For those of you who have high powered motors (like more than 350ish horse), and say that you can run easily on pump gas...is this easy as in running 89 no problem, or easy as in...pushing 93...running 94 or 95 if you can get it, basically just non-alcohol.

For me pump gas is 92-93 octane Amoco/BP or Shell. That is with 10:1 and aluminum heads. I could probably get away with 89 but I haven't really tried.

I guess it really depends on how small the engine is vs. how much HP it makes...

In my case, I make 685 HP (naturally aspirated) and run on 89 (it actually runs cleaner on 87 but i can not bring myself to buy it). 502 inches and 8.75:1 compression.

I do run 93 when I spray - it is just a small (200) shot but I prefer the higher octane just to be on the safe side.

91 octane is as high as we get out of the pump in my area. It was 92 when I built the engine that's in my car now and I didn't notice any problem with the 1 point drop in octane. I would not try to run any lower grade fuel in my car though. I know I am kind of pushing it a little on 91, but I have yet to have a problem (over 5 years). It really depends on the combination.

355 with alum heads, 10.32:1 with a fairly tight quench (39), dynoed at a little over 400 hp Burn 91 with no problems driving sane or under load. Havn't tried anything less with this motor. My 327 10.25:1 steel Camelhump would ping and run on with 89 gas but was okay with 91, I have no idea as to what the quench was on that motor. :D

My 396 pings and runs on with 89 octane if I get at all aggressive with timing, so I have either hard starting or pinging or run on, I would recomend a healthy safety margin, mine wasn't big enough. I have to add some form of octane adder now.

Originally posted by James67RS:
I guess it really depends on how small the engine is vs. how much HP it makes...

Ping resistance depends on octane, compression, and timing. There are a few mechanical dependancies like stroke and piston speed. HP and size have little to do with it. Although, I've heard big blocks are more forgiving on pinging / octane. If this is true, it probably has more to do with the stroke than anything else (meaning a motor that can run higher compression on lower octane gas without pinging).

Well two that I can think of.

1) 9.7:1 355cid, 453 hp on 87; alloy head

2) 10.8:1 355cid, 629 hp on 93; Iron head

The first was real easy. But the second one was right on the ragged edge. It required cylinder and cam timing management to a "T". I would not recommend it for the faint at heart.

est. 400/400, 9.5:1 forged, 5.7 rods,406ci.,stock steel heads w/ gasket match and port and polish, 89 is "ok" if driving "sane", 91 for my "style" of driving , cause you never know, and a measure of safety. With a looser converter and taller gears, 87/89 might be ok.

12:1 comp 396" LT4 running on (the test stand) 93 pump
it should be awful darn close to 600 fly

I've run the TTA on 93 pump but not at full boost

the '68 is approx 10.25:1 alloy headed 333 incher and it likes the 93 just fine too

edit:
DOH!
forgot the '00, of course it runs on 93 w/ stock 10.1:1 compression making 377 @ the wheels

Ping resistance depends on octane, compression, and timing.

There are other factors involved in detonation resistance, like engine coolant temperature, local hot spots like the siamesed exhaust ports in the SBC's, intake air temperature and humidity, altitude, quench, combustion chamber shape, air/fuel ratio, residual gas/exhaust gas recirculation, etc.

Originally posted by onovakind67:
Ping resistance depends on octane, compression, and timing.

There are other factors involved in detonation resistance, like engine coolant temperature, local hot spots like the siamesed exhaust ports in the SBC's, intake air temperature and humidity, altitude, quench, combustion chamber shape, air/fuel ratio, residual gas/exhaust gas recirculation, etc. Exactly. Also, vehicle weight, aerodynamics, gearing, tire size, and torque convertors play a role. Cylinder head design (combustion chamber) is a very crucial element in ping resistance.

My nova (specs in sig) runs ping free with an estimated 450hp at the flywheel (est 350-375hp at the rear wheels) on 91 octane fuel. My truck, with a "magazine" estimate of 375hp at the crank and 180psi cranking compression, will tolerate 87octane, but I typically run 89 for a little saftey margin when hauling weight. A buddy of mines '70 chevy truck, with 305 heads (compared to my vortecs) on a flat top piston'd 350 and a 214/224@.050, 112 lsa cam, also cranks 180 psi. His pings like crazy on anything less than 92 octane, and he has 3.73's compared to my 3.08's AND heavier truck to boot. And my truck is still 1/2 second quicker in the 1/4 mile. Got to love them vortecs :D

Detination has a direct correlation with cylinder pressure. How come nobody mentioned cranking compression and cam specs? Saying I have x compression ratio with x horsepower does absolutely no good. Also just because one cannot hear pinging does not mean it is not happening.

Sorry Travis
Your post showed up after I was done posting.
Gave good info though.

Originally posted by 427ss:
How come nobody mentioned cranking compression and cam specs?We were waiting for you to mention it.

Originally posted by dnult:
</font><blockquote>quote:</font><hr />Originally posted by James67RS:
I guess it really depends on how small the engine is vs. how much HP it makes...

Ping resistance depends on octane, compression, and timing. There are a few mechanical dependancies like stroke and piston speed. HP and size have little to do with it. ... </font>[/QUOTE]My point was the soccerguy gave a HP but not a displacement. The mechanical requirements of a 350HP 350 are vastly different than a 350HP 454. Besides, mechanical dependancies based upon size and HP are entirely relevant, as there are significant differences in SB and BB combustion chambers and DCR/quench considerations. Not to mention all of the on point comments made previously.

That being said, the MTI 396 LT4 in the '97 runs fine on 91 Octane. That is at 11:1 compression with alloy LT4 heads. 460 RWHP. Does not ping but someone better add that computers open up a whole new world with respect to octane tolerances.

www.BGRSA.com (http://www.BGRSA.com)

[ 02-04-2004, 12:04 PM: Message edited by: James67RS ]

my Nova runs great on the 92 octane that's available here- only HEAR a slight bit of pinging under heavy load (lugging it like an idiot) during the hot days.
it's a 355 with flat top TRW lightweight forged pistons with 2 valve reliefs, .015 shim Victor Reinz head gaskets, stock Vortec heads, HOT cam and matching roller rockers, Performer vortec intake with 850 performer RPM q-jet carb, stock HEI with too much advance.
i had a LOT of pinging a couple summers ago when i had thicker head gaskets- in the .050 range cheapos that i used when i built the engine- and i had to back off the timing about 6 degrees or so to get rid of it, which cost me power all over the place. just putting in the thinner shim gaskets got rid of that and added what feels like 20 hp. brought my static compression up from about 9.5:1 to 10:1 and tightened up the quench accordingly. also even allowed a lot more advance in the distributor, which helped off idle performance. it sits at 16 initial now, if i remember correctly, and like 40 when it's all in- which i think is too much, but i need the off idle more than the WOT power. maybe i should pull that dist out and get it re-curved a bit.

365 RWHP on 93 octane. Compression is 11.3:1 with aluminum heads. Like Novaderrick said, quench height and combustion chamber design is critical.