LS1derfull

Ok head porters, what causes turbulence at between .475" and .500" lift on flow bench? I have been chasing this for weeks and i am wondering what you guys do to eliminate this condition? My flow numbers are strong up to this point, and if i can sort out turbulence, i have seen almost 300 cfm at 28" at .550 lift. I also wonder if this flow drop/turbulence would happen if testing with intake bolted up to head. I know you guys have run into this and i would like some guidance to resolving this. TIA <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />

LS1derfull

Private Email answers are welcome! <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />

LS1derfull

TTT ANyone?

BaddMood

What have you done so far with the bowl and short side?

99 Black Bird T/A

iTrader: (4)

LS1derfull,

While I don't know the answer to your question, wouldn't it be best to the flow testing with the intake in place? As I understand it GM requires intake and a six inch pipe on exhaust for flow testing as it more closely simulates the real application.

LS1derfull

BaddMood, i have moved back short side in stages increasing flow each time, opened bowl up leaving valve job alone, only enlarging cross section of bowl to about 89% of valve size(stock).

Black Bird TA, i agree that is best way but i have been comparing flow to others all along to check status of how im doing and if they are getting there numbers with out intake than i should be able to also

LS1derfull

Anyone? Experts please chime in. TIA

Paul J.

I would test the port with a LS6 intake bolted up. My experience has shown that it will change the characteristics of the port and should be considered when porting. A 300 cfm intake port may only flow only 265-270 cfm with the intake attached. With the intake bolted up, I have seen the flow actually increase from .200-.300" lift by 3-5 cfm, so it can change the port flow, good or bad.

Is the swirl vane modified, or eliminated? How does the port sound at .475-.500"? Most likely, the turbulence is occurring around the short side radius area. The manifold will change the velocity distribution in the port, which may help or hurt the situation. Good luck,

Paul J.

LS1derfull

Paul swirl vane is chamfered and laid down some, also widened. Bench sounds funny at that those lifts also. My question is if others who talk there numbers on here have way of cancelling turbulence by method of porting? I have tried every subtle way of eliminating this condition but it comes and goes. Im also not willing to trash head to find answers sop it has been very time consuming. im willing to accept 25cfm loss with manifold on head but i need to know if im missing boat by having low turbulent numbers with only clay on port opening for my tests?

99 Black Bird T/A

iTrader: (4)

LS1derful,

Here are the flow numbers with the clay, LS1 and LS6 intake on my ported heads. All testing was done by the same operator on the same bench. These numbers should not be compared with other benches as benches vary.

Lift clay LS1 LS6
.100 n/a 65.1 65.6
.200 134.5 133.1 133.5
.300 197.9 184.3 189.9
.400 246.0 217.1 227.8
.450 n/a 229.2 241.3
.500 280.6 236.3 250.2
.550 289.7 236.3 247.5
.600 280.6 235.7 245.2

As you can see the LS6 is better. But the numbers are real low when the intake manifold is on. All head lose flow when that LS1/LS6 intake goes on. I think everyone should do their flow testing like GM suggest with intake in place and 6 inch pipe. Data is more meaningful that way. Otherwise the numbers without the intake are pretty meaningless IMHO.

My heads lost over 30 to 40 cfm when the LS6 intake went on. I would suggest, however much a pain it may be to develop your port with the intake in place. I know the flow numbers don't tell the whole story, but this sort of starts making the damn Holley intake look good again.

<small>[ November 17, 2002, 11:49 AM: Message edited by: 99 Black Bird T/A ]</small>

92 B4C 396 LT-1

1derful,
Don't put too much faith in numbers you have not seen flowed with your own eyes. Most sbc heads stall at .5". A friends Lt-1 head was ground full of holes and said to flow 288 @ ?. When he took it elsewhere for repair it was found to flow 250, which is about right.
I have found that results on my SF 600 compare closely (5cfm) to other SF benches. (AFR, Westech, check out Chevy High Perf. magazine for flow numbers on chevy heads)Flow Data benches show significantly lower numbers as they are laminar flow vs orifice.
Some things to consider. Were the results on other heads, you are working to achive, corrected for leakage? What is the port volume of those heads? Large enough to slow velocity enough to stall at higher lift and flow? You might try flowing the head without the valve, clay in the guide, to narrow the scope to the valve, seat, or short side. Mutiple angles on the seat (more than three) are sometimes effective.
Sorry I don't know the trick answer, if I did it would be secret, I could tell you but...

LS1derfull

Thank you guys, Blackbird i just aquired LS1 intake and flow tested with it, my numbers came out very close to yours.But intake raised stall point from .500" to .550", this is interesting. My clay numbers are right with yours also but depending on mood of Superflow bench, tstall or turbulence can come and go, and when it does stall hits around .500" making higher lifts lose flow! Does any body else out there have port technique to eliminate this problem?

LS1derfull

Anyone? TTT <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />

HOWQUICK

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by LS1derfull:
<strong>Anyone? TTT <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">seat angles, length and valve back cut angles....the answer is there. Try some stuff....you will find it <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

99 Black Bird T/A

iTrader: (4)

LS1derful,

Just wondering, did the stall still occur at .500 at different pressures or different bore sizes?

Say at slightly higher or lower pressure?

Stall occur the same with a 3.9 as with a 4.0 bore?

LS1derfull

Howquick, i tried intake valves with no backcut, they did not stall at .500" lift but they flow terrible at low to med. lift, unusable IMHO.What did you mean by length?

99 Blackbird, i tried flowing less pressure and it didnt seem to affect the stall. I only have 4.00" bore or 4.250" to test with but i have tested head biased off center in both directions and this doesnt seem to affect it. Any other input or ideas?

PAULJ99Z

The port is stalling because of high velocity in the short turn radius area. The flow is windowing across the back of the valve. Try these to lower the velocity:

* Widen the short turn radius area where it meets the sides of the runner. By sticking your fingers in this area you can feel the width of the port.

* Make sure you have a nice smooth consistent short side radius from the floor to the valve seat. Try to use the largest radius possible.

* Try laying back the swirl vane an additional amount or removing it altogether. My experience has shown that this area has a critical effect on where the port stalls by increasing the velocity across the short side. This will reduce swirl somewhat, although at higher lifts, the chamber will induce swirl once the port approaches stall.

The manifold will generally increase the stall point by reducing the amount of air available at high lift.

Paul J.

LS1derfull

Thanks Paul every thing you said makes sense, i have maxed out several of your suggestions, but swirl vane may be involved in problem.Larger valve may slow velocity of air across valve also right? I will test more and post results.

LS1derfull

Ok i widened short side to casting limit and flow responded to 285 cfm at .500", 290 at .525", and 294 at .550" Paul J. you hit it on the head, airflow when slowed enough makes flow around short side and valve, but when speed is too high it shoots across valve and drops total flow number. Thanks you helped me big time! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />