Looks like i'll be getting an '85 z-28 with a 305, q jet, t-5 (a spare T-10 w/ it too!!), t-tops, new paint and a messy interior. All for a grand total of $1500.

I was wondering, what kind of power should this thing put out? what kind of mileage?

Everything seems to be stock, not beaten on and this guy seems to simply wants to get rid of it (he seems to be wealthy enough not to care if it goes for 3000 or 1500)

 

Check out this page https://www.thirdgen.org/newdesign/tech/techdb.shtml

Then check the 8th character of your VIN. Is it an "H"? Thought so. That's an LG4, which in a 1985 Z28 M5 had a grand total of 155 equines.

The difference between your engine and the L69 is exhaust, cam, air cleaner, and tuning. Fix those, with even better than L69 exhaust parts & cam, you'll almost double the output.

The T10 would be much more capable of handling more power, but you'd probably miss the overdrive the T5 offers if you drive it on the street. Sell the T10 and use the proceeds to improve your ride.

Have fun!

 

I have yet to pull apart my LG4 since the swap (collecting water in the driveway), but I thought that the Lg4s also have dished pistons as opposed to the flat-top pistons of the L69s..am I wrong?

 

Thanks for the info five7, its nice to know what i'm getting. Does anyone know what kind of mileage is should get with this thing? 10, 15, 20mpg? Also, will it need premium gas?

 

In '85, even the lowly LG4 got flat-top pistons to produce 9.5:1 compression. I have had the heads off my '86, so I know it is true for that year. Since the tech data (and others) indicate the 9.5:1 for '85, I didn't include that in the differences between LG4 & L69 in this case.

So, for an '83, you're right. For an '85, you're wrong.

In good tune, and driven "nice", you should be able to expect close to 20 mpg in combined driving, perhaps close to 25 highway. I'm using regular gas (which is 85 octane in good ol' high-altitude Colorado) with the timing advanced to 7 degrees base, without a hint of pinging.