Okay, explain to me in lamens terms why cylinder heads are called 195's 210's 220's etc yet everything we talk of are fllow numbers like XXX at 550 lift?
AFR makes 195's, where do my LT1/4 heads fit in their numbering system?
ANd what does the bore size used in flowbenching have to do with the results.
I noticed some of this in this thread over here, and didnt want to steal or hijack the thread.
http://forums.corvetteforum.com/show...post1561634839

 

AFR uses the 195,210,220,227 system of numbering to identify their cyl heads by the Intake Port VOLUME in CC's.

For example the AFR 195's have a 195cc intake runner.

They also generally have 4 different ways the heads are configured.
1.)Bare Castings
2.)As Cast
3.)Race ready CNC porting
4.)Competition CNC Porting

The factory GM LT4 heads have a 170cc intake runner that is used in an "As Cast" configuration.
Will

 

The first numbers are what the intake runner flows. Balancing this number to your setup is best. Also what the runner flows is less important then what the valve area flows. So looking at the flow numbers at different lift ranges can tell you a lot about the head. The lift is how much the valve is opened. I am not sure what stock LT1 heads are or flow. The bore size looks to be the cylinder size in that post.

 

I think bore size affects valve shrouding.

In other words, if a valve is so big, when it is opened and down into the cylinder, one side of the valve may be so close to the cylinder wall that that side will not flow much.

It is also widely believed that intake air velocity is more important than actual runner volume at lower rpms -- in other words, if the air column is moving faster (as a given volume of air in a smaller pipe would do), then the inertia of that column of air can be used to "stuff" more air into the cylinder after the piston is on its way back up -- of course this depends on valve timing and such.

Tom Piper

 

Sorry Ardawolf,
But you are incorrect. Their identification system has nothing to do with the flow numbers of the heads. (as an example the new 195 Eliminators flow nearly 300cfm) Please read my first post it explains in detail how AFR's heads are identified.
Will

 

Thanks guys. On the bore size, how does the different bore size affect the testing,a ssome are done with a 4.060 bore then some use a 4.125 bore, How does this skew there numbers they advertise. I mean, if I am going to pay X amount for heads, I want to know I am not getting a load of BS, due to misguided advertising.

 

The model numbers AFR uses are the cc volume of the intake port. Stock LT1 heads are 170cc intake volume and LT4's are 195. In general, the larger the intake port volume, the higher the RPM range for the head on a given size motor.

Flow #'s throughout the range of cam lift are important, though most of the discussion focuses on peak flow or flow at max lift (often .500 or .550). Port velocity is also important to making good power. Too big of a port (for the intake, cam, exhaust, etc.) can actually end up making less power than a smaller-port head because the air will move through the smaller-port head faster and give a better fill.

I don't know what the bore size on the flow bench would matter that much. My guess would be that it still impacts the shape of the combustion chamber (i.e. does the airflow around the valve immediately run into the cyl wall, or is there more space available in a larger bore?).

 

I don't see the difference, it's explained the same way as far as I am reading it. I suppose I could add CC to it. I was not stating CFM numbers.

 

Heads that are flowed on a 4.125 bore fixture will generally flow a few more CFM than if the same cyl heads were flowed on a 4.060 bore fixture (providing the same flow bench was used).

How much more depends on the intake valve size valve spacing and the valve angle.

From my testing experience on a stock type 23 degree head with a 2.02 valve the difference would probally be 5-7 CFM. However on a stock type 23 degree head with 2.08 valves the difference could be considerabally more like 15-20 CFM (espc at higher lifts).

14 degree, 15 degree ,18 degree and SB2 are a completely different ball game from 23 degree heads and each other. SB2.2's are desgined for a 4.125 bore minimum they would be absolutely killed (at lower lifts due to the canted valve) by a 4.060 bore (if the intake valve would even clear the top of the bore at all) but at higher lifts they would lose less (but they would still lose a lot) because of the valve moving towards the center of the bore and away from the cyl wall (unshrouding the valve).

Will

 

My LT1 heads after porting are about 207cc on the intake runner, and flow about 281.

Do a search for Lloyd Elliot on the F body forums; he had a lot of good tech info regarding heads that he has posted. A lot of things I had never heard before reading his posts, and dispells a lot of common misperseptions about heads.

 

95wht6spd,
You say they flow about 281, but at what valve lift? One number like that is meaningless if the valve lift is not known. Don't mean to rain on your parade, just making an anology. Also, I've read that flow numbers should be compared at the .400" lift mark, since that is where the valve is open more often. Unless you have a high lift cam, say in the .600" to 700", then you may want to compare numbers higher, accordingly.

Rich K

 

Since we're talking LTx flow numbers here's my flow sheet (verified on another bench also). These were stock LT4 castings hand ported approx 4.5 years ago....slightly better results can be obtained today w/ LT4s, these are probably on par w/ a really good set of today's LT1s. You also really don't have to worry (too much) with getting the runner volume too big with stock castings.

 

I understand what you are trying to say (now) but you are stating it in the wrong terms and the two terms you are using are not interchangeable.

What you wrote is "what the intake FLOWS". The key word here is FLOW and I have no choice but to tell that you were and still are wrong because FLOW dictates a measurement in CFM.

Cubic feet per minute (CFM) defined: is a non-SI unit of measurement of gas flow (most often airflow) that indicates how many cubic feet of gas (most often air).

If you would have said something to the effect of "the SIZE of the ports" you would have indicated a measurement of volume and been correct as to AFR's identification system.

Cubic Centimeters (cc) defined: is a commonly used unit of volume extending the derived SI-unit cubic metre and corresponds to the volume of a cubed box measuring 1 cm × 1 cm × 1 cm.

Wolf, I'm not trying to start a pissing contest about this - but the two terms are very very different things that are often confused/misued by people.
Will

 

Here is the difference. The 190, 195, 210, numbers are the VOLUMES of the intake ports as expressed in ccs. Adding "CC" to a volume doesn't turn it into a flow number. Flow is not expressed in merely a volume number such as cc. You said, "The first numbers are what the intake runner flows.". That is incorrect. It isn't flow, it is volume. That would be similar to saying that engine displacement (cid) is the same thing as horsepower (performance). It isn't. You didn't use the most common unit of measure of flow, cfm, but by the use of the word, "flow" you implied some unit of volume over some period of time (like cfm). Volume and flow share the same relationship as cubic inches and horsepower. Generally, as one increases, so does the other. But not necessarily, and if so, not necessarily in direct proportion to one another. Sorry.

RACE ON!!!

 

Tossing in a very high-level perspective, if it's of value:

Flow is driven by engine needs - cam, etc.
Port CC is driven to some extent by flow (larger ports are needed for large flow numbers but as noted it's not a direct relationship) but also affects velocity of the intake charge, which affects driveability. Think of it as somewhat like carb sizing - an 1100 CFM carb has amazing flow...but it's not going to have great throttle response due to low mixture velocity at lower speeds

I start with flow needs based on the cam, then work back from there based on usage to pick the port size.

As an example, if I'm using a cam with a .525 lift - then a head that maxes out flow at .550 lift is fine...and one that has increasing flow numbers up past .700 isn't buying you anything but is emptying your wallet. If it's a daily driver, then I select the smallest port size consistent with the flow of that head - i.e. a 195cc head vs. a 215cc head. I have driven a mild daily driver with 315cc intake runners because he "got them cheap"...yech

That's just the way I approach it; always interested in other perspectives.

There was an interesting article on the role of bore size with valve shrouding in the last Hot Rod Magazine "Engine Masters" edition. As noted, it's really beyond our control unless we do things like change the valve angle by angle grinding the heads, etc.

 

The OP asked for "lamens terms" so I did not put CC or CFM or try to imply either or both, I tried to explain to him in a way he would understand. If you guys want to up your post counts by assuming which term I ment to use, go ahead. Sorry I already know what a CC or a CFM is. This info may help the OP though.

 

Not to hijack, but those are some outstanding flow numbers!

Good observation on the stock LTx castings and runner volume - the port cross section can't get a lot bigger on these due to the thinness of the castings on the outer runners (1, 7, 2, 8). I'm pretty new to the GEN II, but I'm learning

 

Those arent average flow number for LT1 heads nowadays. Those would be crazy strong #'s.

 

At .6, and my cam with 1.6 rockers has .6 lift, and I agree to an extent, flow #s are only one part of the story, many other things come in to play, that is why I mentioned LE.

I made 405rwhp on a 350 with weather in upper 90's and very high humidity, so I feel the heads work fairly well with the cam.

 

Sorry dude,
but CFM is flow = moving air
cc is volume, such as a volume of water. like in a drink.

if he has a 58cc combustion chamber, how much does that flow cfm?

what you posted was confusing as can be