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Premium Member
2004 Forester 4EAT
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5,462 Posts
Discussion Starter #1
It's head gasket time for me and started thinking...... Could one build a bullet proof n/a motor buy installing n/a pistons into a turbo block. Could you use n/a heads? Would you need to use DOHC from a 98? I really don't want a turbo. Well, I don't really want the maintenance and other issues that go with them. I would, however, like to build a ~200hp n/a motor that will last 100k+ miles and run on 87 octane. If I could use SOHC heads, this would be a drop in. Is this a waste of time and money? Do you think I would be better off just doing good HG's and mild mods? Cams, intake, exhaust, port and polish ect.
(For those that answered my h6 questions, the donor car had a BAD knock.)
So on to the next fabulous way to waste money!
 

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Premium Member
2008 Forester X Premium 5MT
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8,070 Posts
Yes, you can use a EJ255/7 block and crank but you need to use NA pistons and rods or have custom pistons made for the shorter(1.1mm) turbo rods. You use your heads and all your other supporting items.

Tuning may be an issue but you wont do 200hp on 87 octane, partly because the EJ25 NA is already in the 10:1 compression range which is already pushing the limits of 87.....

I can fill in more tomorrow if you want.
 

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Premium Member
2004 Forester 4EAT
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5,462 Posts
Discussion Starter #3
I was hoping you would answer this.:biggrin: Would I gain any appreciable reliability out of this or just wasting time? I figured I would use N/A pistons and rods. SOHC heads will bolt to turbo block? HP #'s are "approximate":biggrin:
 

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Wasting time lol. A local is running a 257 shortblock with N/A sohc heads, but its build and running a BIG turbo.

Just get a 2.2L turbo motor and run a smallish turbo on moderate boost. Should last forever.

I'd just do the MLS headgaskets, get the block and heads checked/milled, possibly get the heads rebuilt. You're not going to be able to run 87 even on a built NA motor pushing anywhere close to 200. Any increase in compression or more timing is going to need more octane.

I'd just get an XT though if you're going to go through all the trouble of swapping. Not much extra maintenance on the turbo motor aside from shorter OCI's. I average 22-24 mpg highway and the premium fuel doesn't add that much more over the course of a year. I have 135,000 miles and I haven't had to do anything other than regular maintenance and repairs not related to the fact that its a turbo (its been the cheapest car my family has ever owned to maintain, even compared to the lease vehicles)
 

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Premium Member
2004 Forester 4EAT
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5,462 Posts
Discussion Starter #5
The idea of a motor build rather than fixing mine was more for time. Do the build as time allows and drop it in when I'm ready. Motor in and out should be one day job if it's a direct swap. I've got 2 fozzies. 3 motors would make repairs easier. I'm pretty good with the mechanical part of it, but bodging together wiring harnesses is not my strong suit. I may just pick up another n/a motor, r and r it, and play musical motors.
 

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Smooshed FOTY 2011
2005 Lifted 2.5 XT 5-Speed MT Dual-Range
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5,734 Posts
If you need a block and heads, I have them, and need to be rid of them. :biggrin:
 

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Premium Member
2008 Forester X Premium 5MT
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8,070 Posts
This is kind of a list of thoughts more then a how to.

I assume this is for your '99? Do you have the SOHC or are you one of the few that got a remaining DOHC.

Doing a NA build out of a EJ255/7 semi-closed deck block does add a lot of stability to the cylinders, it virtually eliminates the HG issue of the NAs and would be my choice for a NA subaru that I was planning on keeping until it died.

As I said, you would have to use NA rods, pistons.

As far as the heads these are fricken lego cars. just about any EJ head will bolt up to any EJ block. So yes you can use the SOHC NA heads on a EJ255/7 block with out issues.

Stay with what ever heads you have and you would be able to use your current wiring/ECU if you can go open source.

Tuning either open source(if available) or stand alone($$$$). If you have to go stand alone, screw the NA build and just do a swap to a turbo power plant via a donor car and come out about even money wise in the end.

All in all there is not a lot to be had out of the 2.5L NA. The compression can be bumped up to around 11:1 - 11.5:1 and still run on 92-93 octane. much beyond 10.5:1 drivability for daily use will start to suffer. The cam choices out there for the NAs(delta regrinds) suck in my opinion. You get 1-3 options with varying results. Some show zero improvement or a loss and others see gains.

The biggest room for improvement in the NAs is getting them to flow. All the white paper tuning I have seen for the NA (williaty? on NASIOC has some good ones) show that the NA starts starving for air after around 4500 or so rpm. The issue comes when you start porting the heads and trying various cams to satisfy those needs after 4500rpm you now start loosing TQ and HP below 3500-4000 rpm. Which is great if you want a rally car or track car you can keep in mid to high RPMs but sucks for daily street use and can be horrible in traffic. The stock intake will support more air flow then the heads/cams can, sadly the intake on the NA is about the last thing that needs changing.

I went through the options and researched when my NA Baja engine let go a few years back in hopes to gain some MPG and all around power at a time I had money to spare. In the end it went back bone stock with a massaged 12mm oil pump. The potential for gains just wasn't there to justify the cost and the potential for drivability and runability issues were just to great to justify porting, cams, pistons.....
 

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Premium Member
2004 Forester 4EAT
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5,462 Posts
Discussion Starter #10
Sounds like more hp is not gonna happen. I can see your point that these motors are already "tuned" to about as much as they will give. I may just look for a low miliage na motor to r and r. I will then swap into the 04. (Showing beginning signs of hg issues) Then I will r and r that one and install into my 99. Yes, it's a SOHC 99. By that time, I should be pretty good with these motors. Maybe I'll do my 99 motor and sell it to recoup some of my initial outlay for the first motor. Thanks for all your expertise.
 
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