What venturi size?

[Glenn (Gravitywell) Reach]

Hi everyone.  I am putting an OS Max FP .40 into a Fancherized Twister and I need to make a venturi for it.  I have a universal OS spraybar and needle valve that I will be useing for it.  What is a good starting size for the venturi?  Oh yeah....and if you can give me the size in inches I would appreciate it.  I don't have indexed drill bits! LOL  Thanks for all help.

[Phil Coopy]

Don't for a 40 FP but Ive been using a .282 with a ST NVA on LA40's and they work pretty well. I tried .295 but they had a tendency to run away in hot weather.

Phil

[Mark Scarborough]

I used both .275 and .282 venturis on my FP 40s, thats with a ST sized needle assembly. Biggest clue I found, load it with enough prop, and dont be afraid of castor, I was running 10x22 powermaster fuel with an extra 6 oz of castor added to help control the runs

[Glenn (Gravitywell) Reach]

ok...thanks, now what is .282 and .275 in inches.  Or is there a conversion chart I can download somewhere?

[Steve Helmick]

According to Leonard Neuman's chart, with the .135" OS spraybar, the venturi should be .265" (stock?) to (around) .281" for a stock .40FP. Uh, that would be 17/64" and 9/32", respectively.

Are you going to use the stock muffler? Which one is it? Look for the casting number...if it's the late type, leave the cone in it. Some say the APC 10.5 x 4.5 is the magic prop, but from all indications, the 11 x 4.5 Thunder Tiger will work as well or better...and cheaper...and nearly perfectly balanced out of the packet.  

Howzat Vector 40 coming along? Pictures!!!   Steve

[Scott B. Riese]

7mm is a good starting place for those that follow the worldly measurements 

[Glenn (Gravitywell) Reach]

Hi Steve.  Thanks for the info.  I didn't know that Leonard had a chart for this stuff.  I'll have to go and poke around there.  I am going to use the stock muffler on it, but I am going to take it to the shed first and grind a few ounces off her first! LOL

The Vector is coming along very well.  I took a little time off it to build this Fancher Twister.  I wanted a good beater to begin the season.  Unfortunately I can't post any pics till I get my computer fixed.  We're going into the big city tomorrow, so hopefully it won't be too long.