Point of diminishing returns with head flow on an NA application? Such a thing?

big cam, small motor, wickid heads-

is there a point where more head flow just wont help (assuming othre intake restricitons are non existant)

There has to be some point where you just cant feed anymore air into that cylinder. its just "full" You cant pack anymore uncomressed air into 90 cc's of space (rough guess of 302/8 + combustion chambers)

Is there such a thing? is it a non issue...

ok -

nevermind this post
(reasoning edited)

Back to 4th grade to practice the mathematics. ;)

i dont know how accurate the math is and i did'nt compensate for combustion chambers and exhaust left in there and overlap adn whatnot-

but logicly thinking aobut it-
i can almost always cram in more air

i'll edit out the math, i'm sure i messed it up using the calcultor on the computer

Well I wasnt talking about what's realistic and what isnt.

I stopped reading at:

320cfm= 3840 cim = 64 cubic inches per second


Those must be silly Canadian cubic feet, where you get less for what's actually in it.

Volume is a toughie, length x width x height. :D

McCaw, African Grey, Cockatoo?

Mike

Quick Correction. Volume is tricky! :)
552960 CIM = 320 CFM = 9216 Cubic Inches per second

Alex

LOL.. should change the avatar to Toucan Sam mayhaps?



Alright.. enough bastardizing Atech..

Is there a point? Of course.. you can obviously put too much head on something and hurt performance ;). It's a system.. and you can calculate everything considering the entire system & what you're trying to get out of it.

Remember, Pizza Makes Dogs Awfully Sick.

Originally posted by SkarodoM
LOL.. should change the avatar to Toucan Sam mayhaps?




Toucan Sam is not a parrot like Trey!

Mike

In the old days of head porting folks would just gut them, measuring the ports told them how "good" the heads were, obviously its more complex than this.

Point of diminishing returns with head flow on an NA application? Such a thing?

Yep.

Ever heard of Sonny Leonard? Well back some years ago I was one of those guys who had him build a 504 ci small block. I think Sonny's built 3 or 4 since then at my last check..... one of which went to Sweden (thse guys are nuts, and probably threw a 500 hp fogger on it).:D

Anyhow, you can imagine that an engine like that is gonna be severely head-limited. Especially when the goal is to turn it over 9k rpm and make ~1100+ hp n/a.

Only choice on that engine was to use a big-block head. Yeah, I'm kidding but a splayed valve GM head is basically just that.... just a bit smaller on the outside.;)
Now, to the point. You don't really "run out of head". The engine just makes alot less power at alot lower rpm. Take a 427 small block and put a 220 cc (310 cfm) head on it and a 255-ish cam. It might make peak power at 6k. Take that same engine and throw a 280 cc 18* head (390 cfm) on it and it revs to 7k and makes some 120 more hp.
So, a smaller head can still make good power but it limits the engine on it's true potential. Throw an sb2.2 on that same engine and it'll make 30 hp more on top with a few more revs. All in the heads.... well kinda.

-Mindgame

504ci small block? would love to know the bore/stroke and deck height on that one

doesnt surprise me of course that sonny is the one to do it :P

while i'm asking.... what are the common bores 'n strokes on those ~812 cube monster motors he makes?

That brings up an interesting point Mg. I have recorded flow charts for quite a few heads out there to get a little perspective on the flow vs. displacement vs. hp thing. Here are a couple

MTI S2 LS1:
.100 66/56
.200 144/111
.300 210/150
.400 259/178
.500 277/193
.600 286/205

This was on a stock disp. LS1 with around a 225 duration cam. It made around 420-430 rwhp at 6200rpm, IIRC.

Mild-ported SB2.2
.100 --/--
.200 164/105
.300 246/145
.400 300/186
.500 347/231
.600 370/245
.700 381/252

Winston Cup cars make some 700-800hp on 358 cu in engines with heads like these. But they are carbed, turn in the 9K rpm range, and the teams are very hush-hush about their cam specs. And from what I gather, they really don't start making power until 4000rpm.

A while back, Chuck went into great detail about the importance of AUC when comparing flow #s. From reading some of his earlier posts, even that AUC value can be a misnomer because it doesn't take into account the inertial ram effects. I've heard that with a properly designed intake manifold, you can have anywhere from 5 to 10psi waiting on the back of the intake valve when it opens. I guess when you consider this, there really is no point of diminishing returns on head flow in an NA application. It's all in how well your intake can take advantage of 1st, 2nd, 3rd, etc ......wave tuning to get the power band you desire. All within the constraints of compromise, of course.

One of our fellow members here has put a set of SB2.2 heads and intake on a carbed 409 cu in LT1 and talks like he's going to take it up to the 7K rpm range. With the added displacement, I'm very curious as to what kind of power he'll make with it. Obviously, he should be the fastest NA LT1 to date.

Quite interesting

I don't foresee the LT1/SB2 combination to work. By all means I hope he proves me wrong, but a cylinder head with 290+cc runner volume, combined with the limited displacement of the LTx block, would require an extremely high rpm. Combine this with limited block stability (Cap shift etc), and I wouldn't want to spin an LTx block to the range that an SB2 headed sub ~400ci engine would require (All of these cubes which have come by the way of stroke, and not bore, causing insane piston speeds). JMO though.

My personal engine has 240ish cc heads, flows ~360cfm @.700, and is spinning to the 8000rpm range. I think this combination will tend to actually work better, but then again maybe I'm biased. :)

As for the 8xx inch engines, to the best of my knowledge this is basically just a super stroker, w/ a standard 4.6-4.625 bore, and using a stroke in the 6" range. (4.600bore x 6.125stroke = 814ci). Anything over a 4.6" bore begins to become ineffective due to time for the flame front to travel.

There's always a point where it's too much.

A wise man once explained to me, " Your lungs represent the engine
displacement. This straw is analogous to the head runner volume.
The sugar will take the place of the air/fuel mix.

Inhale swiftly and observe the amount of sugar you can suck up.

Now replace the straw with a short toilet paper roll.

Repeat the experiment."

Assuming the same cylinder head volume, I would ASSume no.. there is no such thing as too much flow.

Also, you have to take into account that the cylinder can still fill past BDC due to inertia..

Originally posted by JordonMusser
Also, you have to take into account that the cylinder can still fill past BDC due to inertia..

Well some inertia but more to do with intake pulse tuning, 5psi of pressure is going to overcome the pressure of the piston coming up in the bore.

Bret

Originally posted by JordonMusser
Also, you have to take into account that the cylinder can still fill past BDC due to inertia..

If the velocity gets too low, I'd think that would kinda kill any inertial effects.

Getting back to the original question, given a particular displacement and cam, of course there's going to be a point where additional head flow just doesn't help (or at least you reach a point of rapidly diminishing returns). At that point, you either throw some more cam at it and move the powerband up, or put some additional displacement under the heads to take advantage of the additional flow. Putting too much head on an engine is entirely possible, but I imagine that it's a lot less common than too much cam just because of the cost hit.

Originally posted by Jimmy17
504ci small block? would love to know the bore/stroke and deck height on that one

doesnt surprise me of course that sonny is the one to do it :P

while i'm asking.... what are the common bores 'n strokes on those ~812 cube monster motors he makes?

The 504 uses a 4.25 bore (relocated) in a tall deck rocket block (custom made head gaskets and spark plug relocation). Crank stroke is then 4.437" billet with a special counterweight locations. Titanium connecting rods were 6.1" center to center. Manley titanium valves 2.28/1.68..... valve lift ~.800.... you get the idea. Everything is
BIG... then again it needs to be. HP peak was at 8700 rpm.

-Mindgame

Originally posted by KTamez
I don't foresee the LT1/SB2 combination to work. By all means I hope he proves me wrong,

I have to find that link to that 9 sec NA LT1 video. I saw pics of it before the run and they didn't look like LT1/4 heads or AFR's.

BRB

LS1's server is taking a crap again so I can't search for it. I'll try tomorrow. sorry