Reliability on turbo 86

[Boris_Petrov]

Originally Posted by Irace86.2.0

I was quoting rough numbers in torque and not horsepower because torque is what breaks stuff. I was quoting RON instead of our 91 pump, but I forgot to switch to Nm and kW. Sorry for the confusion.



I don’t think the Cusco gears will help. Forth gear seems to give people the biggest problems, not 1st and second. Also, from what I understand, turbos spool up under load, so even though higher rpms have higher loads, shorter gears aren’t advised like they would be for a supercharged or NA car.



I’ve seen dog gears used. Some have swapped a CD009. There isn’t a common solution for the transmission because there isn’t enough demand from tge aftermarket because few are making so much power or tracking their car with enough power to break transmission.

We still use hp but not kW. Do you think i can mantain stable hp with 12.5 comp and 98 octane cause I don't have access to e85?

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[Irace86.2.0]

Originally Posted by Boris_Petrov

We still use hp but not kW. Do you think i can mantain stable hp with 12.5 comp and 98 octane cause I don't have access to e85?

Sent from my SM-A520F using Tapatalk

Without E85, 10 psi is around the max you will see. You won't see over 300whp with that. More psi just means more changes to timing and cam profiles to be safe, so there are diminished returns running more power. You may get more power going more aggressive with the tune, but then that would decrease reliability.

Check that out. Double the boost did minimal to the power on 91 pump (95 RON) equivalent. Delicious mentions not being a fan of lowering the compression on these motors, but then again, I don't know what they would recommend if E85 wasn't available and you wanted more power. There may be tuning issues or unknowns with the D4S system if you drop compression. You may want to reach out to a tuner like Delicious to see what they would recommend for your power goals.

http://www.ft86club.com/forums/showthread.php?p=2797219

[DarkPira7e]

Originally Posted by Irace86.2.0

Without E85, 10 psi is around the max you will see. You won't see over 300whp with that

Don't you think total CFM the turbo flows should also be considered? I know in general, most people will be running similar sized turbos if they're afraid to build the engine. But what of someone who slaps their GT4088 or GT35? 10PSI on one of those is a whole lot more air than on a GT2867. I'm asking candidly, I don't know!

[Irace86.2.0]

Originally Posted by DarkPira7e

Don't you think total CFM the turbo flows should also be considered? I know in general, most people will be running similar sized turbos if they're afraid to build the engine. But what of someone who slaps their GT4088 or GT35? 10PSI on one of those is a whole lot more air than on a GT2867. I'm asking candidly, I don't know!

10psi of pressure will have the same amount of air regardless of turbo unless there is a difference in tempurature. The only way to get more air into a volume at a given pressure is to have lower temperatures, so there may be a setup that can allow lower temperatures by having better efficiency, but I don’t think the difference will be dramatic enough for properly sized turbos for this engine.

The only other way to alter the amount of air for a given pressure is to alter the volume of the space the air occupies like increasing the size of the intake manifold (if that was a bottleneck), or like how larger exhaust pipes are used to remove back pressure from inhibiting a volume from being filled efficiently (again, if that was a bottleneck).

Say it is true that there is 50 more horsepower available with a more efficient setup at 10 psi, or say the lower temps allow boost to be raised to 12 psi then the limit is still ehh for 91/93 pump gas with a reliable tune. Definitely enough to have fun, but there may be a reason to adjust compression ratio to maximize safe power for 91/93 pump (95/98 RON). I have no clue if that is correct, but we see on the internet many examples of Evo's and STI's making much more power on pump gas than the 86. The disadvantage of a lower compression motor is that there will be more turbo lag, less low end power, less power for a given psi of boost. The advantage of a lower compression motor is there will be safer levels of higher boost that can be achieved for more total horsepower.

https://www.quora.com/Why-do-turbo-c...er-compression

[Irace86.2.0]

Just to add to that, the article talks about how the dynamic compression ratio can be altered at lower rpms via cam phasing, yet there is a limit. Infiniti released a variable compression motor to tackle this issue of wanting high compression at lower loads and low compression when on boost at higher loads:

[ame]https://www.youtube.com/watch?v=A6H66xfEZC4&vl=en[/ame]

[DarkPira7e]

Originally Posted by Irace86.2.0

10psi of pressure will have the same amount of air regardless of turbo unless there is a difference in tempurature. The only way to get more air into a volume at a given pressure is to have lower temperatures, so there may be a setup that can allow lower temperatures by having better efficiency, but I don’t think the difference will be dramatic enough for properly sized turbos for this engine.

The only other way to alter the amount of air for a given pressure is to alter the volume of the space the air occupies like increasing the size of the intake manifold (if that was a bottleneck), or like how larger exhaust pipes are used to remove back pressure from inhibiting a volume from being filled efficiently (again, if that was a bottleneck).

Say it is true that there is 50 more horsepower available with a more efficient setup at 10 psi, or say the lower temps allow boost to be raised to 12 psi then the limit is still ehh for 91/93 pump gas with a reliable tune. Definitely enough to have fun, but there may be a reason to adjust compression ratio to maximize safe power for 91/93 pump (95/98 RON). I have no clue if that is correct, but we see on the internet many examples of Evo's and STI's making much more power on pump gas than the 86. The disadvantage of a lower compression motor is that there will be more turbo lag, less low end power, less power for a given psi of boost. The advantage of a lower compression motor is there will be safer levels of higher boost that can be achieved for more total horsepower.

https://www.quora.com/Why-do-turbo-c...er-compression

I guess my real question, is it the pressure (10 psi) that's causing damage, or the overall airflow added from the turbo. I understand that 10psi in the manifold is 10 psi in the manifold, but the amount of air flowing at that pressure could be completely different. This infers, to me, that it would be putting more stress on the rods per revolution. I know I'm being difficult, but I just want to be sure my thought process is accurate. If PSI were the accurate measurement for failure, I could theoretically run a humongous turbo, making 700WHP at 8PSI and and keep stock block.

I'm only challenging for the sake of understanding and discussion, realistically I understand that saying the "safe limit" is based on average pressure/stress caused by most turbos run at 10PSI in a decent efficiency range on this engine. On another note, wtf, variable compression engine. That is cool.

[steve99]

Torque is what can break rods in these motors. Lot of turbo cars will produce max torque in lower rpm range. 250-300 ft lb torque is arround the max you want to run on stock motors closer to 250 to be safe . This is where good electronic boost control can help by limiting boost at lower rpm where you get torque peak

[gtengr]

Originally Posted by DarkPira7e

I guess my real question, is it the pressure (10 psi) that's causing damage, or the overall airflow added from the turbo.

It's the airflow, but they're not really separable. Airflow is psi at a given temp, where temp determines the density.

Originally Posted by DarkPira7e

If PSI were the accurate measurement for failure, I could theoretically run a humongous turbo, making 700WHP at 8PSI and and keep stock block.

Theoretically impossible unless that huge turbo is cooling the air far below ambient temp. When a big turbo makes more power than a small turbo at the same psi, it's likely because the small turbo was poorly selected (can't hold target boost to redline, operating in a less efficient area on the compressor map, or some other compromise with spool/powerband/cost). The only thing a big turbo truly has on a small turbo is that it's less of an exhaust restriction.

[Irace86.2.0]

@DarkPira7e

^^^ Their explanations answered the questions well. There is no sized turbo that you could put on the 86 that would make 700whp at 8psi, and like they said, torque is what breaks the motor or snaps the rods (among other things), but quoting horsepower and psi provides good enough references, even if it is torque that is the direct cause.

[StraightOuttaCanadaEh]

From what I understand, because the compression ratio is so high, the piston has to change travel direction from up to down in like a split second at a pretty good lick. Add lots of torque and the rod basically tears in half cause the amount of force exerted during that transition is quite high.

[DarkPira7e]

Originally Posted by Irace86.2.0

@DarkPira7e

^^^ Their explanations answered the questions well. There is no sized turbo that you could put on the 86 that would make 700whp at 8psi, and like they said, torque is what breaks the motor or snaps the rods (among other things), but quoting horsepower and psi provides good enough references, even if it is torque that is the direct cause.

I was exaggerating with 700hp, but I just wanted to make sure I understood that psi was a reference, not the force specifically that was causing the damage. Thank you!

[Irace86.2.0]

Originally Posted by StraightOuttaCanadaEh

From what I understand, because the compression ratio is so high, the piston has to change travel direction from up to down in like a split second at a pretty good lick. Add lots of torque and the rod basically tears in half cause the amount of force exerted during that transition is quite high.

That doesn’t sound accurate.

The stroke doesn’t change with higher compression motors unless we are talking about that variable compression Infiniti motor I linked above. To illustrate this, the 2jz motor has a square (86mm bore and stroke) like the 86, yet the compression is much less than ours. Besides headgasket thickness or cylinder head design, the main difference would be piston head height. I believe this is the main way compression is changed.

Higher rpms lead to more inertial stresses than lower rpms due to increasing piston accelerations, so these are always a concern, but it seems (anecdotally) that the failures are happening at lower rpms with high torque. Why could this be the case?

The most likely two culprits are low oil pressure with high torque and premature ignition/detonation. The oil pump is rpm dependent therefore the oil pressure is rpm dependent. With a flat torque curve, the same compressive forces near TDC at low rpms will cause more risk to the bearings. The other issue is premature ignition. This will cause more forces to the piston than torque could (I believe) because the expansion of gasses is happening as the piston is on a compression stroke. This may occur more at lower rpms because there is a transition or higher dependency on the direct injectors at a time where there is likely more heat due to less airflow.

[StraightOuttaCanadaEh]

Originally Posted by Irace86.2.0

That doesn’t sound accurate.

The stroke doesn’t change with higher compression motors unless we are talking about that variable compression Infiniti motor I linked above. To illustrate this, the 2jz motor has a square (86mm bore and stroke) like the 86, yet the compression is much less than ours. Besides headgasket thickness or cylinder head design, the main difference would be piston head height. I believe this is the main way compression is changed.

Higher rpms lead to more inertial stresses than lower rpms due to increasing piston accelerations, so these are always a concern, but it seems (anecdotally) that the failures are happening at lower rpms with high torque. Why could this be the case?

The most likely two culprits are low oil pressure with high torque and premature ignition/detonation. The oil pump is rpm dependent therefore the oil pressure is rpm dependent. With a flat torque curve, the same compressive forces near TDC at low rpms will cause more risk to the bearings. The other issue is premature ignition. This will cause more forces to the piston than torque could (I believe) because the expansion of gasses is happening as the piston is on a compression stroke. This may occur more at lower rpms because there is a transition or higher dependency on the direct injectors at a time where there is likely more heat due to less airflow.

Thanks for clearing it up. I was recalling some old post I read some time ago and at a ripe old age of 33, my memory isn't what it used to be. The question that's been boiling my noodle lately is what can we do to address the oil pump insufficiency at low rpms?

[ST185RC]

What? No LS swap comments for power and reliability? I'm disgusted.