98 LGT short-block compatibility

[996TT]

Hi and thanks for looking

After rebuilding my heads and pretty well replacing everything with new parts, I found out I have an issue with major piston slap when cold, (until the engine warms up, then it's quiet),.... I am planning to swap out the short-block instead of rebuilding it to decrease downtime....so I have an opportunity to buy a super low mileage (maybe 60-100miles)) 2005/6 short-block from a JDM Forestor/Impreza. I was wondering if everything will cross over from the 98 Legacy GT engine onto this newer-age block.......I assume everything will, but I just need some of you guru's to chime in and give me your opinion.
I was hoping to use this new block since it will more than likely not have a lot of those old issues usually associated with the older phase 1 blocks......I also noticed it has domed pistons, which I am sure increase the compression ratio....will this you think present a problem? or should I replace the pistons with the correct style of dished pistons or maybe even thicker head gaskets??....

your opinions are greatly appreciated....

[Huffer]

I would think that the compression ratio of the JDM Forester block is going to be higher, and would require running higher octane to avoid pinging. I assume here the block is from a normally aspirated vehicle, and not a turbo one.

Mechanically I think it would work, but you'd have to be pretty careful with the oil galleys and the mounting locations for your accessories.

Also - if the block is SOHC, then it will definitely not work with your car.

ECU-wise you better have something lined up to take care of the tune.

There is a solution to the piston-slap - TWE make piston sleeve kits which help to make the engine much quieter on startup. They also supply highercompression pistons too.

[996TT]

thanks for the quick reply....

The short-block is from the JDM NA "SOHC" forester/Impreza .....So I guess it won't work...I assumed it would, but oh well....

I guess I'll just find a good short-block and have it re-built by a shop,....then do the re and re...

I am just a little pissed that after redoing the engine heads etc, that the block in my car was the only part we didn't re-do since it had really low miles on it....never again will I assume....:(

thanks again.....

[SammyDaFish]

the block will probably bolt up since it's still an EJ, but Subaru changed a lot of things in 05, dunno if they changed anything with the basic block design.

If the pistons are domed then you need to check valve clearance before you put it all together. The higher compression will probably be good for you. You might need to run premium, but all things relative, it's only a few % more for fuel, and high compression engines tend to be more fuel efficient, so you're probably at a wash. Plus you'll have more power :)

[996TT]

thats cool....but as Huffer was saying since it's from an SOHC engine in won't work? I need to clarify....

I can deal with buying premium, but I just want to make sure that all the accessories bolt up the same. I wouldn't think that Subaru would relocate any of the accessory locations....As for the valve clearance, it's still a 4 valve head on the SOHC car, so shouldn't they clear? Worst case scenario, I'd put in new pistons....All I want to make certain is that everything will bolt on.....heads, manifolds etc.. etc....

[SammyDaFish]

hmm... I dunno, is something on the block different on SOHC engines after 05?

[SammyDaFish]

As for the valve clearance, it's still a 4 valve head on the SOHC car, so shouldn't they clear? Worst case scenario, I'd put in new pistons....All I want to make certain is that everything will bolt on.....heads, manifolds etc.. etc....


valve lift, angle size and timing will all effect piston to valve clearance so you'll need to check.

As far as manifolds go, they need to be matched to the heads, so as long as you run the heads that are already in your car you can be guaranteed that everything else will bolt right up.

[Huffer]

Worst case scenario, I'd put in new pistons....All I want to make certain is that everything will bolt on.....heads, manifolds etc.. etc....

If you're going to put new pistons in, then you would be better off resleeving and putting in new pistons into your existing block. Not buying a random one and reworking it to achieve the same goal.

[SammyDaFish]

Also - if the block is SOHC, then it will definitely not work with your car.


out of curiosity, how come?

[996TT]

okay, cool guys, thanks for the info.....

I'll do do some more research......

thanks again

[Huffer]

Also - if the block is SOHC, then it will definitely not work with your car.


out of curiosity, how come?

My interpretation of "shortblock" is the block + heads.
I see now that the discussion is revolving around the piston section only?

"Long block" to me refers to an engine with all it's OEM-spec accessories attached to it, including the intake manifold, AC, alternator etc.

?

[SammyDaFish]

Also - if the block is SOHC, then it will definitely not work with your car.


out of curiosity, how come?

My interpretation of "shortblock" is the block + heads.
I see now that the discussion is revolving around the piston section only?

"Long block" to me refers to an engine with all it's OEM-spec accessories attached to it, including the intake manifold, AC, alternator etc.

?


nope, short block is the block and what's inside it. Long block is the block plus the heads. a complete engine, or tin to tin, is an engine with the manifolds and maybe accessories.

He's talking about a short block, so no heads are involved in the swap.

[996TT]

sorry for the confusion,...I mentioned short-block in the first post......The heads that actually came with this 2005/6 engine were SOHC with some sort of variable valve timing....so I know for sure the heads won't work...I was just thinking of slapping on my freshly re-built dohc heads and all the existing accessories on this new short-block....if of coarse I can make sure that the hi-comp pistons won't interfere with the valves on my heads....

thanks again

[Huffer]

2005 JDM Forester's came with AVCS...not too many piggybacks will work with that.

So if you're swapping heads, you might as well crack your existing block and just resleeve.

My preference would be to swap the entire engine to the JDM SOHC, because you're running a lighter engine, with less rotating parts, and making (depending on fuel & tune) the same power.

[SammyDaFish]

you can always run the heads without using the variable valve timing. it will just stay static. No benefit, but no loss. You might have to get the intake manifold too if you did that though, I dunno what manifolds will swap onto those heads.

Depending on how subaru's AVCS works, you might be able to activate it with most piggybacks. Many piggybacks support v-tech/axillary output , and AVCS could very well work with that, I've never looked up the electronics on how AVCS is activated, since well, I've never had a set of those heads to tinker with.

[996TT]

if I use this block, I will just reuse all of my accessories,DOHC heads, and intake manifold.....the rest won't be used......of coarse as long as we can keep the compression to a respectable level, and the valve to piston clearance is there....I think our USDM 05/06 2.5L was something like 10:1 compression....I just need to find out what the JDM version is.....

Thanks for all the feedback...

[Sarra]

Our 2003 Outback with the EJ253 is 10.1:1 CR.