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Motor blown any ideas as to why ????

Old 12-09-18, 05:36 PM
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Motor blown any ideas as to why ????

Hello guys I know this is a million dollar question but basically my motor has blown when I was hammering it from 2nd to 3rd , I know the motor is toast but wanted to see if you have the same ideas as I have as to why this has happened , I think it's an injector/ fueling fault that's caused a lean condition blowing the seals , as you can see from the photos one rotor is white whilst the other is black , even the black rotor is down on compression - 30 psi , and you can see the tip is damaged so I presume the destruction of the first has shunted the tips out of the exhaust and back in to the other rotor :-(





I brought the car last year and I haven't really driven it much , it's stock apart from the decat and bigger intercooler , the twin turbo system works perfectly as I refreshed the rats nest myself as per the guide I made and uploaded on here , when I blew it I was hitting 14psi on the apexi ecu , I also have a few other questions and ideas I'd like to run by you as well , I have a spare engine that needs rebuilding and I was wondering what people's thoughts are on these goopy apex tips that are apparently unbreakable , are they a good idea ? Something has to ware and no one has any tagible results cor long term longivity of the engine ,Is porting the engine a good idea on the stock twins as I have read loads of controversial opinions on the matter basically saying due to the exhaust design of the twin turbos your limited to benefits made by porting , also I was thinking about putting an oil pressure gauge in line with the oil squirters so in the future I can see if the omp is working correctly , has anyone done that before ???
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Old 12-09-18, 06:29 PM
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They're not unbreakable but Goopy makes solid products. I still use OEM if I'm going steel and dont need an oversized seal though.

Your SWAG on why it blew is probably correct.
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Old 12-09-18, 09:33 PM
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Damn man, that sucks that your motor blew.

As far as the why, I believe the answer is in your description of the car. It was a fueling fault, trying to push 14 psi on the stock injectors with no cat. That is a quick way to blow an engine. With no cat, there is not enough back pressure and it can over boost. The factory injectors at 14 psi are pretty overworked and if the fuel pump is sick or the fuel filter is clogged, it can easily run lean.

I'm sure others will chime in, but I've always thought 12psi was the conservative limit on stock injectors. I think the Petit unlimited ECU ran 14.

I'd recommend upgrading the secondaries and getting a tune if your going to run that much boost.

I could be wrong, but this is just my opinion.

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Old 12-10-18, 04:17 AM
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It's pretty common to run a bar of boost (14.4psi) on stock fueling in the UK, it is right at the limit though. But you can get creep to even higher levels with a decat pipe if the wastegate isn't ported on the twins, all depends on the rest of the mods.

What surprises me more is that you're in weston super mare... That's like 5 miles from me, didn't know anyone was into rotaries around here! Shout if you want a hand with the rebuild .
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Old 12-10-18, 01:58 PM
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Too much boost on stock injectors/fuel system. Just because people have done it doesn't mean its safe. All it takes is one cold day and a boost spike and boom. Typically we won't tune past 85% duty cycle on the stock fuel system which puts us around 12 psi with a fair safety margin. I never recommend removing the cat entirely on stock twins as the car is almost certain to have boost creep. Also the rear rotor tends to run leaner in a stock setup because the emissions castings into the lower intake manifold cause the runners to be different lengths. You will have to disassemble the motor and survey the damage.
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Old 12-10-18, 02:58 PM
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It's pretty common to run a bar of boost (14.4psi) on stock fueling in the UK, it is right at the limit though.
Right.
I had my stock 8 bit ECU ROM tuned by Nakazoto San at Knightsports in Japan for 14psi on stock injectors, highflow cat (no creep), big IC.

He warned not to run it on anything less than 100 octane RON (about 95 octane RON/MON for us here in the US).

You are running an Apex Power FC which does not have knock control, so your tune/performance level should be even more conservative.
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Old 12-10-18, 05:00 PM
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thanks for the responses guys, i have started to strip the motor down and to be honest im starting to think that yes it was a fuelling issue but also the company that rebuilt the engine in london need shooting !!!, i have a receipt from the previous owner that claim's the engine was reconditioned 7k miles ago for around 3k, upon removing bits from the engine id say if they did strip the motor down they did a **** job !!, i found copper washers missing on the oil return lines from the oil cooler, no gasket on the sump just a **** load of silicone and o-rings that has silicone on them when they was installed within the housings, the rust inside the irons is insane !!!, one of the first things is did when i brought the motor was flush the coolant system and although it didnt look that bad clearly it was !, the bolts holding the irons and housings together had mixed torque settings, some was removed using an urger-derger lol thats slang for battery torque gun and the others by hand with a 17mm spanner, there are bolts on the casting where the coils etc are mounted that had been snapped off in the castings, the engine harness has been dumped on the top of the block with no due care and attention, and the stator bearings have copper marks where the white metal has lifted ..... hardly what i would call a recon engine !!!! id also like to point out that one of the irons lug holes for the gearbox to attach too has also been broken off as they apparently dropped the engine , this was confirmed by the previous owner as i asked him why it was broken and why the general condition of the engine is ****, i know the car was rebuilt in 1998 which is a very long time but the car has literally done less than 10k since the rebuild and i have all the service history of the vehicle and it was all done with the same company costing the owner 1000's , quiet literally !!!! needless to say i will be building it myself and i will keep you all updated,!!!! Ceylon where about do you live ? are you on facebook ? pm me your fb details ill add ya :-) , also guys when i do the rebuild ill recon the turbo unit and ill also port the wastegate as i am aware of the need to do so especially if the cat is removed, but is it worth porting the engine with the stock twins ? and for the secondary injectors which size do you recommend ? i was thinking about putting another set of primarys in along with an uprated fuel pump and fuel pressure reg.
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Old 12-10-18, 05:04 PM
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Old 12-10-18, 05:49 PM
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That rust makes it seem like it’s been sitting in a junk yard! Both rotors blew as I don’t think it’s possible for one to blow a seal and that seal make its way over the the other rotor like you mentioned in the OP.or rather I’ve never heard of it at least.
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Old 12-10-18, 06:22 PM
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Overboost and you can absolutely blow apex seals in both chambers. I've seen it with my own two eyes.
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Old 12-11-18, 09:31 AM
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Put a motor in and put a cat in
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Old 12-11-18, 09:48 AM
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Originally Posted by bpdchief View Post
Overboost and you can absolutely blow apex seals in both chambers. I've seen it with my own two eyes.
yes, I understand that but I was referring to this in the opening post:

, and you can see the tip is damaged so I presume the destruction of the first has shunted the tips out of the exhaust and back in to the other rotor

I donít think itís actually possible for a seal from one chamber to flow through the exhaust housing, turbo and fight back though the exiting exhaust pulse to then take out another chamber. Thatís what I was referring to.....like you mention, more than likely overboost and lean killed both around the same time.
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Old 12-11-18, 09:54 AM
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Originally Posted by Sheldrake godfrey View Post
t no gasket on the sump just a **** load of silicone
its not supposed to have a gasket on the sump. and the bearings are supposed to have a line of copper also, they are made by taking a flat sheet bending it to shape, coating it, and then they get ground round.

not saying the engine isn't junk, it is.

in the USA we can buy brand new ones for basically the same price as a pair of rotor housings, and seals
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Old 12-11-18, 01:41 PM
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That rust makes it seem like itís been sitting in a junk yard! Both rotors blew as I donít think itís possible for one to blow a seal and that seal make its way over the the other rotor like you mentioned in the OP.or rather Iíve never heard of it at least.
I have absolutely had this happen and it was even on a divided single turbo manifold/exhaust housing (but through a single wastegate).
In my case the piece of apex seal exited the rear rotor housing through the manifold, into the wategate, back into the front exhaust manifold runner and entered the front rotor housing through the exhaust port where it dented the rotor up around the seal slots seizing them, but didn't break any front seals.

Your exhaust ports "suck" pretty hard when the throttle plates are closed. It can suck fresh air up into your exhaust system like normal and make flames or it can suck in broken engine bits banging out in the exhaust manifold.
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Old 12-11-18, 09:59 PM
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Wow - amazing to have it happen...is it rare as I haven’t seen it mentioned that often but good to know and thanks for sharing!
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Old 12-12-18, 09:38 AM
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I think it's been said, but definitely go through your fuel system with a fine tooth comb before running in a new engine. You'll want to make it more robust electrically and mechanically in order to maintain that boost. Clean/flow test injectors (I would upgrade secondaries knowing what I know now), new fuel pump, re-wire pump for less voltage drop, bypass or replace bulkhead connector, and add a loggable fuel pressure gauge to monitor pressure.

That really sucks, but at least you'll know your engine insides don't look like something recovered from a shipwreck when it's all done.

Also... did you take that thing apart on a shopping cart?

Last edited by alexdimen; 12-12-18 at 09:42 AM.
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Old 12-12-18, 09:56 AM
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Rotor housing looks damaged beyond reuse. The corrosion sediment are either from never replacing the coolant (should be done yearly) or it was never properly cleaned during the last rebuild. Seems like a lot for a relatively short amount of time. Center plate also seems to have a lot of scoring. Really would need better pictures and measurements. Might be more cost effective for you to start with a brand new motor rather than trying to rebuild that one as the cost of the rotor housings alone is pretty high.

I've seem apex seal fragments make it into the other rotor many times, even if it didn't blow initially.

I'm not sure who you out your way is reputable. Maybe someone else can chime in. Alternately you can ship the motor to several reputable builders. We ship motors all over the world.
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Old 12-12-18, 12:39 PM
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^ Yup. Dependnig on your plans and budget I don't think you can beat new mazda blocks unless you're doing something whacky (and even then its usually cheaper in the long run)
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Old 12-14-18, 06:23 PM
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Originally Posted by Sheldrake godfrey View Post
... is it worth porting the engine with the stock twins ?
Yes it is worth it. With a ported engine you can make more power at lower boost levels even with stock twins. For example, my stock twins made 340hp at the wheels running 11psi. Prior to porting I did 310 to the wheels at 14-15 psi. Of course you need all the supporting mods such as bigger fuel injectors/pump and an ignition amplifier, but more power at lower boost is always a good thing.
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Old 12-16-18, 04:22 AM
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That's for the help guys and the advise , I got a second hand engine I will rebuild , I'll post it on here when it's done :-) what's a good injector size to go for on the secondary injectors ? Shall I buy some more 540cc injectors and put them in ? I never had a cat the guy removed all that as it melted apparently, surly if I port the wastegate I shouldn't need the extra back pressure from the cat ? Or do I still need to put the cat in to make sure it doesn't boost spike ?
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Old 12-17-18, 09:53 AM
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The stock injectors are 550cc primary and 850cc secondary. From what I've seen a lot of people upgrade to 1200 or 1600 secondaries, and that typically requires changing the fuel rail since most replacements are top feed.

If you port the wastegate, it should help, but having a cat with help infinitely with the smell from the tail pipe.

Vince
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Old 12-20-18, 12:14 PM
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The stock setup was basically trash from Mazda even when driving normal boost.
You have to really pay attention to how you drive.
Let the engine fully warm up before boosting.
Let the engine temperatures stabilize after parking for a while before getting on boost. Especially in winter due to the air temp sensor being above the block and not in the intake track.
Religiously maintain the engine.
Every time you drive, boost it for a while to help reduce carbon buildup which is a big killer! Treat it like a race horse, it needs exercise!

Bigger radiator and IC are great safety factors which Mazda did not do.
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Old 01-04-19, 10:38 AM
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all good on point comments above...

more "boost" does not always mean more power.

when you push the OE compressors way past their efficiency area all they do is overheat the charge air resulting in less oxygen molecules entering the engine so less power AND monster non linear overheated air
enters the engine.

i log air temps between my turbo and intercooler w a Type K Thermocouple (similar to EGT). accurate to within a couple of F degrees and a few thousandths of a second. the newer turbos running within proper
output levels routinely spit out air at 400 F. i can only imagine what temps are generated by our 1980 aero OE compressors run waay past their intended pressure.

gasoline autoignites at 536 F. autoignition at the wrong time can create detonation. 3500F instead of the normal 1400F accompanied by a hammer blow shock wave. result w stock apexseals, lots of pieces of metal flying
around in the engine doing carnage. and yes, the front and rear are in communication thru the plenum and violent oscillating forces (normally helping cylinder fill). i broke a one ceramic apex seal and the ceramic grinding
dust scoured both ends of my motor...

newer more malleable 21st century apex seals often do not break but generally cornerseal springs lose height and compression suffers (30%). motor must come apart but generally not a lot of carnage.
stipulate (only) FD inconel corner seals springs not the shiny cheaper RX8 cornerseal springs.

don't try to push the stock turbos or you will be bitten.

good luck

Last edited by Howard Coleman CPR; 01-04-19 at 11:04 AM.
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Old 01-04-19, 07:11 PM
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Nice to see you back Howard . long time.................
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Old 01-04-19, 10:35 PM
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Originally Posted by cewrx7r1
The stock setup was basically trash from Mazda even when driving normal boost.
You have to really pay attention to how you drive.
Let the engine fully warm up before boosting.
Let the engine temperatures stabilize after parking for a while before getting on boost. Especially in winter due to the air temp sensor being above the block and not in the intake track.
Religiously maintain the engine.
Every time you drive, boost it for a while to help reduce carbon buildup which is a big killer! Treat it like a race horse, it needs exercise!

Bigger radiator and IC are great safety factors which Mazda did not do.
Calling the stock setup trash is quite an overstatement. Most cars have room for improvement, doesn't make it trash. My stock FD is quite fun and reliable. My modded FD is more fun and more reliable haha.
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