i have read that normal Pports are 2" , has anyone ever used 2.5" or 2.25" Pports? or is it imposible???

 

2" Diameter P-Ports is probably how it all started but, most Engine Builders or machinist I have found are using 2.25" as a standard now. If your shooting for big horsepower I would use the larger 2.50" style with tapered inlet on the P-Port tube. Now just because the outside diameter is 2.50" does not mean it has to be that big on the inside of the tube. This is when all the black magic stuff happens with porting styles and when you want the horsepower to come in sooner or later. I know a couple of machinist or engine builders that could help you out. I am at work right now so when I get home I'll post some pictures of my housings and contacts.

Albert

 

what is the thickness of 13b rotor housings?

 

80mm.

 

A 2.5" port would have crap velocity unless it could be revved extremly high. MFR ports are 43mm.

 

or 3"

 

This is personal opinion of course but I feel that anything larger than about a 2" or so is too large. Bigger is not always better.

 

So what's the recommended size for a 12a?

 

80mm = 3.1495" not 3"

And I'll have to agree with some others, bigger is NOT always better and velocity is key to making power, not just flow.

~Mike...........

 

I personally went with a 2.5" P-Port sleeve because the transition from the base of my carb to the a 2", 2.25" inlet was radical. I wanted something that would flow much smoother and not have to make such a drastic jump from 2.75" to a 2" intake port. So I decided to go from a 2.75" carb throttle plate to a 2.50" gradually using transition steel tubes into the P-Port at the block.
Majority of the racers are using Fuel Injection and the standard throttle body setup available on the market is the 55mm from TWM. I did something totally different because I am more comfortable with a carb than I am with fuel injection.

 

I used 40mm!

But I'm odd that way.

It was a nice confluence. The port timing I wanted necessitated runners no larger than that, the tubing I used was easy to source in that size, and drilling a larger hole than that in the housing just gave me the *******. Oh, and the location of the hole I bored made it easy to secure the tubing I chose (steel not aluminum) using existing holes in the housings.

More info at http://www.geocities.com/izzmus/shotgun/shotgun1.htm

 

^ Wow nice work.

 

is it running Peejay? looks like a lot of work went into it! hope it's now in a car and all sorted out. sweet mani and intake, very interesting how you flipped those bends and kept under hood clearances.

 

YES it is running. I am just trying to get a carb on it!

The 750 was a bad idea since it will pretty much only run on the primaries. This is causing a fuel starvation issue, since the float valve cannot flow nearly enough volume for the engine. Additionally, the idle circuits need to be reworked (holes drilled in the primary throttle blades so they can be closed enough for the idle circuits to work properly, *may* need to alter the idle circuit fuel restrictors (equivalent of idle jets). figure if I have to do all that I might as well get a decent sized carb like a 390 or a 450, which coincidentally enough my boss happens to have... somewhere. So I am waiting on him to locate the carb in his stash of parts. Until then, I have plenty of work to do in putting the rear suspension back together, which incidentally is done except for the "cover the giant holes in the floor" part. The tough part.

I did try a Nikki. DAMNED small. Way way waaaay too small a carb.