porting heads...

[SappySE107]

However, all as cast heads respond well to gasket matching, bowl blending and valve guide profiling.

Would you care to put money on that statement? Id bet everything I own.

I disagree with your idea of how to improve 3500 heads based on books, because I do have a bench, and I know what those book recommendations will do to the flow. Have you bowl blended a 3500 head and flow tested it? I don't think so. I am not going to tell you what needs to be done and where, but books with general guidelines are best served to the old iron head V8 engines that they are based on.

In some cases, is a flow bench required? YES. You will only ruin 3900 heads with any of the logic read in those books. Gasket match...ruined. SSR blend, ruined. Bowl blend, ruined. Raise the roof, ruined. If I don't sell ported 3900 heads, there is a damn good reason. I do sell 3500 heads, because I can get a worthwhile gain from them. I started my 3500 research in 2006.

[ForcedFirebird]

You can easily ruin your heads, especially the 3550 and up that GM already put effort into the flow characteristics unlike older iron heads.

Ben and I would chat a while back about porting and once I got a flow bench, realized how important it is to use one if you change the shape of the port at all. He hit the nail on the head when he said you can take all that you read in magazines/internet/books about porting rectangular iron head ports and throw it away when it comes to modern high flow designs.

I have been using double cut ferrous burrs on aluminum since 07, still have the same ones and they still work great.

It's very easy to tell people how to port, and it's very easy to think you have done something, but until you are in front a bench for hours and take the time to develop the ports, you are just guessing.

[ForcedFirebird]

Of course you can improve them. Is a flow bench required to do so? Of course not. Does it help optimize results? Well obviously it does. However, all as cast heads respond well to gasket matching, bowl blending and valve guide profiling. You don't need a flow bench to do it but you should at least be measuring the work you do so you can get each port the same. The easy way to do it is get a set of locking telescopic gauges and use them as a go/no go feeler gauge. Working with a good machinist or having a milling machine is a great start because it can establish the size of the port behind the valve. The actual desired size is going to depend on application but there are lots of formulas and recommendations out there that will give you a size based on the percentage of the valve diameter. At the very least clean it up so it is concentric. If you never use a bench to flow your heads you will not have a CFM number you can put on them and you will not know the before and after difference. Knowing this will allow you to come up with an approximate horsepower difference. None of this is a requirement by any means but it is useful data.

Modern castings are pretty damn good so you may not have much work to do. When I went to work on my iron heads it was a different story because the casting flaws and bad transitions are blatantly obvious. All I did were the basics along with gasket matching the intake manifold. I never adjusted the shape of the port I just smoothed it all out. I followed some of the tips I read in Engine Masters magazine where they did work on a Chrysler Magnum head which has very similar port flaws as my iron heads. Their CFM results were impressive with just some simple clean up techniques. When I get a bigger garage I am going to build the same bench that David Vizard recommends in his magazine. The cost is around $150

Well, go ahead and build your bench, then you will realize why Ben, Dave and I say what we say. Sure wish our bench only cost $150, spent that on wood alone to make the plenum and aluminum to make the head adapters - shoot, the wet flow test adapters cost several hundred for the materials alone and took me several days on a CNC machine to make the assembly.

Proof is in the pudding, and we have plenty of pudding.

[ForcedFirebird]

So after reading all of this porting 3500 head is useless and you'll never improve what GM did? Damn I never thought I would hear that one.

I just got a new set of heads and LIM that I'll probably be revisiting... Not sure what I'll do this time but we'll see.

No, but without knowing what you are doing, you will ruin the heads. It takes a nice big plie of ruined heads to learn what needs to be done. Grind out one little area wrong and the heads will be junk, not only will they flow less, but now the velocity has gone down since the CSA to port volume ratio gets worse.

[ForcedFirebird]

2

Maybe 2, closer to 1. That's a half of a percent of gain for spending the time to do so.

Just like the iron heads. People remove the shark fin and they flow the same, yet spent all that time doing it and, again, lowered velocity.

[Z26-T]

Not sure how many of you know Lee Chapman. He is a family friend of ours and did the majority of the head work on our dragsters. He showed us on his flow bench how easy it is to "F" up a cylinder's flow. If you don't have a flow bench, don't do it.. Buck up and pay to have it done by a pro. Otherwise, like has been stated, you can ruin the flow.

[Mars]

One thing I know is that on a stock motor / heads, you always have a ton of carbon build up on the exh. ports... (I've seen this in all my 660's) I've had them all apart, 3.1 2.8 3100 3400 3500 3900. Sometimes it's really thick on there. Can't be good.

If you just sand down the exhaust and not really anything else, the carbon don't seem to stick at all, and it's fairly easy to do.

I'd like to see dyno results of head porting on a 3500 or even 3900 because everyone says they are soo good out of the box. If that's the case, then why bother with porting at all ? Money may be better spent elsewhere... ? Not being a dick, it's an honest question.

[SappySE107]

3900 is difficult to say the least. Leave em alone. 3500, go with experience or leave them stock. Whenever you want to send me some heads and do comparisons, let me know

[ForcedFirebird]

One thing I know is that on a stock motor / heads, you always have a ton of carbon build up on the exh. ports... (I've seen this in all my 660's) I've had them all apart, 3.1 2.8 3100 3400 3500 3900. Sometimes it's really thick on there. Can't be good.

If you just sand down the exhaust and not really anything else, the carbon don't seem to stick at all, and it's fairly easy to do.

I'd like to see dyno results of head porting on a 3500 or even 3900 because everyone says they are soo good out of the box. If that's the case, then why bother with porting at all ? Money may be better spent elsewhere... ? Not being a dick, it's an honest question.

Well then send us the heads you mentioned and put them on the Fiero motor. We know how much you like dyno time, and you know how much pride we take in our work - let's do it up

[3400-95-Modified]

I like your new options in the store for head work, Now my question is I currently have a untouched set a 3500 heads and lower intake... I'd like to have them ported but I'm not sure which stage would fit me well and what the benefits would be. Bottom line I don't want to spend close to $800 for work that wont gain me more than 2hp...

I would be using stock valves, 26986 springs that I have and would have them cleaned before sending out to you. If you can prove to me that the stage 3 porting option will gain me enough to justify the cost then you will probably see my heads coming your way since no I do not know the best things to do. For this new set I was probably just going to polish the hell out of the exhaust ports and texture the intake and not match anything or change any shapes.

I also asked you a while back Ben about a new cam suggestion... do you want me to order the cam profile option and have you do that before giving an answer on the port work?

[geoffinbc]

True most of what I have done is with iron heads. However I still don't believe that there is not a set of heads on the planet that cannot be improved. I will agree that sometimes a flow bench will be requires to get results.

As for the flow bench the one described by David Vizard is a floating pressure drop design that uses a shop vac that gets calibrated with an orifice plate before use. If this design is something he recommends then it sure as hell is going to work well. He has 51 years of experience and over 200,000 Dyno pulls under his belt. He has changed industry thinking on 2 valve, 4 valve and nitrous motors. The bench does not use tubes to simulate the bore you simply do the flow testing on the engine block.

[ForcedFirebird]

That's basically how ALL flow benches work. You just won't be testing at 28" with a single shop vac.

[Superdave]

It would be nice to test on the actual correct bore size though.

[ForcedFirebird]

The bench does not use tubes to simulate the bore you simply do the flow testing on the engine block.

It would be nice to test on the actual correct bore size though.

.....

[geoffinbc]

That's basically how ALL flow benches work. You just won't be testing at 28" with a single shop vac.

No they don't. Most conventional flow benches use a fixed pressure drop. As you open the valve in the cylinder head you increase the volume of air flow to create the 28" difference across the port no matter how far the valve is open.

The bench I am describing is a floating pressure drop. The vacuum source stays constant and the pressure drop across the port changes as you open the valve. The results can be converted to get CFM numbers at 28" if you want. Basically are measuring the change in vacuum pressure instead of CFM.

The reason the industry uses a fixed pressure drop at 28" of vacuum is because of Smokey Yunic and his early work with flow benches and dynos. He discovered that a 28" pressure drop and the CFM increases you see through porting at that pressure drop most closely resembled what he saw in terms of horsepower increases. So it has basically become the standard and it a good tool when comparing heads in a catalog. However a floating pressure drop has many advantages for port development.