Say you have a 5.7 making peak power at 6500rpm.
Which one would you pick

230cc 243 head flows 300 at .600
220cc 862 flows 300 at .600 .
Both same valve size.
With near identical flow curves.
Both 217ish at 300 lift.
I have 7 sets of LS heads. And the above #s are real.

But what you dont see is the 243 is way slower air speed wise in places of the port vs the 862.
Which maybe good or bad depending on what you want

 

I think all other factors being alike, the more velocity the better. A flow bench doesn't actually recreate how ahead works on an engine where flow is intermittent. It's the velocity that helps push more air thru the port than otherwise. I bet the smaller ports make more power, given similar bench flow to the larger ports.

 

I think most of us know a flowbench doesn't have anything to do with a running engine. But it does show alot of useful info.
Alot of that Info isnt published with a set of heads.
So how can you buy a set heads based on cfm #s @ 28"

A flowbench and software like engine mod 4 or dynomation where you can see the pressure traces. You can get a good idea of what works when on the dyno.

 

Do you have any dyno or, more importantly, track time results from the 862 heads? What company did the porting? Stock valves? What kind of valve job? Is the valve job blended? Any combustion chamber work?

 

I did the porting . I have a flowbench and one dimensional sim software . I have a dyno. Unfortunately it's only good for 2 wheeled bikes
In a earlier life I use to do this for a living.

I am going to dyno test these 2 heads. Probably on a 6.0 6500 peak

 

To answer you question more thoroughly.

Valve jobs are little different between the 2 heads.
I wanted close to the same flow curve.
Both have same valve size.
Combustion chamber shape is a little different between the 2. Actually this is called squish area ratio. It's as close to a fair comparison as I can get.
They will both have the same compression and squish thickness

 

there was a dyno test out there that actually saw the 862's outshine 799's, but it was on a smaller displacement LS, iirc.

 

I believe that test was on a 5.3, which is fine, as that's the most common LS out there. In that particular case, it works VERY well, giving some velocity to air feeding a smaller displacement engine.

 

I wouldn't say the airspeed is faster than a stock 243. I would say it's more consistent

 

243 ports are 10cc larger than 706. For the same flow, it will go faster thru the 706 port than the 243 port.

 

243's do seem to have a "ramp" area between where the port starts (at the intake manifold) and necks down to a point maybe an inch, inch and a half in where it has roughly the same cross section as the intake valve seat opening. Then the one wall does sort of kick over past the rocker boss, and get kind of big again. I should go measure that area when i get a chance.

I am sure the 706/862 has that same ramp area, since the mouth of the port is the same shape, but i wonder about the rest of the port now.

I wonder how the two ports look compared to one another. Anyone know of a cross section image between 243/799 and the 706/862?

 

I think non ported the 243 has a ramped floor vs a more flat floor on the 706 and 241 heads which improves the short turn radius(on the 243). Most testing shows the smaller port heads produce slightly more torque than the larger port heads. On a 6.0 the 243 produce slightly more hp. Once ported either produce good hp numbers.

 

I was talking stock. It's not the same flow

 

You look thru other post ,I posted port molds of both heads installed on the eng with intake manifold (no head on one side). 243 short side is pathetic. Its # 1 spot to go to on that head for more flow. The air simply cant turn as is always the case with every v8 head. Some heads worse than others. 706 needs valves and a valve job , to fix the wide seat % as from gm, and some short side and everything else squared up. They are 2 completely different heads/ Port shapes /flow curves /valve size stock obviously.stock 706 less low lift flow as well .
so there is alot going on, in the dyno charts mentioned. The truck heads air speed gets really fast over the short turn after porting. That can turn into a bad thing. Doesn't have the wider csa as the 243 does .
Everything needs a vj
but you will never see what the other things fully do if your ssr isnt correct. Lot guys think it valve size and vj and or csa , not even close. Ssr at top of the list.

 

Here is 243 Vs 241 heads. I will have to look on my other computer to see If I have pictures from any other heads saved.


243 intake Left 241 intake Right

 

 

This is what a port looks like for over 3hp per ci NA.
it will never fit under a hood.

 

Have you ever tested this?

 

Very good illustrations of the port shapes. You can really see the differences in the short side radius.

 

The stock 706 short turn radius looks way to sharp. I've read that the gentler radius on the short turn is better. I think the ramped floor of the 243 increases velocity. Once ported it probably doesn't make a huge difference since they both flow close to 300 cfm.