What octane to use with unkown performance heads?

[88SaleenClone]

I bought the car with all of the mods in my sig already done to the car. The valve covers are chrome and say "Ford Motorsport" on them. I'm pretty sure they are iron...Anyone know which heads these could be? Anyways, I've been using 89 octane and it seems to run good. I just passed smog. But, I'm wondering if I could get away with running 87 octane since gas prices are through the roof again. I have been wondering about what kind of compression ratio my engine is running at too. Does having performance heads generally mean they have a higher compression ratio than stock? I know stock 5.0 heads are 9.0:1 and you only need to run 87...right? Are there performance heads with the same CR as stock? Or is it more common for performance heads to have a higher CR like 9.5-10.5:1?

 

[RYC CUKR]

Compression ratios can vary widely due to different size combustion chambers on different style heads. I would put some 87 in, set the timing to the 10* base timing set up and drive it. If you don't hear and pinging then you can start advancing the timing up to around 14*, as much as you can with out pinging and you should be good to go.

You could also look for casting #s or names on the heads. Usually they are stamped or cast into the front of the head where the accessories attach for aftermarket heads.

 

[jrichker]

Magnets are attracted to iron but not to aluminum. Use it to find out if you have iron heads.

 

[Mustang5L5]

What is your timing set at.

If you have anything other than 10 degrees, it prob won't run on 87 octane without detonating anyway.

Lower it to 10 degrees and try out a 1/4 tank fo 87 octane. If you notice any pinging at all, go add some higher octane.

 

[Foxfan88]

there are so many heads out there to buy and anything could have been done to the heads. the only way to find out the compression ratio is to take the heads. off

and factor in the pistons, chamber size and gasket thickness and all that stuff.

dont worry about compression

 

[blackened88lx]

The valve covers would have nothing to do with the type of head that's on the car. I would do the magnet trick and figure out if they're iron or aluminum to start with. Look on the front of the head, and along the header side for any type of brand name or number that you could identify them by. As far as fuel, I agree with what everyone has said. Set the timing at 10*, put 87 in it and listen closely for pinging.