heads... chamber size... compression ratio. decking.. .. casting #?.... valves size?

ok.... I am trying to rebuild my sons 304 up to give it a little bit more power... and i dont want to go to a 360 or 401....i want to stay with the 304.

that being said....

My understanding is that in 72 the chamber size of the heads increased, thus bringing down compression..... what chamber size are 72 heads? what chamber size are 71 and earlier heads? what can be done to decrees chamber size, ie deck the heads? and how far can you deck them? deck the block? how much can you deck off the block? bigger size valves to decrees chamber size? what are the casting numbers of the smaller size heads? what are the casting numbers of the larger chamber size heads?

was also informed that chevy 305 pistons will work with some boring work and bring up the compression... ???


thoughts????

thx, Paul

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

I would start by looking at the quench distance with factory pistons. All this stuff can be measured (ie deck height, quench, chamber volume) and you can find out what your static compression will be in each case.

Here's an interesting thread about a 304 stroker (with a 390 crank) http://www.ifsja.org/forums/vb/showthread.php?t=95564&highlight=stroker that could give you some ideas. If I were going to spend that much time on an engine, I think I would avoid the entire question of carburetion and do fuel injection first. If the engine runs and is in the car, sorting out the EFI would be my FOOB (first order of business). Then I'd go with a cam, port matching, free-flowing exhaust.

I think the only way you're going to get a significant boost in compression is to go with custom pistons. Maybe there's an off-the-shelf (Chev 305?) piston with the right deck height and diameter that will work. I recall from somewhere that the Chevy pins are the wrong diameter? A cooperative shop can help with that. All this stuff can be figured out with some reading of the catalogs, paper/pencil and a calculator. I'd worry that your 305 pistons might collide with the valves though. Again, a cooperative shop could enlarge the reliefs for you, if there's enough metal in the piston top.

My understanding is that larger valves in the 304 heads won't help, because the side of the big valves will be shrouded by the bore. Maybe ... if you want the big valves, I suggest you start with a 360 block; then you'll get bigger valves in the 360/401 heads.

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

Building a 304. I know you don't want to swap in a bigger motor but it seems you could save a few hunderd to thousand by swaping in a straight bolt in 360 and get what you want.........

I'm building a 401. Cam is a good place to start. I like the comp cams. There is a place down here if FL that has a set of 9.5 (I think it's 9.5) pistons. Go FI if you can swing it. The stock headders flow fairly good from what I've read. The only one's that have any gain are the Doug Thorley Tri "Y"'s.

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

the build will be like this:
edelbrock performer intake
edelbrock performer cam
roller rockers
hooker headers
borla mufflers
edelbrock 650 carb
HEI ignition
a good head job with slightly larger GM valves
.030 over


what do you think my HP and TQ would be?

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

Why? Just plain why? I'll never understand peoples' desire to build a 304 rather than a 360. It's not like you're building a 302 or 327 Chevy versus a 350 Chevy to get more high-rpm capability. The 304 and 360 use the same 3.44-inch stroke. There's virtually no advantage to building a 304 - mileage, durability, rpm capability, longevity, etc. None. Sure, most Jeeps came with a 304, but you can pick up a junkyard long-block 360 for $100 and drive the Jeep with the 304 'till the 360 is built. You'll basically only have 1 day of downtime while you swap engines.

The 304 has a 3.75-inch bore versus the 360's 4.08-inch bore. The 360 has the ability to swallow a much larger valve without running into shrouding issues like the 304. There's more displacement for power and more pistons surface area for torque production. I'll never understand it: 304s are anchors. Keep 'em if they're running well and upgrade them with manifolds or even camshafts that can be swapped into a 360 later down the road - but don't go full-build on them.

As to your specific head questions, a lot of them are answered here: http://en.wikipedia.org/wiki/AMC_V8_engine

Power? No true idea since you'll be messing with the heads but I'd guesstimate 225-265hp depending on valve size and any mild porting or valve angle profiling. Performer isn't the greatest cam, though. Do the same mods (with a better camshaft) for the 360 and you'll be at 335-350hp with 400lb-ft.

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

I am going through this now. I did go the 360 route and I have 2 sets of heads. By Goggling the casting # I was able to determine I had 1 set of 59cc heads and 1 set of 64cc heads. The 59cc will give a higher compression ratio.

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

One possibility is to bore out and sleeve a 304 block to 4.08" and use 360 pistons, flywheel, balancer, and heads. Then your big valve 360/401 heads would work and you'd have a block that says "304" on the side. 'spensive though ... about $100/hole I recall.

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

talked to valley heads again.... they said that can deck the heads .080" and that should give an increases in C/R of 1.5+

opinions? true?

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

It will work as long as your valves don't hit the pistons, and they grind the manifold surface so that manifold still fits (lower the head and that moves the manifold surface closer to the center). The shop can cut the valve reliefs deeper if that's an issue, as long as the piston top is thick enough. Watch your head gasket thickness. You may need shorter pushrods. Put it together with plasticine clay between the pistons and valves and turn it over to see what the clearance is. 30 over will also raise the CR slightly.

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

Chevy pistons, I believe the pin is larger, you would need to modify the rods.
AS far as sleving the block to accept the 360 pistons, I just had my block sleved and the machine shop charged $75 per cylinder, around here 360's are more common than 304's and if you get a complete engine with the flywheel and harmonic balancer it should be a direct bolt in replacement.
As far as the cam I polked around on the FSJ site and a number of guys there prefered the Summet cam over some of the other RV style cams.

 

Re: heads... chamber size... compression ratio. decking.. .. casting #?.... valves s

Milling the heads to increase compression, besides piston to valve clearence issue you can run into problems with intake manifold fitment.