If I put pi Heads on a non Pi 5.4, will premium fuel be required at a 10.5-1 cr?

 

I'm not the best engine expert in the work, but I can tell you compression alone is not even remotely the only factor. Ignition timing is a very big part of the equation as well as how advances the ignition system is. I'm sure there are many other variables someone can add.

 

Read this article it may answer some of your questions.

http://auto.howstuffworks.com/premiu...-vehicles1.htm

 

Sorry but that didn't help.
Based on my experience with motorcycles a 10.5 to 1 cr is still low enough to possibly run regular or plus gas, but that doesn't take into consideration all the variables this truck engine would encounter.
All of the posts I have seen here and the Stang forums suggest it is necessary, but no one has any experience to back it up.
I understand one can back out time to prevent issues, but I wouldnt want the engine to be a slug simply to run regular. I was hoping to find someone with 1st hand experience that could comment.

 

Running 10.5:1 cr on reg gas would be dangerous and counter productive. The ecm will be pulling all kinds of timing out to stop or prevent spark knock thus killing whatever power you hoped to gain. And if the tune doesn't allow it to pull enough timing to stop the knock she's gonna blow. As stated above a lot more goes in to this then just cr and octane. Aluminum heads, cam profile, even head gasket thickness all come in to play along with cylinder pressures. But to keep it simple heres a chart based upon an engine without any kind of ECM. With an ECM the Octane ratings can be dropped by 5-7 points. In a truck thats heavy to start with and may be used to tow I would definitely run 91-93 octane at all times and give the knock sensors the ability to add timing to an extent (based upon data logging and dyno tuning) and remove timing as much as needed to stop a knock on the first or second attempt.
Compression ratio = Octane (no ecm)
5:1 =72
6:1 =81
7:1=87
8:1=92
9:1=96
10:1=100
11:1=104
12:1=108

Since you haven't mentioned any cam change, head porting, or forced induction, or NOS you should be able to get away with this since the heads are aluminum. Aluminum heads transfer heat to the coolant much quicker and efficiently than cast heads thus helping keep cylinder temps down and prevent detonation. I would also run a 170 or 180 stat. Again you will want the highest octane in it at all times.

 

Twinskrewd,

Great info! That's what I was looking for.

Thanks

 

No problem. Just remember if you go through with this tuning, fuel octane and fuel quality will be your keys to sucess . This is something I deal with everyday having a final CR of around 18.1 with the boost I run. Good luck and I hope you will post up the results.

 

I hope to post results!
I have been giving serious thought to doing a 4.6 to a 5.4 swap. The only good engine I can find within 200 miles is a 98 5.4. I would prefer to run a 99, but haven't been able to find one without stupid high miles or one that looked like it still had the factory oil in the engine! I need to get off the pot to make it happen. I only have another 2.5 months before I need to start dragging a boat!