Boring a Tee Dee for pressureized fuel feed

Rusty,

It is not necessary to bore the venturi just because you are using a pressurized fuel system. When I get home tonight I will measure a bored venturi and get back to you.

Bob

You don't bore it out so you can pressurise it you pressurise it so you can bore it out.

Just measured it. .153" with uncertified calipers. A #22 bit was the largest I could get in the venturi without working at it.

fit90 wrote:Just measured it. .153" with uncertified calipers. A #22 bit was the largest I could get in the venturi without working at it.

That's probably the size on mine, seeing as how you're probably the one that bored it. It's just a point of curiosity more than anything. Mine runs good with the current setup. In fact it runs so good, I'm fixing up the plane. I even made a new pilot head for it. The old one must've gotten scared and bailed out while I was test flying.

Rusty,

I just checked the venturi with fractional bits. The venturi was bored to 5/32". If your venturi has a screen on it then I did not bore it out. I always remove the screen first.

You could start out with a 1/8" bit and run the engine and keep working up to bigger bits as long as the venturi does not get too weak and you like how the engine runs with it.

Good Luck,

Bob

Gentlemen,

First off, boring out the venturi only really works well when the engine rpm is expected to go over 20,000.
Assuming your prop/ fuel/ engine combo will do that then you with definately see then benefit of using a pressurized fuel system. Going up to .140" I.D. is the standard number. The late Joe Klauses K/K pressurised venturi's went as high as .150". They work well in the 22-24,000 rpm band. Of course I wanted to know the limit & went up to .165" ID. That venturi lost noticeable rpm compared to the .150 venturi. So I learned that bigger is not always better. IF one cuts the prop down to a silly small diameter & raise the engine rpm up to 26,000, then the .165 can show a small gain. BUT such a prop is useless on a plane & also causes the engine to die a very early death w/ piston failure etc.
And another thing. Joe Klause decribed enlarging the venturi using a tapered reamer, keeping things very nice & smooth. Just drilling out a bigger hole with a common drill CAN in some cases cause a loss of rpm.
If anybody is interested, I have a supply of TD pressure venturi's for sale ($10 each + post) or can ream a new one to your 'magic number' if you wish...

Merry Christmas Everybody!

Paulgibeault wrote:Gentlemen,

First off, boring out the venturi only really works well when the engine rpm is expected to go over 20,000.
Assuming your prop/ fuel/ engine combo will do that then you with definately see then benefit of using a pressurized fuel system. Going up to .140" I.D. is the standard number. The late Joe Klauses K/K pressurised venturi's went as high as .150". They work well in the 22-24,000 rpm band. Of course I wanted to know the limit & went up to .165" ID. That venturi lost noticeable rpm compared to the .150 venturi. So I learned that bigger is not always better. IF one cuts the prop down to a silly small diameter & raise the engine rpm up to 26,000, then the .165 can show a small gain. BUT such a prop is useless on a plane & also causes the engine to die a very early death w/ piston failure etc.
And another thing. Joe Klause decribed enlarging the venturi using a tapered reamer, keeping things very nice & smooth. Just drilling out a bigger hole with a common drill CAN in some cases cause a loss of rpm.
If anybody is interested, I have a supply of TD pressure venturi's for sale ($10 each + post) or can ream a new one to your 'magic number' if you wish...

Merry Christmas Everybody!

Thanks Paul
I have one that's apparently stock and one that's bored. I'm not competing or anything like that, I just play at stunt flying. So whenever I can get some flying time I'll switch between the two venturis I have and just decide whichever one runs best. I'm more concerned with consistent speed than highest speed.