Built motors and detonation
 

We all know detonation kills motors. There's lots of threads about blown stock motors but what about built motors, just how much detonation can they take? Has anyone here blown a built motor? How much boost were you running? How long did it detonate before dying? Now that I'm running 20+ psi with WI detonation is a very big concern of mine.


Discuss.......
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Det breaks any engine. Stronger pistons can resist, but in the end they all die.

That is a lot of boost.

I personally have not blown a built miata motor (yet), but I have friends that have blown built motors due to tuning mishaps. The more power you are making, the more likely something will go wrong. The margin of error gets slimmer and slimmer as the power increases, regardless of the high dollar parts. There seems to always be a weak link that somehow gets over looked. Unfortunately, it is when something breaks that you find out what that link is.

Umm two people popped theirs just last month, savington and neogenesis. Both presumably due to detonation. Sav had forged pistons, neo had B6T pistons (low compression, not forged though), both had forged rods of course. Sav ran 20-ish psi from a 3071R on his 1.8 and neo was at about 18-ish psi from some version of a T3 with a bigger compressor wheel on a 1.6. Sav blew his on track, neo's was at the dyno. I was at that dyno day and heard no knock or ping and neither did anyone else. I don't think Sav had audible knock either, but rather deduced the cause upon teardown. So you're right to be nervous and fearful of detonation. :noes: :x: :D

84mm 8.7:1 supertech:
Attachment 201846

Assembled it in April '09, first startup was May, head gasket leaked. Switched HGs, installed ARP head studs, no more leaks. First two track days done in June 09 at 13psi from my old 2554. Sold the 2554R, installed the 2871R, tuned to 15psi. Did 6 days on the 2871R, so probably 18-20 sessions at 15psi. Popped an IC coupler on the 7th day, ran it all day like that dicking with the MBC and BOV trying to diagnose.

Turned it up to 21psi:
Attachment 201847

and it lasted 9 laps.

You shouldn't be worried - you should be really fucking worried. Best I can work out, mine was caused by high IATs and a slight lean condition in one cylinder (one injector 3% low).

From what I've learned in the last month: On a track car, I wouldn't run 20+ psi without water injection set up as a safety net, and I'd really want to see per-cylinder fuel and spark trims based on EGT so the ECU can automatically identify lean conditions or bad EGTs overall. I'd also want to see limp modes based on IAT. On a street car, an IAT-triggered fuel limp would be nice, but just an IAT gauge that you keep an eye on when doing big pulls would do it. If you're using water to turn the timing up, you must have failsafes.

so a built BP is only good for 6 or 7 psi over what it can handle not built?

i have been curious to know what limits people have hit with fully built motors.....

track car != street car

Lots of street cars could get away with 20+ psi on a well built motor with a good tune. On a track car youre putting lots of load on an engine for an extended period of time meanwhile the cooling system/ intercooler/ charge pipes/ etc are all getting heat logged.

i know that much.........but ideally wouldnt you want your motor to be able to handle even the worst case scenarios in driving conditions? at least for peice of mind........

whats the worst case? salt flat racing at high load, hot air, wide open at max boost for 5 minutes straight? You would have to have an insane cooling system and severely limit power in order to survive that.
Yet a street car could get abused on a stock cooling system while making more power and never blow up.
It cant be generalized.
Your setup and limitations are based on what the car is going to do and what your goals are.

i fully understand....i want to get into road racing when time and money permits....as of right now my car will only be seeing normal everyday conditions.......i want to get my car ready to enter race events over time and right now im just trying to take as much knowledge in as possible! :D

At your boost level you should be avoiding det like the plague.

Built motors are made to make more power, not to be bulletproof and immune to poor tuning. The forces exerted on the rods and piston over 250whp require the forged internals. The cylinder pressures are much higher at 20psi+, and ridiculously high during a knock event.

The worst part is that det achieves max cylinder pressures before the piston has reached TPC...and this is what's dangerous. Forged rods can take the power you're putting down...but no rod is going to live long under detonation because you putting a PRESSURE load on top of the assembly while you still have a MOMENTUM load in the opposite direction, nearly doubling the load it usually sees.

CLIFFS: Don't do it. What takes 3 revolutions to kill regular parts will take 5 revolutions to kill yours.

Neo's pistons didn't look like this, in fact, there are no signs of detonation on the head or piston tops...

That piston looks straight up melted. I've seen exhaust valves that have a similar look after they melted.

So what did kill neo's motor? Poor motor assembly?

http://boostedmiata.com/blown_engine..._piston001.JPG

I've done the melting thing! mmmmmm vertical scoring!


I've also done the failed ringlands thing:

http://boostedmiata.com/blown_engine/pistons.jpg

87 octane + 16* static timing + 7psi = BOOM



Remember kids, brush your teeth before you go to bed...

A moment of violent detonation killed my motor. Ringlands on at least 3 of the pistons are broken. The walls are not scored but you can see vertical wear marks left by ringlands shaking around. Definitely had nothing to do with poor assembly.

This.

You're not running a little turbo that hard, are you?

Do you have easy access to E85?

the 2871 should be bale to handle to boost, it's the lack of octane I worry about.

Cool, I thought he had a 2554. I saw E85 was offered at a lot of stations in the area of FL I went to. It's very knock-resistant fuel, and eliminates the need for the complexities and potential hazards of WI.

All good info guys, keep it going. I think this is an important thread so that people with less knowledge don't think built motors a bullet proof. I'm running 22 psi right now (want to run 25) with a devils own WI kit. I'm using the #7 nozzle set to come on at 10 psi. I've been using Heat which is like 97% meth. I'm going to run an led to the pump so that I know it turns on when I hit 10 psi, other than that what other fail safe could I put in?
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