what octane for 11 to 1 compression

11:1 is right on the edge for pump gas. Most stock 400EXs run 9:1. I'd try mixing in some 100 octane unleaded at about 50/50 and see if the pinging stops. If it does, you might need a cooler spark plug or to retard the timing a couple degrees.

You probably just need to tune the carb better. 11:1 doesn't automatically require race gas if your squish clearance is tight and timing is correct. Make sure the A/F ratio is rich enough at WOT and you're not running lean. My buddy runs 11:1 on 93 with no issues after proper jetting.

I disagree with just jetting it rich. That can wash down your cylinder walls. Octane is about preventing pre-ignition, not leaning out. If 93 isn't cutting it, try a few gallons of 110 leaded or a bottle of Torco. Leaded gas will also help valve longevity on older heads.

You might not need race gas yet. Check your squish band. If it's too wide, you'll get detonation even with high octane. Also, make sure you're not running too much compression for your cam. A cam with later intake closing will bleed off some dynamic compression.

Run at least 93, but I blend in a gallon of 100LL AvGas per tank. It's cheap and works great. Just don't use more than 1/4 tank of straight AvGas because it runs lean. Been doing this for years on my 450R with 12:1.

Before buying race gas, try advancing your timing? Wait, you said you have detonation. Retard timing a few degrees first. Most guys run 11:1 on pump premium with timing set at stock or slightly retarded. If that doesn't work, then look into higher octane.

I've been running 11:1 in my banshee for five years on straight 93 with no issues. But I run a cool head with proper squish and a good tune. Your pinging might be from carbon buildup or a hot spot. Do a compression test and check your cooling system too.

You can get away with 93 if you use a high-quality full synthetic oil. It helps cool the combustion chamber. But I'd still add a splash of race gas to be safe on hot days. Detonation will destroy your new pistons fast.

Partial disagree with the oil comment. Oil doesn't affect octane rating. It might help with friction but won't stop pre-ignition. Stick to octane booster or mixing. I use Sunoco 110 in my 11:1 YFZ450 and it runs perfect. Costs more but peace of mind.

Check your fuel pump pressure if you have a fuel injected model. Low pressure can cause lean conditions at high RPM. On carbs, ensure your float level isn't too low. I chased a detonation issue for months and it was just a clogged main jet.

11:1 on pump gas is fine if you've got a good ignition system. Weak spark can cause misfires that sound like detonation. Replace your plug and wires. Also look at your ground wires. Had a buddy that fixed his pinging by cleaning the frame ground.

I run 100% race gas in my 11:1 Predator. The smell alone is worth it. But seriously, if you ride hard and long, pump gas will cause overheating and pinging. Don't cheap out. One season of damage and you'll spend more on rebuild than on fuel.

What's your elevation? At higher altitude, you can run lower octane. At sea level, 93 might not be enough for 11:1 if the weather is hot and you're lugging the engine. Try retarding timing by 2-3 degrees and see if it helps before buying race gas.

I've been running 11:1 in my 250R on pump premium for years with NO issues. You might have a different cam profile that's causing more dynamic compression. Find your exact static and dynamic compression numbers. That will tell you what octane you really need.

Be careful with octane boosters. Most of them are garbage and can leave deposits. If you must use them, get one with MMT or real toluene. Better to just mix in some 100LL AvGas or buy a few gallons of Sunoco from the pump. It's safer for your O2 sensors if you have EFI.

You said you rebuilt it. Did you clay the pistons to check valve clearance? If the valves are hitting the pistons slightly, it can cause a knocking sound that mimics detonation. Also, make sure your piston-to-wall clearance is correct. Tight clearance can cause siezing.

I'd try running mid-grade or even regular with some octane booster first. Sometimes high octane fuel actually burns slower and can cause carbon buildup if you're not revving it out. 11:1 on 93 should work if everything is dialed. Retard timing, jet rich, and check squish.

Everyone talks about race gas but forgets about cooling. Make sure your radiator is clean and you have a high flow water pump or a fan if you're trail riding. Overheating will cause predet even on 110. I run engine ice in mine.

Partial disagreement with the rich jetting advice: too rich can cause bore wash and dilute oil. Aim for a slight rich mixture at WOT but not pig rich. It's better to use proper octane than to drown it in fuel. I've seen too many washed down rings from people chasing detonation with fuel.

Bottom line: if you're pinging on 93 with correct timing and jetting, you need higher octane. 11:1 is right at the threshold. I'd go to a 50/50 mix of 93 and 100 octane. That should give you the knock resistance without the cost of full race gas. Test it out.