Or Heads 101, or Heads for Dummies. There is a ton of posts on 'which head', 'choosing a head', 'top end combos' etc etc... BUT some of us (read me) are not blue blood mechanics, so while we can maybe understand flow at certain lifts and can compare that figure to another manufacturer when you add in something like the importance of velocity (and maybe swirl) we can get lost. I'm not even sure of my understanding of something like the advertised figures of "245cc intake" and how it fits into the equation. I've read Vizard and will read it again but if someone that has the knowledge and ability to put it down on paper and of course the time, would put the effort into helping us poor souls out and write up a paper on it in plain terms I'm sure a lot of people would benefit from it.

So is there someone that could do a 'Lars' on heads?

If you can, I'm on my knees thanking you.

Bud.

 

Good idea, here's a bump.

I'm pretty sure you can get lots of good info on heads and what you choose and how on some of the bigger manufacturer's websites.

Maybe Edelbrock would have some good stuff.

 

This site has a lot of flow data that I've been using in conjunction with Desktop Dyno to help me make a selection.

http://users.erols.com/srweiss/tablehdc.htm

I would reccomend getting this software and using it to help you visualize various combinations of cams and heads. It, along with advice here, has prevented me from making two mistakes: buying too hot of a cam, which would ahve given me poor low-rpm performance, and buying heads with overly large intake runners for my application, which also would have contributed to poor low-rpm response.

 

Volumes have been written about this topic, so the following primary considerations are vastly over-simplified...

1) A port's ability to flow is more important than it's volume, but its volume generally effects port velocity, which must not fall too low or fuel starts dropping out. Thus, a head that achieves high flow with the smaller port volume will typically out perform one that does it by way of huge ports.

2) For most of us, the amount of flow past the curtain wall of the valve is more important than worrying about how the charge enters the cylinder (swirl). Buy heads from a reputable American company such as RHS, AFR, Edelbrock, Brodix... and leave that to the engineers, unless you're one yourself.

3) The intake runners make up a significant portion of the port. Not only is a proper match where they meet vital, but the volume, length and shape of the intake runners, as well as plenum design and volume, will have much to do with actual flow. Sharp turns and rapid changes in cross-section area and/or shape are not good.

4) Finally, it is a common misconception that big heads need a big cam. Actually, better flowing heads require less cam to get the same amount of air/fuel charge into the cylinder.

Hope that sheds a little light on this complex subject for someone.

 

Trying to determine how to hone and tune this without it turning into a huge discussion thread

TheSkunkWorks post is pretty all-encompassing, and I agree with his assessment that there are some basic guidelines (which he articluates very well ) that help guide the selection process. There are so many factors here that general "rules of thumb" may be all we can put together.

I wonder if the approach might be to work from the intake port outwards - talk about intake matching (types, etc.), port runner size (which I see mostly as a matter of driveability), etc.

Again, don't want to take this off-track; maybe we develop the FAQ here and then do a final posting somewhere?

 

Bud... here are some simple guidlines for heads on street engines..

1. Port Size for SBC- take the Cubic Inches of your engine and divide
it by 2... anywhere from 10 to 15cc less and up to 30cc's more
will be optimal depending on how much power you want to make..


EX: you have a 400 cubic inch SBC.... 400 divided by 2= 200cc..

for lower end HP builds... 190cc to 200cc's for upper HP builds 215 to
230cc's

One yardstick to gauge a head's efficiency/quality is it's flow CFM
per it's Port size...

If you have a 170cc head that flows 240cfm @ .400 lift
and a 190cc head that flows 240cfm @ .400 lift.... the
170cc head is more efficient... you can also use this as a
Hipshot measuring stick for velocity...

If you had 2 hoses filling up 2 swimming pools.. a 1inch dia and a
2inch dia hose... and they filled up their pools in exactly the same
time... the velocity of the water in the 1 inch hose would naturally
be greater because it flowed the same amount of water in the same
time as the 2 inch diameter hose.... the same logic is used on port sizes in heads...

To obtain the best throttle response/efficiency... you want to
use the smallest port cc's that don't limit your final HP production goals.

Gasoline, roughly, has the theoretic potential to make 2hp per every
1 cfm of flow.... So.. when you look at the flow charts of L98 heads
(they suck)...and see that they flow less than 200cfm in stock form
.... you'll understand one of the reasons C4 guys have trouble
breaking 400hp..... not enough air/fuel mixture to make the resulting
HP....

The down side of chosing ports that are to small- motor choked,
can't make nominal hp..

CC/ports that are too large.... soggy motor... won't run right till
you hit astronomical RPM's..

If you would like to understand the science behind power production
in Laymen's terms that you can understand..

buy Both of the Reher Morrison Engine Books

Corky Bell/M.E. is also a great engineer who has written easily
understandable books that deal with the science of power production..
I have his Supercharging book...but he has also written a Turbo Charging book...... both include scientific formulas applicable to
HP production.... His books are EXCELLENT reads... but they are
not to be confused with anything from SA Designs or Motorbooks, etc..

... look for the author... Corky Bell...

 

a good short cut is to find a great combo and copy it.

 

Ok, I've saved the replies in another file, but maybe a FAQ section would worth while. How could that be accompolished?

I love books - while I don't want to be an engineer (too old) I do want to learn more.

Thanks for the replies.

Bud.

 

Here's some good reading about Vortec heads:

http://www.nastyz28.com/forum/showthread.php?t=56505

 

Great reading for anyone looking into a Vortec swap.

Am I correct in thinking the Vortec heads can't be used on the same year LT1 blocks?