I was wondering if anyone had done any flowbenching on stock big block heads(ls5 vs. ls6)? I was wondering if it is worth it to go ls6. I heard in chp that ported ls5's will out flow the bigger ls6's.

Originally posted by nick cagg.:
I was wondering if anyone had done any flowbenching on stock big block heads(ls5 vs. ls6)? I was wondering if it is worth it to go ls6. I heard in chp that ported ls5's will out flow the bigger ls6's. =
Nick,
The oval port won't outflow the rect port but will almost certainly out power them unless you are planning on at least 6500+ RPM on a regular basis which is highly unlikley given your cam spec which I assume is a hyd.
A sewer pipe will outflow both but it doesn't make a real good port :D

Yeah I meant outpower not outflow. sorry guys

Actually they do outflow them under .5", plus the velocity is alot higher.

Go here;

http://www.chevyhiperformance.com/techarticles/41598/index8.html

And here.

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

On all of these charts note that the valve size is smaller on the ovals vs the square ports. graemlins/thumbsup.gif

TJC,
I think you need to reread whatever charts you are referring too.
The numbers will be close at low lift & even better for the oval at .050-.200 or so sometimes but,,,
I don't even need to look at the your charts to tell you the oval does not out flow the rect head in any test I have seen or done but as I said it will usually out power the rect on most street applications on anything less than a 6500+ RPM deal & even then the factory rect heads are probably not the best choice unless you are running a 500+ inch engine.
Please note I said the factory rect heads ;)

Nick,
I think the oval is your best head for a factory head.

Ya, I think I should have emphasized my point about the valve sizes a little more. If you bring the valve size to an equal playing field you will see that the ovals do flow better across the useable range. It's too bad they don't publish velocity data on flow charts as well.... That would be really interesting. I don't know if there's even a standard for that test..... do you??

That standard would be pretty difficult as the way I understand it is velocity is in direct proportion to the difference in pressure between the cylinder & the air pressure trying to fill it along with the size of the port in cross sectional area.
This is all pretty dependant on the RPM you are trying to run to.

If you are talking about measuring air speed with a pitot tube what you are doing is trying to improve the places that you have hi speed air & get rid of the places that are lazy.
Sounds pretty simple huh :D
There are some pretty good formulas for determining the minimum cross section you need for a given cylinder size but I think it kinda boils down to this which I have posted before.

The way I understand it is you want enough port in area to support the rpm you want to run at with the size of the cylinder you have & the type of cam.
A roller will normally take a slightly smaller port for the same rpm than a flat tappet because the cylinder sees the port efficiently for a longer period time.

Now the minimum port cross sectional area is a number I would like to see the head guys post along with there cc numbers which are only a reasonably good indicator of heads in the same family.

As always,,, just my simple minded opinions :D