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Old 01-12-2013, 12:40 AM   #1
Subie_kid
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Default 257 block with sohc heads? will it work and what will I need.

Quick question guys, spun a bearing the other day in my 06 2.5I and know someone selling a ej257 short block and I was wondering if I put in the short block with the sohc heads will the whole thing Still be plug and play or will it be throwing codes left and right on the stock ecu? If so what will I need to solve the problem
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Old 01-12-2013, 10:46 AM   #2
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The CR would be low and it would be a slow dog without changing pistons
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Old 01-12-2013, 10:48 AM   #3
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I THINK TWE makes a set of pistons for this.

We're helping a rally team this year move to open class and we're going the opposite way - ej257 bottom, sohc heads, and adding a turbo.
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Old 01-12-2013, 12:13 PM   #4
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I really wouldn't care if it was slow as hell, it's just to get it back on the road so I can get to work lol no racing now, leaving for the airforce in March
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Old 01-12-2013, 09:54 PM   #5
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If you did this you would end up with an 8.9:1 CR, and shouldn't throw any codes, since the car doesn't really care what shortblock you have under it's hood. If you are looking for a stock rebuild, this block is a little overkill for your application.



~Josh~
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Old 01-12-2013, 10:35 PM   #6
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Quote:
Originally Posted by ballitch View Post
If you did this you would end up with an 8.9:1 CR, and shouldn't throw any codes, since the car doesn't really care what shortblock you have under it's hood. If you are looking for a stock rebuild, this block is a little overkill for your application.

~Josh~
Thanks, I know it will be over kill but for the price I am getting this short block it's too good to pass up. Plus I will have one little part of the build bought by the time I get back from basic
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Old 01-13-2013, 12:03 AM   #7
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Just go for it. I bet you will be surprised how well it runs. I know a shop that imports DOHC turbo motors from Europe and swaps the short blocks into old Outbacks all the time. They run great.
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Old 01-13-2013, 01:10 AM   #8
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Just go for it. I bet you will be surprised how well it runs. I know a shop that imports DOHC turbo motors from Europe and swaps the short blocks into old Outbacks all the time. They run great.
The tq and hp they make its miserable and the gas mileage is even worse. I'm all about getting some good hardware for a great price but if you pay for the savings in gas over a year it's not really the great of a deal anymore
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Old 01-14-2013, 03:33 PM   #9
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A 8.9:1 N/A H4 would be miserable lol!
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Old 01-14-2013, 04:34 PM   #10
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Did someone actually calculate that 8.9:1 CR or just guess? The 257 and 251 heads do not have the same size combustion chambers......


Jay
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Old 01-14-2013, 04:48 PM   #11
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I did using 99.5mm bore, 79mm stroke. 51cc heads, 22cc sti pistons, .6mm stock sti HG.


~Josh~
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Old 01-14-2013, 06:24 PM   #12
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Can anyone say with certainty how much hp and tq going from 10:1 to 9:1 would drop?


There was a build on rs25 where one dude rebuilt with low compression with a plan to eventually add a supercharger. However, before the sc, the car pulled very well on low compression (albeit with full exhaust, delta2000 cams, tune). I remember seeing dyno plots, and the owner saying it was getting full timing (not a big surprise there).
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Old 01-15-2013, 01:48 AM   #13
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Usually if you go up or down a full point you gain or lose 4% of your CHP, that is a generic number and fluctuates based on engine/head design etc, etc...


~Josh~
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Old 10-10-2013, 01:03 AM   #14
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I'm thinking of doing a NA build now with a 257 block, 2.7 stroker kit, 11.2:1 CR pistons from TWE, SOHC, a aiming for 11.5:1 CR. how would that fair for power??
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Old 10-10-2013, 03:35 AM   #15
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Quote:
Originally Posted by Jr_gosetto View Post
I'm thinking of doing a NA build now with a 257 block, 2.7 stroker kit, 11.2:1 CR pistons from TWE, SOHC, a aiming for 11.5:1 CR. how would that fair for power??
So 100mm pistons and a 83mm stroker crank? Add a good EL header and some torque cams and you will have torque for days...
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Old 10-10-2013, 08:01 AM   #16
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100mm pistons don't give you anything except less room to go bigger down the road when the cylinders need to be bored/honed again... and less money in your wallet. Stock pistons are 99.5mm give or take.
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Old 10-11-2013, 12:40 PM   #17
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Originally Posted by RaceFaceXC View Post
100mm pistons don't give you anything except less room to go bigger down the road when the cylinders need to be bored/honed again... and less money in your wallet. Stock pistons are 99.5mm give or take.
Since that guy is talking about an NA build using that stroker kit, really no need to have more room to bore/hone after doing it for the stroker kit.

It would be a blast though for NA because of the torque...
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Old 10-11-2013, 02:06 PM   #18
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And on further research I have found that the stroker kit only goes to 8.5:1 CR the 2.7 stroker kit recommends a sleeved block (pretty much anything over 100mm should be sleeved) so I would think going up to a 2.6 and does that extra .5 mm make that big of a differance?? And plus any extra bore I'd need to match the head aswell, so it's not to heart wrenching if the .5 makes a differance just meens a little more coin to go towards tuning
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Old 10-11-2013, 03:46 PM   #19
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Quote:
Originally Posted by Jr_gosetto View Post
And on further research I have found that the stroker kit only goes to 8.5:1 CR the 2.7 stroker kit recommends a sleeved block (pretty much anything over 100mm should be sleeved) so I would think going up to a 2.6 and does that extra .5 mm make that big of a differance?? And plus any extra bore I'd need to match the head aswell, so it's not to heart wrenching if the .5 makes a differance just meens a little more coin to go towards tuning
That compression ratio is designed around a sti 57cc chambered head. Your heads are in the 50cc range or so. Remember, your power density is much lower than a wrx or sti engine so even if you went with 100mm pistons there is no need to worry about that.

I would do the 83mm crank but with the stock 99.5mm diameter pistons. You would have to get a custom piston though because of the wrist pin height being changed due to the longer stroke.
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Old 10-11-2013, 06:07 PM   #20
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Thanks for the info I didn't even think of wrist pin placement I will get ahold of TWE and see wat they can make up .I found a site that sell a brand new empty 257 case for about 1000 so ill need main studs and oil pan and pistons and the stoker kit and ill be able to start building it just I'm looking at about 6g to build the short block + money into head work so this will be a timely and costly project but should be fun once done
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