Ok so i have a 1987 pontiac firebird with 305 4bl carb engine on it. It is stock besides air cleaner and exaust.

I have headers and a mild cam to go in it, and was thinking about what heads would make it rev up quicker.

I have 3.42 gears and it gets off the line real quick but after that the car isnt really quick. I heard you put some heads off of a 283 or 327 small block to raise the compression and speed it up.


I know both will raise but what im really looking for is horse power not torque. I can already spin the tires just fine says my back right and i really just need more speed from 3000 rpm up

Thanks

 

Where to start....

Hp = Torque x RPM

Make more torque, you make more horsepower. Torque is a real world measurable force, horsepower is an abstract concept contrived from cobbling numbers together.

To make lots of horsepower you make lots of torque at high RPM. The nature of the internal combustion engine means you're limited to a certain RPM range at the top end just because things fly apart, and you're required to have a certain amount of low RPM torque just so you can get moving from a stop without having to rev at 5,000 RPMs.

So the question then becomes... do you want it to "rev" quicker? Or do you want more horsepower? Im going to assume you want more horsepower.

I dont know what comes off a 283, but that sounds like some kind of backwoods farmer john hot rodding to me. Im sure it works fine wherever farmer john is from, but it doesnt hold much water here. The 327's got camelhumps, which were the only factory head for 10 years or so after 1967 that you could make any power at all with. After 1980 or so we came up with a lot better stuff than the old "camelhump/doublehump" 461462 castings we used in the 60s.

In fact, your LG4 has 416 heads which are actually fairly decent heads. Your problem is your compression is a little lower because you have dished pistons.

If your engine is healthy and can handle it, you can make a good bit more horsepower by pulling the heads, having them milled down to lower the combustion chamber volume, and doing some minor bowl blending on em, maybe a little porting, and cut down the valve guides and machine the valves seats for larger springs, or you can run LS family beehive valve springs. (They're triple the price, so balance that out) that sort of thing. From there with a higher compression ratio you can run a larger cam.

If your motor is an 87, I think you should have a roller cam. That's EXCELLENT news for you. That means you can run a nice big roller cam with your 305 and make power that Farmer John with his camel humps on a 383 would be jealous of.

If you can afford it, a cam like a Comp XR270 would make that thing scream. Power is made with camshaft and cylinder heads. Everything else has to be upgraded to work with it.

That means you're gonna need new rocker arms, new valve springs, and maybe a new stall converter on your trans. You already have 3.42 gears, so that's actually fairly decent for a medium cam, but you may want to go higher.

If you cant afford the $300 Comp roller cam, find a used GM LT4 Hotcam, they're a good bit cheaper.

Hotcam + shaved heads + bowl blending = much faster

If you want to go with another set of heads, you can try a set of Corvette 113 heads, but you'll still want to shave them a little to get your compression ratio in a good range.

I would also consider taht 305 living on borrowed time if you regularly spin it up past 5500 RPM with the stock bottom end, but until it blows it will be quick. The XR270 only works up to 5500 in a 350, but it will probably go higher in the 305.

If you replaced the rod bolts it wouldnt be prone to blowing up, but there's no bigger waste of money in the world than spending money on a 305 bottom end.

 

The law of physics require a relative small c.i. engine to be spun higher in a rpm in order to produce a power band for torque or hp.Even with today's tech,it is harder to produce a output in the lower rpm ranges with a smaller displacement.That is a disadvantage to a street vehicle because those commonly driven rpm's are usually not within normal ranges for the higher rpm engine's output.

SCR's ratios with today's gas limits how high a C/R you can go.

Hot camming smaller displacement engines,depending on how big of a cam,the smaller C.I. engines are less accepting of a bigger cam in idle and lower rpm ranges.The example is a 305 with a choppy idle with a given cam and a smooth as silk 350 with the same cam.It gets back to the same limited output I was talking about in lower rpm ranges for small c.i.engines.The smaller one isn't as efficient in lower rpms.

I am going to lightly touch on faster rpms with a 305.There are super light race bottom ends that surely does impact how fast a engine spins up.They are knife edged to cut threw the oil faster and certainly custom build along with super light rods and pistons,better super light wt valve train components,etc.Yeah......$$$$$$$$$$.

So to directly answer your question,the heads are not on it's own what you need to mod.

 

How much would it cost to do this to my own heads? I know my engine budget is quite pitiful and am looking to spend $600 ISH on engine

 

call local machine shops and get some prices. machining them wont cost a whole lot, its the blending and porting that cost. youll probably spend about $400-$600 on that head work.