Can you use coil over 2.5 spring to

Replace the oem springs on a strut? No aftermarket for my avalon. So was just thinking about this, like to lower and stiffen the suspension  a wee bit.

Yep.  Just need the sleeves and cut the old spring perches off.

Now to find out 2000 avalon  spring rate and lenght.. for a starting  base number 

We did that on our Challenge Q45. Think last year we had $150ish into our lowered suspension. I doubt you'll go as stiff as us but watch your dampening ability with stock struts. You might want to measure your strut diameter as some are thicker. 

Front rates are 448 inch pound's, rears are 280 inch pound's, oem

This is what I did on my LeMons 280zx using cheapo swap meet springs. I had to weld together some custom fixed perches, which took a few iterations to get the ride height right, but it was damned cheap.

Little bit Leary of welding on a shock 

I used generic eBay coilover sleeves on my 87 Golf. 

For the Challenge we used 2.5 OD aluminum pipe with an ID to match the strut OD. 

Thanks

Alfaromeoguy said:

Front rates are 448 inch pound's, rears are 280 inch pound's, oem

Are they linear or progressive? That will make a big difference.

Cannot find information on that