Broken rings - which route

[engineermike]

I wish everyone was as conservative as you are. Makes going fast alot easier!

Clearly, you misunderstand me.

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[engineermike]

Let me give an example:

A Whipple stage 2 2015 makes about 575 ftlb at the crank at 11/1 compression on pump gasoline.

If you dropped compression to 10/1 you would have to increase boost by less than 2 psi to make the same power and torque. However, the result would have a higher safety factor and reliability. This combination would actually be on the order of what an oem would offer for day-to-day reliability.

Say you wanted to make 5% more, resulting in 600 ftlb. You would have to increase boost by another 1 psi or so. The result would still have a bigger safety margin than the starting point while making more power and torque.

Drop to 9/1 and the advantage grows, but it is true that you have to have a big enough blower, drive system, fuel system, etc to support the increased airflow.

The above logic is not meant to be applicable to E85.

 

[80FoxCoupe]

Let me give an example:

A Whipple stage 2 2015 makes about 575 ftlb at the crank at 11/1 compression on pump gasoline.

If you dropped compression to 10/1 you would have to increase boost by less than 2 psi to make the same power and torque. However, the result would have a higher safety factor and reliability. This combination would actually be on the order of what an oem would offer for day-to-day reliability.

Say you wanted to make 5% more, resulting in 600 ftlb. You would have to increase boost by another 1 psi or so. The result would still have a bigger safety margin than the starting point while making more power and torque.

Drop to 9/1 and the advantage grows, but it is true that you have to have a big enough blower, drive system, fuel system, etc to support the increased airflow.

The above logic is not meant to be applicable to E85.

I understand the theory. But 11:1 is fine on his setup.

 

[engineermike]

I understand the theory. But 11:1 is fine on his setup.

I don’t understand how you can say that when his setup breaking is why we are having this discussion. Would it have broken at 10/1?

 

[80FoxCoupe]

I don’t understand how you can say that when his setup breaking is why we are having this discussion. Would it have broken at 10/1?

Things happen, parts break. We don't know what caused the failure. Every gen2 car is 11:1, better send out a PSA and tell them the sky is falling.

 

[Jeff's FRC]

I don’t understand how you can say that when his setup breaking is why we are having this discussion. Would it have broken at 10/1?

I thought the general consensus on these cars breaking lands is because the ring gap from the factory is too tight for a boosted application. Rings expand, especially when doing a long pull and kiss each other, and with nowhere to go, the land takes the death blow.

Would lower compression fix that issue?

 

[SolarFlare]

What would’ve fixed/prevented this from happening would’ve been more ring gap. Same ring gap on 10:1 motor could’ve ended up with this same result.

 

[engineermike]

Tight ring gap is a common theory, but incorrect. It turns out that the coyote, predator, 3.5 ecoboost (even the GT version) all run the same top ring gap. The second ring gap is actually larger on the coyote than the other engines listed above.

Secondly, even if ring gap was the issue then lower compression WOULD address the issue anyway. Lowering compression reduces in-cylinder temperature and reduces the chance of detonation.

 

[SolarFlare]

Feel free to lower compression. Don’t complain later because car needs 20psi to hit 950whp. I myself, I’m going the other way. More compression, less boost, E85

 

[SolarFlare]

I also don’t trust 93 to race at ANY boost level. If I intend to do spirited driving I add octanium

 

[80FoxCoupe]

Tight ring gap is a common theory, but incorrect. It turns out that the coyote, predator, 3.5 ecoboost (even the GT version) all run the same top ring gap. The second ring gap is actually larger on the coyote than the other engines listed above.

Secondly, even if ring gap was the issue then lower compression WOULD address the issue anyway. Lowering compression reduces in-cylinder temperature and reduces the chance of detonation.

Looks like low comp is the path for you!

 

[SolarFlare]

Time to tell those junkyard boosted 4.8/5.3 GM guys that their stock 9:1 compression is perfect to prevent ring land failure and widening the ring gap Issa Stoopid.

 

[engineermike]

I also don’t trust 93 to race at ANY boost level.

I wouldn’t either at 11/1 (PFI) or 12/1 (GDI) compression. But the Mercedes CLA45S runs over 30 psi boost on pump gasoline and passes all oem durability testing, which are orders of magnitude more difficult than a few dozen quarter mile passes. The 2.7 ecoboost is another example, making 17-18 psi on 87 octane and also passing oem durability testing. This is made possible by the compression ratio. If the coyote performed like the 10.3/1 2.7eb, it would make 750 ftlb of torque on 87 octane with stock-like reliability.

Feel free to lower compression. Don’t complain later because car needs 20psi to hit 950whp.

If my car needs 20 psi to hit 950 rwhp, but can do it day after day on 91-93 octane without failing, you’ll see me grinning ear to ear, not complaining.

Now for a reality check, the GT500 is 9.5/1 compression and makes 12 psi boost stock. The car pulls 132-133 on pump gas all day long. That’s 3-6 mph more than your typical roush gen3 coyote running the same sc rotor pack and boost level, but the roush car is 12/1. In fact, I’m not sure I’ve seen any flavor supercharged push a 12/1 gen 3 to those speeds on pump gas without octane booster. Then, there’s the GT500 that pulled 154 mph on E85, when the gen 3 coyotes are doing what, 146-148? So where did the advantage of all that compression go?

I myself, I’m going the other way. More compression, less boost, E85

That’s great for you, but not really part of this discussion. I specifically asked the OP what fuel he was going to use and his response was that E85 is not an option.

 

[engineermike]

Time to tell those junkyard boosted 4.8/5.3 GM guys that their stock 9:1 compression is perfect to prevent ring land failure and widening the ring gap Issa Stoopid.

Conversely, you should call up the ford engineers and explain to them they got the predator and ecoboost ring gaps all wrong and they should be much wider.

 

[SolarFlare]

I don't care what OEM does, they have limitations of power, cost, emissions, life expectancy, etc. So they don't design anything with the guy that's gonna shove 20 psi into the motor 1,2, 3 or more years after release in mind.

Furthermore the GT500 you're quoting makes 1050whp or more, a shop car who neither you nor me know what it took to get there so irrelevant to this coyote talk. Are you saying that a 1050-1100whp coyote only goes 148?? LMAO please.

If you want to hit 20psi on pump that's great on you. sounds a lot like the Hellion self imposed issue of "having to have a high horsepower pump gas car" disregarding the fact that it took a built motor and 5-6000 dollar fuel system to make it.

Interesting for someone so smart you make comparisons while leaving small important details out, not sure if on purpose to suit your argument or if because you're clueless. The factory GT500 inverted 2650 is far superior than the traditional roush front fed unit sucking thru stock TB with very limited cooling capability, furthermore its limited by its crappy roush calibration. Yet roush car has gone high 10s and upper 120mph which is fairly on par with GT500s while being 60hp short with its phase 1 calibration.

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