When you speak of inertia, do you mean when the air column is at rest and we are trying to move it?

If so, then yes, we use overlap to get the intake column of air moving, but anymore than that is too much, and yes, the key with overlap on a long runner engine is to just clean out the chamber, nothing more, nothing less.

When you speak of exhaust reversion, you are mostly talking about short runner intakes at low engine speeds. I am specifically talking about what happens with a performance engine with a long runner intake at WOT, these engines just don't do the things most people "think" or profess.

The engine will visually tell you what's going on here, and if you have it right, simply by the amount of carbon in the intake port. I think you would have to admit that if an engine has exhaust reversion into the intake port, it will have a dirty intake port? The intake ports on my engine look like new, with no traces of carbon, or exhaust contamination. If you look at my valve events, my intake centerline is 114, but my engine make 600 lb ft of torque by 4100 rpm. Most would say these two things can't coincide, but a engine with a long runner operates that much differently from a engine with a short runner. We have to open the intake valve later to reduce over scavenging but we can close the intake valve later to take advantage of the inertia ram and ram tuning effects.

Once again I will reiterate, when you have a short runner intake that moves a ton of air, the more you waste out the exhaust during overlap, generally the more torque it makes. When you have a somewhat restrictive long runner intake, the air column is acting like a big spring, and it is hard for it to "refill" the runner before the intake stroke is over, this is why it's so critical to not over scavenge a long runner intake, it will KILL peak hp.

 

I know this is a generalized topic, and your intial statement was more generalized, but now you have specified the application you were implying or cleared it up......

the issue of overlap:
Now when the EVO, the piston coming back up during the exhaust stroke, it is pushing and excuvating the exhaust gases out the cylinder through the open exhaust valve. We can get into wave pulses but thats another saga but it actually helps induce the intake flow... Camshaft valve timing events dictate this opening or closing in a sense of these functions, But my point is that if the camshaft timing is selected properly for a N/A street performance engine(drag or strip car different ballgame), and the exhaust system is selected properly, there should be none to minimal residual exhaust gas left in the cylinder..... Again as I stated earlier this is where camshaft timing events primarily come in and a correlation of exhaust system....

I think you are thinking along the correct lines but are wording in a obtuse way...... One thing to remember, when we talk out loud or post, etc.... people sometimes think these timing events are happening in slow motion or matrix like time, but the time is actually milliseconds or <..... With that said the point I have been saying is that in a literal sense is the cylinder does not care about port size, exhaust system, even camshaft duration.... The only thing the cylinder cares about is how much volume of air and the quality of fresh air to compress,ignite,and and then push out, but the pushing is more of a byproduct function... When you have a condition of mixing the fresh air intake charge and left over residual exhaust gases it hurts VE
and the fresh airflow volume is not optimalized.., flow quality will be delayed or suffer due to poor exhaust gas excuvation. It is vital to have quality cylinder fill during low-mid lift and efficiency in the completion of the 4 stroke cycle, especially at higher rpms, which is the key to making more power at higher rpms along the torque curve... The mixing of the fresh air charge and exhaust gases henders combustion efficiency right? And anytime you mix the fresh air with exhaust gases whether it be residual or of great volume you will have a condition of not making optimal or most efficient power.... But to say that the principle function of overlap is to clean out the cylinder soley is a bit general ... Yes it is true that too much scavenging or overlap can create a condition of blowing out the fresh air intake charge, but its principle function is not to clean out the cylinder soley... Ie conditions of negative overlap and situations like some performance,factory, or some circle track running 116-120 LSA's

For the sake of conversation, even if you if you did say that it cleans out the cylinder, then we can look at it as the EVO/EVC was delayed too long in correlation to the IVO.....

Now think interms of early EVO, shorter powerstroke, less low end torque, but better excuvation of of the exhaust gases... then combine it with delayed intake opening/closing, you will be able to efficiently complete the 4 stroke cycle at later rpms until the point when the cylinder combustion effciency decreases along the torque curve, which is result of fresh air and exhaust gases mixing...


So yes you are correct as I have been saying too that valve timing events are the key in correlation to the square ports and hell even the cathedrals port cylinder heads period...... No carbon in your intake ports are a good sign that you have perhaps done well selecting the camshaft timing events and other systems.... Good job


Bozz

 

Basically it sounds like the long runner factory style plastic intakes are what is the problem for getting BIG performance - NOT the square port heads.

 

Most square port heads have huge valves (2.16"-2.20"), most cathedral port heads have smallish valves (2.10" or less), both will make good power.

The heads with the smallish valves tend to be easier to cam.

Everyone assumes the big, high flowing square port heads that are flowing 20, 30, 40 cfm or more air then cathedral port heads, are going to make a corresponding amount more power, but it reality, that hasn't come to fruition when using a long runner intake.

On an engine like my 454, or some of the other engines that big or bigger, they have all made over 700 hp. My 705 hp 454 makes 1.552 hp/cu in, Steven Rupps 461 with square port heads, that probably flow 20 or 30 cfm more than mine, made about the same hp/cu in, give or take.

So the bottom line for me is, when using a long runner intake, the square port heads are of no real advantage, and are somewhat tricky to cam when used on smaller engines, like the 6.0/6.2 stuff.

 

You can make big power with either...or you're doing it wrong.

My L92 heads made 715 hp from 416ci or over 1.71 hp/ci. Next season I'll push for 1.9-2.0 hp/ci with the same heads and bottom end.

 

The 1.5-1.6 hp/cu in range I referenced related specifically to hydraulic roller cammed engines with Fast intakes with 12:1 compression or less, which is what most people run on their street cars. We've made 2 hp/cu in with cathedral TFS heads, of course when carb style intakes and solid roller cams are thrown in the equation, things change a LOT.

You have a nice buildup, enjoy!

 

Track times?

 

http://speedtalk.com/forum/viewtopic.php?f=1&t=20021

Here is another thread I find infomative. It includes the opinions of some very notable cylinder head porters.

Outside of EMC, we build engines to put in a car and go down the track. All the bench racing and throwing around hp numbers is moot without timeslips.

Keep in mind everyone is selling something...maybe even a full tilt killer LS3/76/92 program

 

It is fresh out of the crate as of one week ago...so not yet. I hope to have some in spring.

You just linked to a thread where Bert the throttle body porter is spouting off "knowledge" and that makes such a thread suspect to begin with.

But I do agree that track times tell the real story.

 

Yes I guess anyone who is a knowledge seeker has read this thread before....
But the problem was that you had a mix of conventional wisdom mixed with new horizon......

What it boils down to is the camshaft timing events need to be selected based on the application and head characteristics.... And in the past when the L92's cam out and sometimes even now, you have guys trying to implement theories that worked for cathedral ports designs with theories that don't work for the square ports and vise versa.....

Its funny because when the gen I,II 23* heads once people finally got a grasp of how to make em work, then the cathedral ports cam out and there was a struggle, arguments and resistance of the new progrssive cathedral ports.... Now you see this happening now with the square ports....

I another thing I find funny was a guy over in the dyno section ran a cam they maybe I deal for L92's(222/234 115) but not for cathedrals and his results were decent with the AFR205...
https://ls1tech.com/forums/dynamomet...5-results.html
But the first thing that was said was, "the camshaft timing events were all wrong for the cathedral ports"... Not taking a shot at AFR but why can't this same conventional thinking or excuse be used when examining square ports, especially when camshaft timing events are not optimal or selected properly?

People often stick to what they know vs what they could possibly learn..... And some people are very slow to change..... We see this socially everyday...

I guess guys are getting lost within the thread as viewing this as a competition of square port vs cathedral port... I don't think this is the premise of the article or thread.... All that is being said is, they are not a slouch, slow, poor head as what has been marketed..... every head has there place or effciency based on a combination of functions and desired goals....


Bozz

 

So...does this mean the cathedral heads win hands down? Based on the thread you posted and track times?

 

We're working on finishing up the PRC LS3 aftermarket casting heads, but currently I really like what some of these well setup cathedral heads are doing. We have a 240s cc cathedral head that moves over 370cfm & is almost production ready!

 

im ready for the aftermarket L92 to be released i know prc wont be the only company on the market, mast already has the small bore L92's but they are quite expensive

 

I am not sure I am qualified to answer that question- and I am certainly willing to admit it. There could be something I missed or some factor of which I am unaware. I only offer that maybe we should all consider there is far more to a cylinder head than flow numbers. In the mentioned thread, Mr. Greg Good makes some very good points that are reasonable and which seem to be disinterested. The points he makes are ones which I believe only a cylinder head porter can claim- which is why I posted the link because I cannot comment on the principles of which he is discussing. There is talk of wet flow, chamber design, casting design, etc... all of which is offered by someone who has the credentials and the experience to say so. (I don't take a lot of what Mr. Bauer has to say seriously because he is rather contrary which calls to question his ego and how that becomes involved in the discussion).

I think what the rest of us might be better limited to, are the results we have recorded and the performance we can report to others that may be interested here on the message board. It seems that time slips are the best sort of real world results to either support or deny claims in either direction.

Bascially, I haven't seen anything that was overwhelmingly impressive insofar as the LS3/L92 builds. For the fact those heads seem to show higher flow rates makes the mediocre results look even less apealing. A lot of the cathedral port guys are getting down the track just as well with "less" cylinder head. Everyone has a motive for what they say- which is why I made the statement that everyone is selling something inlcuding the guy who says he isn't.

Personally, I don't really care either way, because I am using LS7 style heads on my new engine. I just wanted to offer the alternative opinion because some of the stuff in internet land gets a little crazy. Bottom line and real question is: are you having fun building your hot rod? If you get too caught up in this crap, you begin to lose perspective and it can wear down on you. Choose what you will believe wisely.

 

Id be curious to see as to what would happen if you took some of these higher horsepower fast intake engines and put a carb style intake on them?will pwer go up/down
will torque curve shift but peak the same?
would a l92 based head ahve a decisive advantage over a cath port head if they were both carbed?
Brian,kaltech,melsie68,any one else care to share there opinion?

 

When swapping from the Fast to a good carb intake, most engines are going to make more peak horsepower but suffer low end torque loss. The engine can be recammed to crutch the torque loss, but comes at the price of idle and drivability. A larger, higher flowing head with a carb intake, can usually be made to have the best all around power, but may not have the best drivabiltiy.

An engine with a Fast intake makes for good all around torque, power and drivability, but is finicky in terms of head port volume, valve diameters and cam timing. The Hot Rod power testing is a prime example of this.

The big heads when coupled with a good carb style intake on a large engine really start to shine.

 

The reason I was asking is because Greg used to argue this same topic with me, but after the results continued to come in, he agreed. Coleman Roddy running 9.15 on motor with a Fast and a hyd roller cam and James Day (TXCAMSS) running 9.30's with a Fast and hyd roller.

The square port heads with Fast intakes and hyd roller cams just don't seem to be as fast. This is not because the ports are square, it's because the ports and valves tend to be too big to work well with a long runner Fast intake.

 

The newer James and Sheila Day engine I think may even be faster and still with TFS cathedral ports! Hoping to see low bottom 9s with it soon.

 

Update those heads with the 245 intake port and nitrous exhaust port! Nice work on that engine, and James on the setup!

 

So Brian, You say it realy is the oem style intake that is holding the square port heads back.
Ultimately, I dont beleive that aftermarket heads should really be compared to the factory square port heads. The oem heads should be compared to each other, and I beleive the square ports have more potential - oem to oem.
Lets compare aftermaket square ports to the aftermarket cathedral's