I plan on building a 408 how high can I go on compression with 89 safely? 10:5:1? I plan on using afr 225 heads and a custom ground cam

 

Not sure on 89, but on 93, I was running 12:1 with about .038 quench. Motor ran excellent

 

Without a dyno, there is no way someone is going to be able to give you an exact number.

 

Will depend a lot on the camshaft and dynamic compression.

 

I've ran mid-grade in mine without any issues, but honestly the tune plays a big part in it. You can back the timing off a few degrees and be ok I guess....but I"m not sure why you would want to go through the trouble unless you just can't get anything higher in your area.

 

I've run 89 on 10.5:1 compression and it worked fine. Under 50 degrees the 89 runs good. In hot condition I'm pretty sure the car pulls a bit of timing.

 

Has very little to do with static compression and everything to do with dynamic compression.

Which as awesome auto pointed out, is dictated mostly by the cam

I have to ask, why would anyone build a stroker and limit it to 89? When you do the math paying the extra for premium isn't a factor because you get more power and fuel mileage out of higher octane (obviously as long as you compare fuel with the same stoich ratio)