As I’ve said, flow numbers are a piss poor way to evaluate a cylinder head. It’s the easiest way to compare heads, but at best its a poor way of doing it.
Of course, the guys selling heads love to post flow numbers because that’s what sells. David Reher wrote an article in the National Dragster about this and I sure many others have as well. I’m more interested in the shape of the curve and how the port sounds on a flow bench than I am the flow numbers. Thats something you learn after you test a half dozen heads on a flow bench. That and most every article and shot like that are dead wrong.
Talking NA, the wedge head is always better than a Hemi. While the flow numbers look great and line of sight ports are the best you lose when the intake and exhaust valves oppose each other. Again, talking NA.
It doesn’t take long to see how the BBC just KILLS the Hemi NA. You have almost line of sight ports but the exhaust valve isn’t opposed to the intake valve. That changes overlap flow. Most people either don’t know or don’t care about overlap flow, but it’s a big deal.
Another example is the Pro Stock “hemi“ which wasn’t a Hemi. The closest that engine was to a Hemi was the skirted block. And all big blocks have that shitty design. Too bad GM copied that junk. Of course, the OE’s are more concerned with noise and stuff than actual power so there is that.
Anyway, that “Hemi” engine had issues that made it a different cat than a wedge. The skirted block is a power eater. The fix for that was machining that skirt off the passenger side of the block and building an oil pan that for the block after that was done. I also know it was 2 hours just to pull the pan and not jack it up and four hours (or more) to put it back on and get it sealed. When you pull 20 or so inches of vacuum in the engine the thing needs to be sealed tight. It was a nightmare and I saw that junk up close.
Another thing that kills the Hemi (NA) is the huge port with a short runner length. The G3 isn’t any different. Big, short port. What killed the last version of the “hemi” in Pro Stock was that short port. When NHRA passed the EFI and RPM rules, they KNEW it would kill the Hemi and they still did it.
The Hemi was some 700-800 RPM higher than the wedge headed engines. That’s HUGE. So when those two rules were passed, the big short port became a liability. You couldn’t get the manifold runner long enough with the current EFI rules so the Hemi was now way underpowered at the 10,500 RPM rule.
You will ask why does this matter. It matters because you or I can’t change the physics involved in internal combustion engine science.
Enough of that. As far as getting a carbed engine to start and idle like EFI isnt that hard. What it won’t do is start and sit there and idle while you drink a latte.
If you get it right it will start and idle and not be pig fat rich either. But you’d better have your **** together when you plan the build or you‘ll never get it.
Lets not forget I’m not disputing that machining has gotten far better than it was in the 60’s and 70’s. It’s not even close, but we are still dealing with production engines.
To that end, I can’t recall a single virgin 340 that was anywhere near 10.5:1 compression ratio. I found some that were 9.2:1 and that was it. It’s a huge jump from 9.2:1 to 10.5:1, and it doesnt always show up on a water brake dyno.
The newer stuff is far closer to the nominal compression ratio called out. I can also tell you that unless you actually pour the head and cylinder and do the math you most likely don’t have the compression ratio you think you do. That’s why I question guys on here who say “I’m about 10:1“ or whatever. The majority of the time it’s not even close to what they think it is. I can’t tell you how many times an engine came in with “X” compression ratio and was cammed for that and it wasn’t close. And they ran like garbage.
Thats why comparing engines from different era’s is so difficult. When you update the older engine and make it what it should be then you don’t see the big performance differences.
So I compare a G2 Hemi with wedge headed engines of its era and the G3 Hemi with wedge headed engines of its era. And it always ends up that the Hemi (NA) is the loser.
