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Discussion Starter #1
Anyone have experience with the Ford Cobra rocker arms F3ZE-6529-AB? They are 1.7 ratio. I have a set of GT40 heads for my 68 289. Wondering if these pedestal rockers are a good match for this set up.
 

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Yes. I ran that exact setup on my now gone 89 Mustang. Stock GT40 heads with the stock 89 cam. Louder then stock rockers, sounded like a sewing machine. But I got 235RWHP through the AOD which is good considering usually those cars get 190RWHP stock.
 

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Thanks, I am planning to use these to replace the anemic 2V heads on my 289. Add a mold cam , Tri y headers, dual exhaust and an Edelbrock intake should warm it up a little
 

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I ran them for a while on my GT40P with a Mustang 5.0 cam. They were noisy. I was on Corral and it seemed to be the concences that they were. I put the stock stamped rockers back on. Didn't notice any difference in power.
 

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@Flade you're going to loose a full point of compression with the GT40 heads. They have 65cc vs 55cc for the 289. If you have the 13cc dish C code or aftermarket with big valve relief tray, with a 55cc head your at low 8's. Another 10cc will put you firmly into the 7's.
 

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The Cobra rockers are basically Crane Energizer arms. I have old Energizer 1.6 arms on my 347" these are pretty silent. The have to be something in the combo of parts, that trigger the noise and amplifies it, when some people are having loud noise. I'm sure that just the aluminium vs. steel parts will make a difference in how any sound from the valvetrain are transmitted. Maybe some manufacturing tolerances also make some set of theses arms more noisy that others.
 

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Discussion Starter #9
@Flade you're going to loose a full point of compression with the GT40 heads. They have 65cc vs 55cc for the 289. If you have the 13cc dish C code or aftermarket with big valve relief tray, with a 55cc head your at low 8's. Another 10cc will put you firmly into the 7's.
I have the 68 289 2v heads that already have 63CC chambers and crappy compression. How are the GT40 heads different from the GT40P heads many people have been using? I have 66 heards that I could use but figured the GT40 heads would flow better
 

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I have the 68 289 2v heads that already have 63CC chambers and crappy compression. How are the GT40 heads different from the GT40P heads many people have been using? I have 66 heards that I could use but figured the GT40 heads would flow better

The GT40P have 60cc chamber. They also flow slightly better then the GT40 head. The down side is the plug angle. It's more perpendicular. They won't work with a lot of headers but will with some. If you already have headers it doesn't make sense to buy another. If you're using stock exhaust manifold, they will work with some minor grinding around the plug area and the flange area

The GT40P is also more combustion efficient and needs less total timing. They seem to be detonation resistant.
745205
 

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Discussion Starter #11
Thanks for the detailed answer. I knew about the plug angle & headers but didn't realize the combustion chamber was sized differently. Shame since he GT40 heads are in immaculate condition. I may just put them on my 95 instead of saving up for Aluminum heads
 
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