So I picked up a 1998 z28 with the automatic trans and 5.7l engine. I got it with 180,000 miles and I want to modify the engine but Im unsure because of the high mileage. Should I mod as is and do an engine rebuild down the road later? Or save for a lower mileage replacement engine? The mods I plan on doing are heads and cam, longtube headers, fast 92mm intake and NW throttlebody and maybe a cai.

 

180k is definitely not a spring chicken, but it's not necessarily a problem either; just depends on how the engine was maintained and used. If you want a decent evaluation of the engine's health prior to making any decision, here's what I would recommend:

- Compression test. Start with this, and depending on the numbers you may or may not want to do a leakdown test.

- Oil analysis. You'll want to start with a fresh oil change & filter first, so that you'll know how many miles are on the oil prior to sending in a sample. Drive the vehicle as normal and then send in a sample of the oil to a place like Blackstone Labs for a UOA (Used Oil Analysis). In the mean time, you can cut open the current filter after you change it, just to see if there is anything alarming in the media.

These things will give you a pretty good idea about the relative health of the engine; this is no guaranty that you won't have problems if you do an engine build, but at least it'll let you know if there are any obvious weaknesses up front.

 

Like rpm said , compression testing and leak down test would be my first thing. After that a fresh oil change and monitor oil pressure and see how everything is. I've seen 200k mile motors make 20 lbs. of boost and take abuse for years so mileage shouldn't completely scare you

 

Pull the trans pan and see what kind of clutch material is in pan. Give the drive shaft a look in regards to u-joint health. Back lash in the rear end?

 

Sounds like the perfect time for a stroker crate engine.

 

Really depends on what you are looking to get from the car. Are you looking to keep the 17-20 mpg fuel economy and have a reliable daily driver or are you looking to make some power? Regardless, I would be going back through the engine with a fresh set of rings and bearings at a bare minimum before bolting on H/C/I or I'd continue to enjoy the car while saving for something like a stroker to drop in that's plug and play with your 24x system. That is if you are looking to make some more power and if that's the case sell the LS1.