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Old 05-20-2005, 10:10 PM
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new headers question

well ive just installed sum new headers on my 1975 gmc sprint it has a 307 sbc holley dominator intake dual plane design and holley 600cfm carb every thing else stock with like some weak 290 gearing since ive put on the headers seems ive lost low end power and my carb seems to be running rich to id think it would run lean but it almost is flooding well i know some 410 gears are now in order for lowend power thats got to come later though any way to get back my bottom end by the way im running them open for now may be i should put back on my mufflers with the headers ive created problems but does it sound mean oh yea thanks guys

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Old 05-20-2005, 10:19 PM
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Without the muff's you got no backpressure,torque in your case.
Put them back on and it will pick up for you.
The carb problem is related to moving more air now and some tuning will be required.Unless you "did something" during the install.
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Old 05-22-2005, 09:41 AM
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so as far as tuning my carb u think i need to rejet it would that take care of it
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Old 05-22-2005, 10:59 AM
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with you motor being near stock..4.10 gears will hurt you more than anything...try a 3.55 or 3.73 gear...
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Old 05-22-2005, 12:14 PM
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Quote:
Originally Posted by 75sprintguy
well ive just installed sum new headers on my 1975 gmc sprint it has a 307 sbc holley dominator intake dual plane design and holley 600cfm carb every thing else stock with like some weak 290 gearing since ive put on the headers seems ive lost low end power and my carb seems to be running rich to id think it would run lean but it almost is flooding well i know some 410 gears are now in order for lowend power thats got to come later though any way to get back my bottom end by the way im running them open for now may be i should put back on my mufflers with the headers ive created problems but does it sound mean oh yea thanks guys
You didn't say what tube size headers you purchased. Sometimes too large can adversely effect low end power/torque. Putting the mufflers may creat enough backpressure to help get your bottom end back to normal. Your carburetor may be a little to big for the cubes you are running a 450 to 500 cfm would probably serve your need a little better.
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Old 05-22-2005, 01:42 PM
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A 600 CFM carb is fine for a 307. Don't go smaller.

The problem is no exhaust system. Most street engines will loose all their bottom end if you run open headers.
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Old 05-27-2005, 06:35 PM
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back on track

well wanted to let u guys know i turned some screws on the ole holley installed some 27 inch glass packs now i got all my low end power back.from this header install i feel ive may be gained 5 horsepower worth it to me i needed it i think im adicted to horsepower u guys no of any cure
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Old 05-27-2005, 07:17 PM
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Quote:
Originally Posted by 75sprintguy
well wanted to let u guys know i turned some screws on the ole holley installed some 27 inch glass packs now i got all my low end power back.from this header install i feel ive may be gained 5 horsepower worth it to me i needed it i think im adicted to horsepower u guys no of any cure

Marriage, kids?
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Old 05-27-2005, 10:40 PM
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3 speeding tickets over 20 mph of the limit in 2 weeks...
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