Chamfered Intake Ports

[Brrrrp]

I am installing a set of Webers on my '72T. They were originally set up for a 2.4S motor with 36mm ports, so the manifolds have been ported to 36mm. Would there be any benefit in "chamfering" the 32mm port out to 36mm? In theory, it would seem to provide less disruption to the flow than the 90 deg "step down" to 32mm.

Thanks.
Roger

[snowman]

It certainly would be of great benefit. A step is the worst thing you can have in the intake flow. Make the change as gradual as possible, ie take a whole inch in length to accomplish the change.

You can verify this for yourself if you make a flow bench using a shop vac. Make a monometer using a 2 foot u shaped length of plastic tubing. Use water in it. Drill a small hole in the side of the vacuum hose for the manometer to connect to. Now you have a flow device. Start by using the manifold as is. use the head without any valves in it and connect the vacuum so it pulls thru the head like the intake would, have the intake connected. You will get a reading on your manometer. mark it as a referance. Now start champhering the step. Do so until you no longer get a degrease in readings. You could establish a referance by not having the intake connected to the head and use modeling clay, rolled into a one inch diameter roll, and form it around the intake port to smooth the air flow into the port. The clay should slowly and smoothly roll into the port, no steps. You could start without the clay, note a reading, add the clay and mold it until you get the smallest change in manometer readings. Ie full flow vs interupted flow. This may be confusing so I would recommend a couple of books on air flow if you are interested.

[Brrrrp]

Thanks for the feedback. Whatever I do, I'll be doing with the heads still attached to the motor. It's on a stand, so I'll plug the ports and turn the motor so the top angles down (keep the shavings out). I'll probably just try to angle them out a bit to the 36mm point, using a gasket as a guide. Even a 45 deg angle should be better than leaving the step.

Roger

[Wayne 962]

While I agree in principle with snowman, it probably isn't worth it on your T engine. There will be other bottlenecks to performance that chamfering probably won't give you any significant gains. It can't hurt, but I really wouldn't mess with it...

-Wayne

[snowman]

Awwe come on. A T ain't that bad, is it?

[cstreit]

Why not just find a set of the proper intake manifolds? I'd be worried about hogging into my heads. especially when they are still attached. One stray shaving could wreck a cylinder wall.

[snowman]

I wouldn't worry about stray shavings to much as they are Aluminum and are not likely to do any damage unless they clogged up an oil passage. I strongly suggest a carbide cutter though. Stones are messy and stone dust will ruin anything it contacts and is difficult to clean and keep track of. My opinion on the danger from this operation is about the same level as changing spark plugs.

[911pcars]

If you decide to do this, rotate the crank so the intake valve is closed on the port you're enlarging. Place a shop vac nozzle nearby to catch the aluminum chips and wear eye protection.

Use the intake manifold gasket as a template for both intake manifold and intake port so the holes line up. Machinist blue and a scribe helps too. As Snowman suggests, use a carbide cutter and a high-speed grinder, but take it slow and easy. You don't want to end up with 50mm ports.

Sherwood Lee

[snowman]

Good points.

[Wayne 962]

Yikes, didn't realize you wanted to do this with the heads still on the engine. An absolute bad idea.

-Wayne

[Brrrrp]

I'm certainly not an expert, but it really seems more time consuming than "dangerous". Well, I may just get a new pair of manifolds with 32mm dimensions (maybe some "Monsters"). The $350 spent here maybe better than spending the better part of a weekend carefully grinding on my ports.

Thanks.
Roger

[911pcars]

Roger,
I'm sure you can use your 36mm intake manifolds as better-than-even trade bait for a set of 32mm T manifolds. Put the word out and I'm sure you can consumate a deal in short order.

Sherwood