Fuel Type?

Is it safe to run 9.5:1 ratio on 87 octane gas? What differences might I notice.

i think you should be ok. by what changes you might notice do you mean in performance or what you might notice compared to higher octane?

well, ill answer both.
higher compressio will give you higher horsepower, torque, higher rev capabilities and better fuel economy.

using lower octane might cause knocking and that is a bad thing. if your car has a knock sensor it will retard the timing so that it doesn't knock and you will lose performance. if you want to be safe, just run on higher octane but you can try low octane but have a can of octane boost in hand in case you notice some pinging or knocking, then stop your car and dump that stuff in and run on higher octane from then on. i dont see a problem with runing 9.5:1 compression on 87, i think there are many cars that do it but better safe than sorry.

it depends largely on how advanced the timing is, there are cas that run 10:1 on regular but use timing to avoid knock.

whatever gas the car is tuned for (i.e. from the factory) is the gas that should be ran, unless you can advance the timing or the pcm has been tuned otherwise.

Btw, my car stock had a 9.7:1 compression ratio and required 87 octane. Now I have 8.5:1 and I need 93 octane. Of course, a turbo has a major factor in that.

My car should do alright then in that case. Thanks guys. That's all I needed.

Tell us what kind of car it is. I have trouble running my naturally aspirated 454 with 8.6:1 on 87 octane because of antiquated chamber designs, but my 10.75:1 LT1 runs beautifully on 87.

It's a '95 Eagle Summit DL. Many Summit/Mirage/Colt drivers tell me that 93 octane is required to keep it healthy, so I was just curious. Here's the specs anyway:

4G93 16-valve SOHC 1.8 liter specs.
Bore x Stroke: 81.0 x 89.0
Piston Displacement: 1834cc
Compression Ratio: 9.5:1
ECI-Multi(Electronically Controlled Multi-point Fuel Injection)
Horse power: 113 (86kW) @ 5500rpm
Torque: 116 (161Nm) @ 4500rpm

My engine was completely rebuilt about 5000 miles back.

yep. Should be fine. If you notice knock, its not :) By 95 I believe they would have had all the necessary stuff to retard the spark accordingly if it hears knock.