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Jeff's doesn't get a mag article, but it's hard to take pics when parts take forever to come in. Jeff's block is being machined and so are the heads. Intake is here, crank is here, cam is here....hopefully we will have pistons this week.
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Do you prefer the Pond heads over the Edelbrock, or does it still depend on the build???:confused:
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Heads
How about a pro port edelbrock head? Blair Patrick and kuntz have some that flow well at low lift.
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The Pro Port head is basically a raw casting that is not anywhere near finished....
Now, with that being said, the Pond head has unfinished seats, unfinished guides, and needs some work to smooth out the CNC work, but the Pro Port heads are ROUGH. The intake and exhaust ports are tiny so that they can be manipulated, chambers are unfinished, etc. Blair and Jim build engines that have more horsepower demand than the street/strip engines that are built for Cobras and other weekend warrior toys. They mainly specialize in engines for classes like the NHRA SS class, etc. When you modify a head for this type of application, expect to see up to 1" valve lift, valve locations that have been moved, port locations that have been moved, etc. They typically require some specialized support parts and just aren't cost effective for a street engine. Pete, the Pond heads have a lot of potential. I talked with Robert pretty extensively about them. I haven't used them before, but I told Jeff and Anthony that if they don't perform, I'll have them professionally ported on my dime. They have more of a heart shaped chamber, and a new design for the exhaust ports, so I expect them to fair quite nicely. Be patient. |
Let me take a stab at the high velocity port explanation....
In the first half of the intake stroke, there's a vacuum in the cylinbder and the intake charge is accelerating. Toward the end of the intake stroke, the piston is decelerating, and the intake charge has built up momentum. The inertia of the intake charge continues to ram itself into the cylinder, even though there is no more vacuum in there. Actually, between the resonant frequency of the intake runner, and the inertia of the charge is there, the cylinder can actually be "supercharged", in the sense that the engine will have better than 100% volumetric efficiency. Inertia is proportional to velocity squared, so you really want the velocity without sacrificing too much flow. |
Some can explain things a lot better than I can. I can see it in my head, but my fingers don't type what I want sometimes.
The momentum and inertia comments are pretty much dead on and that's why it's best to differentiate between a flow bench and an engine. If some of you guys can remember the Boss 302 Mustangs, you have a very small engine that is relying on a huge head to supply an intake charge. A little engine sucking on a huge port (that has huge flow capability) can't muster enough vacuum to get the intake charge moving quickly. At low rpms, these cars were turds and it really took some rpms to get them to make an efficient pull on things. |
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Check your email history, I recall I suggested Pond heads for my build way back in the peice so that you could have another toy to play with in your sand box. ;) If they need any extra fooling around with, I'm happy for you to just add it to my bill. You've done more than enough already :cool: |
I'm not an expert by any means but its my understanding that one wants a head that flows well with as small a port as possible. So with all these heads you have to compare flow at various lifts (0.100, 0.200, on up) and their respective port size. I do know that Blair Patrick makes a Pro Port Head that flows GREAT at low lifts; which would be perfect for a street application...
That said; I'd love to see how the Pond head compares... |
Low lift is a lot of it, and yes, you want a well flowing head with the smallest port possible. Everytime I say that, I think of the CHI Cleveland heads. They are a mix of old Cleveland 4V head flow, with old Cleveland 2V head port velocity. Best of both worlds.
That's also why the AFR and TFS heads work very well. The 185-205cc heads flow better than most 210-225 heads flow. Good velocity. I'm not knocking Blair's services by any means. I have talked to Blair quite a bit over the phone and emails and have even got his advice on some things. However, I would weigh the "cost-effectiveness" of a head that requires that much labor in comparison to an out of the box head, or a readily available CNC head. Of course all of this pivots around the camshaft selection too. A cam with .750" lift doesn't lean fully on a head that moves big air at .200" lift. The valve job has a lot to do with performance at the low lifts and when you back cut the intake valves you start to see that in action. |
Does a better flowing head allow for a smaller cam??
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Yes it does.....it affects cam selection quite a bit. You don't have to hold the valves open as long to get the food shoved in. :)
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First inertia historically had several definitions that were not correct, but today is generally accepted to describe Newton's first law (in layman's terms) a body in motion tends to stay in motion, unless acted upon by an external force. Inertia is fine to describe the phenomena, but when you want to show relationships or calculate the amount, the term you should have used is Momentum. Momentum is not equal to velocity squared, just mass times velocity. Momentum=P Mass=M Velocity=V P = M * V Energy=E is equal to Mass times Velocity squared E = M * V^2 Back to the port. The Mass of the air times the Velocity provides the Momentum that will compress the air into the cylinder at the end of the intake stroke. CFM is the volume per unit of time. The mass is proportional to the volume and the density. The velocity is proportional to the volume and inversely proportional to the area of the port (which is not constant throughout the port). Therein is the conundrum. The easiest way to get more flow is to increase the area, but at a given flow more area results in less velocity. |
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Everyone focuses on the heads, but the port is quite short compared to the intake. I suspect the intake has much more to do with velocity and air momentum than the heads. I would love to see a mild roller cam in a Boss 302 compared on a dyno to a factory issue. Followed by some choice intake swaps. Wish I had the resources to play. |
The issue is the 230cc port volumes. Even the 351's with the 4V heads didn't have a lot of butt.
It would be the same if you took a modern day 302 or 5.0 and stuck a set of AFR 225's on it. |
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Yeah, I gotta relate to it in any way that I can....
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What happened to this engine build..................?
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Still going fine...
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Engine builds take a bit of time. We're making good progress, but we had to wait a little bit on pistons, little on the block, heads had to be sent out to be ported, etc.
I can post a picture of Jeff's Isky lifters if that would help. ;) |
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