This has probably been covered before, but I couldn't find anything in the archives. What seems to be the concensus for maximum compression for 87 octane fuel in a 460 used for heavy pulling in the 1800 to 2800 RPM range.
Robert

 

 

Even stock compression will detonate (ping) depending on a number of variables such as outside air temp, timing, load on engine, amount of carbon build-up in head chamber, spark-plug heat range, etc.
As an example...my 89 F250 (see my signature for upgrades) will spark knock when towing my 9000 lb. trailer up a steep grade if the outside air temp is above 85-90 F. In addition to what you see in my signature I have advanced the initial timing to 12-13 degrees BTDC. Below that temp it will not spark-knock. Deen

 

My 97 F250 pings on 87 octane at 3/4 throttle in 3rd gear up a hill. I like to run 91 octane most of the time, truck just feels better on midgrade. I don't know what my stock compression is though...

 

Yeah all depends. My 94 F250 460 E4OD 4.10 4x4 supercab runs just dandy any time of year with 87. BUT, if I tow a 8,000+ trailer it likes 92 when in hills or hot weather. On flats 87 works fine with the trailer.

The newer engines computers will often compensate for octane so if you have a newer engine you should be able to run any common grade gas.

Best bet is to experiment with different gases and driving conditions. I think that unless you tow, or you have a hot cam or over 9:1 compression, you will probably do fine with 87.

I read an article once that said you should run your engine on the verge of occasional light pinging. This delivers the best economy etc. However, you should avoid heavy detonation, that can damage things pretty quick.

Good Luck,

Jim Henderson

 

I suppose I should re-phrase the question a bit. What would be maximum compression for 87 octane and still be able to run optimum timing for power, and not have to run an over rich mixture to prevent detonation?
I'm running aftermarket fuel injection now, and I can trim my fuel and spark to eliminate any pinging if my fuel maps can't cope with a particular situation, but what I'm trying to determine is, when it comes to rebuild time and the whole character of the engine can be changed, the compression ratio can be taylored to the particular engine and it's application. There aren't many commercial trucks running gas angines around any more, but in the past, I recall truck engines running lower compression than similar engines used in passenger cars. I suspect it has something to do with the severe duty imposed on a truck engine. I'm sure that more compression will yield more power, but on a sustained basis, it will probably destroy the engine, or at least severely shorten it's life. I want to run 87 octane fuel, so that is a basic limiting factor. I want to build the engine and tune for best power, and best economy using that fuel. There's no point in running 9.5 or 10:1 compression in an engine to get more power, but have to retard the timing or add more fuel to keep it from pinging. Every engine design type responds a bit differnt to compression and pinging, so I was wondering if there has been any conclusions for the 460 in this regard,
Thanks,
Robert

 

Gotta be a smarta$$ on this one. Given that, on mine, factory compression ratio is 8.5:1 and it still sounds like a diesel on 87 octane, I would have to guess that max compression to avoid pinging on 87 octane would have to be about 6:1.