Agreed, but to answer the original ?
YES. I would also like to see some more engineering data an the subject.
Just like flow numbers, we can have two heads same everything (vavle size, Port, etc) and the one with bigger numbers may not make best HP or torque. Are Flow numbers BS? No! (WELL SOME ARE)

I think it is great if the advanced section had more advanced discussions, but just dropping in and saying BS?

 

I would attend those classes as well, and probably fail, but I would never be absent....

 

Great, if you want to call Vizards 80% numbers being applied to say ls1 BS fine. I also agree about it not applying to all lifts.(formulas) But why is considering, and wanting to learn about I E ratio BS?

 

The funny thing is I do not dissagree with old stroker. The problem is Jess never answered the question. My point was if you have an engine whatever it is with out changing cam, just porting or changing valve there is a point that is optimal for the combo. Maybe not all the rpm range, but makes the car go down the track faster. That is what I was trying to get at. It just pissed me off for her to jump in and call BS like she is some head god, with no explaining. I am so great I call BS. It was a ?, with an explainable answer. That is the only reson I even chimed in. I hate forumn pissing contest.

I think you once saidAgreed, But what is you are in a cam limited class, by adjusting I E ratio you would find an optimium point? TRUE?

 

I agree that the ratios espoused by Visard and others were based on small block Chevy heads and were mostly based on single pattern cams as I recall. I think that the 70% rule is a rule of thumb based on experiments (empirically gathered data) using porting techniques that were optimized for that era. However, they didn't have the kind of sophisticated fluid dynamics software that is available to manufacturers today. Now, an OEM can run many iterations of port design variations/valve timing events and lift variations/etc. to meet their design targets. I'm sure that once they narrow down the choices with computer modeling, they try many cams/ports/valve configurations to get their results. I'm also pretty sure that the folks who do the computer modeling have a good intuitive grasp of the task and lots of hands on experience.

I work for an aircraft manufacturer and the folks who are really sharp on computational fluid dynamics (CFD) are also very knowledgeable from a practical sense and can look at the shape of an airfoil and approximately predict what the computer program will tell them. However, they rely heavily on the computer and do wind tunnel verification of the predicted outcomes. All of this is a blend of art and science that exceeds the knowledge base and computational ability that was available a few short decades ago.

Steve

 

Steve, I suggest that there are ways to compliment CFD and actually run a much larger number of iterations to home in on "best case" for a given application. I suggest that there could be people far removed from OEM who do this well. I'm not one of them, BTW.

Part of using stuff like CFD is interpretaton of the results. It's sorta like reading x-rays or an MRI, CAT or PET scan. The knowledgeable radiologist gets a lot more out of the data that the average Swinging Richard, or even the average MD. That's one of the reasons radiologists make big bucks. In our engine world, the "radiologists" are the savvy engne designers who gather lots of good data and understand what it is telling them. They often are also financially successful.

Jon

 

Ol Stroker, I guess you are so proud of your self, or to busy staring at Jess's avitar, that you have not read what I am saying. I DO NOT DISAGREE WITH YOU. BUT why would she call BS to someones question? And better yet why do you try to answer for her? He was not asking how to get a formula to design a head around he was asking. He was asking about the subject. MORE INFO. No matter what it is, there has to be an optimum point. I am not even saying you need to know it!
Sorry I got into this I was trying to get her to explain her point DUH! Maybe I am wrong, to me a simple BS statement with no explanation, seemed lame.

 

I corrected my errors quik and saved Steve a lot of bandwidth.

Time for more Glenmorangie.

 

FWIW Darin Morgan says he looks more for velocity through the exhaust port than cfm from hogging it out. (ie) Efficiency
As has been mentioned temp and pressure is vastly in excess of anything that a flow bench will allow you to measure on the exaust port. So experience of what works on the dyno and at the track becomes very important.
He stated that many times a port with less flow than another port would put down more power.
Dont ask me to figure it out yet, Im still learning

 

Here is an example of what I am trying to figure out>



disclaimer: these flow numbers were taken from sponsor websites their absolute accuracy is unkown to me....

This is a very good pictoral view vs reading numbers. As you can see the intake #'s are very similar....albeit one is a 235cc runner and the other a 250cc . Of note is the very large difference between the two in exhaust #'s.

Now my simple minded brain tells me that in an FI situation the lower flowing exhaust would create higher boost numbers due to what appears to be a built in restriction. Would this also result in better torque when not in boost????? Would I net the same HP rating utilizing the other head, at a lower boost #???

This assumes that boost is strictly a measure of airflow through the motor.....or lack thereof.

Hence my dilema, one head gives me the opportunity of using the LS7 intake, but appears to have lower exit numbers than many of its rivals.

The "other" heads have much higher exhuast numbers, but as we all know the intake runners outflow our intake options......even a ported FAST.

In my case a sheet metal custom intake is not in the cards, I at least need the appearance of OEM for the SMOG squad.

 

b727pic, could it be that the 235 exhaust numbers were tested WITH a pipe and the LS7 exhaust WITHOUT a pipe? You might check into that possibility. It makes a difference if you are comparing heads./ports.

Jon

 

Actually you bring up a good point, the lower flowing head was tested without a pipe. But I am pretty sure that wont make up 50 cfm??? as memory serves I thought 10-15 cfm was the average of pipe vs no pipe???

 

Jon,
I agree that CFD is no silver bullet. I was just looking at the original question about the validity of intake to exhaust ratio targets and b727pic's reference to the Gen IV OEM intake manifold technology. I'm saying that the modern GM head design probably defies conventional wisdom for good reason and tools like simulation software and CFD are probably used by OEM's to factor their design decisions.

In my experience, an OEM will make up a decision ranking matrix (at least on big issues) where by the criteria are chosen and given a weighting factor. You might have criteria like:
Achievement of Performance Goals
Durability
Cost of Production
Ease of Assembly
Maintainability
Typical Production Yield
Weight
Cost per Unit

Each factor is weighted and different production options are assigned a score (maybe by a committee or a group of individuals). The decision is probably going to be based on the weighted score. This is design by committee, but in a production environment of a mass produced product, that's what you have to do to make a return on your investment. I'm just trying to give some insights as to how some of these decisions are made (again in my experience).

Steve


Steve

 

I'm surprised no one has mentioned compression ratio yet... that's got a big effect on how well a given I/E relationship works. Why has to do with delta p...

 

In an NA application I would agree, but for FI I wouldn't think so....

 

Good points, Steve. In the OEM world there are even more factors than you mentioned. As well as the groups work together, the "Platform People" (PP), those responsible for the entire vehicle, seem to pull more weight than the "Powertrain Folks" (PF). Obviously there are mandated emission goals, and Corporate desired fuel efficiency goals as well as peformance goals of the PP. Fortunately in th C6 the PP agressively "designed in lightness" which made the PF job easier to achieve the performance goals. Many of us know that the LS7 has many more ponies lurking just a short distance under it's skin.

In discussion with one of GM's top PF, Ron Sperry, as well as others, the stuff that PF want to do can/is overidden by PP. The LT1 is a good case in point. The details are boring, but PF wanted a somewhat different design which we all probably would have liked more now that we heavily modify them.

IMO, the LS7, L92, etc. heads are the production version of what has developed from racing/high-power development. Truly, the LS7 is not a copy of an SB2 by any stretch, nor a C5R, but there are airflow concepts that have trickled down to production from 2-valve race engines. These concepts are not necessarily the same as what we've always done with the SBC, SBF, etc.

Again, IMO, a good share of the aftermarket engine guys have not yet learned to exploit the LS7/L92 type of heads/inlet manifold. I won't go into my reasons for saying this for a couple of reasons. One is proprietary, another is that I'd probably insult some engine builders and another is that it is my opinion and not necessarily documented facts that I can share.

There are aftermarket folks who have achieved things with GenIII/IV engines that OEM may have tried to duplicate, but have not been able to, as far as I know at last checking. Those aftermarket folks are not using CFD, because it is WAY too costly for them. Remember, CFD is just a tool. It evaluates your design, but it doesn't necessarily create a design. Question: who collaborated with GM's PF on the design of the ports for the LS7 head? A private contractor whose name would probably be familiar. Google knows.

Steve, it's been a long, long, long time since I was in the OEM business, but the decisions may not be as mathematical as you suggest. There were and still are very strong personalities among PP and PF in the OEMs I am somewhat familiar with. My wife just purchased a 2008 Malibu LTZ to replace her Audi. I was amazed by the Malibu. There is so much Bob Lutz in that car when it comes to the lack of compromises that I really like the car. The last Chevy sedan I really liked was my 96 Impala SS killer-whale. The 'bu is quicker.

End of ramble. Time for some more Los Cardos Cabernet Sauvignon.

Jon

 

I think you might want to research that a little further. If you are correct, which head actually is making more power in the real world? If it is not the higher flowing exhaust by a significant margin, why all of the exhaust flow? Does it make you think? It surely does me.

Jon

 

Jon,

That is a very valid point, trouble is finding a true "apples to apples" sampling of the "LS7 style" heads dyno results. found a few NA results, but so many variables between motors its inconclusive. I found nothing for comparison in FI applications.....Just has not been a very popular idea for some reason? May simply be the cost difference between any of the cathedral options vs the LS7.

 

IF I were doing a forced induction LS engine, I would purchase the performance I wanted by getting heads and valvetrain from the same source which were matched to my displacement, boost and desires for output. I then wouldn't need to worry about E/I ratio, valve size, spring load, retainer mass, etc.

BTW how far north of 1000 hp are you looking for?

Jon

 

Jon,

Acutally that is the plan, I will have that discussion with a sponsor soon. and I agree that a matched set is the way to go....

However I am the type that try's to gain as much understanding as to the whys and wherefore's which will hopefully lead to a practical application, vs "experimenting" with high dollar toys.

The whole purpose of my original questions was after much reading, and plotting out head flow data it seemed to be a black art and a bit mystical to me....Lol

As for my goals.....1000 FWHP is about the Max I would want for the street car. Once there I may even have to reign her in a bit...we shall see. In reality its all about the sum of the parts working efficiently with each other...whatever the outcome.