Xtnct00WS6

iTrader: (8)

I think it's more accurate to say that a smooth intake runner would be optimal only in places where fuel does not come into contact with the intake wall. In my opinion, a perfect intake wall for our engines (non direct ported or carb'd where fuel will either not be in the intake wall or will be flowing all the way through it) would be a partially smooth and partially slightly rough surface. These surfaces would be dependant upon whether fuel typically comes into contact with it. If you're aware of boundary layers, then you know that a fluid flows faster on a slightly rough surface (properly sized CNC ridges). This is because the fluid fills in the small spots creating a layer for fluid to flow on top of itself. A fluid will flow faster on top of another fluid as apposed to a "smooth" cylinder wall.

I don't doubt that a CNC'd runner could be improved upon by someone hand porting it. I know, I did it with my 243's I believe this is because of the clearances that a CNC machine is confined by. I've never seen a CNC port that shows that the CNC tool was able to go from end to end. Because they can't reach all the way through there's a point they have to stop and then start back up from the opposite side creating a small ridge. Just by taking out this ridge, I'm sure there is flow to be had.

Adrenaline_Z

I'm not going to argue anything posted because I don't own a dyno, or a flow
bench.

Reading a couple of sources states otherwise however. I found an article on
Wikipedia which was also backed up by an R-M reference that stated:

Smooth surfaces impede air flow due to a thin boundary layer. This slow moving, or static air promotes fuel separation from the air stream.

Rough lines, or small grooves that run perpendicular to the air stream reduce
fuel separation and improve air flow within the intake port.

Quoted from Wikipedia:

"within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished port and a rough textured port is typically less than 1%"

I would imagine track testing would show a larger margin once fuel has been
introduce along with dynamic pressure changes in the runner during a 1/4 mile pass.

Greg Good

This is an amusing thread to say the least.

Studytime

iTrader: (15)

I'm beginning to put less faith in head work. Just Friday I saw a motor go from the mid 280s to 320 cfm head flow on a 23* head. It was a 355 ci SBC that picked up zero on a DTS engine dyno at 7400 RPM with an additional 30 cfm at peak and with improvements all across be board from valve job technology and back cutting the valves. Flow quality went from good to beyond great (for a 23* head) and power didn't change. These were pontiac SBC heads fwiw.

I've also seen atleast two other 355 chevy motors in the last two weeks not pick up anything from an additional 20 cfm. Really baffles me. With all this said, the difference in gains from a slightly low relative surface roughness to a higher one (such as a CNC) would be even less.

This data is coming from a DTS dyno and a SF600. With all this said, if you want more power increase your camshaft size and spin your motor higher. I'm beginning to put less faith in what I thought was the most critical aspect of a performance motor- the cylinder heads.

Ben T.

Studytime

iTrader: (15)

Oh, and I just wanted to say that my posts are written taking fluid dynamics into consideration. I studied fluids at Louisiana State University in my four and a half years in the Mechanical Engineering program there.

Ben T.

Adrenaline_Z

I'm sure there are a few head porters on this site that will jump all over your post (to support your data).

Flow numbers aren't always the tell tale sign of a strong engine. After reading
your post and your findings, it certainly backs up what they are preaching.

Kraest

iTrader: (3)

#1: Port Velocity.


#2: Check out some 3400 lbs stock eliminator cars running stock 23* heads and huge cams in the 10s all day long.

It's about the entire setup, not about each individual part.

Studytime

iTrader: (15)

I wish I could get some more input on this from other head porters. How can an engine go from 280 to 320 cfm and not pick up more power with the same everything else? The port shape on those Pontiac heads is about the best you'll get for a 23* head too. Everything was done right on all three of these engines I'm describing. I could understand that ideal valve events would change as head flow increases, but not showing any gain makes me wonder what's going on. Each case was extensively tested at varying EGTs and timing and on different fuels. The intake and cam weren't changed and the big tube dyno headers were of course not changed.

Ben T.

Studytime

iTrader: (15)

I'm not talking about low speed output, I'm talking about power at 6500-7500 RPM. Cylinder filling should be based more on flow potential than on low-speed velocity, and besides the cross sectional areas remained largely unchanged.

What was your point with the LT1 cars?

Ben T.

Adrenaline_Z

What depression did the improvement occur? Was the head tested at any
other depression? How does the flow react when fuel is added? What did
the low and mid lift numbers look like?

I wouldn't be so sure that valve events would change as flow increases.
The valve events are timed for the pressure pulses and RPM, not necessarily
flow of the runner.

Kraest

iTrader: (3)

Obviously you don't understand about the laws of diminishing returns when it comes to head porting.

To put it simply:
Too much head porting = loss of air speed and the ability to fill = loss of power.

Have you checked out what Advanced Induction has done with their LT1 stuff? Amazing. If you haven't, you need to.

Mike

Studytime

iTrader: (15)

Before you turn this into an emotional debate let me apologize that I didn't realize you were an expert head porter. "The laws of diminishing returns when it comes to head porting"? Please... I'm not even going to point out the ignorance in your naive posts or humor you with a response.

Ben T.

Studytime

iTrader: (15)

No other test were conducted at pressure drops above 28". The intakes were going turbulent at .550-.600" on some runners and each was corrected to not back up. Midlift numers were great and also largely improved. At .300" lift flow was around 230 with a 31* backcut 2.08" valve. The valves were previously untouched and an improvement of atleat 20 cfm was recorded in the .300 range.

Did I read you have been investigating head flow data at higher DPs?

Ben T.

Adrenaline_Z

No, not at all. The extent of my investigating stops at reading posts from credible
head porters, as well as texts from reliable sources.

I've been a little intimidated to port heads to date because of the complexity.
The more I read the more I think I know what I would do starting out...on the
other hand, it seems like a slight error could seriously ruin a port design.

I'd say the biggest tip I've picked up is to start with a relatively small volume
port and concentrate on the valve/valve seat area. Keep the air speed as
high as possible to allow for cylinder filling. Probe around with a pitot to find
the weak spots of the port.

Studytime

iTrader: (15)

Sounds like a good starting point, but meaningful gains will come from the SSR, port design, and the venturi shape around the valve seat. Or just port drag race heads. Port the straight side until you break through the head bolt hole and sleeve it and then port the curved wall until you break through the pushrod area slightly and just epoxy it. Shape the short turns on a bench slowly taking away material at a minimal rate. I'm sort of kidding around, but without trying you'll never know what you're missing out on or how much fun/entertaining it could be.

Ben T.

Greg Good

Ben, the cfm gain should have yeilded some substantial power. There is something else at play here. What is the runner volume of that head? Open carb or 390?

Greg Good

Find someone with a flow bench that will let you use it and just jump in with both feet. That's the only way you'll learn. Forget about surface finish for now because you're hunting elephant. Debating surface finish is akin to the "What's the best wax" debate. If you get up to the Pro Stock level then it'll be a concern. Go to speedtalk andread all of Larry Meaux's posts. While I don't agree with everything he says, he does has a good handle on port sizing.

Greg Good

I'd have to see that to believe it. When I get my hands on a set of these I'll let you know the before/after results. I have yet to see any cnc only head that could not be improved on. The one set I saw that did flow the full potential of the intake valve was huge at the short side. That set of heads has not gone down the track fast. All flow, no go.

Bader-X

iTrader: (2)

well their claim is no cnc ported head will *match the performance* .... that`s hard to do anyway the exact hp or flowor dyno number or what ever .... they didn`t say they are better! just not cpparison .... mayby their the worst and that`s why the other cnc perted heads will not MATCH.. -Joking- and maybe they meant what it`s suppose to mean that they`ll outperform ALL the GM castings CNC ported heads .... well why don`t TEA or PRC take that challenge or an vendor that do cnc porting! but please before they say stage 2 R was the a better choice for that test or our 2e heads or 33ZFGJYTF head talk with them first .... hehehehehe

Kraest

iTrader: (3)

Too late, tough guy. Looks like you need ego-stroking elsewhere. :shrug: