Don Terrill’s Speed-Talk

I am doing up a set of pontiac 6x-4 heads and first time on the bench was very encouraged at low lift flow up to .500 and then port stalls out at 256 cfm at 28". valve 2.11 curtain area at .500 ,3.315 -- Throat 87% area =2.61 MCSA = 2.365. at pushrod first impression is thats the problem but studying the port and listening for turbulence I'm not so sure that is the limitation, and opening up the throat might help to achieve more flow. Does any one have any Ideas to help me out.
Len

Len, enlarging the push-rod choke will likely help some. It may, or may not be the limiting factor at the moment, but if you're after better numbers at higher lifts, it will be. What lift-range do you want to operate in?

Why wouldn't you want the MCSA at the throat instead of the PR pinch?

I realize that the pushrod pinch is the smallest area but if you look at curtain area at .400 lift =2.652 and throat = 2.61 and no flow increase at .500 and .600 lift and the fact that the throat is adjacent to the curtain makes me believe that it could be a restriction. I opened up the throat to 90% with no other changes and hope to put it on the bench tomorrow. Any bets ???? I can lower the port floor some but not the roof at the pushrod pinch and that will be my next move. One move at a time.
Len

Len wrote:I realize that the pushrod pinch is the smallest area but if you look at curtain area at .400 lift =2.652 and throat = 2.61 and no flow increase at .500 and .600 lift and the fact that the throat is adjacent to the curtain makes me believe that it could be a restriction. I opened up the throat to 90% with no other changes and hope to put it on the bench tomorrow. Any bets ???? I can lower the port floor some but not the roof at the pushrod pinch and that will be my next move. One move at a time.
Len

I didn't do the math, but I'll be brave enough to post here and tell you that it will do the same thing at the new convergence point.

Please report your findings.

SWB

Okay guys heres the beef I'm an old fart not ancient but at 64 my hands don't like running the grinder a whole lot. I just started doing heads about 5 years ago and I'm really just a beginner but really enjoy developing a port and even though I may not follow your advice I value it very highly (just hard headed ). For this set of heads I did as much work on the bridgeport as I can to limit the amount of hand work, for the divider between the two intake ports, where the head bolt passes through I put a piece of rod the same size as the bolt whole and with a 5/8 long shank end mill indicated off the side of the rod, moved away .090 and then plunged into the intake side of the head and made a cut parallel to the bolt hole from top to bottom of the port, this left a shelf about .090 that was blended towards the bowl, this helped straighten out the divider wall and insured that all were the same and my hands loved it. I did a similar operation on the pushrod pinch but only left .050, For the bowls I used a bowl cutter and then blended to previous work. There is still a lot of hand work that had to be done and over all I probably didn't save any time but I accomplished 3 things ,saved wear and tear on my hands, helped to maintain consistancy in the ports and am developing a method to use on most pontiac cast iron heads. I realize that I can take more but want to evaluate as I go.
Len

Len wrote:Okay guys heres the beef I'm an old fart not ancient but at 64 my hands don't like running the grinder a whole lot. I just started doing heads about 5 years ago and I'm really just a beginner but really enjoy developing a port and even though I may not follow your advice I value it very highly (just hard headed ). For this set of heads I did as much work on the bridgeport as I can to limit the amount of hand work, for the divider between the two intake ports, where the head bolt passes through I put a piece of rod the same size as the bolt whole and with a 5/8 long shank end mill indicated off the side of the rod, moved away .090 and then plunged into the intake side of the head and made a cut parallel to the bolt hole from top to bottom of the port, this left a shelf about .090 that was blended towards the bowl, this helped straighten out the divider wall and insured that all were the same and my hands loved it. I did a similar operation on the pushrod pinch but only left .050, For the bowls I used a bowl cutter and then blended to previous work. There is still a lot of hand work that had to be done and over all I probably didn't save any time but I accomplished 3 things ,saved wear and tear on my hands, helped to maintain consistancy in the ports and am developing a method to use on most pontiac cast iron heads. I realize that I can take more but want to evaluate as I go.
Len

I think they're very good techniques you're using. Consistency is difficult with hand work The more you can use a mill, the closer the "dots' are you'll have to connect with hand work.
Do you have an approximate lift range in mind? Thats going to be a big factor from this point. You're down to .050" at the push-rod pinch now? That would explain your "decision" for the MCSA. While that area, properly shaped will flow more air than you might think, it speeds up the flow just before you need to turn it. Personally, I'd rate the possibility of getting the pinch too big on that head just behind getting the deck to flat. I believe you're right in the pinch being the limiting factor(if not direct, it's overiding). You're stuck with a default min. area. From there, you'll need to adjust the seat and valve-shape to make sure it's "happy" in your desired lift range.

I would like to see these heads max out for .600 lift approaching 270 cfm, from previous experience with the same pushrod pinch I know a little more flow can get by. The short turn radius is decent and quite wide and I think there is a little more there but I don't want to get my feet wet.
len

Boy I sure hate the taste of crow!!!!!!!!!
Len

What seat angles are you using? The stock 30 degree seat may be good at low lift but to flow up higher the 45 degree valves and valve job will open the bowl of the port a lot. The stock Pontiac heads are pinched off in the bowl area big time.

Ron words are on here:

"Personally, I'd rate the possibility of getting the pinch too big on that head just behind getting the deck to flat. I believe you're right in the pinch being the limiting factor(if not direct, it's overiding). You're stuck with a default min. area. From there, you'll need to adjust the seat and valve-shape to make sure it's "happy" in your desired lift range."



Huge speeds over the short turn......for sure. You need to figure out how to slow the air down there and if that's not possible you need to work the valve angles to get as good as you can get. Not optimum but might work.

Used 3 angle seat 30/45/60 with .050 width on seat, I have used 5 angle seats on other heads but wanted to keep this one simple. On the last trial I gained a little from .100 to .400 and then it stayed flat and even lost a little at .500. I rechecked the thickness at the roof and I do have some more to work with there, so will try and gain a little at the pinch.
.050 32.6
.100 71.7
.200 142.6
.300 206.4
.400 252.9
.500 254.2
.600 253.8 could not here any obvious turbulence anywhere during test, I haven't probed the pitot yet but will next time. What max velocity should I see over the short turn???
Len

I also have a set of 6X's to port for my own "resto" project.
How did you make out with these heads?

still not done yet got 259, at 600 am now convinced that I need to increase radius at short turn but am more than a little worried about getting wet. Going to make a 3/4" radius template to check with. one trick I use is to lay plumbing solder along the short side of the port and over the short turn and once you conform it to the port you can pull it out and see if its the shape your looking for. the solder will hold its shape very well without any spring like wire would have. One thing I noticed with the 6x heads is that the short turn hangs over the valve seat and makes it a little more difficult to get a good transition.
Len

Len wrote:still not done yet got 259, at 600 am now convinced that I need to increase radius at short turn but am more than a little worried about getting wet. Going to make a 3/4" radius template to check with. one trick I use is to lay plumbing solder along the short side of the port and over the short turn and once you conform it to the port you can pull it out and see if its the shape your looking for. the solder will hold its shape very well without any spring like wire would have. One thing I noticed with the 6x heads is that the short turn hangs over the valve seat and makes it a little more difficult to get a good transition.
Len

Jim hand shows a widened short turn like a waterfall. Have you investigated that?