Exhaust Manifolds or Exhaust Headers? Go!

[Murdoc]

OK folks, let's take a poll. Which is better Headers or Manifolds? I know Headers allow for higher HP, but there must be some benefit to having the functionality of the manifold with the pre-heater shroud attached, right? What do you think? What's your preference and why?

 

[tony-muscle]

Prefer the added power of the headers. Theoretically, the preheater just helps the car warm up faster, but I see it only functional if driven in the cold winter months.

 

[Hemikiller]

The pre-heat shroud is there to supply a warm air source for the factory closed air cleaner system. The air cleaners are calibrated to maintain inlet air temps in the 100°F range, where carburetors will atomize the fuel better. This also provides a more stable inlet air temp, which helps keep performance consistent in changing conditions. If you're running an open element air cleaner, then a shroud is not going to do anything for you. 

I'm a header guy, and mainly because the manifolds are restrictive. 

 

[mjlan]

My opinion is it depends on what other modifications (if any) have been made to the engine and what one's goals are.

If you are running a stock-ish engine then I don't think the expense and install time is justified.

But, if the breathing on the intake side has been improved then the OE manifolds are going to be limiting air flow out of the engine.

It is also possible to choose the wrong header- a 2" primary header is way overkill for most street engines...

Headers will deteriorate faster than manifolds, hang lower, interfere with more other stuff in the engine bay and are noisier.

Depends on what else is done to the engine.

 

[Don C]

Headers generally also improve low end torque, due to reducing exhaust reversion, and if sized correctly.

The reasons for cast iron manifolds from the factory include cost, ease of installation, longevity, and are quieter.

 

[droptop73]

It depends on what your preferred use for the car is. I drive mine a ton and don't want the added heat, maintenance and noise of a header so it's manifolds for me. 

I'm also not sure how much benefit off the shelf headers are when coupled with a full exhaust system that has any level of sound control. Sound control tends to equal back pressure. 

Headers will undoubtedly make power when well designed and free to flow, to get the best performance they need to be custom made to suit your combination and chassis. 

 

[Lazarus]

Exhaust manifolds for this cat. 
 

My opinion is admittedly very subjective.  I like driver cars and headers have caused me too many headaches in the past.  To be fair, I’ve never sprung for really nice ceramic-coated ones (though the ones I used were not cheapo ones either) so they quickly became rusty eyesores that kicked off too much heat and noise. Great on a dyno I guess - and the track of course - but I found they can easily rob the low end if not set up correctly... I just prefer the manifolds as a result. 

 

[Ryunker]

71 M code. Had nothing, purchased headers installed and found the stock ports of the head larger than the inlet of the 4V headers. Actually gave them to the scrap guy and months later scored a pair of manifolds and never looked back.

 

[73inNH]

Is there any DIY work that can be done to the stock manifolds to increase the flow?

 

[Hemikiller]

You can machine the outlets of the manifolds to 2 1/4" ID, like Ford did on the Boss 351. That's about it unless you send them out for ExtrudeHoneing or spend a bunch of time with a grinder. 

FWIW, the Hooker 6915 that fit the 71-73s are the easiest header I've ever installed, and I've had multiple sets. The new set that I recently bought fit without any issues at all, they bolted right up. Unfortunately, they are now made in China, but the ports now match the heads, the bends are better and the welding was very good. They switched to a flat head flange from the welded sealing flanges, and it sealed up without any sealer, just a Felpro header gasket. 

 

[73inNH]

You can machine the outlets of the manifolds to 2 1/4" ID, like Ford did on the Boss 351. That's about it unless you send them out for ExtrudeHoneing or spend a bunch of time with a grinder. 

Interesting. If the Boss 351 made 330 HP through manifolds, maybe it's worth looking at increasing the outlet to 2.25" ID.

 

[Omie01]

I will be going to stock on my next 73 and I will be running manifolds for quiet operation and ease of install for factory exhaust. My 71 has headers and it gets very warm under the hood!

 

[Murdoc]

Interesting responses here. I've heard a couple people mention easier maintenance with Manifolds. What kind of maintenance needs to be done with headers?

 

[droptop73]

Interesting responses here. I've heard a couple people mention easier maintenance with Manifolds. What kind of maintenance needs to be done with headers?

In my experience, header bolts continually loosen and gaskets fail. They need continual maintenance if you want them to look nice. I've never had a set of manifolds rust through. 

 

[c9zx]

Headers for me. I am one of those guys who thinks that way too much power is just right. Less restrictive, more mid-range torque, more upper RPM power. You must have then coated, preferably inside as well as outside, if you want them to last and reduce under hood temperatures. If a quality gasket is used, and a THIN coat of the RTV of your choice is applied to both sides, installed, and let cure completely (24 hours) they won't leak and they won't burn out. A split or toothed lock washer will keep the bolts retained.

Chuck

 

[Don C]

The bolts loosening are the biggest headache, but there are locking fasteners available, which are their own headache installing them, one example:

FORD Stage 8 Locking Fasteners 8912A Stage 8 Locking Header Fastener Kits | Summit Racing

Headers, and exhaust systems, aren't as prone to rusting out as they were when we had leaded gasoline, so rust isn't the problem it once was. The chlorides and carbon in tetraethyl lead additives combined with water vapor to form mild acids in the exhaust, causing rusting from the inside. Using exhaust wrap to insulate and quiet headers can hold moisture and cause rusting from the outside.

Parking lot speed bumps aren't kind to low hanging headers.

 

[tony-muscle]

I have ceramic coated Hooker headers and haven't had an issue with the bolt loosening. May not be related to the coating at all, but tightened the bolts during installation and retightened them afterwards.

 

[tony-muscle]

You can machine the outlets of the manifolds to 2 1/4" ID, like Ford did on the Boss 351. That's about it unless you send them out for ExtrudeHoneing or spend a bunch of time with a grinder. 

FWIW, the Hooker 6915 that fit the 71-73s are the easiest header I've ever installed, and I've had multiple sets. The new set that I recently bought fit without any issues at all, they bolted right up. Unfortunately, they are now made in China, but the ports now match the heads, the bends are better and the welding was very good. They switched to a flat head flange from the welded sealing flanges, and it sealed up without any sealer, just a Felpro header gasket. 

View attachment 55446

I am very curious about this. You say that the ports now match, how recent did they make this changes?

 

[Sheriff41]

I've been running the ceramic Hooker headers for quite a few years.  I haven't had to tighten any of the bolts since installing the headers, and with the ceramic coating they still look as good as they did new.  Definitely not the same as the ones we used to get in the 1970s!

I think extrude-honed manifolds would be very nice, too.