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Your picture doesn't work. Are you using photobucket?
If they are the headers I looked at from Thornton, they look little better than stock manifolds. Any time exhaust gasses have to make a 90* turn, inefficiency happens.
Despite their ability to allow laminar exhaust flow, I wonder what the price is? One of the threads Joe mentioned linked to an old Ebay auction which sold them for $259.
That is $10 more than the W/Z Thornton's reproduction manifolds! Plus, you can get the dual exhaust driver's side manifold from Thronton's for your B/C body for only $180.
Despite their ability to allow laminar exhaust flow,
I have a hard time seeing how any exhaust flow will be laminar. In any case, the W/Z manifolds are internally divided for a substantial distance down the casting. These are not. Also, they do not interchange with the 65-70 full size manifolds and will not fit that chassis.
FWIW, I emailed about a month ago asking for dyno numbers and the response was that they have none. These "headers" have been on the market for a while now, I would have thought they would have been tested by now.
There is a reason shorty headers don't help much if any with HP as compared to stock manifolds. Long tube headers have the ability to make more HP over shorty headers or stock manifolds for a few reasons. One of them is understanding how the gas that is flowing through a single tube changes characteristics the longer the tube is. The longer the tube the higher the gas velocity is near the edge of the tube as you move away from the source. Near the source the velocity is about the same near the middle of the tube as it is near edge of the tube, the further from the source the faster it is at the edge and the slower it is in the middle. If the tube is long enough air in the middle of the tube is moving towards the source helping push the gas out of the tube, while the gas nearest the tube (edge) is moving really fast; helping extract gases out of the tube. So the long tube headers help "pull" the gases from the source. This in turn helps pull fuel into the chamber for the next cycle to fire. This will never happen on shorty headers or stock manifolds.
Why do people say shorty headers do nothing? There have been engine and chassis Dyno tests that prove they do on multiple engine designs. Do they make as much as full length headers, no, usually 5 to 10 hp/tq less but 15 to 20 more than manifolds and go in much easier. Pipe sizing and piping after the headers is critical. Here is a good example. I own a Dodge Dakota that I put a 5.9 Magnum in place of the 3.9. The Magnum is a good design except in 2 places. One is the thin, crack prone heads an the other is the steel plenum plate on the aluminum barrel intake. My heads cracked in a bad way and pressurized the coolant, had to tow it home. I bought the Magnum EQ heads with bronze guides, sticking valves on other replacement heads. Still only $1000 a pair an they flow what Gearman1969 fully ported #6 heads flow out of box and I got the thick aluminum plate with right length bolts. The plenum gasket had already starting moving after a few miles. Dodge did something curious in 1994 with the Magnum motor line, they shrunk the manifolds and Y pipe down from 2.25" down to 2". They lost 10hp but gained 10 to 15 torque. I like how Dodge realized that torque was more important. I am picking up shorty headers and a JBA Y pipe. JBA was smart, they made a 2" stainless Y pipe but made it with mandrel bends, still keep velocity but gain flow, I am getting both in spring. If GM realized that torque was king in a truck, they would have put something else in their trucks the last 40 years, the sbc and LS severely lacked in low end torque. Dumb, especially considering every other GM motor made more torque. The Gen 5 V8 is much less doggy down low and impressive up top, finally the best of both worlds.
Last edited by olds 307 and 403; Feb 8, 2018 at 06:39 AM.
It is not possible to make blanket statements one way or the other. Any benefits depend on 1) how restrictive the stock manifolds were, 2) the exact design and flow characteristics of the shorty headers, 3) the details of the rest of the exhaust system, and 4) the details of the engine build.
Comparing open manifolds to open shorty and full length headers on a dyno is meaningless, because you aren't running them that way in the car. Comparing stock manifolds connected to a restrictive factory exhaust system to shorty headers with a new large diameter free flow exhaust system is meaningless. Unfortunately, scientific detailed back-to-back comparisons are extremely difficult to get because they are time consuming and expensive to perform. "Butt dyno" comparisons are worse than worthless.
The only data I find relevant are back-to-back drag strip runs, with multiple runs, corrected for weather. This will tell you the real benefits for a specific vehicle and engine combo. Anything else should be taken with a grain of salt.
Also, can we please stop calling these Thornton tubular manifolds "shorty headers"?
Mac, you see by the pics that the Hedman hang 2" lower than the Sanderson headers and are 1 3/4" vs 1 5/8" for the Sanderson headers. I know one guy is in the 11's with Hedman shorties. Pretty sure the gains on the 3.5 JBA headers were probably added after a cat back or RT dual exhaust set up. Remember they are one of the many shorty headers with stock size outlets. They still gain 7 to 9 RWHP, if I could afford a new GT payment every month for 5 years so I wouldn't be messing with my wife's car, it would be the first mod along with a throttle body on the 3.5 with STOCK exhaust, I love how quiet the Challenger is.
Mac, you see by the pics that the Hedman hang 2" lower than the Sanderson headers and are 1 3/4" vs 1 5/8" for the Sanderson headers. I know one guy is in the 11's with Hedman shorties. Pretty sure the gains on the 3.5 JBA headers were probably added after a cat back or RT dual exhaust set up. Remember they are one of the many shorty headers with stock size outlets. They still gain 7 to 9 RWHP, if I could afford a new GT payment every month for 5 years so I wouldn't be messing with my wife's car, it would be the first mod along with a throttle body on the 3.5 with STOCK exhaust, I love how quiet the Challenger is.
You can also see they hang lower by looking at my exhaust, where it turns from the headers. It's pretty scratched up, lol. I'm hoping the hedman full length headers I got for the BB hang at least a little higher than these things.
Macadoo - Any shots under the car to show how low they hang?
Id be interested to see - tried to look from your "pulling the motor" topic, but most pics seem to have disappeared, thanks to photobucket.. Since im pondering between Hedman and Sanderson shorties for my car, im not interested to fudge longtubes there since apparently there isnt any which would fit without major hassle.
Difficult t get the camera at the perfect angle but it looks to me like the top of the horizontal run of the pipe is even with the bottom of the oil pan. So, a pipe-thickness lower than the pan, thereabouts.
The headers exit a little above the bottom of the pan but add the reducer and the bend, things get pretty low.
And yeah, someone should start a class action suit against photobucket to get our photos grandfathered-in. They've rendered DIY threads, all over the internet, useless.
Difficult t get the camera at the perfect angle but it looks to me like the top of the horizontal run of the pipe is even with the bottom of the oil pan. So, a pipe-thickness lower than the pan, thereabouts.
The headers exit a little above the bottom of the pan but add the reducer and the bend, things get pretty low.
Hi all, update to this thread and a question.
I just found these Thornton real shorty headers, not tubular manifolds, for 307 350 403 small block heads. They have a few different application for small blocks.
I've heard BBO heads fit directly on the Olds small block 350.
They look OK, do the 350 heads share the same port spacing and bolt pattern as the 455 BBO? ie, are they going to fit the 455?
That isn't any more ground clearance than you get with real headers. Sorry but I'm still struggling with why one would want to run shorties.
My pipes are above the oil pan with my Sanderson headers, they have 2.5" more ground clearance. I would have went with the Thorton stainless shorties if I was starting from scratch.
