What do I need to change my 2 barrel to a 4 barrel

Would look like basically a bore job. Stroke was 3.31, bore was 3.91 on the 318 and 4.04 on the 340.

318 (5.2) 1967-2002 3.31 3.91 340 1968-73 3.31 4.04

What are the other differences, Aarcuda?

Reply to
<HLS
Loading thread data ...

.130 inches different. Boring out would require a .065 inch cut, that equals roughly 1/3 the thickness of the cylinder wall. It'll run, but it'll probably sag in short order.

The blocks were different although the early 360s shared the same block casting number as the 340. Cylinder centers are the same, deck heights are the same, rods are different weight and casting number from what I've observed, cylinder heads are different in both valve size and combustion chamber volume, camshafts were different, timing chain and sprockets were different, main and rod bearings were different, different water pump, larger diameter by-pass hose, different ring groove depth in the pistons, different valve springs, different oil filter mount...

Reply to
aarcuda69062

Considerable differences, for something that 'looks like a duck'. Thanks

Reply to
<HLS

A 340 is indeed the basic 273/318 block with bore size increased, a forged crank, always with a 4-bbl, and DIFFERENT HEADS :-) The problem with doing a factory parts mix-and-match on a 318 is that putting either

340 or 360 heads on it (to get the bigger ports that flow better) also comes at the expense of getting a larger combustion chamber that would lower the compression ratio to about 7:1 without other added changes :-/ Best "bolt-on and go" heads for a 318 are the 80s "swirl-port" XXX302 casting with minor work to clean up the ports. Now if you start to change the bottom end and can pick pistons with a higher than factory deck height, then sure, use 360 heads and have the best of both worlds!

The 340 gets my vote as the best high-performance smallblock v8 ever. Screw the chevy 350, its good but it doesn't come CLOSE to a 340. A 340 will humiliate most big-blocks, and still leave the front end light enough to set up for handling as well. Sadly, they only built about 1

340 for maybe every 50 small Chevies ever made. And probably 1 340 for every 20 318s, for that matter.
Reply to
Steve

In other words, it is a punched out 318 (273, actually) in CONCEPT, but not in practice. Same block archetecture- deck height, crank geometry, bore spacing, bolt patterns, etc. But in practice the cylinder castincg cores were changed so the block casting is internally different. If you could REALLY "punch out" (ie bore) a 318 to 340 size, the 318 would have inch-thick (a slight exaggeration) cylinder walls. The 360 goes a little further in that the main bearing webs are different to accept larger diameter main bearings.

Reply to
Steve

Yep, yep, yep.... timing chain and sprockets were different, main and

Now all THAT stuff is year-dependent as well. By the time the 340 was being replaced by the 360, for example, all 3 engines were using the same timing case/water pump castings and the bypass hoses were the same, but in earlier years they differed. Sorta the same for rods- the 318 started out using the lighter 273 rods and floating pins, but in late

73/early 74 or about, it went to the 360 rod with a pressed pin. It gets real interesting when a single engine architecture stays in production for >40 years. :-)
Reply to
Steve

What if it is a boat that I'm trying to convert

Reply to
rickk8244

I have a boat with a 2bbl holly carb want to convert to a 4bbl carb

Reply to
rickk8244

What is the cylinder compression ratio? Does it currently require high octane gas? A good 4 bbl engine should draw additional air, otherwise it will be about the same as a 2 bbl engine.

Reply to
Paul in Houston TX

The matching intake manifold? Is this a trick question?

formatting link

Reply to
AMuzi

First you need to understand the problem. I suggest you get hold of these books;

Practical Engine Airflow - John Baechtel

Performance Automotive Math - John Baechtel

Then, when you understand how the engine breathes and, more importantly, makes torque, you will be in a better position to use this website;

formatting link
Of course, you need to consider the type of use. A boat is a little different from a car since you use the prop loading to control engine RPM, gearbox not required - except for reversing and idling.

Reply to
Xeno

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.