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Russ Bellinis
Russ Bellinis

(15 posts)

Registered:
09/06/2016 02:15AM

Main British Car:


Headers
Posted by: Russ Bellinis
Date: September 23, 2016 11:41PM

I just finished reading about one of the cars on this site where the individual talked about work arounds he made to get equal length for all of the tubes in his headers. The late John Lingenfelter pointed out in his book on getting horsepower out of the small block Chevy that any tuning advantage that you receive from headers is cancelled out as soon as you put a muffler in the exhaust system. If you have cutouts in the system for track use, then you can get tuning advantages from equal length headers set up to the correct length. If you use mufflers, all you really need is a free flowing, efficient, low back pressure system. When headers give power increases with mufflers installed, it is not because of tuning advantages, but because the headers flow better than stock exhaust manifolds.

The morale of the story is if you are "going nuts" trying to get a specific tuned length to fit under your hood and around all of the various bits in the engine compartment, don't worry about tuned length or equal length, just build something that flows freely.


ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1165 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

authors avatar
Re: Headers
Posted by: ex-tyke
Date: September 24, 2016 09:56AM

Quote:
..... don't worry about tuned length or equal length, just build something that flows freely

thumbs up!.jpg

Ssshhhhh....don't let Jim Blackwood find out!


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Headers
Posted by: BlownMGB-V8
Date: September 24, 2016 11:42AM

I recall back in 1970 that on a Chevy Nova or Chevelle or Camaro with a 350, Hot Rod Magazine claimed that a good set of headers were worth 40 additional Hp on the street. That would be with mufflers. A 350 then was good for around 300 hp so that was a significant improvement.

You guys are just trying to justify your cramped, contorted, minimalistic, shorty headers as being 'good enough'. Fine, if they are good enough for you, use them. There are plenty of other ways to overpower the car. But until you set up a back-to-back test where the only thing you change are the headers, I'm going to claim BS.

Many of these shorty headers are little more than log manifolds made of steel tubing. Certainly there is nothing magical about the material.

Study gas dynamics. You're sending a slug of gas down a tube. If the tube is too short, the working rpm of the tube is above the working range of the engine. So it will never provide any scavenging benefit. For a visual clue, look at the pipe on a 2 stroke motorcycle engine which relies very heavily on scavenging to even be able to run. The same principles apply. Take note of the length and diameters. Note that initially the gasses are expanding but later they condense because of heat loss. Note how much smaller the outlet is than the head pipe.

OK, this is happening in your headers too. Instead of providing a larger diameter for expansion though the gasses are just propelled at a higher speed down the tube. This slug of gas has inertia and very high velocity, and it is beginning to cool as it approaches the collector. It draws a vacuum behind it and if the tube is long enough and not too large in diameter it will suck the intake charge right into the cylinder on the overlap. The key is having the proper length and diameter, if either one is off scavenging will not take place.

What happens at the collector and beyond is another matter. Collectors are designed to allow one pulse from one tube to apply a suction to the other three tubes but typical collectors are often too short to accomplish this. Then beyond the collector the gasses continue to cool and condense. A pipe and muffler at this point can act as a barrier or it can be almost completely transparent, it all depends on how it is designed and constructed and bigger is not always better. Muffler and pipe design up to now has been mostly pure guesswork with a few lucky discoveries, and it has almost entirely been the easiest solution to getting the exhaust out the back of the car and quietened down a little. Even so called scientifically designed exhaust systems fall far short of the ideal, but occasionally there will be a lucky accident where everything works. But if you put a 2-stroke scavenger pipe designer on the job he would be horrified.

Jim


Jim Stabe
Jim Stabe
San Diego, Ca
(829 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: Headers
Posted by: Jim Stabe
Date: September 24, 2016 12:15PM

I agree with Jim B that tuning of exhaust headers can provide a hp and torque advantage over unturned shorty style headers. I also agree with Mr Lingenfelter that the greatest gains on a muffled system come from increasing the flow and reducing the back pressure. Header length and primary diameter tuning must be done in conjunction with a number of internal engine changes to be effective. Intake design, cylinder displacement, camshaft timing and head efficiency must all play well together for the benefits to be fully realized. Accomplishing that within the confines of a cramped engine compartment can be a challenge.

The exhaust on my car is far from ideal due to packaging constraints; I have 1 5/8" shorty headers dumping into 2 1/2" pipes which then merge into a single 3" pipe and a 3" muffler. To illustrate how back pressure can affect power I originally had a Flowmaster 50 series muffler on the car and the power peaked at 4800 rpm and then fell off quickly. Changing to a Dynomax Ultraflow muffler allowed the power to peak at 5800 rpm with a shallower fall off above that. See the attached chart for a comparison in muffler flow rates. I believe that switching to 1 3/4" shorty headers would increase the power further but I'm happy for the moment where it is.

MufflerComparisionChart.jpg



Edited 1 time(s). Last edit at 09/24/2016 12:24PM by Jim Stabe.


MGBV8
Carl Floyd
Kingsport, TN
(4511 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: Headers
Posted by: MGBV8
Date: September 25, 2016 11:28AM

Quote:
You guys are just trying to justify your cramped, contorted, minimalistic, shorty headers as being 'good enough'. Fine, if they are good enough for you, use them.

They are good enough, Jim. We are not trying to squeeze every last pony out of these engines. Mike Moor's homebuilt mild mannered Buick 300 was rear wheel dyno'd at just over 300hp with the same exact blockhugger headers that were on his Buick 215. I was there. No BS, they are good enough for most of us.



Edited 1 time(s). Last edit at 09/26/2016 10:09AM by MGBV8.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6468 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Headers
Posted by: BlownMGB-V8
Date: September 25, 2016 12:08PM

That's what I said. (look at the quote! ;-) It's a workable solution to an inherent design compromise. And as we've shown, you can always add cubic inches. (The exhaust on the RM is an absolute horror as an example of headers but it's got gobs of power.) But that doesn't mean that a proper set of headers wouldn't make any further improvement. To me, it was worth it. At the same time, I also got better ground clearance out of the deal than you'll see with any other MGB. If I was starting out to build another car for myself, I'd do it that way again.

Jim


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