You are always better off with a port that is the correct size for the
engine than too big. too big and the torque goes down. it is pretty hard to
make any HP without torque. the average engine losses around 15% torque
between peak torque and peak HP. no torque no HP.. A correctly designed
cylinder head has the correct numbe of sq. inches for the proper airspeed
and the greatest flow at that number of sq. inches.
dave
> -----Original Message-----
> From: owner-land-speed@autox.team.net
> [mailto:owner-land-speed@autox.team.net]On Behalf Of Jon.the.Wise
> Sent: Monday, February 21, 2005 7:38 PM
> To: LandSpeed
> Subject: Re: Intake sizing.
>
>
> But bigger is not always better. If you look at Mitsubishi's 4G63 head
> design, you'll see that the older heads had larger intake ports, but
> the newer heads with slightly smaller ports have a better angle into
> the chamber...
>
> What happens is that the larger ports can flow more air, but the air
> along the walls of the ports is moving MUCH slower than the air in the
> middle of the port, and then when it hits the absurd angle it must
> take to get into the chamber, that slows things down even more,
> whereas on the smaller ports, the air velocity stays more consistant
> throughout the entire airstream, and has a more gradual angle into the
> chamber...
>
> Unfortunately, that doesn't really prove a whole lot on it's own, but
> the theory is, you want to be able to size the ports so that they are
> just big enough to flow the air you want to flow, and still small
> enough to flow it with even velocity.
>
> It sounds like you were aware of this and with the timeframe just went
> for bigger, which *IS* better than too small ;o)
>
> As for the other... how long is the line and where are you referencing
> boost from? Does your fuel pump support the amount of fuel you wanted
> to flow that the referenced PSI? What did you use to determine that it
> wasn't increasing pressure, a guage, O2 readings, exhaust temps? Do
> you have a wideband O2 sensor? (very useful in determining the
> rich/lean condition) And are your injectors up to the task you're
> giving them? (I've seen people with 2 liter motors pushing 1200cc
> injectors to their limits with a well tuned motor and a lot of boost)
>
> I'm definately not an expert on tuning, but those are the things I
> would look into... your idea of putting a stronger line on it isn't
> bad either, just may or may not be the problem.
> --
> ~Jon
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