PTS Flowbench Forum

You're correct Shane, they were hand ported with a carbide burr finish. The exhaust ports had a smoother finish.



Ray

So when I am done with a intake port it might help to scratch it up with a 40 or 80 grit roll or sand paper? I have been finishing with 120 grit. From the picture of Larrys work is he kinda makeing small grooves?

haley63042 wrote:So when I am done with a intake port it might help to scratch it up with a 40 or 80 grit roll or sand paper? I have been finishing with 120 grit. From the picture of Larrys work is he kinda makeing small grooves?

The finish in the pictures of Larry's work is made by the carbide burrs Larry ports with.

Darin Morgan posted on SpeedTalk forum his best horsepower making heads were finished with the natural carbide burr texture.

I've used 40 & 60 grit cartridge rolls and 40 & 60 grit utility roll on a split mandrel for 30+ years with good results.

Like John mentioned most customers want to see a smooth finish even though they are losing horsepower.

Ray

The last head I ported had the rough carbide finish on the intake side, and polished on the exhaust side with 60grit rolls.

When I was asked why I didn't polish the intake side, I replied with, "do you want a port that works or a port that looks good in photo?, Because photos don't make power"

Ditto. Exhaust passages get close to polished when I do a 2 stroke. The intake passages get a rough surface so the fuel doesn't settle out.

I did a Rotax engine in a snowmobile used for drag racing. The first time the owner took it out, he almost looped it. Throttle response (and power) caught him off guard.

I'm to the point where I'm going to try anti-reversion grooves/channels near the ports (valve seats in a 4-stroke).

John

Racebrewer wrote:Ditto. Exhaust passages get close to polished when I do a 2 stroke.

I'm to the point where I'm going to try anti-reversion grooves/channels near the ports (valve seats in a 4-stroke).

John

Do you not think this a waste of time? I've never taken an engine apart to find the initially nicely polished pistons, combustion chambers and ex ports still clean and carbon free.....

What kind of ant-rev grooves/channels are you looking at using? I'm certainly no guru and am posting for debate purposes, but wonder if they are of any use at all. I feel that if you get your valve events, port shape and exhaust requirements correct it's the way forward.

Oh, welcome to the forum btw.

Thanks for the welcome!

I think its worthwhile. IMHO(of course), the smoother the exhaust passage surface the less build-up you will get.

I'm working mostly with 2-stroke, piston port, motors so the piston acts as the valve. I believe that a coarser than cast surface in the intake passage helps keep the gasoline from settling out. We are required to run Sunoco 110 (not the best gas for the application), and I think that the rougher surface helps atomize the gas. Throttle response is definately improved.

I haven't had a chance to do a before and after on the dyno yet, but its on the list for the winter/spring.

For anti-reversion grooves, I'm looking at a series of grooves at the bottom of the intake passage close to where the bottom of the piston first opens the port (and where it last closes on the way back down.

John