I'm curious to see what adding clay to the long side/roof of the bowl in the cut 2 and 3 areas (especially 3) would do. This would be a non-destructive test that would just add understanding to the process. Reduce some area in the cut 3 section. I really want to tighten the throat up but that would be destructive. Not ready for destructive yet.
SM Head Modifications on a budget
- Thread starter Earlie A
- Start date
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Remember as you lower the floor you are “pushing” the short side towards the bowl widening the short side creating more volume to slow the airspeed. Do NOT taper the floor thinking it will assist the air making the turn. It won’t. Lower then radius.
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So the push is in the direction of air flow. That makes more sense now. In my mind I was pushing on Herman's head from the chamber side and pushing upstream against the air flow.
And this also makes sense because it is adding volume before the turn, not during or after the turn.
When I “push” from the valve side I am widening. When I “push” from the pinch side I am lowering. Both make area and start my shaping so I can send airflow towards the center of the cylinder. Gotta always think past the head on both ends. Which way is air entering. Which way do I want air to exit. One isn’t controllable and one is. When you get this you will say wholly crap why didn’t I see this.
MAKING the turn. I fixed my mistake.
So if we could bias the port more it could help? The head bolt sort of limits the tilt we can put on the port. A couple of months ago I had a machinist buddy to shift an intake and exhaust valve in another port on this same head. My thinking with that one was bias.
Phew! Glad you didn't use that 1" drum to square it up! I'd hate to see John blow a gasket! lol
Yeah. I hate to muddy up what is supposed to be a post about simple stuff. However, not much other way to get to the bottom of all these issues.
And it's interesting to follow along.
And I thought pushrod pinch was all there was in there. I need to pay closer attention.
We are way past simple where we are headed. Our experiment failed. Lol
But where do you stop? So far there has been another next step to go to. You aren't at the end yet.
If what I told him sinks in he will be heading towards 290 cfm.
Since we've been talking flow separation so much this might be a good time to insert this interesting theory. If flow is separating from the short side of the port, what exists in the 'void' created when the air detaches? In Erland Cox's Speed-Talk post 'Chamber Stall', he says that separation actually starts in the combustion chamber and works its way back up the port. In this theory, the 'void' is actually high pressure air from the chamber blowing back up the intake port. Chamber air is at a higher static pressure than the fast moving port air because the combustion chamber air has low velocity. I thought it was thought provoking.
Mmmmmm clay.
I was watching someone porting Ford FE heads and since on those the pinch is part of the intake, the head is really just the short side area and bowl, kind of made me think the first inch or so of the port is more part of the intake runner than the head itself obviously it's all one from chamber to carb, actually did a quick calculation and each intake stroke on a 360 equals about 600-800cc depending on ve% so basically the total volume of the port runner and probably some of the plenum and which all happens roughly under millisecond per intake stroke.
Got me thinking if it would be helpful to think of the port in a more of the FE type way. Bowl/short side, port entrance/runner? And to think of the volume of the runner as more of a round in the chamber ready to be shot in to the cylinder. (High to low pressure)?
Got me thinking if it would be helpful to think of the port in a more of the FE type way. Bowl/short side, port entrance/runner? And to think of the volume of the runner as more of a round in the chamber ready to be shot in to the cylinder. (High to low pressure)?
I can’t wait till Earlie A posts one of these mornings with some 292cfm numbers.
I believe in racing they actually pay attention to the inlet tract volume as a function of cylinder volume and it is something like a 1 to 1 ratio. The shorter the port the wider the taper, getting larger toward the plenum. The longer the port the more gradual the taper. I think it has to do with the pressure wave tuning.
It's getting way above my paygrade...
So two tests this morning. First was full removal of head bolt bulge. After leaving off yesterday convinced that the area at the apex was the major limiting factor to flow gains, it seemed reasonable to remove the rest of the HB bulge. That still fits in our initial step 1-5 plan. I did cheat a little on removing the bulge and used a burr. That was a huge time saver, but it could have been done equally well with a 1/2" cartridge roll. At the same time that I felt the bulge was 100% removed, I broke through to the brass tube. That can just be seen at the blue arrow in one of the pics. If the head bolt hole is not tubed, I think 100% removal of the bulge is not possible, certainly not wise. Flow test was test number 618. While peak flow did go down, average cfm went up a little and the shape of the curve improved. I do not see a downside to removing the bulge completely if the hole is tubed.
Second test was adding 4 cc clay to the port roof to try to reduce some flow area during/after the short turn. The thinking was that this may help reduce separation in the turn. Flow numbers were down across the board. The one positive from adding the clay is the shape of the curve improved. Peak flow was at 850 lift instead of 500 lift. It really didn't hurt flow at all at the highest lifts. 4 cc is a lot of clay and a lot of volume reduction. I intentionally chose this spot for the clay because at high lifts and high air speeds this part of the port becomes 'dead' anyway. The flow wants to window and follow a straight line from port opening to valve opening. It does not want to follow a curved roof, at least not on the cyl center side of the port.
My takeaway from these two tests is this. Yes, more area is needed at the apex as PBR often preaches in his posts. At the same time, PRH has repeatedly said that the SSR is in control. I'm not sure the two can be separated. To reshape and lower the SSR the area at the apex will increase. I also don't think there's much improvement to be had until the SSR/apex area is addressed. I included a picture of the port mold to show the abrupt/tight short turn. It's easy to see why air wants to jump the turn.
As far as next steps. I think we are moving on to step 6, whatever that is. Would it make sense at this point to clean up the ridges in the chamber a little and lay back the areas that Brian suggested? That's still a fairly easy step.
Second test was adding 4 cc clay to the port roof to try to reduce some flow area during/after the short turn. The thinking was that this may help reduce separation in the turn. Flow numbers were down across the board. The one positive from adding the clay is the shape of the curve improved. Peak flow was at 850 lift instead of 500 lift. It really didn't hurt flow at all at the highest lifts. 4 cc is a lot of clay and a lot of volume reduction. I intentionally chose this spot for the clay because at high lifts and high air speeds this part of the port becomes 'dead' anyway. The flow wants to window and follow a straight line from port opening to valve opening. It does not want to follow a curved roof, at least not on the cyl center side of the port.
My takeaway from these two tests is this. Yes, more area is needed at the apex as PBR often preaches in his posts. At the same time, PRH has repeatedly said that the SSR is in control. I'm not sure the two can be separated. To reshape and lower the SSR the area at the apex will increase. I also don't think there's much improvement to be had until the SSR/apex area is addressed. I included a picture of the port mold to show the abrupt/tight short turn. It's easy to see why air wants to jump the turn.
As far as next steps. I think we are moving on to step 6, whatever that is. Would it make sense at this point to clean up the ridges in the chamber a little and lay back the areas that Brian suggested? That's still a fairly easy step.
PRH
Well-Known Member
I’m enjoying your journey.
It does seem like you’re going thru a similar situation I described in post 181, although you’ve done even more exploratory work without unlocking any secrets/magic yet.
In the last port mold pic, the SSR looks a bit worse than I’d imagined.
It does seem like you’re going thru a similar situation I described in post 181, although you’ve done even more exploratory work without unlocking any secrets/magic yet.
In the last port mold pic, the SSR looks a bit worse than I’d imagined.
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