I'm curious about how far i can port my 305 heads. They are bolted to a 4-bolt 350, and are performing pretty well, but not up to what I expected. I found the the heads at a local swap meet sporting 2.02 1.60 valves, with the chamers slightly clearanced to fit them (the guy called it "bowl hogging"). It looks like the intake runners have not been touched, though. I only want to do the intake, because the cam in the motor is heavily off balance in favor of the exhaust side.

I just wanted to see if anyone knew how much these things can be ported before I hit water. I think they are 416 castings if that helps. Also, can I do this on the car, or do I have to drop the valves on the bench and adjust the rockers again?

 

yes the heads need to come off the car to port and polish...

 

The port walls are about .100" thick. You can carve quite a bit of steel out of them without busting throu. About 10 cc's from each port. You definatly have to remove the heads from the motor, dissassemble them completely and you definatly want to fully port the exhaust ports. They are very weak but respond to porting even better percentage wise than the intake ports do.
(cause they are physicaly smaller)
You almost cannot make these heads "too big"
If you have 2.02" intake valves then deshrouding the chamber around them is most critical to getting the flow you would expect from porting.
This is not "bowl hogging"
I use 1.94's with this head and get tons of flow with minimumal deshrouding. you don't want to deshroud for more flow all the way around the valve. its not nessessary cause the intake flow is concentrated towards the spark plug as the air exits the port.

The 2.02" valve can work for ya but will need more deshrouding work than a 1.94"
Don't grind the chamber beyond the cylinder bore wall.
A head gasket's hole is larger than the cylinder bore.
Its typically 4.166" the steel shim gasket is 4.10".
So keep your grinding smaller than the gasket.
Spray some water, using the garden hose through the intake port at different positions and you'll see where the flow is concentrated and where it is not. The area within 5/8" of the spark plug is the most critical area.

The potential spots where you might carve thru on the intake port are right where the intake port wall "common wall" passes by the cylinder head bolt. If you try to straighten that wall 100% you will bust throu into the bolt hole. don't be shy here go about 90%. This is a high flow area and responds well to straightening.
The other spot is the pushrod pinch. You want to open up the width of the port here but again if you get too carried away you'll bust throu.
Both these areas are repairable using epoxy putty.

On relatively small street type cams used in street motors thru muffled exhaust you can ignore intake/ exhaust port flow ratios and all the therory etc that goes with it. Most of these motors (like yours) just work better overall using a dual pattern cam with more exhaust duration.

You definatly want to fully port the exhaust side. More is better. ( no need to make the exhaust por exit any bigger than the header flange. measure the inside diameter of your headers before you start.

Basicly the floors of both the intake and exhaust port just need to be cleaned up and smoothened. All the big metal removal is on the roof, guide boss, bowl area and walls, in that order. You want to make the port as tall as possible by raising the roof, especially with a single plane intake like a Vic JR and a high lift cam.
Bowl hogging refers to opening up the funnel shaped area just below the valve seat (valve bowl) when new larger valves are used.
It just saves you time. Then you want to blend in the short side radius from the bowl to the port floor eliminating the sharpe machineing edge left by the bowl cutter.
Both the bowl must be enlargened, and the chamber deshrouded, to allow the new oversize valve to flow to its potential.

 

In this pic of a 416 chamber the green areas are the area that needs deshrouding. The points where the red arrows indicate are not really high flow areas but do need to be relieved for the larger than stock valve. ( about .080 to .100" clearance between the valves edge and the chamber wall. (but don;t make the chamber wider than the cylinder bore. The purple arrow indicates the intake port's flow pattern that hugs the roof and common wall and curves toward the sparkplug as it enters the chamber.
Do not grind down the little ring around the spark plug threads as you'll just expose more of the spark plug's threads to combustion heat. (hot spots create detonation and preignition)
Only the plug's tip and ground strap should protrude into the chamber. I perfer a slightly cooler than stock non projected tip plug like Champion RV8c or ACdelco R42T for High performance use. The stock R44TS or R45TS is good for "low performance" City driving, but you need a little cooler performance oriented plug for high compression WOT use. (detonation protection)
Spark plug heat range is always a compromise for street driving but this heat range seems to work well overall for daily street and WOT drag use on the 416's. Especially with NOS.

 

Woops forgot the pic

 

take a look at this head.
Althou you can't and shouldn't try to make your head just like the one in this pic, youn can see where the critical flow area that needs to have the chamber wall radiused to unshroud the intake valve is.

A lot of people think that bolting on a 305 head onto a 350 will result in too high a compression ratio for pump gas.
Well by going to the larger than stock valves and (enlargening) "deshrouding" the combustion chamber a bit the typical 58cc 305 head ends up being about 61 to 65cc just right. If you want 58cc's when done, just mill the head a bit.
(about .006" per 1cc)

 

Trucks, Suburbans and Vans with the 305 and 416s, 624s, or 601s, spec R43TS plugs. Higher constant load means they will get hotter and need a cooler heat range. They are however hot enough to burn off deposits that form around town as well. Your normal LG4/L69 specs R45TS like you mentioned.

 

You can start by printing this:



Scale the drawing so the 6" scale is exactly 6". Cut out the templates, make thich plastic or metal (shim stock) templates from the patterns, then port your runners accordingly for best fit. That will involve a lot of roof and guide work (as previously stated) and some heavier short-side radius cutting.

Another way to maintain compression is to fit the new valves a little deeper, which will also naturally provide for a little less shrouding. You'll need to watch the piston dome clearance, however.

You can also fit up valves slightly smaller than the "standard" 2.02/1.60 by using older Ford 351 valves or some Buick or Pontiac variants. The longer stems on some of them make for a better valve train geometry without having to cut the spring seats heavily. Just watch the spring installed height and rocker geometry (stud height, too) and you should even be able to use close to stock length push rods.