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Discussion Starter · #1 ·
So i'm doing a 251 build and ya know i do a lot of searching and reading on here. But the STi headers/manifold bolts directly up, and all you have to do is change a $100 crossmember.

So why aren't more people doing turbo set ups rather than a swap?

Like heres my thing, alot of you are straight up mechanics and know what your doing. All you have to do is get the block machined, low compression pistons, and a few other misc. crap and tadaa! a magical turbo set up without paying for a swap.

Correct me if i'm wrong, but lets say you put 8:1 compression, swap the nesc. (oil pump, injectors, fuel pump, piggy back ect.) put an aftermarket STi manifold on your car, THAN!, utilize any up/down pipe for the manifold (most likely have to shorten the down pipe) into any 3 inch exhuast, and THAN, you can use a stock STi turbo or get a direct fit TD05 run 12-18psi, make proper boost to spool the turbo, and theres your set up!

If any of ya'll see any flaws in this please let me know. If not, i know how i'm doing my build. Also... quick thought before i post, wrx manifold will also fit.
 

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I'm doing a homebrew build. Swaps are expensive for no more than you get, except you do get near factory reliability. But there are plenty of people doing the so-called homebrew turbo build. However I fear it's getting cheaper to do the swaps because the wrx's are getting older and more plentiful nowadays.

The problems you get when turboing N/A blocks is the wall strength, especially the EJ251. The bores aren't overly sturdy and you take more stength away when you overbore them for new pistons. There are people who have run a lot of boost on the 251, but the way to hold things together is to get a really good tune. Detonation is the engine killer.
 

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Discussion Starter · #3 ·
I'm doing a homebrew build. Swaps are expensive for no more than you get, except you do get near factory reliability. But there are plenty of people doing the so-called homebrew turbo build. However I fear it's getting cheaper to do the swaps because the wrx's are getting older and more plentiful nowadays.

The problems you get when turboing N/A blocks is the wall strength, especially the EJ251. The bores aren't overly sturdy and you take more stength away when you overbore them for new pistons. There are people who have run a lot of boost on the 251, but the way to hold things together is to get a really good tune. Detonation is the engine killer.
Agreed when it comes to the walls thats why i'm trying maybe only .030 over which ain't as much as some of the NA high compression bores.

The reason i don't want to do a swap is i've seen/heard way to many issues and complaints about EJ20's to the point where i won't even bother looking at one for a good price. I just feel the EJ25's are alot better built for the price.
 

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I would say a lot of people do that exact thing.

There is a couple issues that i know of. 1) You have to use a turbo water pump because the NA one will hit the header. 2) After you install, the turbo will be right behind the manifold and with the RS manifold there isnt enough room for a turbo inlet pipe to fit through, so you have to have a restricting 90 degree angle bend right before the turbo or something similar.

As far as using the STi manifold AFAIK it isnt easily possible. A rule of thumb i always here around here with frankin builds is that the mani\cams\ecu should match. And its not possible to run STi cams in RS heads (SOHC vs DOHC). And as far as using the STi heads, after already using STi crank, rods, pistons and then your throwing on the STi heads, mani, header. Thats just a STi engine with a weaker RS block housing lol you might as well have just swapped a long block.

Let me know if this clears things up or if i didnt understand what you were asking
 

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Usually overboring only goes to .020" over and that's usually plenty to start with fresh cylinder bores.

The EJ20 is setup for the turbo and the walls are stronger than the 251. However in stock form they lack low end grunt which steered me away. The 25s have a longer stroke, which gives a bit more torque along with the fatter bore. However if you wanted top end, the 20 can easily out rev the 25 safely.

But all of this is irrelevant until you know what power you want to run. How much do you think you want to run? Also remember more power = more money.
 

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Because swaps are reliable and make more power with far less work. What's more, the most important thing in any FI EFI setup (Engine management) - especially when concerning an NA-T are either inconsistent (AEM FIC, Emanage) or exorbitantly expensive (AEM EMS etc). If you ran a budget breakdown you'd find that swaps are actually significantly cheaper if providently planned for in advance.
 

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Eeeeeeek, a N/A setup gone Turbo OH NO!!!!...LOL...I almost did it too.

A 251 block really isn't much different than a 257 semi closed deck, if you ever saw them side by side you'll know what I'm saying. This is as long as your not going for 500HP it can take up to around 350hp or so on a 251 safely. So that is not the problem.
You'll need a Denso ECU or a piggyback because a stand alone will not pass emissions. Up until 2001 with the Jegs system then the 2002 WRX went to Denso and ever since been Denso. Jegs systems so far have not been cracked in the way the Denso have been so you would need to cut in a harness for the new ECU.

I just finished my N/A build at 11.5 compression with all the best parts I needed and it cost me around $ 8000.00 when I was done. This includes supporting parts, clutch, 12mm oil pump, fuel pump, oil relocator, exhaust, headers, PNP everything, gauges, bearings, crankshaft, customs pistons, K1 Tech rods and so on and so on.
Very reliable so far and runs about as fast as my now gone 2007 STI. Granted the 2 door GC / GM is about 500 Lbs. + lighter than the STI.

I am hoping to swap out my ECU for a Denso soon and wire it in so I can run a Raptor Supercharger after I have about 3000 miles on this motor.

The point I am making is that you can do any build and it can work, it just comes down to what you want.

I solved my block issue by not using a used block and just went out and got a BNIB 2010 257 and went from there, machined, line honed and hot tanked and I still have a fresh block to overbore later if needed. Currently running 99.5 pistons so it leaves me with options 99.75 / 100 mm bore pistons for later.

So yes a swap is cheaper and you can achieve lots of power but there is more to it than just throwing a turbo at it and calling it a day which you know.


The internals just can't take it, the bearings suck the rods are shit and the pistons well there not good. The only good part of a N/A motor is the crank which is the same as a STI one except after 2009 which are nitrited and have better oilers.
 

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I wouldn't say the rods are shit nor the bearings are crap. The rods are decently stout, some of the older EJs are forged, essentially WRX rods. The bearings aren't the problem, its the oil quality and the shortcomings of the oil system. In fact OEM bearings are much nicer to your components if you ever are unfortunate enough to have oiling issues. STI rods are a definite improvement however, I've put them side by side with my old EJ22 rods and despite the fact that they are almost 10 grams lighter, the design is obviously much better.





The pistons are definitely a weak link. Pretty much any OEM subaru piston is weak, even STIs and WRXs. Ringland failure is a common occurrence.

EJ257 blocks are ridiculously strong, I've ridden in and helped work on several 450+ hp STIs that have stock internals and have been for many thousands of miles. To this day they have had no issues, no noticable bearing wear in the oil analysis, ect. Several on NASIOC claim that the stock sleeves are good to 600+ in stock form. The sleeves are a much better 'webbed' design (as per NASIOC) which is why they can take so much more abuse than the standard cast sleeve that the N/A engines have. They 'look' similar, but even disregarding the bracing of a semi closed deck, they are much stronger overall. I'll try to find that thread and post it when I do.

EDIT: Not the one I was looking for but it talks about what I'm getting at.

http://forums.nasioc.com/forums/showthread.php?t=1313158&highlight=ej257+stock+limits

Here it is:

http://forums.nasioc.com/forums/showpost.php?p=16337127&postcount=45

Now this is obviously people talking about race engines, but still has detailed info.
 

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So i'm doing a 251 build and ya know i do a lot of searching and reading on here. But the STi headers/manifold bolts directly up, and all you have to do is change a $100 crossmember.

So why aren't more people doing turbo set ups rather than a swap?

Like heres my thing, alot of you are straight up mechanics and know what your doing. All you have to do is get the block machined, low compression pistons, and a few other misc. crap and tadaa! a magical turbo set up without paying for a swap.

Correct me if i'm wrong, but lets say you put 8:1 compression, swap the nesc. (oil pump, injectors, fuel pump, piggy back ect.) put an aftermarket STi manifold on your car, THAN!, utilize any up/down pipe for the manifold (most likely have to shorten the down pipe) into any 3 inch exhuast, and THAN, you can use a stock STi turbo or get a direct fit TD05 run 12-18psi, make proper boost to spool the turbo, and theres your set up!

If any of ya'll see any flaws in this please let me know. If not, i know how i'm doing my build. Also... quick thought before i post, wrx manifold will also fit.
what are you using for engine management?
 

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The reason you do not want to boost a N/A ej251/253 is the cylinder walls will start to flex therefore wear the HG out causing failure. The cyl wall flex and walk due to them not having extra support like the 257, the ej20 gets away with it because it has very thick cyl walls the 251/253 does not. You can usually get away with about 6psi of boost and the motor will be semi happy. You can do whatever you want really but just put some $$ away for the rebuild you will have a little ways down the road.

Also the factory limit for over boring a ej engine is .020

Josh
 

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Discussion Starter · #11 ·
I would say a lot of people do that exact thing.

There is a couple issues that i know of. 1) You have to use a turbo water pump because the NA one will hit the header. 2) After you install, the turbo will be right behind the manifold and with the RS manifold there isnt enough room for a turbo inlet pipe to fit through, so you have to have a restricting 90 degree angle bend right before the turbo or something similar.

As far as using the STi manifold AFAIK it isnt easily possible. A rule of thumb i always here around here with frankin builds is that the mani\cams\ecu should match. And its not possible to run STi cams in RS heads (SOHC vs DOHC). And as far as using the STi heads, after already using STi crank, rods, pistons and then your throwing on the STi heads, mani, header. Thats just a STi engine with a weaker RS block housing lol you might as well have just swapped a long block.

Let me know if this clears things up or if i didnt understand what you were asking
Biggest thing i've been asking about on here maybe you can further clarify for me. Some very very usueful information for me by the way. If i get a 257 instead of another 251 to build. Will that 257 work on an auto tranny?

And did not know that about swapping the ECU for the manifold... whys that?

Because swaps are reliable and make more power with far less work. What's more, the most important thing in any FI EFI setup (Engine management) - especially when concerning an NA-T are either inconsistent (AEM FIC, Emanage) or exorbitantly expensive (AEM EMS etc). If you ran a budget breakdown you'd find that swaps are actually significantly cheaper if providently planned for in advance.
I never doubted about the reliablity of swaps, i doubted the EJ20 engine. If i wanted a wrx i would have gotten an 02-03 instead of hunting down a GM6. I've seen guys on this forum and others blow there EJ20's sky high just to put another one in and do the same thing... Not saying i beat the hell out of my car just every now and again i'd like something to romp on and have peace at mind its not going to bite me in the ass.

Eeeeeeek, a N/A setup gone Turbo OH NO!!!!...LOL...I almost did it too.

A 251 block really isn't much different than a 257 semi closed deck, if you ever saw them side by side you'll know what I'm saying. This is as long as your not going for 500HP it can take up to around 350hp or so on a 251 safely. So that is not the problem.
You'll need a Denso ECU or a piggyback because a stand alone will not pass emissions. Up until 2001 with the Jegs system then the 2002 WRX went to Denso and ever since been Denso. Jegs systems so far have not been cracked in the way the Denso have been so you would need to cut in a harness for the new ECU.

I just finished my N/A build at 11.5 compression with all the best parts I needed and it cost me around $ 8000.00 when I was done. This includes supporting parts, clutch, 12mm oil pump, fuel pump, oil relocator, exhaust, headers, PNP everything, gauges, bearings, crankshaft, customs pistons, K1 Tech rods and so on and so on.
Very reliable so far and runs about as fast as my now gone 2007 STI. Granted the 2 door GC / GM is about 500 Lbs. + lighter than the STI.

I am hoping to swap out my ECU for a Denso soon and wire it in so I can run a Raptor Supercharger after I have about 3000 miles on this motor.

The point I am making is that you can do any build and it can work, it just comes down to what you want.

I solved my block issue by not using a used block and just went out and got a BNIB 2010 257 and went from there, machined, line honed and hot tanked and I still have a fresh block to overbore later if needed. Currently running 99.5 pistons so it leaves me with options 99.75 / 100 mm bore pistons for later.

So yes a swap is cheaper and you can achieve lots of power but there is more to it than just throwing a turbo at it and calling it a day which you know.


The internals just can't take it, the bearings suck the rods are shit and the pistons well there not good. The only good part of a N/A motor is the crank which is the same as a STI one except after 2009 which are nitrited and have better oilers.
$8,000 :bonk: holy balls! And yes i understand its no easy task. From what all of you told me i'm just going to get a 257 block the 251 seems reliable(i like it so far) but as for power + money = 257
 

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95 EJ205(WRB), & 02 R6
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Biggest thing i've been asking about on here maybe you can further clarify for me. Some very very usueful information for me by the way. If i get a 257 instead of another 251 to build. Will that 257 work on an auto tranny?

And did not know that about swapping the ECU for the manifold... whys that?
AFAIK all the subaru bell housings are the same. So can essentially bolt any subaru engine to any subaru tranny after 1992. Auto uses 4 bolts instead of 6 so you will be missing a couple but thats how it is stock.

And idk about the mani and ECU as i have a complete swap. I believe its because all the sensors are unique to the mani, so you cant run the RS sensors on a WRX\STi manifold
 

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AFAIK all the subaru bell housings are the same. So can essentially bolt any subaru engine to any subaru tranny after 1992. Auto uses 4 bolts instead of 6 so you will be missing a couple but thats how it is stock.

And idk about the mani and ECU as i have a complete swap. I believe its because all the sensors are unique to the mani, so you cant run the RS sensors on a WRX\STi manifold
every trans after mid-99 is a 6 bolt pattern, 98 and earlier are all 4bolt whether auto or 5spd, 6spd, ect
 

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97'OBS/94'SVX LSi/00'OBS/01&#8
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The manifold and ECU is related to sensors and the TVGs and IACV and the EJ255 and EJ257 throttle bodies are drive by wire and don't accept cable throttle bodies. EJ253's use TBW and some(like I) choose to build an STi swap with a 253 intake manifold as a TVG delete and large pelum with long large runners.

Swaps are done cause you do pretty close to the same amount of work for a tunable ECU that passes inspection and is better capable of calculating and compensating.
Low boost "bolt on" homebrews are cheap and easy but for real boost you'll want more. The block it's self isn't able to hold power. There are plenty who do a 255/7 shortblock with 251 heads.
It all falls down to budget, what the owner wants, and how much time and experience they have.
 

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Discussion Starter · #15 ·
AFAIK all the subaru bell housings are the same. So can essentially bolt any subaru engine to any subaru tranny after 1992. Auto uses 4 bolts instead of 6 so you will be missing a couple but thats how it is stock.

And idk about the mani and ECU as i have a complete swap. I believe its because all the sensors are unique to the mani, so you cant run the RS sensors on a WRX\STi manifold
Okay that makes sense now with the ecu going with the correct mani. And as some know medically i can't drive manual right now so i'm trying to do a build with the auto tranny its just from my experience with mustangs, i know its one hell of a job to make an manual motor work with an auto trans.

every trans after mid-99 is a 6 bolt pattern, 98 and earlier are all 4bolt whether auto or 5spd, 6spd, ect
Thank you! As you read this has been my biggest concern. Now that i have ya'lls hel i can finally build my first import correctly.

The manifold and ECU is related to sensors and the TVGs and IACV and the EJ255 and EJ257 throttle bodies are drive by wire and don't accept cable throttle bodies. EJ253's use TBW and some(like I) choose to build an STi swap with a 253 intake manifold as a TVG delete and large pelum with long large runners.

Swaps are done cause you do pretty close to the same amount of work for a tunable ECU that passes inspection and is better capable of calculating and compensating.
Low boost "bolt on" homebrews are cheap and easy but for real boost you'll want more. The block it's self isn't able to hold power. There are plenty who do a 255/7 shortblock with 251 heads.
It all falls down to budget, what the owner wants, and how much time and experience they have.
I never thought about that. I'm just still learning about all the different blocks ect with subaru. This is a huge help i'll keep this in mind when doing my build and making my decisions with what to buy. And with the 251 heads, wouldn't it just be easier to have the 257 heads on it?
 

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I never thought about that. I'm just still learning about all the different blocks ect with subaru. This is a huge help i'll keep this in mind when doing my build and making my decisions with what to buy. And with the 251 heads, wouldn't it just be easier to have the 257 heads on it?
Personally, the EJ251 heads good heads to build with. They flow pretty well, are pretty easy to setup and upgrade. The EJ257 heads have to go with STI coil on plug ignition, which the your car won't have unless you do an STI swap.
 

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Discussion Starter · #17 · (Edited)
Personally, the EJ251 heads good heads to build with. They flow pretty well, are pretty easy to setup and upgrade. The EJ257 heads have to go with STI coil on plug ignition, which the your car won't have unless you do an STI swap.
Okay understandable. I'm thinking more and more about the STi swap since talking to ya'll about it. I would like to do a purchase this week. Another question concern i have, is... With an STi engine or a 257, do i need to do a dash swap?
Or am i still utilize my dash and just splice or remove wires where needed. I have a triple gauge pod already with all the gauges nessicary. And quite honestly i like the simplicty of the GM6 dash.

I've obviously been in newer STi's and the red lighting is very distracting and bright as hell for me. Plus i think its odd having a newer dash set up in an older car.


^( I actually found the wiring merges for the motors last night to be able and utilize the stock dash)
 

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i would say that that the main reason people avoid this swap is because of engine management. there aren't any good options anther than a stand alone which will usually cost over $1000 is you aren't tuning yourself. i was considering this swap before "silent" told me his opinions on a N/A build (he's done a sti swap and a built 251).
 

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Discussion Starter · #19 ·
i would say that that the main reason people avoid this swap is because of engine management. there aren't any good options anther than a stand alone which will usually cost over $1000 is you aren't tuning yourself. i was considering this swap before "silent" told me his opinions on a N/A build (he's done a sti swap and a built 251).
And forgive me for asking but what is a stand alone? Everything i'm doing myself minus a dyno tune (if that makes a difference).

If anything last night i may just end up doing a triple build and seeing what happens from there. WRX, STi, and the 2.5rs (EJ251).

Everyone says the WRX swap is relativly easy. So what i'll do in the mean time is swap it. Re-build the 2.5 to put in anther car (would like to do a wagon GF6). Get the STi engine do little tunes and tweaks to that on the side, get another auto trans, rebuild that to hold the STi power, and swap that into the coupe in the summer if the EJ20 isn't cutting it. Or just pick up another body.

In which case i can familarize myself with each motor, understand these builds and wiring systems a bit further, and in case i get too reckless have a back up engine for tragic meltdowns
 

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i dont know this is fit in here but im running ej22 block (93 94 legacy) with 99 rs heads (sohc) for about 2 years now. still using the 2.5 rs ecu not problems lots of torque n power. turbo is the older vf11. thinking of a turbo upgrade but i have to move some things around. very happy with my hybrid.
 
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