I have been led to believe that headers, because there is less restriction will give you less torque, at least that's the ol wives tale that rears it's ugly head on a daily basis around here.

I have always been in the camp that says if you make more power you make more power, you don't lose anything, hope this helps those who preach the ridiculous theory about back pressure and it's way of making more torque.

What happens when the engine is restricted in any way including small heads, small pipes etc is the HP comes down and is closer to the torque,
The torque doesn't increase just the HP decreases making it appear the torque is going up. Now open up that engine with big heads exhaust etc and you will get more torque and more HP across the board.

Unfortunately evidence like this will not sway anybody.

 

Kind of a side question regarding the stock manifolds, but can someone refresh my memory. Way back when OEM big blocks were being installed in our antiques, was the dyno gross hp ratings of those engines made with stock cast iron manifolds, or some other manifold/header setup?

 

Headers can be very durable.

32 years and counting for a cheap set of Blackjack Alumkoate headers. 27 years on my vette and 5 on another vette. My 99 Trans Am has had the same set of Hooker long tube headers for 15 years without any issues.

 

Thanks to the chirren in china, you can get a set of 304 stainless headers for less than $200. Should last every bit as long as a crap 80 lb cast iron header.

http://www.ebay.com/itm/171951954576?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Other than needing to dink a couple of spots for plug wire clearance with the blueprint aftermarket heads, the look good.

But throw the bastard bolts in the trash. They're 3/8 coarse but have a 10mm head, and seem to be lesser cheese grade.

 

The differences at "street driving" temps aren't going to be any different. Headers aren't going to "just" help or "help more" when it's cool vs when it's hot.

Zwede gave up 46 peak RWHP on a fully muffled 454 with a I'm sure a milder flat tappet cam, less cubes and I believe similar heads at that time (but I don't think they had any porting done). Knowing Marcus I would expect it was tested with "normal" temps.

The 496 gave up 60 FLYWHEEL HP using lightly ported heads, a bigger carb, probably toss up on intake, a healthier hyd roller cam and a 500 RPM higher HP peak. There was more air moving through the 496...so exhaust impacts things a little more....but........

Now drop that same 496 in Marcus' Vette with the same exhaust...what do you think you'd see for a RWHP loss? Do some math....

When I see someone say "who drives around at 5500-6000 RPM constantly"...well no one...and it doesn't really matter.

As mentioned above, tuning is the most important thing for street driving. All this dyno testing is at WOT....even in the 3500 RPM range. What it makes at WOT at low RPM range is of little value to what you feel cruising around on the street at light throttle. You're not even getting close to having those cylinder "full" at part throttle. So timing and carb work will get you the part throttle cruise feel and response we all like. The heads on my engine are *huge* compared to what many folks would use...but I've thrown the keys to lots of folks to drive it and not once have I heard anyone say it was lazy feeling. They usually had a hard time not spinning the tires!

 

Only a sicko like you!!

JIM

 

I was beginning to think no one would catch me on this. Ain't nothing getting by you!

Steve

 

Heres my two cents...

When I bought my car(68 L36) it had hooker 1 7/8" long tubes and some"turbo style" mufflers on it, I decided to go down the NCRS road(has since top-flighted) so I installed the factory manifolds and a Gardner full exhaust.

I can tell you from direct experience the headers make a huge difference on the butt-dyno. With the headers, it had alot more top end and would easily break the tires loose halfway though first and sometimes second gear while now it struggles to do it in first. I don't know whether it mostly due to the mufflers or the headers(I suspect it the headers) but I can say with confidence there is a big difference.

 

To the best of my knowledge, on the research I have done regarding this.... It seems that most of the OEM manufacturers, tested engines with headers, no accessories, no air cleaner assemblies... These were the "GROSS" engine ratings. In 71', they started using the "NET" rating system which added some of the basic accessories, a different correction factor for weather condition variations, but still used headers.

So basically whatever the factory HP rating of an engine was, you can subtract the loss for manifolds...

Basically, all of the numbers/ratings were "funny" numbers anyway... Some over rated, some under rated, most of them were BS.... Judging by the MPH that most of these cars in the muscle car era trapped in the 1/4 mile, I bet most ratings were very optimistic...

 

One example that is well known....the 302 CID for a 67-69 Camaro. Rated at 290HP...what a JOKE!. YES it made 290 HP...but WHERE they took that reading when it was being tested was not the REALITY of what that small block actually can do.

DUB

 

This post has really been interesting, I was getting ready to install my stock exhaust on my 66 w/454, but with the results and comments it seems headers is the way to go.

In the thread I see "long tube" headers, and I always thought they would drag with the collector being low. I did consider the Sanderson shorty "block hugger" header, as it seems to keep the collector out of the way of being beat up on these Oklahoma roads.

Would it matter if they are shorty or long tube to see improved flow?

 

Shorty headers don't work. The primary tube length is to short and so is the collector. It is a bit of a challenge to find and under chassis header for the BBC vette that does not give clearance problems. The length and width of BBC headers also make it difficult to go through the factory cross member holes.

 

In 1983 when we put the Blackjack headers on the 72 the improvement was noticeble in normal driving.

Noticeable at 2500 rpm and especially so passing another car 3000 to 4000rpm.

With stock manifolds the average gas mileage was 14 and a half miles a gallon to 15 miles a gallon. with the headers average gas mileage was 15 to 15.5 miles per gallon. The stock manifolds best highway gas mileage had been 17 mpg. With headers the best highway gas mileage was 19mpg.

It was easy to consistantly get 17 to 17.5 mpg highway after headers.

A nice improvement in overall in mpg. Yes the carb was adjusted correctly with manifolds and retuned with headers.

 

My manifold:
http://www.airflowresearch.com/index.php?cPath=79_81
SBC Titon Manifolds

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15 plus horsepower & torque more than competing manifolds!
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Cast-in nitrous bosses.
Modular design. Interchangeable Runners
Dual distributor hold-downs.
Reduce carburetor vibration 5%
Rubber Viton Gaskets - No Leaks.
Includes distributor clamp and 12pt 3/8" bolts and washers.
Manifold Installation Instructions

 

You might need to ask yourself a question.

I am all for an improvements...but in most cases there is a trade off. If you are just normally driving this car and do not expect to be driving at light speeds...then put the factory system back on due to you having concerns about road conditions....

If you want to get MORE power...regardless of what it takes...as you see the headers will do...then this is where you have to determine what it will take so you can drive your car and not have to worry.

I am well aware about road issues...because we have them here in Charlotte. And I have had numerous people want me to lower their Corvette....or install a lower aftermarket front air dam even if the Corvette is still at stock ride height. I HIGHLY advise them against it in both scenarios. WHY??? Because as odd as it seems...they will be back in the shop with damage. Mainly because ...the bad road conditions come up on them so fast...they can not react fast enough and WHAM.....busted air dam...or mangled header exhaust flange or skid bar being busted to all get out.

I agree ...block hugger headers are nothing more than what GM began installing on the 1980+ small block Corvettes. Basically tubed short headers from the factory. If these are used...I am sure it is questionable that they would preform as what you have seen on the results from others.

DUB

 

I still want to see chassis dyno tests comparing cast iron manifolds versus long tube headers and using stock mufflers. I'd be willing to bet the gain would be too small to offset the expense and increased interior heat. For drag or track use I can certainly see an advantage to using long tube headers but not for steady point A to point B street use where revs rarely exceed 3500 rpm.

 

When the 1973 oil embargo hit us gasoline because a scarce commodity and the big three automobile manufacturers scrambled to increase the fuel mileage of our vehicles. If long tube headers really provided the increased torque and fuel economy the header manufactures CLAIM they do logic tells me the big three would have put them onto every one of their new vehicles from 1973 on. But to my knowledge no car has ever left the factories with long tube headers. Why?

 

I posted a dyno chart of that exact scenario.

I saw an interview with the dev team for the 2012-2013 Boss 302 Mustang. They said the only area that was left for significant improvement were the exhaust manifolds. They had looked into headers, but it was not possible due to the way the assembly line works. The engine + trans is fully assembled, and then goes into the car from the bottom. Headers wouldn't allow this and would have to be installed after the engine was in the car. Due to this, headers got nixed by management.

 

I have LT:s on my `72 454.
I got 17mpg on my stock engine, remains to see what i get with the new engine..(468 and cam ).....
I had a Mustang `07 before the Vette, with LT:s and it it was a nice improvment both in power and mpg!