Is valve shrouding a concern in a 318 w/ 2.02 & 1.6 valves

yellow rose said
I get EXACTLY what you are saying. What I am saying to you is that you can do all the math you want (considering valve shrouding here) and I can't tell you how many flow tests I have done regarding valve shrouding, including in the chamber. There is more than one way to skin a cat. You can be closer than 3/16 (don't know where you got that number) and NOT lose flow. But you need to look at the valve job, back cut ( I almost NEVER backcut a valve anymore as it may gain flow but LOSE power) and the shape of things. All are important.

I get all the rod ratio stuff and I'm with you. I'm about the only guy I know who thinks a 360 is a waste of time (going to catch holy hell for that) because all your math on that is correct. I get it. But don't step on your wiener here. I'm not even considering valve shrouding, because there are ways around it. I'm talking about HORSEPOWER. While your percentages may look like bore size is minimal in HORSEPOWER, it is HUGE. Not necessarily in peak power, but power under the curve. If you take a .030 over 340 (4.07) verses a .060 over 318 (3.970) you are talking about a pretty big swing. You are talking about .100 of an inch. Don't think about shrouding now. Think about how much more PRESSURE is exerted on a piston that has a bore that is .100 larger! That is where the power comes from. The exact same cylinder pressure on a 3.97 bore will make LESS horsepower than the exact same cylinder pressure on a 4.07 bore. And the 318 will have thinner cylinder walls!

I don't have any spare 340's or I'd give you one. I see them here on FABO all the time for fairly cheep coin.

That 273 crank is PERFECT...........................IF IF IF you use a light piston and rod. Get the bobweight down and it is very nice. My last drag engine I did for my self had a 1680 gram bobweight. And I used a 273 crank. Turned it 8500. And made power. The crank is NOT an issue IF IF IF you keep the bob weight down AND get a good damper on the crank. I always use fluidampers. I'm not a fan of elastomer type dampers (that is a whole 'nuther thread) for many reason. But your crank is the least of the issues you have.

I suggest finding a good used 340 block and not putting any money in the 318. You will be better off in the long run. And it will make more HP.

And like you, I did the math on the 360 in 1979. Didn't like it then, don't like it now. The small amount of torque you lose, I make up with gear ratio.

Thank you Yellow Rose :D Now that's information I can work with :burnout: What you're saying about power under the curve (which is what really matters) makes complete sense and I can see where my numbers may be misleading me. People have so many claims without any supporting theories and or evidence behind them, I don't listen to those because most people don't know what they are talking about; so please forgive me if what I said was rude or obnoxious.

Haha I appreciate it, that's probably the best option; I agree. If my budget allows me to find a 340 or if somebody has a crusty one that they don't feel like messing with and they want to give it to me; that's what I'll do. Otherwise I'll just have to stick with the 318 for the time being until I get some more cash and can swap everything over to the 340 block. Going for a 340 block makes total sense, but everybody was arguing in favor of a 360 block which is a step backwards in my opinion.

Awesome, I'm planning on getting the crank magnafluxed and polished soon. I hope it's a good piece as one of the rod journals is kinda rough. I actually want to have a bead welded around the journals on the filet (or the space between the journal surface and the web) so I can have it machined and it will have radiused journals for extra insurance.