93 + 1/2 shot glass of 108 octane boost at 3 gallon fill up

 

There are some really big engines running on just 91.
If the little HD is pinging with it, it has other problems.

 

 

Compression ratio is only half the compression formula. Cam timing is the other half.

You can only build compression when both valves are closed. Well, as the motor starts it's compression stroke, the intake valve is still hanging open. So the piston starts coming up, but the intake valve is still open for awhile, and no compression is building.

So the timing on when you close the intake valve has a big effect on how much compression you get out of a given compression ratio. The earlier you close it, the more of the compression stroke is used for compression, and therefore the more compression you get. Likewise, the later you close it, the less of the compression stroke is used for compression, and therefore the less compression you get.

Bottom line, increases in compression ratio are normally only done in combination with a change in intake close timing, which of course is controlled by the cams. So to answer your specific question, if you for example raise your compression ratio to 10.5:1, but keep your stock cams, then yes absolutely, you'll likely create a detonation issue.

On the other hand, if you change your cams to a set that has later intake closing, at the same time you raise your compression ratio, you may end up with the same actual compression, therefore allowing the same octane fuel to be used. At least that's the idea.

Likewise if you swap in cams with late intake close timing, but you don't increase the compression ratio to match, you'll lower your compression and that reduces power and efficiency, especially at low to mid range rpms.

So cam timing has to be matched to compression ratio. It can all be calculated by the way. Knowing the compression ratio and intake close timing, along with a few other parameters such as rod length and bore/stroke, you can actually calculate out how much cranking compression to expect.

The reason for later intake close points is high rpm torque, which is better known as "power". The idea is to keep filling the cylinder as the rpm rises. Cylinder fill keeps happening during the early stages of the compression stroke because the incoming fuel has inertia. So for maximum cylinder fill, you want to close that intake valve at the precise moment the filling stops. The higher the rpm, the later in the compression stroke when that happens. So later intake close points are all about high rpm cylinder fill. You raise the compression ratio to allow the later intake close timing.

 

I would hazard a guess, that top engine builders/racers & high-performance ppl use the best & high octane fuel. If you are getting what you pay for at the pump, ( and that can be a IF), you should be getting cleaner additives on top of higher octane, I am poor & tight as anyone, but no more fuel than my bikes burn, I ALWAYS put in the best grade I can find, Regards "Big E"

 

 

Just a FWIW, aswracing = Arron from Hammer Performance
http://www.hammerperf.com/hpcrew.shtml

T.

 

The above is the explanation between static and dynamic CR.
The two can be very far apart.
Keep in mind as the RPM goes up the VE starts to move in.

 

 

With the stock cam, the engine will run out of air as it is not opening the doors quick enough or holding them open long enough.
The beauty is in the high perf cam , high RPM, one cylinder is helping fill the other if the correct exhaust is used.
Free dendrites right here ! LOL