mills281e

LT's will make you lose boost too....

defconfire

Anything that increases the engine's airflow efficiency will lower the manifold pressure.

A prime example of this is when people get sets of blower cams, they end up "losing" maybe 1psi but see a significant gain in hp.

DeathRattle

Ok, there are several different things that will lower the boost...however boost is not the say all end all...a choked up inefficient engine with x amount of boost will make far less power than an engine that is more efficient with less boost...thats why installing heads, cams, intake, extra displacement, and so on will increase power despite causing a decrease in boost...and THEN when you increase boost to the more efficient engine you have a monster...

RuffCat

The long of the short, larger diamter tubing like big powerpipes and oversized headers or Longtube headers all lower boost. The larger air pocket inside the heads due to a larger dish is what lowers the boost as well as the gas pressure. The actual boost pressure is lowered, but in all reality the same amount of air is being pushed through, it's simply the gas pressure that is being reduced.


Beond that information, there is an additional component of the problem to consider, the gas expansion. After the mixture is combusted, the higher compression engine achieves higher cylinder pressure due to the higher initial pressure (and higher temperature). The higher compression engine also sees higher combustion temperatures. Things change very quickly as the piston moves away from TDC however... because the high compression motor had a lower initial combustion volume, it's cylinder pressure drops twice as fast. By the time both systems reach the bottom of the combustion stroke, the high compression cylinder has half the initial/final pressure ratio. Becuase work is calculated by the integral of P*dV, this means that it produces less work; even if both engines had the same cylinder pressure and temperature initially, the low compression motor would produce significantly more torque at a given RPM.

It is thus safe to say that reducing the compression and increasing the boost will in any situation yeild more power than the opposite. The high boost setup is of course less tolerable in traffic because it takes more time to respond to throttle inputs. If higher compression and lower boost were more effective, what would be the point of a turbocharger anyway?

98SN95

BOOST= replacement for displacement

Sxynerd

Glad you added that, i'm sure it really helps.

DeathRattle

haha, that's funny...but anyway, it's not like your car is not gonna move when the CR is low...besides, a twin screw or roots style blower will give you all the low end response you need...and if you have a centrifugal blower you could swap in a smaller pulley which will increase the boost and bring you into boost at a lower rpm anyway...it's not like grandma in the Toyota Corolla behind you is gonna pulling up on your bumper ya know...and if you're gonna race some a-hole you could always stall it up too...