long tube headers

Not a tech issue.
Moved to 94-95 talk.

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Part Number: TF9434 (Ceramic)
Part Number: TF3945 (Chrome)

You're welcome

wgonzalez said:

hey guys i am looking for a set of long tube headers for my 94 gt i need 1 3/4 with 3'' collectors. the only set i can find is cooks they are too much $$$$ does anyone out there have a 94 or 95 with 1 3/4 headers any other brand?

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Those are big headers. For a naturally-aspirated 302 or stroker, the MAC 1-5/8" long tubes with 2.5" collectors are more than big enough. The only time you're gonna need headers as big as the ones you're looking for is if you have a stroker with forced induction or a transplanted naturally-aspirated big block.

I have 1 3/4 to 1 7/8" stepped Bassani's they have a 3" merge collector. They are for a fox, and yes, they fit. Mines only a 331 though...but the heads flow what some big blocks do...

Bullitt95 said:

Those are big headers. For a naturally-aspirated 302 or stroker, the MAC 1-5/8" long tubes with 2.5" collectors are more than big enough. The only time you're gonna need headers as big as the ones you're looking for is if you have a stroker with forced induction or a transplanted naturally-aspirated big block.

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Very wrong!

Grn92LX said:

Very wrong!

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So will these be to big for a 306 with afr 185 heads?

Noone but the cam guy can tell you which header is to small or to big

Many 302/306 custom camshaft guys will recommend a 1.625" header. A few will go with a 1.750" header.

Many 331/347 custom camshaft guys will recommend a 1.750" header. A few will go with a 1.875" header.

It all is dependent on the camshaft valve timing events and overall package goals.

BBK headers have 3.00" collectors. They come down to 2.33-2.37" at the ball/socket connection for sealing. One can get out a dremel and open it up a little bit. Many of these are going into a 2.5" mid-pipe.

95mustang_gt said:

So will these be to big for a 306 with afr 185 heads?

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"It depends..."

Grn92LX said:

Very wrong!

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Please explain. Unless you want to toss your low rev torque down the toilet, there's not much point in going for a header that has a primary pipe diameter significantly greater than the exhaust valve diameter. Bigger isn't always better and I agree with the last post about the cam timing events being a major factor in header selection.
A dual 2.5" exhaust system can support up to 500 crank HP with minimal restriction, so 3" collectors are only necessary if you plan to go for more HP than that.

I think its pretty dangerous to use a rule of thumb for anything. Does anyone really think going from a 1.625" OD to a 1.750" OD header is going to make driveability go from "perfect" to "no low end torque?" Its a difference of .125" A quarter is .069" thick. So the thickness of not even two quarters is going to make or break a hot 306?

I would assume an AFR 185 headed 306 would get spun 6500rpm+ anyway. 5spd GT is correct in saying the cam is the deciding factor, but based purely on head and displacement I wouldn't hesitate to run 1.750" headers. And if you decide to stroke it or add a power adder, you won't need to upgrade later. A 4.10 or 4.30 rear end in this scenario, especially with a heavy vert, would make a great runner in my opinion.

Adam

So the thickness of not even two quarters is going to make or break a hot 306?

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It could. That's flawed logic as well. By the same logic, you could say 5° of timing or a few milliseconds of valve timing doesn't matter since those are pretty small values.

Zero Signal said:

It could. That's flawed logic as well. By the same logic, you could say 5° of timing or a few milliseconds of valve timing doesn't matter since those are pretty small values.

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Neither of those have to do with physical size.

A similar argument would be that a 70mm throttle body is perfect for the street but 5 more mm will make the car unstreetable.

Or that since a 347 only can flow about 650 cfm, a 750cfm carb will be a huge waste.

I've read the George Klass hour glass argument, and it makes sense, but when you actually go to the track and see what the fast cars run, well, I think its fine to do a little thinking on my own too.

Adam

Whether one sees gains or not is really going to be determined by your camshaft's valve events.

With a camshaft that has less and later exhaust activity, as opposed to "vice versa," you may see some gains. With later exhaust timing, and adding larger exhaust to what already exist, it can decrease cylinder pressure, and there-by relieving you of some torque you once had.

HP = Torque x RPM/5252. What happens to the end product of horsepower, if your "plugged-in" torque is decreased (loss of cylinder pressure)?

I would only upgrade the exhaust, if the camshaft intake/exhaust valve events have been constructed around the larger exhaust point. This is why choosing the camshaft should be done last and with the long-term goal of the car is going to be.

This is why you see gains with some small to large swaps, and losses from some small to large swaps. It is the entire package, mainly the camshaft events.

That is correct, there is only an 1/8 of an inch difference between each; 7.7% difference in o.d.

I am going to take the outside diameter as the inside area, hypothetically.

I get 2.072" (squared) for the 1.625" long tube.

I get 2.404" (squared) for the 1.750" long tube.

Now, long tube headers range in many different lengths: 30-38".

Using a 36" tube, no taper, and assuming uniformity you are getting near 1420cc for the 1.750" pipe.

Using a 36" tube, no taper, and assuming uniformity you are getting near 1225cc for the 1.635" pipe.

Could this have an effect? Possibly...

The O.D. is not as drastic as one may seem, as Adam pointed out, just like a cylinder bore. A 4.030" bore is .015" on each side. Now it suddenly does not seem so big, does it?

But run that down the entire length of the pipe and it begins to seem to matter.

2.404" - 2.072" = .332" of area difference. Now multiply this difference down the length of a tube, and you see the difference increase all the way down the tube.

Now factor in the different collector lengths, styles, lengths, design, and you see how not all headers are the same in power.

Either way, I would rather have a "small" diameter tubing, but a long pipe, than a large diameter tubing, and a short tube header.

Spinning it another way...

Hooker - 18 gauge
Kooks - 18-16 gauge
Mac - 16 gauge
BBK - 14 gauge
Bassani - 14 gauge
JBA - 14 guage

All are rated at 1.75" outside diameters right? Does a higher gauge (least thick) header have a larger cross section for exhaust flow?

Another question...

We all know that a 1.625" header works just fine on an average to higher performing 302. So...

302 - 1.625" header

A 347 displaces 14.9% more cubic inches than a 302. So should we increase the header to a 1.875" header (15.3% larger than a 1.625" header).

Or, what about a daily 408, which is 35% larger than a 302. So should we increase the header diameter to 2.2" (35% larger than a 1.625" header).

Then, we have to keep in mind that many of the exhaust ports are the same size or very close throughout a variance of smaller and larger cylinder heads.

AFR 165 - 68cc
AFR 205 - 70cc

Just more questions to ponder over


In the end, all we can give someone is a place to start, and let the custom cam guys give you an idea that works for them and your goals.

I plan on investing in PipeMax soon.

Looking for thoughts...

5spd GT said:

Looking for thoughts...

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I didn't quote the whole thing because its long, but that was a great post.

This is beyond my knowledge of how airflow works, but air does travel down the sides of the pipe in a swirling motion, so I'm not sure if the volume of the pipe matters so much as the diameter. But how much does the diameter matter? My point being that worrying about 1.625 vs. 1.750 isnt as critical as the other pieces.

I also know that interrupting that swirling flow has major consequences, so that the point of interconnection to the head is important, and the point of merging collection is important.

You want the header to be small enough that velocity of the flow is not slowed to prevent scavenging, but large enough so that the volume of air exiting the head can escape. We don't know if the car is street or strip either...

I like your point about the "normal" 302 header size vs. 347. I think you illustrated well that displacement shouldn't be the determining factor of header size.

Adam

Black95GTS said:

I didn't quote the whole thing because its long, but that was a great post.

This is beyond my knowledge of how airflow works, but air does travel down the sides of the pipe in a swirling motion, so I'm not sure if the volume of the pipe matters so much as the diameter. But how much does the diameter matter? My point being that worrying about 1.625 vs. 1.750 isnt as critical as the other pieces.

I also know that interrupting that swirling flow has major consequences, so that the point of interconnection to the head is important, and the point of merging collection is important.

You want the header to be small enough that velocity of the flow is not slowed to prevent scavenging, but large enough so that the volume of air exiting the head can escape. We don't know if the car is street or strip either...

I like your point about the "normal" 302 header size vs. 347. I think you illustrated well that displacement shouldn't be the determining factor of header size.

Adam

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I really like your thought process as well

I wish I had more time to read up on it.

Have you ever read of any of Gordon Blair's stuff?

He has a book called: Design and Simulation of a 4-Stroke Engine.

From my understanding, it goes VERY in-depth on topics such as this, and anything you can think of with an internal combustion engine. I was thinking of purchasing it soon...

I figure understanding just 5% of his stuff would be more than the 100% I have learned elsewhere

5spd GT said:

I really like your thought process as well

I wish I had more time to read up on it.

Have you ever read of any of Gordon Blair's stuff?

He has a book called: Design and Simulation of a 4-Stroke Engine.

From my understanding, it goes VERY in-depth on topics such as this, and anything you can think of with an internal combustion engine. I was thinking of purchasing it soon...

I figure understanding just 5% of his stuff would be more than the 100% I have learned elsewhere

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To be honest all of my air flow knowledge comes from an entry level fluid dynamics course I paid keen interest in at college. I think I was the only one awake at some points but because I could relate it to engines I loved it.

I feel bad for the poster, we probably just in the words of Grady "hosed him up."

So how about it wgonzalez, more info on the what you want to do with the car, shift points, etc!

Adam

sometimes there are good deals out there for the larger tube headers

a good deal is hard to pass on

i might not need a 75mm throttle body
but if i was looking for one and the money was right

im still confused on what size would be good for my combo?:dizzy: really no conclusions?