Mikkel Jensen Posted February 8, 2020 Share Posted February 8, 2020 Hello, I'm the unlucky owner of a hawkeye STI, that has a blown head gasket. Along with some other problems with the car and no service history from previous owners, I thought it would be a brilliant idea to get a new block, so I'm sure there's no other funny business in store for me. I'm standing to save quite a lot of money between 2 different engines from 2 different places with forged components, I'm looking to add a bit of power, not too much as its a daily driver. So to my question... Is there any strength/material differences between OEM STI EJ20 head bolts to a OEM STI EJ25 head bolts? Quote Link to comment Share on other sites More sharing options...
savage bulldogs Posted February 8, 2020 Share Posted February 8, 2020 I think they're the same fitment, have you tried cross referencing the oe part numbers , to see if they're the same ? Unfortunately I dont know if there's any difference in the strength of the materials used , just that my 2ltr arp headstud said both ej20 and ej25 fitment on the box . 1 Quote Link to comment Share on other sites More sharing options...
Mikkel Jensen Posted February 9, 2020 Author Share Posted February 9, 2020 Unfortunately I don't have OE part numbers, and I doubt from OE numbers I can find out if there's any difference in materiale and strength. The reason I'm asking, is that in the one block there's OEM head bolts and a friend with primarily experience in EJ20 engine (mine is a EJ25) says that he experienced the original head bolts for the EJ20 couldn't handle up towards 400 HP. Quote Link to comment Share on other sites More sharing options...
savage bulldogs Posted February 9, 2020 Share Posted February 9, 2020 I just thought if they're definitely the same part number and fitment, they'd be the same item and strength made from the same material 😉. The ej207 is reportedly good for 450hp in standard guise , so I'd thought the standard head bolts would be too . Saying that I when I rebuild my old ej207 I used cosworth headgaskets and standard bolts but when I rebuilt my ej20 cdb I used cossie headgaskets and arp's. Think "safe" 400hp is more about deck type (open deck being the weakest) and piston type (early classic and 2.5 pistons being the weakest). If the 2.5 block is open deck and not semi closed or your using the standard 2.5 pistons (prone to ringland failures) I'd say they were the weakest link , rather than the head bolts . If you've gone to the expense and effort of fitting uprated internals and reinforcing the deck type ,I'd just use arp's anyways (to protect your investment) Quote Link to comment Share on other sites More sharing options...
Mikkel Jensen Posted February 9, 2020 Author Share Posted February 9, 2020 Thank you for your insight and previous experiences. 🙂 It's purely a question of money, seeing if it's possible to save some money here and there. As its my daily driver, I'm not looking to get very high HP. Somewhere between 300 and 400 is fine for me. But I want it to be reliable and future proof too, 'cause I plan to give it a little it more "oompf". 😛 It's a difference of 700 GBP between the 2 blocks I'm looking at. I think I'll go with the more expensive one. Should be good for 650HP/850NM. I can't be bothered with any weak links Quote Link to comment Share on other sites More sharing options...
savage bulldogs Posted February 9, 2020 Share Posted February 9, 2020 I try to give advice from experience rather than what I've read on the internet but I've never built a 2.5 and my cdb is running a very over engineered sub 400hp .due to refusing to pay over £1.5K for a 400hp + turbo and injectors. I'd say cosworth or rcm stopper headgaskets are worth the extra £100 ,whichever block you go for . Best of luck with the build and feel free to start a build thread or just keep us posted on progress, chap 👍 Quote Link to comment Share on other sites More sharing options...
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