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I'm not sure I understand either... Seems to me it is torque which can break things in a transmission, not so much HP... HP, I suppose, could generate heat that maybe has to be dealt with (in the lubricant of the manual transaxle and maybe more so the automatic)... but I think we're talking about the (relatively weak) manual.

So, keeping the turbo from generating much torque at lower revs, I'm not sure how that eases the forces on the transaxle, if it then makes torque at higher revs?
 

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Discussion Starter · #82 ·
I'm not sure I understand either... Seems to me it is torque which can break things in a transmission, not so much HP... HP, I suppose, could generate heat that maybe has to be dealt with (in the lubricant of the manual transaxle and maybe more so the automatic)... but I think we're talking about the (relatively weak) manual.

So, keeping the turbo from generating much torque at lower revs, I'm not sure how that eases the forces on the transaxle, if it then makes torque at higher revs?
I'm sure there's probably some physics to it, but the biggest impact, in the way I understand it atleast, is that you rarely go above 3000rpm in normal day to day driving, unless you're intentionally trying to go fast, therefore only getting the high torque when you want it and reducing unnecessary load. Which is why there isn't any gains in mpg usually, unless you're racing lol.
 

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Your understanding of the physics is equating to "delaying the inevitable". Nothing wrong with that, but consider this: When the boost suddenly appears it will suddenly bring all that torque through the clutch and then into the transmission. The same torque that will damage it at less than 3000 will damage it at 3000 and beyond. What I have heard said over the years is that when you have a delicate manual transmission you don't install a steel or multiplate clutch. Instead, you install a clutch with just a slight bit more bite than stock. In this way it can transfer a bit more torque than OEM, but should things go bad, the clutch acts as a fuse and will burn out before transferring too much torque to the box. Replacing a clutch is far cheaper than replacing a transmission. Plus, the driveability of a smaller turbo is often times far more advantageous than a snappy, laggy big turbo. Remember, power corrupts, and absolute power corrupts absolutely. Just my $0.02 there, though.
 

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Your understanding of the physics is equating to "delaying the inevitable". Nothing wrong with that, but consider this: When the boost suddenly appears it will suddenly bring all that torque through the clutch and then into the transmission. The same torque that will damage it at less than 3000 will damage it at 3000 and beyond. What I have heard said over the years is that when you have a delicate manual transmission you don't install a steel or multiplate clutch. Instead, you install a clutch with just a slight bit more bite than stock. In this way it can transfer a bit more torque than OEM, but should things go bad, the clutch acts as a fuse and will burn out before transferring too much torque to the box. Replacing a clutch is far cheaper than replacing a transmission. Plus, the driveability of a smaller turbo is often times far more advantageous than a snappy, laggy big turbo. Remember, power corrupts, and absolute power corrupts absolutely. Just my $0.02 there, though.
100% on all aspects 👍. It is a delicate 'box.
 

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I'm sure there's probably some physics to it, but the biggest impact, in the way I understand it atleast, is that you rarely go above 3000rpm in normal day to day driving, unless you're intentionally trying to go fast, therefore only getting the high torque when you want it and reducing unnecessary load. Which is why there isn't any gains in mpg usually, unless you're racing lol.
I think a lot of folks find that the Skyactiv-2.5G is underwhelming by way of (especially) low-end torque. I certainly am in that camp. For being a 100mm stroke 2.5... it should have a more convincing bottom end response. Now the fuel economy is decent but I'd personally be pleased with more under-2800 rpm response. The supercharger does this, i.e. specifically the VT unit. Now, a small turbo (like say in a 2 litre VW) can provide a flat torque curve from 1500 to 5000 RPM's. I'd like that... but engineering that, for me, would be more of a PITA than I'd want. So, a tune for 92 AKI fuel, or possibly the VT package, is what interests me. Shooting out the lights? No, I don't want to re-engineer the whole car (my estimation of what it'd take to do that satisfactorily)...
 

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Discussion Starter · #86 ·
Your understanding of the physics is equating to "delaying the inevitable". Nothing wrong with that, but consider this: When the boost suddenly appears it will suddenly bring all that torque through the clutch and then into the transmission. The same torque that will damage it at less than 3000 will damage it at 3000 and beyond. What I have heard said over the years is that when you have a delicate manual transmission you don't install a steel or multiplate clutch. Instead, you install a clutch with just a slight bit more bite than stock. In this way it can transfer a bit more torque than OEM, but should things go bad, the clutch acts as a fuse and will burn out before transferring too much torque to the box. Replacing a clutch is far cheaper than replacing a transmission. Plus, the driveability of a smaller turbo is often times far more advantageous than a snappy, laggy big turbo. Remember, power corrupts, and absolute power corrupts absolutely. Just my $0.02 there, though.
Yeah, but I have the automatic, and I think the guy with the turbo does too.
I think a lot of folks find that the Skyactiv-2.5G is underwhelming by way of (especially) low-end torque. I certainly am in that camp. For being a 100mm stroke 2.5... it should have a more convincing bottom end response. Now the fuel economy is decent but I'd personally be pleased with more under-2800 rpm response. The supercharger does this, i.e. specifically the VT unit. Now, a small turbo (like say in a 2 litre VW) can provide a flat torque curve from 1500 to 5000 RPM's. I'd like that... but engineering that, for me, would be more of a PITA than I'd want. So, a tune for 92 AKI fuel, or possibly the VT package, is what interests me. Shooting out the lights? No, I don't want to re-engineer the whole car (my estimation of what it'd take to do that satisfactorily)...
The supercharger idea is nicer and simpler, Im thinking of trying to DIY one with a centrifugal supercharger, my current problem is trying to find a way to add the pulley without interfering with the engine mount and ac line, might even make it go under the intake in a position where its not easily seen from above. Gotta get a few parts and bearings to add a long extension from the pulley at the accessory belt to the supercharger which I intend to put at the side where the airbox is. If 8 psi can be proven to create 280+ hp on this engine or so then the 20hp loss I estimate shouldn't be bad. Adding a boost controller would be a great way to manage different modes, like a lighter economy boost or a higher race boost. I'm not sure how that would play along with the ECU but definitely an idea to consider.
 

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I'm not sure I understand what you mean here. A larger turbo will not spool until later, meaning you get neither torque nor power at low rpm. Unless I'm not correctly reading what you're saying.
I was shooting for more "top end" power on my car, and didn't want a smaller turbo in that regard. Simply put, since the turbo won't spool until around 3k rpm or so, I won't have any extra torque from the turbo below that rpm since it has not spooled yet. I'll also have the timing retarded until around 3500-4k rpm to keep the torque down low when the turbo is actually spooling. I've raised my rpm limit to 7k since I've tuned my car N/A, allowing to have a longer power band and have more useable power for this turbo. I'm fine with any lag down low considering if this car were to be used for purposed other than cruising around, I can easily downshift into a lower gear and have boost since I'll be higher in the rpm range anyway.
 

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I was shooting for more "top end" power on my car, and didn't want a smaller turbo in that regard. Simply put, since the turbo won't spool until around 3k rpm or so, I won't have any extra torque from the turbo below that rpm since it has not spooled yet. I'll also have the timing retarded until around 3500-4k rpm to keep the torque down low when the turbo is actually spooling. I've raised my rpm limit to 7k since I've tuned my car N/A, allowing to have a longer power band and have more useable power for this turbo. I'm fine with any lag down low considering if this car were to be used for purposed other than cruising around, I can easily downshift into a lower gear and have boost since I'll be higher in the rpm range anyway.
I was shooting for more "top end" power on my car, and didn't want a smaller turbo in that regard. Simply put, since the turbo won't spool until around 3k rpm or so, I won't have any extra torque from the turbo below that rpm since it has not spooled yet. I'll also have the timing retarded until around 3500-4k rpm to keep the torque down low when the turbo is actually spooling. I've raised my rpm limit to 7k since I've tuned my car N/A, allowing to have a longer power band and have more useable power for this turbo. I'm fine with any lag down low considering if this car were to be used for purposed other than cruising around, I can easily downshift into a lower gear and have boost since I'll be higher in the rpm range anyway.
Also, you both are only referring to the transmission. I'm mainly referring to the rods, even though they are forged aluminum from factory, it helps to keep the torque low in the lower rpm range to avoid snapping or bending a rod.
 

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I suspect they're forged steel... but they are very slender. Not likely h*ll-for-strong...
This is the article I grabbed my information from. If it’s correct, we have a forged steel crank, forged aluminum rods, and non-forged aluminum piston heads with molybdenum steel cylinder walls.
 

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Forged steel crank, forged steel conn rods. Mebe I'm a dummy, but I have never heard of aluminum conn rods. Titanium, yes. Aluminum alloy no. The article doesn't say Al rods.
Here’s one site that sells forged aluminum rods. BME Forged Aluminum Rods

I also did reread that paragraph from the article and you are correct in stating that the article did not specify the material for the connecting rods. That information is up in the air, regardless, however, steel is stronger than aluminum, and if they were to be forged steel, rather than forged aluminum, we would have less worries regarding the engine itself then.
 

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Here’s one site that sells forged aluminum rods. BME Forged Aluminum Rods

I also did reread that paragraph from the article and you are correct in stating that the article did not specify the material for the connecting rods. That information is up in the air, regardless, however, steel is stronger than aluminum, and if they were to be forged steel, rather than forged aluminum, we would have less worries regarding the engine itself then.
'Ya learn something every day... Thx...
 

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Here’s one site that sells forged aluminum rods. BME Forged Aluminum Rods

I also did reread that paragraph from the article and you are correct in stating that the article did not specify the material for the connecting rods. That information is up in the air, regardless, however, steel is stronger than aluminum, and if they were to be forged steel, rather than forged aluminum, we would have less worries regarding the engine itself then.
The attached is longish and a bit hard to listen to... but the beginning particularly is interesting...
 

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Discussion Starter · #95 ·
The attached is longish and a bit hard to listen to... but the beginning particularly is interesting...
Lol, idk about that, I have big doubts about carbon fibre, especially in high-heat settings, not to mention different types of forces. Maybe would be useful in niche applications but there's a reason they're not OEM even though the material has existed way too long. Body parts, yes, engine, no.

Edit: Watched the rest of the video, realized he explains it correctly lol.
 

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The hardest part of boosting the Skyactiv-G engines is getting out tuned and understanding that this is an unusual engine...

To be honest I think it is foolish to try to DIY a boost kit, even though I considered that when there weren't any options, now that they're ARE options that is the smart move.
It may seem like it'll save money to cobble together your own setup, but in the end it'll likely cost more, and have lesser results or end up blowing the engine or trans when you do try to get more power...
FWIW
 

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The hardest part of boosting the Skyactiv-G engines is getting out tuned and understanding that this is an unusual engine...

To be honest I think it is foolish to try to DIY a boost kit, even though I considered that when there weren't any options, now that they're ARE options that is the smart move.
It may seem like it'll save money to cobble together your own setup, but in the end it'll likely cost more, and have lesser results or end up blowing the engine or trans when you do try to get more power...
FWIW
That's my sentiment too. My opinion, my sole opinion fwiw, is that 'lotsa folks are wannabe automotive engineers. First up, it's hard work to fabricate all and have it fit and have a design that is reliable. Second off, this world is full of compromises. Most car company engineers refine their designs and end up with a carefully-hewn set of compromises that are most often true to the basic concept and target audience of the car. It is very hard for an individual who is not practiced in examining and trying out the various ways of achieving that fine balance to do this from scratch. Not impossible, but pretty improbable. The beta-testers have had their go at this VT design. It seems to be robust enough. I like it... No, I am not a shill for VT. What I am for, is easy, bolt on, already-tested solutions...
 
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