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Discussion Starter · #1 ·
A little intro for those of you just joining us:
We've tested the power and noise output of a range of exhaust systems on a fresh 302 that's been bored 0.20" over, running Trickflow heads and stage 2 cam with an Edelbrock Performer intake and carb. The testing was done in a non-ideal acoustic environment, don't tell us we know this, and the results may vary for your particular engine, but our reasoning is that the loudest exhaust with this engine is likely the loudest for your engine. It is a comparative test and was done the way it was done, we will not be repeating it or looking kindly on suggestions after the fact and we welcome anyoone who wants to do stage 2 of testing to go ahead, we'll even donate some hard-earned coin:)

Method: Each system was run through one to two pulls on the dyno from 3,500-6,200RPM. We would have liked to record sound files but time and manpower did not allow. Sound measurements were performed with a precision sound meter which had been calibrated the day of the test. The microphone was outside of the dyno test cell as the meter redlined when it was in the same room. However the external conditions were the same for each run so this should not affect the relative ranking. Similarily, we did need to run with flex pipes over the pipes as the plenum in the dyno was not wide enough but this should not affect relative deltas.

Test Subjects:
Ported J-pipe & Aerospike: see Rod's post for pics of this
Cats: Standard FFR cats
Crossover: as per previous posts on the subject
DNA 1: standard DNA helical silencer
DNA 1.5: 1/2 a DNA spliced to the back of a full one
Lobaks: standard spiral silencer
Einar's Pipes: a custom baffled pipe




As you may have noticed, 4-into-4's are not listed as it turned out there was no way to accomodate their width in the test cell. The j-pipes were fine as the ball joint allowed them to be mounted at an angle.




Results:
Hopefully we'll have more video of some of the pulls up but in the meantime here's the data. If anyone can host it or tell me how to post a spreadsheet here, I'd be willing to upload it so people can sift through the actual numbers themselves.

My software for making a .jpg of a screen capture is not working so until I get to work you'll have to live with the following crappy text chart that shows the changes in values for each combo.

Deltas
OSHA Scale Noise [db] Peak Torque Peak HP Avg. HP* Avg.Torque*
Ported J-pipe 1 0 -11 0 1
Aerospike 0 0 -12 -2 -3
Cats 4 13 -2 6 10
Crossover 0 -1 -18 -6 -2
DNA 1 N/A 2 -14 -8 -5
DNA 1.5 -1 -1 -18 -10 -7
Einar's Pipes N/A 2 -11 -5 -2
Lobaks 3 8 -3 0 3
* Averaged over 3,500-6,000 RPM range Positive is Improvement Negative is Improvement
The N/A on the DNA 1 and Einar's pipes are because the noise pegged the sound meter at 115db meaning the noise level was somewhere above that. As you can see the cats and Lobaks were the only combos to significantly lower noise from the stock setup, the cats soaked up some power to do this the Lobaks not so much. As for power adders the aerospike was a clear winner (though whether it needs a ported j-pipe to work is a question we didn't have time to answer). Einar's pipes and the DNA's also increased power.

Over several repeat runs our noise data repeated within a db, the peak power and torque numbers are +/- 3 and the average power and torque values are +/- 1. Units are db, horsepower and ft-lbs. More to come tomorrow including plots of all of the runs.

Jason

[ March 22, 2007, 07:07 AM: Message edited by: Aero Guy ]
 

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Send it to me. I'll post it
 

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Discussion Starter · #3 ·
Erik, I've mailed the file to you. I still plan to post jpgs tomorrow for those of you without Excel.
 

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Jason I have the videos on dvd and will meet up with Rod so he can post them.
 

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Discussion Starter · #6 ·
The averaged results are very dependent of what range of RPM's you choose. There is little to choose from all of the different setups at lower RPM's, but above 5,000 to 5,500 RPM is where things start to diverge and some combos give big gains at the top end. So if you look at averages over a higher range, say 4,500 to 6,000 you'll see much larger differences. If Erik doesn't beat me to it I'll put up some plots so you can see the differences over the entire rev range.
 

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THere is a ton of info on the file. Looks like you guys did a TON of work! Let me be the first to say thank you!.... AND THANKS now I need to go add a crossover to my LOBAKS :D :D
 

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Cat's out of the bag so here's some additional info. Notice that Jason's 303 (304) pulled 390 HP and 357 ft-lb of torque!!!

Here is a copy of the overall results table. Note that the deltas are separated into to categories because the DNA, 1-1/2 DNA's, Einar's and the lobaks were only tested with the super ported J-pipes so they were compared to the Super ported J-pipe and the stock FFR pipes.



A couple of numbers not shown in the delta table is that the super ported J-pipes (SP J's) and aerospike with the FFR pipes were good for 23 HP over the stock J-pipe and FFR sidepipe combo! Also, the 1-1/2 DNA + SP J's were good for 29 HP over the stock J-pipe and FFR sidepipe combo!! We did not get a chance to try the 1-1/2 DNA + SP J's + aerospike combe but from the results there may have been another 12 HP to be had by adding the aerospike. While the 1-1/2 DNA + SP J's were 1 db louder than the stock setup I think it would be possible to do additional mods to quite them down a bit and retain, or still exceed, the stock setup on power and torque. More work to do I guess.

Cheers, Rod
 

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Discussion Starter · #9 ·
Personally I'm thinking of starting with cats and a crossover with some mild porting (I'm not the welder that Rod now is) and possibly an aerospike. Then when the glass blows out of my FFR side pipes I can decide if I can live with the noise and add DNA's for more power or if I want to go quieter yet and add Lobaks. Maybe I'll paint my car green since with the cats I'll be saving the environment everytime I go for a spin.
 

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Darn your fast Erik!

Here are some more pics.

The proud owner. He had a pretty big smile when it pulled over 380 on the first run!



Note the red glow, time for a timing change!



SP J's heating up.



Aerospike after it's runs and before we cut it off for the stock runs.



Limey69's crossover:



1-1/2 DNA's + SP J's:



The aerospike before testing:



 

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Wondering if having the O2's after the crossover for EFI would be an issue??
 

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Here are some charts. Like I said in the other post, Jason did a lot of work on the weekend!

DNA's:



Aerospike + SP J's:



Lobaks:



Einar's:



Crossovers:



FFR Cats:



All pipes:



All headers:



[ March 19, 2007, 07:01 PM: Message edited by: dv/dt ]
 

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Originally posted by Erik W. Treves:
Wondering if having the O2's after the crossover for EFI would be an issue??
I've seen something about this messing with the computer in past posts.
 

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Jason and Rod,
You guys did an absolutely awesome job! WOW! Three cheers to you both!


Now that the aerospike and porting the j-pipe produces such an improvement, a lot of us are going to have to learn how to weld.

I'm definitely interested in the crossover, porting, spike and Lobaks. Looks like next winter's project.

One question ... all of the previous posts stated a sound level reduction for the crossover. Your data didn't show that. I wonder if the sound spectrum changes to a more tolerable frequency range, like less high frequency "bark" and more mellow, but loud low frequency. Did you notice a change in the sound spectrum for the crossover?
Pete
 

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Wow. Pretty impressive. I'd like to see 1 1/2 DNAs, ported J-pipes, Areospike, and a cross-over all at once :D Plus I really wonder if a proper merge collector would help as well.

I think we have proved here that going from 1 to 4 is very dispuptive and the areospike smooths things out a bit. Going from 4 back to 1 also is probably pretty rough without a merge collector. Why not cut out the 1-to-4-to-1 all together and just have one pipe going out of the side of the car? You could hide a real central pipe inside a cluster of 4 fake pipes if you wanted to.

Mike

PS. Nice to know that 1.5 DNAs are the same volume as the stock FFR setup when new (which get louder with time), but give about 30 more HP. How do they sound subjectively at idle and RPM. Are they sexy?
 

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Discussion Starter · #17 ·
GoGS, the sound meter used the OSHA scale which assigns a weighting to each frequency in the spectrum. There are other ratings, A, B and C, and the difference between each is the weighting it gives to various frequencies. What all of these weightings try to do is give a weighting to the frequencies that simulates how humans perceive noise. Because identical sound pressure levels at high and low frequencies will sound louder or quieter to us. Humans aren't very objective listeners and that's why the automakers spend months tuning exhaust and playing it for market survey folks who judge the sound based on who knows what!

So in our case the crossover didn't have a significant effect on noise, it may have had a profound effect on a certain frequency, which would change the tone, but if that frequency is not weighted highly it would not change the perceived volume. Maybe it just didn't change the sound, whatever the case all we can report is what we saw, little effect on sound, big effect on top end power.

Similarily, for Michael's question on whether they sounded sexy I thought they all sounded sexy and without listening back to back would have had a hard time discerning any difference. The only noticeable differences were from the cats and Lobaks, each time I thought something was wrong because they were so much quieter it sounded like the dyno operator cut off the run early. But no, they're just damn quiet.
 

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Discussion Starter · #18 ·
One more note, you'll notice the last two points of the baseline run spike upwards after the curve starts falling away. Early in the day we were having problems with the dyno surging, couldn't handle all of that power I guess, we didn't notice the effect on the data right off but eventually it was fixed. I assume those last two points are garbage which is why I was curve fitting the data and why the averages cut off at the 6,000 RPM level. In most cases the power has peaked by 6,000 RPM anyway.
 

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Very cool. Not really as big a difference in DB as I would have thought.

Cross over produced more then I would have expected - very interesting.
 

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Discussion Starter · #20 ·
Remember that for the decibel scale a 3 db reduction means the sound power level has been cut in half.
 
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