Here's a comparison that is very close comparing a stock shortblock with GN1 ported heads with .040 gasket for a net of 8.3:1 CR to a good strong rotating assembly with a girdle netting 9.3:1 CR. With just about everything the same except the cam @28-29psi the stocker with 8.3:1 trapped 135-136mph. At 25-26psi the 9.3:1 engine trapped 137-138mph. Both were numbers were acquired with a tnetics 6680 that was run for all it was worth in lousy 80*+ air at 1100'. There's a lot more than 3% there for 1 point increase in CR. Those that say oh it's only one or two psi more boost to offset it clearly don't understand why that's not really possible in the examples I just gave. There a window on the CR just like the turbo. If I had a turbo on there that would flow over 80lbs/min that one or two psi statement would be more accurate. If the turbo flows 75lbs/min then it doesn't matter what boost or rpm. 75 is 75 and it's the limitation. if the turbo is being used close to where it's flowing it's max CR increases will help a lot if they are below the window. Especially with a back pressure combo like just about everyone else on here is using on their street cars.Alky V6 said:I've built more than a few 8 to 1 motors for people, mainly street use, and performance and spool up have never seemed to be an issue. If anything, with the turbos that most people are using on the street, the spool up was too quick for my liking. One was spooling so quick, transitional knock was a problem. He was running a turbo tweak chip that had to be sent back to be re-programmed. You guys make it sound like 8 to 1 is such a pig. Isn't the stock CR 8 to 1? A lot of people have done some pretty amazing stuff with an unopened short block, yet 8 to 1 is for pigs? I don't get it.
You know, some people have no business playing with CRs above 8 to 1 to begin with. I'm sure Norbs will do fine, but you know what I mean. Sometimes you have to look out for people and set them up with something that will survive the stupid stuff that happens sometimes. Even 8 to 1 doesn't guarantee damage won't occur with a novice behind the wheel.
8 to 1 makes a pig. Amazing. I guess my customers are just coming up with better combos.