel cut dozens of times on multiple engines, piston and rotary, and while I'd prefer not to hit it I've never had any adverse consequences. Now I don't know if your Haltech has an air temperature correction table for the boost control or not but you need to use that capability if possible.

I don't like running race plugs--9's are actually pretty damn cold--but with that much boost and exhaust temperature it's time to bite the bullet and do it. I also disagree that leading timing was conservative for 27psi, even with C16.

 

11.3 mixtures on c16 is ok. Abit rich in my opinion. What kind of timing were you running? What seals are you using?

THe rich mixture would be your low power or your porting could also be your low power.


1900f is pretty hot but i have seen engines survive hotter. if your using 9 heat range plugs, id put 200 bucks this is what killed your engine.

I run 11.5 plugs in a everyday street car makes 700hp+ and they never foul. You need to fix your motor. Check your timing map. Run the right spark plugs and you should be ok.

 

I agree plugs are too hot.

Also to correct a few statements made 1100hp methanol engines do not run 1700 degree egts.
Please don't post misinformation as it degrades your posts.

 

Fall is always the best time of year for engine builders. Cracks me up that people blow this many engines every fall when temps drop.

Sucks for your loss. What dyno was used for tuning. The numbers don't seem rightfor the setup. Ofcourse I'm sure there ate plenty of variables I'm not aware of

 

If you have never tuned one you would never know as shown above lol.

I doubt the car would jump from 450rwhp to 600rwhp with an extra 5 pounds of boost.

 

I think your original dyno numbers where misleading. Your engine is a full bridge running 22psi on a Gt42 on c16 should be making more than 457whp. Where was it tuned at? Your cars weight and trap speed at the 1/4 mile will give you a better indication of your power if the dyno readings can't be trusted. Since you spiked to 27psi, sounds like you easily hit 600+whp to me before it blew. To compare, a friend of mine was making 600+whp with c16 and on a street port (no exhaust porting at all) and 74mm triple ball bearing turbo. He would swap in his race plugs only for his hi boost settings and used the 9's for low boost daily street driving. Engine ran very reliably till he sold the set-up. I'm like everyone else. I think your plugs killed your engine because you have to be making more power than the dyno is telling you (even when it was dynoed at 22psi). 5 psi and colder temps (which will put that turbo more in it's efficiency range) also didn't help since your not tuned for it.



Edit: I also admire your willingness to learn from your mistakes. These engine DON'T just break by themselves. There is ALWAYS a cause and effect.

 

Thought about this earlier today. I'm definitely going to use this next time!


Timing was 6 degrees. What would you consider conservative?


I agree. The numbers seemed pretty low. We ran it at a local Dynojet, which was also unable to pick up a tach signal. If the dyno was right, I wonder if something wasn't already going south before it blew. The engine has always had a slight coolant leak (even before I ever put any boost to it) and has smoked a little more than I thought normal. I planned on tearing it down in a month or so anyway to see what the issue was. This is just going to expedite things a bit!

 

First lemme start off with DON'T DRINK THE KOOL-AID ABOUT METH!!!

6* is way too retarded and I'm surprised that not one other person has seen it. As RPM's increase you need to add timing back in as the rotor speed increases, the physical time to ignite the mixture shortens.

Your EGT's are so damn high because the flame is still burning as it exits the housing. This is also the likely culprit for your low tq/hp numbers. Timing makes tq/hp. Let me put it this way. You only made 52 more hp than I did and I'm running a street ported 13B-RE with BONE STOCK REW TWINS AT NEARLY 1/2 THE BOOST!!!!!!!!!!

Something else to think about, and this is why I'm not a fan of BP'ed engines.... the overlap that they have sounds great at idle, but it allows more exhuast gases to be introduced into the intake charge which can ... and obviously does lead to auto-ignition. Sure meth can raise the auto-ignition temp, but it's just a fricken band-aid for crappy tunes, loose engines, bad ecu set-ups etc etc etc.

I agree 120% I've hit hard boost cut and while not pleasant... I'm glad I did it. I've also got a few other safety measures in there as well including a percentage trim on boost duty cycle as it starts to rise, MAP vs FP main fuel table trim etc etc. People should really learn more about thier ECU's instead of the cookie cutter maps a few so called "tuners" just load up and leave. Makes me sick actually.

Well ok, one person caught it, but are you saying to retard it MORE than 6*? I'm running ~17* @ 7k and 15psi and I'm thinking about advancing it a touch and seeing what it does to my EGT's.... which at that level are right at 1700*

 

See my above post; too far on the side of conservative is a bad thing too.... why not make it -5*? 11* of timing isn't that much in that direction.... or make it 17*... 11 degrees of timing......... well see where I'm going?

I have no direct tuning experience with BP'ed turbo rotaries but I can certainly give you a lesson in street ported rotary tuning and you are WAY TOO RETARDED on your timing maps

 

In my opinion I think a lot of that has to do with tuning for max power when its warm and not leaving enough safety margin. And then it gets cold so the engine naturally makes more power and what was safe, no longer is.

I have zero experience with race fuel but for whats it worth, EGT's just like running hot on high output rotaries. I ran 1850*F+ EGT's on my rear rotor with a 500R-SP for the entire 2009 season doing 16-17 PSi on Sunoco 94 with no AI at all. I was running around 11.0 AFR with 12-13 leading (peak torque) to ~14 degrees (7.2k+ RPM) running a 10 split at the time (I know this is aggressive but on the dyno this made a ~15 rwhp increase). The knock sensor never detected any knock at all under WOT so I was happy. I did around 10+ track days that year running 20-30 minute sessions even on hot and humid days and the car never missed a beat. I installed my EGT sensors to aid me in tuning but really they became more of a novelty in my logs as it completely proved me wrong with everything I had assumed to know. When I make my new manifold, I'm not gonna bother installing EGT probes as their basically going to tell me I'm running too aggressive but I'm fine with that on my car. Also to note, I'm running NRS ceramic seals.

I also agree 1000% with the overboost fuel cut. My wastegate recently failed and my motor saw 26+ PSi on pump gas 94 octane quite a few times. Engine is still intact. I have the fuel cut set to 1.6 bar which is really like 1.8 with the way the PowerFC does it. Also, recently started running 23 PSi with pump gas + water (although it needs to be tuned properly up there, waiting for new wastegate to come in)

thewird

 

Was the green trace air temp or TPS? Looks strange for air temp.

 

+1. Too hot a plug given the boost, power levels, and the symptom that you saw/felt on the dyno. No doubt about it.

B

 

If your running a stock REW, its natural you can run more timing at high RPM as the engine is running out of breath so you can use timing to give it a little more as it trails off. With largely ported motors and nonrestrictive exhaust, your timing ramp is A LOT flatter as your torque isn't dropping off as fast at high RPM past peak torque. Apples and oranges, they're not the same. It still ramps but not as drastically as you can do with a stock motor to give those nice peak HP numbers.

Also a timing map for 93 twins and a GT42R aren't going to look even remotely close to each other if tuned out on the dyno.

I recently tuned a 20b peripheral port race car and after testing pull after pull trying different timing combinations decided on leaving the timing perfectly flat at 22 leading across the powerband (pump 94 octane).

thewird

 

isnt it ironic B we were just talking about plugs the other day and we are still running around on a factory 9 heat range plug and double the power? better change mine before its too late......

 

In my opinion, if the ecu is setup propely, installed properly, tuned properly, and safety margins properly accounted for, short of a sticking injector, the engine should be fine. I tuned my car in the heat and humidity of summer. Ran it into January and never had a problem.

Here are the things that I would change next time out.

1) Get some proper timing maps from others that have similar setups. I wouldn't mind seeing them posted here as I'd be willing to bet they are no where near 6*

2) Overboost Cut. This has been covered.

3) Proper air temp correction tables, no brainer. This is the whole reason so many prefer MAF to MAP based systems, although they both have thier advantages and disadvantages.

4) Proper coolant/oil temp correction tables

I wouldn't mind seeing pics of your porting either. In my setup, I did quite a bit of porting, but I didn't change the exhaust closing, nor did I change the intake opening. Overlap is something that I don't like. BP's and P-ports have way more overlap than SP's

If your knock sensors aren't showing any hints of knock, yet your EGT's are high, isn't it safe to assume that you could add a litte more timing to see if you could get those EGT's down a little bit? Also, running richer slows the burn time, so more timing can be added in.

I know on the MoTeC the overboost cut is...
So if the PFC works in the same way, the boost is still climbing for that one second before the cut in initiated. Lower it to what your max boost is or only a few kPa above it.

I'm running a 13B-RE just like he is with different porting. I'm using REW sequential twins.

Timing is timing. His rotors aren't in any different location than mine are at any giving degree.

This is why I am big on logging EMAP. It's gotten to the point with some of the more engineer educated guys that they are using EMAP to trim both fuel and more importantly, ignition. Again, this relates directly to what I have been saying about overlap and the need to keep the cycles seperate. Think about this, seriously, this is not me being the dick that I've been known to be, but if the people that are designing these ECU's, and building and tuning these engines for a living are using EMAP to trim the fuel and ignition in real time, don't you think we as hobbiest should at least be looking at it?

This also relects on your comment about non-restrictive exhausts. Turbo's create pressure, both in the intake and the exhaust manifold. Both have an effect on how the engine is running. I recall one post that was something along the lines of, "the engine won't idle worth a ****, I can't figure it out. Everything is exactely where it should be fuel is ***, timing is ***, MAP is ***, L is *** EMAP is 11 psi! I can't figure it out." A few weeks later after some turbo shop pointed out the glaring obvious he changed hotsides and EMAP dropped to 0, the engine idled fine and ran much better. Imagine that right? Point being, unless he is logging EMAP, we can't talk intelligently about restrictive exhausts.

Now, let me ask you this. At 13ish pounds of boost, what do you think the EMAP is on the stock REW twins. Keeping in mind that everyone in the internet world thinks they are nothing but shitty little hairdryers that pump out superheated air and are an exhaust back-pressure nightmare. This is a serious question that anyone can guess at. I have the answers and the datalogs.

By this logic our timing would also look drastically different when MAP is <100kPa. Something else I disagree with.

I disagree, up to the point where the GT42 can outflow the twins, they should be very similar if places on the same engine. This isn't to say that @ 15psi the timing would be the same becuase 15psi on 2 HT-12's is not the same as 15psi on a GT42. The big difference here is the amount of overlap that he's running versus the stock amount that I am.

I'm assuming that's an N/A P-Port 20b as you mentioned nothing about turbo's or boost level. This is completely irrelevant. Now we're talking about turbo's vs N/A's and there is a HUGE difference there. But, for what it's worth... I'm running a pretty flat 25* <100kPa and have often thought of increasing that as well, but lets face it; if I'm driving around in vac, I'm probably cruising around town and don't need the tq.

 

As for the question of "is 6 degrees at 27psi conservative?" Well, timing does vary greatly with porting etc. I'm actually running 6-7 degrees at peak torque and then about 13 degrees at redline, 16.5 psi on a T67/T04R. 8.5:1 rotors, 93 octane only. It could handle more timing but I've chosen not to advance it for safety. EGT hit 1700F preturbo before I melted the probes, so I imagine they are pretty high up there.

A lot of people used to say that 15 degrees split is too conservative, but Mazda runs it from the factory on multiple generations of rotaries.

This may be a bit of an "apples and oranges" comparison, and I don't want to get side tracked too much: FYI the Evo X runs more boost from the factory than any other mass produced gas engine that I know of. It peaks at 23psi for peak torque and then tapers down. For what it's worth, here is the factory "high octane" timing map for when no knock is detected:



The yellow traces through the cells that the ECU is using. Y axis is rpm, X axis is load which is a function of mass airflow divided by rpm. Here's a datalog of a bone stock Evo X:



You can see they are running 8 degrees at peak torque from the factory. AFR richens up to 10:1 or richer though. There are plenty of people running 27psi on Evo X's on pump fuel only. Now granted they have a lot smaller turbos, but I guarantee you they aren't running 10+ degrees timing advance at that much boost. And I'm sure the preturbo EGT's are at near-rotary levels. But Evos do have sick factory knock control systems.