Which type/size headers do I need?

[95Coupe]

331 Stroker 10.1:1 compression
Twisted Wedge ported heads
Systemax 2 intake matched to heads
Custom camshaft

I plan to rev the motor to around 6,500rpms. I have a set of BBK shorty unequal length headers but they just look like they are going to be WAY too small. I was looking at some Accufab midlength headers like these below. They are 1 3/4" runners. Would that be the size I needed? Also I was thinking about some long tube headers but I'm worried about clearance issues.

 

[5spd GT]

1.750" (1 3/4") headers would be a great header diameter.

Talk to George Klass at Accufab about there headers. They make some nice ones.

 

[Rockin GT]

I have a similar set-up and question . . . I'm trying to decide between 1 5/8" vs. 1 3/4" BBK LTs. How much torque would I lose w/ the 1 3/4's? I hope to add a supercharger down the road, but my current combo is a 331 w/ GT40x alum heads (mild porting), about .600" lift cam, trick flow street heat intake, 70 mm TB, 73 mm mass air, and AFM power pipe. What diam header would be a better choice?

 

[Grn92LX]

I use bbk 1 3/4" longtubes on my 347. They fit fine and they fit with a mcleod scattershield bellhousing.

 

[95Coupe]

Does anyone know the difference between the fox headers and the sn95 headers?

 

[Vipersix]

1 3/4" is pretty large for a 331 ci n/a motor. You'd almost be best using 1 5/8" IMHO.

 

[Grn92LX]

1 3/4" is pretty large for a 331 ci n/a motor.

Incorrect.

 

[Vipersix]

Uh... ok.

I don't have time at the moment to post a rebuttal, but in the meantime why don't you school me on my errors instead of simply telling me I'm wrong.

 

[Grn92LX]

"I don't have the time for a rebuttal either".

 

[95Coupe]

I agree with Vipersix. If you are going to say a tech advice is incorrect then you should atleast explain why so someone (me) can actually learn something.

 

[white 89 GT]

1 3/4" is pretty large for a 331 ci n/a motor. You'd almost be best using 1 5/8" IMHO.

I too agree, 1 5/8 is more in line for a not all out n/a 331 but longtubes are going to help the over 6k range.

 

[Vipersix]

I ran some numbers for you to estimate an approximate size for your headers. I had to estimate on items such as VE, peak RPM, and your cam numbers, but they won't change the following all that drastically.

-Shorty Headers-

Primary: 1.487" x 24.4 - 27.3"
Collector: 2.510" Tuned at 11.6" and 23.2 or 46.4"
H-Pipe: 11.6"
X-Pipe: 92.7"


-Long Tube-

Primary: 1.487" x 45.3 - 48.2" (Max 77.6")
Collector: 2.760" Tuned at 23.2"
H-Pipe: 23.2"
X-Pipe: 92.7"

Of course, this estimates around 392 hp. If you spill your secret cam and head specs I could get you a bit closer.

 

[Black1987Stang]

I ran some numbers for you to estimate an approximate size for your headers. I had to estimate on items such as VE, peak RPM, and your cam numbers, but they won't change the following all that drastically.

-Shorty Headers-

Primary: 1.487" x 24.4 - 27.3"
Collector: 2.510" Tuned at 11.6" and 23.2 or 46.4"
H-Pipe: 11.6"
X-Pipe: 92.7"


-Long Tube-

Primary: 1.487" x 45.3 - 48.2" (Max 77.6")
Collector: 2.760" Tuned at 23.2"
H-Pipe: 23.2"
X-Pipe: 92.7"

Of course, this estimates around 392 hp. If you spill your secret cam and head specs I could get you a bit closer.

How does this formula work? I'm debating on 2.5 inch or 3 inch collector and 1 5/8 or 1 3/4 primaries for a h/c/i 351W. Any advice? I want to keep my 2.5 mid pipe so if I can't use a 3 inch collector with my current midpipe I'm staying with 2.5 collector headers...I'm going turbo down the road with a single downpipe so I don't want to spend money on a new midpipe if I dont have to. Can you figure what I should go with?

 

[vristang]

331 Stroker 10.1:1 compression
Twisted Wedge ported heads
Systemax 2 intake matched to heads
Custom camshaft

I plan to rev the motor to around 6,500rpms.

The ONLY person you should be asking for advice on your combo, is the guy who did the cam.
In fact, if it is a real custom cam, that question has already been answered


Contact the guy who designed the cam specs....

jason

 

[Black1987Stang]

The ONLY person you should be asking for advice on your combo, is the guy who did the cam.
In fact, if it is a real custom cam, that question has already been answered


Contact the guy who designed the cam specs....

jason

Not sure if you're replying to the original or to me but I asked the last question. I'm probably going custom cam too but I don't have one yet so I want to decide what sizes I should go with first.......

 

[Vipersix]

The answer to everyone's questions all comes down to accuracy. You basically need to ask yourself how accurately you want your exhaust system to match the motor. If you have no idea what cam you're going to choose and still have plans to add more go-fast parts and tweak and tune the motor in various ways, I would recommend that you not worry too extensively about the exhaust. If, on the other hand, you have the motor specifics down pat and you want to eek every single ounce of power out of your combo I would recommend that you have your exhaust tuned to the motor.

Exhaust theory is an extensive and complicated subject, but I'll give you a quick rundown in order to show you what I refer to. In short, the combustion process creates a high pressure "slug" of gas which is blasted out of the port and down the header pipe in the form of finite-amplitude waves. When the exhaust valve opens, a slug moves down the port and into the exhaust header pipe. These high pressure waves drive gas particles in the same direction as wave motion which assists with the outflow of exhaust gases. When the slug reaches the end of the header pipe that's open to the atmosphere, a negative pressure wave of almost the same intensity is created and begins to travel back up the pipe toward the cylinder. Negative pressure waves move gas particles int he opposite direction as the wave, so this returning wave also assists with exhaust gas outflow. When the negative slug reaches the cylinder it delivers a substantial drop in pressure. If this wave arrives during the valve overlap period (when both the exhaust and intake valves are open) the pressure drop will help draw in fresh charge (scavenging).

So as I said, exhaust theory is a complicated process which allows a motor to utilize the Kadenacy principle to assist with the combustion process. Most people completely ignore this concept because it is not practical. If you prefer an exhaust which sounds good and looks nice... go for it!

Black1987Stang, I would recommend 1 5/8" with 2 1/2" collectors.

 

[vristang]

Not sure if you're replying to the original or to me but I asked the last question. I'm probably going custom cam too but I don't have one yet so I want to decide what sizes I should go with first.......

You're looking at it all wrong....
A custom cam guy will tell you what parts to use.

Here is my experience working with Jay Allen (Camshaft Innovations).

I filled out his buildsheet online. emailed it to him, and he gave me a call to discuss some specifics.

My previous setup used a Lightning lower. He explained that the lightning would hold me back, so he suggested a couple of other possibilities. The decision was ultimately mine on what intake to use.

If you haven't pruchased ANY parts when you talk to your cam guy, then the cam guy will have greater flexibility to get you the motor you will be happiest with.

I suggest not limiting your cam guy, by purchasing random parts before talking to him....




Vipersix,
That is decent info on the theory of pipe tuning, and if the OP were asking EXACTLY what length his LT's should be it could come in handy.
To this day, I have not found anyone on this board who is going to put their motor on an engine dyno and vary the primary lengths.

Everyone here is going to buy a set of headers that will clear the crap they have in the engine bay, and call it a day.

I just think that getting into 'tuned length' is WAY more detailed than what should be worried about here.
IMHO of course.

AND there is no way you are going to convince me that you will be able to pick better headers than the man who designed the cam.
The cam guy knows ALL the details on this setup, you are guessing at a lot of variables.

I don't mean that to sound as combative as it did, but I'm not sure how else to say it.




CALL YOUR CAM GUY!

jason

 

[5spd GT]

Outside diameters like 1.625", 1.750", 1.875", etc., make the header appear larger than what the exhaust gases actually see. That does not even take into account the different guage thicknesses either (14-18 gauge).

Calling a custom camshaft guys is the best advice. More than likely they will direct you to a 1.750" header diameter.

With a nice flowing top-end, get some nice flowing exhaust system. With the 4:1 exhaust types that we would use, the collector becomes more important than pipe diameter anyways. With the collector, go large and long.

 

[Vipersix]

To this day, I have not found anyone on this board who is going to put their motor on an engine dyno and vary the primary lengths.

Everyone here is going to buy a set of headers that will clear the crap they have in the engine bay, and call it a day.

Agreed. I tend to get carried away with things sometimes. But as I said at the end, most people completely ignore this concept because it is not practical. Oh, and apparently there is at least one on here...

AND there is no way you are going to convince me that you will be able to pick better headers than the man who designed the cam.
The cam guy knows ALL the details on this setup, you are guessing at a lot of variables.

That's funny, because there is no way you are going to convince me that a cam guy who designs cams at a factory somewhere will be able to pick better headers than the guy who designed and built the motor in question bolt by bolt (which in my case is me).

But that's why the automotive world is so cool, everyone has their own ideas!

 

[vristang]

That's funny, because there is no way you are going to convince me that a cam guy who designs cams at a factory somewhere will be able to pick better headers than the guy who designed and built the motor in question bolt by bolt (which in my case is me).

But that's why the automotive world is so cool, everyone has their own ideas!

1. The 'Custom Cam Guy' I am talking about isn't sitting in a factory somewhere. He is THE guy who designed the cam to work with THAT set of parts.
He is THE guy who set that combo together.

2. Nothing personal, I am sure you are a smart guy...
But, a true 'Custom Cam Guy' would pick a better cam for your motor than you would.
Again, that isn't personal... In fact I gave up on 'designing' my own cam myself...
Now, if we are talking about calling the general tech line at one of the major cam companies, and getting a 'custom cam' from the lacky working the phone.... then yeah, the odds are a little better that one of us 'hobbyists' can pick a better cam than that guy.


95Coupe hasn't been back to say who designed his cam...
That will settle ALOT

jason