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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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I really want to buy something off the shelf that works.
Tubes are what make headers work.
Something to do with flow and scavenging.


Both manifold examples you provide look cool, but would be a compromise in exchange for reduced performance. These styles are typically used in vintage hotrods where a certain look may be preferred, and squeezing out maximum torque and horsepower just isn't as important. Of course these near stock styles are also used where there are fitment issues.

The Hedman 68600 are a GREAT fit in the Astro and offer improved performance, sound, horsepower, and even improved fuel economy. They are extremely popular and do quite well. I currently have them on my 92. Full length tubes on the other hand, are even better (for performance), and can be easily fit (in the RWD) by moving the passenger side motor mount forward, rather than using the commonly used adapter mount.

AWD however, apparently has issues. Lifting the engine (with lifted vans) resolves the oil pan issue, but unclear if it resolves the header fitment issue. I'll be tackling this one soon in my near future. In my world, I couldn't DREAM of putting in a performance V8, then finishing it off with near stock exhaust.
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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It's not so much the fact that it is tubing as it is the consistency of the inside profile and the gentleness of the bends compared to a cast iron manifold.
This is incorrect.. you apparently do not understand how "tubes" work with regard to flow and savenging. It not just about being cast or bends.. although smooth flow is essential. The "siphoning effect" of EACH tube creates the scavenging effect, litterally drawing out (or vacuuming) "spent exhaust" from the individual cylinders, increasing efficiency. This flow also creates motion... that not only affects exhaust, but with bigger cams actually helps draw in the intake stroke, depending on cam overlap. I have simplified my reponse, but there's quite a bit to header technology beside not being cast. The worst thing that happens with stock manifolds is the exhaust pulse from one cylinder is pushed directly into the one next to it. Even the shortest tubes from each cylinder is a BIG improvement.

But your point about whether the performace improvements are worth what you consider issues with headers is valid. Top HP numbers aren't as important as many people think they are in daily driven street machines that never see full throttle excessive rpms.

And you point about stock type manifolds not leaking like headers do is also valid. Reliablity over small performance gains is certainly a consideration.

I have ZERO issues with my headers. No leaks, but I properly installed them and retorqued them at some point later. They don't leak (maybe it's because I live in South Florida and they never get really cold). Like I said... I would NEVER dream of putting stock exhaust on a nice V8 upgrade (but that's me).. even if it's only mild performance. There are fuel-economy improvements too. But it's understood that the torque differences will be mostly neglible (under normal conditions) and you already have a BIG power gain with the V8 upgrade... more than enough.

But let me also clarify.. the manifold designs you posted are certainly an improvement over stock.

Regarding my exhaust routing... even with V8 upgrades many people still route the two sides together and down one side (like stock). Performance mufflers and proper sized pipes will yield sufficient results. But I'm old school... you run headers into true dual exhaust. Even still, both pipes and mufflers "can" still be routed on the passenger side with creative design, and come out great.

I cheated with mine and just pointed my driver side exhaust around the outside of the tank, with short turn exiting just before the rear tire. It was meant to be only temporary, but I was SO pleased with it, I've kept it that way since (it's been a few years now)

Not pretty.. but simple & functional (and good enough for me)
Tire Wheel Vehicle Automotive lighting Automotive tire

Here's an example of someone who did it nicely!
Wheel Tire Automotive tire Vehicle Tread
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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You seem to know things, yet with all this information, and you still missed the point.
You've even repeated some of what I've already said.
Yes... scavenging AND velocity... both vital and important, and why headers work.
I merely attempted to keep my reply relatively simple enough... without going into the whole science. I'm not really interested in a debate either.
If you don't like headers, then don't use them.

But we agree on downstream. Do what works for you.

PS: No need for a 1000 word reply.. it won't change the laws of physics.
Cheers!
 
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