Power increase with aftermarket headers?

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hux340

hux340

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Hi All,
My previous post I was asking for a good quality set of headers for my 71 340 Demon. Thanks for everyone's comments, really appreciated.
I've decided to go Doug's D453's long tube ceramic coated ones. I can only get them from the states, (live in Aus). They're going to cost me nearly $1,000 aus landed. Man I hate our $ to you guys. End of the day I only want the best for my car as I plan only on keeping it for a long time. I've had my Demon for nearly 3 years now & have kept the original cast iron headers on as I'm a fan for originality, but seeing how I don't go to a lot of car shows where I pop the bonnet up I've decided to put the doug's on as I wasn't to free up some hsp.
My question is if it's not to hard to answer is approx. how much hsp will I gain by doing this?
Cheers,
Glenn.

Dodge at Norieal Park July 15 007.JPG
 
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On a stock engine probably 15-20 hp.
Where headers shine is with cams with moderate to large overlap ones you'd use to get 350 plus hp. Under that there helpful but not mandatory.

Good thing about headers is they give a boost of power across the entire powerband.
 
No disrespect 273, but that sux. 6 weeks from now, here in my home town in Wodonga, we have, "Chryslers on the Murray", the biggest Mopar meet in the southern hemisphere here in Aus. Do your self a favour mate, get a cheap flight, cruise on over & I'll play host & show ya what it's all about.
Cheers,
Glenn.
 
You can't get a custom set of headers built there for $1000 and avoid all of the hassles of shipping? My last set was $900 and they are BEAUTIFUL and fit perfectly because they were made for my car only. That price did not include coating!
 
I remember the 10 - 15 number, but it was %, not h/p. What, you expect to get 15 hp from a /6 AND 10 h/p on a hemi.. Back in the day of 3/4 race cams, and 4:11 gears, the Rod rags and articles I read, quarter mile, and dyno test showed more than 15 h/p on most every engine with open headers, and 10% gains with closed headers.. IIRC.. 15 h/p on a hemi, come-on. Most articles agreed, a 4 bbl and headers were the most cost effective h/p gains you could make, without no2.
 
It's not just about the power.
The power peak with a stock or mild 340, and an automatic with 3.23s, may not occur until 48mph in first gear. And it may continue to about 50/53 mph.
But the headers also give a boost in torque through-out the rpm range, at rpms you most often drive.And if you also install a X-over, you can boost the very low rpm s as well.
But as to performance; the next bigger rear-end will make the car quicker and more responsive,and overall,IMO a more fun car, than just the headers. And a Hi-stall, can really launch you outta the gate.

You gotta look at it in terms of road power.
Headers increase road power at a rising rate as a function of rpm.They start off adding very little at low-rpm rising to a peak as the engine rpm builds.
Gears increase road power instantly, at a constant rate,and independent of speed and rpm.
The hi-stall TC, increases road hp right on the starting line, the rate declining as it reaches equilibrium, at some higher rpm when torque multiplication has decreased to a minimum.

So... where do you need a performance increase?

If you can already spin the tires all thru first gear, and rarely have opportunity to travel at speeds over 65 mph, and are rarely at WOT when you do.........then
the headers would be mostly for looks. Or sound
the gears would kill your fuel-mileage, and
the TC would just spin the tires with less throttle.
 
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it's a 4 speed AJ.
stock cam?..rear tire size?
if you have tall 275 / 28" rear tires i would trade up to 3.55 for instant performance gain.
Is 15 hp at mid to upper rpm worth the $1000?
I'm like you...i love the original look and wouldn't add headers.
 
ir3333 said:
it's a 4 speed AJ.
stock cam?..rear tire size?
if you have tall 275 / 28" rear tires i would trade up to 3.55 for instant performance gain.
Is 15 hp at mid to upper rpm worth the $1000?
I'm like you...i love the original look and wouldn't add headers.
Click to expand...
Oh I missed that in post #1,lol
 
Think of you engine as a 4 inch air pump. With a 2 bbl carb, and single exhaust, your pump has a 2 inch inlet, and 2 in. outlet. Add a 4 bbl, dual exhaust, now have 3 in inlet, 3 in outlet. Add cam, heads, porting, hi-rise, now have a 4 in. inlet, and still have 3 inch outlet. Add pistons, stroke it, now 5 inch pump with 3 inch outlet.. hope it helps
 
I guess you could gain 10-15 but thats not worth hearing that tinny tin tin sound, i took the hi po manifolds to my engine builder when he was building my 340 and he was impressed with how well they looked, he was surprised how well they flow for being a stock manifold. we also cleaned up some of the flashing off the inside of the manifolds prior to giving them to the engine builder
 
It's more like 8 to 16..............percent
8% with a low overlap cam, 16% with a hi overlap cam, as compared to lo-po logs.
On a 300hp 360, you could expect 24/30hp .But on a 350hp you might expect 40hp; and on a 375 maybe 50; and on a 400, maybe the full 16%, or 60hp. 340 logs are gonna post lower numbers on account of well , everybody says they're almost as good as headers,lol.
If you remember the tin-tinny sound, you're probably remembering the 1-year cheepie headers of the 60s and 70s.
Quality headers today are PDQ in comparison. You can hardly tell my car has TTIs.
 
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