Worth going forged internals for reliability ?

[86MLR]

Originally Posted by Irace86.2.0

So 35+ tq is all the transmission will be able to handle?

That's why mine is staying NA.

My old RB 25/30 Skyline went thru gearboxes like oil changes, it was always easier to buy a used box for a couple of hundred than outlay 25-20k for a built box

The 750nm of torque would eat the case hardening right of the gears, sticky tyres and big torque = broken stuff

For me, to have a reliable (ish) car, it cannot go too far past the OEM limit, this is why I'm staying NA

If I was to boost it, I would need to upgrade the driveline to give me some more confidence

I'm not saying you cannot give it some boost, some superchargers won't push the limits, and a well chosen turbo may not as well, but, why spend that much money for 30nm and ??hp, not good bang for buck IMO

If I had more disposal income I would build a sweet 350-400hp car, with a gearbox and rear end built to take the additional power, mad skids would be had...

But, the kids have got to eat and stuff, and the girl does like to shop

Building cars was so much simpler when I was single and didn't have kids

[Verl0r4n]

Speakin of trannys has anyone done an up rated box yet? (From what I understand its essentially the same 6speed that was in S15 silvias, not known for their strength)

Sent from my SM-G950F using Tapatalk

[CSG Mike]

Originally Posted by Irace86.2.0

I'm not surprised with 38 track days at 450hp. Let me guess, beginner group? Ya, probably not.

I misspoke. I was thinking 400hp, not torque, was the common consensus, but that would mean like 300ish tq. I'm sure someone can break the stock transmission just like they break the stock engine when NA.

Saying any power level that requires a clutch upgrade... What do you consider requires? The stock clutch might handle who knows how much torque for a few dyno pulls. Can you clarify? Do you mean for the life of the car or for at least a few years? The stock clutch is not rated very high. I have the Exedy Stage 1 which is essentially just a pressure plate upgrade and is rated to hold like 205 tq, but the consensus is it holds much higher. I'm at 13 psi, and the clutch is holding fine, and so it the gearbox. You are saying I didn't need to upgrade the clutch, or are you saying that since I did, I am putting the transmission at serious risk?

Does it matter that I likely don't see the low end torque that your turbo'ed 86 does, let alone the same absolute level of torque?

The stock clutch will easily hold basic FI, as well as basic FI and a mild Ethanol tune. While each clutch is different with the individual user and condition, OEM will generally hold 250wtq (300 crank) comfortably. Some will hold as high as 280wtq. Clutches are either going to hold or not hold; there is no in between.

Telling me you're at 13 psi tells me nothing; I need output figures, not a measurement of pressure. My 360whp/450 crank hp, is at only 10.5 psi.

I've broken transmissions at as low as 230whp/200wtq (Superlap battle 2017 estimated hp), but this was at the end of a track session in pretty extreme weather. That one literally gave out on my cooldown lap, when I wasn't even really putting any stress on it.

[falcon_wizard]

Originally Posted by CSG Mike

Detune it a bit, or build in a lot of failsafes. Do every supporting mod as appropriate.

I have 38 track days on my turboed stock engine, with maps going up to 450 crank hp on Ethanol.

So going back to the topic of the cost/benefits of having an engine rebuilt with forged pistons, rods, etc, for reliability purposes rather than pursuing increased power output; based on the posts above, based on actual experience, have the motor been a weaker link than the transmission, or vice versa in that power range ? (Say 260/270 wtq/whp range on 94 oct) my understanding was that the rods were the weakest link, but maybe the tranny is not far behind ? For reference, when I replaced my stock clutch, it was almost 6 yrs old with 90k km on it (25k with the turbo on), and still had about 33% left on it. So arguably I could have kept it for a while still, but started to feel a bit of loss of torque transfer to the wheels during acceleration and so went ahead with an upgraded one.

Going through the logic a bit, if forged blocks allow for increasing the power and torque, it would seem to indicate that such block would be able hold better still than a stock block at lower power levels - assuming quality parts & worksmanship on the build, are there reasons why this would not be the case ? Or is it simply that people would rather edge their bets and change the block when and if it failed, rather than proactively have it reinforced before it goes ? My understanding is that the cost of profesionally building/installing my block would be about the same, propably a bit less than the total cost& labor of replacing mine after it failed with a used stock block. In this equation, I include labor by a qualifie shop, as I do not DIY. So I am trying to assess the cost/benefit of doing this proactively - cash flow aside, if there is a high degree of certainty that I would have to have the block replaced or rebuilt sooner or later (based on me wanting to keep the car 6-8 more years), then I would also weigh in the benefit of choosing a convenient time to build the block, vice having my year round Daily Driver stranded anywhere/anytime and being forced to do something then, require towing, etc.

Thoughts ?

[gtengr]

The math to me looks like ~$5500 for a built engine (after good engine core is returned) plus install labor. I'm not sure what the labor is for swapping an engine but it doesn't look hard on this car so maybe $8000 all in for a built motor installed and tuned. If you roll the dice and lose, your core is no good, so it would be ~$10k plus rental car because it would take some time before your new engine is ready. So, if you lose the gamble, it would essentially cost an extra ~$2500 plus rental car. If you win the gamble, you save ~$8000.

I would just lower the boost a touch and forget about the risk that is introduced by trying to run it near the stock limit for 6-8 years.

[Irace86.2.0]

Originally Posted by CSG Mike

The stock clutch will easily hold basic FI, as well as basic FI and a mild Ethanol tune. While each clutch is different with the individual user and condition, OEM will generally hold 250wtq (300 crank) comfortably. Some will hold as high as 280wtq. Clutches are either going to hold or not hold; there is no in between.

Telling me you're at 13 psi tells me nothing; I need output figures, not a measurement of pressure. My 360whp/450 crank hp, is at only 10.5 psi.

I've broken transmissions at as low as 230whp/200wtq (Superlap battle 2017 estimated hp), but this was at the end of a track session in pretty extreme weather. That one literally gave out on my cooldown lap, when I wasn't even really putting any stress on it.

No in between? Then how to stock clutches go bad? Because they start getting worn down or the surfaces get glazed. A clutch will start slipping at high loads then slip everywhere. I’m sure your experiences are more immediate and extreme because of your use, but to say it will hold or not is not accurate. Some people burn through a clutch in a few pulls. Some burn through them in a few thousand miles. Some in 20k. Some in 200k. That is why I asked for clarification because saying once someone REQUIRES a new clutch then the tranny is at high risk is not really very specific at all.

I did a remote tune with DT. I didn’t dyno tune, and I don’t need to waste money on seeing a dyno number. I said above I’m on 91 with a Harrop kit with an 85mm pulley. You should know the approximate numbers. You have more hp with less boost because you have better AITs and I’m sure less resistance: my roots is hotter than your turbo; my 91 is hotter than your E85; my cats give more resistance so higher boost pressures than your catless setup (I’m assuming you’re catless here).

Im sure running super sticky tires and tracking the shit out of a car can do that to the transmission. Which part of the transmission broke?

[CSG Mike]

Originally Posted by Irace86.2.0

No in between? Then how to stock clutches go bad? Because they start getting worn down or the surfaces get glazed. A clutch will start slipping at high loads then slip everywhere. I’m sure your experiences are more immediate and extreme because of your use, but to say it will hold or not is not accurate. Some people burn through a clutch in a few pulls. Some burn through them in a few thousand miles. Some in 20k. Some in 200k. That is why I asked for clarification because saying once someone REQUIRES a new clutch then the tranny is at high risk is not really very specific at all.

I did a remote tune with DT. I didn’t dyno tune, and I don’t need to waste money on seeing a dyno number. I said above I’m on 91 with a Harrop kit with an 85mm pulley. You should know the approximate numbers. You have more hp with less boost because you have better AITs and I’m sure less resistance: my roots is hotter than your turbo; my 91 is hotter than your E85; my cats give more resistance so higher boost pressures than your catless setup (I’m assuming you’re catless here).

Im sure running super sticky tires and tracking the shit out of a car can do that to the transmission. Which part of the transmission broke?

Perhaps you misunderstand. Let me further clarify.

As you said, a clutch is either holding the power, or not holding the power. It either is, or it isn't. The state can be stated as 1 for holding, and 0 for not holding. There is no "sort of holding", or 0.5 state; it is binary. If at any point the clutch is slipping when unintended, it is not holding the power.

If a good condition clutch that can hold power as intended from the factory, cannot hold your FI power, you are putting your transmission at risk. Subaru is very good about engineering cascaded failure points into their cars. The clutch is intentionally designed to fail before something else does.

An air-water heat exchanger has lower IATs than an air-air intercooler for burst output. My output figures are on a stock front pipe and stock exhaust.
The main cat is deleted by the turbo kit. I have enough exhaust restriction that my car's net exhaust volume is quieter than stock.

Likewise, I run tires all across the spectrum, but I cannot load the transmission more than what the engine's output is. The example of my low output transmission failure was on Michelin Pilot Super Sport, which is not a sticky tire at all.

[GrandSport]

Forged doesn't make it wear out slower. Forged stops things from cracking/breaking/stretching/snapping/etc. It can also give you some knock resistance. If you want reliability, get a good conservative tune.

[Irace86.2.0]

Originally Posted by CSG Mike

If a good condition clutch that can hold power as intended from the factory, cannot hold your FI power, you are putting your transmission at risk. Subaru is very good about engineering cascaded failure points into their cars. The clutch is intentionally designed to fail before something else does.

Likewise, I run tires all across the spectrum, but I cannot load the transmission more than what the engine's output is. The example of my low output transmission failure was on Michelin Pilot Super Sport, which is not a sticky tire at all.

Clutches fail from brute force and from excessive heat. They don’t see the heat brakes do because clutches work statically as you know, but there is heat and slip that occurs. The weaker the pressure plate and/or the softer the material, the more slip can occur. A person can go through a clutch that can hold the power much the same way as weak-material brake pads may only survive a few track days. I’ve read many threads with comments that the OEM clutch failed quickly after FI, but I haven’t seen many threads on broken transmissions, except from people tracking their heavily modified and high powered cars. I’ve seen far more engine failures discussed over transmission failures. While you are knowledgeable, I feel your experiences don’t mirror what the average person will do with their car on the track and/or with FI in general.

It is disengenuous to say the transmission broke during a low output situation. Unless you had torn it apart to see, it is just as likely the damage/fracture/stress/deformation occurred beforehand, but finally failed later. That would be like throwing a straw on a camels back and declaring that straw broke the camels back, but not the other weight that was already there.

While torque will stay the same, stickier tires and lower gears will cause more resistance. Consistently dropping gears while flooring it or doing launches from a dig will put considerably more stress on the transmission too. If every transmission was rated for the worst case scenarios while expecting OEM longevity then everyone here should be considering a built engine, clutch and transmission upgrades, even if they are stock.

The reality seems to be that the engine will fail before the transmission. Considering the transmission was rated at 185 tq, and the OP has 260 tq, it seems to be holding. If it blows then a used transmission is cheaper than a new clutch, but the same can’t be said about the engine. If the OP wants to add reliability, a built engine isn’t a bad idea and cheaper done before the engine blows.

[CSG Mike]

Originally Posted by Irace86.2.0

Clutches fail from brute force and from excessive heat. They don’t see the heat brakes do because clutches work statically as you know, but there is heat and slip that occurs. The weaker the pressure plate and/or the softer the material, the more slip can occur. A person can go through a clutch that can hold the power much the same way as weak-material brake pads may only survive a few track days. I’ve read many threads with comments that the OEM clutch failed quickly after FI, but I haven’t seen many threads on broken transmissions, except from people tracking their heavily modified and high powered cars. I’ve seen far more engine failures discussed over transmission failures. While you are knowledgeable, I feel your experiences don’t mirror what the average person will do with their car on the track and/or with FI in general.

It is disengenuous to say the transmission broke during a low output situation. Unless you had torn it apart to see, it is just as likely the damage/fracture/stress/deformation occurred beforehand, but finally failed later. That would be like throwing a straw on a camels back and declaring that straw broke the camels back, but not the other weight that was already there.

While torque will stay the same, stickier tires and lower gears will cause more resistance. Consistently dropping gears while flooring it or doing launches from a dig will put considerably more stress on the transmission too. If every transmission was rated for the worst case scenarios while expecting OEM longevity then everyone here should be considering a built engine, clutch and transmission upgrades, even if they are stock.

The reality seems to be that the engine will fail before the transmission. Considering the transmission was rated at 185 tq, and the OP has 260 tq, it seems to be holding. If it blows then a used transmission is cheaper than a new clutch, but the same can’t be said about the engine. If the OP wants to add reliability, a built engine isn’t a bad idea and cheaper done before the engine blows.

Let me clarify more since you use the word static.

Friction is either static (clutch held) or kinetic (clutch did not hold). There is no in-between state between static and kinetic.

The transmission failed on the first outing with the turbocharger at the low output level. It was never ran with FI prior to that, and was never ran with stickier tires than a 200TW, non-71R/Rival-S/A052/Sur4G.

[Irace86.2.0]

Originally Posted by CSG Mike

Let me clarify more since you use the word static.

Friction is either static (clutch held) or kinetic (clutch did not hold). There is no in-between state between static and kinetic.

The transmission failed on the first outing with the turbocharger at the low output level. It was never ran with FI prior to that, and was never ran with stickier tires than a 200TW, non-71R/Rival-S/A052/Sur4G.

Right. The clutch sees both types of friction. The coefficient of static or kinetic friction will change with heat, as the material properties change. Heat can shorten the clutches life dramatically besides torque. I’m still of the mind that a clutch upgrade could be needed, yet doesn’t mean the transmission is now a ticking time bomb. It could be there to manage heat or to minimize heat by getting a better bite so there isn’t as much slip or kinetic friction. The OEM clutch could hold the peak torque, but not be able to manage the heat enough to manage that torque for very long before it is eventually not holding the peak torque at all. Clutch destruction can be immediate or gradual.

Regardless of all that, you’re basically saying the OP is already surpassing the trannies abilities, so any goals for extra power will inherently be even less reliable. You’re also saying 450hp with the right supporting mods is reliable because your engine didn’t break with that power after intense track days (and he is a beginner), so he doesn’t need to do a built engine.

That one literally gave out on my cooldown lap, when I wasn't even really putting any stress on it.

That quote is what I meant when I said the transmission probably didn’t break then, even if it finally gave out on the cool down lap. Maybe you didn’t mean it to sound like the transmission is such glass that it will break in such a scenario, but that is how it sounded.

[CSG Mike]

Originally Posted by Irace86.2.0

Right. The clutch sees both types of friction. The coefficient of static or kinetic friction will change with heat, as the material properties change. Heat can shorten the clutches life dramatically besides torque. I’m still of the mind that a clutch upgrade could be needed, yet doesn’t mean the transmission is now a ticking time bomb. It could be there to manage heat or to minimize heat by getting a better bite so there isn’t as much slip or kinetic friction. The OEM clutch could hold the peak torque, but not be able to manage the heat enough to manage that torque for very long before it is eventually not holding the peak torque at all. Clutch destruction can be immediate or gradual.

Regardless of all that, you’re basically saying the OP is already surpassing the trannies abilities, so any goals for extra power will inherently be even less reliable. You’re also saying 450hp with the right supporting mods is reliable because your engine didn’t break with that power after intense track days (and he is a beginner), so he doesn’t need to do a built engine.



That quote is what I meant when I said the transmission probably didn’t break then, even if it finally gave out on the cool down lap. Maybe you didn’t mean it to sound like the transmission is such glass that it will break in such a scenario, but that is how it sounded.

If a driver is putting a significant amount of heat into the clutch, they need to revisit their technique; clutches are not designed for that. The clutch should have minimal amounts of kinetic friction time; static friction will not introduce heat to the system.

Yes, I maintain that anyone who upgrades past what the stock clutch can handle is now putting their transmission at significant risk. Subaru engineers stepped failure points into their vehicles.

[86MLR]

Unless at drags with a boosted manual, you slip the clutch a heap

I love the smell of burnt clutches in the evening, it's the smell of drag racing

Or is that just me...???

[Irace86.2.0]

Originally Posted by CSG Mike

If a driver is putting a significant amount of heat into the clutch, they need to revisit their technique; clutches are not designed for that. The clutch should have minimal amounts of kinetic friction time; static friction will not introduce heat to the system.

Yes, I maintain that anyone who upgrades past what the stock clutch can handle is now putting their transmission at significant risk. Subaru engineers stepped failure points into their vehicles.

Heat generation and transfer in automotive dry clutch engagement

https://link.springer.com/article/10...Fjzus.A1700481

The abstract summaries the concept that heat is generated from clutch slip during engagement with a focus on managing the coefficient of friction to limit heat-related-degredation of clutch function.

The other concept is to increase the pressure or force, besides changing materials, so there is less slip during engagement or quicker grab. Many factors will determine the amount of slip. A clutch that is overbuilt compared to the torque may have minimal heat issues. As the materials and pressure get closer to the amount of torque that will overcome static friction, the shorter the life of the clutch will be.

While it is a reasonable assertion to say that Subaru designed the OEM clutch to fail before the transmission, that really doesn’t say much. It doesn’t mean that anything slightly past the OEM clutch’s abilities is ticking time bomb territory. Take the Supra’s V160 GETRAG: bpu 400whp is about max for the stock clutch, but the box will hold double that or more.