Head Bolts
15 August 2013, 06:36 PM
#1
Head Bolts
Whats the most bhp 2003 STI standard head bolts will take? My engine was rebuilt last year with wossner pistons, Manley rods, ACL Bearings and a Nitrided crank.
I am running a SC46 turbo @429/380 but want more and thinking of another turbo but not sure if the heads will start to lift at 500BHP on standard head bolts?
other option is to source a 2.5 and fully forge it etc and go from there...
Any ideas?
I am running a SC46 turbo @429/380 but want more and thinking of another turbo but not sure if the heads will start to lift at 500BHP on standard head bolts?
other option is to source a 2.5 and fully forge it etc and go from there...
Any ideas?
15 August 2013, 07:57 PM
#4
The thing is you can't put a figure on it. ARPs will take more than standard & Cosworth studs will take even more. Some have run over 500 on standard bolts with no problems but others have failed at 400 or less. Most forged builds use ARPs as a minimum but ultimately it up to you how far you want to push it.
15 August 2013, 09:57 PM
#8
I wouldn't bother with a 2.5, it will cost a fortune & a 2L is far stronger. A 2.35 is the ultimate but pricey, I'd go for a 2.1 as it costs little more than a 2L. Every engine will have a different limit, but I think Banny ran over 520BHP on an STI engine with standard head bolts. Why don't you PM him to confirm.
15 August 2013, 10:01 PM
#9
Jacko, are you sure your engine builder didn't use ARPs as most forged builds use them as standard. You could get more power from the 46 with the right mods & a Meth map.
16 August 2013, 10:19 AM
#11
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It's not just the bhp figure you need to consider, the CR is critical as well, it's cylinder pressure that lifts the heads. For example ive recently built a 2.1 and the Customer said he wanted 400bhp with good spool, so I built it with 9.0:1 as the CR, all was fine until He got it mapped and achieved 450bhp. It lifted the heads! Moral of the story is that engines with lower CR will achieve more power with std bolts as the cylinder pressure is lower.
16 August 2013, 03:33 PM
#12
It's not just the bhp figure you need to consider, the CR is critical as well, it's cylinder pressure that lifts the heads. For example ive recently built a 2.1 and the Customer said he wanted 400bhp with good spool, so I built it with 9.0:1 as the CR, all was fine until He got it mapped and achieved 450bhp. It lifted the heads! Moral of the story is that engines with lower CR will achieve more power with std bolts as the cylinder pressure is lower.
16 August 2013, 04:12 PM
#13
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It had arp's fitted, the combination of high Cr and boost caused enough cylinder pressure to lift the heads. My rally car runs 10:1 and only 1.3 bar but it needed a CDB and 14mm studs to keep it together.
16 August 2013, 08:06 PM
#14
Mine runs 8.67:1 with Cosworth gaskets & ARP studs on a CDB. I'm running 450 on my Meth map but plan on upping this soon. Every engine is different & if you push it you only know you have gone too far when it fails. Next time it's apart I'm upgrading to Cosworth studs & supertech valves but I need a reason to take the engine out before I do this.
16 August 2013, 09:36 PM
#15
It's not just the bhp figure you need to consider, the CR is critical as well, it's cylinder pressure that lifts the heads. For example ive recently built a 2.1 and the Customer said he wanted 400bhp with good spool, so I built it with 9.0:1 as the CR, all was fine until He got it mapped and achieved 450bhp. It lifted the heads! Moral of the story is that engines with lower CR will achieve more power with std bolts as the cylinder pressure is lower.
I won't go as high as 9:1 then
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