I'm in the process of buying a set of heads for a project and something occurred to me that I never questioned before. Why in the world are "sportsman" level performance heads not cast closer to an optimum port shape? It's kind of frustrating to spend ~$1,000 per bare casting only to have to spend $500+ getting each of them ported.

I understand why at the high buck "pro" level people want castings with small ports and thick walls. They are likely to have a very specific idea of the port they need and the means to pay someone to achieve it. But for what I'd guess is at least 95% of the aftermarket customers, a casting that was much closer to a generic hand port would save a lot of time and money.

Are there technical reasons for this? Is it just poor understanding of the customers needs? Do they want to be able to sell their own CNC porting? It does seem as though there is a trend towards better "as cast" ports. One head I'm considering is the Dart "Pro1", which seems to be more in that direction than their other offerings, for example.

Rich

 

I agree that the Dart Pro1 stuff especially the newer Platinum castings are closer to a finished shape.

Porting IMHO is to get you a better more efficient port for the motor you are going to run.... with that said I've seen tests where the Dart as cast heads are better than a CNCed AFR casting. To me the CNC is used as a crutch, there is a huge difference in CNC work and the ports they reproduce, I'd much rather have a port that Carl Foltz designed for a BBC head than something that came out of AFR, even with the awesome flow numbers. There is probably 40hp in that difference of porting.

Rich, what motor are you looking for a set of heads for? The BBC? If so there are a few excellent cheap CNC programs done that get you top notch porting for a very reasonable price.

Bret

 

Bret: yeah, I am building a motor for the race car. I have a block (Dart, short deck) and rods, the rest is still up in the air. But I am thinking strongly of a 4.25" stroke and a 4.560" bore. I am going to run alcohol and EFI. The idea of the motor will be to use the cubes to make hp rather than super high rpm - I am aiming for a very reliable setup that I can beat up regularly with little maintainence. On the order of 7,000rpm is what I am thinking about. The budget is an issue, as always and right now I am leaning toward the Dart heads out of the box.

Rich

 

Since we're talking BBC... look at all the variation in displacements today. Guys like Dart and ProFiler try to offer enough variety so as to suit just about any build.

Sooo, if you're up on BBC and know about what you need then you can probably choose something close to "optimal" for the get go.

Big SBC's are another matter cause most of the heads out there don't cut it when you want to go 7k with one.

Either way, I mentioned my two choices for a 555 ci BBC build. RM has a killer Dart 360 "Beast" that'd work like a charm if you have the $.

-Mindgame

 

We use the dart pro 1's on our 700hp 502's, but they still get lots of port work. As cast, they are one of the better heads. I have used the trick flows several times now, and they have nice ports as well. We used world products heads on a blown 900fwhp in a boat and they needed a decent amount of re-shaping.

I think your best bet is the pro-1's, but still even some minor portwork and radius valve job w/ back cut by an experianced hand will give great results on any as-cast head.

For small blocks, I am really happy with the pro-topline/RHS heads as cast. Although I have a lot of trouble with getting a matching pair, I have had on at least 5 occasions, heads with the same part number that have chambers vary by 7cc head to head, and intake ports that are .090" taller on one head. So if you use those, make sure to measure.

 

I have designed tooling for aluminum castings.

Most people have heard of parting lines on castings.

The cores used to form the internal passages are made in core boxes and have parting lines also.

My guess is that the core boxes would get more complex if the ports where closer to final shape.

Any shape that can not be split down the center with a cutting plane can't be made with a 2-part core box. Offset parting lines can help some but still there are shapes you can't make.

If you have a "D" shaped port with a crowned bottom, higher in the center than the edges. This would lock the core in the core box. Not a great example but you see what I am getting at. Just to make matters worse the runner cores have to lock into the mold or the cores that make the chamber shape.

I think you could cast a very good shape if you were willing to build some complex core boxes.

That will cost more money for tooling. But I don't see areason why it could not be done.

Z28

 

Thanks, that's the kind of info I was wondering about. The only casting I know anything about is the "lost wax" method used for jewelry.

Rich

 

Please show me these tests. I love how you say CNC is a crutch are you being serious here. CNC porting is a good way to reproduce repeatable ports at a good price and faster than a human could

 

How about you call up Dart or Roush and just ask.

OR you can read the LS1 Dart post again http://www.ls1tech.com/forums/showpo...&postcount=118

I thought you would have read that already since you are getting 30 sets or whatever, too bad Dart doesn't call you up and ask you your opinion of their heads.

BTW how much do you actually know about CNC machines? I look at 4 of them almost every day.... and they are only as good as the program the, operator and the design they are trying to reproduce.

Bret

 

Couldn't be better said.

We have 4 hass vertical's, 1 cnc lathe, manual lathes and mills, EDM..etc...in the wrong hands they are not worth pennies...

Yes the repeatability of a cnc port may be better, but it is only as good as the original port it reproduces. I have not seen a set of cnc heads that we couldn't make significant improvements on...they are getting better, but still, a port job by an experianced hand for your specific application is more desirable. CNC is a way to produce similar quality ported heads at a much lower cost.

 

What do you guys do with an EDM machine?

That's something I've never seen in an engine shop.

-Mindgame

 

There's the "lost foam" method a few OEMs use for aluminum engine parts. Saturn used it extensively for the head and block. The Vortec 4200, 3500 and 2800 family was designed to use it.

It works much like lost wax, so almost any shape can be accurately duplicated. It's not an economical alternative for low volume engine parts.

Here are a couple of references:

http://www.castsolutions.com/pdf/Engine_2004.pdf

http://www.findarticles.com/p/articl...15/ai_98901454

 

Thanks! I knew that very complicated shapes can be cast using this method and was surprised at the limitations referred to by Z28barnett. It sounds like the reason the port shapes aren't better "as cast" is primarily technical as related to the casting process?

Rich

 

The lost foam process still has the same limitation of shape as the sand core system. Since you have to use a mold to make the foam shapes that you are going to use. You then coat the foam with a thin layer of ceramic and vibrate sand into all of the voids.

Tricky process to get right, you use the metal to burn away the foam, gasses hydrogen ect. can cause a lot of porosity. Done right you can make some nice parts.

You will still need to build complex care box shapes with mutiple parting lines if you have an undercut core shape. The boxes will hold up better since you don't have as much wear from the foam as you see with sand.

The foundry I used to work for called it the "Lost Process" since they had such bad luck with it that they gave it up. I have never worked with it but know the general approach.

Z28

 

The posted links covered it fairly well. GM invented tons of money into the process. Several million engines so far and counting. I especially like the cast-in features like oil passages which minimize tough machining.

There aren't cores, which fill negative space in standard castings. The foam is just what the aluminum will be after casting, right? By building up molded foam layers without undercuts you eliminate the need for cores, but can still get undercut shapes. It's especially useful if the parts are designed initially to use lost foam casting.

Looking at an early Saturn head, you can see the small parting/glue lines (~.010) between the foam layers both on the outside of the head and inside the ports.

I'd really like to tour the foundry and watch the process.