305 heads

[luxeryvic]

i got a set of 305 heads and i work in a machine shop, i know these engines are kinda low compresion so i was thinkin of milling some material off the heads to raise the compression but still be able to run pump gas and have clearance for the valves? also while i have the heads on the milli was thinkinkin of milling some material out of the intake and exhaust ports and then clean up by polishing them how much materail can i take out of each side without running into problems or would it be better tto just port them regularily

[MagicRat]

I presume you are putting the heads on a 305 block, right?

IMO you need to CC the heads and work out the combustion chamber volume. Then you can accurately compute the real compression ratio that you have.

Next, you can put the heads on the engine with a gasket, temporarily, and use a tiny amount of putty on top of the piston, and carefully turn the engine over by hand. The valves will squish the putty to show you the actual clearance you have right now.

Using the info gathered you can calculate the amount of material you can safely remove to achieve the desired compression ratio. IMHO 10:1 is the absolute upper limit.

But IMO proper porting, a 3-angle valve job, gasket matching etc should have priority.
You want to avoid a parts mismatch.

I once bought an engine not knowing the parts combo. I think it was 305 heads on a 350, (not sure)..... anyways the parts mismatch meant I had sky-high compression ratio with the poor flow of 305 heads....... so I had a low-power engine that needed premium gas with an octane booster..... a disappointing combo, because it was slower than a stock 350 but more expensive to operate.

[silicon212]

Just remember before you go off and remove a lot of material from the deck on these:

These heads are of the "lightweight casting" variety, meaning the deck isn't as thick as on older, pre '78 heads. There is a fixed amount of material that may be removed, and remember that as they are, they're prone to cracking. Decking them will exacerbate this problem.

You're really far better off with S/R Torquer 305 heads if you want to liven your 305 up.

[luxeryvic]

im not goin to buy new heads i dont want to spend much money on a 305 especailly when i have a spare set and can play around with them

ok so how do you figure out the combustion chamber volume and the compression ratio i have now? and there dog dish pistons does that effect it

then with that info how do i figure out how much materail to remove to bring it to a better compression ratio for more power?

also is this goin to be worth much more power? and is it right that 350 heads have bigger valves

[silicon212]

Originally Posted by luxeryvic

im not goin to buy new heads i dont want to spend much money on a 305 especailly when i have a spare set and can play around with them

ok so how do you figure out the combustion chamber volume and the compression ratio i have now? and there dog dish pistons does that effect it

then with that info how do i figure out how much materail to remove to bring it to a better compression ratio for more power?

also is this goin to be worth much more power? and is it right that 350 heads have bigger valves

350 heads have bigger valves, AND bigger chambers. The former is good, the latter is BAD as it reduces compression. Most 305 heads have 58cc chambers, later 350 heads have 64cc chambers. You also have to worry about valve-to-block interference with some 350 heads with 1.94 or larger intakes. 1.94 is pretty much as large as you can go, and valve lift factors in here too.

A good set of 416 heads can be reworked to allow the use of 1.94s on a 305 (the 416s are 305 heads with 58cc chambers). They won't flow as good as the Torquer 305s I mentioned above, but it is what it is.

All else being equal, 416s are your best bet. These came on H.O. 305s from the late 70s through the mid 80s.

You can use steel shim head gaskets in place of FelPros, along with minor milling of the heads to achieve decent compression. Just keep in mind what I said above about warpage and cracking with these lightweight casting heads.

Typical compression on a standard (LG4) 305 is around 8.2-8.5:1.

[luxeryvic]

ok but how do i figure out how much i can take off to raise compression

[silicon212]

Originally Posted by luxeryvic

ok but how do i figure out how much i can take off to raise compression

I wouldn't take off more than a couple hundredths ... these are notoriously weak castings.

Figure .020 max.

[luxeryvic]

these heads are from a 305 out of a 77 monte so wood they still be the thin castings?

ok now with steel shim haed gaskets and .020 shaved off the haeds what kind of compression would i see and how much of a power gain wood there be also with the raised compression would i have to do anything with timing

[silicon212]

Originally Posted by luxeryvic

these heads are from a 305 out of a 77 monte so wood they still be the thin castings?

ok now with steel shim haed gaskets and .020 shaved off the haeds what kind of compression would i see and how much of a power gain wood there be also with the raised compression would i have to do anything with timing

If it's a '77, it might have thicker castings, but it also might not.

All else being equal, I'd imagine that your compression would be around 8.8:1.

[luxeryvic]

ok wat about power? wood i have much of an increase with the raised compression?

and is there a formula to figure out how to do this on any engine like magic rat was talkin about

[silicon212]

There's more science to it, larger valves (1.84 are the typical 305 intakes, 1.94 will work with certain cylinder heads, 2.02s are right out), cam timing, carb, exhaust, etc. Also factor in axle ratios and weight of car.

As long as the engine can breathe, you should get a decent boost - it will have more torque. Just how much more depends on the above factors and more.

[rickpilgrim1]

The best stock heads on my kids 87 305 Camaro were the ones off my 86 305 powered 1/2 ton truck. They were 58cc chambers, 1.84/1.50 valves and we port matched and did quite a bit of valve bowl and port smoothing work and with the 87 short block he ended up with 194-199 psi cranking compression. At which point running 92 ron fuel you could only have 32 total ign timing, and the computer(Weird hybrid half vacumn, half computor with knock sensor) kept pulling the timing back to 28 or so and you lost more than you gained.He ran 10 gal 110 octane race fuel, set the timing at 36 degree total and that really made a difference in power, but in the end 58cc heads and flatop pistons w/4valve reliefs on pump gas didn't work, 9-1 cast iron, 10-1 aluminum are about the limit on pump gas IMO