OK heres the basics of what I have.
13b motor with T2 side housings with 12a center running a weber Ida carb.

Main issue I see is the T2 ports are huge compared to the NA holes that are in the manifold. I was thinking about port matching them to the T2 size. I was told to leave them small and not to take them to the T2 size for 2 reasons 1) It would kill velosity 2) The small wall helps to stop reversion.

I have the manifold off now and am looking at the ports again I can see the reversion point, but as far as it killing fuel velosity I would think it would be the same when it leaves the intake runner and hits the actual port. Plus I would think it would flow better If I ramped the runner to match the port.

What do you guys think?

 

No one has any input?

What did everyone her do that runs a aftermaket intake do? Did you cut it out to match the gasket or just leave it alone?

 

what porting work do you have done? if its not larger than a half bridge leave it be. the area of and length of your intake will change how power is made. if you bore it out to match you will have little charge at low rpm making idle harder to achieve and round town suck, however if all your power is made uptop and you don't need a stable low*ish* idle or street driving you can open it up a bit.

 

If your runners in the housing plates is twice as large as the runner diameter in the intake, then your losing flow and depending on how the runners match up you can cause turbulence from the air hitting the sides. I bored the crap out of my IDA intake manifold and port matched all my runners on my 12a and picked up quite a bit of power. You obviously don't want to go overboard and make the runners too big also as you will lose velocity. With the large primary ports on the 12a center plate, and with the very small primary ports on the intake manifold, I had to bore alot of metal to get it right. I spent about 6 hours porting my intake and I could have done more. If you look down your IDA manifold from the top two large holes(where the carb bolts too) you can see how poorly the casting and flow is. Where the runners fork off there is a big thick divider/wall. Port that sharp like a knife so the air coming down just flows right down without hitting those walls. At least port match the intake to the runners and smooth down all the casting flaws in the manifold. Its a good idea to leave the port diameters on the intake about 1mm smaller than the diameter of the runners on the housings side.

There is alot of power to be made from the stock manifold with proper porting. It's just going to take practice and alot of know how because you have to have proper exhaust, jetting, timing for it all to work together properly for your application. Here are a couple of pics of my intake that I ported.

 

Thanks for the pics Thats great info. I think what I will do is port out to like 1/16" smaller then gasket size. I already smoothed out the roughness But I like what you did at the top.
I will work on that too.

Thanks again

 

No problem. Just take your time.

 

--------------------------------------------------------------------------------

OK heres the basics of what I have.
13b motor with T2 side housings with 12a center running a weber Ida carb.

How are you going to seal the water jackets? The 12A has the water O-rings in the rotor housing. The 86+ motors have the water o-rings in the irons. If you want to build a 13B motor with 12A irons use 84/85 GSL-SE rotor housings and 12A irons all the way around.

 

Motor is already built



Just getting info on what to do about intake while i had it back apart