Polished vs. rough intake tract, which flows better?
Thread Starter
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Polished vs. rough intake tract, which flows better?
It seems intuitive that a polished intake will flow better, purely because it's smoother.
But, throw in some fluid dynamics and it doesn't seem so obvious.
A polished surface is supposed to be stickier and result in more viscous forces acting between the air and walls. More air comes in contact with the walls, and is akin to braking on a smooth road surface.
A slightly rough surface induces a turbulent boundary layer, and can free up more flow potential at certain flowrates. This would be more like braking on a washboard road. Small vortices and low pressure regions caused by irregularities near the surface prevent laminar flow from occuring.
Does this apply to out MPFI vettes? or are our flow rates well beyond this transitional region?
:lurk:
But, throw in some fluid dynamics and it doesn't seem so obvious.
A polished surface is supposed to be stickier and result in more viscous forces acting between the air and walls. More air comes in contact with the walls, and is akin to braking on a smooth road surface.
A slightly rough surface induces a turbulent boundary layer, and can free up more flow potential at certain flowrates. This would be more like braking on a washboard road. Small vortices and low pressure regions caused by irregularities near the surface prevent laminar flow from occuring.
Does this apply to out MPFI vettes? or are our flow rates well beyond this transitional region?
:lurk:
Melting Slicks
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Re: Polished vs. rough intake tract, which flows better? (CentralCoaster)
Well, air flows over air better than it does aluminum (golf ***** come to mind). With that said, too much roughness and it gets turbulent (sp?) a nice 80 grit seems to work well, maybe a touch rougher depending on application.
it also helps mix fuel and air from what i hear, not too sure. the combustion chambers you want polished though- not sure why- that it matters.
it also helps mix fuel and air from what i hear, not too sure. the combustion chambers you want polished though- not sure why- that it matters.
Drifting
Joined: May 2003
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From: Lakeport CA
Re: Polished vs. rough intake tract, which flows better? (TreyZ28)
Yup, word I got when I took my heads in to FreightTrain Petes for a cursory look at my port/polish was, "rough intake promotes fuel atomization, don't over polish combustion chamber as it also needs the turbulance or you will get reduced power due to unburned charge pockets". So, I re-ruffed up the one combustion chamber & continued on with the rest of the job as it was good.
Racer
Joined: Apr 2003
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From: OLD DIRTY BASTARD LIVE AND UNCUT
Re: Polished vs. rough intake tract, which flows better? (Trog)
Yup, word I got when I took my heads in to FreightTrain Petes for a cursory look at my port/polish was, "rough intake promotes fuel atomization, don't over polish combustion chamber as it also needs the turbulance or you will get reduced power due to unburned charge pockets". So, I re-ruffed up the one combustion chamber & continued on with the rest of the job as it was good.
A cylinder head intake track should be "rought" and not perfectly smooth though like you said.
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From: SE NY
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Re: Polished vs. rough intake tract, which flows better? (CentralCoaster)
I'm not sure where these flow dynamica come into play; the air flow in TPI runners is somewere between 200-300ft/sec (if my math is in the park).
I've read that the intake runners/ports and exhaust ports for TPI, which are "dry", should be smooth, whereas the chambers want a golf ball "divit" finish for best swirl and complete combustion.
I've read that the intake runners/ports and exhaust ports for TPI, which are "dry", should be smooth, whereas the chambers want a golf ball "divit" finish for best swirl and complete combustion.
Drifting
Joined: May 2003
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From: Lakeport CA
Re: Polished vs. rough intake tract, which flows better? (reallycoolcorvette)
Curious why you would thing injection would not still be "wet"?? It may be introduced further downstream, near the valve and if you injector is working properly a nice pattern but still you are adding wet liquid fuel into the air stream??
Sorry, re-read your message & yes, much of the intake tract is smooth but the intake port on the head is wet & that is all I was considering at the time.
[Modified by Trog, 6:09 PM 11/14/2003]
Sorry, re-read your message & yes, much of the intake tract is smooth but the intake port on the head is wet & that is all I was considering at the time.
[Modified by Trog, 6:09 PM 11/14/2003]
Team Owner
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Re: Polished vs. rough intake tract, which flows better? (Trog)
Right, so I'm thinking that for our TPI intakes swirl-polished valves are a real must on the intake for best power.
