304 rebuild

[GatorBate]

Have any of you rebuilt a AMC 304 using Buick 305 pistons? I would like to increase my compression to around 9.5. The only piston I can find for the AMC 304 are dish and will only give me about 8.4:1 The Wiseco 5014H6 is a flat top piston and should give me higher compression.

 

[Scooter402]

You'll need a LOT of information before deciding on a different piston in your bores.

Please do not be offended if you already know all below information:

First, you need to know the AMC 304 's deck height -- that's the distance from the centerline of the crankshaft to the mounting surface of the cylinder head.

Second, you need your crankshaft stroke length.

Third, connecting rod length.

Fourth, you need the compression height of the piston -- this measurement is the centerline of the wrist pin to the crown of the piston.

Now, take half of the crankshaft stroke length, add the connecting rod length, and add the compression height of the piston. If they come within .020" of your deck height, you're golden.

Now, as far as bore, you will have to determine how much piston-to-wall clearance you need for the type of piston (i.e. cast, hypereutectic, or forged). For example, I have a SBC 402. Some may think I mean BBC 402. I have a set of pistons that only require a 4.130 bore (vs. 4.125 stock), using a 6.00" connecting rod with a 3.75 stroke length giving me 402 cu. in. My compression height is 1.125, yeilding a total of 9", in a 9.020 deck height block.

The tighter you can get the quench area (this is the area from the crown of the piston to the deck surface, plus the thickness of your head gasket) to be below .060", you'll be good.

Let me know if you need any more info.

 

[DHugg]

Have any of you rebuilt a 304 using Buick 305 pistons? I would like to increase my compression to around 9.5. The only piston I can find for the AMC 304 are dish and will only give me about 8.4:1 The Wiseco 5014H6 is a flat top piston and should give me higher compression.

I seem to remember when I was a kid, wishing I had a V-8 to work on (where did those 50 years go?), that some guys shaved the heads to reduce compression stroke volume. Might be that it was only on flatheads, but sounds like a one-size-fits-all step.

Of course, remember too a friend who stole 115-145 AVGAS from the Memphis Air Nat'l Guard to run in his Ford flathead. He wound up burning off the valve heads until they looked like pencils. There are lots of ways to get more zip, some better than others.

 

[Scooter402]

I seem to remember when I was a kid, wishing I had a V-8 to work on (where did those 50 years go?), that some guys shaved the heads to reduce compression stroke volume. Might be that it was only on flatheads, but sounds like a one-size-fits-all step.

Of course, remember too a friend who stole 115-145 AVGAS from the Memphis Air Nat'l Guard to run in his Ford flathead. He wound up burning off the valve heads until they looked like pencils. There are lots of ways to get more zip, some better than others.

True story, good info. I'd be leary of the Av gas, though... It does tend to get those exhaust valves....hot...

Milling the heads .020" typically yeilds a little shy of .5 point in compression, depending on head chamber volume and shape. Going over .020" is not recommended, because you'll start running into alignment issues with the intake port runners between the intake manifold and the cylinder heads. If one goes beyond .020", the intake manifold head mating surfaces will have to be milled to match the heads.

 

[BIGTRUCKNUT]

I thought about using other engine pistons to increase compression on my AMC 304 but I decided that it just wasn't worth the hassle to eak out performance from the little engine. Instead I used .060" over dish pistons (16cc), zero decked the block, and had a skim cut on the heads to get me to 9.0:1 CR on the AMC 304 I built this summer. With a little more head milling (.020 to .030") you can easily get to 9.5:1.

I'm happy were my AMC 304 is - it's a solid performer, has good power (even with current 3.55 gears and 35" tires!!!), and runs all day on 87 octane fuel. In additional to decking the block, I also installed bigger chevy 1.94/1.5 valves, notched the cylinder walls, and installed a Howards 214/220 duration, .525/.540" lift cam. I'm still running the stock 2 bbl intake with a early Motorcraft carb that I took from a early 70's V8 Mustang. I have a 4 bbl Edelbrock SP2P manifold but I didn't used it because of it's extremely small intake ports - smaller than the stock 2 bbl intake. I also did the oiling sytem mods to increase overall oil pressure and flow to the rear of the motor. I may install a Performer intake and 4 bbl carb someday if I find a good deal on the intake but for now what I have is good - the current 2 bbl Motorcraft carb is running well on and off road and is extremely easy to tune.

 

[gert]

if you dont mind dropping off some cash you can skip the milling
Bulltear-Online

 

[ksouthw80]

Oh man, they haven't made avgas like that in a minute

 

[Jimbos76cj]

HAve you looked for a thinner head gasket? Id shave the heads a little then go with a thinner gasket to bump the compression.. or go with the bulltear pistons.

 

[BIGTRUCKNUT]

HAve you looked for a thinner head gasket? Id shave the heads a little then go with a thinner gasket to bump the compression.. or go with the bulltear pistons.

I looked/researched head gasket options all over before I did my rebuild this past summer and found nothing thinner than .045". That's the main reason for zero decking my block - wanted to get quench distance down below .050".

 

[chris989604]

if you dont mind dropping off some cash you can skip the milling
Bulltear-Online

X2,,

I was going to post the same link,

Chris

 

[gert]

X2,,

I was going to post the same link,

Chris

good people, great product, I have dropped off some good money on their stuff and am very satisfied customer