Hooker Headers, good/bad/ugly

I have Hooker Comps on my car.

As Ratio411 said they are not coated inside but,
The flange is thick and straight and fitment is great.
Now installing them took some floating the block off the mounts to
get them in and bolted, but they clear everything without dinging any tubes.

Now the bad, they hang low.
It they would have swept the pipes upward closer near the floorboard /firewall bend and moved the collector forward.
The ground clearence would allow for a lower front stance.

I hear the FPA have done that and tuck up nicer,
but the price puts a dent in the wallet.

PB

ratio411 said:

Mass is not the issue. Mass is a measure of weight.
I would think that mass is not affected by heat.
However, volume is affected by heat, and the gasses displace more volume the hotter they are. So you are creating restriction by increasing heat in the same pipe. The pipe is the constant value of volume capability. The gas varies in volume depending on temperature.
That is why I said that you can have the heat wicking of the headers, which is a big benefit, while having higher backpressure and velocity, just by using smaller uncoated primary pipes.

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I gave it a bit more thought and I think it's the gas velocity relative to gas velocity at speed of sound (Mach number) that determines how restricted the flow is. When the flow reaches sonic speed, the pipe won't flow any more, regardless of the pressure difference. An intake ports/manifold, becomes restrictive if the Mach number exceeds ~0.5. Not sure if the same number also applies to the exhaust.

If you increase gas temperature, the speed of sound goes up, but a little less than the density goes down. This means that the maximum flow capacity (@Mach 1) goes down a little. If you for example increase gas temperature from 1000 to 1500 deg F, the density goes down 26%, while the speed of sound goes up by 26%. 0.74 x 1.26 = 0.93. If you don't want the Mach number to increase, the pipe area needs to go up by 7% and the diameter by 3.5% (for example from 1 5/8" to 1 11/16") to compensate for the temperature increase.

So, you are correct that the pipe becomes slightly more restrictive. However, the higher velocities and temperate can also enhance the scavening effect that a good header has which may well be of more influence on volumetric efficiency than the increased flow restriction.

ratio411 said:

Heat in the engine bay is good. It is not in the engine if it is in the bay.
All this is why hood scoops are used in the first place. The only thing heat in the bay hurts is if your air cleaner is not exposed to incoming cool air.

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Well, 90% of all the classic Mustangs discussed here in the classic forums do suck their air from the engine bay. The hotter it is in there, the lower the density of the incoming air, which reduces power.

To keep it slightly on topic: I have Hooker Super Competitions too. I liked the way they fitted in the engine bay, but hated the very limited ground clearance. I damaged them within 20 ft of driving
After struggling with them for a few years, I decided to cut them up and use the bends to make Tri Y's out of them . How that affected performance is hard to tell. I probably lost some, won some but at least I get to enjoy 2" more ground clearance every time I drive it.

This is the only picture I have. It's raining outside, so I'm not getting any from under the car.

If you guys had 351w you wouldn't have ground clearance issues (extra 1" deck height) I have Hooker Comps that are coated inside and out and they are great. A few dents here and there to clear steering components is all that is needed. I do have some clearance issues with the header reducers near the transmission cross member support. The headers are tucked almost too high and the header reducer had to be dented to get it to clear. I have the 2.5" Magnaflow stainless exhaust kit.

I've got some pictures. This is on a 67' Fastback with a 289 and a Toploader. I didn't take pictures with a can but i measured the lowest point which happened to be the collector flange at 7". There's no interior in the car, but i doubt that will drop it too much more if it was in there. These 6901's fit perfect and we didn't have to raise the motor either. It might be different for your 65'. The instructions say if you have to do some modifications to the headers, if you can believe them.