Weber intake question

[Bill D]

I received my Weber intake manifold today and intend to port match the intakes. But I was also considering fully polishing the runners from carb mounting flange to the intake manifold flange. My intention is to improve air flow and velocity. Does anyone see potential problems with this idea?

Thanks
Bill D

[bobcowan]

Yes, there is. The rough intake ports help keep the fuel in suspension until it gets to the pocket. If you polish that up real nice, it will make the engine run worse at low rpm's. If you're using EFI, that's not an issue.

Also, be very careful about how tall you make the intake ports. If you're running big heads, port matched to a 1262R gasket, some manifolds can't be ported that big. Before touching the manifold, set it on the mounted heads and get the basic fit. They do a gasket match. Without the carbs/TB's, you can look right down the ports and see how they fit together.

[Bill D]

Thanks Bob

[Bill D]

I found some very good information on this topic. I thought I would share it

"This is def one of those subjects that can get people heated up but here's what MotoMan has to say about the matter...

Homework

Why Not Polish The Ports ??
Doesn't Air Flow Better on a Smooth Surface ???

Remember that the ultimate goal isn't "flow" ... it's POWER !!

The intake port is going to flow both fuel and air. The problem with fuel is that, since it weighs more, it's difficult to keep it evenly mixed with the air as it follows the contours of the port.

Boundary Layer

The next time you drive a car in the rain, notice that when the car is going 60 MPH, the rain drops go up the hood of the car at walking speed. That's because the smooth surface of the car creates what's known as a boundary layer, and the portion of that layer of air that's nearest to the surface is almost still.

The same thing happens inside an intake port. Except instead of raindrops, it's fuel droplets that will run down the port wall slower than the air. That causes a serious change in the fuel air mixture by the time it reaches the cylinder, ruining much of the engine's potential power.
Polishing the port walls will ensure that this happens.

The phrase "Port & Polish" always makes me laugh ... I think the idea came from 70's Hot Rod magazines or something. Anyways, the last thing you want to do is polish your ports !!!

Instead, by making a series of rough 60 grit lines that purposely go against the flow, the "boundary layer area" will be turbulent, and the fuel will stay suspended in the air.

Remember: Rough is Good !!"

[mickmate]

I was going to mention laminar flow and boundary layers but you got the idea already.
Injection has better atomisation and can be smoother, carbs like it rough. Spend the time on port matching instead.

[Bill D]

Will do Nick. Thanks everyone

[Snake2998]

Must say that on my Weber manifold the drillings were no where close to being correct for Webers - fortunately I am making up my own injection system so could weld up the mounting holes for the plenum mounting flange and sort things that way, but I wouldn't have been happy had I been using Webers. In fact I wasn't happy anyway.

[blykins]

I would barely touch them if anything at all. You do want velocity with the Webers, but you don't want to do anything to disturb that either.

Which heads do you have? I just made 475 hp with a 331 and Trick Flow heads, with a 1262 (not R) gasket, and a Victor Jr. intake that I pulled out of the box, cleaned up, and bolted on. The intake ports were smaller by a significant amount, so you can see the horsepower potential with a small runner.

[Bill D]

I have Trick Flow 205cc CNC'd heads, domed pistons (static 11.5:1 compression), Lunati hyd roller cam (.571/.587 lift, 112LSA). The TF heads use the R gasket, but i plan to port match the Weber manifold to the 1262 gasket..

Do you think I'll be making close to that number? Would be great if I did. Thanks

[blykins]

What duration?

With a 228/230 degree hydraulic roller with .560" lift and a 113 LSA, that engine made 433hp @ 6000 with a set of TFS Track Heat 185cc heads.

I would watch about port volume and valve size with the 205's, you want velocity with the Webers. Even more reason to leave the intake manifold alone.

[Bill D]

Cams specs as follows:

Advertised duration: 282/290
Duration @ .050: 231/239
Valve lift: 571/587
LSA: 112

[Gaz64]

As others have said, if you must touch the manifold, only a cleanup to remove the casting flash would suffice.
Smooth flowing is good (no bumps) but a rough finish is desirable to keep the fuel in suspension.
A slightly smaller manifold port than the cylinder head gives a step to reversion pulses and can help reduce "standoff".

[blykins]

IMO, that cam is not ideal for a Weber setup, especially combined with with the larger cylinder head. Webers prefer small amounts of overlap and reversion, even more so with a street setup.

With that being said, your cam is pretty stinkin close to the hydraulic roller that I used, so horsepower numbers should be very similar.

[bobcowan]

Originally Posted by Bill D

The TF heads use the R gasket, but i plan to port match the Weber manifold to the 1262 gasket..

That doesn't make sense. The goal of port matching is to match the ports to each other. You want a nice smooth transition from the intake port to the head port. Any steps will create unwanted turbulence.

If the heads are 1262 R, then the intake manifold should be the same.

BUT.... like I said before, many IR manifolds cannot be ported that much. Set the manifold on the engine and see how it fits before touching it. If it doesn't match, you need a different manifold. Been there, done that.

[Bill D]

I don't think the Weber manifold has enough material to port to an "R" gasket. I need to take the one off the engine and see how it fits up

[Rick Parker]

Double check with the carbs mounted on the manifold, be sure the Throttle bore in the bottom of the carb matches the manifold. Any mismatch there will cause problems.