I'm working on a couple of heads/ports starting with bare Speedmaster heads. Pictured are the specs on two different flow bench runs. If these heads are used on a 408 for street or street/strip, which would you choose? In my mind the answer is clear, but I know some of you racers and dyno guys have experienced a lesser flowing head making more power. Is there any way that head A outperforms head B, and why? No other changes between motor pulls, just changing the heads. I know, I know - timing might need to change, cam might need to change, carb might need re-jetting. Let's keep this simple. Given the information here, is it reasonable to say that head B is better, or is there just not enough information?
Speedmaster head hypothetical
- Thread starter Earlie A
- Start date
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PRH
Well-Known Member
Based on the outlined criteria, the choice would be pretty clear in my mind.
I've wondered how far to go with port volume and larger pinches. As we have discussed, sometimes enlarging the pinch will hurt the flow. There is also a point of diminishing returns with making a port larger. After the port gets so large (volume wise), additional volume increases yield less and less flow increase. Of course the volume has to be added in the right places to keep the velocity profiles correct and to delay separation. But in general, volume increases early in the porting process yield significantly better flow increases.
As rpm increases, pressure wave tuning is more significant. Darin Morgan references 6500 rpm as a loose transition point between high and low speed engines. Tight pinch points kill pressure wave travel in high speed engines.
Does Santa ever deliver dynos?
As rpm increases, pressure wave tuning is more significant. Darin Morgan references 6500 rpm as a loose transition point between high and low speed engines. Tight pinch points kill pressure wave travel in high speed engines.
Does Santa ever deliver dynos?
I can't find it but I have post it before, forget what class but they had like a 162 cc limit with stock j heads and something like 370 spinning 7500+ rpm , to go faster obviously they needed more port volume but they couldn't so they lowered the flow (lowered the velocity 330 to 320) and gained hp by quite a bit and set records.
So if were not pushing these ports near there velocity limits B probably win every time but I could imagine A could be better in some applications.
So if were not pushing these ports near there velocity limits B probably win every time but I could imagine A could be better in some applications.
I've spent some time looking at Chad Speir's ports and the shapes he uses. I think he is often porting for the stock classes so he is forced to get as much flow as possible from a set port volume. Much the same as you are discussing.
Newbomb Turk
Well-Known Member
Why is the bowl not at 91% for the 50?
I’ll hold my thoughts for now but I’m sure most of you know what I’d say.
I’ll hold my thoughts for now but I’m sure most of you know what I’d say.
If porting for a general application guess you got to pick a happy medium for a general built 408 and or 340/360 of X hp, say 500 hp at what rpm these engines generally make 500 hp and what port volume and pinch generally needs to go along with that.
My opinion and experience (for what it's worth) is that throat size is a result, not a goal in and of itself. The size of the throat is a result of getting the bottom cut angles and blending to direct the air where you want it to go. I have also found that the throat size can be used to regulate flow separation to some extent. Bottom cut angles and blends will be manipulated based on the port in front of the throat and the chamber after the throat. To say a throat needs to be X% is just incorrect in my way of thinking.
PRH
Well-Known Member
It would be interesting to test how much influence the pinch has on something where increasing it yielded basically no flow increase.
Like a moderately ported TA head……ported to the mid-260’s, and installed on a stout enough stroker to be sure it would exceed 2hp/cfm.
Heads like that will still have a separation problem at the SSR that increasing the pinch won’t solve, but increasing the pinch will slow the air down
……… at the pinch.
Dyno Test A would be with the pinch done in a pretty conservative manner.
Then pull the heads and open the pinch up to nearly the limits of the casting, reinstall, retest for B.
I don’t care enough to actually do it, but I think it would be interesting.
Like a moderately ported TA head……ported to the mid-260’s, and installed on a stout enough stroker to be sure it would exceed 2hp/cfm.
Heads like that will still have a separation problem at the SSR that increasing the pinch won’t solve, but increasing the pinch will slow the air down
……… at the pinch.
Dyno Test A would be with the pinch done in a pretty conservative manner.
Then pull the heads and open the pinch up to nearly the limits of the casting, reinstall, retest for B.
I don’t care enough to actually do it, but I think it would be interesting.
Not saying your right or wrong, I've never ported a set of heads in my life, (why I'm glad your sharing your progress) but seems to me with lot of porters the throat size is the starting point they seemed to have sizes for a given application same with short side csa and pinch csa and the taper angle out from the short side csa.
You are correct that most porters assign a certain % to a throat size. That is because it is quite difficult and time consuming to find what works then to manufacture it, especially if bottom cuts are not concentric with the valve seat and top cut. The purpose of the bottom cuts and blending is to transition the air from the port and set it up for the chamber beyond. The chamber is all different shapes and angles. To make the best throat, it has to be customized as well.
PRH
Well-Known Member
I take my hat off to you.
You’ve spent waaaaaay more time trying to sort out that head/port configuration than I’ve spent on any one type of head.
I’ve said it before, but I’ll repeat it here…….
I like getting the most amount of gain, for the least amount of work.
I’m not interested in chasing the 1’s and 2’s.
You’ve spent waaaaaay more time trying to sort out that head/port configuration than I’ve spent on any one type of head.
I’ve said it before, but I’ll repeat it here…….
I like getting the most amount of gain, for the least amount of work.
I’m not interested in chasing the 1’s and 2’s.
PRH
Well-Known Member
Another part of it for me is……..I have to be able to actually complete the job and supply the finished heads to the customer.
So, I look at how much time can be invested and still get paid for all of it.
So, I look at how much time can be invested and still get paid for all of it.
Agreed, Unless your building for a highly competitive class and money is no object, like I think it was Super Stock Hemi's where they sink like 20+ grand in labor per head to gain 600 rpms for better shift points. There's tons of easier low hanging fruit to make power especially these day.
PRH
Well-Known Member
When someone would call and say, “I’m looking for a max effort set of heads”, I’d tell them…….”I’m not your guy”.
Newbomb Turk
Well-Known Member
I’m not suggesting you make the bowls a given number, but steeper than 45 degree seats usually want the bowls over 90%.
I’m not sure how you do your seats/valve job but I start with a cutter that sets the bowl at 91ish%.
I’ll hold my comments a bit longer but your flow numbers gave away that your bowl % was smaller than I’ve ever used with other than 45 degree seats.
Again, we are getting into the nebulous realm of is the flow bench telling you the truth or not.
Also, have you flowed both ports in reverse? What about at lower or higher than 28 WC?
Newbomb Turk
Well-Known Member
If I was to do a test like that, I think fully porting the head except the pinch then open the pinch in stages to see it's effect, it's effect probably be on peak power, rpm and over rev rpm.
Seems to me a lot of larger displacement sb don't have decent over rev rpm, lot seem to shut down after peak.
Seems to me a lot of larger displacement sb don't have decent over rev rpm, lot seem to shut down after peak.
Which curve and why?
Newbomb Turk
Well-Known Member
The 50. Look at your low lift numbers. Are you using a cutter or stones to do the seats?
Edit: I forgot to mention your high lift numbers. Or mid to high lift anyway.
I care far far more about the shape of the curve over .25 l/d than I do low lift flow numbers.
For me, testing low lift (lets say .100-.350 lift) testing should be done at the highest test pressure the bench will pull.
If I’m testing just lifts above that I usually test at 10 inches or so. Plus all the other ways I’ve mentioned.
It makes a ton of paper and data but you start to see why CFM isn’t the best indicator of what a head will make for power.
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