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Old 10-31-2001, 04:05 PM   #1
oman
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java black pearl

Default 2.5 closed deck from COBB

Anyone have an idea how much boost you can safely run with a modified 2.5 closed deck?
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Old 10-31-2001, 04:23 PM   #2
iodine23
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You mean if the block was the weakest link in the system? Because a closed deck with everything else stock probably won't help you out at all.
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Old 10-31-2001, 04:37 PM   #3
STiShawn
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So far very few, if any, have destroyed blocks. The weak links are the pistons, trannies and fuel system. A closed deck EJ25 should be the last thing in a big build up....IMHO.
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Old 10-31-2001, 04:48 PM   #4
oman
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Default big buildup

this is a planned mod for my WRX.
I'm just trying to figure out if I should use a 2.5 modified block, a 2.2 closed deck or track down an STI RA from Japan.

Is the STI going to have the most potential for power?
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Old 10-31-2001, 04:52 PM   #5
skywalker
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I have talked to Cobb Tuning about engine blocks and they said they have some really wierd experiences. For some odd reason all Subaru engine blocks are not built equally.

They said some blocks can handle just about as much boost as you can imagine with a stock block and other blocks will break at as little as 5 pounds of boost. They don't seem to be able to tell what blocks will hold or not either. Just one of those things. Subara goes to the lowest bidder probably and so who knows where your engine was made.

This seems to be the same issue with many other parts on Subaru's some parts will break under the littlest stress where the same part on other Subaru's can handle anything.

In the end beefing up all the internals and getting a closed deck from Cobb would make the engine bullet proof, if it was already or not, you know it is with Cobb rebuilding it.

Just my $0.02...
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Old 10-31-2001, 06:58 PM   #6
bsquare
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oman:

It depends a LOT on the rest of your components and your facilities for tuning (both engine management and dyno access). I'd skip the RA block as the EJ22T block is at least as strong, is a ton cheaper (under $1200 for a short block from subaruparts.com!), and has a 10% advantage in displacement to really help with torque.

The EJ25 is known to be quite powerful when combined with a turbo, but the upper bound on boost for a built EJ25 motor is something I haven't heard anyone talk about. With lowered compression (8.5:1 or so) you could certainly run 15psi with the right electronics, possibly more.

Speed costs, how fast do you want to go?


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Old 11-01-2001, 04:34 PM   #7
FuJi K
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so what is the recommended compression ratio pistons for the EJ25 block if one was to go turbo and not lose that awesome low end power?


FuJi K

Last edited by FuJi K; 11-01-2001 at 04:42 PM.
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Old 11-01-2001, 05:00 PM   #8
HOK
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actually with all the failures on the pistons being almost identical including mine... I was wondering if the open deck design had anything to do with it.. theory: as the engine is boosted.. the cylinders vibrate and the pistons are knocking against the cylinder walls and the piston crown cracks and breaks off...?

Just a thought... no proff or anything..
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Old 11-01-2001, 05:30 PM   #9
iodine23
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Quote:
Originally posted by FuJi K
so what is the recommended compression ratio pistons for the EJ25 block if one was to go turbo and not lose that awesome low end power?


FuJi K
I'd guess about 8.5:1. I think I saw that on Cobb's site too. And there was a post somewhere that DSM owners liked 8.0:1 more than 8.5:1 because you get more boost. But since you're talking about keeping more low end then I'd say 8.5:1 is the loewst CR you'd want to go.
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Old 11-01-2001, 05:31 PM   #10
bsquare
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Group N EJ20-based rally cars generally run around 8.6:1 and because they have inlet restrictors, they are optimized for immediate torque (obviously, ALS and really expensive turbos help with this). 8.5:1 seems a good compromise between absolute maximum boost and off-boost performance for a street car.


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Old 11-01-2001, 06:19 PM   #11
Kevin Thomas
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Default EJ25 blocks

Here's a good post to read about the limits of the EJ25.

Shiv Dyno Results
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Old 11-01-2001, 11:00 PM   #12
iodine23
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bsquare: I read on some site that restrictors have the added bonus of helping to increase torque even though they decrease how much your engine can breathe. This is because they increase the velocity of the intake air and propte beter air/fuel mixing, swirl, etc.

But I'm sure anti-lag and nice turbo setups (I think Mitsus ran twin-scroll titanium turbos or something like that) also help them out too.
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