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Tech Editor's DeskProjects, papers, writings, thoughts, musings of our technical editor Joe Padavano. To begin with, he will be making threads and can approve posts to it if he wishes. This can be changed in the future if it does not work out well.
Frequent readers will know that I am not a fan of shorty headers since they pretty much ignore the whole point of headers, which is tuning the tube length to help breathing and thus increase engine output. Here's an interesting article that confirms my beliefs. Yeah, it's ONE test with ONE engine with ONE example of each type, so no, not exactly a statistically valid sample size, but the differences in HP and torque at all RPM levels should make you think twice about putting up with the nuisance factor of long tube headers.
It would be interesting to see stock manifolds compared also.
From the article:
Originally Posted by Hot Rod
After running the stock manifolds, it was time to install the shorty headers. We made quick work of that task and were somewhat surprised that the shorty headers offered no change in the power output over the stock manifolds.
After running the stock manifolds, it was time to install the shorty headers. We made quick work of that task and were somewhat surprised that the shorty headers offered no change in the power output over the stock manifolds.
That didn't surprise me at all. And now you know why I was so vociferous about those ridiculous tubular BBO manifolds from Thornton. Talk about a complete waste of money.
The stock manifold used in that article is a factory "tubular style" manifold, if you look at the photos. I'm not surprised the aftermarket shorty header was the same as the factory tubular manifold.
I am surprised at the amount of power difference in the mid-RPM range. I thought it would be mostly at peak RPM.
A mild 400-450 hp SBO or BBO comparing factory cast manifolds, to shorty headers (Hedman or Sanderson), to full length would be nice to see.
There is a difference for sure but shorties gain over factory log manifolds. There was an article done in Mopar Muscle magazine using a 300 hp 360 Magnum crate motor. They used truck/van manifolds, restrictive like SBO manifolds. Then 360 manifolds 11 hp, 340 hp manifolds 13 hp, short headers 20 hp and stepped full length 1 5/8 to 1 3/4" full length headers 28 hp. Torque close to hp gained. If you are comparing 5L HO Ford tubular manifolds, which are basically short headers to sucky SBO manifolds, about the same as the Mopar truck/van manifold, necked down to fit under the van dog house, you are high as a kite, not a like at all.
Last edited by olds 307 and 403; July 4th, 2018 at 02:09 PM.
There is a difference for sure but shorties gain over factory log manifolds.
I would be willing to bet that the difference among W/Z manifolds, the Thornton tubular manifolds, and shorty headers is within experimental tolerance of being nothing. The W/Z manifolds ARE internally divided. Yeah, that doesn't apply to an SBO, but I only have big block cars...
I run the SBO only and I think there will be some gain with Thornton shorty headers, assuming a good 2.5" exhaust behind it. The BBO Thornton tubular manifolds are much more questionable in design and gains.
Thread is a little dated but , here's my short header install story .
*** Dyno/track #'s aside*** ***BBO's aside as well *** for obvious reasons. Nobody I know, dyno's performance addition parts to stock engine internals.
From what I hear ,
Most people say that you can't 'feel' any difference with a 5-15 hp mod on a lets say 350 hp built engines after installing headers.
I think that is the what kills the thought about going with Short headers. Actually, even long tube headers for that matter .
Actually.... Most guys that have had headaches with long tubes , still feel , manifolds are the way to go over any header application. Most simply didn't feel any noticeable HP gain in headers after adding them to an already driven 350HP rebuild.
That being said,
I'n my opinion, their are noticable gains with short headers over factory manifolds on a stock SBO with a 2" - 2- 1/4 max dia true dual exhaust.
This would be more aimed for the stock guys that are just looking for a little bit more, little at a time.
I already know that long tubes are better if matched to your cam. My comment is about the exhaust port dividers and wether it is good to have the gap like the factory head or the separator like Edelbrock. Maybe it only matters above 6000 rpm? Even if the header is separated, a factory head will allow some flow between the ports. I've seen people weld it shut and the aftermarket heads also have a separator. Why is it better to have the separator? Doesn't the added volume of the gap increase flow and improve scavenging?
I see you've been busy resurrecting a lot of old threads...
To this question (that you've asked in several resurrected threads), the divider causes flow disruption. Any disruption hurts flow. When the exhaust pulse hits the opening, it causes a reflection that runs back into the port, hurting flow. The low center divider is irrelevant if the ports just dump into an open log exhaust manifold. If you are going through the trouble to use divided manifolds or headers, the center divider wants to be welded and machined. This has been shown to be an improvement on Olds heads time and time again.
[QUOTE=joe_padavano;1159755]I see you've been busy resurrecting a lot of old threads...
To this question (that you've asked in several resurrected threads), the divider causes flow disruption. Any disruption hurts flow. When the exhaust pulse hits the opening, it causes a reflection that runs back into the port, hurting flow. The low center divider is irrelevant if the ports just dump into an open log exhaust manifold. If you are going through the trouble to use divided manifolds or headers, the center divider wants to be welded and machined. This has been shown to be an improvement on Olds heads time and time again.[/
If i was Thornton and was selling the shorty manifolds i would dyno test the original logs then dyno test the shorty's to see what the gain if any. I asked him and he claims he as not dyno tested them, perhaps their is little or no gain which doesn't incentivize many to spend their hard earned $500.00 for them. That being said Bill Trovato told me the any headers will be better than the stock manifolds. Until some one dyno test the originals against Thornton shorty's we wont know.
If i was Thornton and was selling the shorty manifolds i would dyno test the original logs then dyno test the shorty's to see what the gain if any.
Yeah, the silence is deafening...
I put shortie headers in the same bucket as Thumper Cams. All the gasket sealing problems of real headers with none of the pesky extra HP.
I think that Mark's recent test of long tube headers vs W/Z manifolds speaks volumes. The W/Zs are internally divided and are nowhere near as bad as open log manifolds. Despite that, the long tubes still picked up noticeable HP and torque at the low end. Personally I'd use W/Z manifolds before shorties. Similar performance, without the header problems many people complain about.
Of course, I use long tube headers in most places anyway.
July 4th, 2018, 06:57 AM
