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Old 04-15-2011, 09:05 PM   #1
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Cobra head swap

I was wondering if you could replace the stock 2v heads from a 1999 gt and upgrade to a set of 99 cobra heads. And how much work would it be to have the ecu flashed for such an upgrade.

If this can be done I have found me next project. Would you still be able to use the track heat intake with these heads please I am looking for hp.
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Old 04-15-2011, 09:23 PM   #2
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I would spring for the complete engine swap. Still gonna have that 2v bottom end in it.
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Old 04-16-2011, 08:05 AM   #3
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Re: Cobra head swap

the 4 valve has a diff block than the 2 valve , dont think it can be done ?
just pick up a 4 valve engine , if you look for just the engine they want a ton of cash for them , try and track down a used mid 90's Lincoln Mark 8 , my Dad bought one for $1800 with only 88,000 miles on it and it runs Strong !!!
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Old 04-16-2011, 08:36 AM   #4
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Re: Cobra head swap

What Stampede said..
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Old 04-16-2011, 11:16 AM   #5
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Re: Cobra head swap

Thats the way to di it.
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Old 04-16-2011, 12:41 PM   #6
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Quote:
Originally Posted by stampde
the 4 valve has a diff block than the 2 valve , dont think it can be done ?
just pick up a 4 valve engine , if you look for just the engine they want a ton of cash for them , try and track down a used mid 90's Lincoln Mark 8 , my Dad bought one for $1800 with only 88,000 miles on it and it runs Strong !!!
I wouldn use the heads a off a cobra then the mark 8 heads and u can Change the intake
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Old 04-16-2011, 06:34 PM   #7
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Re: Cobra head swap

FORD DOHC 4.6 Motor--56K Complete Running Engine | eBay
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Old 05-02-2011, 05:52 AM   #8
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Quote:
Originally Posted by stampde
the 4 valve has a diff block than the 2 valve , dont think it can be done ?
just pick up a 4 valve engine , if you look for just the engine they want a ton of cash for them , try and track down a used mid 90's Lincoln Mark 8 , my Dad bought one for $1800 with only 88,000 miles on it and it runs Strong !!!
The heads can be used on the 2 valve block. But you need the intake, fuel, exhaust, etc. Besides the stock bottom end is the same internals that an auto mach 1 has. Only difference is that the mach 4v block is aluminum. The gt bottom end is good up to 400+ hp more than enough for a head swap.
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Old 05-02-2011, 07:41 AM   #9
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Re: Cobra head swap

The reason the 4v head swap is not cost effective is that you need lots of parts to make it work. Aside from the heads/intake and tune you would also need crank, pistons, timing chains, front cover, alternator, inlet tube, 24lb injector and matching MAF, harness or modifiy stock harness to work, flywheel (cobras are 8 bolt 96-98, 01-03 GT's are 6 bolt). Reason you need crank is that the Cobra motor makes it's peak power above 6K RPM and you need to be able to rev to 7K regularly to take advantage of the power band. Pistons you need becuase without them you will only have about 8.5:1 and 4v motors have 9.5:1+.

If you simply bolted on the heads and did the swap minus the internal parts I would be surprised if you saw more than maybe 5-10RWHP peak gain because the peak would never be reach with the stock 2v rev limiter and you would lose a good amount of torque down low. If you ever get a chance compare a stock GT to stock Cobra dyno chart and you'll see the GT makes more torque down low and it's due to small port size for better velocity.
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Old 05-02-2011, 02:55 PM   #10
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Agree about compression, if boosted then that's idea. But disagree on crank, mach auto crank is the same. now if he is planning a high horsepower car I would say upgrade but for something mild on the street, on a budget then run what you brung. Plenty of 2v or there running stock cranks with hp. As said previous post, find a mark motor, use your heads get some cams, and a tune.
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Old 05-04-2011, 08:45 PM   #11
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Re: Cobra head swap

um. just incase anyone wanted to do the swap. i have a set of 97 cobra 4v heads for sell. new with new valves. no cams.
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Old 05-04-2011, 10:46 PM   #12
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Re: Cobra head swap

Quote:
Originally Posted by lowflyn View Post
The reason the 4v head swap is not cost effective is that you need lots of parts to make it work. Aside from the heads/intake and tune you would also need crank, pistons, timing chains, front cover, alternator, inlet tube, 24lb injector and matching MAF, harness or modifiy stock harness to work, flywheel (cobras are 8 bolt 96-98, 01-03 GT's are 6 bolt). Reason you need crank is that the Cobra motor makes it's peak power above 6K RPM and you need to be able to rev to 7K regularly to take advantage of the power band. Pistons you need becuase without them you will only have about 8.5:1 and 4v motors have 9.5:1+.

If you simply bolted on the heads and did the swap minus the internal parts I would be surprised if you saw more than maybe 5-10RWHP peak gain because the peak would never be reach with the stock 2v rev limiter and you would lose a good amount of torque down low. If you ever get a chance compare a stock GT to stock Cobra dyno chart and you'll see the GT makes more torque down low and it's due to small port size for better velocity.
Disregard every post in the thread but this one. This is spot on.

It can be done....it's just not worth it.

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