Subaru Turbo B25 Heads Vs D25 heads - What is the difference?

[@kyle5555ify]

So i have a weird scenario. I have b25 head and a d25 head that came on my motor. Whats the scenario im dealing with? Has what im assuming 4 b25 pistons

[@FlatironsTuning]

That is definitely odd. At a minimum, that would mean that you have mismatched heads, and that could certainly run into some driveability and reliability issues with the car. i'd recommend having a machine shop inspect both heads, and if the D25 head is in good shape, get another matching D25 head to put back on the engine. You may want to start from scratch for the build though. If someone put an engine together with those parts, I don't think that I would trust any of the rest of the build without a thorough inspection. Hope that helps and Stay Tuned!

[@kodypierce3507]

Can you tell me the difference between D25 and N25 heads?

[@FlatironsTuning]

Thanks for your question. The N25 heads are an update of the W25 heads which were the Dual AVCS STI heads. In short, the difference between those two is basically the same as the B25 and D25 heads discussed here. Thanks for watching and Stay Tuned!

[@subierecycler3487]

Also a quick way to tell would be the presence of an air injection pump on the car. D25 heads have ports on the back of the cylinder heads for the air injection, B25 heads do not.

[@FlatironsTuning]

This is a good point. Thanks Allen!

[@wooder30]

What's the difference between a 05 Baja 2.5t and the sti 2.5t. From what I have read it's basically the turbo exhaust and the tune

[@HeidiFegles]

I had to rewrite the entire tune from scratch when porting and changing heads. Also took 3 degrees timing out to compensate for compression and knock in the peak load range of 2500-4000 rpm as well as changing the entire maf scaling curve. So yes you need to tune the car custom when switching to the d25 heads. But the torque gains at low rpm say 2-3k are incredible. It’s almost like driving an na car but then the turbo takes over and the torque curve is drastically changed for the hood by changing to d25 heads. And yes ethanol, my car runs so good on ethanol due to the compression bump. And porting this is for pump 92 octane map. Ethanol I put the 3 defrees back plus 2 more degrees is some areas and run a couple more pounds of boost, as well as the injector rescaling. have not done an ethanol dyno tune but based off the 92 octane tune that’s verified, it makes more torque and hp for sure. It’s Avery noticeable difference

[@darrenwells7216]

Thanks for the video. I put together my outback xt with b25 block and d25 heads willy nilly. Good mpg and peppier around town. but like you said the factory tune doesn't like the higher comp and it will absolutely ping without a tune.

[@FlatironsTuning]

Thanks for watching Darren, and thanks for your information!

[@jrod9733]

Quick question...I am new to the Subaru game and recently purchased an '03 bugeye WRX. I bought a '13 ej257 short block off a guy with nothing but crank, rods and pistons. I don't have a way of getting the VIN and would like to figure out which heads would have been attached to this block.

[@SkaBob]

I have noticed that in many ads. They say 8.5 ej255/257 wrx/sti pistons, but they don't say what heads that number is for. But I have a weird motor, 2005 Baja Turbo, so it's basically an ej257 with a td04. But it has higher compression (8.4 vs 8.2) than an STI, but pistons, heads and headgasket are the same part number the the STI. So I don't know where they get the extra .2 from.

[@FlatironsTuning]

Thanks for your question. If you have the B25 heads, which you should, then your engine is 8.2:1. You are most likely seeing 8.4:1 referenced to the EJ255 engines, but that is only the ones that have the D25 heads. As to the pistons, yes, you need to look at the combustion chamber volume that the manufacturer used to calculate the compression. That volume will tell you which heads they were using to calculate. For example, Manley calculates all of their compression ratios around the D25 heads which have a 51cc chamber volume. I hope that helps, and Stay Tuned!

[@robcacioppo1210]

The 04-06 Baja Turbo seems to usually be glossed over in these comparisons and it's hard to find info. From what I can gather, the 04 & 05 Baja Turbo used the B25 heads, and the 06 used D25. So am I correct in inferring that the only differences between the 04/05 Baja Turbo and the 04-06 STI are the turbo and intercooler (and paint color of the intake manifold)?

[@FlatironsTuning]

Thanks for the question. The Baja Turbo is a really hard car to work with because it doesn't follow many (if any) of the part fitment trends of the other car. For instance, yes, the engine has B25 heads, but side feed injectors, and a WRX manifold, not an STI manifold. And it uses the FXT Intercooler. They are so different from the other cars, and there are so few of them (comparatively), that we don't talk about the Baja specifically. They are very challenging to find aftermarket parts for. Hope that helps, and Stay Tuned!

[@robcacioppo1210]

@@FlatironsTuning Hmm what is the difference between the Baja/WRX manifold and the 04-06 STI manifold? They are both aluminum, so I thought they were the same other than the paint.

[@FlatironsTuning]

@@robcacioppo1210 The biggest one is the throttle body. The WRX is a cable throttle, as is the early Baja I believe. That puts the throttle body in a different location, and has a different bolt pattern compared to the drive by wire cars.

[@Cooper_Andersen]

These videos are under appreciated! I watch them more than once. Can you share information about heads and the pros and cons of upgraded heads? Like porting, valve work, cam sizes and the effects.? Applications for these modification. Currently I'm doing a Daily Driver New OEM Short block Ej257 build with new OEM B25 heads (Stage 1 non-AVCS cams, beehive springs) Valves are the question?? What size +1.00 mm? Is more flow good or can it have a negative effect? Should you do larger valves on exhaust side only, Vice versa or Both? What type of head work is possible? Thank you for any sort of Info. You are the Subi Guru. Cooper

[@juliolucero3412]

I dont think all 2007 STI came with V25 heads. I have seen two 2007 STIs with D25. Both STIs were unmodified and original engine.....can someone double check this. thanks

[@FlatironsTuning]

Thanks for your question. I can tell you that no STI ever came from the factory with D25 heads. In the Subaru catalog, there is only one part number for each head for the model year 2007 STI, and those are the V25 heads. Hope that helps and thanks for watching. Stay Tuned!

[@juliolucero3412]

@@FlatironsTuning that's so weird. The reason I'm bring this up is because my 07 STI is unmodified ive been the only owner and it came with D25 heads. I noticed this while doing the clutch. Car runs with no issues. So maybe there are few exceptions. The other 07 STI I know with D25 heads it's in San Bernardino. Car was unmodified, but unfortunately ring land failed on 3 and 4.

[@andradee5103]

Also I have a 2006 wrx but it has b25 heads it has a all cylinder missfire would I need a tune to fix that

[@FlatironsTuning]

Thanks for your question. If you have a misfire, you need to diagnose that by itself. That indicates that you have a mechanical issue, and that would not be fixed by a tune. Thanks for your question and Stay Tuned!

[@andradee5103]

So I bought a 2006 wrx but it had b25 heads instead of the d25s right now it has a missfire in all cylinders is it because of the swap or the heads need work?

[@andradee5103]

@@FlatironsTuning so if I put b25 heads on a d25 motor it shouldn't misfire ? Also thank you for the reply!!

[@FlatironsTuning]

@@andradee5103 At that point, I'd recommend working with a mechanic to trouble shoot. There are a number of reasons that you can have misfires. But if you put B25 heads on an EJ255 block, that will cause a somewhat large drop in compression which would not be ideal. You definitely need to find the reason that the car is misfiring. I'd recommend doing a compression and leak-down test as well. Hope that helps!

[@FlatironsTuning]

@@andradee5103 Just responded to your other question, and covered this as well. Thanks!

[@chasejustice8219]

So I just put b25 heads on my 2006 wrx ej255 stock block and now knowing about the difference between the d25 what should I do

[@FlatironsTuning]

Thanks for your question. Have you started and ran the engine yet? Is it in the car? Ultimately, your compression ratio would go down. The good news is that this should not hurt anything, but it may cause some loss of power, etc... If you can, open up a live chat with us with more details about where you are with your build and we'll do our best to help out. www.flatironstuning.com is where you can find that live chat.

[@chasejustice8219]

Will it be ok to drive it like this with cobb mods

[@alexudolkin2146]

@Flatirons could you please compare the W25 and N25 heads (dual avcs)? Thanks!

[@FlatironsTuning]

Thanks for your question. The short answer is that from a combustion chamber stand point, there really isn't any significant difference to the B25 and V25 heads. But we will keep that in mind. Thanks for watching and Stay Tuned!

[@alexudolkin2146]

@@FlatironsTuning thanks for the reply. I was referring to the 2008-2017 W25 heads vs the newer N25 heads on the 2018+ Type-RA. It seems these are the current EJ design

[@FlatironsTuning]

@@alexudolkin2146 They are different part numbers, but we have yet to find a significant difference between the two.

[@MarkGamingTV]

My buddy is helping me rebuild my engine and has a set of b25 heads hes willing to let me use. Problem is I have an 07 sti with the v25 heads, I've already deleted my secondary air pump, so my question is does the b25 and v25 have the same compression ratio? Is the only difference the secondary air pump application?

[@FlatironsTuning]

Thanks for your question. Yes, compression is the same, and the only key difference is the addition of the secondary air ports as you mention. Hope that helps, and Stay Tuned!

[@dumpsteroo5956]

On later model 08-14 WRX or STi are the B25 and D25 cams, springs, and valves the same? Just curious because I'm looking to push my stock D25 head out to 7600 rpm at 29psi so I can stay in 4th gear through the end of the traps at the drag strip. I've seen stock B25 heads get pushed to 8K without issue.

[@FlatironsTuning]

Thanks for your question. I believe that the springs are the same on all STI heads. On the B25 STI heads, they use sodium filled exhaust valves (2004 STI has sodium filled intake valves as well), and starting in 2008, all of the STI's went to metal valves, which I believe are the same as what are used in the WRX. Not to say that would have any effect on max RPM, but I mention it because those are the majority of the differences between the model years. I hope that helps, and Stay Tuned!

[@saki10man]

@Flatironstuning I have some 8.2cr pistons(99.75) and I want to rebuild my 06 OBXT with? Right now I was planning on using my factory heads. Awesome video btw if I didn't see this I would assume the lower compression pistons can work in any 255/b25 block/head combo or can it but a tune would be needed? Would porting/cams/valves/valve size cause issues for the worst. Just looking for a ~325 to~350 capable daily. But will drive on ~275ish.

[@FlatironsTuning]

Thanks for your question. I'd recommend looking at any information that the piston manufacturer has on the pistons you have with your heads. Many manufactures will give you the compression ratio with both common heads. From there, if you do have the D25 heads and STI pistons, you can run a 1.1mm head gasket to get compression back close to stock. For the power levels that you are shooting for, that thicker HG would be a good option. Hope that helps and Stay Tuned!

[@saki10man]

@@FlatironsTuning This helps a lot. Thank you for your response. So b25 heads mated with 8.2cr pistons would require what HG thickness? And if it’s on the more stockish thickness which one would offer the better sealing of the head/block?

[@gavin__]

How much do the big port EJ207 AVCS spec c big port heads compare to either of these?

[@FlatironsTuning]

Thanks for your question. The castings are roughly double the cost of the USDM options. Here is a link to them on our site: www.flatironstuning.com/genuine-subaru-ej207-avcs-spec-c-big-port-cylinder-head Thanks for watching and Stay Tuned!

[@gavin__]

@@FlatironsTuning hey thanks for the quick reply but I was actually wondering about the physical size difference in port of these vs the big port jdm heads. I have these on my current ej207 and was wondering if they are worth keeping once I drop in one of your shortblocks

[@FlatironsTuning]

@@gavin__ Gotcha. This thread on NASIOC has the best picture comparisons of all of the heads: forums.nasioc.com/forums/showthread.php?t=903873 Generally speaking the 207 big port heads are in the direction of the fully ported 2.5 liter heads, but some of those 2.5 liter ported heads are opened up a bit more than the 207 big port heads. I hope that helps and Stay Tuned!

[@gavin__]

@@FlatironsTuning That helps a ton, been scouring the internet all morning for an answer. Thank you!!

[@samsonburque114]

This is a helpful video thank you. Here’s my question ej25 bore=99.5mm stroke=79mm volume=614.28cc. If the head volume for b25 block and pistons is 55cc+22cc(head volume+dish volume). 614.28/77~8.0-1 compression ratio. Am I missing something that makes the head volume like 2 cc smaller? Spark plug I assume!

[@FlatironsTuning]

Thanks for your question. From what you are describing here, it looks like you are calculating volume based on the bore and stroke only. To calculate compression ratio, you actually need to calculate the entire volume of the cylinder at top dead center and bottom dead center. That will give you the best calculation. I hope that helps, and Stay Tuned!

[@Aaron2000Subaru]

I have a 2004 XT that blew a turbo and it needs a motor. Well I acquired a Ej255 from a 06 Wrx and have been looking for the B25 heads that are for the XT. Should I be worried about compression or would I be fine since the XT is a 255 as well?

[@FlatironsTuning]

Thanks for your question. I'd recommend going back through this video again, as this is exactly what we discuss here. We also have a blog about the same topic, and here is a link to that: www.flatironstuning.com/blog/what-is-the-difference-between-an-ej255-and-an-ej257 Hope that helps and Stay Tuned!

[@tranwrx]

What better B25 or N25 heads 🤔

[@grantgarver7520]

Hello there I’m lookin into doing the full 2.5 swap in my 02 wrx I’m using an RA block and was wondering if there’s benefits to using single or dual AVCS heads and If I have to block off secondary air stuff if I’m not utilizing it? Great video

[@FlatironsTuning]

Thanks for your question. We cover all of that here: kzbin.info/www/bejne/bIndoKOdlt6qbcU That is the video where we go into detail of making that conversion. Hope that helps and Stay Tuned!

[@HeidiFegles]

I run d25 heads on my 06 sti 85 rx swap with 100mm bore, 18 psi, 400 wheel torque, 8.8:1 compression d25 heads have more meat to port, and flow better, and actually the intake cam has more lift than the sti. More compression, and it actually loves ethanol.

[@rpdallast5965]

I have D25 heads, and I'm wondering if the JE hybrid pistons will work with them or do I have to get different pistons that match the D25 heads? Thank you

[@FlatironsTuning]

Thanks for your question. The JE Hybrid pistons are for 2.0 liter heads only. If you are using D25 heads then you would just use the standard JE pistons for your build. Thanks for watching and Stay Tuned!

[@rpdallast5965]

@@FlatironsTuning ok I understand I already have the hybrid pistons will they work with a tune with little complications?

[@rpdallast5965]

@@FlatironsTuning I am only asking because it was stated they closely resemble ej205 since they are only off about 2CC?

[@andradee5103]

Hey how's it going, so when you said that it if you put d25 heads on a ej257 it would need a tune, would the accesport have a good tune for that ? Also what head gasket do you recomemd when putting d25s on a ej257 shortblock. Thanks alot man you're probably one of the best subie channels. ✅️

[@FlatironsTuning]

Thanks for your question. The reason you would need a tune is because of the bump in compression. Yes, the Accessport will allow a tuner to tune your car for that, and anything else you might need. If you run a 1.1mm thick headgasket, that will drop compression nearly back to what your EJ255 came with stock. Roughly 8.5:1. It would still be recommended to tune the car with that configuration, but I would say that it would not be as critical as if you were running a stock thickness headgasket. Hope that helps and Stay Tuned!

[@andradee5103]

@@FlatironsTuning would the ej257 come with the 1.1mm head gasket or no?

[@FlatironsTuning]

@@andradee5103 No, the stock headgasket thickness is about .7mm. 1.1mm head gaskets are thicker than OEM.

[@cargeekscott1871]

Hi. I'm trying to find all the right parts to build a reliable ej257 to match with the ej205 computer. What are the differences between the 10103AC870 and 10103AC890 blocks. I'm aiming around 300awhp. And I'm looking at a blouch TD05-16G and 565cc injectors. Any help appreciated.

[@FlatironsTuning]

Thanks for your question. First, on those blocks, the 10103AC870 is the block that originated in the 2004 - 2007 STI. The 10103AC890 is the block that originated in the 2008+ STI. Originally, the cranks in these blocks were different, but since about 2010, all of the 2.5 liter turbo blocks have used the hardened cranks (heat treated or nitride treated depending on what Subaru is using at the moment). So at this point the only difference between the two is the rods. The 10103AC890 block has a somewhat more durable rod. It isn't something that would be on part with an aftermarket rod, but it is better than what comes int he 10103AC870, and because the cost is the same, most customers go with the block that has better rods. On your turbo, I'd say that you would want to look at a 20G at a minimum to get to the 300 whp mark. Or, I'd also recommend the Turbo Dynamics MDX-400. We are pretty impressed with that turbo for an application like this ( more on that is in the works ). www.flatironstuning.com//mdx555-400-hybrid-turbocharger-400hp And more than likely you would want injectors that are a bit bigger than 565cc. I'd recommend the Cobb (which are made by Injector Dymanics) 1050X injectors: www.flatironstuning.com/cobb-1050x-top-feed-fuel-injectors-w-pnp-adapters-subaru Hope that helps, and thanks for watching!

[@eze8024]

Awesome video! 👍 How do I figure out comp ratio of stock usdm ej205 heads on stock v7 ej207 shortblock? 🤷‍♂️

[@FlatironsTuning]

Thanks for your question. Start by looking at the combustion volume of the two cylinder heads. I think that the EJ205 and EJ207 heads are very close, if not the same. Then look at the piston dish. I think that some of the STI engines did have higher compression, and I'd guess it came from the piston dish, not the cylinder heads. Hope that helps and Stay Tuned!

[@FizuhcuL]

i got a 06 wrx and im looking to upgrade the pistons/rods for a bigger turbo... will a lower CR by changing to a b25 head be worth it?

[@therideszz]

You have d25 heads with air injection. You'd have to block off the air injection system and have it tuned most likely.

[@OggaDugga]

For my 07 wrx. I plan on deleting the secondary air injection. Therefore would is it alright to go with the B25 heads? Or do I still need the V25 heads specifically?

[@FlatironsTuning]

Thanks for your question Brandon. If you have D25 heads, you should really stick with them. Any of the STI heads will have a larger chamber volume, so you will be changing your compression ratio by changing heads. If you are doing a full build, including new pistons, this can be addressed, but if there isn't anything wrong with your heads, I'd say stick with them, and just use some of the plates to cover up the ports on the heads. I hope that helps, and thanks for watching!

[@OggaDugga]

FlatironsTuning I actually have an IAG stage 2 Tuff block on the way so I’m looking to do a full build and a tune is inevitable. I’m just looking at what my possible routes are in regards to STi heads. I’ve been told that the 257 heads are better for boost but the D25 combustion chamber shape give them better flow. I’m stuck on what to do.

[@FlatironsTuning]

@@OggaDugga They are both good options, and I guess that the best way that I could answer is that if there is nothing wrong with your heads that would require them to be replaced, there wouldn't be enough gains had by going with STI heads to justify the cost. If it is more from a time standpoint, where you want to build the long-block before you pull your engine, then it could make sense to get new castings. But even in that case, I'd probably stick with the D25 heads that are correct for your car. They are not bad at all, some builders actually prefer them compared to the older B25 heads especially. And if you were set on STI heads to drop compression a little, then I'd look at the V25 heads because they would still have the Secondary air ports. They are closer to your WRX heads, so you will most likely have more options long term than going with the older B25 heads. Hope that helps!

[@LyubomirStoychev]

Hi there! I am really curious, you mentioned under one comment that valves are interchangeable, however I've seen my B25 heads the exhaust valves are marked ED3 and the D25 have marking ED4. I've looked up and it turns out ED4 valves are no longer sodium filled. Is that for all D25 heads and does that make D25 OEM heads weaker and more detonation prone when it comes to going for higher boost and power? So if I swap my B25 heads with D25 with ED4 valves and keep it tuned to ~300hp will that cause issues?

[@FlatironsTuning]

Thanks for your question. From a size and fitment standpoint, the S20 heads, B/D/V/W 25 heads all use the same size valves. Subaru went away from the sodium filled exhaust valves fairly quickly in the STI and LGT/FXT. There just wasn't that much of a benefit for the sodium filled valves unless you really needed the better heat transfer. And if they snapped from piston contact, it made a heck of a mess in the head. The STI has been running standard valves from 2008 on, and the WRX always had them (D25), and plenty of those cars are making reliable power with the stock valves. I'd say keep it simple. Factory valves or the equivalent will be fine for your build. Hope that helps and Stay Tuned!

[@RChero1010]

Wow, what a great channel! I just blew up an EJ20x in my 05 legacy gt and I'm evaluating my options. I've found a 257 shortblock and I really want to go back to the ej25 for the responsiveness in daily driving and I'm trying to figure out if I'm alright keeping my dual avcs heads or if I should shop around for some B25 heads. Is the year of EJ257 relevant to which heads I should be running? I want to use a factory sealed block so everything will be completely stock. No big power here, just 300 wheel or so

[@FlatironsTuning]

Thanks for your question. If you have EJ20X heads, I believe that they have a similar, or possibly smaller combustion chamber than the S20 heads that were on the 2.0 WRX here. Definitely take a look at our Hybrid Build video: kzbin.info/www/bejne/g2mzk3-XirKDmq8 And maybe our Hybrid build blog: www.flatironstuning.com/blog/what-is-a-subaru-hybrid-swap Compression ratio is going to be the big question with those heads. Or, just go back to a full 2.5 liter engine. That is definitely a good way to get a solid platform to hold 300 whp. Hope that helps, and Stay Tuned!

[@brianrobinson9979]

So what about the differences between the V and W heads?

[@FlatironsTuning]

Thanks for your question. The V25 heads are only on the 2007 STI, and they are single AVCS. The W25 heads are on the 2008 - 2017 STI, and they are dual AVCS. From a compression stand point, they are the same. The main difference is single vs. dual AVCS. I hope that helps, and Stay Tuned!

[@RACEME0911]

I have some heads marked "LH B 003"... what are those?

[@naitomea_st]

good info!!! didnt know you guys had a youtube channel. This is great info. thanks for uploading!

[@b70dub]

Are the valves interchangeable between the B25 and D25 heads?

[@FlatironsTuning]

Thank you for your question. Yes, the valves are the same between the B25 and D25 heads. They are actually the same for all of the EJ25 turbo heads. Hope that helps and Stay Tuned!

[@MisterS4League]

I got a 2018 WRX STI, do I have a dual AVCS Head or not?

[@FlatironsTuning]

Yes, all STI's since 2008 have had Dual AVCS. So you have it. Hope that helps, and Stay Tuned!

[@BP-fx3qc]

You have w25 heads dual avcs.

[@jerryderidder8302]

So I can safely use stock d25 heads on a stock ej257 as long as I get a tune?

[@FlatironsTuning]

I would not say it is ideal. But it can be done. If you want to get the compression back close to what it is in the STI, you can run the 1.1mm head gasket to compensate. I hope that helps, and Stay Tuned!

[@alexudolkin]

@@FlatironsTuning Any downsides to running this setup (D25 + EJ257 pistons) with the 1.1mm head gasket? Prone to gasket failure, high detonation risk? trying to understand if the slightly raised comp. ratio is the issue or if it's the shape of the chamber and piston combination. Thanks!

[@davidsandberg3109]

I have a 2005 LGT with B25 heads and someone else has a same year same model claiming to have D25...thoughts?

[@FlatironsTuning]

All I can tell you is that isn't what they came with from the factory. Thanks for watching.

[@neilclark359]

So I a 2007 STI with the V25 heads. I just got a fresh reman long block with D25 heads and the valve covers don't match up. I can also tell the cams are different. Should I just send it all back and require the V25 heads or will these be fine once I plug the holes where the valve covers don't match?

[@FlatironsTuning]

Thanks for your question Neil. The first thing to keep in mind is there will be a compression difference between the D25 heads and your V25 heads. And if possible, it would be worth finding out what pistons were used in the shortblock, because that can cause a difference as well. If your valve covers are not fitting, there is a pretty good likelyhood that the D25 heads that were used are from a newer WRX than your 2007 STI. Again, it would be worth trying to find out exactly what year they are off of so you can get the correct valve covers. In regards to the cams, they should be the same as what came on your 2007 STI, so if you are seeing significant differences, that would be worth getting more information on as well. So long story short, it would definitely be worth following up with whomever built that longblock, and get all the information available, and if at all possible, get them to help you make sure that all of the components that went into the build will be compatible with your car. Good luck with your build!

[@jam00723]

Great vid. One thing to add would be which head had a better VE. I've seen cut-aways of these heads and some will argue that the D25 have a better flow capability rather than the B25, can you confirm?

[@FlatironsTuning]

Thanks for your question! That is definitely a pretty common thought because of the more hemispherical design of the D25 heads, that they are a more efficient design. I will say that if you look at similarly built WRX's and STI's (B25 and D25 heads) with the same turbo on them, there isn't usually much of a difference in actual real-world power numbers. So from that stand point, it would hard to say that you should really favor one head design over another because of a significant difference in power. But as more testing gets done, or as the power numbers get higher, there may be one design that starts to pull away from the other. We'll just have to do more testing :-)

[@jam00723]

Awesome that would be a great idea. Also, there has been some misconceptions that the EJ is a far more superior platform for power than the FA. What are your thoughts on this as well?

[@FlatironsTuning]

Hello James. In regards to the EJ versus the FA, it is way too early to tell. There are a lot of promising things with the FA heads, but they are so new, it will almost certainly take the aftermarket a few years to really figure them out. Only then will we know how they compare to the outgoing EJ heads. Considering it is the first really full re-design of an engine/cylinder head since the late 90's, it s pretty likely that Subaru has improved a number of things with the FA heads.

[@jam00723]

FlatironsTuning right on thank you for the reply.

[@therideszz]

My 05 LGT has b25 heads and my buddys 08 has d25. In Mexico, after 3rd gear, he pulls away hard every single time. I also have a vf52 and he's got the stock turbo.

[@rayleal2109]

Can u use the heads of a non avcs on a avcs engine block?

[@FlatironsTuning]

Thanks for your question. That would most commonly be called a Hybrid swap, and the short answer is yes. In fact, we have a video no that as well. Here is a link to it: kzbin.info/www/bejne/g2mzk3-XirKDmq8 I'll link this video for your as well: kzbin.info/www/bejne/bIndoKOdlt6qbcU Hope that helps, and Stay Tuned!

[@ALtheDoctorWho]

Great video I have been looking for information on Spark plugs on 2.5L subaru. I think I know the answer but the heat range would be in question because because they razed the compression on the 2019 models or so I understand. However do all the boxer engines heads take the same size/type spark plug? Thanks for making these videos.

[@FlatironsTuning]

Thanks for your question. First, they did not raise the compression in 2019 from what I have seen. The STI has been 8.2:1 since 2004. All of the 2.5 liter EJ turbo engines do use the same plug, but it is a much different plug than what was used in 2.0 Liter heads. I hope that helps and Stay Tuned!

[@mazan7824]

How durable are D25 Heads when it comes to making big power, say 850hp

[@FlatironsTuning]

Thanks for your question. All of the 2.5 liter heads are equally strong, so I wouldn't say that strength would be the deciding factor. You would need to do some valve work, port and polish, and cams to be able to hit that power target, so the newer castings would most likely be a good starting point. The biggest factor may come down to combustion chamber volume. Since the D25 is smaller, if that pushes your compression higher than you like, you may need to look at the V25 or W25 heads. I hope that helps, and thanks for watching!

[@centralmoment]

Wow! I love your videos!

[@FlatironsTuning]

Very cool and Glad to hear! Thanks for watching and Stay Tuned!

[@TheThecharliejolly]

So what car do D25 heads come out of?

[@FlatironsTuning]

Basically, if you have a 2.5 liter turbo car with single AVCS and secondary air injection, and it is not an STI, then you have D25 heads. All STI's are B25 heads (architecture). If you have a 2.5 liter turbo with single AVCS, and you don't have secondary air injection, then you have B25 heads. Hope that helps, and thanks for watching.

[@TheThecharliejolly]

@@FlatironsTuning ok so i bought a 06 wrx and didnt realize till yesterday when i started taking apart the engine that it said ej25 and the heads where D25 heads. Im not sure if the shortblock is a ej257 or a 25 from a forester xt. How can i check to make sure?

[@FlatironsTuning]

@@TheThecharliejolly The heads are stamped "D25" I would start there. and the 06 - 14 WRX had the D25 heads with the different block. The Forester XT only had the D25 heads from 2006 on. On the block itself, there are not any easy distinguishing marks to find. But the blocks that were paired up with D25 heads have a much deeper dish on the pistons compared to the STI. But I don't know that you could tell that just by looking.

[@TheThecharliejolly]

@@FlatironsTuning Ok thanks for the info i guess ill find out later today when i open the case halves up. I bought the car from some old man that bought it from an auctiom so he didnt know anything about it. Cheers brother 👍

[@vgnfab]

Thank you very much for making this video!

[@FlatironsTuning]

You bet. Thanks for watching and Stay Tuned!

[@paulschaschlick9383]

You make great videos. Thanks for that. I have a H25 cylinder head on an ej 207 S20C block. What is this for a cylinder head? I can not find any info on them. Thanks in advance.

[@FlatironsTuning]

Thanks for your question Paul. I have to say that I haven't heard of that before. From what I can dig up, they came on the Turbo Forester in Japan. In theory, they are single AVCS 2.0 liter heads. I'd recommend checking the volume of the combustion chamber. My guess is that it would be the same as other 2.0 heads, but that is just a guess. I'd compare spark plugs too. I hope that helps, and Stay Tuned!

[@New2Sube]

These videos are great!! Sub'd

[@FlatironsTuning]

Awesome! Thanks for watching :-)

[@Cooper_Andersen]

These videos are under appreciated! I watch them more than once. Can you share information about heads and the pros and cons of upgraded heads? Like porting, valve work, cam sizes and the effects.? Applications for these modification. Currently I'm doing a Daily Driver New OEM Short block Ej257 build with new OEM B25 heads (Stage 1 non-AVCS cams, beehive springs) Valves are the question?? What size +1.00 mm? Is more flow good or can it have a negative effect? Should you do larger valves on exhaust side only, Vice versa or Both? What type of head work is possible? Thank you for any sort of Info. You are the Subi Guru. Cooper

[@FlatironsTuning]

Thanks for your question Cooper. This is a pretty deep topic, but I'll give you the short answer here, and you can contact us directly for more specific answers. So for your power level, stock size valves will be fine. If you can get a 5-angle valve job. For head work, a bowl blend could be helpful, but you don't need to go further than that. A full port and polish could hurt your low end performance, especially if it is an aggressive one. Long story, keep it simple, and you should be in great shape!