Can you use 89 octaine with 9.6-1 comp.pistons or are you just looking for trouble?

please provide the following:
thermostat rating (150, 160, 170?)
iron or aluminum heads
combustion chamber design (fast burn/squish/quench)
cam intake valve closing point and valve timing
humidity and elevation also are contributing factors

The most critical factor aside from the static compression ratio (CR) is the cam's intake valve closing point (and valve timing)

a squish/quench design will allow you a few points on the CR
aluminum heads will lower the combustion chamber temp allowing a few points on the CR too.

With 9.6:1, iron heads, and a stock cam, detonation is probable with lower octane fuel.

If you have large duration (aftermarket) cam and efficient heads than you should be able to get away with it.

If you hear a tin-like pinging then use higher octane, retard valve timing, retard ignition timing, and/or run richer.

What is the manufacturers octane recommendation?

Why risk it...

On 100 gallons of gas here's the cost...

87 Octane - $245
89 Octane - $255
93 Octane - $265

The point I am trying to get across is that you pay $10 extra for a tank of 89, that's 2 octane higher than 87. Why not pay another $10 for 93 which is 4 octane higher than 89?

My motors are 9.6:1 compression. Last year I used to run a combination of 87 and 93. That will give you the same cost as 89, but you will average 90 octane.
After replacing 4 pistons on one engine, I decided to run 93 octane forever.

You most likely will not hear detonation in a boat. As Baja said 93 really isn't that much more and it is a good idea at 9.6-1. Boats are lugging the motor all the time and unless your spark curve is perfect, there is a possibility of detonation somewhere in the rpm range. On the other hand if this is in a vehicle there should be no problem at 89 octane.

Thanks, BajaIceBreaker,Wobble and d1mbu1b for your input onthis subject
This is a new boat I am building and I am trying to find a balance between spending way to much money on a custom engine build and a low hp engine
Why would I use 89 Octaine? Thats all you can get around here on the water and the boat is way to big for me to take it out of the water just to filler up, 33 feet

I will be using Stellings Dry Headers 2 1/8 primary
Engine ?
ZZ572 : recomended fuel 92 octaine (GM)
Aluminum Heads
agressive Cam
140 thermostat could be used
Sea level use

I may end up taking the 572 apart and changing out the pistons check all clearances including valve guides(these have been prone to failure I have been told on several occations)

Thank you allonc again for your input and stories on this subject.

I'd leave the timing alone and move up to the grade of octane it takes to stop the knocking.

I wish I could gas up where you do. I just payed $3.40 a gallon for 93 octane the other day.

http://www.sallee-chevrolet.com/Chev...ckV8s/572.html

here are some things for you to consider:

recommended octane is 92
you should run 92
if you can only get 89 then...

Since the ignition timing advance recommendation is 36 degrees, which is quite a bit, you can put a 140 thermostat in and retard the ignition a bit that may do it for you. this is probably the easiest solution. (Make sure though, you dont want to melt your pistons)

Also, I understand there are aftermarket knock gauges out there the supercharged import guys use which may help you determine if the 89 is safe or not.

Usually an EFI engine can detect detonation and automagically account for it some how, maybe by richening the mixture or retarding the timing (not sure exactly)

I am surprised, it seems to me that 9.6:1 with aluminum heads is pretty mild. It must be that 36 degree total ignition timing as the culprit.

just put a zz 572 620 hp in a 30 checkmate for customer . put timing at 32 not 36 had to go 1 jet size bigger on secondary he has ran couple tanks of real 89 oct with no problems and boat gps 80 mph

Thanks for your input Dodsonartic1,thats great news, did you modify the engine? Cheers



Anyone else using ZZ572 please chip in!