Porting SU's

[col]

I have been reading a heap of threads that referred to porting SU's, but have not been able to find any posts on how its done.

Is it able to be done by hand , or are they referring to increasing the actual bore and adding bigger buterflys?

Thanks Col

[WEBEZEEed]

I would suggest you go pick up a book by David Vizard, Tuning the A-Series Engine. There is a lot of useful info about SUs along with all other aspects of a motor.There are some things you can do that do not cost hardly anything(mostly labor) that make a nice improvement in performance.In my case I saw H.P.& torque improvements in the 20-25% range!

[Dane]

I've thought about this quite a bit myself. Just by looking at the inside of an SU...I think the airflow is too turbulent...improvements in laminar flow might be just as good as simply getting a bigger SU.

 

For example, even when the air piston is at full lift, it still protrudes into the bore, so that air passing through the top of the bore smacks into the air piston and has to make a sharp turn to go around it. Grinding down the edges of the air piston so that it makes a smooth transition with the roof of the bore when at full lift would probably help, just so long as the portion of the air piston that goes directly over the bridge still makes full contact to maintain decent vacuum.

 

The bridge itself could probably be improved. It forms a fairly steep angle with the floor of the bore. If metal could be added in front of and behind the bore, then smoothed out to reduce the angle formed between the bridge and the floor of the bore, it might smooth out the flow even more.

 

You could also grind down the throttle shafts to reduce the obstruction it causes as well as making a smoother transition between the throttle shaft and butterfly valve.

 

Then theres air horn design and the availability of different air filters. A high flowing CAI wouldn't hurt...but would need to be fabricated somehow.

[col]

The air filters that are on my SU's now are the round paper type .These have a flat chrome plate less than 2" from the SU opening, so that the air has to turn 90 deg and then go through the filter. Even this must make some difference at high rpm (air flow).

Do the domed foam filters make any difference?

[WEBEZEEed]

Dane, use caution in the bridge area. It is important in fuel atomization, for drag racing it's probably ok.The other things you mentioned are covered in the book I suggested to col.

[gogriz91]

Have you thought about just polishing as much of the interior of the carb instead of porting it? I thought I had read somewhere where that had been done.