Ok,I have a 120,000 mile lt1
I know the best way to do things is to just rebuild the whole block.
Would I be making a big mistake if I put on heads,port matched intake and a new cam without rebuilding the lower end.
What kind of trouble could I run into.

 

Spun bearings seem pretty common with cam swaps on high-mileage motors....other than that, just be prepared to spend some time getting the tuning sorted out.

 

Keep it clean and take your time and you wont have any problems. Like mentioned above you could spin a bearing but that would be the consequence of getting dirt and gunk into the block or if you already have a problem occuring in the bottom end. There's a few guys on the board with a good amount more mileage with heads and or cams running good times and laying down good power.

 

I agree it can be done as long as the motor has been taken care of, and you take your time and do the swap right. A lot depends on if its 120,000 highway miles, 120,000 mobil 1 miles or 120,000 hard city driving ragged out never changed the oil miles.

I've changed cams twice on my car, once at 45,000 miles and again at 55,000, and the cam bearings were worn pretty good. I can guess at 120,000 they are about shot!

 

Too many variables: depends on condition of bottom end (if well worn) you are certainly taking a risk, especially if you are going with a large cam needing a higher RPM. Have seen on here, including moi, instances of bottom ends going with VERY few miles when the wrong combination or bad installation of heads/cam mods.

If you have the money and a low-stress personality, go for it. Otherwise, I believe you will be happier if you make sure you have a good bottom end before subjecting it to too much overhead power.JMHO

 

I agree w/ Bubba, I'd be leary of doing all that work with the motor in the car and all the associated headaches that come along with it. If it were my 120k mile car, I'd pull the motor, have a basic rebuild, and do the heads and cam on the stand in a clean room where it could be done neatly and easily with more attention to detail and knowing that the chance of success and reliability increase probably 10 fold.