Advantages of F+T CR? How much boost @9.8:1 = 14#s boost @8.7:1

[Steve C]

I bought another 760 with a blown engine, second one I bought in a year. The first has my rebuilt B230ft and runs great. I need to put together/find another engine (low/med budget) for the new car. I am considering using a b230f shortblock cause they are easier to find and cheaper.

If I wanted about the same power output from the b230f as I currently get from the b230ft @14#s what kind of boost level would I require?

It occurs to me that I could just use my extra good TD05 on a b230f at a lower boost level for the same output. Less boost equals less heated from the turbo and less need for an NPR swap, right?

I must be missing something though. In order to get x horse power I will need to use y amout of gas and z amount of air, right? Or does y amount of gas and z air equal higher horsepower at a higher CR. If it is that simple why the factory lower CR on the turbo motor. Less prone to detonation right?

I woke up thinking about this but it's too early for me to make sense out of it. Maybe it'll kick in later.

Thanks

[davidmacq]

Higher CR is slightly more effecient. Lower CR is used in order to use higher boost, and more threshold for detonation resistance.

[JohnMc]

A higher CR just mechanically harnesses more of the power from a combustion. It's the amount of expansion over which the piston gets pushed by the expanding ball of burnt gas before the exhaust valve opens and the remnants get puffed out into the exhaust system. That is one of the reasons diesels get better MPG, they have *very* high CR's (~20:1). (efficiency and HP are closeley related).

It's a fairly subtle curve, though, HP gain to CR increase.

[benflynn]

i did the swapp and it is night and day, i love the +t and it makes all sorts of power out of the t3/t4(.60/.48) at 13-16(spike at 18). The only setback will be the upper limit of boost but all that can be gained back w/h2o inj, sam ran upward of 25psi on his well tuned +t