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Old 10-24-2012, 05:05 PM
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Loss of power, alot....

Ok guys tell me what I think I already know.... I have a 1971 Pontiac 455 HO bored 30 over with a edlebrock 278 degree cam, 750 edelbrok carb. I got the engine installed in my Grand Prix and the Engine had open headers on it. Tons of power. I installed some glass packs directly onto the headers to get it to the local car show and there is a huge decrease in power. when I step on the gas it hesitates and "putt putts" when held to the floor. Before with the headers it would spin wheels till i let off it...Does my Carb need to be adjusted?
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Old 10-24-2012, 05:56 PM
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Thats a typical problem with the old glasspacks. The back pressure they cause (somewhere around 15-18psi) is robbing power from the motor. A good quality muffler like Magna Flow, Walker Ultra Flow, Thermal, A'PEX, Borla, etc. are good low back pressure mufflers. Any of these will only cause about 1-2psi back pressure. It's not the tuning, it's in your mufflers.
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Old 10-24-2012, 06:19 PM
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I'm going with dual exhaust next week so the glass packs are coming off, it was just a quick fix. Magnaflow was on my mind. want a diffrent tone than the typical Flow master.
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Old 10-24-2012, 06:40 PM
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Thanks, Still working on it. Pontiac excitement!
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Old 10-24-2012, 07:11 PM
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Quote:
Originally Posted by S10 Racer View Post
Thats a typical problem with the old glasspacks. The back pressure they cause (somewhere around 15-18psi) is robbing power from the motor. A good quality muffler like Magna Flow, Walker Ultra Flow, Thermal, A'PEX, Borla, etc. are good low back pressure mufflers. Any of these will only cause about 1-2psi back pressure. It's not the tuning, it's in your mufflers.
Please show your references for these data. I'd be very interested in reading it.
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Old 10-24-2012, 08:39 PM
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buy a 3 inch system and get the mufflers as far back as possible. I use an X pipe for sound,its a lot quieter than true duals
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Old 10-24-2012, 09:31 PM
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Seems like Flowmaster is what everyone's using. I don't have anyone around here with Magna Flow. Any sound diffrence between the 2? These Glass Packs got to go....
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Old 10-24-2012, 10:46 PM
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Keep in mind that Flowmaster has 5 different series of mufflers, each with their own sound level. Google it and find out what you want.

1. Super 10 -The loudest of the five, close to open exhaust.
2. Super 40
3. Super 44
4. 50 Series Delta Flow
5. 70 Series - Quietest of all of them with a mild tone
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Old 10-24-2012, 11:03 PM
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noise level will also be affected by power output and cubic inches.Aluminum heads make a different sound than cast iron.ported heads sound different
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Old 10-28-2012, 02:34 PM
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I went through a pile of mufflers on my Pontiac 455 (462) until I tried the Magna Flow #12640..

If you want better performance, try a Cliffs Quadrajet with a stock Iron Quadrajet intake.. That carb isn't the best for your set up....
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Old 10-28-2012, 02:58 PM
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Whats wrong with the Edelbrock? I've had people say Holly, haven't heard of Cliffs.....
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Old 10-29-2012, 08:26 AM
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Turbo mufflers on a 3 inch sytem behind a big motor like that sound absolutely amazing. I guarantee you will love the sound.

The 750 edelbrock is perfect by the way. Best street carb out there imo.
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Old 10-29-2012, 11:09 AM
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Big engines are sensitive to restricted exhaust flow. On a Pontiac 455 in a 4x4 Blazer that the dude insisted on using the column shifter, I had to use factory exhaust maniifoolds. It literally KILLED that engine! I bet it loped off a hundred HP and that much torque to boot!

On the same engine I had used 3" Flowmaster 40's w/an H pipe connecting the two sides. Had turndowns about a foot long out the back of the mufflers. They ended right under the rear seat area.

This was in an '81 Camaro. You'd have thought the droning would have been bad- and it probably would have been, had I not used heavy factory-type insulation (tar/felt type) scavenged from junkyard vehicles.

About the best thing that could be said for it was it wasn't very restrictive. But it would set off car alarms just idling through a parking lot- which was something I enjoyed doing where the ricers congregated in the K-Mart parking lot on W. Colonial Dr. in Orlando on weekend nights. Not so enjoyable while driving through residential neighborhoods, like my own.

But it ran great. Effortless 12's w/a 3.08, lower 12's w/a 3.31 rear gear.

Check out Cliff Ruggles: Cliffs High Performance Quadrajets :: Qjet Carburetor Rebuild Kits, Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning

That said, no good reason you can't tune the Edelbrock 750 to work. I don't much care for the non adjustability of the secondary opening rate, unless it's a Thunder series carb.

Last edited by cobalt327; 10-29-2012 at 11:14 AM.
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