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Old 04-11-2009, 09:22 PM
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Glasspacks... how bad?

I know that most glasspacks are terrible when it comes to flow. I've used two (duals) on a stock 305 before and although I hated the sound, they didn't restrict any of the raw, brutal 160 hp Because they don't flow well, and because I don't like the sound, I've never researched them. I just wrote them off as "not for me."

But the other day I found a few youtube videos of guys who had put 'packs on their F150s (just like mine) and with the stock cats it actually sounds really good. This is a stock 4.6L which is rated at 220 hp. I'm thinking it might be a $50 solution to my desire to make my truck sound better. I would probably remove the stock muffler and put in a Y-pipe to two glasspacks, then duals to the back.

How does one go about choosing one of the glasspack brands that won't kill flow? Also... anyone have a link to a resource that shows me how much exhaust flow I need per HP? Ballparks are OK.
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Old 04-11-2009, 09:32 PM
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here curtis something to read maybe it will help. http://www.popularhotrodding.com/eng...xh/index1.html . cole
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Old 04-11-2009, 10:08 PM
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Ah come on Curtis, stick some classic turbo mufflers on it and let the deep tone make the glassc pack guys envious. However, there were some glass packs years ago called "turbo II`s" and "Hollywood deep tones" that both sounded good, but hollywood has since went under, and I don`t know if the turbo II`s are avalible anymore either.
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Old 04-11-2009, 10:49 PM
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i run thursh glass packs i like the sound they put out i dont like the idea of a y pipe it dont matter to much how they breath becuase you have a single pipe coming off the motor
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Old 04-11-2009, 11:06 PM
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I have true duals with glasspacks on my 03 Silverado and I think they sound damn good
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Old 04-11-2009, 11:19 PM
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I've got nothing for a link to recommended flow figures, but I do need to ask this since I must be missing something. I have a single 3' by 2 1/2 diameter glasspack that couldn't possibly restrict the flow, as you can see all the way thru it. Seems I read somewhere a while back that you need some sort of back pressure for good engine health. If all glasspacks are the same (like mine), wouldn't having no back pressure be worse than having some restriction to the flow?


In a while, Chet.
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Old 04-11-2009, 11:38 PM
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Quote:
Originally Posted by backardracer
i run thursh glass packs i like the sound they put out i dont like the idea of a y pipe it dont matter to much how they breath becuase you have a single pipe coming off the motor
I'm afraid a single glasspack would be way too restrictive. Splitting it into dual 'packs would be the only way to provide adequate flow... unless you know of one that doesn't wheeze like emphysema
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Old 04-11-2009, 11:44 PM
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i dont think that it will restrict you any more than stock muffs and a added y pipe
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Old 04-11-2009, 11:48 PM
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Quote:
Originally Posted by schnitz
Seems I read somewhere a while back that you need some sort of back pressure for good engine health. If all glasspacks are the same (like mine), wouldn't having no back pressure be worse than having some restriction to the flow?


In a while, Chet.
Not at all. Backpressure is one of those words that older rodders used to use, but in any form its bad for power production. The term backpressure is confused with exhaust flow vs exhaust velocity. If you design an exhuast with greater velocity, it favors low end torque production at the expense of high-end flow; which kills HP.

You want it to flow enough to support the HP, but not so big that it unnecessarily slows down velocity to the point where it kills torque.

In general, most of the glasspacks tested flow terribly, so they would induce backpressure which is bad. Back in the day when glasspacks were first used, engines like the flathead were lucky to make 120 hp, and they had a sound that people liked. The sound has carried their popularity to today, but most of them haven't improved flow to keep up with the fact that engine output is MUCH higher these days.

Basically, the way a glasspack is designed, if it adequately cancels noise its very restrictive. Modern mufflers use geometry and waveform cancellation to allow good flow while still killing sound waves. In general, a glasspack is a very inefficent design - the straight-through design doesn't cancel much sound without hurting flow. Since I'm a physics and engineering geek, I have little use for things that don't make the best use of their design.

But the frustrating thing is that the sound of 'packs on this particular truck with stock cats ends up very bass-y and mellow and I like it. So I'm trying to find a way to get enough flow through a 'pack so I can duplicate that sound without killing flow and what little HP I have.
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Old 04-12-2009, 12:06 AM
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you dont like glass packs so why use them get a high end muff i dont use stock pipes on any thing but my every day drivers and every thing ells has headers and glass packs works fine for me my 66 new port sounds very nice with duel glass packs 383 bbc seems to breath pretty good and sounds great
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Old 04-12-2009, 12:09 AM
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Quote:
Originally Posted by backardracer
you dont like glass packs so why use them get a high end muff
Because I've been out of work since February and a $20 glasspack is a lot more apealing than a $150 muffler with an expensive name stamped on the case.
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Old 04-12-2009, 12:15 AM
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ok the thrush packs are a striat threw desine its what ive been useing they sound good not to loud and good price
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Old 04-12-2009, 12:32 AM
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cool, thanks.
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Old 04-12-2009, 12:44 AM
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If it were me (which of course it isn't, meaning it's not my money, which means it's alot easier to have an opinion!), I'd go with the glasspacks... You like the sound and it's one of those nickel and dime horsepower things, maybe 5 or 10 on average? I can't tell a 5 HP difference, in reality my street car has swings greater than that just due to air temperature I'd figure. When it comes to muffler choice I think unless you need ever last god-forsaken horsepower point, it's just what sound do you like? That said, I like the sound of your basic turbo muffler after having all of them, but that's on my Galaxie and think that the 390 in it is the nicest sounding "engine" I've had (the actual sound under the hood, the mechanical sound). If you like how it sounds, there's plenty of glasspacks that have excellent flow characteristics on the cheap. Dynomax makes the Ultraflos, you can get aluminized straight thrus for a good price IIRC and they flow excellent. I honestly have thought about switching to a pair just for the sound, but like I said I like the engine racket of some sollid lifters rackin' away.

EDIT: It must sound pretty distinctive, I just got back from some friends, the first time the Galaxie's ran since December, and they still recognized the exhaust note. Hell's ya.
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Old 04-12-2009, 08:35 AM
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did some headers into side pipes, used 3 in. pipe from napa, stuck 1 auger (speedway motors part) on each side and they sound great !!!

I pituitary like the roll off.......... you get off the throttle, throaty and powerful ..... a barking 327
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