So basically that shows you that it helped to widen the pinch up to .500 and hurt after that. Who would have thought that would happen. That bolt bulge sure is ugly.
SM Head Modifications on a budget
- Thread starter Earlie A
- Start date
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I'm curious to know why you ask. Care to elaborate?
I'm fabricating a 5" long 2% tapered intake entry plate that will act like a perfectly straight intake manifold runner. I want to test the pushrod pinch changes with a different entry plate. I hate the phrase but I'll use it here. What if the flow bench is lying to us? With a short entry plate we basically have a venturi right at the port entry. That could do weird things and certainly different things than in a running engine.
Can you show us what entry plate you are using.
Here's a picture where I was trying to focus the camera on the head bolt intrusion. The entry plate is 3/4" thick with a 3/4" round over.
I know this is theoretical mumbo jumbo and may not really belong here, but the numbers represent the current port being worked on. As in other posts, I'm trying to understand what limits the flow.
If we define the discharge coefficient as 146 cfm per square inch of minimum cross sectional area available for flow, then the red line represents 100% efficiency or a discharge coefficient (Cd) of 1. The sloping part of the red line represents maximum flow as the valve opens and the valve curtain area increases. Once the valve curtain area hits 1.86 in², the pushrod pinch becomes the minimum CSA and it limits the flow. That is the green horizontal line. The blue horizontal line represents the flow limit if the enlarged PRP area of 1.91 in² is limiting the flow. If the pushrod pinch is ignored, the throat eventually becomes the minimum CSA and it will limit flow. That's the horizontal red line at the top of the graph.
The area or vertical distance under the flow curve represents the port efficiency (pink line). The area or vertical distance between the flow curve and the theoretical flow maximum (in this case I chose the green line to represent 100% efficiency) is the port inefficiency (the blue line).
Let's ignore the pushrod pinch and assume the red line represents 100% port efficiency. At high lift the distance between the red line and the actual flow curve is huge. This is the inefficiency caused by friction, turbulence, flow separation, the valve, bends in the port and any other imperfections. These losses increase rapidly as velocity increases.
This theoretical limit of 146 cfm/in² or 350 fps through the minimum CSA is not really correct. If the minimum CSA is acting like a venturi, those numbers can be exceeded (locally, not in the entire port) if the CSA being measured is at the vena contracta (the most narrow point) of the venturi. I have seen average velocity of 375 cfm through the pushrod pinch and more than that through the valve curtain.
One last point and I'll stop the rambling. The shape of the theoretical flow curve explains why the actual flow curve is shaped the way it is - why it eventually flattens out.
Sorry for the digression. Please post corrections or rebuttals to these thoughts. Searching for the true answers here.
If we define the discharge coefficient as 146 cfm per square inch of minimum cross sectional area available for flow, then the red line represents 100% efficiency or a discharge coefficient (Cd) of 1. The sloping part of the red line represents maximum flow as the valve opens and the valve curtain area increases. Once the valve curtain area hits 1.86 in², the pushrod pinch becomes the minimum CSA and it limits the flow. That is the green horizontal line. The blue horizontal line represents the flow limit if the enlarged PRP area of 1.91 in² is limiting the flow. If the pushrod pinch is ignored, the throat eventually becomes the minimum CSA and it will limit flow. That's the horizontal red line at the top of the graph.
The area or vertical distance under the flow curve represents the port efficiency (pink line). The area or vertical distance between the flow curve and the theoretical flow maximum (in this case I chose the green line to represent 100% efficiency) is the port inefficiency (the blue line).
Let's ignore the pushrod pinch and assume the red line represents 100% port efficiency. At high lift the distance between the red line and the actual flow curve is huge. This is the inefficiency caused by friction, turbulence, flow separation, the valve, bends in the port and any other imperfections. These losses increase rapidly as velocity increases.
This theoretical limit of 146 cfm/in² or 350 fps through the minimum CSA is not really correct. If the minimum CSA is acting like a venturi, those numbers can be exceeded (locally, not in the entire port) if the CSA being measured is at the vena contracta (the most narrow point) of the venturi. I have seen average velocity of 375 cfm through the pushrod pinch and more than that through the valve curtain.
One last point and I'll stop the rambling. The shape of the theoretical flow curve explains why the actual flow curve is shaped the way it is - why it eventually flattens out.
Sorry for the digression. Please post corrections or rebuttals to these thoughts. Searching for the true answers here.
replicaracer43
Grumpy Old Man
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Wonder if you have to much airspeed over the short turn now, especially with the pushrod pinch opened up. I'd bet adding width to the short turn might help?
You are absolutely right. Our objective with this post is to keep the modifications to simple things that most people could do on their own, with the exception of a professional valve job. Short turn modifications are beyond the capabilities of most. Ultimately this post might end up there.
PRH
Well-Known Member
That would be my assumption.
The “test piece” is what I consider “SSR challenged”, so anything you do that might result in more volume trying to make it thru the port, makes any inadequacies of the SSR profile really show up.
However, I am curious to see what the long runner inlet adapter might do, particularly as the flow numbers go up.
I have had some “better” flowing sbm heads that had high lift flow issues(turbulence/regression) that responded well to extending the inlet opening…….. on only the floor.
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It would for sure. What I was hoping for was to see how close we could get to 285-290cfm with the least amount of work and cost for guys that can’t afford to pay for a full port job. Knowing what a 2.055 and 2.08 valve are capable of I can size the port accordingly. The shortside width and height is the biggest time factor on these heads. A 285-290cfm smooth flowing port would get most of our members the horsepower they are seeking. Doing it on a budget would be a bonus
Newbomb Turk
Well-Known Member
I like that idea. Bolting on an intake or at least a runner like you are saying is eye opening.
As for the cutter blades, I asked because I’ve seen 4 or 5 angles on the B sized cutter but once you get more than 3 angles on those you are out of room to make the cuts much more than .100 wide if that.
When I was buying cutters or when I was developing a cutter I always put them on the A cutter so I’d have more room.
Ok I don’t want to step all over your post but I drilled a customer’s second head today and took some quick measurements. These are top to bottom. I will be opening these up to the tube but this is at .950 without touching the common wall so I don’t cheat myself out of more area I can gain when I work the common wall. You may not be able to see it but I had to go in the pushrod side over one inch to get my .950.
Ok just working the common wall for five minutes I gained .030 the length of the pinch. That’s a nice gain and I’m no where done. Just working down some of the bolt bulge look how much short turn area I gained already and I didn’t tube them yet. My thinnest area at the pinch is from .062-.118 so I wouldn’t push that .950 number unless you are tubing everything. But like I said don’t touch the common wall till you have your .950 so you can pick up another.030 like I just did.
My pinch on the first head after tubing is 1.015
What port height do you get out of them ?
Earlie A posted stock pinch height as 2.08"
2.08" x 0.95" = 1.98"
1.98" x 1,100,000 / cid = rpm, 367 = 5,935 rpm, 408 = 5,338 rpm
2.08" x 1.015" = 2.11"
367 = 6,324 rpm, 408 = 5,689 rpm
How close to straight can you get the common wall without tubing the head bolt?
Pretty straight but it’s so easy to tube I just tube everything. 4 pushrod holes and 2 bolt holes per head. Man she was warm in the shop today. 92 outside and I forgot to check but it was somewhat cooler.
Brian Hafliger
Well-Known Member
Dude you have to work the chamber wall, especially when you go to a larger valve! The pinch won't show you anything until you unlock seat area (bottom of the valve job to the deck).
Thanks for the nugget. I always appreciate the input and welcome the advice.
In defense of what we are trying to achieve with this thread, we are trying to take steps that the average guy at home could take in modifying heads with inexpensive or readily available tools. Each modification will then be flow tested to see the improvement or lack of improvement. So far, we have been avoiding deep port modifications, serious bowl work or chamber work. In the end, we'll probably have to go there.
I got the 5 1/2" entry plate finished up and ran a couple of tests this morning. More on that later when I've had a chance to use it more.
I did open the PRP up to 0.995" and still have not broken through. My holes are tubed as well, so I'm not really worried about making a hole. Flow test is attached. As can be seen from the three tests of stock PRP vs 0.950" PRP vs 0.995" PRP, the increased area is helping increase flow up until 0.450" lift. At 0.500" lift, flow separation starts taking over.
So, @pittsburghracer, are we out of easy, cheap options for increasing flow? Are we now searching for area over the short turn to increase high lift flow? Time to address the head bolt bulge? That's still a fairly simple modification.
I did open the PRP up to 0.995" and still have not broken through. My holes are tubed as well, so I'm not really worried about making a hole. Flow test is attached. As can be seen from the three tests of stock PRP vs 0.950" PRP vs 0.995" PRP, the increased area is helping increase flow up until 0.450" lift. At 0.500" lift, flow separation starts taking over.
So, @pittsburghracer, are we out of easy, cheap options for increasing flow? Are we now searching for area over the short turn to increase high lift flow? Time to address the head bolt bulge? That's still a fairly simple modification.
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