Question : Octane adjust or pulley up ?

[Problem5.0]

2 months ago, my motor blew( 2 cylinders melted, lean condition maybe) but no one has been able to tell me what really happened. I just want to make sure i don't blow my motor again....

I want to help eliminate the bad gas idea and help with possible lean conditions.

So, should I replace my 3.625 pulley and go less boost with a 3.75 pulley or should keep my current pulley and use Whipple's guardian "octane adjust" setting?

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[engineermike]

Personally, I believe the coyote community is far too quick to rule out lowering the compression. 11/1 compression and 10 psi boost is off the charts In cylinder pressure. Notice that no oem provides forced induction on anything over 9.5/1 compression with port injection. Before 2011, it seemed like everyone who wanted to run more than 6 psi boost was dropping compression. 8.5/1 was the norm but that typically allowed well over 10 psi safely. I don’t have my spreadsheet with me but I can use an industry trend to determine actual oem-safe boost levels at any compression ratio. Keep in mind that the oem chooses cylinder pressure such that a high degree of reliability can be achieved even in the event of other failures such as a bad fuel pump, bad gas, plugged filter, overheat, failed sensor, etc. I don’t know what happened to your motor but any number of things could have caused it to fail. I’m personally planning to lower my boost down to around 8 psi for the above reasons.

 

[EFI]

Personally, I believe the coyote community is far too quick to rule out lowering the compression. 11/1 compression and 10 psi boost is off the charts In cylinder pressure.

That's the beauty of having twin variable cam timing...you can control cylinder pressure with cam timing.

I agree that with big boost you should go lower static CR, especially if it's a Gen 3, but not for sub 10psi of boost.

 

[Ruiner46]

2 months ago, my motor blew( 2 cylinders melted, lean condition maybe) but no one has been able to tell me what really happened. I just want to make sure i don't blow my motor again....

I want to help eliminate the bad gas idea and help with possible lean conditions.

So, should I replace my 3.625 pulley and go less boost with a 3.75 pulley or should keep my current pulley and use Whipple's guardian "octane adjust" setting?

I think the most important thing to prevent problems is to learn to datalog and read logs. Monitoring knock is probably the simplest way to know if you get bad gas, or if something changed to put the engine in danger.

I datalog every 1/4 mile run with HPTuners, but on the street, using an app that allows custom PID's with an OBD2-bluetooth adapter will allow you to monitor knock and many other things in real time for cheap. I use Torque Pro for Android, not sure what Apple phones would use.

 

[engineermike]

You can lower cylinder pressure with cam timing but it’s either ineffective or defeats the purpose. You see, if you lowered cylinder pressure to an actual safe number, then you would be making just over stock torque numbers. But we know the supercharged coyotes are making a lot of torque/cid. Torque is proportional to mean cylinder pressure and cid. So, when your 302 cid engine is putting 530-600 ftlb to the wheels, the mean cylinder pressure is very high and cylinder pressure is not being bled off by cam timing. Lower compression with boost gives you more mean cylinder pressure (throughout the power stroke) while keeping the peak cylinder pressure low and safe. For instance, a 13/1 compression NA Mazda skyactiv-g engine could have more peak cylinder pressure than a Subaru EJ turbo, but the lower compression boosted Subaru makes more power (and reliable) due to higher mean pressure.

Even though higher compression nets better fuel economy, the oems still elect to run 9.5/1 or lower any time they boost with PFI.

The bmw b58 engine runs 11/1 compression, but it has gdi and still only runs 7 psi boost.

 

[EFI]

You can lower cylinder pressure with cam timing but it’s either ineffective or defeats the purpose.

What do you mean defeats the purpose? If your purpose is to lower cylinder pressure, then it's doing a good job.

Using cam timing to lower cylinder pressure is much more efficient than doing it with hard engine parts eg. low compression pistons. The beauty is you can have dynamic control of cylinder pressure based on need. At low engine speeds and load, you can keep higher cylinder pressure to increase efficiency, then at high engine speeds and loads you can reduce it to increase knock resistance and keep the engine together.

 

[Cory S]

If two cylinders melted, it wasn’t a boost/octane problem. You are correct on leaning of the AFR. These engines are fairly hard to make fail with closed loop fueling and active/adaptive knock strategy. Like mentioned, logging periodically and checking STFT’s, and knock activity will keep you knowing how the engine is acting and how well the system is adjusting.

90% of Coyote failures are from tuners desensitizing the knock sensors, but in your case, probably been on the lean side for some time.

 

[SolarFlare]

Check all plugs and have your injectors tested/cleaned. Idk why you said you don’t know what happened, you literally lost 2 pistons

 

[lx347cd]

2 months ago, my motor blew( 2 cylinders melted, lean condition maybe) but no one has been able to tell me what really happened. I just want to make sure i don't blow my motor again....

I want to help eliminate the bad gas idea and help with possible lean conditions.

So, should I replace my 3.625 pulley and go less boost with a 3.75 pulley or should keep my current pulley and use Whipple's guardian "octane adjust" setting?

Start from the beginning and go with the 3.75 pulley with 93 octane and take a bunch of logs and send to whipple to make sure they look ok or if you know what to look for then you check. Then pulley down if you want.

 

[engineermike]

What do you mean defeats the purpose? If your purpose is to lower cylinder pressure, then it's doing a good job.

Because the purpose of a supercharger is to increase cylinder pressure which results in more torque. If you reduce cylinder pressure with cam timing then you are reducing torque, which defeats the purpose of supercharging. However, blown coyotes make a lot of torque, which means they aren’t actually reducing cylinder pressure, or at least aren’t reducing significantly.

Using cam timing to lower cylinder pressure is much more efficient than doing it with hard engine parts eg. low compression pistons. The beauty is you can have dynamic control of cylinder pressure based on need. At low engine speeds and load, you can keep higher cylinder pressure to increase efficiency, then at high engine speeds and loads you can reduce it to increase knock resistance and keep the engine together.

More efficient, yes. Higher compression is almost always more efficient than low compression. However, if it were an effective way to manage cylinder pressure then you would see many more oem high-compression boosted engines. You also wouldn’t see variable compression ratio engines being developed and manufactured. The Nissan variable compression ratio turbo engine also has variable cam timing but they still added variable compression ratio so they could lower it under boost and the engine would live.

 

[EFI]

Because the purpose of a supercharger is to increase cylinder pressure which results in more torque. If you reduce cylinder pressure with cam timing then you are reducing torque, which defeats the purpose of supercharging. However, blown coyotes make a lot of torque, which means they aren’t actually reducing cylinder pressure, or at least aren’t reducing significantly.

I'm not saying completely kill the cylinder pressure, I'm saying manage it so that it doesn't do damage to the components (the same as you would suggest to reduce the CR).

Also, they are not reducing cylinder pressure because it's not really needed since the components are pretty stout. Which further proves that going to such drastic measures are going with low CR is not really needed unless you're building an all out racecar with 1000+hp

 

[engineermike]

I figured this would happen....I’m trying to explain over a few forum posts what took me years of data gathering, thermodynamic modeling, and testing to figure out, and what the oem engine designers already knew.

I'm not saying completely kill the cylinder pressure, I'm saying manage it so that it doesn't do damage to the components ...

But it does do damage to components. That’s what the OP started the thread to discuss. The failure rate of boosted coyotes is orders of magnitude higher than oem forced induction engines. And it’s not for lack of engine management. Detonation is a function of many things, but mainly pressure and temperature of the compressed charge in the cylinder. There is a distinct pressure-temperature line that the oems do not cross regardless of engine size, boost level, manufacturer, etc. Boosted 11/1 pfi and 12/1 gdi coyotes are way over the line. If everything is perfect then it may last a good while, but if anything goes wrong the engine is toast. This isn’t true for oem forced induction because they don’t cross the pressure-temperature limit line. I’ve modeled probably 50 production engines and found that no oem crosses the line. The correlation is astonishing, actually.

Also, they are not reducing cylinder pressure because it's not really needed since the components are pretty stout. Which further proves that going to such drastic measures are going with low CR is not really needed unless you're building an all out racecar with 1000+hp

...or want it to reach oem or near-oem reliability levels at high duty cycles or during off-design operation.

We don’t have to look far for examples. The demon/hellcat/red eye all use 9.5/1 compression. The gt500 is also 9.5. The 5.8 liter gt500 was 9.0/1 and the 5.4 version was 8.4. The closest thing GM has is the LS9 and it’s 9.1/1. If high compression could be done reliably, then for sure the current gt500 with tivct and 6 knock sensors would be designed that way. But, I bet you could take a 9.5/1 gt500 and put 87 in it, plug the fuel filter, plug a cat, or overheat it and it will live. I had actually already created the pressure-temperature limit line before getting the specs on the predator and, lo and behold, it fell just under the limit.

 

[Slow306stang]

I figured this would happen....I’m trying to explain over a few forum posts what took me years of data gathering, thermodynamic modeling, and testing to figure out, and what the oem engine designers already knew.



But it does do damage to components. That’s what the OP started the thread to discuss. The failure rate of boosted coyotes is orders of magnitude higher than oem forced induction engines. And it’s not for lack of engine management. Detonation is a function of many things, but mainly pressure and temperature of the compressed charge in the cylinder. There is a distinct pressure-temperature line that the oems do not cross regardless of engine size, boost level, manufacturer, etc. Boosted 11/1 pfi and 12/1 gdi coyotes are way over the line. If everything is perfect then it may last a good while, but if anything goes wrong the engine is toast. This isn’t true for oem forced induction because they don’t cross the pressure-temperature limit line. I’ve modeled probably 50 production engines and found that no oem crosses the line. The correlation is astonishing, actually.



...or want it to reach oem or near-oem reliability levels at high duty cycles or during off-design operation.

We don’t have to look far for examples. The demon/hellcat/red eye all use 9.5/1 compression. The gt500 is also 9.5. The 5.8 liter gt500 was 9.0/1 and the 5.4 version was 8.4. The closest thing GM has is the LS9 and it’s 9.1/1. If high compression could be done reliably, then for sure the current gt500 with tivct and 6 knock sensors would be designed that way. But, I bet you could take a 9.5/1 gt500 and put 87 in it, plug the fuel filter, plug a cat, or overheat it and it will live. I had actually already created the pressure-temperature limit line before getting the specs on the predator and, lo and behold, it fell just under the limit.

Mike, how far off of the charts am I when running 30psi on 12:1 compression?

 

[engineermike]

Mike, how far off of the charts am I when running 30psi on 12:1 compression?

I’m guessing you’re not running 91 octane...

The limit is not for E85, methanol, or race gas.

 

[Meatball]

I figured this would happen....I’m trying to explain over a few forum posts what took me years of data gathering, thermodynamic modeling, and testing to figure out, and what the oem engine designers already knew.



But it does do damage to components. That’s what the OP started the thread to discuss. The failure rate of boosted coyotes is orders of magnitude higher than oem forced induction engines. And it’s not for lack of engine management. Detonation is a function of many things, but mainly pressure and temperature of the compressed charge in the cylinder. There is a distinct pressure-temperature line that the oems do not cross regardless of engine size, boost level, manufacturer, etc. Boosted 11/1 pfi and 12/1 gdi coyotes are way over the line. If everything is perfect then it may last a good while, but if anything goes wrong the engine is toast. This isn’t true for oem forced induction because they don’t cross the pressure-temperature limit line. I’ve modeled probably 50 production engines and found that no oem crosses the line. The correlation is astonishing, actually.



...or want it to reach oem or near-oem reliability levels at high duty cycles or during off-design operation.

We don’t have to look far for examples. The demon/hellcat/red eye all use 9.5/1 compression. The gt500 is also 9.5. The 5.8 liter gt500 was 9.0/1 and the 5.4 version was 8.4. The closest thing GM has is the LS9 and it’s 9.1/1. If high compression could be done reliably, then for sure the current gt500 with tivct and 6 knock sensors would be designed that way. But, I bet you could take a 9.5/1 gt500 and put 87 in it, plug the fuel filter, plug a cat, or overheat it and it will live. I had actually already created the pressure-temperature limit line before getting the specs on the predator and, lo and behold, it fell just under the limit.

I'll bet you're exactly right. The OEMs need their cars to withstand a beating by owners who are buying them for fun rather than basic transportation and so need to have a very good chance of not breaking before 5/60K.

Besides reliability, I wonder if using a lower cr allows the cam timing to be used a bit more as they are intended to in NA cars: to enhance torque at lower rpm and power at high (and emissions and mpg), rather than just tools to compensate for potentially excessive combustion chamber pressure. Maybe it frees up some spark advance authority also. I know from reading some older posts that the Coyotes are especially susceptible to detonation at low rpm (with a pd, there's all the boost at low rpm and the piston recedes relatively slowly)and the tunes may have to play with cam timing and spark advance just to keep it in one piece. But if you're on a poor tune or if the engine config is not exactly what the tune is expecting (like issues with the timing chain) the engine's probably going to die quickly.

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