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Need some advice. I have a 69 z28 which has a 454 in it, obvioulsy I know its not the original engine, but supposedly has 12:5 to 1 compression. Previous only told me he had the engine built 3 years ago and has been running it on pump gas 93% since. I have recently been told by a friend that this is impossisble. Some of the engine and drive train components include the following.

468 cid 12.5 compression
Merlin Rectangular Port Heads 219 188
Mechanical Comp Cam 637 lift 270 Duration
7/16 Full Floating Rods
GM steel crank
TRW Pistons
Moroso deep pan and Windage Tray
Hooker Super Comp Headers
Super T- 10 Rebuilt 4 Spd trans
Hurst Shifter
Hays Clutch
Lakewood Blow Proff Bell Housing
3" Exhaust With Flowmasters
Original BU 12 Bolt With 411 Richmond Gears

Is it possible this car can run on 93 octane without damaging the engine? I have been using it and it doesn't make any strange noises that would indicate there's a problem. The only thing I can think of is that maybe the engine shop lied to the previous owner about the compression. But still I have receipts for the installed pistons which indicate the 12.5 to 1.

Thanks in advance for your opinions.

 

Nice Camaro. Love that color combo.

I would suggest that you need to do some more homework here. The "12.5:1" pistons do not indicate your actual compression ratio (it is an estimate).

Your actual static compression ratio will depend on several factors: how far the pistons sit below the deck (was the deck milled?), the combustion chamber volume of the heads (were the heads milled?), the head gasket thickness & diameter, and the pistons themselves (not to mention chaning the stroke in any way). Without pulling a head off, you may not be able to determine these variables. I would assume that the head & decks were not milled & calculate your CR with those heads & a few different head gaskets to see the range of CR that you are probably in.

To make things more interesting, you can play with your timing to make it advance more slowly to prevent detonation (to a certain extent). It would be good to understand your initial & total timing. Knowing when your timing is "all-in" would also be good for you to understand. Some people really get into understanding the duration of the cam in order to calculate the dynamic compression ratio - but that is another subject that is rather touchy with certain crowds (not everyone buys into that line of thinking).

I would pull a plug & look for signs of detonation. Google it & you will find plenty of info out there on the subject. You can seriously damage that engine if your running it on fuel with an insufficient octane level.

 

Nope.

Maybe it could be 11.5:1,but not 12.5:1 without adding a mix of race gas...even with aluminum heads.

 

Thanks for the thumbs up on the color combo!

I will do some more homework like suggested.

 

Do some searching on dynamic compression ratio as that, not static, is what determines octane requirements.