Muffler replacement huge horsepower gains!

[mickmate]

There was an article in Kit Car magazine before they went down the gurgler with the economy problems on installing new mufflers in Cobra side pipes. It came out at the time I was replacing some mufflers on an SPF. There has been some good discussions and threads on here already about the baseball shooting mufflers and resultant horsepower gains etc. In the absence of a good thread on how to actually install them I thought I would document what we are doing here as I'm doing several sets right now. It should be interesting to see these mufflers cut out, cut apart, measured and compared side by side. I will carry it through to the most fun part of these projects which will be testing them on the cars for noise and performance. As I said we have a few of these going through now but feel free to comment on any potential improvements or ask any questions as we go.

[RodKnock]

Will you be testing the Hushpowers, which are made by a subsidiary of Flowmaster? I have them on my Kirkham. Their schpiel (claim) is that they make more HP (i.e, less restrictive) and they're quieter. Thank you.

[RedBarchetta]

Originally Posted by mickmate

...There has been some good discussions and threads on here already about the baseball shooting mufflers...

Never in my wildest dreams would I ever have imagined that one photograph would have generated so much notoriety.



Looking forward to following this thread and reading up on your findings. It's good for everyone to know the pros/cons of BIG pipes. Will this thread require ear plugs, too?

-Dean

[DocDirk]

Yea!!!!!!!!!! I've been searching for the kind of answers Mickmate is proposing to bring to this forum!!! Now in the deciding stage, I'm back on hold in rapt anticipation of the hard data!

Where was that DONATION button again.....???

Thanks!

Dirk

[shelby racer]

I have heard that the stock side pipes cut at least 100 hp. I am still waiting to dyno my car to see once the new motor is broken in. My engine builder estimates that it should be about 650 both ways at the crank. If it was actually a little quieter, that would be a bonus. I actually feel sorry for my neighbors who other wise like the fact that I have loud cars up at my house.
John(;-)

[kbutler971]

Greetings:
This is great, and as an owner of an older CCX very much appreciated. I can only imagine the improvements which can be realized with a fresh look at the exhaust side of the engine breathing equation. These are on my list of improvements.
Kirk
CCX-3057

[RICK LAKE]

mickmate You can save yourself alot of time and money by doing a backpressure test on each exhaust system if you are looking for just power. They have a gauge with an O2 sensor end on it. Drill tap and weld a bung to the pipe between the collector and the muffler. Go out for a test and look at the pressure reading at WOT If the is no pressure you are hurting the motor and lossing power, you are looking for 1-2.5 psi of pos+. This is where the most power will come from the motor. There are some varibles on this. Size of motor and any power adders. Anything over the 3.0 is lossing power from the exhaust system. This way is a quicker and faster way to test exhaust systems. Most exhaust systems ( sidepipes ) are toned down because of noise. Some cars need an ear plug in the L/S ear unless you like the ringing after you have been out of the car for an hour. Will someone answer the phone!! Side pipes can cost anywhere from 10-40 HP at the high rpm band. Under normal driving and up to about 4,000 rpm with a 427 cube motor stock you only loose a 10 HP. The less the back pressure the loader the pipes. Rick L.

[cobrarkc]

Here is an interesting article I read about camshafts. I mentions backpressure in engines in respect to overlap of your cam. It seems that depending on how your engine is built will determine how much if any backpressure you will need.
Overlap: How Much Is Too Much?
Assuming we are choosing a cam for a streetable engine, how much overlap can we use before it becomes a problem? The answer here is that it depends on the valve sizes in relation to the cylinder displacement. If the heads have small valves in relation to cylinder cubes, then the amount of overlap we can use is significantly more than the same cylinder with much larger valves. For instance, a 500-inch big-block Chevy can tolerate not only more overlap, but a much bigger cam because the cylinder heads are so under-valved for the displacement. A 350 small-block with a set of decent heads has a lot more valve-per-cube, so it does not need so much overlap to get the job done.

Now that we have covered the effect overlap has on street manners, it is time to look at its effect on power output. Let's make one thing clear here: Big (but not excessive) overlap is a prime key to big power numbers, but only if your exhaust system sucks. Literally. If you have ever heard that an engine needs a little backpressure, you might want to ask yourself why an engine would want an exhaust system that literally pushes exhaust back into the combustion chamber rather than sucking it out. The simple answer is, it doesn't. If a big-overlap, big-cammed engine has an exhaust system with any measurable backpressure, the price paid is a big drop in output.

Although the foregoing might be interesting info, it doesn't actually help you make a decision as to how much overlap your engine needs. Just in case you might ask, I use a one-off computer program that was 18 years in the making to do what we are doing here, but that is no help to you. So that you have something of a guide, I have made up the nearby chart. To make the most of this chart, you will need to take into account where, in terms of valve size per cube, your engine falls. For, say, a 302-inch engine with decent-sized valves, the overlap selected needs to be toward the short end (left side) of the segment that fits your application. If it's a typical 350-inch small-block, then choose something around the middle of the relevant segment. If the engine in question is a big-block or a really big-inch small-block (both of which are typically under-valved), then select the overlap toward the larger, righthand side of the relevant segment

Here is the rest of the article.

http://www.popularhotrodding.com/tec...ics/index.html

[RodgerH]

I too have read the posts about an engine needing a "little back pressure" and it makes no sense to me. I believe the ideal exhaust system will create a negative pressure in the cylinder during the cam overlap period and thus pull fresh fuel/air through the cylinder. This provides a fresh combustible mixture undiluted by exhaust gases remaining in the cylinder due to poor scavenging caused by back pressure.


Here's a quote from "21st Century Performance Book":
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Few tests have been done that clearly show the effect of changing back pressure. Most muffler and exhaust comparison tests change more than one parameter simultaneously, making the identification of exhaust back pressure as a culprit difficult.

However, Wollongong (Australia) mechanic Kevin Davis has done extensive testing of varying back-pressure on a number of performance engines.

These range from turbocharged Subaru Liberty (Legacy) RS flat fours to full-house traditional pushrod V8s. In not one case has he found any improvement in any engine performance parameter with increased exhaust back pressure.

The tests came about because Kevin has developed a patented
variable-flow exhaust that uses a butterfly within the exhaust pipe. He initially expected to use the system to cause some back pressure at low loads 'to help torque.'

However, he soon changed his mind when any increase in back pressure proved to decrease torque on a properly tuned engine. What increasing the back pressure does do is dramatically quieten the exhaust.

One of the engine dyno tests carried out by Kevin was on a modified 351 4V Cleveland V8. Following the extractors he fitted a huge exhaust that gave a measured zero back pressure. Torque peaked at 573Nm (423 ft-lbs) at 4700 rpm, with power a rousing 329 kW (441 hp) at 6300 rpm. He then dialed-in 1.5 psi (10.4 kpa) back pressure.

As you'll see later, very few exhausts are capable of delivering such a low back pressure on a road car. Even with this small amount of back pressure, peak torque dropped by 4 per cent and peak power by 5 per cent. He then changed the exhaust to give 2.5 psi back pressure. Torque and power decreased again, both dropping by 7 per cent over having zero back pressure. These results were achieved on a large engine with a large overlap cam - one of the type some people suggest is 'supposed' to like back pressure.

If, in fact, power does increase with increased exhaust back pressure, it is most likely the air/fuel ratio and/or ignition timing that are no longer optimal for the altered state of engine tune."

The exhaust system is much the same. Just changing back pressure is a bogus way of trying to create the "ideal" pressure in the system. The exhaust system should work like a correctly conceived header. It should extract the exhaust from the header, to minimize pumping pressures.

The only way to create a system that will serve as an extractor is to properly size the tubing to allow the flow velocity to create a sort of "vacuum" behind it.

In the stock ITR, backpressure becomes a power "liability" by the time the engine's making 210 flywheel HP. Relative to wheel HP, if you're making more than about 11 HP more than "stock", the system's costing you....and yes, [b]detonation can be caused by excessive back pressure.

The other problem you face with excessive back pressure is one of reversion. The higher the back pressure, the more inert exhaust components re-enter the cylinder. A few of these bad-guys can really steal big hunks of power in a hurry. If you don't believe me, just run a pipe from your exhaust tip up near the air cleaner on your next trip to the dyno. A little sniff of the exhaust will absolutely kill your power.

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Maybe I'm missing something??
Rodger

[KarlCSX2498]

Hey, Can you post more photos that show the process from start to finish?
thanks, karl

[767Jockey]

Nick has some pictures of the internal core of my early Contemporary mufflers. I was floored to see how incredibly small and restrictive they are. I can't imagine not making huge gains in horsepower with the new 3" core glasspacks from Classic Chambered. Nick, if you have time post a picture of my mufflers to show the Contemporary guys what they're choking their cars with. I can't believe that regardless of the engine you're running that you won't pick up over 50 HP with a very mild engine and over 100HP with a strong engine just by switching mufflers. The mufflers themselves are in the area of $200 with all the various pieces needed, then add on Nick's labor for cutting and welding, some shipping charges and possibly coating if you wish, and this replacement program is the most affordable horsepower bonanza available to the typical Cobra owner. Where else will you get the chance to add 100 HP or more for this kind of money? Show the pictures, Nick - they speak for themselves.

[1985 CCX]

I am choking....

[Mdman352]

I have a Contemporary at Nicks now and I stuck a bore scope (used for examining rifle bores) inside of my collectors and I do not have ANYTHING in mine. WHAT DID YOU SAY??? I have taken to wearing small ear plugs during driving (26 dba reduction. available at Walmart) that I use to compliment my hearing protection while shooting. Stopped the ringing and you can still hear.
David

[CobraEd]

No backpresure is good

.

[Rick Parker]

Several years ago there was a company in Phoenix Arizona, Arizona Exhaust Fabricators @4009 Nth 39th Ave (no longer in business). They had the tooling and were making glasspack style mufflers with louvers or slots cut in the interior. At the time many folks on this site were using his products. They were available in any requested length and different diameters. I had some done for my 289 with 3" OD and 2.5" core ID. Without exagerating, they were around $20.00-$25.00 each in mild steel. Does anyone in or around Phoenix remember this person Lucien Donofrio or his business? Is the tooling being used by someone else??

[Silverback51]

Originally Posted by CobraEd

No backpresure is good

.

That is why so much time and effort is put into equal length headers, and collector design. You want the exhaust pulse of one cylinder to cause a negative pressure zone in the other primary tubes so you have a scavenging affect.

This rumor of backpressure being good has been around since I was a kid.

[Rare Iron]

Originally Posted by CobraEd

No backpresure is good

.

Here's an exhaust teaser - & I will maintain that correct flowpath & exhaust pipe diameter IS critical, as well as using mufflers of some sort in an exhaust system. A good friend of mine is one of the supervisors for floor operations at the Chrysler Viper development plant on Featherstone in Auburn Hills, MI.

Several years ago, while experimenting with different exhausts for the Vipers, they decided to plumb & run a 3" straight-pipe system on a test mule Viper, and dyno it. Like, no mufflers = no backpressure = a good thing! Plus, maybe it would sound good on the V-10 to boot. They did their thing & then brought it up to operating temp., where they discovered the motor was running about 30 degrees hotter, plus it lost about 30 HP. They shut it down, let everything cool off, & then they installed Super Turbo mufflers & re-ran the test. Everything went back to normal. They concluded there was an "expansion chamber" needed in the exhaust system for optimum running conditions. Also, on any application, if you reduce backpressure too much or use too large of a system diameter, you will lose bottom-end & midrange performance - you'll FEEL it. You must pay attention to what power your motor is putting out, & relate that to an optimum exhaust system diameter. My advice is that you transition to a 3" muffler flowpath when you are up around 480 HP, IF you are looking for optimum performance. There is a quantum leap in exhaust flow cfm when going from 2.5" to 3" diameters.

-Eric

[CobraEd]

This is because when you open up the exhast, you need to richen the mixture to compensate or it will run lean and hot !!!!!!!


.

[CobraEd]

during the 60s when I was in high school, a lot of kids would go to the drag strip with basically stock cars. the cars would run fine. But when they would disconnect the exhast system at the manifold for a run down the track, the cars would break up badly. This is because they did not richen the jetting as necessary to work with the freer flowing exhast


.

[vector1]

here's a template for an exhaust system for a 427 with 10.5 comp and mild cam.

--- Single Primary Pipe Specs --- for 427.650 CID from 4600 to 7100 RPM
Diameter= 1.873 to 1.998 Length= 29.6 to 32.4 inches long
--- 2-Step Primary Pipe Specs ---
1st Dia. inches= 1.873 Length= 14.8 to 16.2
2nd Dia. inches= 1.998 Length= 14.8 to 16.2
--- 3-Step Primary Pipe Specs ---
1st Dia. inches= 1.873 Length= 14.8 to 16.2
2nd Dia. inches= 1.998 Length= 7.4 to 8.1
3rd Dia. inches= 2.123 Length= 7.4 to 8.1

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 3.422 to 3.672 Tuned Lengths= 17.1 best and also 8.6 or 34.2

--- Header Collector Specs (Megaphone or Diffuser Cone Shape) ---
Diameter= 2.922 taper to 3.922 Megaphone/Diffuser Length= 17.1 inches

Best HP/TQ Tuned Collector Lengths= 17.1 , 34.2 , 68.4 , 136.9 inches long

Worst HP/TQ Loss Collector Lengths= 25.7 , 51.3 , 102.7 , 205.3 inches long

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 130.7 inches long ... typically never used
2nd Harmonic = 49.5 inches long ... longest recommended
3rd Harmonic = 29.6 inches long ... highly recommended , best Torque Curve
4th Harmonic = 20.6 inches long ... shortest recommended
5th Harmonic = 15.5 inches long ... typically never used
6th Harmonic = 12.2 inches long ... typically never used
7th Harmonic = 9.9 inches long ... typically never used
8th Harmonic = 8.2 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 136.9 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 68.4 inches long ... longest recommended with Mufflers
3rd Harmonic = 34.2 inches long ... more bottom-end Torque
4th Harmonic = 17.1 inches long ... highly recommended , best Torque Curve
5th Harmonic = 8.6 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.3 inches long ... reduced Torque , not recommended

as you can see it is based on harmonics.