How often do engines fail because of FI?

[steve99]

Originally Posted by Ryan GT86

Does this mean even turbo kits marketed for stock engines could put the engine at severe risk of failure if the engine wasn't rebuilt with stronger components?

To me its counterintuitive that FI engine failures occur at lower rpms. Is there a reason why this occurs?

Torque


FI engines can produce more torque at lower rpm that upper rpm


torque is what breaks rods


part of tuning will be to limit torque (hence power) at lower rpm)


stock engine less than around 300ft lb is usually reasonably safe


http://www.epi-eng.com/piston_engine...and_torque.htm

[gtengr]

Originally Posted by Irace86.2.0

I think you are isolating this example to typically sized turbos. Big turbos for the engine size can barely be building boost at 4k rpms.

I think the majority of failures are detonation... This is why rods break on stock cars and not on 400hp track cars.

I'm just assuming typical parts. Why would I put an oversized turbo on a stock engine? A gtx3067 makes big torque under 4000 rpm so it's a moot point anyway.

If the majority of failures are detonation, why do E85 cars bend rods?

Originally Posted by Irace86.2.0

A big supercharger will still be putting boost down at any rpm at anytime.Centrifugal SC have a linearly rising torque curve—not a flat one

So?

[JimmyMac]

9~10 psi bent rod cylinder #4. I think #3 was slightly bent. #2 looked straight. #1 threw everything through the block. haha I think cause was valve float and/or tossed rocker. You can see in the intake port pic where only one valve was bent/damaged. Exhaust side was fine. Stock 2012 engine. This was awhile back but just now getting to look at the damaged engine out of curiosity. If the valve spring/rocker incident didn't happen, it would have been a matter of time before something else would have.

[Ryan GT86]

Originally Posted by steve99

Torque


FI engines can produce more torque at lower rpm that upper rpm


torque is what breaks rods


part of tuning will be to limit torque (hence power) at lower rpm)


stock engine less than around 300ft lb is usually reasonably safe


http://www.epi-eng.com/piston_engine...and_torque.htm

So what would have to be reinforced in the stock engine to prepare it for FI to increase longevity and prevent failures? I'm planning on track days with a turbocharged 86 in the distant but inevitable future.

[steve99]

Originally Posted by Ryan GT86

So what would have to be reinforced in the stock engine to prepare it for FI to increase longevity and prevent failures? I'm planning on track days with a turbocharged 86 in the distant but inevitable future.

best talk to an engine builder thats done some FA20 FI

rods are main weak point , but if your going to build an engine you likely want to do a few more changes

[majixmatrix]

Dude.....

Originally Posted by Hags86

So the symptom of the bent rods is the air/fuel ratio changing. I had some problems with the A/F drifting over a few weeks and the ECU needed to perform a lot of fuel trims to try and compensate. We couldn't figure out why. Faulty MAP sensor or Lamba sensor? Changing the engine efficiency table an it would be sweet, and then drift away again.

Turns out the compression ratio was changing as the rods bent and lowered the CR. All 4 rods were in fact bent - the photo is just the worst two of the four.

[Hags86]

Originally Posted by majixmatrix

Dude.....

Tell me how you'd figure rods are slowly bending? There was no engine noise or knock - until there was...

[Tcoat]

Originally Posted by Ryan GT86

So what would have to be reinforced in the stock engine to prepare it for FI to possibly increase longevity and reduce the risk of failures? I'm planning on track days with a turbocharged 86 in the distant but inevitable future.

FIFY

[Hags86]

Originally Posted by Ryan GT86

So what would have to be reinforced in the stock engine to prepare it for FI to increase longevity and prevent failures? I'm planning on track days with a turbocharged 86 in the distant but inevitable future.

Nothing. Just have $7-$10k cash at call when you need to build the engine. There is no guaranteed way to do it safely. You might be OK for a while, maybe not.

You could just pop some forged rods as they are absolutely the weak link. But once the engine is open the slippery slope starts. Just need to deck it to get a good surface for the seal. Hone the bores and now you need +0.1mm pistons. Those valves are very slightly bent.... You get the picture.

My advice is don't do anything and run the gauntlet. Just be ready to reach for the cheque book one day. If that will break you, then don't put the turbo on in the first place.

[gtengr]

Originally Posted by Hags86

My advice is don't do anything and run the gauntlet. Just be ready to reach for the cheque book one day. If that will break you, then don't put the turbo on in the first place.

I agree. It's tempting to build in advance in order to resell/reuse a healthy stock core, but my power goals are low enough that I think I have a good chance of it staying healthy for a few years until I'm ready for a different car. If I was planning on keeping the car for 5-10 years or more on boost with E85 I'd lean towards building in advance.

[Hags86]

Originally Posted by gtengr

I agree. It's tempting to build in advance in order to resell/reuse a healthy stock core, but my power goals are low enough that I think I have a good chance of it staying healthy for a few years until I'm ready for a different car. If I was planning on keeping the car for 5-10 years or more on boost with E85 I'd lean towards building in advance.

This, in my opinion, is a perfectly sensible approach.

[Ryan GT86]

Originally Posted by Hags86

This, in my opinion, is a perfectly sensible approach.

I might reinforce in advance when I can then, I'm planning on keeping the car for as long as I can.