GOTPLZ2

I was wandering if flow is the only indicator on how a head will perform or if the port size has anything to do with it. I'm asking this because on the AFR heads you can get 195cc heads that flow 282 with the competition package for $2524 or the 203cc heads that flow 272 for $2070 and the 227cc heads that flow 295 for the same price. Wouldn't it better to buy the 227cc heads for $2070 that flow 295 than pay $2524 for the 195cc that only flow 282 or does port size make a differance. Is there any advantages to having a smaller port size with same amount of flow. If you had a a 195 head that flowed 282 and a 227 head that flowed the same, would there be any differance?

Also I'm building a 383 street engine. How much flow or port size would be too much to keep my engine streetable.

Thanks in advance for any help.

BUBBA

Let me take a guess: I would say that if you can get the same amount of flow with the smaller ports that your velocity would be better and therefore you would develop more power.JMHO

GOTPLZ2

Ok if you have better velocity with smaller port sizes how do you optimize this for an application. Say I started out with a bare set of AFR 180 heads for my 383 street project. Can these be ported out to 195, 203 ?? How do I figure out the optimal port volume vs flow for my application? I know it wouldn't be as easy as picking the numbers and taking it to a porter and saying I want these numbers. Is there a way to figure up a flow number that would be optimal for a project and take it to a porter and have them try to keep the port size as small as possible while trying to reach these numbers?

BUBBA

I haven't a clue. Fred?

WS6T3RROR

first thing flow will not affect streetability. when it comes to flow you want the absolute best you can get, but not at all costs. the size of the port will in general have a direct effect on cross sectional area. which in turn affects velocity and that will have an effect on tq. also the size of the motor and the rpm range define about what you want in terms of port volume. in general with street motors all things being equal the smaller port that flows the same as a large port will make more tq and thus be the best head. there are however other considerations. with larger motors you have to have larger heads to achieve the same rpm levels. the reason is that the walls of the port create a friction on the air as it flows through and after a point it will "overspeed" the port and power/flow will fall off. as for how to optimize it thats a tough one my suggestion is to read what other people (pro's) have done and look at the dyno results. use time and money that others have spent to your advantage. but when doing this remember the devil is in the details, and just because THEY can make it work doesnt mean you can.

the important thing to remember is when it comes to cylinder heads dont get caught up in the hype of flow numbers. there are so many ways a company can skew them to make them look better that its rediculous. a few of those tricks are things like messing with bore orientation or using a much bigger bore than the engine will have or using valves that are so cut down they could never be used etc etc etc.

that being said afr is not a bad choice when it comes to lt1's. my suggestion for your 383 would a set of 210cc afr's as cast and then send them to a GOOD well known head porter to get them worked. tell them your intended use rev range etc etc and they should be able to work with the port a little to make it best for you. after that pick out your compression and select a cam to work with the heads and cr and you're on your way.

GOTPLZ2

Thanks that helped out a lot. Do you know if the AFR sells bare heads for the 210? I've seen that you can buy the 180CC bare that are the LT1 style but not the LT4. I'd rather stay with the LT1 style so I don't have to buy another intake. Can the 180CC be ported out to 210CC? Does AFR start out with the same bare heads for the LT4 and port them out to 195 or 210?
I'd like to keep the compression ratios down to where I could run 87 octane(because of gas prices) and get a cam that would be streetable. I'm also going to get a hydra rev kit so that I can rev it up to a safe range. I guess I need to look around to see what other people have done too.

1racerdude

Get the 227's and make HP.... They don't flow what is advertised. After port work they can make 600+ HP.
Comparing port volume as advertised won't work. A high port head has automatically got more CC's due to port length. It isn't so much the port volume as it is cross sectional area. The only way to compare port volume is know the center line measurement(length) of the ports you are comparing.
If the port is to small for the given CFM then the port will be to high in the MACH number's. A big port,I mean stupid big will be lazy,but most stories you here about ports being to big for the street are cam or compression related and not the head.
I have always said "you can't put to much head on it" Most castings for a given model engine won't let you get that big. I have run 350CFM on a 302 with 14 to 1 and turned it 9000 and made plenty of torque and HP,mostly in the upper RPM's but with the gear it was drivable if you knew how. The bigger the head the smaller your cam has to be for a given HP level and you have to have an intake to flow with the head.

OldSStroker

VERY good points. As logical as that is, folks forget it often.

GOTPLZ2

What is a mach number? I would also like to make torque and horsepower in the lower rpm's would a 227 be too much for that?

Is there anyone out there that runs a street 383 lt1 with 210's or 227's? What are your horsepower and torque curves like?

And how much flow can a ported lt4 intake handle?

1racerdude

Mach#= air speed
The 227 will be just right.
I am running a set of converted heads that flow 330 ish making 675+HP so you won't have a problem just let someone at a cam co. spect your cam and don't listen to other peoples opinion. They can give you more of everything than 10 opinions. Call several and compare and when you start getting close to the same spects from several different cam co's you know you are getting real close and no a CC306 is not your optimal cam for that set up.

OldSStroker

Mach number refers to airspeed and it's relation to the speed of sound.

Mach 1.0 is the speed of sound, about 1100 feet per second (fps) at sea level and 60 deg. F. 1100 fps is about 750 mph. The Concorde flew at M2.0 at 65000 ft. where it's about -60F, so M2.0 is only about 2000 fps at that temp.

Instead of talking about mph or fps with airflow going into an engine, it's more convenient to speak of Mach Number (or M# or just M). So M.55 is .55 x 1100 or just about 600 fps.

If you want to know more about what happens as airspeed gets closer to M1.0, do some searching on Advanced Tech, or Google it.

NOMAD

You want the largest CFM of flow without losing velocity. I think the only way to properly do this is with hours on a flow bench.

-Shannon