i am in the process of changing out my header gasket collector gasket, just all sorts of stuff. right now i am waiting for a set of header bolts from clifford and have the upper and lower intake manifolds off. would it be worth it horsepower wise to get them ported and polished while i am waiting. thanks

 

the head is what gets ported and pollished. you just make the intake ports to match the bigger ported heads. port the head when it is off so you can keep the engine free of shavings.

 

well maybe i heard wrong but someone told me that gaining hp from doing that is possable.

 

Not for your torquey little six banger!
Porting and polishing is something done to the High Revvers to get more RPM/fuel air flow. That operation sacrifices Torque for a higher Horsepower curve.
You could not possibly ever get that much RPM out of your six.
On the other hand, you might go through all the expense and work to put a 4Bbl carb, port the Head and polish the intake and exhaust ports and install headers, and still not notice much of a difference in the performance. That kind of enhancments requires a lot more engineering to make it work well.
For your six you want the rough intake and exhaust passages. It all helps with the Torque.
Leave it as it is, and be happy with the reliability and economical operation. Buy something else to race!

 

true true, just figured i'd ask

 

The 300 responds very well to flow bowl work, there is a lot of restriction just below the valve seats which costs a lot of flow, therefore a lot of torque at all RPM. You want to limit port work though to cleaning up obvious imperfections. Do not remove any more material than necessary; increasing port size lowers flow velocity which costs torque at lower RPMs. Leave the intake ports rough, polish the exhaust ports. The rough surface helps keep the atomized fuel in suspension, obviously not an issue on the exhaust. Polishing the combustion chambers to a mirror finish eliminates hot spots and allows you to run a bit more compression and/or timing without detonation.

 

Agreed.

 

Is that something that can be done in the garage, or would a guy be better off having a machine shop do it? I'm a competent mechanic (H-D tech), but I don't really wanna ruin my head. Any advice by those in the know?

Frank

 

For the macine shop to do this procedure correctly would cost a pretty penny. But you know that you wouls get the maximum flow through your head. Additionaly you would need a machienist that proves he knows the design of the 300 head, porting cylinder heads can be a trial and error method of research to get the maximun flow(messing up lots of heads for practice) unless you have hundred thousands of $ in flow bench tools and airflow meters. To port them yourself I would grab a respectable high performance how to book or video the best bet is to ask someone expierenced to show you how to. Porting your heads will decreace resistance to flow allowing more velocity of air fuel ratio less turbulance 1 wrong move can create longer flow of air to travel and slow down the air-speed or worse yet grind into your waterjacket. Remember every head has different casting imperfections.
I have had some expierence flow benches correctly do it yourself porting on stock sb chevy 350 heads can give you around 35 hp increace, figuring with every 1 CFM more flow .43 hp increace.
THERE IS NO DECREACE IN TORQUE, More flow=more air fuel ratio=more air fuel ratio into the cyl=more cylinder pressures=bigger and longer power cycle=more push on the piston=more TORQUE AND HORSEPOWER .

 

Larger ports do not decrease the maximum torque value but they raise the RPM at which the torque peak occurs. This decreases the available torque at lower RPM.

 

StrangeRanger has certainly hit this right on the HEAD!!
If you are gonna do any of this, leave the intake alone, and just do the exhaust!
I'm happy with my stock INLINE, I'm just waiting for the exhaust to fall apart, then you can say, bye-bye, cats....! Only 64k on this puppy as of this typing, and I haven't got much of a commute to work!!!!!!!

 

This is very true you would be raising the peak torque rpm on major port jobs. But for gasket matcking purposes and by eliminating casting obstructions also giving the valve guide a teardrop shape will to excersize more flow, you will increace the velocity of the air for the low end torque by reducing the turbulance. Making the flow bowl 85% the size of the valve seat will also increace the swirl effect or more air at lower speeds.

 

Here,here. Great explanation, and thank you for not making me type it. Your a very brilliant man.