"Porting" my blast gates - anyone else out there do this?

[Yitah Wu]

So I'm installing some aluminum blast gates from Rockler - they are decent quality "made in Taiwan" generic cast aluminum, appear to be like the Jet and all the other blast gates.

I decide the wall is much thicker than it needs to be and just so happen to have a fresh 2" 80 grit drum on the OSS.

Here are the results. The ID went from 3-33/64 to 3-44/64. Wow, 11/64, I'll have to dig out my fluid mechanics text to see what the difference in pressure drop might be.

At the same time I added a strip of velvet tape inside to help keep the gate from sliding too easily, and also a strip of tape to the outside to prevent the "self cleaning" leak when it's open. The way it will be positioned will more than likely keep it clean.

[Yitah Wu]

Here's the pix - the upper one is the one I "ported"

Yitah

[Jim Becker]

That's a great idea, Yitah! One of my biggest complaints about these cast blast gates, as nice as they function, is the big hit in duct diameter you take with them sitting inside the duct as they need to be.

[Dan Friedrichs]

I'll have to dig out my fluid mechanics text to see what the difference in pressure drop might be.

I'd actually be really curious to know that, if you actually check

I might have to do this to some of my gates...

[Jim O'Dell]

No, I haven't done that, but I did take a Dremel with a cone shaped grinding stone bit, and smooth out all the molding flanges inside the PVC wyes I used. Didn't really make them larger on the inside, but it did smooth the flow where the pipes join. I'm sure that gained me, oh lets see...... Jim.

[Yitah Wu]

Geometry says that the difference is a 10% improvement in area - 9.7 square inches vs 10.7 inches.

I measured the wall thickness at 0.165" at the base (Due to the draft angle it gets thinner towards the top)

11/64 is just a hair under 3/16 total in diameter, but since it comes off either side it's 3/32 off of a wall thickness which basically says I thinned the walls down by about 50%. To my eye the wall thickness is determined by the minimum casting wall thickness rather than strength
is well over 1/8".

a 10% increase in cross section says 10% reduction in velocity. I don't know the original velocity but since pressure drop is to velocity squared, this should reduce the backpressure drop by 20%

Not bad for 20-30 minutes on the sander!

[Anthony Whitesell]

I don't have the aluminum gates, but that is a great idea. Even if you don't go to that extreme, just kissing them on the OSS to smooth off some of the rough edges would help tremendously.

I use the black ABS ones. I got them before I knew about the 'creek and knew better. I have been slowly reporting the ABS 90's. They are about 4" ID at the outer edges, but only about 3" diameter at the center of the bend. There's a lot of overmold and flashing were the two "halves" meet. To clean them up, I put a drill press sanding drum on a pnuematic air grinder and turn down the air pressure (to slow the RPMs some). To prevent making a HUGE mess, I connect the opposite end to a piece of 4" hose and then a reducer to attached to my shop vac. The ABS plastic sanding debris gets sucked up right away, rather than blown all over and stuck to me. To get the wall thinned out and the hole opened up takes me on the order of 20-25 minutes each. But if you're like me an stuck with the 4" stuff, then it's best to get all you can from what you have. The wye's don't have the same over mold problem, just flashing at the intersection and clean up in just a few minutes.

[Michael Schwartz]

I have all cast gates on my system but I am tempted just to make my own next time around.

[Ed Labadie]

For 4" hose adapters on my homeade blast gates I used pvc reducers, 4" to 3". The 4" hose fits over the 3" end quite well.
Chucked em' up in the metal lathe and hogged out all the extra material I could to gain flow.

Every little bit helps.

Ed

[Paul Atkins]

That reminds me, I've got to do the same to my Edelbrock intake for my 289 ---(in my spare time)

[Chris Damm]

I used 5" and 6" blast gates and reduced to 4" or 5" at the machine. I think this is a much better way around the problem.