i'm not very familiar with engine machine work, but i'm getting ready to go carbed, and wanna get the most outta my 305. i have a set of L05 350 TBI heads i wanna put on the 305. 1.94/1.50 valves not sure on chamber size. i wanna have them cleaned up and machined, but what is required to run a cam with .510 lift? i know i need valve springs but doesn't the valve guide area have to be cut down?. on that note what would be the estimated cost for putting new valves in and cleaning it up? thanx

 

Useing 350 heads on a 305 is going to lower the compression ratio a lot. (chamber size is a lot bigger) A bad choice. Locate a set of common easy to find "416" 305 castings and install 1.94 valves in them. If you want more performance, home port them. They flow very well when fully ported. If you want to run .510" lift you'll want to shorten the valve guide boss top.
shorten them .200" A machine shop will use a special cutter to reduce the guide diameter for better aftermarket seals. they can shorten the boss at the same time. Tell them .200" shorter please.

Use Lunati #73943 springs. After the new valve job, locate 8 more retainers like the 8 intake valve retainers and buy this Comp cams spring shim kit. #4753 (48 shims)

Throw away the exhaust rotators . install 1 .030" shim on each intake valve spring pocket. Install 1 each of .015",.030" and .060" shim together (3 shim stack) on each exhaust spring pocket. Install the Lunati 73943 springs using stock retainers. Follow this and you're good to go for .510" lift. If you thuroughly port the 416 heads they will actually make use of all that lift. Sell those 350TBI heads to someone who wants to go slow(er)

Note: If you prefer the newer centerbolt valve covers use a set of "081" 305 TPI heads from a 305 TPI motor. The rest of the job is exactly the same.

 

Bumping this post up. I decided to machine my stock TBI heads from the 305. they already provide 9.5:1 compression. does anyone know how much lift these heads will handle stock? using my repair manual i figured the stock cam only opens the valves .351". if i can get away with using these heads and save some money that makes me happy. also. which casting number would these be? idk where to find the 3 digit number everyone refers to. I.E 081 or 416...

 

The casting number is on the heads, should be hard to miss. It'll have more digits, the last 3 are the important ones. You should have 187.

.351"? Seriously? Hooboy...

You can go up to .450" or so without too much trouble, but the main thing that comes to mind, is with a cam that punches out a fair bit of lift, it's going to have more duration than stock, and TBI heads aren't good high RPM heads. That's where they turn up the suck, so to speak.

 

The purpose of more lift is to increase flow. Right? OK.....

Consider a garden hose. Consider that this garden hose is ½" diameter, and it's hooked up to a 1" valve.

When you open that valve, what happens? How much flow do you get? What's limiting the flow?




The answer of course, is that water begins to flow, you get ½" worth of water, and the hose is limiting the flow.

Now consider what would happen if you thought that wasn't enough water, but hose is expensive; so you install a 2" valve. What happened? How much flow do you get? Why?




Again, the answer is of course, that nothing happened. You still get ½" worth of flow. And that's because the HOSE is controlling how much flow you get, NOT the valve.

Same deal with those crap heads. The tiny handful of partisans who claim irreproducible results notwithstanding, EVERYBODY who tries to mod those motors discovers that ALL mods are in vain as long as those heads are sitting there. They are designed a specific way in order to accomplish a specific purpose (which they do quite well - the guys at the factory aren't stupid), and they WILL DEFEAT all attempts to change their purpose. Opening the valve farther is like increasing the size of the garden hose valve, and the port is like the skinny hose. You could put 3" valves in those heads and open them to .700" lift, and STILL not get any more flow; BECAUSE THE VALVE OPENING ISN'T THE LIMIT TO THE FLOW.

The secret to effective hot-rodding is correctly identifying the current limit to the CAR'S performance, and correctly correcting it. Notice that I said CAR, not MOTOR.

Oh.... and DON'T put that crappy "RPM" cam in your 305. You know, the one that's 234°/244° @ .050", .488"/.510". Don't even use the "smarter" Summit or whoever version that's identical but comes without the Edlebdrock cover charge. It sucks bad enough in a 350; it's even worse in a 305.

Like F-bird said, if you want to get more out of the motor, the FIRST THING you should do, is lose the TBI heads. Get one of the castings he called out: there's no such thing as "almost as good", "almost the same", "all 305 heads are the same", etc. You'll hear that out of the junkyard guys. Then, get yourself a quality ROLLER cam, with something more in the 210° - 215° @ .050" duration kind of range; such as the Comp XR264HR. There's others that will also work well, but I happen to know that that particular one works QUITE WELL in a 305.

Then after that, leave the motor alone, and work on the CAR. In fact you might get more results out of the car work than motor work. Your car needs gears, a torque converter if it's an automatic, and a full exhaust, all the way from the heads to the back bumper. Without the exhaust, head and cam mods won't do what you wish they will, because the exhaust simply becomes the new flow limit.