Raising port floor question

[Truckedup]

From what I understand raising the port floor can increase the distance between the short side radius and valve allowing a better flow around the open valve. And it increases velocity that will be slowed by the port change in direction. Are both these statements true?

[mag2555]

just adding in material to raise the floor will increase the port velocity even if no increase in flow comes about as you have made the port area to port flow ratio smaller!
If raising the flow also brought about more high lift air flow in and of itself then the port was not shaped right to begin with and once again the before mentioned ratio would change even more!

And most important this type of work is not something you want to thrust into without good access to a flow bench!

[Truckedup]

I had a guy do headwork on my vintage 650 cc Triumph LSR race bike.I can see where the port floors were raised and the port roof slightly raised but overall the port area is a bit smaller.....On the dyno the head work gave 8 percent more peak power at 300 rpm higher than before the work. This gave 3 more MPH to my existing class record.....

I'm interested in the theory that raising the port floor and increasing the distance from the short side port radius and valve seat straightens air flow around the valve...

[pamotorman]

back in the day I did my 390 CFM carb,9:1 CR short track heads filling in the "dip" in the port floor with marine epoxy. got to be carefull these days as the all chemicals in the gasoline could soften the epoxy.

[twl]

Well, each application is a little different, and there are some things that "generally" apply very often, if they are done correctly for the application at hand. These things you mention don't always work the way you surmised, but sometimes they do if they are done well.

Very basically and generally, the higher the floor, and the gentler the short turn, the better the air can approach the valve without(or with less) separation at higher flow speeds. If separation happens from too tight a short turn, then most of the air blows out the long side of the port/valve, and you don't get effective use of the entire valve circumference.

[jim_ss409]

I'm interested in the theory that raising the port floor and increasing the distance from the short side port radius and valve seat straightens air flow around the valve...

I gather that even if you didn't change the short turn in any way, there's a potential benefit to raising it.

One of our Speedtalk members, Erland did some testing with pipes and found a big improvement in the flow simply by adding an extension to the pipe after the bend.

This pipe flowed 259 cfm.



The same pipe with an extension flowed 289.9 CFM (12 percent more )



This 90 degree bend with an extension flowed 286.6 CFM (almost 11 percent more than the top 45 degree pipe with no extension)



Just as a reference a straight pipe with no bends flowed 293.4 CFM

[jmwsb2]

FROM MY ESPERIENCE RAISING THE FLOOR AND TOP OF THE RUNNER MADE THE CAR RUN FASTER. I AM NOT A PORTER BUT I KEPT RAINING THE TOP AND BOTTOM AND 100 THOUSAND AT A TIME. EACH TIME THE CAR WENT FASTER. BY RAISING BOTH 300 THOSAND IT PICKED UP TWO TENTH'S.

JOHN

[Truckedup]

Those pipes photos above might also say slight turnouts used on exhaust pipes might be more restrictive...

[MadBill]

To some extent, the iterations of raising the floor then raising the roof just amount to gradually straightening the port towards a Superbike/F1 configuration...

[MadBill]

Those pipes photos above might also say slight turnouts used on exhaust pipes might be more restrictive...

Wonder if he's tried a flow vane down the center of the pipe?