1Restorick

My answer is that you will lose some horsepower just from going from a long tube header to exhaust manifolds. When I was a little younger, I bolted Hedman Headers on my 72 442 with the base 455 and it really woke up the low end and midrange power. That car would just boil the rubber off of the back tires with ease. It has been published that good headers on an Oldsmobile big block are worth 25 Hp or more. With your performance cam, they are even more important.

Rick

joe_padavano

It's been proven time and again. The only saving grace is that the W/Z manifolds have individual runners and are slightly better than the common open log manifolds.

Koda

I meant to say on the pipe only. Headers to manifolds should be as described above.

Koda

Now is about when someone mentions those shorty headers.

Fun71

I answered that question in post #22. Do you not believe Mark's dyno results, or is there another reason why you disregarded that answer?

gs72

Then how do you explain this???

72455

I couldn't find the results...do you have a link?

joe_padavano

Overcompensating?

joe_padavano

I was waiting for it.

Vintage Chief

joe_padavano

This is long tube vs shortie headers. About 20 HP and 20 ft-lbs difference. Expect manifolds to be even worse.

https://classicoldsmobile.com/forums...eaders-177221/

72455

Thanks Joe...so would the "butt dyno" notice that difference?

olds 307 and 403

Also if you want fully 2.5" exhaust with the W/Z or Thornton shorties, you need custom. All the down pipes are 2 1/4" at the manifolds then go to 2 1/2". You may as well go factory replacement. A truly fair comparison would be Hooker Comp 1 5/8" primary tube headers and 2.25" pipes. Mark was copying the customer current exhaust and also to match his exhaust upgrade plans, which is understandable in that test. Everything is a compromise, one way or another. Weather fit, power or periodic maintenance, depending on the choice. Even the thick flange shorties need occasionally tightened, manifolds, not really.

BangScreech4-4-2

Nice Moody Blues sub-reference.

CANADIANOLDS

going to a factory style exhaust will really hurt your power over what you have now.

72455

We're gonna find out...cuz I'm all in on the swap.

CANADIANOLDS

then I don’t think you care.

72455

I do, but I had to make a decision...either keep listening to the header leak and deal with the hassle of trying to work on it with headers, or make my life easier. I chose the latter.

Fun71

What is the hassle? My ‘71 has headers since 1990 and my ‘70 before that since 1982. I never had header leaks or hassles working on things.

Koda

I mean, I've got some sort of ugga duggah cam in my H/O, and it has factory exhaust, and it's enough fun on the streets.

BangScreech4-4-2

That's a good point. Lots of people (me, for instance) run engines with bigger than factory cams through factory manifolds. May be leaving a little bit of horsepower on the table, but what the hell, those W/Z's flow well enough.

android 211

The '70 Chevelle SS 454 LS-6 had 2" tailpipes factory. But it also had log manifolds. With that 224/234 cam I would run 2 1/2" pipes back to the mufflers even if you had to neck down the head pipe to fit the W&Z manifolds. After the mufflers you should run 2 1/4" tailpipes. Finally you'll have to neck down the exit to bolt on the trumpets. Does anyone make a 2 1/4" chrome trumpet?

BangScreech4-4-2

I was able to get the muffler shop to hog out a pair of Year One repops to fit over 2.25" tailpipes.

Did the LS-6 really have 2" tailpipes? Color me amazed!

joe_padavano

Before mandrel-bent A-body tailpipes were readily available, I would use the 2.25" pre-bent pipes from a 1970 GTO. With a little work, they line up with the bumper cutouts. The OEM trumpets will slide into a 2.25" pipe.