NO ONE IS ARGUING THAT HEADERS ARENT A GOOD UPGRADE...The OP asked if they are worth it for his motor. He has 250 hp when it was new and is currently running 2.5 manifolds and 2.5 inch pipes. So the answer is no, its not worth the money for little to no gain over what he has going on now....He isnt going to go from 250 hp to 280 or 300 hp with headers...if they were that great you would see them advertised as the single biggest bolt on HP gain you can get which isnt true

 

The Nick's Garage test was a good watch. Those Max Wedge "Manifolds" are essentially CAST shorty headers, though. I'd be great if all headers were that good. (I vaguely remember Hooker Headers came out with a very shorty header-like set of cast manifolds for LS engines, too.)

Adam

 

That is a VERY strange dyno test...
A 327 turned into a 383 with stock camel hump heads and a stock intake, and a NOT stock hyd roller cam that's had a bit of extra exhaust duration, which should have HELPED out the restrictive manifolds.
Those dyno headers' primary tubes in the video look HUGE, too. (Can't find the primary ID anywhere, though.)
--If you put too big of headers on an engine, you lose low-RPM power from exhaust velocity slowing down but then you don't gain any thing up top. (I can't see the dyno chart below 3,100 RPM) but given that 3,100 RPM is that engine's torque peak and it's also where the dynograph starts, we can't even see what happens below the torque peak on that dyno graph, either.

The 1964 Impala with the high perf 327 engine made peak torque at 3,200 RPM; I'd expect it to go down if they just bolted the heads and intake onto the now 383 cubic inches. Maybe the significantly bigger than stock roller cam with more exhaust duration helped it carry out to 3,200 RPM still, but I'd SO love to see that dyno chart another 1,000 RPM lower...

That engine made peak torque at 3,100 or 3,200 RPM and dropped from there.
That engine is massively air intake limited, not exhaust limited like the SMOG-era 350s have been proven to be.
(I was shocked at how similar the flow of the camel humps and 882 / 624s are, though.)

It's a pretty intensely weird test.

If I had to choose between whether that 327 turned into a 383 but with a modern roller cam added or David Vizard's test on a 1979 Z28 350 better represents a SMOG ERA 350 in a Corvette, I'd definitely choose the Camaro 350. -You don't agree?


Adam

 

I'm slow sometimes... The OP has a 74 Corvette, which was the last year without cats, right?
If, so I tend to agree that the Vizard 79 Camaro test doesn't apply and he won't see that kind of benefit. (I was thinking of later C3s with garage pellet cats.)

The wave tuning benefits are still real, but that particular Vizard test was definitely testing manifolds vs. headers on an exhaust with a lot of back pressure...
I do not have a good dyno test squirrelled away that looks like a pre-catalytic converter SBC like the OP's engine.

Adam

 

If you have a 250 HP motor, at what power gain is it "good enough" to invest in headers? I'll agree if nothing else is done to the motor then the gain is gong to be minimal. But it could net you 15blft of torque a @ 2500 RPM that is a 6% gain. So is it worth it to him? I don't know.
Like I said I would do it. But with the thought in mind that I may make other changes in the future. I think you will feel the difference at the street level performance below peak torque due to scavenging vs what is there now.
It will have to re-tuned the accommodate the flow differences. If a guy can't tune to maximize the effort then ya probably skip it.
On my 77 there was a huge difference from stock installation vs the side pipe installation. But it was in contrast to a stock exhaust installation, so one would expect a significant difference.

 

I’m still here taking it all in! The feedback and opinion/advise has been awesome - I have learned a lot! This is my only Vette - original owner. I took the AIR system off in ‘75. Added the 2.5” manifolds in ‘85 (stock GM). 4spd, 3.55. HEI last year. 85,000 miles - although 20,000 since ‘79. Garage
kept. Thought about side pipes as well but thought they might be too loud with no benefit.

 

If you were thinking of factory S.E. you thought right. The exhaust path of those is actually only 1 5/8” and you would loose power but make a lot of noise.

 

Could you feel the difference when you added the 2.5" manifolds?

 

Sounds like a very nice car.
If it was mine, I would do the ceramic coated headers, a nice 2.5 dual exhaust system, add an aftermarket intake and air cleaner, then send your QJet to Lars and let him perform his magic.
You will probably get a little seat of the pants performance gain and depending on the mufflers you choose a nice rumble while cruising and at stop lights.

 

Yes, headers are worth while for your L82, in my opinion & experience. Lays good ground work for getting the most out of additional mod's later.

In 1983, my 72 Corvette (L46?) picked up ~2-3 mph with set of 1 5/8 long tube headers vs stock manifolds in the stretch of highway we did our standing start testing on. Did the test a dozen times and was consistently ~2-3 mph faster. Motor had been recently rebuild, had a mild compression bump from 8.5 to 9, stock cam had been reground to a slightly more aggressive spec, stock intake manifold and open element air filter.

Use high quality exhaust manifold gaskets & make sure the header flange face is flat. That will help avoid leaks etc.

 

This is exactly what the OP SHOULD do if he wanted some power...make the motor need the headers....its a smarter way to spend the money. Li et the motor tell you what you need.

For the OP. The stock 69 side exhaust wont add power but it looks really cool. If you go to the chrome 4 into1 Hooker style the can be quieted bown with a baffle and Again it looks awesome....just decide which way you want to go....more expensive power and be silly and have fun or boulevard cruiser looking cool and being cool. Both are fun choices and you can do both. Just plan a budget

 

Yes in the freer flow of the exhaust and some added power? Nothing measured.