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Best headers for 318?

33K views 32 replies 6 participants last post by  maachine 
#1 ·
So my truck has a 1970 318 with a mild cam intake and Holly 650? It already has a custom exhaust but for some reason no headers. Will I really be seeing any HP gains with headers?
 
#3 ·
I personally believe headers aren't worth it unless your engine makes power over 5-6k rpms. It's believed that "shorty" headers won't make as big of a difference as "long-tube" headers.

The stock exhaust manifolds are more than adequate to channel gasses to the pipes. You can even mill-out the exhaust manifolds, if you feel it necessary.

Plus, headers are prone to warping/cracking...and they tend to rot-out faster...

Sure, they look awesome and have a different sound. On a close-to-stock motor? You will probably see a miniscule difference for a huge cost (buying headers AND installing them).

Unless you are building a drag racer or hardcore mud bogger, I believe there is money better spent elsewhere (like ignition, gearing, accessories, etc).
 
#5 ·
only reason i bought long tube headers for my truck (the exact same hookers you are looking at) is because i have plans to turn a 318 into a beast of a motor. and for the sound too.
 
#6 ·
they are also a lot lighter than the iron manifolds....much much lighter. in regards to warpage, those hooker headers you are looking at are the thickest manifolds i could find.....well on the cheaper side anyway. i did find some more expensive headers that had thinner metal.
 
#10 ·
i agree with moparite, a lot of guys here will tell you that a 4 bbl carb, an updated intake, and headers will increase breathability of the engine. increasing HP as well as MPG's
 
#11 ·
what do you have going on with that 318 to be putting out so much HP anyway? if i recall stock HP was like 170 or so
 
#12 ·
I would LOVE to see dyno-proof that headers make SUBSTANTIAL power gains on a stock motor with an aftermarket intake and carb.

Allowing a motor to breathe better? Anything the same size as the individual exhaust ports is more than adequate. If you blow through a straw, you will have resistance. If you blow through a straw with a giant cone on the end, you will have the same resistance. The cone (header) doesn't make more air magically flow through.

Headers change the WAY the air flows out the ports, not necessarily how MUCH air flows through. That's why they sound different. Even then, it won't make much difference unless the motor is pushing a LOT of gasses through (5-6k+++ rpms). For a motor to do this, it will need more than just an intake and carb. It will need a different cam, valves, stroke, etc. That's what makes a "race" motor...

As for headers weighing less than stock intake manifolds, I don't think an extra 25 (?) lbs will make much difference on a 5-6,000 lb pickup...and it is a pickup...not a ferrari...so weight shouldn't be a big issue...unless you ARE building a race motor...in which I highly recommend installing it in smaller/lighter vehicle...like a car...

I'm not trying to flame anyone, I'm just trying to be practical and realistic. Hopefully this will save you from a huge disappointment if you think headers are going to give you 100 hp...
 
#13 ·
The truck's a 1975 but its got a 1970 318. Between 1967 and 1971 they came from the factory with around 220 230 HP if I remember right and mine seems to have a pretty nasty cam in it. It used to be a drag truck with a 340 so its got a posi. I stepped on the gas on the way home from buying it doing about 10 mph and the truck went competly sideways and I almost went into the ditch on the other side of the road lol. The engine was built by a guy who built engines for nascar but I wasn't able to talk to the guy who built it to ask what else he did to it. I bought it from the brother and he didn't know much about it. It had been sitting about 4 years. I was only hoping to see maybe a 10 15 HP gain if less no big deal but I need new manifolds or headers so I might as well get headers. Thanks for the help guys
 
#14 ·
Allowing a motor to breathe better? Anything the same size as the individual exhaust ports is more than adequate. If you blow through a straw, you will have resistance. If you blow through a straw with a giant cone on the end, you will have the same resistance. The cone (header) doesn't make more air magically flow through.

Headers change the WAY the air flows out the ports, not necessarily how MUCH air flows through. That's why they sound different. Even then, it won't make much difference unless the motor is pushing a LOT of gasses through (5-6k+++ rpms). For a motor to do this, it will need more than just an intake and carb. It will need a different cam, valves, stroke, etc. That's what makes a "race" motor...
:ugh

I'm not even going to try to explain it to you.


You might want to read this....


http://www.shop4exhaust.com/t-Stock-Exhaust-Manifold-vs-Aftermarket-Headers.aspx

http://auto.howstuffworks.com/question172.htm
 
#15 ·
again, i agree with moparite. if you look at those old iron manifolds then look at long tube headers, the way the exhaust flows through the long tubes is much more efficient. the iron manifolds are tiny and have a choke point. the exhaust is pushed into a chamber that is shared with 3 other cylinders, then pushed through a choke point.

headers are the same as porting and installing larger valves, increases flow and breathability

i didnt say we'd get a large increase in HP either. but they way your engine sounds built, moparmanintn, you should see a decent increase in HP i assume
 
#16 ·
But odd someone would go to the trouble of building up the engine and not use headers. Must be a story there.
 
#17 ·
ya right? cause if its a good build, the exhaust is obviously the weak link
 
#18 ·
please, moparman, its not a posi. its a sure-grip. get yourself a set of headers. they flow better and your 318 will thank you. its like opening up the sinuses. should pick about 15-20 horses for under 200 bucks. i've had the same set of hookers on mine for 9 years. got em from summit. and they just look so damn cool
 
#19 · (Edited)
I understand how headers work, I'm not an idiot.

I also understand that engines work like air pumps. You can bolt all the fancy crap you want on them, and they absolutely cannot produce any more air until you change the internal components. There is a mechanical limit, until you change the mechanics.

Hence: stock vs "race" engines. Stock engines have an internal mechanical limit to airflow, and a "race" engine has the internal mechanics changed, to produce more airflow, requiring extreme changes to the entire exhaust system.
 
#20 ·
who's to say that the iron manifolds or intake/carb arent the weak point in that air pump system? the internal valves will only suck in as much air as the carb and intake will allow. same thing on the exhaust side, you put a 1/2" exhaust pipe on 4 cylinders it will choke up the engine. maybe its possible the exhaust valves can move more exhaust than the manifolds will allow? they built these cars to be financially friendly. i highly doubt they so finely tuned the best possible flow rate between the exhaust valves and manifolds. one or the other is going to be the weak spot.
 
#21 ·
Oh I don't doubt these are not "finely tuned" manifolds... haha ;)

The manifolds do not create as much of a choke-point as people think, that's why headers don't magically add 50 hp. You are only increasing the size of the "tube" by a tiny bit. Anything larger than the size of the actual exhaust port probly won't make any difference.

5, 10, 15 hp? I don't see why not... It still isn't a significant difference and I don't see why people can justify spending hundreds of dollars on a minimal power increase. Which is why I played devil's advocate and told the other half of the story... :D
 
#22 ·
I understand how headers work, I'm not an idiot.

I also understand that engines work like air pumps. You can bolt all the fancy crap you want on them, and they absolutely cannot produce any more air until you change the internal components. There is a mechanical limit, until you change the mechanics.

Hence: stock vs "race" engines. Stock engines have an internal mechanical limit to airflow, and a "race" engine has the internal mechanics changed, to produce more airflow, requiring extreme changes to the entire exhaust system.
The manifolds do not create as much of a choke-point as people think, that's why headers don't magically add 50 hp. You are only increasing the size of the "tube" by a tiny bit. Anything larger than the size of the actual exhaust port probly won't make any difference.

5, 10, 15 hp? I don't see why not... It still isn't a significant difference and I don't see why people can justify spending hundreds of dollars on a minimal power increase. Which is why I played devil's advocate and told the other half of the story...
You just don't get it do you. I was going to post a link of a comparison that was done on a motor. Same everything but it was dyno tested before and after the stock manifolds vs the headers. You are right it won't produce a 100 hp gain just about 80! With nothing but a header install!

I understand how headers work, I'm not an idiot.
:thatfunny
 
#23 ·
Go ahead and put headers on everything then. I've put headers on engines and owned various vehicles with headers and manifolds. From experience, they don't make a lot of difference on a stock or close-to-stock motor.

but...

you can go ahead and read "comparisons" on the internet... ;)
 
#24 ·
i understand what you are saying lunchbox. on a low HP stock engine they wont make a difference. but when you start upgrading.....they will. add a 4 bbl carb and intake that allows the engine to suck in more air/fuel mixture. you wont see the a big increase in HP with that because without the upgrade on exhaust, the engine cant "exhaust" properly. and without exhausting properly it cant intake properly as well. it all works hand in hand. you dont get the full benefits of any upgrade until you do them all properly.

like i said, a 4 BBL, intake, and headers......and the engine will "breathe"
 
#25 ·
Thank you for getting what I've been trying to say, Maachine!

...and I agree with you as well. What I was trying to get at was the uselessness of adding bolt-on performance to something with a mechanical limitation, without having all the other necessary elements to make the effort worthwhile. It's like installing a blower on top of your engine and leaving the belt off. It looks cool, but it ain't doing much.

I would also add that an intake/carb along with headers still isn't using the headers to their potential. Albeit, it helps, but there is so much more to the science of headers than just a supplement to intake and carbs. It takes a lot of internal parts/adjustments before the headers will really start to wake things up. THAT'S what makes a "race" motor, and makes headers very worthwhile... ;)
 
#26 ·
i agree with your last statement too. the 318's with their small exhaust and intake valves.....they do have a limit. most high HP engines i have read about have the typical 1.60 or 1.68 size....cant remember the exact value off the top of my head. but still, that is only a small bump up from the stock 318 valves. so the internal components on 318's arent the weak link when doing the simplier upgrades.
 
#27 ·
Yes, but there is more to it than just valves. There's cams, bore, stroke, compression, porting/polishing, piston design, balancing, etc. All of which are internal mechanical modifications. Unfortunately I am not as familiar with the 318 as I would like to be, but these principles hold true for almost all engines.

Until you change/enhance those internal components, the engine itself (not including the intake or exhaust) won't pump any more air. That's what I was referring to when I mentioned the size of the exhaust port. It's a restriction in of itself...

Also, the speed at which the motor makes its power is a HUGE factor with headers. As far as I know, headers really make a difference with high-rpm power. That's when the motor is pumping most of its air and it actually NEEDS the larger exhaust.
 
#28 ·
Well-designed headers produce a "scavenging" effect. When an exhaust gas pulse exits a header tube into the collector, a negative pressure wave is created that travels back up the header tube to the exhaust port during valve overlap. This negative pressure helps pull any remaining exhaust gas from the cylinder and also helps draw the incoming intake charge into the cylinder. This, of course, is very beneficial to engine performance but the tubes must be long enough for it to be effective during a useable rpm range.
Stock exhaust manifolds DON"T do this! You are missing the point. NO engine components need to be changed to benefit from headers! Read the entire article....
http://www.carid.com/articles/should-i-install-headers-on-my-car.html

:banghead:
 
#29 · (Edited)
Buddy, calm down, I get the point. I understand long-tube vs short headers. "shorty-headers = shorty-gains".

There just simply ain't that much of a difference on stock motor. I've been there and done that!

Well-designed headers produce a "scavenging" effect. When an exhaust gas pulse exits a header tube into the collector, a negative pressure wave is created that travels back up the header tube to the exhaust port during valve overlap. This negative pressure helps pull any remaining exhaust gas from the cylinder and also helps draw the incoming intake charge into the cylinder. This, of course, is very beneficial to engine performance but the tubes must be long enough for it to be effective during a useable rpm range.
This is another point I've been trying to make. You have to get the RIGHT header for the RIGHT rpm range to get the most out of the upgrade. From the little I know, the engine has to be making most of it's power at a higher rpm in order for the headers to be used optimally.

However, as we will see, the quality of manifold exhaust flow varies from vehicle to vehicle. Regardless of the manifold, we recommend that before you install headers you make the rest of the exhaust system less restrictive. This usually means installing larger diameter, mandrel bent pipes and definitely means using more free flowing mufflers. It doesn't make any sense to put headers on if the exhaust flow is only going to be choked further down the line.
Here is another good point. Most people who install headers, have to make significant changes to their ENTIRE exhaust system. They don't just change headers alone... The change of the exhaust sytem, from the collectors-back, is where people see the biggest difference in performance. The stock muffler, cat, and all the poor factory tubing bends restrict more than manifolds ever could...

The aforementioned scavenging effect is most pronounced on long tube headers, however these headers are usually more expensive, the most difficult to install and take up the most space. Long tube headers require that the exhaust pipes be cut and flanges attached that will connect with the header collector.
Once again, we need to weigh the costs and benefits. Is it worth spending around $250 +++ on a decent set of long tube headers? If it were me, I would wait till the engine actually NEEDED them before dropping that kind of coin... However, I completely understand if someone installed them because they looked and sounded different, but don't expect a miracle performance bolt-on!

Steel headers will not last very long unless they are coated. The paint they are delivered with is just something to keep them from rusting in the box; they must be painted with high temperature paint before they are installed. Even that kind of paint won't last however, and they must be periodically recoated or they will rust away. Stainless steel headers will not rust but they will usually turn blue near the head flange. Ceramic coatings are durable and can withstand higher temperatures. A quality set of headers will have a substantial head flange to prevent exhaust leaks and all connections will have high quality welds. Finally, an engine works as a system, and the effectiveness of individual components is therefore very dependent on the other parts. While long tube headers are generally better for maximum performance than short tubes, the amount of power increase either type can provide depends on the camshaft design, intake system, cylinder head ports, and how restrictive the stock exhaust manifolds are. In general, a quality set of headers should provide an increase of approximately 10 horsepower, and if you're restrained with your right foot, you may even see an increase in fuel mileage.
That sums up just about everything I've been trying to say. Straight from your article you wanted me to read. There is a maintenance factor, you get what you pay for, there are mechanical limitations of the rest of the engine system ("camshaft design, intake system, CYLINDER HEAD PORTS"), and the website says approximately 10 HP gain...

There's no miracle to headers. Period. Do stock manifolds restrict? That's subject to extensive examination and reverse-engineering. The manufacturer wouldn't put an over-engineered and expensive engine component on their average production vehicle, however, they DID put at least SOME thought to their design of the stock manifolds. Sure, they were cheap and cost-effective to produce, but they also WORKED.

Stock manifolds make the ol' engine fart just fine... ;)

So, I ain't an idiot, I "get it", I read your article, and I hope people understand my point of view now! lol
 
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