What is the Highest Compression i can run with 93 oct safely ?
Depends on how cool your motor runs inside, what kinda work you have in the combustion chambers, how high or low is the ambient temperature, how the motor disipates heat and heat soaks.
The one and only detonation aka knock aka pre-ignition should be on your mind.
I personally think 11:1 would be pushing it.
Best time:"""11.946""" @ 114.73 mph @17psi 1.83--60"
11 second daily driver!!!!
Race Related 727-561-9440
Shop of choice for your 11 second J body!
Also, built bottom end and or top end LSJ and L61's available.
13's
----12's
----11's
----10's
Hurmmm and how is that shifted ? and also lets say 11:1 with a 75 shot will 93 cover it or even 10.5:1 ???
so with the software no MSD is NEEDED ?
Just curious what kind of power are you making now with the software ? timeslips
?
Yes, you can run 13:1 but if you pull the crap out of the timing like you have to do then you are really NOT benefiting from your high compression.
More like bragging rights to your friends.
I have a 13:1 that could make 200 to the wheels at 19 degree advance but I am running it at 11degrees because at 19 it is knocking like the police on the crack house door and I am only making 160, what is the point??
Best time:"""11.946""" @ 114.73 mph @17psi 1.83--60"
11 second daily driver!!!!
Race Related 727-561-9440
Shop of choice for your 11 second J body!
Also, built bottom end and or top end LSJ and L61's available.
13's
----12's
----11's
----10's
Just curious to see how many of you know the actual PSI number that the engine's cranking compression can not surpass without needing to go past 93 octaine gas.
yes there is an actual limit and the compression ratio really doesn't play into it as much as you all may think. I know this sounds like a crock of sh-t but I assure you its not.
So does anyone know?
Semper Fi SAINT. May you rest in peace.
head design, piston head, compression and timming play alot on the tolerance of detonation. Eliminate any sharp edge, dent and other little piece that are sharp and you'll be able to get high compression with 91-93 octane. IE: the surface between the valves, the edge of the combustion chamber, ... It's not as easy as putting parts together and start the engine.
Take the Ho for example. They need 91octane from factory and they run at 10:1 compression. Yet, the Eco run at 10:1 compression and run on 87 octane gas. They have different head and pistons, casting is better, ....
Btw, pre-ignition and detonation are 2 different things. They are not the same.
Pre-ignition is mostly cause by sharp edges and dents that get too hot and ignite the fuel before the piston reach TDC.
Detonation is when the gas doesn't burn uniformely. It will explode in a bunch of place while it's suppose to explode on top and burn going down.
Gilles
2.3 Ho
The Ho, at 10:1 compression, as 210-215psi. If you use 89 octane, the engine will run like s***.
Gilles
2.3 Ho
^ ^ ^ ^ Thats because 210-215 psi is pushing the limit of even 93 octain gas. Take for example the new 572 Chevy big block, it has 13:1 compression BUT only 200psi cranking compression due to its cam profile. So even tho its running 13:1 compression you can still run pump gas in it with no problem. Now my old Pontiac big block ran
10.5:1 compression but had 210 psi of cranking compression so technicly my 10.5:1
engine had more compresion then the 13:1 engine. Cranking compression has the final word in what fuel you need to run not compression ratio.
Semper Fi SAINT. May you rest in peace.
^ I know the cams have something to do in the compression ratio. Alot of people here said no to me a few years ago when I said that cams can change the compression.
Like I just bought a set of W41 hot grind 2 (.430" lift and 222° duration compare to .410" lif and 212° duration of the Ho cams) for the Gtz. I'm anxious to see what the numbers are going to be. I had 195psi with 9.63:1 compression. 175psi for the 9.5:1 compression of the Lo.
Gilles
2.3 Ho
Heres where the confusion starts. The cams don't actualy change the engines compression ratio but rather they allow some of that compression to bleed off. If you have a lower compression engine you want a cam profile that will make sure the valves are shut before the piston starts its compression stroak. That way you get as much cylinder presure as possible to make the biggest bang possible. The famous choppy sound all the hot rods have is because the cam allows some of the presure to bleed off there-by lowering the cylinder presure. It has to due with cam timeing and where the center line of the cams lobe profile is. But basicly the higher numaricaly the center line is the higher the cylinder presure will be allowing the engine to take better advantage of the compressed air. Thats why my old Pontiac engine even tho it was only 427 cubic inches ( 7 litres ) it was putting down over 550 hp at the rear wheels. Less the 100 hp difference between my 427 and the new 572 and my numbers were at the wheels not the engine. Compression ratio is only the begining and if someone trys to tell you differently Mfk-223 its cause they really don't know how an engine works. All the compression in the world isn't worth squat if you don't seal the cylinder and thats the job of the valves driven by the cam.
Semper Fi SAINT. May you rest in peace.
