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Well I'd assume when theoretically discussing Heads and Cam that proper/ideal intake, exhaust etc.. would be used unless other wise stated. One fact being over looked is overlap (getting the air moving) and inertia to keep filling the cylinder through the begin of compression stroke.

Depends what your trying to do, a port on the slightly larger size could allow you to get away with less cam for similar rpm and hp, which I'd argue would generally be more streetable.

rev or make power to 6k + ?

Can do with the right top end.

At full throttle (demand) you only run out of supply :)

Difference is were talking over time (rpm) not just one sitting (cid x ve%).

Never said it did, just that calculation suppose to predict flow bench cfm reading needed not actual physical amount of air in cfm.

I don't see that calculating an actual displacement of air over time. It calculates estimated cfm at 28" which is airflow on a bench. cid x ve% x rpm / 3456 = cfm calculates a close approximation to actual volume of air used/needed.

Here's A 493 270 Trick Flow making 788 hp at 6300 rpm and 710 tq at 5400 rpm.

100%, this thread started as a hypothetical the only reason I brought up the formula.

It started off as a hypothetical but the OP is figuring out the best heads for a 650 hp 493, PRH already gave the answer. I disagree, yes peak ve will occur at peak torque but rpm is lower, at peak hp ve will be down but more rpm so should be flow more air overall, just less per cycle.

When you say average (x 0.6872) you talking ports average flow numbers ? I wouldn't use the formula at all for deciding a head, even though Chris Speier seems to highly believe in these formulas where I first mainly heard of them. To me there just a curiosity obviously there based off some one...

That to me would give vary low cfm estimates. A 408 x 6000 x 0.0009785 / 8 = 300 cfm so a 190cc trick flow head x 0.6872 = 205 cfm a J head. The trick flow seems to be the right call for that application might get away with a little less but not a J head, at 100% ve the formula says 241 cfm so a...

Most of the formulas and or rules of thumb got to take with huge grain of salt, just curious what cid and rpm was off by 100 cfm's ? Just in case your curious, you can modify the formula for any VE%, below 100% VE would be cid x rpm x 0.0007895 / 8 = cfm demand "Cubic capacity * peak rpm *...

That formula based on a VE of 125%

I wouldn’t shop for heads based on that formula maybe as a guide line, I shop based off known results the heads can produce with the combo you want to run, cid, cam, cr etc..

Be nice to make 2+ hp per cfm :)

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The 6 pack if rated like a 4 bbl is more like a 950, they probably could get away with it easier with both of those because most of the % of cfm (less restriction) came in only when kick down. Plus I don't think engines are as sensitive to cfm (less restriction) as some make them out to be, I...

If I was to build a fairly serious street strip engine I'd shoot for 1.8 cfm per hp as a goal any hp above that be a bonus. Eg.. 500 hp / 1.8 = 278 cfm so I'd would want a head that flowed at least 280 cfm around .500-.600" lift to try make 500 hp. (Obviously with a decent overall curve...

You basically got a handful of head choices so unless you build an engine to take full advantage of one the available heads you looking at a bunch of compromises.

Depends what level of builds were talking about here but most average guy builds generally don't even get over 2 hp per cfm.

I wouldn't necessarily say smallest but the right size for the application.

Is that formula ideal ? Don't know but it seems reasonable. Definitely there's no ideal air flow just to cubic inches, you have to factor in rpm and volumetric efficiency for what I call dynamic displacement the size of the engine at any given rpm (cfm). Basically cid x rpm / 3456 x ve% = cfm...

There's a formula cid x rpm x 0.0009785 / amount of cylinders = cfm So 360 x 5500 x 0.0009785 / 8 = 242 cfm

The question is really what's the rate of failure ? It's hard to believe that it can be a relatively high percentage and these cam companies could still stay in business.

What I don't get If the failure is high as people make it out to be how would any of these cam companies stay in business, none has done nothing to fix the problem ?

probably against the rules

MY cousin ran the stock two barrel over the eddy for his late model, one of the open wheel guy's said on the dyno the stock made more hp, enough to make up for the extra weight up high given faster lap times. Try both what ever gives better lap times go with that.

I don't get that why wouldn't it? 340 comes with decent heads and cr the two main things you require in a good shortblock, everything else to get there is basically a bolt on. We basically know you can get over 2hp per cfm, on a healthy street car it's more like 1.7-1.9 hp:cfm say 1.8 hp:cfm as...