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Old 02-17-2020, 10:54 AM
1966GP 1966GP is offline
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Default Looking headers to grandprix

Hello! Im looking some better exhaust manifold to my 389 1966 grand prix. Is there any other options than dougs headers? They will be little too expensive if i order them here in Finland

How bad are originals exhaust manifolds? Think they are number 9779325.

I have ported 092 heads, edels carburetor, rpm intake and edels camshaft. Is there any reason even put money to headers?

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Old 02-17-2020, 11:32 AM
mgarblik mgarblik is offline
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Factory exhaust manifolds for Pontiac engines are not great, but not absolutely terrible like some other brands. Part of that is due to the "dog leg" outlets already built into the head castings. Headers have their own issues, poor fitment, leaks, rust, ground clearance, adaption to rest of exhaust system. On a stock engine with stock 092 heads in the operating range it likely runs at, possibly 10 HP gain. A much better option if the 5-10 HP means anything to you would be the factory long branch iron H.O. manifolds. But these cost as much as tube headers, require an oil filter adapter block, flanges and modifications to the head pipes. The advantage vs headers is the will fit properly, not leak, and ground clearance is not an issue. They also look really cool. But it's a big expense on a stock engine that you probably won't feel driving it. Personally, I would repair, reseal the stock manifolds if needed, and move on to other projects the car may need. BTW, love the Grand Prix those years.

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Old 02-17-2020, 11:34 AM
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F ROCK F ROCK is offline
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I had hooker super comps and I hated them.
they would come loose and blow gaskets, hung real low on the passenger side and would hit the ground on occasion.
needed to bend special wrenches for install and go through the wheel wells.
Also it killed some of my low end because I had 3.08 gears and a t400 and the engine never revved high enough to see any performance gain.
Also had to move brake lines for install and the pipe was very close to my oil filter making oil changes very messy.
I'm using the RA headers (RARE I think) They are iron headers like what was installed on the Judge cars. MUCH better. never comes loose never have to change gaskets never hits the ground and my low end is back.

Just my experience.

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Old 02-17-2020, 05:08 PM
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Lee Lee is offline
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The attached dyno graph shows my personal testing, where I compared stock standard exhaust manifolds against a set of tri-Y headers. The motor was a very mild 455, about 7.8:1 compression, unported heads, Performer intake, Q-jet carb., and a fairly mild low lift (around .440") camshaft.

The only change was to install richer metering rods in the Q-jet, as my wide-band oxygen sensor told me the AFR leaned out with the headers.

Beyond a doubt, the headers significantly increased the performance of my motor. The increase was greater than I had anticipated. The only caveat I can offer is that I used engine modeling software to develop the cam design, and it WAS designed for a low-restriction exhaust - so perhaps my performance loss due to the manifolds was more than what others may see.
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Old 02-17-2020, 06:29 PM
1966GP 1966GP is offline
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Thanks for the answers guys!

It seems like i have to find some headers..

Do u have any ideas how big difference is, for example between -65 gtos and GPs headers?

For example flowtechs 11170 what are for GTO/lemans, cost like ~300e here. Or is my only chance buy dougs d521-r?(1000e) I havent found any else that would fit to my car just bolt on.

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Old 02-17-2020, 07:28 PM
694.1 694.1 is offline
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You want 67-69 Firebird HO manifolds.

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  #7  
Old 02-25-2020, 05:03 AM
1966GP 1966GP is offline
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Hello

I found thread where someone installed second gen firebirds headers to -66 Catalina. Do u think that first gen firebirds headers would fit better?

http://forums.maxperformanceinc.com/...79#post5649679

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