Heads...intake Vs Ex ratio's ??
 

I suppose I am overanalyzing yet again.....but would really like some input from an engineering point of view.

I am considering new heads for my Procharged 408. As usual the "search" function comes up with dozens of threads bordering on civil war as to who make the best product....

Using Brian Tooley's "under the curve" formula has brought some enlightenment....thanks.

seems everyone is focused on the intake side of the flow charts. I am of the opinion, that what ever goes in has to go out somehow?? especially in an FI situation.

So here is the question, is there an optimum Intake Vs. Exhaust ratio? I realize that it will be different for an NA vs FI application, but would really like to see some engineering data on this.

Assuming I am supposed to leave specific brands out of this thread, I will be vaugue.

I was planning on utlizing a certain head that would allow for the better flowing Gen IV OEM intake manifold. Then I find out that the exhaust flow is no better than the "budget" heads I currently have. On the surface it seems pointless to spend big $$ for better intake numbers, only to hit a roadblock before I even hit the header???

2 things....

Intake to exhaust ratio is BS

"Area under the flow curve" is BS as well.

Well I have learned alot already.......thanks:thumb::bang::bang:

Your knowledge surprises me, Jess. You do seem to hang out with some savvy folks.

OK, I'll buy into both of those statements.

Are you goin' to tell (some) of us who don't buy into that why it is?

I'm guessing that flow at higher lifts is way more important than flow at lower lifts which makes AUTFC invalid. Am I close?

It always amazes me how much bad information becomes Gospel to so many people. One little part of me says that perhaps that is a conspiracy among those who really know what works and want to keep the good information from the masses.

That's not true, because the folks who I deal with who know what works and make money building engines/parts that work (read that as "make power") actually feel sorry for the folks who believe the BS, but if they tell the truth they are mocked or put down for going against the Gospel. After a while they give up trying, and just make money helping folks go fast.

Sad state of affairs, ain't it?

"Who do your trust?"--The Joker

I do not agree intake to exhaust ratio, how can "THAT" be BS. Crappy formulas or ideas, on the subject? What are you calling BS on. Please explain.

i would like to know what she thinks as well,or anybody else that doesn't agree with an "ideal intake to exhaust ratio"
i know of several other experts that don't subscribe to this theory also,and they don't post up on this board,at least not very often..
does anybody else have an opinion,or different theory they would like to discuss?

Ah, so your saying you can have an intake port than is four times the size of the exhaust port and all will be well?

look at the L92/LS3/LS7 heads,they definately go against the old 70% exh. to int. ratio theory...but GM invested a lot of time and money in them,and they definately work..so i think Jessica is on to something..

If GM, for some reason, has a goal of 4:1 int/ex port, they'll design the shit out of it, and all will be well.

Just how did you mean that, deuce? :)

My take is that if your intake port makes lots of power (not flowbench numbers) your exhaust port has to get the residual products of combustion out efficiently. Because the delta p in the exhaust is huge compared to the intake, each exhaust port needs to be tailored to match the power the intake port allows to be made. I can't imagine coming up with one intake/exhaust flow ratio when tested steady-state on a flowbench that would be valid for many head/port configurations on a running engine.

So let's work on getting more air into the running engine and then doing the exhaust port well enough to let it out. That leads to large intake/exhaust valve diameter ratios like 2.2/1.6, but not necssarily intake/exhaust flow ratios from a flowbench. LS7/L92 look familiar here?

Anyway that's my take on it. Jess or others may have a different take.

my take on it was that you can't use X percent exh/int ratio for all heads/port configurations/valve sizes,etc..you have a hell of a lot more knowledge of what happens in a running engine than i do,and explained your theory very well...
and just to show more of my lack of knowledge to the tech world,what the hell is delta p?:emb:

as with everything its a systems approach...

its about "where" you want the torque peak(bmep), its about emissions, its about BSFC, its about countless other factors.

Delta P is very important (Pressure at location 1 minus pressure at location 2) because without differential pressure, there will be no FLOW.

all we need is an in cylinder pressure plot to get the full picture.. it makes so many things considered "black art" much easier to grasp.

the question is, how much energy to pump exhaust are you willing to give up to ensure excllent cylinder filling

Could someone, anyone, elaborate on this?

Good post, Dan O. (Why do I always want to say, "Book 'em, Dan O!"?)

Yeah, delta p is just the difference in pressure. It is why we have wind in our climate. Air flows from those big Hs in the weather map toward the big Ls. Same thing in an engine.

I suggest that good engine designers take into account those varying pressures inside the operating engine when they create port shapes, design intake and exhaust manifolds and specify valve events.

As far as exhaust pumping losses, I would continue to favor the intake until I lost power. Of course determining where that point is what separates the winners form the also-rans. Anyone making his/her living from this knowledge or ability to determine same isn't about to tell. They may sell you parts, however. :)

Jon

One reason I used the term delta p was to get folks thinking about what it means. It's no sin not to know. The sin is not asking.

FWIW, the Greek letter Delta (Ä) is often used in math to mean a difference. The p is often used for pressure.

Good question, deuce!

Jon

Still no answer to the question? Why is it BS? Old formulas? What? I promise you exhaust flow matters. It did on my Nitrous motor. I question was
Short answer. Yes! Not BS. Do I know of a formula to find what is right for your combo. No. Maybe someone does.

Hopefully someone will step up and give some guidance. thanks for getting back on point.

Maybe for a given head in a given application there is an optimum int/ex. ratio.
But to think there is a certain percentage that is the best is just wrong. Different applications will want different results. The very idea that you may would want to limit one or the other to reach an certain percentage is just goofy. Get as much as you can out of both sides and design the cam to accomodate the head.

i believe our statements above show that it is BS. While after you optimize all of the events.. you can 'calculate' your intake to exhaust flow ratio.

Basically, we are saying that flow RATIOS are BS, GM has proven this.

Here is my basic comment for NA engines..

-You only have a maximum of 14.7psi/101.325 kPa pushing the air into your cylinder (best case)

-But you can have sigificantly more pressure pushing the air out of the cylinder

You betcha, Dan O! Most of the exhaust gasses get out of the engine in relatively few degrees of rotation and at a high delta p. I liken the intake to older, experienced sex: not too fast, but very fulfilling. Exhaust on the other hand is more Wham, Bam, Thank You Ma'm! Some of you younger sprouts might relate. :)

If you ever get a chance, look at the difference in porting between intake and exhaust ports on high-end heads that make high-end power. What works in an exhaust port doesn't necessarily work in an intake. That's more important than the flow ratio at 28 in. H2O.

Jon