The cathedral port has velocity? Let's see.... the L92 head has 3.05 square inches of port area near the intake manifold....the LS1 has 2.6 square inches ( and most ported versions are near 3.0) and the manifold runner quickly expands to 4 square inches near the plenum. I don't call that a head that produces good port velocity (and people wonder why their 6.0 truck motor won't pull a trailer in overdrive). That, and the radical change in shape of the port from plenum to valve, has been the downside (one of very few) of the LS1 from the beginning. GM has known this since they raced this engine, which is why the C5R head was a different port design from the start. The truth is that the size of the LS7/L92 intake port is STILL too large for anything other than a 427+ inch motor making 750+ crankshaft HP.

Brian
HiTech Motorsport

 

When will you have my l92's done brian? Then we can swap my heads out to see the differance to my ls6 heads.

 

What are you doing home???? Shouldn't you be working on my new shop right now?........come on...... you can sleep all you want when your dead!

 

Mike - Is Brian porting some L92's for you and what intake are you using? Curious to what valve size, combustion chamber cc, etc you're going with.

Gino

 

And the chrysler 5.7 hemi has port that are to big to i geuss huh. Have you seen them they dwarf the l92 head.When are you guys gonna realize the port size has little to do with velocity. Secondly the longer the pipe the smaller it acts. thats been the problem with the ls6 FAST intakes for years working north of 6400rpm or so.I geuss the engineers at GM and chrysler just don't have acess to the development tools everybody in the aftermarket does.

 

In light of all this discussion about the intake port, i've been looking for an answer to this question for a while.

Does anyone think it would be a good idea to do a full port & polish on the exhaust ports, and only a polish (no port) on the intake side? Maybe not even touch the intake port at all? That, with a ported L76 intake would be a decent combo, not open the intake port too large, and maybe even save some money by not going through with the full port. Also possibly run a slightly smaller valve - would this all be beneficial?

Thoughts?

 

Let think about the intake port. Deflash and bowl blend to seat along with good valve job. Yes exhuast could use a bit more volume.

About the port size issue.

2 ways to think about this. granted we are dealing with a fluid distrubition system that has an almost capilary action in it behavior lets compare this to an elecrtical circut.

circut A is a High mpedence 8 ohm subwoofer. This subwoofer make 90 db at 4amps and 25 volts. coclusion 100watts of current will flow.

circut B is a 2 hom Low impedence subwoofer. This subwoofer makes 100db at 10 amps and 10 volts or 100w.

electrically both of these subwoofers apear to be similat but they are not.

Subwoofer A and B use the same amount of current but they use it differently.

Subwoofer A is lazy due to it weaker magnetic field. Subwoofer A also has less output per Watt then Speaker B becuase Speaker B creates more magnetic field for a given wattage becuase more current is consumed.

How does this affect and engine. velocity is like voltage. its not the amount of current but its the Pressure like water in a pipe behind the current.

Speaker B Has more output becuase at a given pressure it moves more current. Now what more interesting is that Speaker B is cripser clean and louder at the cost of one electrical property. dynamics.

Speaker A will be more responsive across a broader range of Frequencys becuases its field is more easily varied. Less total current but more voltage. The voltage is higher so speaker A is smooth and flatter becuases it easier to control pressure then flow.

Speaker B has less overall sonic range but does have large amplitueds and is faster at changing state backwards and fowards at a given FQ. Outside that FQ however speaker A takes the lead.

engines are not really that different in reality. Cathedrals help flatten the TQ curve by driving up voltage and they do so by keeping the totalt flow pressures high.

these new port should allow you to make more power in a given range but will not have the dynamic width of the catherdrals. the catch in this is of course what is the helmholtz tunning region and the difference in impedence between the ls6/Fast catherdral and the L76/ls7 rectangle.

Just remember honda engines have Huge valve areas and cross sections and with variable vlave timing arrangements manage to make Low end T and High end HP by juggling the cam timing to chagne the Input and Output impedence of the port and take advatage of it.

Enjoy.

 

Well written unbiased post!
I believe that most of the people (including myself) that are excited about these heads are searching for big HP numbers with their project.
As such, everyone will be running a 2,800+ converter with their combo, so the small difference in power below 3,000 rpm is not of much concern.
Even with a street car, the time spent driving at or below 3,000 rpm
will be during light acceleration or cruise, so what is the big deal.
I am waiting to see someone post dyno results with a turbo L92 setup.
I might be the first guinea pig with my twin turbo L92, if I can just get it ready by spring. Time will tell....

 

I have a set of L92s being "done" by the guys who developed the GM carb manifold as tested for GM. They have been working with these heads for many months prior to introduction. Their CNC program which evloved from this testing does not do much other than valve jobs and a bit of clean up on the exhaust side. I am having some milled of of course, but as you can see from the picture I took at the Chicago show last year, there is not much one can or should do, on the intake side.

 

Robin,

LOL I didn't know your mom raced?

Thank god someone else backs me up on this L92 deal.... there is room for improvement with the valvejob, but like all stock valve jobs thats the case. Other intake port modifications take one hell of a trained eye.

Your LS7 example is perfect, in fact modified versions actually HAVE lost power.

These two intake ports were well designed and not crippled by the need to have perfectly straight pushrods. I like that Ron designed the original motor like that and the cathedral shape was made like that to get the proper CSA for the motor, but this new stuff is so much better it's scary.

Bret

 

LOL, yeah they have a little bit of velocity in them. 350fps on the walls thru the pushrod restriction or "pinch" and well over 400fps over the short side radius. Numbers that are usually considered very high by most head porters who know what they are doing in there. I'm not saying that's good as far as a velocity profile (the L92 is MUCH, MUCH better) but it does work even on very small displacement, low RPM LS race motors.

On these things I measure the port entry CSA about 1" down the port to get the injector boss out of the equation and it's a little smaller than what you mention and your right most people screw that up by enlarging it TOO much.

Dam those L92's and LS7's being TOO BIG, GM and who they hired (Mike Chapman) to do those ports must be on something because they make shitty power and are way too big.

Bret

 

Now all you need to put in your analogy is "frequency response" and we would have a winner. The correlation of that in speakers and head ports is interesting as well.

Bret

 

Those boys you talked to on those heads are no dummys. It's funny on who out there agrees about touching the L92 intake ports. HAve you asked them what they are getting out of the circle track motors with those heads using the old showroom stock cams? It's scary! Yep these motors don't like overlap at all

Bret

 

haha I just left again.. I,m about to go beat on the wifes car now........

 

We're not sure yet with all the boost and all. But yes we asre doing l92 heads.

 

Yes.....it does.
The laws of physics must be different on your planet....
see above....
No... they just have different priorities than we do. You know, smog limits, fuel economy, etc. I have no doubt they know how to make even more torque than they are doing now... the problem is the more power they make, the more people break things that they have to warranty and auto makers don't like to do that..... means they lose money!

Bret.... how's that nice touch of sarcasm?

 

exactly which prioritys do the Big 3 have that are different from yours and mine ??? they want more power,More economy better emissions. due you think they would build a slug cylinder head and attempt to achieve these goals ???

You problem is that your are drawing assumptions based on smoke blown up your *** by advertisers who just want your money. Secondly I see you are one of the Asscrevice smoke filling machines.

Velocity is alot of hype period. There is more to a cylinder filling then velocity. Are you fimilar with sonic flow nozzles. Maybe do some reading on fluids and their behavoirs under pressure before you bring your aparently uneducated gestimations into a topic with serious merit.

Here is the only bone i am going to throw today. Sonic nozzles tend to choke off total delivered flow well before their actual break into sonic flow velocitys.

As fr your comments on emissions they do not actually work in your favor. Cam timming has more to do with emissions production then people give it credit for. If you have a high velocity head that doesn't flow the volumes then you end up with a slug of an engine that requires a massive camshaft to produce the same power that an engine with a high volume head produces with a much tammer camshaft. Maybe the reason these heads have the chareteristic they do is becuase they need to tame down the cmahsafts but keep the performance level the same. This would prompt a total rethink of the port layout and design. I see nothing in the design of this head the L92 that says it is in fact a low velocity port. Just your speculation.I would be willing to bet that velocitys being equal this head will simply outflow the ls1 cathedral port hand down all day at any given pressure differential. but then gas expansion propetys and the reusltant impact on output are not something to be discussed here.

 

No... they want ENOUGH power to outperform their competitors and get you to buy their product.
If they can make ENOUGH power to achieve their goals and only have to make one cylinder head instead of 4 different ones to BEST fit each application.....YES! The accountants highly recommend it.

You got me there..... I don't have a clue how you get that or even what it's supposed to mean.

Hey Bret, did you hear that? Those 350 and 400 fps numbers you were pointing out earlier don't mean squat!
No I'm not.... but unless they involve a compressable fluid that changes vectors by 500+ fps at a frequency of 50 to 60+ Hz, I'm not sure how it relates to cylinder head design.
Sean, you really should think hard about calling someone uneducated when you have no idea who it is you are talking to. btw - you mispelled "behaviors", "apparently" and "guestimations" (although "guestimations" isn't an actual word so I guess you could spell it any way you want).

So what you are saying is the head might not be ideal for the performance level but it works because of other goals such as emissions? MY GOD! YOU JUST STATED WHAT I'VE BEEN ARGUING THIS WHOLE TIME! Now this post seems like such a waste....
On a 550 HP 500" motor, it's velocity is just fine... on a 400 HP 370" motor, it's low.
It's a bigger, straighter port with more cross section and a bigger valve.... of course it flows more at the same pressure differential and velocity....
Thank God!

 

Plain and simple you are a one hit wonder. there is velocity and nothing else. you fail to look at the engine as the accustical,fluid handling,thermodynamic deive it is. If velocity was all there is then maybe you would be right but most likely not. The point about sonic nozzles has to do with the intake tract. Smaller is not always better and somtimes it is. Sonic nozzles are just that. Once they hit sonic airspeed they choke and no matter what the pressure change the flow will stay the same. that is given that the low side pressure IE expansion area behind the nozzle stays at the same pressure.

A straighter port with an improved tapper with less shape changes along its length will in fact have a higher output velocity due to the lack of velocity and pressure changes across its length. You have obviously missed out on fluid dynamics 101. back to college.

Secondly displacement can and will affect FPS velocitys as measured but not as substantially as you are infering. Yes velocity is important but so is gross flow. Maybe if you designed the cmashaft correctly in the first place the velocity issue would be a moot point.

the fact is that Gross flow is gross flow regardless of the speed of the port.

Back to the example i posted earlier. these are just exmplae numbers. I didn;t bother to map it out with a calculator.

400fps flow 400cfm in a 2 inch orifice.
200 fps flows 400cfm in a 4 inch orifice.

do you really belive the cylinder cares weather the air comes in at 400fps or 200fps ? no it doesn't what does require attention is that your CAMSHAFT doesn't blow the charge back out of the exhuast or back into the intake tract. this is where displacement start to work in your model But only if your camshaft selection and design is **** poor in the first place. Fact is higher flowing cylinder heads make more power regardless of your endless banter on port volume.

that however is not to say that there is not something to port velocity but that it should not be the only means of comparison. Secondly I don;t think GM would waste alot of money on a cylinder head that couldn't keep pace or be an improvement of the exisiting cathedral port unless it really was an upgrade. also agian the chrysler Hemi has no problem making excelent TQ and HP under the curve with a larger Port and less displacement. So really the whole volume vs velocity argument is really a dead horse so stop beating on it already.

I think you have alot of time and $$ invested into catherdral port heads just like alot of sponsors here and the thought of these heads not only being cheap but actually being better means you will loose revenue. These are not new things to be learned. Sometimes a bigger port flows better and sometimes a smaller port flows better. Oddly enough sometimes a properly shaped port flow even better regardless of its volume in comparison to the other ports. I think you know this ( well maybe not) and refuse to accept it. Shape is 10x more important then size. size is always the byproduct of the proper shape.

 

No Sean, you simply ASSUME I don't look at an engine that way. I have not made ANY statements about any aspect of engine design or operation outside the scope of port velocity in this thread since my ONLY complaint about the L92 head is it's intake port size. It is YOU who has made the ASSUMPTION that velocity is all I care about. Like I said before.... you REALLY should know who it is you are talking to and what their experience is before implying they are stupid!.... So take your "holier than thou" attitude and jam it.
Believe it or not Sean, I know exactly what an engine does when port flow goes sonic.... I've seen it many times on the dyno.

Higher output velocity given what?.... same pressure differential?... same flow?....what? Wait a second..... did I ever go to college?

[QUOTE=Sean Collins] Secondly displacement can and will affect FPS velocitys as measured but not as substantially as you are infering.[/ QUOTE]
I proposed a 35% increase in engine size and a 37.5% increase in power....I'd call that pretty substantial!
So now I can't design a camshaft right either?!? I don't remember even discussing camshafts with you!

That's strange because just a post or so ago you said size doesn't necessarily
affect velocity!

Yes, I do!
David Reher would disagree with you! www.rehermorrison.com/techTalk/16.htm
Is he stupid too?

I didn't say it was... again, you ASSUMED that I meant that!
....went over this before AND I never said it wasn't an upgrade!
Compared to what?
Then I guess all you have to do is not respond.....

No.... I don't
WOW.... that's the first correct assumption you've made!
I don't know about 10x.... I would say shape and size go hand in hand....

Whew! That's too much typing.... I need a break.