Hey everyone I have an 8 with most boltons. I am upgrading to gsc s2 cams and a ef2 map turbo. We did a compression test and leakdown. The leakdown had 5% in cylinders 1-3 and 12% in #4. Should I replace my valves or do you think it will be ok.

 

I would just have a trusted machine shop do a valve job on the head..cleans up the mating surfaces between the valve and valve seat and is usually cheaper than new valves

 

If I pull the head I'm going new valves since I am putting in new springs and retainers. My tuner says leave the valves but my mechAnic says replace them. Trying to figure out if the mechanic is doing it for the extra money.

 

Well leaking valves are a bad thing. The mechanic may just not want to give back an engine like that but he can also be just trying to squeeze you for some extra money if he's taking off the head and you're not taking it off yourself. I would personally just remove the head myself and get them reseated.

 

If you're in there you might as well go with bigger valves and new valve seats.

 

12% isn't enough to bother with, drop your cams in... You may never have an issue-- and its not always the valves that cause compression leakage-. Only way to tell is pull the head. Drive it and when it goes---then do the valve job and anything else.

 

That right there.

12% is still fine, typically the rule of thumb is over 20% is when you need to get in there and see whats up. For all you know it could be a ring too.
Granted we all want 5brazilian HP evos and everything top notch and only date 10's etc, but real world numbers it is fine if your compression is level.
If you had a significant compression number variation because of it, that could be cause for work, but you didn't mention that.