What is the highest compression ratio that can safely be run on 93 cotane with aluminum heads? I want to get new heads and I like the looks of the 2.02 1.60 summit cast iron heads but with 67cc combustion chambers it would put my compression at about 10.6-1. Is this ok.

What are the specs on the cam you are going to run? As far as advertised duration on the intake and exhaust, lobe seperation angle and intake lobe centerline.

What are the specs on the cam you are going to run? As far as advertised duration on the intake and exhaust, lobe seperation angle and intake lobe centerline.

I have no idea what Im talking about so dont think I am arguing. But what does the cam have to do with anything? Both valves are closed on the compression stroke, so I dont think the fuel knows any difference other than compression ratio. Are you just asking for fun or am I an idiot? Or both?

My stock LT1 had a 10.5 to 1 compression ratio and ran great on 93 octane, but if I were building an engine I'd try to keep it around 9.5.

Your cam timing will play a major role in how much compression you can tolerate on pump gas. Just because your compression works out to be 10.6 static there are more variables in detonation resistance. With different cams your dynamic compression could be higher or lower meaning a lower or higher resistance to detonation.

Cylinder head combustion chamber effficiency, rear gearing, convertor selection. Compression alone will not determine pump gas ability. As much as magazine will have you believe it does. Just like their over exaggerated engine dyno numbers.

Car Craft is probably my favorite magazine because its mor geared toward the average car guy. I have to say when they built a supposed 540hp 383 and the car only ran 7.60's at best in the 1/8 was a complete joke.

Just trying to help.

Try here if it works??

http://members.uia.net/pkelley2/DynamicCR.html

I have to say that Pat Kelley's great ECR/DCR site is a good one!!

pdq67

bretd85

if both valves were closed on the start of the compression stroke what you say is true.

the problem is that the intake is still open when the piston is going up on the compression stroke.

depending on the cam timing this will bleed off cylinder pressure and allow you to run a higher static compression.

the dcr calculator is a very good tool to play with cam timing

Sorry it took me so long, the engine is built but I want more power. It is a Comp magnum 270 cam with .470 lift.

No more than 11:1,thats the highest I have seen people run real pump gas on. I had no issues with a iron head 289 10.75:1 on 93 octane.