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Old 04-10-2009, 05:15 AM   #1
Gigabelova
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Default EJ257 short block with lower stroke?

Hi,

I am getting my hands on a EJ257 shortblock soon. I was wondering about piston stroke as my tuner had mentioned that a shorter stroke is better as it supports higher revving. I understand the WRX's EJ205s have a shorter stroke compared to the STi's EJ257. My question how could we use the 257 block to obtain the added displacement while still using a shorter stroke.

Which crankshaft and rods would you use? Pros/Cons? Thanks in advance.
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Old 04-10-2009, 06:03 AM   #2
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You would need +2mm length rods to be able to use stock STi pistons with a WRX crank in a STi block. Or you could go the other route and get pistons with a taller compression height, or any combo of the two.
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Old 04-10-2009, 09:24 AM   #3
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sti 2.5 block
wrx crank - the wrx has a 75mm vs sti 79mm
+2mm longer custom rods - to make up for the lost 4mm from the sti crank (2mm each side)
sti pistons

i think the engine ends up being a 2.34 ltr

ibHomemadeWRX
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Old 04-10-2009, 10:53 AM   #4
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Quote:
Originally Posted by kevinh211 View Post
sti 2.5 block
wrx crank - the wrx has a 75mm vs sti 79mm
+2mm longer custom rods - to make up for the lost 4mm from the sti crank (2mm each side)
sti pistons

i think the engine ends up being a 2.34 ltr

ibHomemadeWRX
well, I use an even longer rod and custom piston so that CR is proper and where ever the customer wants it. Each set is custom made...if you are interested, I just go my VA tax ID so paper work for vendor account is being faxed monday. So from there about 3 weeks until I'll have a group buy going under my vendor account. No more building motors on the side

Regardless, that is kinda the formula, kinda.
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Old 04-10-2009, 11:06 PM   #5
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Thanks guys for the replies. Anyone heard of increasing bore at the same time? As in getting new iron sleeves with a larger bore.
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Old 04-11-2009, 12:35 AM   #6
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Quote:
Originally Posted by Homemade WRX View Post
well, I use an even longer rod and custom piston so that CR is proper.
Does your comment imply that the 2mm plus on OEM pistons lead to an incorrect final CR? - I’m not so sure I’d agree, though your posts to date indicate you have some good research work on this.

Advantage of using off the shelf up-rated pistons for the run of the mill de-stroke project means that the quench area and the overall combustion chamber shape and performance remains intact if one uses STI heads.

Rod length affecting stroke (shorter than 79 or longer) affects timing a bit and if one is really determined then cam off set on duration can be adjusted compensating for the change in stroke to restore the engine’s VE through the BTDC TDC and ATDC cycle.

Same as on Evo’s moving from 88mm to 100mm (much greater change than on any Scoob) and variable cam gears are used to bring back some balance to timing events on the 8. (The 9 is another story.)

My own shop STI 07 engine will use the de-stroked method so it lasts longer and can maintain revving to 7800 comfortably. Spec C crank, and off the shelf CP pistons with 2+ billet rods from Pauter. Stock CR.
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Old 04-11-2009, 11:39 AM   #7
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using an off the shelf STi piston with a +2mm piston will give proper quench height but will leave you with lower CR than stock.

Using standard rods and sti piston, quench height would be huge and you'd have a much lower CR...that's how turbo mike has it if I recall.
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Old 04-11-2009, 01:06 PM   #8
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I can't comment on the WRX heads (they have a different volume combustion chamber and Phill from Element has the specs on those), but on the STI 2,5L heads, STI off the shelf pistons with 2mm+ rods on a 75mm crank all be same as stock.

Simply reducing displacement to 2,34l, which i think is a better option than sticking a 2,5L crank into a 2l block to make 2,1l.

I have been wondering why only now this is becoming more and more popular.
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Old 04-11-2009, 01:10 PM   #9
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Quote:
Originally Posted by popadel View Post
I can't comment on the WRX heads (they have a different volume combustion chamber and Phill from Element has the specs on those), but on the STI 2,5L heads, STI off the shelf pistons with 2mm+ rods on a 75mm crank all be same as stock.

Simply reducing displacement to 2,34l, which i think is a better option than sticking a 2,5L crank into a 2l block to make 2,1l.

I have been wondering why only now this is becoming more and more popular.
I'm guessing...More revs than a 2.5?
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Old 04-11-2009, 01:42 PM   #10
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Quote:
Originally Posted by popadel View Post
but on the STI 2,5L heads, STI off the shelf pistons with 2mm+ rods on a 75mm crank all be same as stock.
no, it won't....compression ratio is the ratio of the volume at BDC/ volume at TDC...now the volume at TDC will remain the same, however you are taking 4mm out of the initial volume (BDC) by reducing the stroke. That removed stroke is 4mm out of the height of the cylinder.


Last edited by Homemade WRX; 04-13-2009 at 10:48 AM.
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Old 04-12-2009, 12:05 AM   #11
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OK, i see where i missed something out ... kept focusing on the top end of the 75mm stroke and the final piston clearence and head volume at TDC but forgot tha BTDC is no longer a 79mm stroke.

thanks.
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Old 04-12-2009, 12:30 AM   #12
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To overcome the CR issue using STI heads which have a larger dome volume than WRX heads, it looks as though one would need a shallower piston dish (lower volume) like in the case of WRX pisons vs STI pistons.

Well, guess its time for less speculation and more calculation.



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Old 04-13-2009, 10:48 AM   #13
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or just go to someone who has it all done already
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Old 04-26-2009, 04:21 PM   #14
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Ok so I have been looking into some maths. I have some Eagle forged H-beam rods and plan to purchase Wiseco K598M995 pistons. Lets say I do not intend to use the WRX crankshaft. Here are some specs:

Rod Length: 5.137mm (stock length)
Crankshaft stroke: 79mm (STi crank)
Piston Bore: 99.5mm (Wiseco K598M995)
Piston Dome Displacement: -19cc (Wiseco K598M995)
Head Gasket Thickness: 0.021cc (stock Subaru Head Gasket)
Volume of Heads: 49cc (EJ205 Heads)

Wiseco claims that these piston produces an 8.9 to 1 compression ratio on an EJ257. I would like to know how much compression would increase if I used the WRX heads. Also, what are the advantages of using the WRX crankshaft?

Last edited by Gigabelova; 04-26-2009 at 04:27 PM.
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Old 04-26-2009, 10:13 PM   #15
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i have been seeing more and more threads about the de-stroked engine. can a stock ECU be tuned to use one of these motors or do you need like a hydra or some standalone ecu to use this? i would love to do this to my spec.b and have a 8K revving monster with a rotated turbo.
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Old 04-27-2009, 12:49 AM   #16
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Can anyone direct me on how to calculate compression ratio? Do I have enough variables covered?
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Old 04-27-2009, 06:10 PM   #17
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Quote:
Originally Posted by kirbwrx View Post
i have been seeing more and more threads about the de-stroked engine. can a stock ECU be tuned to use one of these motors or do you need like a hydra or some standalone ecu to use this? i would love to do this to my spec.b and have a 8K revving monster with a rotated turbo.
you can use the stock ECU you just need a good tunner .

My question is......Most of the 2.34L use the EJ207 crank, but is it really need it if you are just reving to 9k? Why not use the newer EJ205 crank?

ty
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Old 04-27-2009, 09:58 PM   #18
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nice to know i can use the stock ecu...now the real question is, can i use the stock ecu from any car i drop this in? meaning if i dropped one of these in a 98 GC8, its ecu could handle it or would my spec.b ECU be able to handle this engine as well?
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Old 04-27-2009, 10:50 PM   #19
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Right. So no one knows how to calculate static compression ratios?
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Old 04-27-2009, 11:02 PM   #20
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I do and have an in-depth spreadsheet I use for it...same one I use for all my builds.

off the top of the head you'll need...

actual deckheight
actual piston volume (dome or dish)
actual piston to deck clearance (+/-)
actual combustion chamber volume
headgasket thickness
stroke
bore

now its just initial volume over final volume

Last edited by Homemade WRX; 04-27-2009 at 11:16 PM.
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Old 04-28-2009, 09:28 AM   #21
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Ok.

some of those numbers should already be floating around right? I already have piston dome displacement, bore, stroke and hg thickness. What about head displacement?

And how do I use those variables?
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Old 04-28-2009, 09:43 AM   #22
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I'm assuming 03 EJ205 heads?
What are your other specs? can you please post in a list.

I ask for actuals as having decked the block or the head will change the variable used to calculate the CR...so I'm going to assume you are stock heads and block for now. Still need the rest of your numbers. Then I'll help walk you through it.

If you are trying to calculate for destroked motor, as I'm assuming you are, please include rod length and compression height of the piston being used. Thanks
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Old 04-28-2009, 01:10 PM   #23
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Quote:
Originally Posted by Homemade WRX View Post
I'm assuming 03 EJ205 heads?
What are your other specs? can you please post in a list.

I ask for actuals as having decked the block or the head will change the variable used to calculate the CR...so I'm going to assume you are stock heads and block for now. Still need the rest of your numbers. Then I'll help walk you through it.

If you are trying to calculate for destroked motor, as I'm assuming you are, please include rod length and compression height of the piston being used. Thanks
That's very nice of you. Thank you in advance!

I am using WRX heads yes. However, I'd like to calculate both for the WRX and STi Crankshaft. Heads are milled 4/1000 of an inch. For the destroked motor, 75mm stroke is used while normal is 79mm. Piston choice for now is CP Pistons SC7420. Size is standard bore: 99.5mm, compression height: 1.208. Compression ratio is 8.2:1 for standard EJ257 heads and block. Rod length is 5.137mm Eagle rods which are similar to stock length. For destroked motor, will use custom rods with 7.137mm length.
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Old 04-28-2009, 01:46 PM   #24
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If you do want to do it yourself, there are several easy/basic ones online that you can use. Just plug and chug.

P.S. 5.137 inch rod not mm and you can't fit a 7.137" rod into a subaru motor without having about 50mm of stroke I'm going to guess you mean +2mm rod...?

still need dish volume for the piston as you switched from wiseco to cp...don't want to know what the manufacturer 'says' the CR will be. It doesn't help.

Last edited by Homemade WRX; 04-28-2009 at 02:08 PM.
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Old 04-28-2009, 04:25 PM   #25
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Yea that is right. It's 5.137 inch and +2mm for the destroke. The dish volume of the piston is still not determined yet. I'll get that info soon.
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