82 usa 911 sc

[Farrell]

Hi Guys -

I have started down the slippery slope. I have a 82' SC with a USA stock 3.0L motor. i have the small port (34mm?) heads, and need to get them ported to the large port heads (39mm?) to take advantage of my 46mm PMOs. I want to purchase the correct size manifolds rather then buying the smaller set now and then the bigger set once my motor needs to be rebuilt.

I live in southwest Michigan, does anyone know of a good, traveling porter, that could do this with the motor assembled? I've talked with Richard at PMO and he said any good porter should be able to do this on an engine stand with the engine upside down using a carbide cutter, something that is non grit based?

Any help is appreciated.

Cheers,
Farrell

[Dpmulvan]

How many miles on the car?

[Farrell]

100k

[fred cook]

Just because something can be done does not mean that it should be done! I would never consider porting a head on the engine because of the debris that is made and because the valves will be in the way. Since your engine has 100k miles on it, you really should pull the heads and have them reconditioned at this time. Also, this would be a good time to replace the dilivar head studs in your engine. They are prone to breaking and need to be changed out for steel studs or aftermarket ARP or similar parts. Good luck with your project!

[Dpmulvan]

What Fred said

[Steve@Rennsport]

Fred is spot on.

Without understanding head flow in these engines, indiscriminately "porting" the heads to the early SC size can easily ruin the flow at all valve openings. Simply enlarging the port openings without addressing the area around the guide boss and the throat does nothing for you.

Having used a flow bench on 911 heads since 1977, I've learned a lot about these things and I simply shudder when someone decides to "home port" their heads as I know what they will do on the flow bench. I won't even mention what happens when even the smallest bit of aluminum finds its way into a cylinder at the wrong time,.......

FWIW, we do CNC these later small-port heads into the big-port versions and they do come out even better than factory ones, due to the consistency of that process. While not cheap, its a good way to go, especially for Spec 911 racers where every little bit makes a difference in performance.

My best advice, considering your mileage, would be to remove the heads, replace the (worn out) guides and replace valves as needed, if this hasn't been done. You can have them professionally ported at the same time by several people around the US who specialize in this work,

[Turbo_pro]

Originally Posted by Steve@Rennsport

Fred is spot on.

Without understanding head flow in these engines, indiscriminately "porting" the heads to the early SC size can easily ruin the flow at all valve openings. Simply enlarging the port openings without addressing the area around the guide boss and the throat does nothing for you.

Having used a flow bench on 911 heads since 1977, I've learned a lot about these things and I simply shudder when someone decides to "home port" their heads as I know what they will do on the flow bench. I won't even mention what happens when even the smallest bit of aluminum finds its way into a cylinder at the wrong time,.......

FWIW, we do CNC these later small-port heads into the big-port versions and they do come out even better than factory ones, due to the consistency of that process. While not cheap, its a good way to go, especially for Spec 911 racers where every little bit makes a difference in performance.

My best advice, considering your mileage, would be to remove the heads, replace the (worn out) guides and replace valves as needed, if this hasn't been done. You can have them professionally ported at the same time by several people around the US who specialize in this work,

I've read over the years about your flow bench and CNC work.
I was wondering what type of flow bench you use and what CNC machine you own?
I'm thinking about buying both.
I've owned a Super Flo 600 in the past but what do you own? pictures

I am leaning towards a Mori Seiki mill but I'm open to suggestions. What do you own?

[Farrell]

Yes, It was put in my ear that it was possible to do it while the heads were on. I thought it was ludacris as well.

However, I've decided to drive it for the summer and then pull the motor back out this winter and build it along with the trans.