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Why has no one done this?

6K views 23 replies 12 participants last post by  seraphinwolf187 
#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.
 
#2 ·
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.
 
#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.
 
#4 ·
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
 
#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
 
#5 ·
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.
 
#6 · (Edited)
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.
 
#7 ·
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 · (Edited)
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.
 
#10 ·
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
 
#14 ·
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.
 
#18 ·
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).
 
#19 ·
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
 
#20 ·
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.
 
#21 ·
WRX and STi swaps are not plug and play with each other. Different ECUs and other things that make it better to pick one or the other.

Standalones are aftermarket unwritten ECUs that are open to run just about any motor depending on which unit you get and what it needs to control on the motor. They have far better control over the motor but do no have the ability to pass a plug in emissions test for inspection testing.

The homebrew path does have options other than standalones. The limitations compared to WRX or STi ECUs are there but still competent means. Some run with no electronic tuning what so ever to still good results.

As for the red lights of the STi dash. Red is actually the least aggressive color of light on the eyes. If you were having an issue maybe it was that it was up too high or you already have night time issues.
 
#23 ·
WRX and STi swaps are not plug and play with each other. Different ECUs and other things that make it better to pick one or the other.

Standalones are aftermarket unwritten ECUs that are open to run just about any motor depending on which unit you get and what it needs to control on the motor. They have far better control over the motor but do no have the ability to pass a plug in emissions test for inspection testing.

The homebrew path does have options other than standalones. The limitations compared to WRX or STi ECUs are there but still competent means. Some run with no electronic tuning what so ever to still good results.

As for the red lights of the STi dash. Red is actually the least aggressive color of light on the eyes. If you were having an issue maybe it was that it was up too high or you already have night time issues.
Thanks for the tech talk on the stand alone system. Is that a must for doing a swap if i have no ECU and just get a long block?

And you hit it on the nose i do have night time driving issues lol

From my experience most people who turbo kit end up swapping anyway because of engine management issues (or just blowing it up). Do it right the first time and swap it.

If you need to run an auto transmission your best bet is to grab up an auto WRX. If you like the STi then get an 06/07 WRX and swap turbos and tune and swap the whole wiring harness over. At that point you can choose to keep your dash or swap the dash, it's up to you. I would stay away from the dash swap because you shouldn't run airbags and it doesn't fit right. If you keep the stock dash it just means the cluster needs to be modified to fit and the HVAC wired up. It more wiring work that way, but less mechanical work.
Sounds good i actually with all of this talk just purchased an 03 WRX longblock for $400 off a buddy of mine doing an STi swap. Only has 100K miles on it, (newer TD04 06/07 wrx, STi intercooler, pink top injectors) but am going to rebuild it anyways (just for safe keep).

And when wiring it all up would you recommend getting like a v4-7 JDM STi cluster just so the RPM's are on track?
 
#22 ·
From my experience most people who turbo kit end up swapping anyway because of engine management issues (or just blowing it up). Do it right the first time and swap it.

If you need to run an auto transmission your best bet is to grab up an auto WRX. If you like the STi then get an 06/07 WRX and swap turbos and tune and swap the whole wiring harness over. At that point you can choose to keep your dash or swap the dash, it's up to you. I would stay away from the dash swap because you shouldn't run airbags and it doesn't fit right. If you keep the stock dash it just means the cluster needs to be modified to fit and the HVAC wired up. It more wiring work that way, but less mechanical work.
 
#24 ·
Good luck. I'd say switch out the TD04 though. the 06/07's were set to 3lb's vs the 02-05's which where I think 8lb wastegates. Besides... Who wants a TD04...

You don't need a standalone if you don't have the ECU that came with that motor. Just pick up a used one. I would suggest finding an 04/05' since they switched to a 32bit from 16bit ECU if I remember.

JDM cluster you will want V5/6. 7 is the newer GD dash and V1-4 is the older style GC dash.
 
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