What are the advantages of each one? I would be interested to hear what experienced members have to say.

 

Not an expert but imo i dont think the shape matters as long as the flow quality is there for the given application. By quality i dont mean just a flow number but rather velocity profile and sound of flow on the bench. A good exhaust port will have a balanced velocity profile and steadily increase in flow as lift goes up. It will sound stable, not noisey like a turbulent port would be. Just like an intake port, except exhaust usually is at a much greater pressure differential and higher velocity.

So shape of port should do what the application requires, and the header needs to work with the port shape. It should match well and after that, the header design from collector shape to tube size/length all need to work with the cam valve events to maximize scavenging and improve volumetric efficiency of the motor.

So a lot of things going on. Not many heads are d-shaped but doesnt mean its a bad design

 

http://www.summitracing.com/parts/tfs-30300002

These are the heads I'm looking at (And having to fight the urge to whip out the speed card since it isn't the right time yet). They also make them in D port.

Headers are 2055s. I should probably be switching to longtubes for what I'm building but beyond the engine I don't want to have to get too custom mod crazy with the car. For practical street use anyways I think shorties will do just fine.

 

Short tube headers should do just fine for what your doing. I use them with 200cc heads and wouldn't change a thing.

Mark

 

Yeah these are going on a 305 (Well the block is a 305 anyways) that will rarely see track use and is intended to scoot around on the street so I think shorties would be a better choice anyways.

 

https://www.thirdgen.org/forums/engi...er-2055-a.html

 

What am I looking at?

 

Said shorties for sale.

 

I also bought mine for a 305 build but ended up going with a 350 instead. They worked out well as I got a great deal on a shortblock with dished pistons. These let me stay close to 10-1. And, they DO make torque by the boatload. Check out my sig.

 

Yes the current 305 that is in my car is a raging POS I bought years ago out of the autozone rebuild catalog when I didn't know what I was doing/Didn't have alot of money.

It is a peanut lobed tappet cam that makes in the neighborhood of probably 190WHP and will not spin past 4500rpm to save it's own life. I could have done a cam swap but that would have left me with the problem of still having 8.5:1 compression on a 305 that I didn't plan to boost so I just decided to build a whole new motor.

In the meantime I figured since I had no hope at improving topend I might as well capitalize on where I could make power with bottom end torque. Some exhaust work, intake porting, rocker arm swap and a few other mods later and I was ripping consistent 2.0 sixty foots and actually got that POS motor to run high 14s.

 

I already own them. I've had them on my car since later 2011. Coated them myself too.

 

Ow-

 

This is a stock Z06 head.

http://www.web-cars.com/images/vette...PT_PP059_a.jpg

Most of my heads are square-port, but I feel the d-ports are superior.
The D-shape encourages LESS low velocity areas in the port, and that normally helps the engine "come on the cam" at a lower RPM.
The lower edge of the D-port also makes an effective reversion-dam when combined with round header primary pipe, and that also boosts low RPM power a bit.
When porting I find the D-ports to lend themselves to easier port-biasing as well.

The actual difference in performance between the two exhaust port shapes would be extremely difficult for the average individual to properly test on a track, so much of the mystery remains.
I do think it significant that you see the D-port show up on certain factory castings.

 

Sorry. You're going to have to explain this one is as well.

Ow (Ouch)?

Oh Wow (Sarcastic)?

 

Here's an AFR CNC'd exhaust port:
http://www.treperformance.com/images...ustPorts-1.jpg

Though I think most of AFR's heads use square ports, I have seen several head series for SBCs with the D-ports.

 

This proves interesting. As the theory I had heard behind the D-Port was that it promoted MORE exhaust gas velocity thus leading to greater torque. Looks like I have some studying to do...

 

The "advantages" of the D-port i mentioned are things that would not show up on a flow bench.
The flow-bench tests at standard pressure & velocity.

If these advantages exist then they would be best utilized with a valve-job that promotes great low-lift flow, and matched to an engine combination that is rather heavily biased towards low RPM torque.

That doesn't exactly explain the Z06 heads, but perhaps they went with the D-shape in order to utilize a relatively large port area without creating excessive dead-space in the port at low RPM, possibly for emissions reasons.
I can't say for sure, but would be an interesting question to bring up with GM engineering.

 

Lingenfelter also preferred the D-ports for his "street" engines, and square ports for his dirt-track engines.
He was very sharp, so I tend to think there is something to the low RPM torque thing.

That was an interesting question you posed there.
I don't think about it much because I have to work with whatever the head has & can't very well transform a square port into a D-port.
As I said I do prefer working with the D-ports because you can achieve effective port biasing without leaving a lot of excess port area.

Vizard has also talked about TIG'ing extra material to the port floor in order to get an even velocity gradient over the entire port area, - resulting for him in increased power output and both low and high RPM.
That is beyond me right now, but I believe that he did accomplish his claim.
If you want to know what Vizard book that is from I can look it up so you can follow up on it.

 

I am a big advocate of Lingenfelter's studies. He was a brilliant man with his life cut short.

I'm not running a superram under my hood, however when I custom ported my TPI my decisions on what to do with the divider wall were influenced by his research.

Any opinion of lingenfelter I do not take light heartedly. I think the chevy world took a great loss on the day of his demise. He was the carrol shelby of the smallblock.

 

Yes I wish he was around so he could write more books.

I also wish I was a much better welder. I would weld up the ports on some heads for track testing.


The big difference between the LPE "street" heads and "dirt" heads is that the street heads spend an extremely short period of time at high RPM, and even then rarely above 6k.
the dirt heads spend most of their time between 6k and 8k and are usually on 400+ cid engines.

back in the early 90's AFR started making a specific head as a bolt-on upgrade for TPI engines. They had the D-ports.
It would be possible for you to call an AFR tech and ask them what they think.
Also, Tony Mamo regularly posts on some forums like ls1tech.

 

I would be getting AFRs however they make nothing I feel would optimal for a N/A 305 based smallblock. That's why I chose the trickflows because with the 1.94 valves, 56cc chamber and 175cc runner combo I think they're perfect for a 3.7xx bore motor.

This is going to be a really oddball motor and for the mostpart I have my work cut out for me due to lack of support and prior builds.