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2.1 or 2.5 engine

Old 09 October 2018, 12:23 PM
  #1  
rsjohn
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Default 2.1 or 2.5 engine

Probably been asked before but hey ho.

So im looking at uprating the engine in my impreza sti widetrack and iv seen a few engine options, 2.0, 2.1, 2.35, 2.5, theres probably more but the main ones iv seen.

Iv seen a couple of engines for sale a 2.1 which is built to a good spec and a 2.5 again built to a good spec.

The 2.5 is alot more ££ than the 2.1.

My aim is to get a quick road car and maybe the odd track day in the future and looking for around 480-500bhp

So which would be better the 2.1 or the 2.5?

thanks
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Old 09 October 2018, 02:13 PM
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hackisfun
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The best thing to do would be list the relevant spec and prices of the engine options you are looking at. Parts used will be a big factor on reliability etc.


the 2.5 will have more torque over the 2.1
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Old 09 October 2018, 04:39 PM
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The 2.5 will have much better spool and pick up over a 2.1
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Old 09 October 2018, 04:46 PM
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Originally Posted by ScottyPPP View Post
The 2.5 will have much better spool and pick up over a 2.1
What turbo did you run on your 2.1?
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Old 09 October 2018, 04:48 PM
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Originally Posted by rsjohn View Post
What turbo did you run on your 2.1?
Biggest I had on it was a 20G at 380bhp.
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Old 09 October 2018, 07:08 PM
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A 2.1 cdb has gotta be the reliable one with quality parts of course, 2.5 cd inserts are reliable upto a certain bhp because of thin liners, a 2.35 using a 22t block is great and a in between of both but at a great cost also but the best choice for big power builds.
take your pick in what you want, any 3 will be fine at your level but needs to be a good build with good parts for reliability
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Old 09 October 2018, 11:32 PM
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rsjohn
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This any good, it’s a 2.1?

Ej20 semi closed deck block

Group n arrow billet crankshaft

Group n arrow Conrod’s

ACL race bearings

Omega group n pistons

RCM 14mm head stud conversion

Spec c big port heads with oem spec c cams

Uprated valves and spings

RCM 12mm modified oil pump

Group n Twinscroll baffled sump

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Old 10 October 2018, 05:59 PM
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Thats a very good spec, but I don’t understand why spend so much on a arrow crank and use a scd?
get a recipt for that build to confirm
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Old 10 October 2018, 06:18 PM
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Originally Posted by bustaMOVEs View Post
Thats a very good spec, but I donít understand why spend so much on a arrow crank and use a scd?
get a recipt for that build to confirm
Chevron built the engine
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Old 10 October 2018, 07:32 PM
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Originally Posted by bustaMOVEs View Post
Thats a very good spec, but I donít understand why spend so much on a arrow crank and use a scd?
get a recipt for that build to confirm
same.....

i thought the standard subaru crank was good for 600-700 bhp so see no reason to pay ££££ for a billet one
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Old 10 October 2018, 09:40 PM
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My issue is, pay upwards of 2-3k for a arrow crank but yet use a scdb? The arrow crank can take some serious rpm!
the rest of the build is more than perfect though
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Old 10 October 2018, 10:06 PM
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Originally Posted by bustaMOVEs View Post
Thats a very good spec, but I donít understand why spend so much on a arrow crank and use a scd?
get a recipt for that build to confirm
Originally Posted by the shreksta View Post
same.....

i thought the standard subaru crank was good for 600-700 bhp so see no reason to pay ££££ for a billet one
Originally Posted by bustaMOVEs View Post
My issue is, pay upwards of 2-3k for a arrow crank but yet use a scdb? The arrow crank can take some serious rpm!
the rest of the build is more than perfect though
iv not paid that for it so Iv gained a very good spec engine for less £££
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Old 10 October 2018, 11:35 PM
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Originally Posted by rsjohn View Post

iv not paid that for it so Iv gained a very good spec engine for less £££
You haven't paid for it - but the point being made is that it doesn't match the rest of the build. But, if you got it at a good price, and don't push it too far, bargain
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Old 11 October 2018, 06:21 AM
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had both the 2.1 and my current 2.5 ,,, prefer the 2.5 for the road ,, 2.1 for the track
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Old 11 October 2018, 06:49 PM
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Originally Posted by scoobypaul_temp View Post
You haven't paid for it - but the point being made is that it doesn't match the rest of the build. But, if you got it at a good price, and don't push it too far, bargain
this.
p.s I'd want proof of that billet crank as that's a lot of pee. And pics of build from seller?
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Old 14 October 2018, 07:43 AM
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if built propperly , a 2,5 will be better on every aspect. it will have better torque and earlier spool. that spec you have given for the 2.1 is over kill regarding the crank and the oil pump. both the crank and the oil pump would be a good investment if you want to achive 700+bhp at some point but want to hang around at 450bhp mark for a while. but then you wouldn't take a semi cd as your base (scd runs out of breath after 550ish bhp). also there is the 14mm stud issue for me. i dont have experience building a big hp 2 liter so not sure about clearances but on a 2.5 semi cd it would be a big no no for me to put 14mm studs as they touch the liners and thin the liners down. if when they drill bigger holes (for the 14mm studs) on a 2 liter block and touch the liners you could easily crack a cylinder wall. i beleive the arrow crank, 12mm rcm oil pump and the 14mm studs belong to a cdb or even a sleeved block aiming for at least 700+ bhp. you dont put an arrow crank in your engine for 450 bhp. it is like giving a gold plated barbie doll to your 3 year old.
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Old 14 October 2018, 09:04 AM
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Originally Posted by k_duraman View Post
if built propperly , a 2,5 will be better on every aspect. it will have better torque and earlier spool. that spec you have given for the 2.1 is over kill regarding the crank and the oil pump. both the crank and the oil pump would be a good investment if you want to achive 700+bhp at some point but want to hang around at 450bhp mark for a while. but then you wouldn't take a semi cd as your base (scd runs out of breath after 550ish bhp). also there is the 14mm stud issue for me. i dont have experience building a big hp 2 liter so not sure about clearances but on a 2.5 semi cd it would be a big no no for me to put 14mm studs as they touch the liners and thin the liners down. if when they drill bigger holes (for the 14mm studs) on a 2 liter block and touch the liners you could easily crack a cylinder wall. i beleive the arrow crank, 12mm rcm oil pump and the 14mm studs belong to a cdb or even a sleeved block aiming for at least 700+ bhp. you dont put an arrow crank in your engine for 450 bhp. it is like giving a gold plated barbie doll to your 3 year old.
how come so many engine builders recommend 14mm head studs then? only 1 place i have spoken to said they are not needed and that an extreme version of the 11mm will be more than enough.

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Old 14 October 2018, 05:07 PM
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I'm with k duraman 100% there, apart from the 2.5 better in every aspect (not as good as a 2.1 cdb on track when at extreme temps the 2.5 liners will be weaker and could crack etc)

amd yes 11 extreme are fine for most applications, shrek, most say 14 as it's probably sounds safer for the customer lol. What folk tell you take with a pinch of salt and figure the wider picture out yourself and go from there on what's suitable and what's not.

Last edited by bustaMOVEs; 14 October 2018 at 05:08 PM.
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Old 14 October 2018, 06:50 PM
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Originally Posted by bustaMOVEs View Post
I'm with k duraman 100% there, apart from the 2.5 better in every aspect (not as good as a 2.1 cdb on track when at extreme temps the 2.5 liners will be weaker and could crack etc)

amd yes 11 extreme are fine for most applications, shrek, most say 14 as it's probably sounds safer for the customer lol. What folk tell you take with a pinch of salt and figure the wider picture out yourself and go from there on what's suitable and what's not.
really dont know which way to turn now lol
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