Since I was bored I decided to make a little spreadsheet. I own several small blocks and love them all. I like a challenge and I like building something a little different, so I am always interested in the 305 debates. Attached is a spreadsheet comparing several combinations,unfortunately it wouldn't let me upload an excel file so I just pasted it into a text file. Enjoy!

 

What are you trying to show?

 

Sometimes people complain that you can't put a good cylinder head on a 305. I guess my point was that you don't need a 2.02, 1.6 valve to make a 305 efficient and that if you build one scaled equivalent to a larger engine it can make as much horsepower per cubic inch. Sure it will never make the same numbers but that's not the point. This also gives some insight as to valve shrouding.

 

What insight does it give about valve shrouding?

 

+1

 

I always read/heard from some good engine builders that you want to be around 50-52% of your bore size for your intake valve size. Thats around 1.84-1.94" for a 305 at stock bore, 2-2.08 for a 4" bore combination and 2.06-2.145 for a 4.125" bore.

Although there are some port designs that can tolerate smaller valves and higher velocities in the port to give good hp results... LT1 heads for example do real well at 2.00" valves or no bigger than 2.02".

 

About valve shrouding, I was just suggesting that certain valve sizes would have similar valve shrouding characteristics based on valve to bore ratios. Like a 1.94 in a 305 would be shrouded similarly to a larger valve in a 350, like a 2.05 or 2.08 which doesn't stop anyone from using these large valves in race engines.

 

Shrouding isn't just about geometry. It's about how the head flows in that region, on different bore diameters. Putting a 1.94" valve in a 305 head won't be as affected by shrouding as swapping Vortecs. If you're wanting to try a max-effort small-valve 305, then you need the '76 heads, which were the only year for the heavy castings. They also came with 1.72" / 1.50" valves. They can easily be cut safely for 1.94", so this won't be any hassle. Then get some stainless, swirl-pilished, 1-piece, undercut-stem 1.94" valves, and have them cut down to 1.84" plus the back-cutting Now get those '76 heads cut to match, putting the seat as far out on the valve as possible. Finish with a 7-angle valve job, from 15 to 75 in increments of 10. This'll be the best you can practically hope for from a 1.84"-valved 305. If you want a 30-degree seat for low-lift flow, just go for 1.94" in any 305 head.

 

Valve shrouding is more about how the curvature of a small cylinder wall follows the curvature of the valve more closely than the curvature of a large cylinder wall. Just looking at ratios doesn't say anything about that.

 

Well I finally got what I wanted, some discussion. BTW I have 1.94's in my 305, engine runs strong, along with a bunch of other mods.