Every swap from manifolds to headers has been more power for me too.

The last pump gas 472 C.I. hemi motor I dyno tested in SO CA on a DTS engine dyno at Vrbancic Bros. in Ontario, CA did a little bit better, 625 HP @ 6200 RPM) than theirs did

I've never run manifolds on my car.

yeah numbers seem a little disappointing .

Tex

The dyno testing I did when I was developing my fast motors does not agree with there's whatsoever. 612 versus 588 horse, and 795 vs 762 horsepower. Nicks Hemi seemed to stumbled at the top end of the pull with the manifolds. I wonder if something was going away, or if the jetting was off?

Nice numbers for a semi mild small block stroker, but a 472 hemi?

Watch this vid and to me it tells so so much.

https://www.youtube.com/watch?v=2SbInV5RVM8

He said they had problems with that engine that cut down the power. 80 lbs of spring pressure on the seat.

How? Cam selection? Better suited to the manifolds?

What does it tell you? J.Rob

I watched one of his vids with a G2 that had a misfire and rough idle for a few seconds after a pull. They could find nothing wrong and deduced it was a pushrod problem?

I called him the next day and told him if he looked at his VE% numbers it would read abnormally high like in the +hundreds of percents maybe 700-800%.

I pretty much guarantee he had an exhaust valve seizing open. He didn't believe me I don't think. Swore the pushrods fixed it. J.Rob

I spoke with that guy once. There was this "You haven't heard of me? But I'm famous!" attitude that totally put me off.

Take the same motor, test it with two different cams, and try the headers and manifolds with both cams.
One cam, manifold friendly, one cam more of a typical mid-level bracket race cam that needs headers........ and you’re going to see a big difference in the spread in power output between the manifolds vs headers with the two different cams.

Trying to come up with a blanket figure to say headers are worth “xx” power over manifolds is kinda pointless.
It’s absolutely one of those “it depends” things.

Someone here recently tested a 505 with TF240 heads and observed a 90hp difference.

A headers vs. manifolds dyno test on a performance engine is a waste of time. The engine is either tuned for headers or it is tuned for manifolds and just changing the exhaust without changing the tune gives you bogus numbers.

Headers vs. manifolds is one of the "forks in the road" that you take early in the engine build process.

You guys are dead on, as usual. In my F.A.S.T. builds it was known that the class rules required factory intake and exhaust manifolds, and a 2.5" exhaust system to the rear bumper. Cam profiles were selected accordingly. The same motor with a radically different cam would have different results in a manifold vs header comparison.

Bringing this back from the dead.

The 612 vs 588 horsepower, was that on as-cast or ported manifolds? Trying to decide between headers and porting my manifolds.

Thanks!

When I was deciding on the final pieces for my 540 Hemi, I spoke to Indy about the exhaust. I was considering the 2 1/8 rather than the 2 1/4 TTIs. But they told me that the Hemis did not like any exhaust restrictions. So I have the 2 1/4 tubes and 3" straight thru exhaust with electric cut-outs. I have not experimented with the exhaust to know what works or what doesn't. Just passing along some advice I got from someone that probably knows what they are talking about.

Coming up next,,,will a rochester 1 barrel out perform a pair of dominators..Tune in next week to see if 78 series polyglass will out 60 hooiser 34.5 17 16

With out a doubt it’s not everyone’s cup of tea. But to some, me included, like a stock looking muscle car that performs better than expected. There were a couple of thing here that made this an awful comparison. One there was no tuning done after the switch to manifolds. The jetting will not be the same for both. The other thing is look at the exhaust on both set up. It’s clear that it was pretty much open headers on the Hemi but was run through 2.5 inch exhaust pipes on the manifolds. I’m not saying the manifolds will perform with the headers but the playing field was definitely tilted in this comparison.

^ Yes, obviously the headers will outperform the manifolds, that in itself is not the question but to what degree is.

Right now I have manifolds that fit perfectly and bolt up to my exhaust with no rattles/leaks/problems so for those reasons it's tempting to re-use them with some port work.

Nothing crazy, all iron 426.

Would I leave 50hp on the table? No, but if the 24hp example above was with untouched manifolds and that differential could be brought closer to 20 with port work or even welding I would certainly consider that option.