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Old 10-24-2012, 06:05 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, 06:56 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, 07:19 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, 07:24 PM
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Love the car i had almost the same setup. 71 gp sj 455 ho 472. Edelbrock heads built block. Same issue with old exhuast car was flat. Installed flowmaster dual kit with 40 series. It made as much power as open headers. Think i got a kit for a g body and some extender pipes and it was bolt on. Mufflers in front of the rear end.

Glass packs always kill power. They have onthe to cars i tried them on.
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Old 10-24-2012, 07:37 PM
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Quote:
Originally Posted by billonwheels View Post
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.
Go big 2 1/2 at smallest. Those engines love to breath. I did 2 1/2 and it made good power. Hard to beat an exhuast that makes the same power as open headers as far as my butt dyno could tell. Felt faster actually. Sound was loud it would shake the ground like open headers. Neighbors hated it. Didnt sound anything like a mustang with flowmasters.
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Old 10-24-2012, 07:40 PM
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Thanks, Still working on it. Pontiac excitement!
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Old 10-24-2012, 08:11 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, 09:39 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, 09:54 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
Not so easy on a gp the motor really far back and very low in the chassis trans and drive shaft are in the way for crossover. I am not sure if anyone makes a bolt in system for that car 3" crossover.

3" i totally agree. Flowmastwr for me was a quick fix. I was shocked at the quality when i opened the boxes. Sales dude at jegs new what i needed and got me everything including clamps and turndowns in one shipment. He had a monte.
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Old 10-24-2012, 10:31 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, 11:46 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 10-25-2012, 12:03 AM
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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, 03:34 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, 03:58 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, 09:26 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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