havent read it all yet, thanks for all the results though, makes me glad a bought your heads and that there are still a few sponsors that continually post info to back their products, saves time searching over 100's of threadsd lol

 

Not wanting to derail my own post, but the reality is that strong low and midlift numbers do in fact have a significant impact on power production. Look at what the AFR 205 heads have been producing routinely with "only" 300 CFM's of peak airflow. Some of this is attributed to the higher airspeed the smaller runner produces, and some of it is attributed to the strong flow curve created by having good low and midlift flow as well.

Good low and midlift flow numbers do NOT increase low and midrange power...common misconception. They simply add to the total volume of air the engine can process, subsequently allowing the engine to generate more power everywhere....especially at higher RPM's where valve events happen so fast, any increase in air consumed will make a significant difference. Heads with good low and midlift flow usually produce power curves that "hang on" well after peak HP is achieved. At higher RPM's the momemtum of the intake charge is significant....good low and midlift flow on the intake side helps to further take advantage of the air's momentum and inertia, increasing the cylinder fill right before the compression stroke as the intake valve is about to close. An intake port with 15 additional CFM's of airflow at say .150-.350 lift will be much better able to take advantage of that high speed column of air right before the valve snaps shut, allowing for a stronger cylinder fill and obviously more power. A higher speed port design (such as the 205 and 225's) will enhance this feature even further due to the higher velocity and inertia the smaller, efficient port provides.

Other factors to consider when discussing peak flow versus low and midlift flow, is how much of that extra peak flow actually makes it into your engine. For example, if you were to glance over the list, only a select few heads actually outflow the 225's at over .550 lift. Assumimg your typical .600 lift hydraulic roller, how many degrees of crank rotation will actually be spent in an area that the head was truly flowing more air?...it wont be a tremendous amount of time which may or may not compensate for the number of crank degrees it was down across the low and mid lift points. Now lets throw this into the mix...how much of the extra peak flow will actually make it past the intake manifold? Meaning as peak flow continues to rise, the need for a less restrictive manifold becomes even greater. Considering what most of us will probably be bolting on, both the LS6 intake and even the FAST will represent a restriction and will ultimately handicap the cylinder head....some more than others. Under actual operating conditions (intake in place, TB, airbride, filter etc.) you might have close to the same flow at .550 as you do at .650 due to the restrictions further up the line. Assuming less airspeed (than say a 225) and only average low and midlift flow, what will the end result yield in power and torque production....possibly not as much as you would have liked in this type of engine combination. There are ALOT of things to weigh and consider when designing an engine, and for that matter designing a cylinder head as well. Its not as cut and dry as peak flow numbers on a bench might lead you to believe.

I know I had a few other thoughts I wanted to share on this topic, but its getting late and this post is getting long...When I remember and have a minute I will try and share them with you as well.

Thanks,
Tony M.

 

Great post man, some of the best info I have ever read on here.....

 

I would say they produce more power simply because most people bolting them on are running them with 11.8:1 compression when seting them up the way you recommend.
59 cc chamber with a .040 gasket.
I am sure the mid lift helps ,but if you want to compare apples make sure everyone has apples

 

i will be dynoing my set up out of the box as recommended by tony, as soon as i can get time to dyno i will post up my results with these heads and f13 cam

 

umm, i've always heard Tony recommend a .024 mill and .040 cometic gasket, that puts compression at 11.1 assuming a stock shortblock. this is with the 205's.

 

.024 mill puts the head at what cc? I am guessing real close to 62cc's. What are you using for out of the hole? I am using -.007 and getting 11.3 on my calculator. and getting 11.35 set up that way. Still it is a good bit over 11.00:1

Now if someone was to do the math wrong and use .007 for the out of the hole measurment instead of a negetive number it would show 10.95 on my calculator.

 

Come on , quit haten and start porting the afr head if you want to sell a better product. I think if I bought a set of cyl. heads right now , it would be either AFR's or Tea heads. Both make great power no doubt but I can see where teh afr's are the true advantage.

 

milling puts the chamber at 62.57 according to my calculations, i used -.008 out the hole (oem clearance)

exact number i get is 11.28, still a half a point lower then 11.8 and nothing more then what anybody else is running. most PP ls6 style guys are running 59cc chambers and the 5.3 guys are running near the same compression. its apples to apples IMO.

 

I thought you just said it was almost 11:00:1.... now your saying it is 11.3 what one do you want to use?

for evey .006" milled off we loose 1cc on average. So that puts it at 62cc assuming they are at 66cc's to start with.

Patriot does run them with a 59cc chamber (I was under the impression that AFR did also my bad there) but with a .057 stock gasket or there abouts. so about 11.3:1 with worse quench than the AFR.

Our 5.3 heads come off of the CNC machine at 64.5

 

11.1, 11.28, 11.3; we both know that there is a minimal difference.

and im sure everyone runs your heads unmilled and with stock gaskets right . im sure if you took a consensus you'd find the average compression to be around 10.8 - 11.3 with all the difference chamber volumes and gasket thickness out there.

the point is the AFR setups unless otherwise specified (as i've seen some in the 11.8 - 12.0 range for specific applications) are still apples to apples.

and yet even with unmilled afr's i've seen people put down some killer numbers with there combinations.

 

I would think that mainly because of the 250+cfm @ .400 with a 205cc port and the improved combustion chamber.

 

There is a big difference in 11:1 and 11.3 to one on pump gas. In one case your living large and making a bunch of power in the other your breaking stock pistons from detonation.
You would be surpised at hom many people run our heads unmilled or flat milled. And most opt for the GM Gasket over spending the big dollar on Cometics. I can understand why when you see the cost difference.
Of course I would not reccomend a .040 gasket on a factory short block either. To many tolerence differences seen so far. not to mention I think .030 is to tight on quench

11.3 is doable with good tuning heck 11.7 is doable with good tuning in some areas depending on what fuel you can get. But for the average person 11.1 is about right in the southern areas in the summer time.

I have also seen guys say well just add more fuel.. or take out some timing..adding fuel is not goiong to work when there isn't enough octane. Pulling timing won't always make up for not enough octane either.

 

Like this guy....

https://ls1tech.com/forums/dynamometer-results-comparisons/310532-afrs-205s-224-224-cam-a4.html

HUGE Compression....

What I usually recommend with our 224/228 cam is 62 cc's, an .040 gasket, and no need to notch your pistons. Last time I checked, with a piston .007 out of the hole, that yields about 11.2 to 1 and many guys across the country are running them that way on pump fuel. Our chamber design does have a higher tolerance against detonation due to its more efficient double quench pad and overall chamber shape in general. The 59 cc build has been my more aggressive recommendation that takes into account 2-3 cc's of valve notches and more overlap from the larger cams (X3 and the like) which will tolerate and benefit from slightly higher CR. (11.35 ish). Some of those customers aren't opposed to octane boost or a splash of race fuel if needed, but many in the land of 93 or better octane are running straight pump with set-ups just like that.

I wanted to keep this thread technical in nature without a bunch of BS. No need to muddy this thing up with "opinions" that have little to back them up. The AFR heads work, right out of the box...both the 205's and the 225's....whether a customer deems they are worth the extra money is another topic entirely, but they have been consistently putting down the numbers and thats worth paying for in my book if I'm the consumer.

This thread was also posted to shed some light on the various flow curves and cross sections of heads we have had the opportunity to test, how the AFR 205's and 225's obviously compare, and also provide our customers (and potential customers) with a little more insight and perhaps a better understanding of "why" they perform the way they do.

Tony M.

 

Maybe you should have quoted what I said then not just part of it that suits you.
I also stated that the mid lift numbers had to help...You seem to have left that part out.
point me to the calculator you use..



On this we disagree..but no one is suppossed to agree with you on everything right?




so 59cc head a 3 cc valve notch is 11.35:1 but a 62cc head with no notch is 11.2:1??? OK I am just not seeing how both of these combinations are not yielding the same compression ratio.

I thought I was trying to be technical when I posted.

I thought it was mostly marketing otherwise you would have posted 3.9 bore flow numbers. Sorry I was trying to stay technical

 

Brent,

Your killing me here....

Yes...going form a 3 cc to a 2 cc valve notch will increase the CR from 11.2 to 11.3 or so. Assuming you didn't notch them as deep and perhaps only removed 1.5 cc's (Lou at LG sometimes only cuts the intake pocket) you would now be in the 11.35ish area.

Regarding your "request" for 3.900 bore info, trust me when I tell you that the AFR's would have shined even brighter. The 205's would have ousted a fair share of the larger runner heads when flowed on the small bore. (Some of the larger valved heads are very unhappy on the 3.900 bore). This comparison was aimed at the "big" runner stuff (which typically tout big advertised flow numbers) on the larger 4.125 bore. Had I flowed them on the smaller bore everyone would have crucified me for not testing them on the larger bore which they were more intended for in the first place.

Tony

PS....forgot the smiley guy

 

Yeah but you a have requests for all of the flow #s for the 3.900 on that list. It may have been a lose-lose situation either way Tony.

 

again, i offer this challenge!!!

here's an interesting challenge: i have a 99 6 speed vette witha 422 iron block stroker, best internals, billet rods, diamond, etc, with TEA 6.0 heads. before moving to the northern parts of the universe, I had TEA replace a head gasket and freshen up the heads, as i live in memphis and the drive is going to be more than just a whim to run up to bowling green. while up at their shop, i had them install kooks 1/7/8, x ipie, etc, as i already had them put the fast 90 etc on. car dynoed at 526 rwhp, forot torgue, 50something. if we were to put a set of the 225 heads on this car, is what i am seeing true that it would be faster? i am asking? if this were to be the case, im up for a test bed and see if there is any "improvement". not intending to flame tony or brian. just opening up the possibilities of real back to back comparison. if they in fact pick it up, ill gladly flop down the coin. anyone that has dealt with me knows i can back up my offer. joe in memphis
__________________

 

comparsion would be interesting

 

I think one thing that people miss when comparing stock castings to purpose designed castings (like the AFR, All Pro, etc.), is that in a stock casting you are dealing with less then optimal conditions, which can lead you to larger port volumes.

One point of obivious concern is the short turn. In a stock casting you are given a short turn and you have to work with it. If your air speed is to high over the short turn, then you need to get more area to slow it down. This means that your port volume is going to increase. A stock casting/short turn can only flow so much air per square inch due to the lack then optimal design (or uses other then GM intended). Aftermarket castings can flow more air per square inch of area due to the "optimal" or at least improved design cast into that area. This will lead to smaller port volumes over the short turn, and also smaller port volumes because you don't have to transition to a larger area.

The point of that rambling, if it made any sense, was just to say that it is rather hard to compare stock ported castings vs purpose desinged castings (especially if you are only going to refer to port volume). Now, lets get a set of as cast AFRs out to all those good porters and see what everyone ends up at