How often do engines fail because of FI?

[firekat]

Good Point - one more for the discussion. So using your rationale the turbo would be the better way to go.

I considered a turbo installation, as it is by nature more efficient. Reasons why I did not pursue it were for me that there was only one kit that was CARB compliant, in that case the gains did not seem worth the investment, there always seems to be heat issues with all turbo installations, and the kits do not seem to be up to level of a factory turbo'ed car which seems more mature technology wise. Also wanted a more uniform addition of power across the entire operating spectrum.

If you use larger turbo for more grunt down low, you better make sure that you have a really good waste gate when you higher in the rev range.

I have owned two turbocharged cars, a 1982 Porsche 924 Turbo, and a 2013 Mini Cooper Clubman S. Operationally they were both transparent as to the effects of the boost. They were pretty much effective throughout the power band. When you have a full corporation behind those turbo installations you can do that. Maintenance wise there was no turbo problems with the Mini whatsoever. The 924 T liked to shit turboshaft seals, so as you would go down road it was as if you were like the local mosquito abatement vehicle.

I guess if you use the fact that Edelbrock guarantees their installation on a new vehicle you can use their limit on boost as to what a stock build can take. They advertise 242 WHP & 186 ft/lbs on a 2014 BRZ. You can stop there if you want to be safe.

Cosworth also set a limit on the output on a Stage 1 installation, for internal issues if I remember correctly.

Of course Irace I know you know all this stuff since you probably researched your Harrop for a while before you purchased it. This is all just for the benefit of the OP

[gtengr]

Originally Posted by Irace86.2.0

Wouldn't it also matter whether the kit was a SC vs turbo?

A supercharger may dyno at 300 whp like a turbocharger, but the supercharger is pulling some of the power to run itself. Say it takes 30 hp to run the SC, then a 300 whp SC'ed car would be making 330+ plus drive train losses at the pistons (if that makes sense), meaning the pressure on the rods/pistons/bearings will be higher. Also, a supercharger is more direct with more low end, so the potential for damage could also be higher for an equal rwhp to a turbo'd car.

I don't think that's a major factor because I don't think it's the peak hp that matters, it's the low end torque that the peak hp number might represent. It's the 200 lb-ft at 3500 rpm that breaks stuff on this car, not so much the 300 rwhp at 7000 rpm (numbers aren't exact, just to illustrate). SC should do better in this regard since it's still building boost while a turbo peaks at lower rpm.

Originally Posted by firekat

I guess if you use the fact that Edelbrock guarantees their installation on a new vehicle you can use their limit on boost as to what a stock build can take. They advertise 242 WHP & 186 ft/lbs on a 2014 BRZ. You can stop there if you want to be safe.

Cosworth also set a limit on the output on a Stage 1 installation, for internal issues if I remember correctly.

It's also worth considering that the stock engine is limited to the boost range that the Edelbrock kit operates in when it comes to 91 octane, so it's not entirely by choice that Edelbrock stopped there.

[Irace86.2.0]

Originally Posted by gtengr

I don't think that's a major factor because I don't think it's the peak hp that matters, it's the low end torque that the peak hp number might represent. It's the 200 lb-ft at 3500 rpm that breaks stuff on this car, not so much the 300 rwhp at 7000 rpm (numbers aren't exact, just to illustrate). SC should do better in this regard since it's still building boost while a turbo peaks at lower rpm.

That might be true for a centrifugal SC and for a small turbo, but a PD SC or a large turbo would reverse that statement.

High rpms should put more stress on the components, but maybe there is higher oil pressure at high rpms to manage the forces on the bearings, or more efficiency and less jerk at high rpms. Maybe there is better knock prevention. Maybe there is better fueling. I don't know. I can think of all types of reasons why low rpms seem to be a place where failures occur that have nothing to do with power down low, but could be low end power too.

Do turbos fail more than SC of equal power levels?

[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?

[Irace86.2.0]

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?

The following are reasons why engines could fail, which would be compounded by adding more power over stock design:

There is more jerk (change in force or acceleration) at lower speeds and rpms. There is less oil pressure too, so significant forces on a bearing then could lead to rub easier. There may be less flow or efficient flow of exhaust gases at low rpms, which could increase the chance of knock or detonation. There could be a change over in fueling from 4 to 8 injectors (I don’t know) or closed to open mapping (I don’t know) that could put the motor at risk during the transition. There could be lugging of the motor at low rpms, which causes strain; ie, going WOT in a high gear at low rpms. Traction plays into resistance which plays into transional forces, so traction changes at low speeds and low rpms under jerk could be problematic like having to overcome static forces of a drag race versus a rolling race.

[gtengr]

Originally Posted by Irace86.2.0

That might be true for a centrifugal SC and for a small turbo, but a PD SC or a large turbo would reverse that statement.

Based on boost logs the Edelbrock comes on with a higher boost than a centri, but still increases boost based on rpm and doesn't hit peak as early as a turbo.

Originally Posted by Irace86.2.0

High rpms should put more stress on the components,

Higher rpm does equal higher stress, but those forces are more likely to eat rod bearings or break rod bolts. Rod bending is a compression failure mode, more likely from either low rpm+high cylinder pressure or detonation/pre-ignition issues imo.

Originally Posted by Irace86.2.0

I don't know. I can think of all types of reasons why low rpms seem to be a place where failures occur that have nothing to do with power down low, but could be low end power too.

Originally Posted by Ryan GT86

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

Horsepower has the same relationship to cylinder pressure as torque does except rpm is involved, but lowering rpm doesn't decrease torque until you get very low. The catch is that the combustion gas is expanding in a combustion chamber that is independently expanding at a different rate along a mechanical path as the piston moves down the cylinder. For this reason, an engine generating similar torque numbers at 4000 and 7000 rpm would be generating more compression in the rod at 4000 rpm.

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?

IMO no it really just means be careful how you treat a car that isn't FI from the factory.

[Ryan GT86]

Originally Posted by gtengr

IMO no it really just means be careful how you treat a car that isn't FI from the factory.

How careful? Like only using the turbo/supercharger manufacturer's tunings?

Just wondering if something like a track day could cause engine failure.

[Tcoat]

Originally Posted by Ryan GT86

How careful? Like only using the turbo/supercharger manufacturer's tunings?

Just wondering if something like a track day could cause engine failure.

Having the right tune is important and although the manufacture's tune is usually fine you reduce risk (a little) with one specific to your car.
You could blow the engine with the car sitting at idle in your driveway or you could do 100 track days perfectly fine. Many guys track with no issues but it does increase the risk though. Even a fully built engine can blow so there is no sure way of going about it.

[gtengr]

Originally Posted by Ryan GT86

How careful? Like only using the turbo/supercharger manufacturer's tunings?

Just wondering if something like a track day could cause engine failure.

I wouldn't ever expect 100% confidence against failure on the track with FI, but there are things that can be done to improve the odds like higher octane gas, avoiding extended hard use on exceptionally hot days, avoiding WOT at low rpm especially in higher gears, monitoring oil temperatures and backing off when they go up too much, etc. It's a matter of risk tolerance. If I could not stomach the cost of an engine build, I would play it safe and stay away from road courses or maybe go and soft pedal a few of them.

[mrg666]

Enough dabbling. Be conservative and intelligent about FI while doing it. It is fairly safe if you are not boosting like an idiot. If the engine still blows after all precautions, I will either fix it or replace the engine and boost again. FI is awesome. I can't imagine driving with stock engine again.

[Irace86.2.0]

Originally Posted by gtengr

Based on boost logs the Edelbrock comes on with a higher boost than a centri, but still increases boost based on rpm and doesn't hit peak as early as a turbo.

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. A big supercharger will still be putting boost down at any rpm at anytime.

Higher rpm does equal higher stress, but those forces are more likely to eat rod bearings or break rod bolts. Rod bending is a compression failure mode, more likely from either low rpm+high cylinder pressure or detonation/pre-ignition issues imo.

I think the majority of failures are detonation when the piston is trying to go up but there's preignition and gases are expanding at the wrong time. This is why rods break on stock cars and not on 400hp track cars. Just my feeling.



Horsepower has the same relationship to cylinder pressure as torque does except rpm is involved, but lowering rpm doesn't decrease torque until you get very low. The catch is that the combustion gas is expanding in a combustion chamber that is independently expanding at a different rate along a mechanical path as the piston moves down the cylinder. For this reason, an engine generating similar torque numbers at 4000 and 7000 rpm would be generating more compression in the rod at 4000 rpm.

Centrifugal SC have a linearly rising torque curve—not a flat one

[mrg666]

Looking at these curves
http://blog.vittuned.com/jackson-rac...ft-86-fr-sbrz/

Torque is rising but more like a sublinear curve, getting flatter at higher rpms. Power curve is almost linear

[Irace86.2.0]

Originally Posted by mrg666

Looking at these curves
http://blog.vittuned.com/jackson-rac...ft-86-fr-sbrz/

Torque is rising but more like a sublinear curve, getting flatter at higher rpms. Power curve is almost linear

And another.

[mrg666]

Originally Posted by Irace86.2.0

And another.

Yes, those charts are with HBP (+E85+header). That is why higher rpm range torque is not flat anymore. And that is probably where engine reinforcements are now necessary. The link I have given above shows the same thing. See yellow dotted line (stock pulley) vs yellow continuous line (high-boost pulley)


Vittuned claims it is fine to use HBP with the stock engine in that link but I would not try myself or recommend anybody else. JR does not recommend without engine reinforcement either.