[Rocky Rotella]

Well, I do need to point out that the 42582 Flowmaster muffler we loaned the Hands was actually the very first version of this muffler. It is actually about an inch smaller than the current 42582. Also, the inlets and outlets were about a inch closer together than the current production unit.

As far as being able to tell, the original we used for the testing was a 16 gauge steel unit. It was originally black but my dad painted it silver. The newer unit is aluminum and slightly larger. For a while, the 42582 disappeared all together and in it's place, the 42585 came out. The newer 42582 came out and my dad bought one and installed it on the 72. While there was absolutely no difference in performance, the newer, larger, aluminum version had a bit more hollow sound and didn't seem to "cackle" as much as the first design.

My 76 is the aluminum 42585 top inlet/side outlet muffler. It sounds very, very close to what the 42582 sounds like. I'm not sure how much I'm hurting/helping performance with this particular muffler but I really like the sound and I was prepared to give a few ponies for the sound. Like I said in my initial post, the wav files are all different mufflers but all have the distinct Flowmaster sound. The "2041" sound is my dad's car with the newer 42582. This can be compared to the Hand's 42582 test to differenciate the sound quality. My 42585 has an X pipe but it's still has the same tone.

On one hand, I can understand why the Flowmaster doesn't flow as much air as a straight through design muffler. On the other hand, I do see why people do not like them. It's a take it or leave it sound. Fortunately I love it [img]/infopop/emoticons/icon_biggrin.gif[/img]

[Z Code 400]

Originally Posted by Jim Hand

Larry,
While running 2 1/2" mufflers, we tested 2 1/4" tailpipes against 3" tailpipes and saw almost no difference. As a result, I ran 2 1/2" mufflers and tailpipes with the 3" Dr. Gas system for years.

If you use a single transverse muffler that has 2.25" or 2.5" inlets, it is unlikely that the tailpipes will adversely affect performance. That is one of the unseen advantages of the X crossover - it allows each cylinder to see both sides of the dual exhaust system. That means that any restriction of the dual pipes or mufflers will be about half of what would be found with conventional duals. But again, the single muffler changes the equation - they just do not flow as well as conventional mufflers. I checked some numbers from our Silent Power CD project and here are several flow values:

Walker Super Turbo PN 17449, 2.5" - Flowed 70% of 2.5" open pipe.

Walker Ultra Flow PN 17288, 2.5" - Flowed 99% of open 2.5" pipe.

Flowmaster 42582, 2.5" Flowed 55% of open 2.5" pipe.

Jim Hand

[ January 28, 2002: Message edited by: Jim Hand ]</p>

Tom,

One interesting thing I was made aware of during a conversation with Flugger about chambered mufflers and scavenging effect involves the differential between flow values in in/Hg of Vacuum Vs. cfm & Pressure.

As most exhaust headers have a relatively small primary tube diameter (1-3/4" for instance) the flow value of this tubing would be very low on a Flowbench when subjected to a vacuum. However, the tubing has greater flow potential under pressure when the scavenging effect takes place.

The same factors pertain to chambered mufflers and other systems which accelerate and decelerate exhaust gasses.

A friend of mine is employed by Honda's Indy car Research and Development Team. Although he is bound to secrecy as far as his work is concerned, he has shared a few interesting things with me over the years.

Honda has determined through testing that vacuum is not an accurate method of estimating the flow capabaility of a component part. The only accurate way to estimate the flow potential of a component part is to determine the approximate amount of pressure and cfm that will be generated at a given rpm and load, then subject said part to those conditions.

They have also seen component parts that flow more pressure and cfm than they will flow vacuum.

This was proven by engineers at the Toyohashi University of Technology with respect to components that were designed to exploit the scavenging effect of the supersonic exhaust pulse on Suzuki Racing Motorcycles.

Flugger maintains that you cannot accurately estimate the flow capability of a Flowmaster with vacuum. In fact, the average Flowmaster muffler has much more volume than most other mufflers, a fact which can be proven by filling a Dynomax Super Turbo and a Flowmaster side-by-side with water.

Engines do not work like flow benches by blowing a constant stream of cold air. Engines have pulses of heat, gases and sound frequencies traveling down the exhaust pipes.

Recently, at my request, a family friend confirmed Flugger's claims of 2.5" straight pipe flow at 624.7 cfm. For comparison, a Hooker Aero Chamber Muffler with 2.50" Inlets/Outlets flows 441 cfm.

A Magnaflow Straight-Through Muffler flows 595 cfm. Seems odd that a muffler you can see through doesn't flow 100% of an open 2.50" pipe, doesn't it???

Only Hooker posts the actual flow values for their mufflers. Other manufacturers claim a certain percentage of an open pipe, but they never tell you what that value actually is. That should tell you something.

A very interesting topic to say the least...Robert

[Tom Hand]

Zcode,
Muffler advertisements and manufacturers can claim a lot of things. What matters is:

a) how they sound,
B) how they run,
C) how loud they are.

At 20.3" of water pressure, a 25" long piece of 2.5" pipe flows around 475 to 500 cfm. Not sure what yours was tested at, maybe 28" of water? I have confirmed the 475 to 500 many times at 20.3" inches of water pressure.

Not sure why anyone would be using a vacuum to test the mufflers on benches. Most bench operators would be testing mufflers using pressure. We were able to run them and measure backpressure on the car which can be compared to bench flow and you get some pretty cool relative bits of information out of them. High back pressure compared pretty evenly with poor bench flow and low back pressure compared well with high bench flow. Pretty easy to confirm.

Hooker’s Aerochamber at 441 cfm is pretty darn good. I bet that was a center in, center out configuration. We saw their offset-offset to be around 380 to 400 cfm, which is still 20% better than the typical offset-offset chambered muffler.

Fortunately, consumers can always decide what sound they like and that is the best thing about different mufflers, like Rocky pointed out. Luckily, many have also been able to tell how the mufflers actually let the engine run and how loud they are by using tests. Test data does not lie.

There is a reason the guys on the Engine Masters Challenge always win with straight-through, packed, acoustic-style mufflers (MagnaFlow for example) and not chambered ones, no matter how large they are. Sure, volume helps flow and that is why the newest Flowmasters are now "improved" by upping their case dimension. That helps the air flow through them, recuces the measured back pressure, and helps the sound reduction somewhat.

Walker has given their mufflers' flow values for a long time. Pick up any of the catalogs and you will see the numbers.

But again, muffler buying is a personal preference. If you like the sound, buy it for that alone. But if you want optimum performance and sound control, you need to look at test data and blend it with manufacturers' advertisements. By doing this, you can always get exactly what you want and that is good thing right?
Tom

[Z Code 400]

Tom,

Flugger's data was based on 28 in/H20 and I asked the same parameters be used to verify the baseline.

I'm not a fan of the Flowmaster sound, but their muffler is a much better engineered piece for a second generation 'F' Body.


When you look inside a Dynomax or a Walker, they have pass tubes that flow only through small louvers or perforations, in typical turbo fashion. Inside a Super Turbo (the muffler we used for years) they have flow directors, but they don't seem large enough to handle the full velocity of the flow path. I cannot see these flowing any better than a chambered muffler.

The Hooker Offset/Center flows 441 and the Center/Center flows 595. That's on Hooker's website and in the Summit catalog. They don't mention testing standard, but I would assume it is 28 in/H20.

I have read a lot of the testing (here) and shared the opinion that Flowmasters, basically, didn't flow that well. In fact, I became so biased that I would not even consider using one, even though the #42585 fits better than any other muffler on the market (under an 'F' Body) and the tailpipes have fewer and more gradual bends. However, after reading several posts in this forum from members who swapped on Magnaflows and saw no improvement in ET or MPH, I began to re-think my (prejudiced) position.

I started talking with a local muffler shop when I began to plan an exhaust swap on my Firebird. They sell more Flowmasters than anything else, which isn't surprisining, considering their aggressive advertising campaign. However, the owner became a big fan of Magnaflows and decided to change out his 2.50" 40 series Flowmasters with 2.50" Magnaflows. This is on a 454 Chevrolet in an early Camaro.

Horsepower is in the 425 range with torque in the 480 lbs/ft range.

He ran back to back dyno tests and nothing changed....nothing.

I can supply at least (3) links to posts in this forum where members dropped the exhaust and/or swapped in a Walker or a Magnaflow with no change in ET or MPH.

However, like you, I prefer the old perforated core glasspacks over everything else. I even considered mounting two in 'rack' fashion behind the rear axle, but felt the gradual bends of the 17104 Flowmaster Kit was far superior to the 90° bends in a typical crossflow application.

One thing I am certain of after talking in depth with Jim Butler...headers have a much more pronounced effect on a Pontiac (due to their exhaust port design) than it does on other engines in general. Case in point...

We had a 440 Chrysler with Cast Iron upswept exhaust manifolds, 2.50" exhaust pipes and factory Hemi Mufflers. It was a street car, but ran consistent 13.50's @ 109 mph. We switched to headers and 'low restriction mufflers' (Cyclones or Super Turbos I think) and we actually lost ET and MPH (especially 60' times) and no amount of tuning would ever bring it back. We switched back to the stock system and the performance came right back.

We believe the Chrysler setup was so good, and the exhaust ports of the 915 closed chamber head were so well matched to the overall combination that no improvement could be made.

Perhaps Pontiac's (like Jim Butler attests) are different in that respect.

Interesting subject matter. My #17104 Flowmaster Kit will be installed on the Formula Wednesday. Although this is completely unnecessary for the stock 350, it is intended for the 413 and any other engines that I might install in the future.

I also plan on posting dyno results of the pending modifications in the near future...Robert

[Tom Hand]

Robert, you bring up many valid points. One should always do what sounds and works best for him/her regardless of what anyone else says. That is why there are so many muffler companies. With your smaller engine, you will be able to run a "louder" muffler and not deal as much with resonation and roar.

One thing to remember is the gradual bends of a nice madrel bent, over-the-axle system are way better than exhaust having to radically change direction instantaneously inside of a muffler. That directional change is where the performace drop starts to become apparent.

Regarding mufflers outflowing pipe? The Walker UltraFlo does. The perforations in mufflers create small eddys that can and do create resistance to flow. Walker gets around it by using larger diameter internal cores for many of their mufflers. Goerlich does it by not having perforations in the bend areas. That is where Walker and Goerlich outshine Magnaflow.

Regarding change in performances, we have seen many cases where a muffler's back pressure does affect it. Every tenth is pretty important to some. I agree that in many cases, mufflers make only slight variations however, many can make huge sound level differences and again, the level and tone are matters of personal preference. Might check in with the other postings on this forum recently; one deals with resonation and one deals with sound. Both issues the guys are having are consistant with reactive type mufflers but fortunately, occur to a lesser degree with larger cased, acoustic absorbing material-packed mufflers.

So, I know you will enjoy your chosen system and that is the greatest part of all. You can pick exactly what you like to hear and what you want to be heard driving around with. Does not got any better than that does it?

Thanks!
Tom

[Larry Navarro]

Flowmaster offers two different style crossflow mufflers.
I had the #42582 on the SD and swapped to the PYPES transverse.
The SD immediately came to life, over the restrictive #42582.
The #42585 must have a different internal configuration since the inlet pipes enter the upper case of the muffler as opposed to the side-walls of the #42582.

[Z Code 400]

Tom,

Actually, I place very little emphasis on sound. I don't particularly care for Flowmaster's tone, but I thought their kit had the best physical fit under the car. That is why I chose that setup.

I would hope you did not consider me to be a non-thinking exhaust lemming that was driven only by the car's sound at a stoplight.

You may also recall the unique muffler on the early Z-28's that the #42585 Flowmaster is patterned after. A chambered system was also available on those cars and was later seen briefly on the market under the title 'Turbo Tubes' which were very loud without resonators.

I'm not all that well versed on exhaust systems, since we never used them on our race cars, we just extended the collectors as far as we could. We ran a lot of 'Hemi' mufflers and the old Dynomax Super Turbos on our street cars, but I always favored perforated core Mitchell brand glasspacks personally.

Here is what I can tell you from our limited experience with street cars. It obviously pales in comparison to what you have done, but you might find it interesting.

We used to braze fittings into the exhaust ahead of the mufflers and attach pressure gauges. My 429 Ford with a full-length 2.50" system and Dynomax Super Turbos could generate around 5psi @ 7000 rpm. On that car, we swapped in glasspacks and saw 0 psi from that pont on.

On our 1967 Coronet R/T with a 440, full-length 2.50" exhaust and stock 'Hemi' mufflers, we saw 0 psi all the way to 6200 rpm.

Your comment about my smaller motor is valid. However, I believe it is more a factor of compression than displacement that will result in its lower sound levels.

The 413 was actually designed for my 1979 WS6/SE that had to pass CA. Smog Inspection, so it was purpose-built on the mild side. When I sold the SE to a forum member, I kept the engine, which seemed like a good idea. :-)

To that end, I will tell you that I have a 455 (.030" oversize) in the works with 9.50:1 compression and a custom designed camshaft profile featuring
.500"/.500" lift and 229°/235° @ .050" lift on a 113.5 LSA which I feel would perform adequately through the system I am installing on the Formula.

As far as flow is concerned, I have been paying close attention to a local performance shop that does a lot of chassis dyno testing on customer vehicles. I am yet to see them test a crossflow, but they have done considerable testing on other Flowmasters, Magnaflows, Terminators, Raptors, Aero Chambers, Borlas, Edelbrocks, Warlocks, Super Turbos and about every other configuration you can think of.

Some of these vehicles are producing well over 400 horsepower.

So far, there has been little, if any difference between any of these mufflers, even on the V-10 Fords, Duramax and Power Stroke Diesels. While some of the systems are 3" or bigger, most are 2.50" systems on early Camaros, Chevelles and Novas.

Basically, I have watched them pull Flowmasters (because of resonance) and replace them with Magnaflow's and read no change in HP or TQ with an established baseline.

I find this interesting based on your comments about replacing Flowmasters with mufflers that will outflow them. So far, I am yet to see this proven on the dyno.

I will also challenge the notion that engines like backpressure. I have heard this numerous times in conversation, but in actuality, engines do not respond well to backpressure. We have seen big HP and TQ reductions when artificial backpressure is induced.

What I have seen is a change in exhaust velocity from different mufflers that changes the frequency of the exhaust gas pulse. I believe that this 'slowing' of exhaust flow can be beneficial to some engines, especially those in near-stock form.

I have personally seen a number of problems with Hilborn Injection and over-scavenging where the exhausts indicate the engine is rich when in fact, the cylinders were very lean. Changing to a 'Turbo' style muffler (the type with 3 internal tubes and no direct gas path) corrected this problem. However, we never saw the exhaust system go into pressure.

Since backpressure was never induced, what we did was change the exhaust gas velocity, slowing it somewhat, which allowed a more complete combustion process to take place.

We should also keep in mind that camshaft overlap will have a tremendous effect on engine characteristics. Typically, what I have seen in personal experience, is the more radical engines prefer a straight-through style exhaust system and the milder engines seem to produce better dyno numbers with more conventional muffler.

I am convinced this is due to the '5 Cycling Effect' Ed Iskenderian pioneered with early, long duration camshafts.

My point is, regardless of flow capability, a muffler should not be chosen for a gievn application simply by its flow values alone. Some engines can derive great benefit from a high flowing exhaust system and others may not realize the same benefits.

Flowmaster (and others) have spent a lot of money on dyno and airflow testing and so far, Flugger is the only person to acknowledge flow velocity, not backpressure in his technical writings.

I tend to think that a perforated core glasspack is the best muffler one could use from a flow standpoint. The Magnaflow is a good unit and the larger case would help to quiet the note somewhat. However, I did not like the crossflow muffler that they offer for the 'F' Body.

I also considered two 'rack mounted' glasspacks that could be mounted transversely, but didn't like the bends going into and out of the unit.

I haven't tested the Walker or the Dyn0max versions of the crossflow, but I would have to agree with your test results that they flow fairly well, although I am yet to see any of Walkers specifications. I would like to see those if anyone has a link.

I have been working with a local enthusiast who has an Atlas-Copco Screw-Type Compressor capable of developing well in excess of 2000 cfm of air pressure. It would be interesting to tether a muffler (and the lines) and see just how much cfm and psi of air can be pushed through a muffler before pressure can be read at the inlet.

I am still waiting for someone to map the CFM out of a single 2.50" pipe on a 400 to 455 cubic inch Pontiac V8 at 5500 to 6000 rpm. It is my belief that then and only then, will we be able to accurately determine whether or not a given muffler has adequate flow capabilities.

Food for thought, don't you think???...Robert

[Tom Hand]

Robert, if you have not already done so, you might want to read pages 106 through about 108 in our book. We graphically show how backpressure/airflow affects the Pontiac engine's performance. From this data, you can surmise how much airflow you need to not affect power negatively.

As another point of interest, the standard from SAE papers over the years is that about every PSI measured static back pressure reduces engine output by about .75 to 1.25%. This was shown to be true by independent researchers too. Walker uses 20.3" of water pressure as a standard because they know that it takes about 2.2 cfm per HP at this pressure to keep the muffler from not affecting the power, assuming of course that the pipes' flow enough air to the muffler. This is obviously why some manufactures now post their mufflers' flow figures, like Walker has been doing for many years. Others that have mufflers that do not flow as well tend to highight other benefits of theirs, and this only makes good business sense.

Have fun with your new system and please shoot some images to share when you get it on and adjusted. Thanks again Robert for the nice and technical as well as thoughtful conversation.
Tom

[Z Code 400]

Tom,

2.2 cfm per horsepower would require 440 cfm per cylinder bank on a 400 horsepower V8 engine. This would be in agreement with your data of a 2.50" pipe flowing 475 to 500 cfm @ 20.3" inches of water pressure.

However, I would still have to agree with Honda engineers that actually measuring the exhaust gas flow in cfm and psi from the exhaust tubing at the maximum horsepower production rpm is the only accurate way to determine the adequacy of an exhaust component.

This is a value you will never see in any manufacturers publications. Much like cylinder head airlfow values...they are a good estimation of a port airflow capability, but they cannot simulate actual operating conditions within an engine.

For example, if you have an exhaust port on a Pontiac head that flows 200 cfm @ 28 in/H20 on the bench, how much hot exhaust gas can it flow??? I will assure you that at 5800 rpm, there is much more than 200 cfm of exhaust gas exiting that exhaust port. And then, what happens when you multiply that value X 4 for the average flow capability of a bank of (4) cylinders???

What happened to the 440 cfm value of that bank's exhaust tubing??? Does it not look as though we have exceeded that value???

In January 2005 at the HPP Pavement Pounders Shootout at LACR, Alan Mandella, running a mild 462 in a 1974 Trans Am, pulled off 5 back to back runs that were separated by only 0.03 seconds. The best run was a 12.86 @ 105.90 mph.

All this with 1-3/4" headers, 2.50" exhaust and Flowmasters.

There is one question I continue to ask myself. Why do so many Pontiac's at the HPP Shootout run so fast and consistent with Flowmasters if they flow so poorly as to actually hamper performance???

Interesting...

Thanks for the data Tom....and by the way, which book are you speaking of??? I would love to purchase it for reference...Robert

[Z Code 400]

Tom Hand wrote: "One thing to remember is the gradual bends of a nice madrel bent, over-the-axle system are way better than exhaust having to radically change direction instantaneously inside of a muffler. That directional change is where the performace drop starts to become apparent."

Interesting view of the inside of a typical 'turbo' style muffler. Seems to be a number of direction changes and no direct path for the exhaust gas to follow.

Any cut-a-ways of the Walker and Goerlichs???...Robert

[Larry Navarro]

Originally Posted by Z Code 400

.....There is one question I continue to ask myself. Why do so many Pontiac's at the HPP Shootout run so fast and consistent with Flowmasters if they flow so poorly as to actually hamper performance???

Interesting...

One word...."Marketing".

Just as K&N has brainwashed everyone in thinking that they can't run faster or develop more horsepower without one.
I can't speak for everyone but my back to back track test prove to me that the K&N is no better than a paper filter.....AND the K&N is porous which allows fine grit to be introduced into the engine.

I would like to see someone test the flow of straight-thru mufflers vs. a Flowmaster, using a differential pressure approach. Install pressure taps on either end of the muffler necks and observe flow across the muffler.
I would be willing to bet that the straight-thru muffler would exhibit a "0" pressure differential, over a baffled flow master.
The only Flowmaster product that would come close to performing better than a straight-thru would be their center-inlet/center-outlet, "RACE" mufflers, which most everyone is not using on the street.

[Tom Hand]

Larry that is the best point to be made. Center in-center out versions do a fine job of not hurting performance.They do not however make a street car sound quiet enough that one can drive them around comfortably (single or dual chambers anyway). However, install the offset-offset on powerful applications and you will see a difference.

Why do many run them? Simple, most people do not have the time nor the money to test and compare all mufflers to sqeak out the best and highest performance. Many go with who pays the best. Other love the sound. Some cannot fit the best mufflers on and others may not want the weight from the really quiet ones.

The Engine Masters the first year or so all ended up with MagnaFlow for just that reason, straight through mufflers do abetter job of not affecting power negatively.

Robert, the cutaways are on Goerlich's site and Magnaflow's site. Walker may also have them on theirs but their new site is pretty active and my computer will not let me get to them.


Tom

[Tom Hand]

Robert,
I am terribly sorry I neglected to address your questions about the cutaway muffler. In fact, we tested that one and not surprisingly, it was relatively loud but the flow is not too bad. Take a look at the numbers from it. I have included the worst flowing HiPo and best flowing Hi Po 2.5” muffler so you can see how this one relates sound level and airflow-wise. I have also added another one or two for comparison and some 3” ones just for fun. The one you showed I have called “Cutaway”.

2.5” Versions
Airflow (compared to open pipe) Level, dBA at 750, 2200, and 3500 rpm
Cutaway 81% : 74, 89, 97
Worst 53% : 77, 92, 100
OEM Corvair “Turbo” 53% : 69, 83, 91
Gen. HEMI replacement 36%: 68, 78, 87
SuperTurbo (14”) 70% : 69, 83, 93
Best 99% : 71, 84, 91

3.0” versions
Worst 47% : 78, 95, 102
Best 97% : 71, 82, 92

By the way, the best ones and the quietest ones are straight through, oval versions. In fact the 18” long Xlerator X123 (labeled as “Best 97%) is one heck of nice flowing and nice sounding as well as relatively quiet muffler for A-body GM cars. You can see how it is on par with the OEM Corvair Turbo muffler in sound level but flows darn near as much air as a 24” long, three inch diameter pipe. Goerlich's engineers did a great job on this muffler and their longer X141, although at 22" long, it is a tight fit on some A-bodies.

Take care and sorry for neglecting to address this in the other post.
Tom

[Ccass]

Originally Posted by Z Code 400

Tom Hand wrote: "One thing to remember is the gradual bends of a nice madrel bent, over-the-axle system are way better than exhaust having to radically change direction instantaneously inside of a muffler. That directional change is where the performace drop starts to become apparent."

Interesting view of the inside of a typical 'turbo' style muffler. Seems to be a number of direction changes and no direct path for the exhaust gas to follow.

Any cut-a-ways of the Walker and Goerlichs???...Robert

fyi, The Pypes Street Pro Muffler pictured is not considered a 'turbo' style muffler. It is a 'chambered' style muffler. It is a medium flowing muffler just like most chambered mufflers. Dynomax super Turbo shows what the inside of their 'turbo' style muffler looks like right on the front of their muffler box!

[Z Code 400]

Thanks to all for the informative replies.

Larry,

I agree with you on the K&N Filters. We were using them here in our police vehicle fleet and they netted us not a single MPG more than paper. Plus, we had to deal with the grit issues you mentioned.

I will also agree with you about Flowmaster's marketing strategy. However, I am still yet to see the 'striaght-throughs' register better performance numbers on the chassis.

There is a local gentleman here with a 455 Buick that is running a center/offset Flowmaster 70 series that is turning mid 11.00's at close to 118 mph in street trim. That's hard to argue with and I doubt the car would instantly run 10.00's by swapping in a Magnaflow.

Additionally, a flow bench cannot create a supersonic pulse and it is this factor that allows a chambered muffler to create a scavenging effect.

Tom and Ccass:

I dropped off the Formula at the muffler shop this morning an unpacked the Flowmaster #17104 Exhaust System. The quality of material is very good with smooth, mandrel bends in what apprears to be 14 ga. aluminized tubing.

The #42585 Crossflow (with inlets in the case) is very rugged looking, yet surprisingly light. It has a spot welded heat shield to protect the fuel tank.

I took my bore scope and entered the muffler through the inlets. What I saw was interesting. The interior of this muffler is shaped like a funnel, bent into a sort of 'J' shape. Immediately past the inlet tubes, the exhaust expands into a chamber with 2 directional baffles followed by a 'diamond' shaped cahmber.

The chamber has small cutouts where it is welded to the floor or body of the muffler, like tiny archways. It would seem that this serves as an acoustical chamber.

There is a third directional baffle with a very large hole (nearly 3" it seems) hole in the center that directs exhaust gas into the curvature near the bottom of the muffler.

The gases pass into this 'flume' (similar to the flow directors on a Super Turbo but much, much larger) and turn up toward the outlets. Very gradual and smooth and you can definitely see the exhaust gases are being accelerated.

Where the 'Super Turbo' flow director is only about 2" wide inside a 4" or 5" case, the Flowmaster director is as large as the case, therefore making it impossible for any gas to deviate from its intended pathway.

The 'flume' guides the gas path upward, fanning out slightly and blending into the outlet. Both sides are completely separate and each side of the muffler has a small drain hole to dispell moisture.

We once cut apart a Super Turbo Offset/Offset and the exhaust actually traveled in an 'S' pattern inside the muffler. However, the flow directors were far to narrow (in my opinion) to adequately funnel the flow of gas and we saw evidence of exhaust 'piling up' where the directors could not handle the 'curve' of the exiting gas path.

It would be interesting if someone could test the old Z-28 '302' muffler that the #42585 is patterned after. The inlets also went into the case which eliminated the up and over the axle tubes. That was said to be a very good flowing unit, but quite loud.

With respect to my Formula, I was faced with a number of challenges in designing what I felt was an adequate exhaust system that would support up to 425 horsepower in the future.

The Hedman #28150 1-3/4" Primary Headers were chosen for their fit and 'user friendly' ground clearance.

Although I originally designed a system with twin center/offset Magnaflows mounted where the stock catalysts would have been, the muffler shop that was commissioned to install the system did a very poor job and I scrapped the project.

I considered the Pype's Crossflow System but do not like the tone of the X-Pipe or the difficulty in removing the gearbox with a welded X in place. Additionally, I am yet to actually see a Dr. Gas X Pipe produce a performance gain on the local dyno. The only thing I have witnessed is a change in pitch and it is not one I find particularly pleasing.

I decided on the Flowmaster Crossflow because it had the best overall fit, ground clearance and radii of any other pre-fabbed system, based on my observations. I have personally seen the Pype's Crossflow and the Torq-Tech pre-fabbed systems installed and I think the Flowmaster 'inlets in the case' method of guiding exhaust flow up and over the axle allowed for additional ground clearance and a more efficient gas path through the bends.

I also see no reason why this 2.50" system, which looks quite large under my F-Body, would have any difficulty whatsoever supporting a 462 inch 425 Horsepower Pontiac V8.

I will soon be subjecting the stock 42,000 mile 350 in the Formula to dyno testing just for fun. I will post photos of the installation and other interesting facts in the very near future.

Have a great week!!!...Robert

[Tom Hand]

Robert, thanks again for the information. Iam sure you will love the sound and performance of the system you chose.You are defintely right that it should have no trouble handling the output of your current engine or planned upgrade!
You too have a fun but safe Memorial Day.
Tom

[Z Code 400]

Thanks Tom, I hope you have a great Memorial Day as well...

One thing I thought you might find interesting. As previously discussed, I challenge the theory that backpressure improves performance. However, we have seen a number of exhaust systems that 'over scavenge' on competition vehicles as well as 'hot' street cars.

The 'H' Pipe has been proven to broaden the torque curve as well as cut down the interior noise caused by resonance in the exhaust system. The 'X' pipe is hailed as a significant reduction in system backpressure, when nothing could be farther from the truth.

The X-pipe union simply flows the two branches together without changing the direction of exhaust flow. However, all we have personally seen on the dyno, thus far, is a change in exhaust pitch. Perhaps this attests to the overall efficiency of the systems being tested???

What we have seen with chambered mufflers (on the Dyno) is an increase in TQ over the straight through mufflers. However, there was never an incidence where the exhaust went into pressure ahead of the mufflers during testing.

So, without any backpressure, what accounts for the increase??? Again, I would have to maintain that this is the result of exhaust gas velocity reduction and minimization of over-scavenging.

I am also convinced this is a bigger problem on engines with better flowing cylinder heads.

It should be noted that Yunick even discussed a benefit to slight exhaust system backpressure (the real thing, not just a velocity change) that prevented over-scavenging of the exhaust system.

Knowing that the Pontiac engine is intake-deficient by design, all the emphasis on exhaust flow seems to strike an imbalance. I am not against a slightly longer exhaust duration of 4° to 6° under some circumstances, but dynometer tests have proven that camshafts with shorter exhaust durations will often provide more HP and TQ with intake-deficient designs.

Most current 'Cookie Cutter' cam grinders are predisposed to running camshafts with longer exhaust durations, whether they need to or not. This would be counter-productive in the case of an intake-deficient design, such as the Pontiac.

The popular Summit K2801 is one such camshaft with a 10 degree spread of exhaust duration. A good choice on a street car with stock exhaust, but what about 'big' camshafts I am seeing people have ground with 10°, 12° and even more exhaust duration, running 2" primary headers, high-flowing HRE Heads and 10.50:1 compression???

On racing engines, we have seen exhaust systems so efficient that the over-scevenging effect was immediately evident by high exhaust gas temperatures, overly rich exhaust gas samples and glowing headers. We have had people challenge us stating this was the result of "late" ignition timing, but the fact is the fuel which should be burned in the cylinder, was being scavenged out the exhaust.

In the case of an intake-deficient cylinder head design, a very slight back pressure is preferable to avoid over scavenging. This is a long established opinion reflected in the writings of Iskenderian, Yunick and others.

On our race cars, we used to extend the collectors back as far as we could go and either chassis dyno the car or do actual track testing. At the conclusion of these tests, we would see a blue ring on the collectors a good distance back from where the primary pipes merge into the collector.

At the point of this blue ring, we would cut the collector off and add a mandrel formed reducer of about 2.50" to 2.75" in diameter. Into this short extension, we added an inverted cone spark arrester arrangement, often seen in off road vehicles.

Now, you can buy the same dvices we used to make. We should have patented them back then.

This gave us some of our best performance on circle track and drag racing applications. We never ran fully open exhaust, even on applications with over 500 HP on tap.

Now, fast forwarding to 2006, I am watching the results of many performance modifications at the local dyno shop. What I am seeing is surprising. In every instance, the chambered mufflers are producing more overall torque. In fact, I have seen several cars where Flowmasters were removed in favor of a Magnaflow and rear wheel torque figures not only dropped, but peak torque was moved higher into the rpm range.

On the other hand, I have seen chambered mufflers installed in place of a straight-through version (where a dynometer baseline had been previously established) and the chambered muffler always improved overall TQ output and moved the peak TQ lower into the rpm range.

Interesting, since on the street, torque is king...Robert

[Ccass]

Originally Posted by Z Code 400

Now, fast forwarding to 2006, I am watching the results of many performance modifications at the local dyno shop. What I am seeing is surprising. In every instance, the chambered mufflers are producing more overall torque. In fact, I have seen several cars where Flowmasters were removed in favor of a Magnaflow and rear wheel torque figures not only dropped, but peak torque was moved higher into the rpm range.

chambered mufflers normally produce better low end torque. On lower horsepower cars they may also exhibit better overall torque. What matters for most is, e.t. and mph in the quarter mile and numerous racers have reported lower e.t.'s and higher mph's with straight through design mufflers when switching from chambered style mufflers.

Since we sell both technologies, we have no vested interest in seeing one technology win over the other. And I believe that the Hand's extensive dyno testing yielded similar results. Since the Hand's don't sell automotive products and aren't hired by exhaust manufacturers, they also have no vested interest in seeing one technology win over the other. We just want to give the consumer the best possible information to help them make the best choice for their applications.

The Flowmaster crossflow system is a perfect system for your 350 Firebird if you like the sound it produces. If you install your new motor and intend to 1/4 mile race, it will NOT be the perfect system. It will be very loud and you will go slower.

[Ccass]

Originally Posted by Z Code 400

The X-pipe union simply flows the two branches together without changing the direction of exhaust flow. However, all we have personally seen on the dyno, thus far, is a change in exhaust pitch. Perhaps this attests to the overall efficiency of the systems being tested???

And we have performed numberous dyno tests and have seen pretty much the opposite. Additionally, there are many 'real-world' results that support it. One that comes to mind is Member 'hotrod' Running open headers; 10.90 1/4 mile. Adding full exhaust (100lbs) 10.80's with higher mph. (straight thru mufflers were used)

[Z Code 400]

Ccass:

No argument from me, just an observation that the X is not showing the gains listed here on cars I have personally watched on the rollers.

I think what I am looking for is some level of consistency. I am not saying you or Tom Hand is 'tainting' the results whatsoever. What I am saying is several local shops cannot 'see' the same yield that Pype's is reporting with their X system.

I wrote: "I also see no reason why this 2.50" system, which looks quite large under my F-Body, would have any difficulty whatsoever supporting a 462 inch 425 Horsepower Pontiac V8."

Tom Hand wrote: "Robert, thanks again for the information. I am sure you will love the sound and performance of the system you chose.You are defintely right that it should have no trouble handling the output of your current engine or planned upgrade!"

Ccass wrote: "The Flowmaster crossflow system is a perfect system for your 350 Firebird if you like the sound it produces. If you install your new motor and intend to 1/4 mile race, it will NOT be the perfect system. It will be very loud and you will go slower."

Consistency...

I did my time behind the wheel of our team car in Division 7. I don't plan on racing for a living anymore, but perhaps, I might try my hand at the HPP Shootout just for fun.

Honestly, I think you have missed the true technical, friendly nature of my post. I have raised a few questions and sought input from the forum at large. I find the exchange of information here in this forum valuable and interesting.

In fact, a recent examination of the Pype's Website shows dyno tests where the chambered muffler produced more HP and TQ than a straight through...a point I expressed in an earlier post.

This isn't personal guys, but it is a fact finding mission and when I watch a car go on the rollers and the results hailed here are not replicated, with engines approaching 500 HP, I want to ask a few questions to see where the discrepancy lies.

I think the crossflow is fine behind the stock 350 and will serve equally well behind the 9.00:1 413 and later behind a 9.50:1 462. Jim Butler had some very nice things to say about the time and attention to detail invested into that 413.

I just dropped about $650.00 into the complete system, including the labor to install it and MiG weld everything into place. I could have bought anyone's system, but I felt the overall design of the Flowmaster just fit better and the chambered muffler makes better torque overall.

I think Tom is right, here is the data and decide for yourself. When I see an X pipe make a difference similar to what I am reading about here, I will be the first one to post it.

Additionally, the intake-deficient nature of the Pontiac cylinder head is not my invention, it is a known fact; not a flame to the hobby.

To that end, I hope everyone has a safe and happy weekend...Robert