Hope somebody can point me in the right direction!

I'm building a closed desk stroker engine for my WRX. Original plan was to use my WRX heads, as i wasn't concerned with AVCS. However i've since been told that the WRX heads would limit me to around 400bhp in the future if / when i go for a bigger turbo due to flow restriction and less aggressive cams. However 2 of the buckets fell out when i was dissembling the engine and separated from their shims and i have no idea which way round they went so have been told the heads are scrap unless i get a whole new bucket and shim set made up.

So i've been searching thoroughly for a set of UK STI AVCS heads, however the 1 or 2 sets i've seen up for sale in the past few months have been cracked around the spark plug. As the majority of STI heads being sold are cracked, is it actually a problem? Most of those have been removed from working engines, so i guess a large majority of STI owners are driving round with cracked heads by the spark plug without even realising.

As it doesn't appear i'm ever going to find a good set, would i be fine running a set with a crack by the spark plug (and can anything be done to fix them>), or would i get the same performance (without AVCS ) by getting a set of WRX heads, porting & polishing and putting in fast road cams? Or is there an alternative set of STI heads i can look for which flow better than WRX (regardless of AVCS).

Any thoughts & advice is appreciated!
Cheers

 

better tell a certain Mr. Forrest that the WRX heads will only flow 400..........he campaigned them with just a little success on various stroker builds before he started down the EG33 route

not sure what age car you have but the later new-age had solid buckets from memory and only the very first variants had the 'over-bucket' style shim
they are designed to part company and this certainly does not render them "scrap"

something like V5/6 STi heads work very effectively depending on your target

 

How much power was Andy getting from the wrx heads?

 

Thanks for the replies!

It's an 03 Bugeye WRX (presumably a late registered 02). Reason i think they are scrap is because the shims fell out of 2 of the buckets, i have no idea which way round they went (was told they come in pair sets from the factory) or which valves the buckets come out of.

I'll take a look for some V5/6 STi heads! Thanks for the tip.

Still curious if anybody has knowingly installed STI AVCS heads cracked by the spark plug and if there are / were any ill effects, or if anything can be done to fix them?

 

My current heads have cracks by the plugs on one cylinder. No issues

 

You will need to do is fit the shims into the buckets then fit the buckets into the head. Tighten down the cams correctly and check the clearances. If they are wrong take out the cams and swap the shims over and then rebuild and recheck. If they are still out you may need to swap the buckets round.

 

Thanks guys. Boosted - Very interesting that you're knowingly running a cracked one and its fine, i will have to look into this more, there was a set on ebay cracked by 1 spark plug in each cylinder head but the company claimed they had pressure tested the heads etc and they were perfect.
360ste - Thanks for the tips for rebuilding i'll do it that way when i inevitably fail to find a decent set of STI heads.

 

Not only running a cracked one, but running it at an elevated power level 👍

 

What power are you running them at if you don't mind me asking? I'm looking at being in the 400bhp area, think that would be safe?

 

Depends on the depth of the cracks etc.
I have in the region of that power

 

you can get the cracks X-rayed for suitability, my wrx heads had cracks on all four sparkplug holes and were passed fit for use. As Boosted says it depends on how deep the cracks run.
Trev

 

Wonder if the cracks could be welded otherwise? I know a lot of turbo converted bmws have the blocks welded for example, so don't know why a spark plug crack couldn't be fixed in a similar fashion

 

Finally someone who doesn't think that "JDM Large port" are the hallowed cylinder head to have