ok, i know absolutely nothin about cylinder heads except for the fact that they can pretty much make or break your setup. besides the fact that better flowing heads make more hp, what makes one set of heads better than the next? for example lt1 and lt4 heads, what exactly makes the lt4 heads better, whats different about them? would a set of fairly ported stock lt1 heads match up to regular lt4 heads? what makes the afr's better than lt4's? i was under the impression that when you buy a set of heads they were like bolt-on out of the box, but people seem to be porting what are supposed to be top of the line heads !...if thats the case why not just port the hell out the stockers until you get the flow numbers you want? are the aftermarket heads thicker or somethin that allow you to port them farther than the stockers can go, or do the different heads have completely different designs or somethin?

i know i ask alot of questions, but ya gotta learn somehow !

 

You cnat really just port and port to get flow numbers. Two things: you run out of material to take out, and your mid lift (where the valve spends the most time) flow will suffer terribly.

AFR heads simply have more material to take out and some other advantages especially for FI applications with their thick deck.

 

stock lt1 "561" castings flow average 210cfm stock on the intake. my heads with a full port job with bigger valves (2.00/1.56) flow 271 on the intake. the stock unported heads peaks flow about .45 and the ported lt1 heads peaks around .6
you need good low and mid lift numbers, not just high peak flow numbers.

oh a little more info. i believe the average LS1 stock head flow unported is around 240 and the LS6 is 260. i think, someone correct me if im wrong.

 

thanx guys but i need more clarification.

 

I will LIKE to see some flow numbers and prices on the top heads on the market

 

any of you pros know, i dont wanna post this in advanced tech b/c its really not advanced, but ide like to get some good answers .

 

well heh what more do you want to know

 

ok, what differs in the design of the LT4 heads that makes them that much better than the LT1 heads. same with the AFR's vs. LT4's. and lastly for a car that will be making serious hp but still street driven (somewhat) what are the best heads? thanx

 

AFR makes LT4 heads as well as LT1 heads. The LT4 heads have a different angle for the intake and they have raised runners I believe. The AFR LT1 heads are just like the ones on our cars stock, but they do have more material to be taken out and can be made to flow better. But I'm pretty sure the LT4 style heads will always out flow the LT1 style heads, if you port both of them. Hope this helps a little.

Benji

 

No one ?

 

the lt4 heads have a bigger intake runner size i believe 190cc??? and i think the lt1 head is 180cc intake runner??? which means the LT4 will outflow the LT1 (ported vs. ported) and (stock vs. stock)
someone please correct if im wrong on the intake runner size
AFR makes a 220cc runner.....
Jesse

 

the LT4 is also shaped to flow better as well as having a bigger runner.

Another thing is that flow numbers aren't the end all. After hours of talking to some of my classmates about heads- I decided it was best to pay someone to do it.

Little things can skrew up your heads terribley. For instance having turbulant air, poor combustion chamber shape, and obviously poor velocity.

As far as "make or break" you, i think thats true to a certain degree. It seems like there are people that know what they are doing and those that have a dremmel. In each category you will find a smaller variance of power gains.

ie, Advanced induction, Combination motorsports and a few other top guys will all do great jobs and have similar power output as a general rule of thumb. All these guys know what they are doing.

The backyard mechanic will not come close to them because he is not aware of many of the fundimental rules. There was a guy on this forum porting his own heads and selling them that did not know the most aerodynamic shape to flow around nor could he explain why velocity was important.

To sit there and compare the guys at the top is trivial for a street car. 10hp either way. ::::. The differance between joe schmoe hacking your heads and a top guys is huge- especially fow low end power.

 

here is an extreme simplification of heads:
Heads first and foremost are another routing device for the air. air starts comging in through the throttle body, goes into the intake manifold. from there, there are 8 ports. those 8 ports line up with the 8 ports on the heads. air flows into the runners (ports) of the cylinder head and when the valve opens, air is sucked into the cylinder.

Cylinder heads are your primary restriction on most cars, which is why its so important to have them flow air into the motor. when they are ported (the runners are opened up and redesigned to flow air better), they allow for more power to be made.

Combustions chamber design: here is a VERY important aspect. Its also extremely complicated. I cant begin to explain it because i am not familiar with it.
close up of my combination motorsports stage II combstion cambers

Unshrouding valves is a very important thing. This is taking away as much material from around the valves as possible (within limitations and not just hacking) so air can flow out easily. this is why big bore motors are so desired (recent thread in advanced tech for further reading- a VERY good read)

you can see how the valves were unshrouded and how the combustion chamber was reformed in this pic view fullsize image

There are a **** ton of other factors like valve angels, vavle jobs and all kinds of other aspects that you can do a search on.


edit:
I almsot forget, heads also route exhuast out of the cylinders!