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The first question depends on whether the goal is performance or a mainstream engine with good MPG that runs regular grade fuel. My assumption is that Subaru is going for the latter choice. 240 to 270 HP with a reasonable torque output of 210 to 250 lb-ft should be attainable with direct injection and without turbocharging.
They already made a 3.0L H6 that fell within those figures...in 2005...with no direct injection.

Mine is 245 HP / 215 lb-ft of torque, and with something as simple as better headers and a tune you're up to the mid-high end of your range.

I don't see any reason why closer to 300 HP wouldn't be pretty easily attainable on regular fuel out of a 3.0L H6 today.
 

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Discussion Starter #22
They already made a 3.0L H6 that fell within those figures...in 2005...with no direct injection.

Mine is 245 HP / 215 lb-ft of torque, and with something as simple as better headers and a tune you're up to the mid-high end of your range.

I don't see any reason why closer to 300 HP wouldn't be pretty easily attainable on regular fuel out of a 3.0L H6 today.
That sounds about right. Subaru gotta have one engine for both vehicles. Originally, the bigger car got the smaller one's engine with predictable results. Let's see if Subaru goes the opposite route now.
 

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They already made a 3.0L H6 that fell within those figures...in 2005...with no direct injection.

Mine is 245 HP / 215 lb-ft of torque, and with something as simple as better headers and a tune you're up to the mid-high end of your range.

I don't see any reason why closer to 300 HP wouldn't be pretty easily attainable on regular fuel out of a 3.0L H6 today.
Thanks but it's probably safe to say that everyone here knows about the 3.0. 245 HP in a performance tune running premium fuel sounds about right.

We were theorizing about a mass production (as in no low flow exhaust or cold air intake or anything like that) engine running regular and tuned with an eye toward economy and low emissions. I think you're right that 240-250 HP should be within reach, but it's debatable if they could get a 100 HP per liter on regular with reasonable economy and low emissions. I guess we'll see.
 

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Does the current 3.6 have variable valve timing on both cams or just the intake? And the dual stage lift that the 4H has?
 

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Thanks but it's probably safe to say that everyone here knows about the 3.0. 245 HP in a performance tune running premium fuel sounds about right.

We were theorizing about a mass production (as in no low flow exhaust or cold air intake or anything like that) engine running regular and tuned with an eye toward economy and low emissions. I think you're right that 240-250 HP should be within reach, but it's debatable if they could get a 100 HP per liter on regular with reasonable economy and low emissions. I guess we'll see.
I think you're missing my point. 245 HP has been done. That's what the 3.0 is bone stock on premium. No tunes or mods at all to achieve that. So, of course that's within reach with newer tech...it was already done 10 years ago. I would think a new 3.0 should do significantly better than 245 HP.

100 HP/liter has also been done on a naturally aspirated engine. The BRZ has a 200 HP 2.0L N/A H4.
 

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A turbo Outback would be wonderful to have again
 

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I think you're missing my point. 245 HP has been done. That's what the 3.0 is bone stock on premium. No tunes or mods at all to achieve that. So, of course that's within reach with newer tech...it was already done 10 years ago. I would think a new 3.0 should do significantly better than 245 HP.

100 HP/liter has also been done on a naturally aspirated engine. The BRZ has a 200 HP 2.0L N/A H4.
You're right, 250 HP+ from 3.0L is no big deal. Subaru had that in the previous EZ engine that's in your car. It requires premium fuel to produce peak power, as does the BRZ engine. They could simply go back to that design if they were willing to return to a premium fuel requirement.

However, Subaru's number one publicly-stated reason for redesigning the EZ engine in 2007 was to switch it to regular gas. They had to increase displacement to 3.6L and basically redesign all the internals to keep roughly the same power and still run regular.

So, what is the reasonable probable output from a 3.0L six cylinder engine running regular fuel? Right now the engineering limit seems to be around 80HP to 85 HP per liter. That's 240-250 HP from 3.0L. It will be interesting to see where the technology takes us from here.
 

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You're right, 250 HP+ from 3.0L is no big deal. Subaru had that in the previous EZ engine that's in your car. It requires premium fuel to produce peak power, as does the BRZ engine. They could simply go back to that design if they were willing to return to a premium fuel requirement.

However, Subaru's number one publicly-stated reason for redesigning the EZ engine in 2007 was to switch it to regular gas. They had to increase displacement to 3.6L and basically redesign all the internals to keep roughly the same power and still run regular.

So, what is the reasonable probable output from a 3.0L six cylinder engine running regular fuel? Right now the engineering limit seems to be around 80HP to 85 HP per liter. That's 240-250 HP from 3.0L. It will be interesting to see where the technology takes us from here.
I believe the actual reason for the premium fuel requirement on the 3.0 is related more to cooling than performance. Can't remember the whole story behind that. It's explained in a thread somewhere on here.

I run it because the extra expense isn't enough to worry about and because that's what the engine was built to run. I'm actually not sure how different my 3.0R would be with regular fuel since I've never run it. I tried it in my older 3.0 a few times (EZ30D) and the main difference was that fuel economy took a big enough hit so that it made more sense to just run premium.
 

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I remember reading somewhere here that the cooling issue on the EZ30 was that the cooling channels were in series, leaving the cylinders at the rear of the engine getting less cooling than those at the front. The 3.6 has a parallel cooling feed that cools all cylinders equally.

IIRC, that is. And that doesn't make it accurate ;)
 

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I believe the actual reason for the premium fuel requirement on the 3.0 is related more to cooling than performance. Can't remember the whole story behind that. It's explained in a thread somewhere on here.

I run it because the extra expense isn't enough to worry about and because that's what the engine was built to run. I'm actually not sure how different my 3.0R would be with regular fuel since I've never run it. I tried it in my older 3.0 a few times (EZ30D) and the main difference was that fuel economy took a big enough hit so that it made more sense to just run premium.
Your memory matches mine I recall a heat study map done on the old 3.0 that someone found and posted. It was actually really interesting included pictures based on heat under load and the hot spots that the old 3.0 generated under load is why the premium ie more stable fuel was needed given those hot spots created under load would cause pre ignition of less stable lower octane fuels.

The 3.6 was a ground up design job to get the power, reliability,mileage and proper cooling ie no not spots that create the need for higher octane fuel etc. However I do not think the 3.6 was designed with any sort of DI and new engine tech in mind when Subaru did it.
 

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What is the reasonable probable output of a new, smaller, say 3.0, H6?
Assume 70 lb-ft per liter at 6000 rpm: p = 3.0 x 70 x 6000 / 5252 = 240 hp

And that is a very optimistic assumption. The current 3.6R generates only
61.7 lb-ft per liter at 6000, so 240 hp from 3.0 liters would require a 13%
boost in specific torque, compared to today's 3.6R.

You might reach that goal with direct injection, but I seriously doubt that
MotherSoobie would invest that much money/effort in a (doomed-by-CAFE)
dead-end project. The only other path would be greatly improved breathing
to move the power peak out to 6800 rpm …not an insignificant investment.


…300 hp from 3.0 liters? Nothin' in the way but physics …uhh, and economics,

Looby
 

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I remember reading somewhere here that the cooling issue on the EZ30 was that the cooling channels were in series, leaving the cylinders at the rear of the engine getting less cooling than those at the front. The 3.6 has a parallel cooling feed that cools all cylinders equally.

IIRC, that is. And that doesn't make it accurate ;)
Yes that's pretty much it. The original EZ design had a coolant flow arrangement where coolant flowed from one cylinder to the next. Naturally the cylinders that were downstream always got hotter coolant and ran hotter, while those that were first and got their coolant fresh from the radiator always ran cooler. The hotter cylinders are of course more prone to knocking.

During the 3.6 redesign the cooling arrangement was changed. Each cylinder now has its own coolant feed, and the cylinders run at about the same temperature. This allows the 3.6 to safely run slightly more spark advance than the 3.0 version without knock consequences. I believe this added a few (maybe five?) of the HP gained in the redesign.

It's definitely possible that the uneven cooling was one of the reasons the 3.0 required premium. I don't know that but it makes sense.
 

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I guess I don't get the point of downsizing it. They only sell that engine in places where displacement isn't specifically taxed.

So why not whip up some DI heads, tune the pipes a little and keep cranking out the short blocks as is to minimize cost?

They'd get a power kick/efficiency boost without having to sink much in.

I think the ultimate goal is to give that engine a home in the new 3-row car and hopefully sell enough of that car to use every 6-cylinder they can build.

Offering it in the up-trim legacy for now is just a way to help amortize the costs, and a hedge against the 3-row bombing the way the Tribeca did.
 

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I guess I don't get the point of downsizing it. They only sell that engine in places where displacement isn't specifically taxed.

So why not whip up some DI heads, tune the pipes a little and keep cranking out the short blocks as is to minimize cost?

They'd get a power kick/efficiency boost without having to sink much in.

I think the ultimate goal is to give that engine a home in the new 3-row car and hopefully sell enough of that car to use every 6-cylinder they can build.

Offering it in the up-trim legacy for now is just a way to help amortize the costs, and a hedge against the 3-row bombing the way the Tribeca did.
Simple when you want to have an engine design that supports future tech that can bump power you need a design that supports the cooling needs and other factors that come with it. A back yard builder might do as you suggest but a Auto Company needs to make sure the whole package actually works or they end up with lawyers knocking on the door. Go read the angry comments on the forms about paint its paint for christ sakes!!! Could you imagine an engine that has less than ideal failures when used under pretty normal use?
 

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I'm not convinced that anyone is going to be able to push 6-cyl engines for much longer.

Also, Subaru is pretty close to a backyard builder given their overall volume.

I think it makes perfect sense for them to do one last revision to their H6, sell as many as they can, and at that point join all the big automakers with smaller displacement turbo-4s and hybrid electric drivetrains.

Yes, I realize they have those today as well, but I suspect they can't make enough of any one to put them across the whole line- plus there is some wisdom in diversifying it anyway.
 

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Sadly, I bet you're right. I love my H6 but the winter fuel economy is pretty hysterical for a ~250 HP vehicle. There's just something about the flat torque curve and sound of a Boxer 6, though...
 

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you guys need to read between the lines a little more

If Subaru does anything with the H6 they will do a ground up new H6 designed to accept DI tech which case the 3.0 comment sorta makes sense - engine with DI capability does not need to be turbo to see pretty sizable performance bump in power.
I agree for the most part.

The Tribeca replacement will see to an H6 (old highly doubtful, new most likely) for sure. There's no way Subaru can properly compete with the other three-row SUV's in the segment without an H6 or some variant of a 6-cylinder engine. A turbocharged 4-cylinder being the only option will not cut it with their target audience.
 

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Assume 70 lb-ft per liter at 6000 rpm: p = 3.0 x 70 x 6000 / 5252 = 240 hp

And that is a very optimistic assumption. The current 3.6R generates only
61.7 lb-ft per liter at 6000, so 240 hp from 3.0 liters would require a 13%
boost in specific torque, compared to today's 3.6R.

You might reach that goal with direct injection, but I seriously doubt that
MotherSoobie would invest that much money/effort in a (doomed-by-CAFE)
dead-end project. The only other path would be greatly improved breathing
to move the power peak out to 6800 rpm …not an insignificant investment.


…300 hp from 3.0 liters? Nothin' in the way but physics …uhh, and economics,

Looby
From my reading, direct injection should make 300 HP out of 3.0, with economy comparable to what a conventional 2.5 gets now entirely possible. The question is spending the money to find the way around the problems with intake valve coking. I do not know much about Mazda's solutions, but Audi certainly has had some teething issues.

I am pretty sure Mother Subie will not release a powerplant with those sorts of issues.

Myself, I would just like to see them do a TDI of about 2.5l displacement.......And 40+mpg.
 

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Discussion Starter #39
Myself, I would just like to see them do a TDI of about 2.5l displacement.......And 40+mpg.
Ugh, no, thanks, all that torque coupled with all those savings at the pump will ruin me:28: (I mean, I will be driving around too much and lose my job;))
 

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From my reading, direct injection should make 300 HP out of 3.0...
What are you gonna believe ...reading or physics?

100 hp per liter would require nearly 88 lb-ft per liter at 6000 rpm,
(that would correspond to peak torque well over 95 lb-ft per liter).

Mazda's 2.0 DI engine generates peak torque of only 75 lb-ft/liter,
and less than 68 lb-ft per liter @ 6000 rpm (peak hp). Their 2.5L
direct injection engine has nearly identical figures.

Please identify JUST ONE naturally aspirated production automotive
engine that generates 100 hp/liter @ sane rpm -- on 87 octane fuel!

Looby
 
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