Is my combo safe for 87 octane fuel?

[travisr1988]

Okay, so when I built this engine I asked my dad if I should be concerned with running premium (91-93 octane) gas to which he replied premium won't hurt but you probably won't need it. Now that it is running and driving I want to be sure it's safe before trying 87. My combo is as follows:

·355cid, flat tips with 4 valve reliefs rest of bottom end is stock replacement, block was checked and said to be stock with .030 overbore. Standard gaskets.
·iron vortec heads (casting 062) stock replacement
·lunati voodoo 10120701 cam; 256/262 adv. 213/219 @.050 .454/.468 intake closes @ 34.5 btdc
·quadrajet carb; may need rebuilt...again
·edelbrock performer intake
·cheap headers
·stock bro
·ac delco r44lts plugs

Truck seems to run good on 93 shell, timed at 16 degrees advanced. Can even bump timing up some, but I would rather not risk blowing up the engine.

From what I found my scr is around 9.3-9.8:1 and dcr is around 8.1-9:1 which was confusing because the calculators are all different. Anyone have a similar set up and run 87 or 89 without issue?

[frotosride]

So this is a tricky question because on paper you should be just fine but every engine is different. A lot of times especially with case heads are the combustion chambers and a lack of even burn and heat distribution. These hot spots often cause detonation or knock. The only way to be sure is try it. Theoretically you shouldn't have any issues running 87 because the Dynamic compression ratio is where it counts... LSA plays a huge role in cylinder bleed off and effectively lowers your compression ratrion. Did you factor in the compression height of the pistons when you used the online calculators as well as verifying your block hasn't been decked and is still 9.25 deck height. If so you shouldn't have any issues

[rich weyand]

Run the tank down close to empty and then just put a third of a tank in to try it.  If you get knocking, immediately go fill it the rest of the way with 93 to up the average octane in the tank.

[BIG RED 1983]

IN REALITY YOU SHOULD HAVE ABSOLUTELY NO PROBLEM. DO YOU KNOW HOW FAR DOWN THE CYLINDER THE PISTONS ARE AT TOP DEAD CENTER? DO YOU KNOW THE THICKNESS OF YOUR HEAD GASKET? IF YOU CAN GET YOUR INITIAL AND TOTAL TIMING BOTH UNDER CONTROL YOU SHOULD HAVE NO PROBLEM AT ALL.

[travisr1988]

I do not know how far the piston is in the hole, The headgaskets are standard replacement felpros.

[BIG RED 1983]

The distance between the top of the piston at top dead center and the bottom of the deck of the cylinder head is called the quench area. If you can get this distance under .040 of an inch you have alot less chance of detonation, however all this has to be done in the engine machining process and it is better to assume that your quench is over .040 of an inch. You want to run as much initial timing as possible without the engine being hard to start and as much total timing as possible without the engine detonating. Your total timing on a street driven vehicle should all be in by 3,000 r.p.m.