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Nothin' like a little head
Heads are not the high point of any small block Chevy so these will need to be changed. Vortech heads are an inexpensive alternative and they can make some good power. Vortech heads also require special self-aligning rocker arms or pushrod guide plates; in the long run you will spend about as much money to install the guide plates, as you will on the rocker arms. There are also some performance aluminum heads available for the 305, if you plan on spending that kind of cash you might as well spend a little more and just get a 350 (you know the old adage, there's no replacement for displacement) the power will be easier to come by.
If you choose to "hot-rod" a 305 you will need the appropriate heads. The 305 heads came with a small combustion chamber (52 cc) and small valves (for 2 reasons) 1) small valves help to make low end torque 2) big valves wouldn't fit in the small combustion chamber. If you just bolt on a set of 350 heads with stock compression pistons, (8-8.5:1 with 52 cc heads) your compression will be so low you will only make about 75 horsepower. Plus the bigger valves of the 350 heads will deplete low-end torque. So don't use 350 heads on a 305, unless you want to spend unnecessary cash to modify them and the pistons. You can however use 305 heads on a 350, this is an inexpensive way to raise compression. Bolting a set of 305 heads onto a 350 will raise compression at least 1 point. However there are many variables to this swap. 1) You must leave the pistons "as is"2) this is also assuming that your block and or heads haven't been milled (some material removed from the deck to ensure that the surfaces are flat or "flush") 3) You must also use a head gasket that is the correct thickness (the thinner the gasket the higher the compression) Small valves help make low-end torque so you could expect a little boost in acceleration.
But this low-end torque isn't free; it's robbed from the high-end of the power band. 305 heads are good for power up to about 5000 rpm, after that your motor will pretty much run out of breath. So if you have a cam with lobes that look like the Rocky Mountains (high duration), and you want a boost in compression, you might as well just get different pistons or get the decks milled. Now if you have a mild cam (low duration low-end torque) that doesn't make power past 5000 rpm 305 heads on your 350 will be a godsend.
Getting the shaft
The camshaft is one of the single most important components in any engine. Too much cam and you will have many downfalls, too small of a cam and you wont make all the power that is possible. One of the most important things to consider when selecting a cam is compression. A 350 can handle a bit more cam than a 305 (this I will highlight in a minute) so you must not confuse them. One of the biggest mistakes people make when building a motor is too big of a cam. There are a million good cams for the 305 but nobody highlights them, well that's what I'm doing now. When you are looking at the specs of a cam, and you look at the power band it will read something like "1500-5400 r.p.m.". This figure is estimated for a 350 cubic inch engine, if you put this cam in a 305 the power band will be higher (i.e. 2200-6000 r.p.m.).
For a 305 the most cam that should be used is no more than .481 lift, and no more than 230 degrees duration @ .050. This cam should be used with higher compression about 9.5:1, and steep rear gears. This is an awfully big cam to be used with the 305 but it can be done. This is all the compression that can be used on the street (using pump gas) any higher and you will need 1 of 2 things. 1) Octane booster 2) aluminum heads. An ideal cam for a daily driver 305 would be about .465 lift and 224 degrees duration @ .050 lift. Try to get a little more lift on the exhaust lobe to help out the smaller valves. This cam can handle a bit lower compression like 8.7:1. Too big a cam will make your motor idle like a sweaty pig, and it wont have any low end torque, and to top it all off it will use a whole lot of gas.
So when you choose a cam keep these numbers in mind, .465/. 470 lift, 224/ 228 degrees duration @ .050 lift (for a cast iron headed, daily driver that uses low buck gas) Roller lifters are also worth a few horsepower, but roller lifters require a specially made roller cam and specially made shorter pushrod. 87 and later engines were equipped with roller lifter/cam setups so a roller lifter/cam setup will be cheaper on one of these engines. No matter how you figure it, to put a roller setup in a non-roller motor setup will cost at least $500.
Oiling/Cooling system
The oiling system is a very important system in any engine. The small block Chevy has a very good oiling system as is, so little or no modifications will need to be done to the oil passages unless your motor will be seeing very hard use. The only thing you must do the oil passages is to make sure they are clear of all abnormal obstructions. A misconceived notion is that a high volume oil pump will increase performance; well it actually reduces performance. Unless you plan on using your f-body to tow a motor home through the mountains, a non-high volume oil pump will suffice. A bigger oil pan couldn't hurt, but it isn't obligatory. But it would be wise to use a good name oil pump, as apposed to a choice cheapie no name oil pump.
Many racers often use the stock oiling system on the small block Chevy. The cooling system on the 3rd gen f-bodies need some help if you have a monster motor slumbering between the fenders. Anything more than a stock 305 will warrant a better radiator. Many aftermarket companies offer 3 row rads for 82-92 firebirds. An oil cooler couldn't hurt things; it will just make the motor run cooler. If you bore an engine, install a bigger engine, or modify an engine to make more power, you will need to perform some adjustments to the cooling system.
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