Hey guys, I have an 02 Lightning that I am building the engine in. I had a local shop order the frist roatating assembly and it was all 4.6 stuff which wouldn't work except for the pistons (or so I thought). I did not double check the compression ratio until I got the heads on and the cams timed. The pistons are Arias .020 over. They are 9.7:1. the heads were ported and polished with larger valves by Champion Racing heads. The combustion chamber was slightly enlarged. I am not sure how much. But my question is will I have TOO much compression. I wanted 8.5:1. I am running a t76 from proturbo. Do you guys think I will be ok with this or do I need to tear the thing back down and buy a larger dish??? I also have a Kellogg Crank and Manley rods. Snow W/M system, 55 LbHr Inj, 5/8" Motoblue fuel rails and dual 255 pumps with zex plugs and accel coil packs.

 

9.7 is fine. I would have went with a little more.

 

I would run it. Not sure on those accel coils I would put ford ones back in.. I have had nothing but problems with after market coils..

 

9.7 will be fine

 

i would never build a boost motor at 8.5

my turbo motor was setup for 10.25cr

 

I think 9.7/10:1 is the norm these days. Mine is around 9.8:1

 

Compression is fine, cam it for the combo not build to the cams. I would like to see bigger injectors, better coils. Depending on the turbine side of that turbo, it and fuel will be your limits.

 

If you ordered 4.6 pistons set to be 9.7:1 in a 4.6 then you will be at 9.11:1 in a 5.4 with stock stroke. This will be fine and fairly close to 8.5:1 and keep in mind that the higher compression ratios out there are running better than 92 octane fuel with any boost over 16 psi.

 

deleted

 

I agree with all the posts indicating 9.7 CR will be ok. But there seems to be too many traps here. I doubt you will ever have a clue what compression ratio you have. You need to pull the heads off and CC the combustion chambers and measure your piston deck height.

You have added 7.5cc volume due to the .020' overbore. The lightening has a 4.157 stroke but the 4.6 is a 3.543 stroke. What rods are you running? What is the piston deck height? What is the thickness of the head gasket? How much did they enlarge the combustion chamber? Without cc the combustion chambers and measuring all the other stuff you don't have a clue.